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Minimum Design

Loads for Buildings

and Other Structures

This document uses both the

International System of Units (SI)

and customary units

ASCE STANDARD

ASCE/SEI

7–10

A S C E STA NDA RD ASCE/SEI 7-10

American Society of Civil Engineers

Minimum Design Loads

for Buildings and

Other Structures

This document uses both the International System of Units (SI)

and customary units.

PR_version_1.indd i 4/14/2010 1:40:42 PM

Library of Congress Cataloging-in-Publication Data

Minimum design loads for buildings and other structures.

p. cm.

“ASCE Standard ASCE/SEI 7-10.”

Includes bibliographical references and index.

ISBN 978-0-7844-1085-1 (alk. paper)

1. Structural engineering–Standards–United States.

2. Buildings–Standards–United States. 3. Strains and stresses.

4. Standards, Engineering–United States. I. American Society of

Civil Engineers.

TH851.M56 2010

624.1′75021873—dc22

2010011011

Published by American Society of Civil Engineers

1801 Alexander Bell Drive

Reston, Virginia 20191

www.pubs.asce.org

This standard was developed by a consensus standards development

process which has been accredited by the American National Standards

Institute (ANSI). Accreditation by ANSI, a voluntary accreditation

body representing public and private sector standards development

organizations in the U.S. and abroad, signiﬁ es that the standards devel-

opment process used by ASCE has met the ANSI requirements for

openness, balance, consensus, and due process.

While ASCE’s process is designed to promote standards that reﬂ ect a

fair and reasoned consensus among all interested participants, while

preserving the public health, safety, and welfare that is paramount to

its mission, it has not made an independent assessment of and does

not warrant the accuracy, completeness, suitability, or utility of any

information, apparatus, product, or process discussed herein. ASCE

does not intend, nor should anyone interpret, ASCE’s standards to

replace the sound judgment of a competent professional, having

knowledge and experience in the appropriate ﬁ eld(s) of practice, nor

to substitute for the standard of care required of such professionals in

interpreting and applying the contents of this standard.

ASCE has no authority to enforce compliance with its standards and

does not undertake to certify products for compliance or to render

any professional services to any person or entity.

ASCE disclaims any and all liability for any personal injury, property

damage, ﬁ nancial loss or other damages of any nature whatsoever,

including without limitation any direct, indirect, special, exemplary,

or consequential damages, resulting from any person’s use of, or

reliance on, this standard. Any individual who relies on this standard

assumes full responsibility for such use.

ASCE and American Society of Civil Engineers—Registered in U.S.

Patent and Trademark Ofﬁ ce.

Photocopies and reprints. You can obtain instant permission to photo-

copy ASCE publications by using ASCE’s online permission service

(http://pubs.asce.org/permissions/requests/). Requests for 100 copies or

more should be submitted to the Reprints Department, Publications

Division, ASCE (address above); e-mail: [email protected]. A

reprint order form can be found at http://pubs.asce.org/support/reprints/.

ISBN 978-0-7844-1085-1

Manufactured in the United States of America.

18 17 16 15 14 13 12 11 10 1 2 3 4 5

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iii

STANDARDS

In 2003, the Board of Direction approved the revision

to the ASCE Rules for Standards Committees to

govern the writing and maintenance of standards

developed by the Society. All such standards are

developed by a consensus standards process managed

by the Society’s Codes and Standards Committee

(CSC). The consensus process includes balloting by

a balanced standards committee made up of Society

members and nonmembers, balloting by the member-

ship of the Society as a whole, and balloting by the

public. All standards are updated or reafﬁ rmed by the

same process at intervals not exceeding ﬁ ve years.

The following standards have been issued:

ANSI/ASCE 1-82 N-725 Guideline for Design and

Analysis of Nuclear Safety Related Earth

Structures

ASCE/EWRI 2-06 Measurement of Oxygen Transfer

in Clean Water

ANSI/ASCE 3-91 Standard for the Structural Design

of Composite Slabs and ANSI/ASCE 9-91

Standard Practice for the Construction and

Inspection of Composite Slabs

ASCE 4-98 Seismic Analysis of Safety-Related

Nuclear Structures

Building Code Requirements for Masonry Structures

(ACI 530-02/ASCE 5-02/TMS 402-02) and

Speciﬁ cations for Masonry Structures (ACI

530.1-02/ASCE 6-02/TMS 602-02)

ASCE/SEI 7-10 Minimum Design Loads for

Buildings and Other Structures

SEI/ASCE 8-02 Standard Speciﬁ cation for the Design

of Cold-Formed Stainless Steel Structural

Members

ANSI/ASCE 9-91 listed with ASCE 3-91

ASCE 10-97 Design of Latticed Steel Transmission

Structures

SEI/ASCE 11-99 Guideline for Structural Condition

Assessment of Existing Buildings

ASCE/EWRI 12-05 Guideline for the Design of

Urban Subsurface Drainage

ASCE/EWRI 13-05 Standard Guidelines for

Installation of Urban Subsurface Drainage

ASCE/EWRI 14-05 Standard Guidelines for

Operation and Maintenance of Urban Subsurface

Drainage

ASCE 15-98 Standard Practice for Direct Design of

Buried Precast Concrete Pipe Using Standard

Installations (SIDD)

ASCE 16-95 Standard for Load Resistance Factor

Design (LRFD) of Engineered Wood

Construction

ASCE 17-96 Air-Supported Structures

ASCE 18-96 Standard Guidelines for In-Process

Oxygen Transfer Testing

ASCE 19-96 Structural Applications of Steel Cables

for Buildings

ASCE 20-96 Standard Guidelines for the Design and

Installation of Pile Foundations

ANSI/ASCE/T&DI 21-05 Automated People Mover

Standards—Part 1

ANSI/ASCE/T&DI 21.2-08 Automated People Mover

Standards—Part 2

ANSI/ASCE/T&DI 21.3-08 Automated People Mover

Standards—Part 3

ANSI/ASCE/T&DI 21.4-08 Automated People Mover

Standards—Part 4

SEI/ASCE 23-97 Speciﬁ cation for Structural Steel

Beams with Web Openings

ASCE/SEI 24-05 Flood Resistant Design and

Construction

ASCE/SEI 25-06 Earthquake-Actuated Automatic Gas

Shutoff Devices

ASCE 26-97 Standard Practice for Design of Buried

Precast Concrete Box Sections

ASCE 27-00 Standard Practice for Direct Design of

Precast Concrete Pipe for Jacking in Trenchless

Construction

ASCE 28-00 Standard Practice for Direct Design of

Precast Concrete Box Sections for Jacking in

Trenchless Construction

ASCE/SEI/SFPE 29-05 Standard Calculation Methods

for Structural Fire Protection

SEI/ASCE 30-00 Guideline for Condition Assessment

of the Building Envelope

SEI/ASCE 31-03 Seismic Evaluation of Existing

Buildings

SEI/ASCE 32-01 Design and Construction of Frost-

Protected Shallow Foundations

EWRI/ASCE 33-01 Comprehensive Transboundary

International Water Quality Management

Agreement

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STANDARDS

EWRI/ASCE 34-01 Standard Guidelines for Artiﬁ cial

Recharge of Ground Water

EWRI/ASCE 35-01 Guidelines for Quality Assurance

of Installed Fine-Pore Aeration Equipment

CI/ASCE 36-01 Standard Construction Guidelines for

Microtunneling

SEI/ASCE 37-02 Design Loads on Structures during

Construction

CI/ASCE 38-02 Standard Guideline for the Collection

and Depiction of Existing Subsurface Utility Data

EWRI/ASCE 39-03 Standard Practice for the Design

and Operation of Hail Suppression Projects

ASCE/EWRI 40-03 Regulated Riparian Model Water

Code

ASCE/SEI 41-06 Seismic Rehabilitation of Existing

Buildings

ASCE/EWRI 42-04 Standard Practice for the Design

and Operation of Precipitation Enhancement

Projects

ASCE/SEI 43-05 Seismic Design Criteria for

Structures, Systems, and Components in Nuclear

Facilities

ASCE/EWRI 44-05 Standard Practice for the Design

and Operation of Supercooled Fog Dispersal

Projects

ASCE/EWRI 45-05 Standard Guidelines for the

Design of Urban Stormwater Systems

ASCE/EWRI 46-05 Standard Guidelines for the

Installation of Urban Stormwater Systems

ASCE/EWRI 47-05 Standard Guidelines for the

Operation and Maintenance of Urban Stormwater

Systems

ASCE/SEI 48-05 Design of Steel Transmission Pole

Structures

ASCE/EWRI 50-08 Standard Guideline for Fitting

Saturated Hydraulic Conductivity Using

Probability Density Functions

ASCE/EWRI 51-08 Standard Guideline for

Calculating the Effective Saturated Hydraulic

Conductivity

ASCE/SEI 52-10 Design of Fiberglass-Reinforced

Plastic (FRP) Stacks

ASCE/G-I 53-10 Compaction Grouting Consensus

Guide

PR_version_1.indd iv 4/14/2010 1:40:43 PM

FOREWORD

The material presented in this standard has been

prepared in accordance with recognized engineering

principles. This standard should not be used without

ﬁ rst securing competent advice with respect to its

suitability for any given application. The publication

of the material contained herein is not intended as a

representation or warranty on the part of the American

Society of Civil Engineers, or of any other person

named herein, that this information is suitable for any

general or particular use or promises freedom from

infringement of any patent or patents. Anyone making

use of this information assumes all liability from

such use.

In the margin of Chapters 1 through 23, a bar has

been placed to indicate a substantial technical revision

in the standard from the 2005 edition. Because of the

reorganization of the wind provisions, these bars are

not used in Chapters 26 through 31. Likewise, bars

are not used to indicate changes in any parts of the

Commentary.

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PR_version_1.indd vi 4/14/2010 1:40:43 PM

vii

ACKNOWLEDGMENTS

The American Society of Civil Engineers (ASCE)

acknowledges the work of the Minimum Design

Loads on Buildings and Other Structures Standards

Committee of the Codes and Standards Activities

Division of the Structural Engineering Institute. This

group comprises individuals from many backgrounds,

including consulting engineering, research, construc-

tion industry, education, government, design, and

private practice.

This revision of the standard began in 2006 and

incorporates information as described in the

commentary.

This standard was prepared through the consensus

standards process by balloting in compliance with

procedures of ASCE’s Codes and Standards Activities

Committee. Those individuals who serve on the

Standards Committee are:

Voting Members

Donald Dusenberry, P.E., F.ASCE,

Chair

Robert E. Bachman, P.E.,

M.ASCE, Vice-Chair

James R. Harris, Ph.D., P.E.,

M.ASCE, Past-Chair

James G. Soules, P.E., S.E.,

F.ASCE, Secretary

James R. Cagley, P.E., M.ASCE

Dominic Campi, M.ASCE

Jay H. Crandell, P.E., M.ASCE

James M. Fisher, Ph.D., P.E.,

M.ASCE

Nathan C. Gould, P.E., M.ASCE

Lawrence G. Grifﬁ s, P.E., M.ASCE

Ronald O. Hamburger, P.E.

John D. Hooper, M.ASCE

Daniel G. Howell, P.E., M.ASCE

Richart Kahler, P.E., M.ASCE

John R. Kissell, P.E., M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Robert B. Paullus Jr., P.E.,

M.ASCE

Timothy A. Reinhold, P.E.,

M.ASCE

John G. Tawresey, P.E., M.ASCE

Harry B. Thomas, P.E., M.ASCE

Thomas R. Tyson, P.E., M.ASCE

Peter J G. Willse, P.E., M.ASCE

Alan Carr

Majed A. Dabdoub

Mo A. Madani

Jonathan C. Siu, P.E., M.ASCE

Christos V. Tokas

Finley A. Charney, F.ASCE

Ronald A. Cook, Ph.D., P.E.,

M.ASCE

Bruce R. Ellingwood, Ph.D., P.E.,

F.ASCE

Theodore V. Galambos, Ph.D.,

P.E., NAE, Dist.M.ASCE

Robert D. Hanson, Ph.D., P.E.,

F.ASCE

Neil M. Hawkins, Ph.D., M.ASCE

Marc L. Levitan, A.M.ASCE

Timothy W. Mays, A.M.ASCE

Therese P. Mc Allister, P.E.

Michael O’Rourke, Ph.D., P.E.,

M.ASCE

Andrew S. Whittaker, Ph.D., S.E.,

M.ASCE

David G. Brinker, P.E., M.ASCE

Bradford K. Douglas, P.E.,

M.ASCE

Gary J. Ehrlich, P.E., M.ASCE

Satyendra K. Ghosh, M.ASCE

Dennis W. Graber, P.E., L.S.,

M.ASCE

Kurt D. Gustafson, P.E., F.ASCE

Jason J. Krohn, P.E., M.ASCE

Bonnie E. Manley, P.E., M.ASCE

Joseph J. Messersmith Jr., P.E.,

M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

Thomas D. Skaggs, P.E., M.ASCE

Brian E. Trimble, P.E., M.ASCE

Eric H. Wey, P.E., M.ASCE

Distinguished Members

Jack E. Cermak, Ph.D., P.E., NAE,

Hon.M.ASCE

Gilliam S. Harris, P.E., F.ASCE

Nicholas Isyumov, P.E., F.ASCE

Kathleen F. Jones

Kishor C. Mehta, Ph.D., P.E.,

NAE, Dist.M.ASCE

Lawrence D. Reaveley, P.E., M.

ASCE

Emil Simiu, Ph.D., P.E., F.ASCE

Yi Kwei Wen, Ph.D., M.ASCE

Associate Members

Farid Alfawakhiri, P.E., M.ASCE

Leonel I. Almanzar, P.E., M.ASCE

Iyad M. Alsamsam, Ph.D., P.E.,

S.E., M.ASCE

Bibo Bahaa

Charles C. Baldwin, P.E.,

M.ASCE

Philip R. Brazil, S.E., M.ASCE

Ray A. Bucklin, Ph.D., P.E.,

M.ASCE

Alexander Bykovtsev, P.E.,

M.ASCE

James Carlson

Anthony C. Cerino, P.E.

Robert N. Chittenden, P.E., F.ASCE

Adam Cone, S.M.ASCE

William L. Coulbourne, P.E.,

M.ASCE

Charles B. Crouse, Ph.D., P.E.,

M.ASCE

Mukti L. Das, Ph.D., P.E., F.ASCE

Richard J. Davis, P.E., M.ASCE

Yong Deng, Ph.D., M.ASCE

David H. Devalve, P.E., M.ASCE

Ryan J. Dexter, P.E.

Richard M. Drake, S.E., M.ASCE

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viii

ACKNOWLEDGMENTS

John F. Duntemann, P.E., M.ASCE

Sam S. Eskildsen, A.M.ASCE

Mohammed M. Ettouney, M.ASCE

David A. Fanella, Ph.D., P.E.,

F.ASCE

Lawrence Fischer, P.E., M.ASCE

Donna L.R. Friis, P.E., M.ASCE

Amir S.J. Gilani, P.E., S.E.,

M.ASCE

David E. Gloss, P.E., M.ASCE

Charles B. Goldsmith

David S. Gromala, P.E., M.ASCE

Reza Hassanli, S.M.ASCE

Todd R. Hawkinson, P.E.,

M.ASCE

Mark J. Henry, P.E., M.ASCE

Mark A. Hershberg, P.E., S.E.,

M.ASCE

Joseph R. Hetzel, P.E., M.ASCE

Thomas B. Higgins, P.E., S.E.,

M.ASCE

Xiapin Hua, P.E., S.E., M.ASCE

Mohammad Iqbal, Ph.D., P.E.,

S.E., F.ASCE

Christopher P. Jones, P.E.,

M.ASCE

Mohammad R. Karim

Volkan Kebeli, A.M.ASCE

Jon P. Kiland, P.E., S.E., M.ASCE

Lionel A. Lemay, P.E., M.ASCE

Philip Line, M.ASCE

Scott A. Lockyear, A.M.ASCE

John V. Loscheider, P.E., M.ASCE

David K. Low, P.E., M.ASCE

Mustafa A. Mahamid, Ph.D., P.E.,

M.ASCE

Lance Manuel, Ph.D., P.E., M.ASCE

Shalva M. Marjanishvili, P.E., S.E.,

M.ASCE

Andrew F. Martin, P.E., M.ASCE

Scott E. Maxwell, P.E., S.E.,

M.ASCE

Dennis McCreary, P.E., M.ASCE

Kevin Mcosker

J. S. Mitchell

Kit Miyamoto, P.E., S.E., F.ASCE

Rudy Mulia, P.E., M.ASCE

Javeed Munshi, P.E., M.ASCE

Frank A. Nadeau, M.ASCE

Joe N. Nunnery, P.E., M.ASCE

Robert F. Oleck Jr., P.E., M.ASCE

George N. Olive, M.ASCE

Frank K.H. Park, P.E., A.M.ASCE

Alan B. Peabody, P.E., M.ASCE

David Pierson, P.E., M.ASCE

David O. Prevatt, P.E., M.ASCE

James A. Rossberg, P.E., M.ASCE

Scott A. Russell, P.E., M.ASCE

Fahim Sadek, Ph.D., M.ASCE

Jerry R. Salmon, M.ASCE

Jeremy T. Salmon, A.M.ASCE

Phillip J. Samblanet, P.E., M.ASCE

William Scott, P.E., M.ASCE

Gary Searer

Thomas L. Smith

Jean Smith

Alexis Spyrou, P.E., M.ASCE

Theodore Stathopoulos, Ph.D.,

P.E., F.ASCE

David A. Steele, P.E., M.ASCE

Sayed Stoman, P.E., S.E., M.ASCE

Yelena K. Straight, A.M.ASCE

Lee Tedesco, Aff.M.ASCE

Jason J. Thompson

Mai Tong

David P. Tyree, P.E., M.ASCE

Victoria B. Valentine, P.E.,

M.ASCE

Miles E. Waltz, P.E., M.ASCE

Terence A. Weigel, Ph.D., P.E.,

M.ASCE

Peter Wrenn, P.E., M.ASCE

Tom C. Xia, P.E., M.ASCE

Bradley Young, M.ASCE

Subcommittee on Atmospheric

Ice Loads

Alan B. Peabody, P.E., M.ASCE,

Chair

Jamey M. Bertram, P.E., M.ASCE

David G. Brinker, P.E., M.ASCE

Joseph A. Catalano, A.M.ASCE

Maggie Emery

Karen Finstad

Asim K. Haldar

Kathleen F. Jones

Jack N. Lott

Lawrence M. Slavin, A.M.ASCE

Ronald M. Thorkildson, A.M.ASCE

Subcommittee on Dead and

Live Loads

Thomas R. Tyson, P.E., M.ASCE,

Chair

Adam W. Dayhoff, A.M.ASCE

John V. Loscheider, P.E., M.ASCE

Mustafa A. Mahamid, Ph.D., P.E.,

M.ASCE

Frank A. Nadeau, M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

John G. Tawresey, P.E., M.ASCE

Harry B. Thomas, P.E., M.ASCE

Subcommittee on Flood Loads

Christopher P. Jones, P.E., M.

ASCE, Chair

Subcommittee for General

Structural Requirements

Ronald O. Hamburger, P.E., Chair

Farid Alfawakhiri, P.E., M.ASCE

Iyad M. Alsamsam, Ph.D., P.E.,

S.E., M.ASCE

Philip R. Brazil, S.E., M.ASCE

Dominic Campi, M.ASCE

Theodore V. Galambos, Ph.D.,

P.E., NAE, Dist.M.ASCE

Satyendra K. Ghosh, M.ASCE

Nathan C. Gould, P.E., M.ASCE

James R. Harris, Ph.D., P.E.,

M.ASCE

Todd R. Hawkinson, P.E.,

M.ASCE

Thomas F. Heausler, P.E.,

M.ASCE

Jason J. Krohn, P.E., M.ASCE

Philip Line, M.ASCE

Timothy W. Mays, A.M.ASCE

Therese P. Mc Allister, P.E.

Brian J. Meacham

Timothy A. Reinhold, P.E.,

M.ASCE

Jonathan C. Siu, P.E., M.ASCE

James G. Soules, P.E., S.E.,

F.ASCE

Peter J. Vickery, M.ASCE

Subcommittee on Seismic Loads

John D. Hooper, M.ASCE, Chair

Dennis A. Alvarez, P.E., M.ASCE

Victor D. Azzi, P.E., M.ASCE

Robert E. Bachman, P.E., M.ASCE

David R. Bonneville, M.ASCE

Philip R. Brazil, S.E., M.ASCE

Philip Caldwell

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ACKNOWLEDGMENTS

Dominic Campi, M.ASCE

James A. Carlson

Finley A. Charney, F.ASCE

Robert N. Chittenden, P.E.,

F.ASCE

Charles B. Crouse, Ph.D., P.E.,

M.ASCE

Bradford K. Douglas, P.E.,

M.ASCE

Satyendra K. Ghosh, M.ASCE

John D. Gillengerten

Nathan C. Gould, P.E., M.ASCE

Ronald O. Hamburger, P.E.

Robert D. Hanson, Ph.D., P.E.,

F.ASCE

James R. Harris, Ph.D., P.E.,

M.ASCE

John L. Harris III, P.E., S.E.,

M.ASCE

Ronald W. Haupt, P.E., M.ASCE

Neil M. Hawkins, Ph.D., M.ASCE

Thomas F. Heausler, P.E.,

M.ASCE

Douglas G. Honegger, M.ASCE

Y. Henry Huang, P.E., M.ASCE

William V. Joerger, M.ASCE

Martin W. Johnson, P.E., M.ASCE

Richart Kahler, P.E., M.ASCE

Dominic J. Kelly, P.E., M.ASCE

Jon P. Kiland, P.E., S.E., M.ASCE

Charles A. Kircher, Ph.D., P.E.,

M.ASCE

Vladimir G. Kochkin, A.M.ASCE

James S. Lai, P.E., F.ASCE

Edgar V. Leyendecker

Philip Line, M.ASCE

John V. Loscheider, P.E., M.ASCE

Nicolas Luco, A.M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Bonnie E. Manley, P.E., M.ASCE

Igor Marinovic, P.E., M.ASCE

Scott E. Maxwell, P.E., S.E.,

M.ASCE

Kit Miyamoto, P.E., S.E., F.ASCE

Rudy Mulia, P.E., S.E., M.ASCE

Bernard F. Murphy, P.E., M.ASCE

Frank A. Nadeau, M.ASCE

Corey D. Norris, P.E., M.ASCE

Robert B. Paullus Jr., P.E.,

M.ASCE

Robert G. Pekelnicky, P.E., S.E.,

M.ASCE

Maurice S. Power, M.ASCE

James A. Rossberg, P.E., M.ASCE

Rafael G. Sabelli, P.E., S.E.,

M.ASCE

Phillip J. Samblanet, P.E.,

M.ASCE

William Scott, P.E., M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

John F. Silva, S.E., M.ASCE

Jonathan C. Siu, P.E., M.ASCE

Jean Smith

James G. Soules, P.E., S.E.,

F.ASCE

Harold O. Sprague Jr., P.E.,

F.ASCE

Bill Staehlin

Sayed Stoman, P.E., S.E., M.ASCE

Jason J. Thompson

Christos V. Tokas

Mai Tong

Victoria B. Valentine, P.E.,

M.ASCE

Miroslav Vejvoda, P.E., F.ASCE

Miles E. Waltz, P.E., M.ASCE

Eric H. Wey, P.E., M.ASCE

Andrew S. Whittaker, Ph.D., S.E.,

M.ASCE

Ben Youseﬁ , P.E., S.E., M.ASCE

Seismic Task Committee on

Ground Motions

Charles B. Crouse, Ph.D., P.E.,

M.ASCE, Chair

Robert E. Bachman, P.E., M.ASCE

Finley A. Charney, F.ASCE

Neil M. Hawkins, Ph.D., M.ASCE

John D. Hooper, M.ASCE

Edgar V. Leyendecker

Nicolas Luco, A.M.ASCE

Maurice S. Power, M.ASCE

William Scott, P.E., M.ASCE

Andrew S. Whittaker, Ph.D., S.E.,

M.ASCE

Seismic Task Committee on

General Provisions

Jon P. Kiland, P.E., S.E., M.ASCE,

Chair

Robert E. Bachman, P.E.,

M.ASCE

David R. Bonneville, M.ASCE

Philip R. Brazil, S.E., M.ASCE

Dominic Campi, M.ASCE

Finley A. Charney, F.ASCE

Satyendra K. Ghosh, M.ASCE

John D. Gillengerten

Nathan C. Gould, P.E., M.ASCE

Ronald O. Hamburger, P.E.

James R. Harris, Ph.D., P.E.,

M.ASCE

John L. Harris III, P.E., S.E.,

M.ASCE

John R. Hayes Jr., Ph.D., P.E.,

M.ASCE

Thomas F. Heausler, P.E.,

M.ASCE

John D. Hooper, M.ASCE

Martin W. Johnson, P.E., M.ASCE

Dominic J. Kelly, P.E., M.ASCE

Ryan A. Kersting, A.M.ASCE

Philip Line, M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Bonnie E. Manley, P.E., M.ASCE

Kit Miyamoto, P.E., S.E., F.ASCE

Rudy Mulia, P.E., S.E., M.ASCE

Robert G. Pekelnicky, P.E., S.E.,

M.ASCE

Rafael G. Sabelli, P.E., S.E.,

M.ASCE

William Scott, P.E., M.ASCE

Eric H. Wey, P.E., M.ASCE

Andrew S. Whittaker, Ph.D., S.E.,

M.ASCE

Ben Youseﬁ , P.E., S.E., M.ASCE

Seismic Task Committee on

Foundations / Site Conditions

Martin W. Johnson, P.E., M.ASCE,

Chair

Robert N. Chittenden, P.E., F.

ASCE

Charles B. Crouse, Ph.D., P.E.,

M.ASCE

Neil M. Hawkins, Ph.D., M.ASCE

Dominic J. Kelly, P.E., M.ASCE

Maurice S. Power, M.ASCE

Eric H. Wey, P.E., M.ASCE

Seismic Task Committee

on Concrete

Neil M. Hawkins, Ph.D., M.ASCE,

Chair

PR_version_1.indd ix 4/14/2010 1:40:43 PM

ACKNOWLEDGMENTS

Satyendra K. Ghosh, M.ASCE

John R. Hayes Jr., Ph.D., P.E.,

M.ASCE

Jon P. Kiland, P.E., S.E., M.ASCE

John F. Silva, S.E., M.ASCE

Miroslav Vejvoda, P.E., F.ASCE

Ben Youseﬁ , P.E., S.E., M.ASCE

Seismic Task Committee

on Masonry

Jason J. Thompson, Chair

Robert N. Chittenden, P.E., F.ASCE

Jon P. Kiland, P.E., S.E., M.ASCE

Seismic Task Committee on Steel &

Composite Structures

Rafael G. Sabelli, P.E., S.E.,

M.ASCE, Chair

Thomas F. Heausler, P.E.,

M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Bonnie E. Manley, P.E., M.ASCE

William Scott, P.E., M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

Seismic Task Committee on Wood

Philip Line, M.ASCE, Chair

Philip R. Brazil, S.E., M.ASCE

Robert N. Chittenden, P.E.,

F.ASCE

Bradford K. Douglas, P.E.,

M.ASCE

Vladimir G. Kochkin, A.M.ASCE

Bonnie E. Manley, P.E., M.ASCE

Jonathan C. Siu, P.E., M.ASCE

Miles E. Waltz, P.E., M.ASCE

Ben Youseﬁ , P.E., S.E., M.ASCE

Seismic Task Committee on

Non-Structural Components

John F. Silva, S.E., M.ASCE,

Chair

Dennis A. Alvarez, P.E., M.ASCE

Robert E. Bachman, P.E., M.ASCE

David R. Bonneville, M.ASCE

Philip J. Caldwell, A.M.ASCE

James Carlson

John D. Gillengerten

Nathan C. Gould, P.E., M.ASCE

Ronald W. Haupt, P.E., M.ASCE

Thomas F. Heausler, P.E., M.ASCE

Douglas G. Honegger, M.ASCE

Francis E. Jehrio

William V. Joerger, M.ASCE

Richard Lloyd, A.M.ASCE

Michael Mahoney

Kit Miyamoto, P.E., S.E., F.ASCE

Rudy Mulia, P.E., S.E., M.ASCE

William Scott, P.E., M.ASCE

Jean Smith

James G. Soules, P.E., S.E.,

F.ASCE

Harold O. Sprague Jr., P.E.,

F.ASCE

Bill Staehlin

Chris Tokas

Victoria B. Valentine, P.E.,

M.ASCE

Eric H. Wey, P.E., M.ASCE

Paul R. Wilson, P.E., M.ASCE

Seismic Task Committee on

Administrative and QA Provisions

Jonathan C. Siu, P.E., M.ASCE,

Chair

Robert E. Bachman, P.E., M.ASCE

Philip R. Brazil, S.E., M.ASCE

John D. Hooper, M.ASCE

Jon P. Kiland, P.E., S.E., M.ASCE

Robert G. Pekelnicky, P.E., S.E.,

M.ASCE

John F. Silva, S.E., M.ASCE

Seismic Task Committee on Seismic

Isolation and Damping

Andrew S. Whittaker, Ph.D., S.E.,

M.ASCE, Chair

Robert E. Bachman, P.E., M.ASCE

Finley A. Charney, F.ASCE

Robert D. Hanson, Ph.D., P.E.,

F.ASCE

Martin W. Johnson, P.E., M.ASCE

Charles A. Kircher, Ph.D., P.E.,

M.ASCE

Kit Miyamoto, P.E., S.E., F.ASCE

Seismic Task Committee on

Non-Building Structures

James G. Soules, P.E., S.E.,

F.ASCE, Chair

Victor D. Azzi, P.E., M.ASCE

Robert E. Bachman, P.E., M.ASCE

Philip J. Caldwell, A.M.ASCE

Charles B. Crouse, Ph.D., P.E.,

M.ASCE

Ronald W. Haupt, P.E., M.ASCE

Thomas F. Heausler, P.E.,

M.ASCE

Douglas G. Honegger, M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Rudy Mulia, P.E., S.E., M.ASCE

William Scott, P.E., M.ASCE

John F. Silva, S.E., M.ASCE

Harold O. Sprague Jr., P.E.,

F.ASCE

Sayed Stoman, P.E., S.E., M.ASCE

Eric H. Wey, P.E., M.ASCE

Subcommittee on Snow and

Rain Loads

Michael O’Rourke, Ph.D., P.E.,

M.ASCE, Chair

Timothy J. Allison, A.M.ASCE

John Cocca, A.M.ASCE

Bradford K. Douglas, P.E.,

M.ASCE

John F. Duntemann, P.E., M.ASCE

Gary J. Ehrlich, P.E., M.ASCE

James M. Fisher, Ph.D., P.E.,

M.ASCE

James R. Harris, Ph.D., P.E.,

M.ASCE

Thomas B. Higgins, P.E., S.E.,

M.ASCE

Daniel G. Howell, P.E., M.ASCE

Nicholas Isyumov, P.E., F.ASCE

Scott A. Lockyear, A.M.ASCE

Ian Mackinlay, Aff.M.ASCE

Joe N. Nunnery, P.E., M.ASCE

George N. Olive, M.ASCE

Michael F. Pacey, P.E., M.ASCE

David B. Peraza, P.E., M.ASCE

Mark K. Radmaker, P.E.

Scott A. Russell, P.E., M.ASCE

Ronald L. Sack, Ph.D., P.E.,

F.ASCE

Joseph D. Scholze, P.E., M.ASCE

Gary L. Schumacher, P.E.,

M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

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ACKNOWLEDGMENTS

Daniel J. Walker, P.E., M.ASCE

Peter Wrenn, P.E., M.ASCE

Subcommittee on Strength Criteria

Bruce R. Ellingwood, Ph.D., P.E.,

M.ASCE, Chair

Therese P. McAllister, P.E.

Iyad M. Alsamsam, Ph.D., P.E.,

S.E., M.ASCE

Charles C. Baldwin, P.E., M.ASCE

Theodore V. Galambos, Ph.D.,

P.E., NAE, Dist.M.ASCE

David S. Gromala, P.E., M.ASCE

Ronald O. Hamburger, P.E.

James R. Harris, Ph.D., P.E.,

M.ASCE

Nestor R. Iwankiw, P.E., M.ASCE

John V. Loscheider, P.E.,

M.ASCE

Sanjeev R. Malushte, P.E., S.E.,

F.ASCE

Clarkson W. Pinkham, P.E.,

F.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

James G. Soules, P.E., S.E.,

F.ASCE

Jason J. Thompson

Yi Kwei Wen, Ph.D., M.ASCE

Subcommittee on Wind Loads

Voting Members

Ronald A. Cook, Ph.D., P.E.,

M.ASCE, Chair

Gary Y.K. Chock, M.ASCE

Jay H. Crandell, P.E., M.ASCE

Bradford K. Douglas, P.E.,

M.ASCE

Charles Everly, P.E., CBO

Charles B. Goldsmith

Dennis W. Graber, P.E., L.S.,

M.ASCE

Lawrence G. Grifﬁ s, P.E.,

M.ASCE

Gilliam S. Harris, P.E., F.ASCE

Peter A. Irwin, Ph.D., P.Eng,

F.ASCE

Ahsan Kareem, Ph.D., M.ASCE

Marc L. Levitan, A.M.ASCE

Mo A.F. Madani

Joseph J. Messersmith Jr., P.E.,

M.ASCE

Jon A. Peterka, P.E., M.ASCE

Timothy A. Reinhold, P.E.,

M.ASCE

Donald R. Scott, P.E., M.ASCE

Emil Simiu, Ph.D., P.E., F.ASCE

Douglas A. Smith, P.E., M.ASCE

Thomas L. Smith

Thomas E. Stafford

Theodore Stathopoulos, Ph.D.,

P.E., F.ASCE

Peter J. Vickery, M.ASCE

Robert J. Wills, P.E., M.ASCE

Associate Members

Timothy J. Allison, A.M.ASCE

Roberto H. Behncke, Aff.M.ASCE

Daryl W. Boggs, P.E., M.ASCE

William L. Coulbourne, P.E.,

M.ASCE

Richard J. Davis, P.E., M.ASCE

Joffrey Easley, P.E., M.ASCE

Gary J. Ehrlich, P.E., M.ASCE

Donna L.R. Friis, P.E., M.ASCE

Jon K. Galsworthy, P.E., M.ASCE

Gerald L. Hatch, P.E., L.S.,

M.ASCE

Mark J. Henry, P.E., M.ASCE

Joseph R. Hetzel, P.E., M.ASCE

Thomas B. Higgins, P.E., S.E.,

M.ASCE

Nicholas Isyumov, P.E., F.ASCE

Anurag Jain, Ph.D., P.E., M.ASCE

Edward L. Keith, P.E., M.ASCE

Robert Konz, P.E., M.ASCE

Edward M. Laatsch, P.E., M.ASCE

Philip Line, M.ASCE

Scott A. Lockyear, A.M.ASCE

John V. Loscheider, P.E., M.ASCE

Andrew F. Martin, P.E., M.ASCE

Patrick W. McCarthy, P.E.,

M.ASCE

Kishor C. Mehta, Ph.D., P.E.,

NAE, Dist.M.ASCE

George N. Olive, M.ASCE

Robert B. Paullus Jr., P.E.,

M.ASCE

Rick Perry

William C. Rosencutter, P.E.,

M.ASCE

William L. Shoemaker, Ph.D., P.E.,

M.ASCE

Peter J G. Willse, P.E., M.ASCE

Tom C. Xia, P.E., M.ASCE

PR_version_1.indd xi 4/14/2010 1:40:44 PM

PR_version_1.indd xii 4/14/2010 1:40:44 PM

xiii

DEDICATION

Thomas R. Tyson, P.E., S.E.

The members of the Minimum Design Loads for Buildings and Other Structures Standards

Committee of the Structural Engineering Institute respectfully dedicate this Standard in the

memory of Thomas R. Tyson, P.E., S.E., who passed away on December 19, 2009.

His structural engineering expertise complemented his dedication to our profession, and these

qualities guided the members of the Live Load Subcommittee, which he chaired during the prepara-

tion of this Standard. His practical advice, quick smile, and good nature will be greatly missed.

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PR_version_1.indd xiv 4/14/2010 1:40:44 PM

CONTENTS

Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Deﬁ nitions and Notations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.1 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.2 Symbols and Notations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Basic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1 Strength and Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1.1 Strength Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3.1.2 Allowable Stress Procedures . . . . . . . . . . . . . . . . . . . . . . 3

1.3.1.3 Performance-Based Procedures . . . . . . . . . . . . . . . . . . . . 3

1.3.2 Serviceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3.3 Self-Straining Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3.4 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3.5 Counteracting Structural Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4 General Structural Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.1 Load Combinations of Integrity Loads . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.1.1 Strength Design Notional Load Combinations . . . . . . . . 4

1.4.1.2 Allowable Stress Design Notional Load

Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.2 Load Path Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.3 Lateral Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.4 Connection to Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.5 Anchorage of Structural Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.4.6 Extraordinary Loads and Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5 Classiﬁ cation of Buildings and Other Structures . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5.1 Risk Categorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5.2 Multiple Risk Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5.3 Toxic, Highly Toxic, and Explosive Substances . . . . . . . . . . . . . . . . . 5

1.6 Additions and Alterations to Existing Structures . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.7 Load Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.8 Consensus Standards and Other Referenced Documents . . . . . . . . . . . . . . . . . . 6

2 Combinations of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Combining Factored Loads Using Strength Design . . . . . . . . . . . . . . . . . . . . . . 7

2.3.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.2 Basic Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.3 Load Combinations Including Flood Load . . . . . . . . . . . . . . . . . . . . . 7

2.3.4 Load Combinations Including Atmospheric Ice Loads . . . . . . . . . . . . 8

2.3.5 Load Combinations Including Self-Straining Loads . . . . . . . . . . . . . . 8

2.3.6 Load Combinations for Nonspeciﬁ ed Loads . . . . . . . . . . . . . . . . . . . . 8

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CONTENTS

xvi

2.4 Combining Nominal Loads Using Allowable Stress Design . . . . . . . . . . . . . . . 8

2.4.1 Basic Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.4.2 Load Combinations Including Flood Load . . . . . . . . . . . . . . . . . . . . . 9

2.4.3 Load Combinations Including Atmospheric Ice

Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4.4 Load Combinations Including Self-Straining Loads . . . . . . . . . . . . . . 9

2.5 Load Combinations for Extraordinary Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5.2 Load Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5.2.1 Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5.2.2 Residual Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5.3 Stability Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Dead Loads, Soil Loads, and Hydrostatic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1 Dead Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.1 Deﬁ nition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.2 Weights of Materials and Constructions . . . . . . . . . . . . . . . . . . . . . . . 11

3.1.3 Weight of Fixed Service Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2 Soil Loads and Hydrostatic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2.1 Lateral Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.2.2 Uplift on Floors and Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4 Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Loads Not Speciﬁ ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3 Uniformly Distributed Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3.1 Required Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3.2 Provision for Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3.3 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.4 Concentrated Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.5 Loads on Handrail, Guardrail, Grab Bar, Vehicle Barrier Systems,

and Fixed Ladders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.1 Loads on Handrail and Guardrail Systems . . . . . . . . . . . . . . . . . . . . . 14

4.5.2 Loads on Grab Bar Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.3 Loads on Vehicle Barrier Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.5.4 Loads on Fixed Ladders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6 Impact Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.2 Elevators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6.3 Machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.7 Reduction in Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.7.2 Reduction in Uniform Live Loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.7.3 Heavy Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.7.4 Passenger Vehicle Garages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.7.5 Assembly Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.7.6 Limitations on One-Way Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.8 Reduction in Roof Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.8.2 Flat, Pitched, and Curved Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.8.3 Special Purpose Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.9 Crane Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.9.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.9.2 Maximum Wheel Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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4.9.3 Vertical Impact Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.9.4 Lateral Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.9.5 Longitudinal Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5 Flood Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.3 Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.3.1 Design Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.3.2 Erosion and Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.3.3 Loads on Breakaway Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.4 Loads During Flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4.1 Load Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4.2 Hydrostatic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4.3 Hydrodynamic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4.4 Wave Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.4.4.1 Breaking Wave Loads on Vertical Pilings and

Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.4.4.2 Breaking Wave Loads on Vertical Walls . . . . . . . . . . . . . 23

5.4.4.3 Breaking Wave Loads on Nonvertical

Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.4.4.4 Breaking Wave Loads from Obliquely

Incident Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.4.5 Impact Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

5.5 Consensus Standards and Other Referenced Documents . . . . . . . . . . . . . . . . . . 25

6 Reserved for Future Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7 Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.1 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.2 Ground Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.3 Flat Roof Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.3.1 Exposure Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.3.2 Thermal Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.3.3 Importance Factor, I

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.3.4 Minimum Snow Load for Low-Slope Roofs, p

. . . . . . . . . . . . . . . . 29

7.4 Sloped Roof Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4.1 Warm Roof Slope Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4.2 Cold Roof Slope Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4.3 Roof Slope Factor for Curved Roofs . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4.4 Roof Slope Factor for Multiple Folded Plate, Sawtooth, and

Barrel Vault Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4.5 Ice Dams and Icicles Along Eaves . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.5 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.5.1 Continuous Beam Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.5.2 Other Structural Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.6 Unbalanced Roof Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.6.1 Unbalanced Snow Loads for Hip and

Gable Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.6.2 Unbalanced Snow Loads for Curved Roofs . . . . . . . . . . . . . . . . . . . . 32

7.6.3 Unbalanced Snow Loads for Multiple Folded Plate, Sawtooth,

and Barrel Vault Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.6.4 Unbalanced Snow Loads for Dome Roofs . . . . . . . . . . . . . . . . . . . . . 32

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7.7 Drifts on Lower Roofs (Aerodynamic Shade) . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.7.1 Lower Roof of a Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.7.2 Adjacent Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.8 Roof Projections and Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.9 Sliding Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.10 Rain-On-Snow Surcharge Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.11 Ponding Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.12 Existing Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

8 Rain Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.1 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.2 Roof Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.3 Design Rain Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.4 Ponding Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.5 Controlled Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

9 Reserved for Future Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

10 Ice Loads—Atmospheric Icing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.1 Site-Speciﬁ c Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.2 Dynamic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.1.3 Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

10.3 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4 Ice Loads Due to Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.1 Ice Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.2 Nominal Ice Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.3 Height Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.4 Importance Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.5 Topographic Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

10.4.6 Design Ice Thickness for Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . 48

10.5 Wind on Ice-Covered Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

10.5.1 Wind on Ice-Covered Chimneys, Tanks, and Similar Structures . . . . 49

10.5.2 Wind on Ice-Covered Solid Freestanding Walls and Solid Signs . . . 49

10.5.3 Wind on Ice-Covered Open Signs and Lattice Frameworks . . . . . . . 49

10.5.4 Wind on Ice-Covered Trussed Towers . . . . . . . . . . . . . . . . . . . . . . . . 49

10.5.5 Wind on Ice-Covered Guys and Cables . . . . . . . . . . . . . . . . . . . . . . . 49

10.6 Design Temperatures for Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

10.7 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

10.8 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

10.9 Consensus Standards and Other Referenced Documents . . . . . . . . . . . . . . . . . . 50

11 Seismic Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.1.3 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.1.4 Alternate Materials and Methods of Construction . . . . . . . . . . . . . . . 57

11.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

11.3 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

11.4 Seismic Ground Motion Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

11.4.1 Mapped Acceleration Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

11.4.2 Site Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

11.4.3 Site Coefﬁ cients and Risk-Targeted Maximum Considered

Earthquake (MCER) Spectral Response Acceleration Parameters . . . 65

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11.4.4 Design Spectral Acceleration Parameters . . . . . . . . . . . . . . . . . . . . . . 65

11.4.5 Design Response Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

11.4.6 Risk-Targeted Maximum Considered (MCER) Response

Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

11.4.7 Site-Speciﬁ c Ground Motion Procedures . . . . . . . . . . . . . . . . . . . . . . 67

11.5 Importance Factor and Risk Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

11.5.1 Importance Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

11.5.2 Protected Access for Risk Category IV . . . . . . . . . . . . . . . . . . . . . . . . 67

11.6 Seismic Design Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

11.7 Design Requirements for Seismic Design Category A . . . . . . . . . . . . . . . . . . . . 68

11.8 Geologic Hazards and Geotechnical Investigation . . . . . . . . . . . . . . . . . . . . . . . 68

11.8.2 Geotechnical Investigation Report

Requirements for Seismic Design Categories C through F . . . . . . . . 68

11.8.3 Additional Geotechnical Investigation Report Requirements for

Seismic Design Categories D through F . . . . . . . . . . . . . . . . . . . . . . . 68

12 Seismic Design Requirements for Building Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.1 Structural Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.1.1 Basic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.1.2 Member Design, Connection Design, and Deformation Limit . . . . . . 71

12.1.3 Continuous Load Path and Interconnection . . . . . . . . . . . . . . . . . . . . 71

12.1.4 Connection to Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.1.5 Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

12.1.6 Material Design and Detailing Requirements . . . . . . . . . . . . . . . . . . . 72

12.2 Structural System Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

12.2.1 Selection and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

12.2.2 Combinations of Framing Systems in Different Directions . . . . . . . . 72

12.2.3 Combinations of Framing Systems in the Same Direction . . . . . . . . . 72

12.2.3.1 R, C

, and Ω

Values for Vertical Combinations . . . . . . . 72

12.2.3.2 Two Stage Analysis Procedure . . . . . . . . . . . . . . . . . . . . . 72

12.2.3.3 R, C

, and Ω

Values for Horizontal

Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

12.2.4 Combination Framing Detailing Requirements . . . . . . . . . . . . . . . . . . 78

12.2.5 System Speciﬁ c Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

12.2.5.1 Dual System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

12.2.5.2 Cantilever Column Systems . . . . . . . . . . . . . . . . . . . . . . . 78

12.2.5.3 Inverted Pendulum-Type Structures . . . . . . . . . . . . . . . . . 78

12.2.5.4 Increased Structural Height Limit for Steel

Eccentrically Braced Frames, Steel Special

Concentrically Braced Frames, Steel

Buckling-restrained Braced Frames, Steel Special

Plate Shear Walls and Special Reinforced Concrete

Shear Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

12.2.5.5 Special Moment Frames in Structures Assigned to

Seismic Design Categories D through F . . . . . . . . . . . . . 79

12.2.5.6 Steel Ordinary Moment Frames . . . . . . . . . . . . . . . . . . . . 79

12.2.5.7 Steel Intermediate Moment Frames . . . . . . . . . . . . . . . . . 79

12.2.5.8 Shear Wall-Frame Interactive Systems . . . . . . . . . . . . . . 80

12.3 Diaphragm Flexibility, Conﬁ guration Irregularities, and Redundancy . . . . . . . . 80

12.3.1 Diaphragm Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

12.3.1.1 Flexible Diaphragm Condition . . . . . . . . . . . . . . . . . . . . . 80

12.3.1.2 Rigid Diaphragm Condition . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.1.3 Calculated Flexible Diaphragm Condition . . . . . . . . . . . 81

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12.3.2 Irregular and Regular Classiﬁ cation . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.2.1 Horizontal Irregularity . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.2.2 Vertical Irregularity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.3 Limitations and Additional Requirements for Systems with

Structural Irregularities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.3.1 Prohibited Horizontal and Vertical Irregularities for

Seismic Design Categories D through F . . . . . . . . . . . . . 81

12.3.3.2 Extreme Weak Stories . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

12.3.3.3 Elements Supporting Discontinuous Walls or Frames . . . 82

12.3.3.4 Increase in Forces Due to Irregularities for Seismic

Design Categories D through F . . . . . . . . . . . . . . . . . . . . 82

12.3.4 Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

12.3.4.1 Conditions Where Value of ρ is 1.0 . . . . . . . . . . . . . . . . . 83

12.3.4.2 Redundancy Factor, ρ, for Seismic Design

Categories D through F . . . . . . . . . . . . . . . . . . . . . . . . . . 84

12.4 Seismic Load Effects and Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

12.4.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

12.4.2 Seismic Load Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

12.4.2.1 Horizontal Seismic Load Effect . . . . . . . . . . . . . . . . . . . . 84

12.4.2.2 Vertical Seismic Load Effect . . . . . . . . . . . . . . . . . . . . . . 86

12.4.2.3 Seismic Load Combinations . . . . . . . . . . . . . . . . . . . . . . 86

12.4.3 Seismic Load Effect Including Overstrength Factor . . . . . . . . . . . . . . 86

12.4.3.1 Horizontal Seismic Load Effect with Overstrength

Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

12.4.3.2 Load Combinations with

Overstrength Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.4.3.3 Allowable Stress Increase for Load

Combinations with Overstrength . . . . . . . . . . . . . . . . . . . 87

12.4.4 Minimum Upward Force for Horizontal Cantilevers for Seismic

Design Categories D through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5 Direction of Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5.1 Direction of Loading Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5.2 Seismic Design Category B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5.3 Seismic Design Category C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

12.5.4 Seismic Design Categories D through F . . . . . . . . . . . . . . . . . . . . . . . 88

12.6 Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

12.7 Modeling Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

12.7.1 Foundation Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

12.7.2 Effective Seismic Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

12.7.3 Structural Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

12.7.4 Interaction Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

12.8 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

12.8.1 Seismic Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

12.8.1.1 Calculation of Seismic Response Coefﬁ cient . . . . . . . . . 89

12.8.1.2 Soil Structure Interaction Reduction . . . . . . . . . . . . . . . . 90

12.8.1.3 Maximum Ss Value in Determination of Cs . . . . . . . . . . 90

12.8.2 Period Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

12.8.2.1 Approximate Fundamental Period . . . . . . . . . . . . . . . . . . 90

12.8.3 Vertical Distribution of Seismic Forces. . . . . . . . . . . . . . . . . . . . . . . . 91

12.8.4 Horizontal Distribution of Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

12.8.4.1 Inherent Torsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

12.8.4.2 Accidental Torsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

12.8.4.3 Ampliﬁ cation of Accidental Torsional Moment . . . . . . . 91

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12.8.5 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

12.8.6 Story Drift Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

12.8.6.1 Minimum Base Shear for Computing Drift . . . . . . . . . . . 92

12.8.6.2 Period for Computing Drift . . . . . . . . . . . . . . . . . . . . . . . 93

12.8.7 P-Delta Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

12.9 Modal Response Spectrum Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.1 Number of Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.2 Modal Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.3 Combined Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.4 Scaling Design Values of Combined Response . . . . . . . . . . . . . . . . . 94

12.9.4.1 Scaling of Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.4.2 Scaling of Drifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.5 Horizontal Shear Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.6 P-Delta Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.9.7 Soil Structure Interaction Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.10 Diaphragms, Chords, and Collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.10.1 Diaphragm Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

12.10.1.1 Diaphragm Design Forces . . . . . . . . . . . . . . . . . . . . . . . . 94

12.10.2 Collector Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

12.10.2.1 Collector Elements Requiring Load Combinations

with Overstrength Factor for Seismic Design

Categories C through F . . . . . . . . . . . . . . . . . . . . . . . . . . 95

12.11 Structural Walls and Their Anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.11.1 Design for Out-of-Plane Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.11.2 Anchorage of Structural Walls and Transfer of Design Forces

into Diaphragms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.11.2.1 Wall Anchorage Forces . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.11.2.2 Additional Requirements for Diaphragms in

Structures Assigned to Seismic Design Categories

C through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.12 Drift And Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

12.12.1 Story Drift Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

12.12.1.1 Moment Frames in Structures Assigned to Seismic

Design Categories D through F . . . . . . . . . . . . . . . . . . . . 97

12.12.2 Diaphragm Deﬂ ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

12.12.3 Structural Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

12.12.4 Members Spanning between Structures . . . . . . . . . . . . . . . . . . . . . . . 98

12.12.5 Deformation Compatibility for Seismic Design Categories D

through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13 Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.1 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.2 Materials of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.3 Foundation Load-Deformation Characteristics . . . . . . . . . . . . . . . . . . 98

12.13.4 Reduction of Foundation Overturning . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.5 Requirements for Structures Assigned to Seismic Design

Category C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.5.1 Pole-Type Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

12.13.5.2 Foundation Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

12.13.5.3 Pile Anchorage Requirements . . . . . . . . . . . . . . . . . . . . . 99

12.13.6 Requirements for Structures Assigned to Seismic Design

Categories D through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

12.13.6.1 Pole-Type Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

12.13.6.2 Foundation Ties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

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12.13.6.3 General Pile Design Requirement . . . . . . . . . . . . . . . . . . 99

12.13.6.4 Batter Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

12.13.6.5 Pile Anchorage Requirements . . . . . . . . . . . . . . . . . . . . . 99

12.13.6.6 Splices of Pile Segments . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.13.6.7 Pile Soil Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.13.6.8 Pile Group Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.14 Simpliﬁ ed Alternative Structural Design Criteria for Simple Bearing Wall

or Building Frame Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.14.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

12.14.1.1 Simpliﬁ ed Design Procedure . . . . . . . . . . . . . . . . . . . . . . 100

12.14.1.2 Reference Documents. . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

12.14.1.3 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

12.14.1.4 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

12.14.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

12.14.3 Seismic Load Effects and Combinations . . . . . . . . . . . . . . . . . . . . . . . 104

12.14.3.1 Seismic Load Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

12.14.3.2 Seismic Load Effect Including a 2.5 Overstrength

Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

12.14.4 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.4.1 Selection and Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.4.2 Combinations of Framing Systems . . . . . . . . . . . . . . . . . 106

12.14.5 Diaphragm Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.6 Application of Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.7 Design and Detailing Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.7.1 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

12.14.7.2 Openings or Reentrant Building Corners . . . . . . . . . . . . 107

12.14.7.3 Collector Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

12.14.7.4 Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

12.14.7.5 Anchorage of Structural Walls . . . . . . . . . . . . . . . . . . . . . 107

12.14.7.6 Bearing Walls and Shear Walls . . . . . . . . . . . . . . . . . . . . 108

12.14.7.7 Anchorage of Nonstructural Systems . . . . . . . . . . . . . . . 108

12.14.8 Simpliﬁ ed Lateral Force Analysis Procedure . . . . . . . . . . . . . . . . . . . 108

12.14.8.1 Seismic Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

12.14.8.2 Vertical Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

12.14.8.3 Horizontal Shear Distribution . . . . . . . . . . . . . . . . . . . . . 108

12.14.8.4 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

12.14.8.5 Drift Limits and Building Separation . . . . . . . . . . . . . . . 109

13 Seismic Design Requirements for Nonstructural Components . . . . . . . . . . . . . . . . . . . . . . 111

13.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.2 Seismic Design Category . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.3 Component Importance Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.4 Exemptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.5 Application of Nonstructural Component Requirements to

Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

13.1.6 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

13.1.7 Reference Documents Using Allowable Stress Design . . . . . . . . . . . 112

13.2 General Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

13.2.1 Applicable Requirements for Architectural, Mechanical, and

Electrical Components, Supports, and Attachments . . . . . . . . . . . . . . 112

13.2.2 Special Certiﬁ cation Requirements for Designated Seismic

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

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13.2.3 Consequential Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.2.4 Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.2.5 Testing Alternative for Seismic

Capacity Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.2.6 Experience Data Alternative for Seismic Capacity

Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.2.7 Construction Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.3 Seismic Demands on Nonstructural Components . . . . . . . . . . . . . . . . . . . . . . . . 113

13.3.1 Seismic Design Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

13.3.2 Seismic Relative Displacements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

13.3.2.1 Displacements within Structures . . . . . . . . . . . . . . . . . . . 114

13.3.2.2 Displacements between Structures . . . . . . . . . . . . . . . . . . 114

13.4 Nonstructural Component Anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.1 Design Force in the Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.2 Anchors in Concrete or Masonry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.2.1 Anchors in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.2.2 Anchors in Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.2.3 Post-Installed Anchors in Concrete and

Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.3 Installation Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.4 Multiple Attachments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.5 Power Actuated Fasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.4.6 Friction Clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

13.5 Architectural Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.2 Forces and Displacements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.3 Exterior Nonstructural Wall Elements and Connections . . . . . . . . . . . 116

13.5.4 Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.5 Out-of-Plane Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.6 Suspended Ceilings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.6.1 Seismic Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

13.5.6.2 Industry Standard Construction for Acoustical Tile

or Lay-in Panel Ceilings . . . . . . . . . . . . . . . . . . . . . . . . . 117

13.5.6.3 Integral Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.7 Access Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.7.2 Special Access Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.8 Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

13.5.8.2 Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

13.5.9 Glass in Glazed Curtain Walls, Glazed Storefronts, and

Glazed Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

13.5.9.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

13.5.9.2 Seismic Drift Limits for Glass Components . . . . . . . . . . 119

13.6 Mechanical and Electrical Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

13.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

13.6.2 Component Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

13.6.3 Mechanical Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

13.6.4 Electrical Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

13.6.5 Component Supports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

13.6.5.1 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

13.6.5.2 Design for Relative Displacement . . . . . . . . . . . . . . . . . . 122

13.6.5.3 Support Attachment to Component . . . . . . . . . . . . . . . . . 122

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13.6.5.4 Material Detailing Requirements . . . . . . . . . . . . . . . . . . . 122

13.6.5.5 Additional Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 122

13.6.5.6 Conduit, Cable Tray, and Other Electrical

Distribution Systems (Raceways) . . . . . . . . . . . . . . . . . . 123

13.6.6 Utility and Service Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

13.6.7 Ductwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

13.6.8 Piping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

13.6.8.1 ASME Pressure Piping Systems . . . . . . . . . . . . . . . . . . . 124

13.6.8.2 Fire Protection Sprinkler Piping Systems . . . . . . . . . . . . 124

13.6.8.3 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

13.6.9 Boilers and Pressure Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

13.6.10 Elevator and Escalator Design Requirements . . . . . . . . . . . . . . . . . . . 125

13.6.10.1 Escalators, Elevators, and Hoistway Structural

System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

13.6.10.2 Elevator Equipment and Controller Supports and

Attachments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

13.6.10.3 Seismic Controls for Elevators . . . . . . . . . . . . . . . . . . . . 125

13.6.10.4 Retainer Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

13.6.11 Other Mechanical and Electrical Components . . . . . . . . . . . . . . . . . . 125

14 Material Speciﬁ c Seismic Design and Detailing Requirements . . . . . . . . . . . . . . . . . . . . . 127

14.0 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1 Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.1 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.2 Structural Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.2.2 Seismic Requirements for Structural Steel

Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.3 Cold-Formed Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.3.2 Seismic Requirements for Cold-Formed Steel

Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

14.1.3.3 Modiﬁ cations to AISI S110 . . . . . . . . . . . . . . . . . . . . . . . 128

14.1.4 Cold-Formed Steel Light-Frame Construction . . . . . . . . . . . . . . . . . . 128

14.1.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

14.1.4.2 Seismic Requirements for Cold-Formed Steel

Light-Frame Construction . . . . . . . . . . . . . . . . . . . . . . . . 128

14.1.4.3 Prescriptive Cold-Formed Steel Light-Frame

Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.1.5 Steel Deck Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.1.6 Steel Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.1.7 Additional Detailing Requirements for Steel Piles in Seismic

Design Categories D through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2.1 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2.2 Modiﬁ cations to ACI 318 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2.2.1 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2.2.2 ACI 318, Section 7.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

14.2.2.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

14.2.2.4 Intermediate Precast Structural Walls . . . . . . . . . . . . . . . 130

14.2.2.5 Wall Piers and Wall Segments . . . . . . . . . . . . . . . . . . . . . 130

14.2.2.6 Special Precast Structural Walls . . . . . . . . . . . . . . . . . . . 130

14.2.2.7 Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

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14.2.2.8 Detailed Plain Concrete Shear Walls . . . . . . . . . . . . . . . . 130

14.2.2.9 Strength Requirements for Anchors . . . . . . . . . . . . . . . . . 131

14.2.3 Additional Detailing Requirements for Concrete Piles . . . . . . . . . . . . 131

14.2.3.1 Concrete Pile Requirements for Seismic Design

Category C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

14.2.3.2 Concrete Pile Requirements for Seismic Design

Categories D through F . . . . . . . . . . . . . . . . . . . . . . . . . . 132

14.3 Composite Steel And Concrete Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.3.1 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.3.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.3.3 Seismic Requirements for Composite Steel and Concrete

Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.3.4 Metal-Cased Concrete Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4.1 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4.2 R factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4.3 Modiﬁ cations to Chapter 1 of TMS 402/ACI 530/ASCE 5 . . . . . . . . 134

14.4.3.1 Separation Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4.4 Modiﬁ cations to Chapter 2 of TMS 402/ACI 530/ASCE 5 . . . . . . . . 134

14.4.4.1 Stress Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

14.4.4.2 Reinforcement Requirements and Details . . . . . . . . . . . . 134

14.4.5 Modiﬁ cations to Chapter 3 of TMS 402/ACI 530/ASCE 5 . . . . . . . . 135

14.4.5.1 Anchoring to Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

14.4.5.2 Splices in Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . 135

14.4.5.3 Coupling Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

14.4.5.4 Deep Flexural Members . . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.4.5.5 Walls with Factored Axial Stress Greater Than

0.05 fm′. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.4.5.6 Shear Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.4.6 Modiﬁ cations to Chapter 6 of TMS 402/ACI 530/ASCE 5 . . . . . . . . 136

14.4.6.1 Corrugated Sheet Metal Anchors . . . . . . . . . . . . . . . . . . . 136

14.4.7 Modiﬁ cations to TMS 602/ACI 530.1/ASCE 6 . . . . . . . . . . . . . . . . . 136

14.4.7.1 Construction Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.5 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.5.1 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

14.5.2 Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

15 Seismic Design Requirements for Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . 139

15.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

15.1.1 Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

15.1.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

15.1.3 Structural Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . 139

15.2 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

15.3 Nonbuilding Structures Supported by Other Structures . . . . . . . . . . . . . . . . . . . 139

15.3.1 Less Than 25 percent Combined Weight Condition . . . . . . . . . . . . . . 139

15.3.2 Greater Than or Equal to 25 Percent Combined Weight

Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

15.3.3 Architectural, Mechanical, and Electrical Components . . . . . . . . . . . 140

15.4 Structural Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

15.4.1 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

15.4.1.1 Importance Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

15.4.2 Rigid Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

15.4.3 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

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15.4.4 Fundamental Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

15.4.5 Drift Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.6 Materials Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.7 Deﬂ ection Limits and Structure Separation . . . . . . . . . . . . . . . . . . . . 145

15.4.8 Site-Speciﬁ c Response Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.9 Anchors in Concrete or Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.9.1 Anchors in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.9.2 Anchors in Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.4.9.3 Post-Installed Anchors in Concrete and

Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.5 Nonbuilding Structures Similar to Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.5.2 Pipe Racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.5.2.1 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

15.5.3 Steel Storage Racks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15.5.3.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15.5.3.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15.5.3.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15.5.3.4 Alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

15.5.3.5 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.3.6 Operating Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.3.7 Vertical Distribution of Seismic Forces . . . . . . . . . . . . . . 147

15.5.3.8 Seismic Displacements . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.4 Electrical Power Generating Facilities . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.4.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.5 Structural Towers for Tanks and Vessels . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.6 Piers and Wharves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.5.6.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

15.6 General Requirements for Nonbuilding Structures Not Similar to

Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

15.6.1 Earth-Retaining Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

15.6.2 Stacks and Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

15.6.3 Amusement Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

15.6.4 Special Hydraulic Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.6.4.1 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.6.5 Secondary Containment Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.6.5.1 Freeboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.6.6 Telecommunication Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.7 Tanks and Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.7.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

15.7.3 Strength and Ductility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

15.7.4 Flexibility of Piping Attachments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

15.7.5 Anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

15.7.6 Ground-Supported Storage Tanks for Liquids . . . . . . . . . . . . . . . . . . 152

15.7.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

15.7.7 Water Storage and Water Treatment Tanks and Vessels . . . . . . . . . . . 155

15.7.7.1 Welded Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

15.7.7.2 Bolted Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

15.7.7.3 Reinforced and Prestressed Concrete . . . . . . . . . . . . . . . . 155

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15.7.8 Petrochemical and Industrial Tanks and Vessels Storing Liquids . . . 155

15.7.8.1 Welded Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

15.7.8.2 Bolted Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

15.7.8.3 Reinforced and Prestressed Concrete . . . . . . . . . . . . . . . . 155

15.7.9 Ground-Supported Storage Tanks for Granular Materials . . . . . . . . . 156

15.7.9.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.9.2 Lateral Force Determination . . . . . . . . . . . . . . . . . . . . . . 156

15.7.9.3 Force Distribution to Shell and Foundation . . . . . . . . . . 156

15.7.9.4 Welded Steel Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.9.5 Bolted Steel Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.9.6 Reinforced Concrete Structures Reinforced concrete

structures for the storage of granular materials shall

be designed in accordance with the seismic force

requirements of this standard and the requirements

of ACI 313. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.9.7 Prestressed Concrete Structures . . . . . . . . . . . . . . . . . . . . 156

15.7.10 Elevated Tanks and Vessels for Liquids and Granular Materials . . . . 156

15.7.10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.10.2 Effective Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156

15.7.10.3 P-Delta Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

15.7.10.4 Transfer of Lateral Forces into

Support Tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

15.7.10.5 Evaluation of Structures Sensitive to Buckling

Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

15.7.10.6 Welded Steel Water Storage Structures . . . . . . . . . . . . . . 157

15.7.10.7 Concrete Pedestal (Composite) Tanks . . . . . . . . . . . . . . . 157

15.7.11 Boilers and Pressure Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

15.7.11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

15.7.11.2 ASME Boilers and Pressure Vessels . . . . . . . . . . . . . . . . 158

15.7.11.3 Attachments of Internal Equipment and Refractory . . . . 158

15.7.11.4 Coupling of Vessel and Support Structure . . . . . . . . . . . . 158

15.7.11.5 Effective Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

15.7.11.6 Other Boilers and Pressure Vessels . . . . . . . . . . . . . . . . . 158

15.7.11.7 Supports and Attachments for Boilers and Pressure

Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

15.7.12 Liquid and Gas Spheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

15.7.12.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

15.7.12.2 ASME Spheres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

15.7.12.3 Attachments of Internal Equipment and Refractory . . . . 159

15.7.12.4 Effective Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

15.7.12.5 Post and Rod Supported . . . . . . . . . . . . . . . . . . . . . . . . . . 160

15.7.12.6 Skirt Supported . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

15.7.13 Refrigerated Gas Liquid Storage Tanks and Vessels. . . . . . . . . . . . . . 160

15.7.13.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

15.7.14 Horizontal, Saddle Supported Vessels for Liquid or Vapor Storage . . . 160

15.7.14.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

15.7.14.2 Effective Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

15.7.14.3 Vessel Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

16 Seismic Response History Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

16.1 Linear Response History Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

16.1.1 Analysis Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

16.1.2 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

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16.1.3 Ground Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

16.1.3.1 Two-Dimensional Analysis . . . . . . . . . . . . . . . . . . . . . . . 161

16.1.3.2 Three-Dimensional Analysis . . . . . . . . . . . . . . . . . . . . . . 161

16.1.4 Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

16.1.5 Horizontal Shear Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

16.2 Nonlinear Response History Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

16.2.1 Analysis Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

16.2.2 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

16.2.3 Ground Motion and Other Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

16.2.4 Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

16.2.4.1 Member Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

16.2.4.2 Member Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

16.2.4.3 Story Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

16.2.5 Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

17 Seismic Design Requirements for Seismically Isolated Structures . . . . . . . . . . . . . . . . . . 165

17.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.1.1 Variations in Material Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.1.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.1.3 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

17.2 General Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.1 Importance Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.2 MCER Spectral Response Acceleration Parameters, SMS

and SM1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.3 Conﬁ guration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4 Isolation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.1 Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.2 Wind Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.3 Fire Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.4 Lateral Restoring Force . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.5 Displacement Restraint. . . . . . . . . . . . . . . . . . . . . . . . . . . 167

17.2.4.6 Vertical-Load Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.4.7 Overturning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.4.8 Inspection and Replacement . . . . . . . . . . . . . . . . . . . . . . 168

17.2.4.9 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.5 Structural System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.5.1 Horizontal Distribution of Force . . . . . . . . . . . . . . . . . . . 168

17.2.5.2 Building Separations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.5.3 Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 168

17.2.6 Elements of Structures and Nonstructural Components . . . . . . . . . . . 168

17.2.6.1 Components at or above the Isolation

Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.2.6.2 Components Crossing the Isolation

Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.2.6.3 Components below the Isolation Interface . . . . . . . . . . . 169

17.3 Ground Motion for Isolated Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.3.1 Design Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.3.2 Ground Motion Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.4 Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.4.1 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.4.2 Dynamic Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

17.4.2.1 Response-Spectrum Procedure . . . . . . . . . . . . . . . . . . . . . 169

17.4.2.2 Response-History Procedure . . . . . . . . . . . . . . . . . . . . . . 170

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17.5 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

17.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

17.5.2 Deformation Characteristics of the Isolation System . . . . . . . . . . . . . 170

17.5.3 Minimum Lateral Displacements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

17.5.3.1 Design Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

17.5.3.2 Effective Period at Design Displacement . . . . . . . . . . . . 170

17.5.3.3 Maximum Displacement . . . . . . . . . . . . . . . . . . . . . . . . . 170

17.5.3.4 Effective Period at Maximum Displacement . . . . . . . . . . 171

17.5.3.5 Total Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

17.5.4 Minimum Lateral Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

17.5.4.1 Isolation System and Structural Elements below

the Isolation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

17.5.4.2 Structural Elements above the Isolation

System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.5.4.3 Limits on Vs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.5.5 Vertical Distribution of Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.5.6 Drift Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.6 Dynamic Analysis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.6.2 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.6.2.1 Isolation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

17.6.2.2 Isolated Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

17.6.3 Description of Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

17.6.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

17.6.3.2 Input Earthquake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173

17.6.3.3 Response-Spectrum Procedure . . . . . . . . . . . . . . . . . . . . . 173

17.6.3.4 Response-History Procedure . . . . . . . . . . . . . . . . . . . . . . 173

17.6.4 Minimum Lateral Displacements and Forces . . . . . . . . . . . . . . . . . . . 174

17.6.4.1 Isolation System and Structural Elements below the

Isolation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

17.6.4.2 Structural Elements above the Isolation System . . . . . . . 174

17.6.4.3 Scaling of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

17.6.4.4 Drift Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

17.7 Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8.2 Prototype Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8.2.1 Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8.2.2 Sequence and Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

17.8.2.3 Units Dependent on Loading Rates . . . . . . . . . . . . . . . . . 175

17.8.2.4 Units Dependent on Bilateral Load . . . . . . . . . . . . . . . . . 176

17.8.2.5 Maximum and Minimum Vertical Load . . . . . . . . . . . . . 176

17.8.2.6 Sacriﬁ cial Wind-Restraint Systems . . . . . . . . . . . . . . . . . 176

17.8.2.7 Testing Similar Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

17.8.3 Determination of Force-Deﬂ ection Characteristics . . . . . . . . . . . . . . . 176

17.8.4 Test Specimen Adequacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

17.8.5 Design Properties of the Isolation System . . . . . . . . . . . . . . . . . . . . . 177

17.8.5.1 Maximum and Minimum Effective Stiffness . . . . . . . . . 177

17.8.5.2 Effective Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

18 Seismic Design Requirements for Structures with Damping Systems . . . . . . . . . . . . . . . . 179

18.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

18.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

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18.1.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

18.1.3 Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

18.2 General Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.1 Seismic Design Category A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.2 System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.2.1 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . 182

18.2.2.2 Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.3 Ground Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.3.1 Design Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.3.2 Ground Motion Histories . . . . . . . . . . . . . . . . . . . . . . . . . 182

18.2.4 Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.2.4.1 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.2.4.2 Response-Spectrum Procedure . . . . . . . . . . . . . . . . . . . . . 183

18.2.4.3 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . 183

18.2.5 Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.2.5.1 Device Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.2.5.2 Multiaxis Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.2.5.3 Inspection and Periodic Testing . . . . . . . . . . . . . . . . . . . . 183

18.2.5.4 Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

18.3 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

18.3.1 Nonlinear Response-History Procedure . . . . . . . . . . . . . . . . . . . . . . . 184

18.3.1.1 Damping Device Modeling . . . . . . . . . . . . . . . . . . . . . . . 184

18.3.1.2 Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

18.3.2 Nonlinear Static Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

18.4 Response-Spectrum Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

18.4.1 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

18.4.2 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

18.4.2.1 Seismic Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

18.4.2.2 Modal Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

18.4.2.3 Modal Participation Factor . . . . . . . . . . . . . . . . . . . . . . . . 185

18.4.2.4 Fundamental Mode Seismic Response Coefﬁ cient . . . . . 185

18.4.2.5 Effective Fundamental Mode Period Determination . . . . 185

18.4.2.6 Higher Mode Seismic Response Coefﬁ cient . . . . . . . . . . 186

18.4.2.7 Design Lateral Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

18.4.3 Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

18.4.3.1 Design Earthquake Floor Deﬂ ection . . . . . . . . . . . . . . . . 186

18.4.3.2 Design Earthquake Roof Displacement . . . . . . . . . . . . . . 186

18.4.3.3 Design Earthquake Story Drift . . . . . . . . . . . . . . . . . . . . . 186

18.4.3.4 Design Earthquake Story Velocity . . . . . . . . . . . . . . . . . . 186

18.4.3.5 Maximum Considered Earthquake Response . . . . . . . . . 187

18.5 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

18.5.1 Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

18.5.2 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

18.5.2.1 Seismic Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

18.5.2.2 Fundamental Mode Base Shear . . . . . . . . . . . . . . . . . . . . 187

18.5.2.3 Fundamental Mode Properties . . . . . . . . . . . . . . . . . . . . . 187

18.5.2.4 Fundamental Mode Seismic Response Coefﬁ cient . . . . . 188

18.5.2.5 Effective Fundamental Mode Period

Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

18.5.2.6 Residual Mode Base Shear . . . . . . . . . . . . . . . . . . . . . . . 188

18.5.2.7 Residual Mode Properties . . . . . . . . . . . . . . . . . . . . . . . . 188

18.5.2.8 Residual Mode Seismic Response Coefﬁ cient . . . . . . . . 188

18.5.2.9 Design Lateral Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

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18.5.3 Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

18.5.3.1 Design Earthquake Floor Deﬂ ection . . . . . . . . . . . . . . . . 189

18.5.3.2 Design Earthquake Roof Displacement . . . . . . . . . . . . . . 189

18.5.3.3 Design Earthquake Story Drift . . . . . . . . . . . . . . . . . . . . . 189

18.5.3.4 Design Earthquake Story Velocity . . . . . . . . . . . . . . . . . . 189

18.5.3.5 Maximum Considered Earthquake Response . . . . . . . . . 190

18.6 Damped Response Modiﬁ cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

18.6.1 Damping Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

18.6.2 Effective Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

18.6.2.1 Inherent Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

18.6.2.2 Hysteretic Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

18.6.2.3 Viscous Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

18.6.3 Effective Ductility Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

18.6.4 Maximum Effective Ductility Demand . . . . . . . . . . . . . . . . . . . . . . . . 192

18.7 Seismic Load Conditions and Acceptance Criteria . . . . . . . . . . . . . . . . . . . . . . . 192

18.7.1 Nonlinear Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

18.7.1.1 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . 192

18.7.1.2 Damping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.7.1.3 Combination of Load Effects . . . . . . . . . . . . . . . . . . . . . . 193

18.7.1.4 Acceptance Criteria for the Response Parameters of

Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.7.2 Response-Spectrum and Equivalent Lateral Force

Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.7.2.1 Seismic Force-Resisting System . . . . . . . . . . . . . . . . . . . 193

18.7.2.2 Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.7.2.3 Combination of Load Effects . . . . . . . . . . . . . . . . . . . . . . 193

18.7.2.4 Modal Damping System Design Forces . . . . . . . . . . . . . 193

18.7.2.5 Seismic Load Conditions and Combination of

Modal Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

18.7.2.6 Inelastic Response Limits . . . . . . . . . . . . . . . . . . . . . . . . 195

18.8 Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

18.9 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

18.9.1 Prototype Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

18.9.1.1 Data Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

18.9.1.2 Sequence and Cycles of Testing . . . . . . . . . . . . . . . . . . . 196

18.9.1.3 Testing Similar Devices . . . . . . . . . . . . . . . . . . . . . . . . . . 196

18.9.1.4 Determination of

Force-Velocity-Displacement Characteristics . . . . . . . . . 196

18.9.1.5 Device Adequacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

18.9.2 Production Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

19 Soil–Structure Interaction for Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

19.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

19.2 Equivalent Lateral Force Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

19.2.1 Base Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

19.2.1.1 Effective Building Period . . . . . . . . . . . . . . . . . . . . . . . . . 199

19.2.1.2 Effective Damping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

19.2.2 Vertical Distribution of Seismic Forces. . . . . . . . . . . . . . . . . . . . . . . . 201

19.2.3 Other Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

19.3 Modal Analysis Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

19.3.1 Modal Base Shears . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

19.3.2 Other Modal Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

19.3.3 Design Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202

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20 Site Classiﬁ cation Procedure for Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.1 Site Classiﬁ cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.2 Site Response Analysis for Site Class F Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3 Site Class Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3.1 Site Class F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3.2 Soft Clay Site Class E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3.3 Site Classes C, D, and E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3.4 Shear Wave Velocity for Site Class B . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.3.5 Shear Wave Velocity for Site Class A . . . . . . . . . . . . . . . . . . . . . . . . . 203

20.4 Deﬁ nitions of Site Class Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

20.4.1 v

, Average Shear Wave Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

20.4.2 N

, Average Field Standard Penetration Resistance and N

Average Standard Penetration Resistance for Cohesionless

Soil Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

20.4.3 s

, Average Undrained Shear Strength . . . . . . . . . . . . . . . . . . . . . . . . 204

21 Site-Speciﬁ c Ground Motion Procedures for Seismic Design . . . . . . . . . . . . . . . . . . . . . . 207

21.1 Site Response Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

21.1.1 Base Ground Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

21.1.2 Site Condition Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

21.1.3 Site Response Analysis and Computed Results . . . . . . . . . . . . . . . . . 207

21.2 Risk-Targeted Maximum Considered Earthquake (Mcer) Ground Motion

Hazard Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

21.2.1 Probabilistic (MCER) Ground Motions . . . . . . . . . . . . . . . . . . . . . . . 208

21.2.1.1 Method 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21.2.1.2 Method 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21.2.2 Deterministic (MCER) Ground Motions . . . . . . . . . . . . . . . . . . . . . . . 208

21.2.3 Site-Speciﬁ c MCER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21.3 Design Response Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21.4 Design Acceleration Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

21.5 Maximum Considered Earthquake Geometric Mean (Mceg) Peak

Ground Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

21.5.1 Probabilistic MCEG Peak Ground Acceleration . . . . . . . . . . . . . . . . . 209

21.5.2 Deterministic MCEG Peak Ground Acceleration . . . . . . . . . . . . . . . . 209

21.5.3 Site-Speciﬁ c MCEG Peak Ground Acceleration . . . . . . . . . . . . . . . . . 209

22 Seismic Ground Motion Long-Period Transition and Risk

Coefﬁ cient Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

23 Seismic Design Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

23.1 Consensus Standards and Other Reference Documents . . . . . . . . . . . . . . . . . . . 233

26 Wind Loads: General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

26.1 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

26.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

26.1.2 Permitted Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

26.1.2.1 Main Wind-Force Resisting System (MWFRS) . . . . . . . 241

26.1.2.2 Components and Cladding . . . . . . . . . . . . . . . . . . . . . . . . 241

26.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

26.3 Symbols and Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

26.4 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

26.4.1 Sign Convention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

26.4.2 Critical Load Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

26.4.3 Wind Pressures Acting on Opposite Faces of Each Building

Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

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26.5 Wind Hazard Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.5.1 Basic Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.5.2 Special Wind Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.5.3 Estimation of Basic Wind Speeds from Regional Climatic Data . . . . 246

26.5.4 Limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.6 Wind Directionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.7 Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.7.1 Wind Directions and Sectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.7.2 Surface Roughness Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

26.7.3 Exposure Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

26.7.4 Exposure Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

26.7.4.1 Directional Procedure (Chapter 27) . . . . . . . . . . . . . . . . . 251

26.7.4.2 Envelope Procedure (Chapter 28) . . . . . . . . . . . . . . . . . . 251

26.7.4.3 Directional Procedure for Building Appurtenances

and Other Structures (Chapter 29) . . . . . . . . . . . . . . . . . . 251

26.7.4.4 Components and Cladding (Chapter 30) . . . . . . . . . . . . . 251

26.8 Topographic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251

26.8.1 Wind Speed-Up over Hills, Ridges, and Escarpments . . . . . . . . . . . . 251

26.8.2 Topographic Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

26.9 Gust-Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

26.9.2 Frequency Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

26.9.2.1 Limitations for Approximate Natural Frequency . . . . . . 254

26.9.3 Approximate Natural Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

26.9.4 Rigid Buildings or Other Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 254

26.9.5 Flexible or Dynamically Sensitive Buildings or Other Structures . . . 255

26.9.6 Rational Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.9.7 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.10 Enclosure Classiﬁ cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.10.2 Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.10.3 Protection of Glazed Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

26.10.3.1 Wind-borne Debris Regions . . . . . . . . . . . . . . . . . . . . . . . 255

26.10.3.2 Protection Requirements for Glazed Openings . . . . . . . . 257

26.10.4 Multiple Classiﬁ cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

26.11 Internal Pressure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

26.11.1 Internal Pressure Coefﬁ cients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

26.11.1.1 Reduction Factor for Large Volume Buildings, Ri . . . . . 257

27 Wind Loads on Buildings—MWFRS (Directional Procedure) . . . . . . . . . . . . . . . . . . . . . . 259

27.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.1.1 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.1.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.1.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Part 1: Enclosed, Partially Enclosed, and Open Buildings of All Heights . . . . . . . . . . . . . 259

27.2 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.2.1 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 259

27.3 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

27.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 259

27.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

27.4 Wind Loads—Main Wind Force-Resisting System . . . . . . . . . . . . . . . . . . . . . . . 260

27.4.1 Enclosed and Partially Enclosed Rigid Buildings . . . . . . . . . . . . . . . . 260

27.4.2 Enclosed and Partially Enclosed Flexible Buildings . . . . . . . . . . . . . 262

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27.4.3 Open Buildings with Monoslope, Pitched, or Troughed Free Roofs . 262

27.4.4 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

27.4.5 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

27.4.6 Design Wind Load Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

27.4.7 Minimum Design Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Part 2: Enclosed Simple Diaphragm Buildings with h ≤ 160 ft (48.8 m) . . . . . . . . . . . . . 272

27.5 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

27.5.1 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

27.5.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

27.5.3 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 272

27.5.4 Diaphragm Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

27.6 Wind Loads—Main Wind Force-Resisting System . . . . . . . . . . . . . . . . . . . . . . . 273

27.6.1 Wall and Roof Surfaces—Class 1 and 2 Buildings . . . . . . . . . . . . . . 273

27.6.2 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

27.6.3 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273

28 Wind Loads on Buildings—MWFRS (Envelope Procedure) . . . . . . . . . . . . . . . . . . . . . . . 297

28.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.1.1 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.1.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.1.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Part 1: Enclosed and Partially Enclosed Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . 297

28.2 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.2.1 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 297

28.3 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

28.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 297

28.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

28.4 Wind Loads—Main Wind-Force Resisting System . . . . . . . . . . . . . . . . . . . . . . . 298

28.4.1 Design Wind Pressure for Low-Rise Buildings . . . . . . . . . . . . . . . . . 298

28.4.1.1 External Pressure Coefﬁ cients (GCpf) . . . . . . . . . . . . . . . 298

28.4.2 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

28.4.3 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

28.4.4 Minimum Design Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

Part 2: Enclosed Simple Diaphragm Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . . . . 302

28.5 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

28.5.1 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 302

28.6 Wind Loads—Main Wind-Force Resisting System . . . . . . . . . . . . . . . . . . . . . . . 302

28.6.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

28.6.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

28.6.3 Design Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

28.6.4 Minimum Design Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

29 Wind Loads on Other Structures and Building Appurtenances—MWFRS . . . . . . . . . . . . 307

29.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.1.1 Structure Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.1.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.1.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.2 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.2.1 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 307

29.3 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

29.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 307

29.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

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29.4 Design Wind Loads—Solid Freestanding Walls and Solid Signs . . . . . . . . . . . . 308

29.4.1 Solid Freestanding Walls and Solid Freestanding Signs . . . . . . . . . . . 308

29.4.2 Solid Attached Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

29.5 Design Wind Loads—Other Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

29.5.1 Rooftop Structures and Equipment for Buildings with h ≤ 60 ft (18.3 m). . . . . 308

29.6 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

29.7 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

29.8 Minimum Design wind Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

30 Wind Loads—Components and Cladding (C&C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1.1 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1.2 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.1.5 Air-Permeable Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.2 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

30.2.1 Wind Load Parameters Speciﬁ ed in Chapter 26 . . . . . . . . . . . . . . . . . 315

30.2.2 Minimum Design Wind Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

30.2.3 Tributary Areas Greater than 700 ft2 (65 m2) . . . . . . . . . . . . . . . . . . 316

30.2.4 External Pressure Coefﬁ cients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

30.3 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

30.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 316

30.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

Part 1: Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

30.4 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

30.4.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

30.4.2 Design Wind Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

Part 2: Low-Rise Buildings (Simpliﬁ ed) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

30.5 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

30.5.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

30.5.2 Design Wind Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

Part 3: Buildings with h > 60 ft (18.3 m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

30.6 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

30.6.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

30.6.2 Design Wind Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

Part 4: Buildings with h ≤ 160 ft (48.8 M) (Simpliﬁ ed). . . . . . . . . . . . . . . . . . . . . . . . . . . 321

30.7 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

30.7.1 Wind Loads—Components And Cladding . . . . . . . . . . . . . . . . . . . . . 321

30.7.1.1 Wall and Roof Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 321

30.7.1.2 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

30.7.1.3 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

Part 5: Open Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

30.8 Building Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

30.8.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

30.8.2 Design Wind Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

Part 6: Building Appurtenances and Rooftop Structures and Equipment . . . . . . . . . . . . . . 332

30.9 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332

30.10 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333

30.11 Rooftop Structures and Equipment for Buildings with h ≤ 60 ft (18.3 m). . . . . 334

31 Wind Tunnel Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.2 Test Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

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31.3 Dynamic Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.4 Load Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.4.1 Mean Recurrence Intervals of Load Effects . . . . . . . . . . . . . . . . . . . . 357

31.4.2 Limitations on Wind Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.4.3 Limitations on Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

31.5 Wind-Borne Debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358

Appendix 11A Quality Assurance Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

11A.1 Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

11A.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

11A.1.2 Quality Assurance Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

11A.1.2.1 Details of Quality Assurance Plan . . . . . . . . . . . . . . . . . . 359

11A.1.2.2 Contractor Responsibility . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3 Special Inspection and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.1 Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.2 Reinforcing Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.3 Structural Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.4 Prestressed Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.5 Structural Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.6 Structural Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.7 Structural Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

11A.1.3.8 Cold-Formed Steel Framing . . . . . . . . . . . . . . . . . . . . . . . 361

11A.1.3.9 Architectural Components . . . . . . . . . . . . . . . . . . . . . . . . 361

11A.1.3.10 Mechanical and Electrical Components . . . . . . . . . . . . . . 361

11A.1.3.11 Seismic Isolation System . . . . . . . . . . . . . . . . . . . . . . . . . 361

11A.2 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

11A.2.1 Reinforcing and Prestressing Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

11A.2.1.1 Certiﬁ ed Mill Test Reports . . . . . . . . . . . . . . . . . . . . . . . . 361

11A.2.1.2 ASTM A615 Reinforcing Steel . . . . . . . . . . . . . . . . . . . . 362

11A.2.1.3 Welding of ASTM A615 Reinforcing

Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.2.2 Structural Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.2.3 Structural Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.2.4 Structural Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.2.5 Seismic-Isolated Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.2.6 Mechanical and Electrical Equipment . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.3 Structural Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

11A.4 Reporting and Compliance Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

Appendix 11B Existing Building Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

11B.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

11B.2 Structurally Independent Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

11B.3 Structurally Dependent Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

11B.4 Alterations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

11B.5 Change of Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

Appendix C Serviceability Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C. Serviceability Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.1 Deﬂ ection, Vibration, and Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.1.1 Vertical Deﬂ ections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.1.2 Drift of Walls and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.1.3 Vibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.2 Design for Long-Term Deﬂ ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.3 Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

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C.4 Expansion and Contraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

C.5 Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

Appendix D Buildings Exempted from Torsional Wind Load Cases . . . . . . . . . . . . . . . . . . . . . 367

D1.0 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

D1.1 One and Two Story Buildings Meeting the Following Requirements . . . . . . . . 367

D1.2 Buildings Controlled by Seismic Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

D1.2.1 Buildings with Diaphragms at Each Level that Are

Not Flexible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

D1.2.2 Buildings with Diaphragms at Each Level that Are Flexible . . . . . . . 367

D1.3 Buildings Classiﬁ ed as Torsionally Regular under Wind Load. . . . . . . . . . . . . . 367

D1.4 Buildings with Diaphragms that are Flexible and Designed for Increased

Wind Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

D1.5 Class 1 and Class 2 Simple Diaphragm Buildings (h ≤ 160 ft.) Meeting

the Following Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

D1.5.1 Case A – Class 1 and Class 2 Buildings . . . . . . . . . . . . . . . . . . . . . . . 367

D1.5.2 Case B – Class 1 and Class 2 Buildings . . . . . . . . . . . . . . . . . . . . . . . 368

D1.5.3 Case C – Class 1 and Class 2 Buildings . . . . . . . . . . . . . . . . . . . . . . . 368

D1.5.4 Case D – Class 1 and Class 2 Buildings . . . . . . . . . . . . . . . . . . . . . . . 368

D1.5.5 Case E – Class 1 and Class 2 Buildings . . . . . . . . . . . . . . . . . . . . . . . 368

D1.5.6 Case F – Class 1 Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

Commentary to American Society of Civil Engineers/Structural Engineering Institute

Standard 7-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

C1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

C1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

C1.3 Basic Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

C1.3.1 Strength and Stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

C1.3.1.3 Performance-Based Procedures . . . . . . . . . . . . . . . . . . . . 375

C1.3.2 Serviceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

C1.3.3 Self-Straining Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

C1.4 General Structural Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377

C1.5 Classiﬁ cation of Buildings and Other Structures . . . . . . . . . . . . . . . . . . . . . . . . . 380

C1.5.1 Risk Categorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380

C1.5.3 Toxic, Highly Toxic, and Explosive Substances . . . . . . . . . . . . . . . . . 382

C1.7 Load Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

C2 Combinations of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

C2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

C2.2 Symbols and Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

C2.3 Combining Factored Loads Using Strength Design . . . . . . . . . . . . . . . . . . . . . . 387

C2.3.1 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

C2.3.2 Basic Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

C2.3.3 Load Combinations Including Flood Load . . . . . . . . . . . . . . . . . . . . . 389

C2.3.4 Load Combinations Including Atmospheric Ice Loads . . . . . . . . . . . . 389

C2.3.5 Load Combinations Including Self-Straining Loads . . . . . . . . . . . . . . 389

C2.3.6 Load Combinations for Nonspeciﬁ ed Loads . . . . . . . . . . . . . . . . . . . . 390

C2.4 Combining Nominal Loads Using Allowable Stress Design . . . . . . . . . . . . . . . 391

C2.4.1 Basic Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

C2.4.2 Load Combinations Including Flood Load . . . . . . . . . . . . . . . . . . . . . 393

C2.4.3 Load Combinations Including Atmospheric Ice Loads . . . . . . . . . . . . 393

C2.4.4 Load Combinations Including Self-Straining Loads . . . . . . . . . . . . . . 393

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C2.5 Load Combinations for Extraordinary Events . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395

C3 Dead Loads, Soil Loads, and Hydrostatic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

C3.1.2 Weights of Materials and Constructions . . . . . . . . . . . . . . . . . . . . . . . 397

C3.2 Soil Loads and Hydrostatic Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

C3.2.1 Lateral Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397

C3.2.2 Uplift on Floors and Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398

C4 Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

C4.3 Uniformly Distributed Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

C4.3.1 Required Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

C4.3.2 Provision for Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408

C4.3.3 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408

C4.4 Concentrated Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.5 Loads on Handrail, Guardrail, Grab Bar, and Vehicle Barrier Systems,

and Fixed Ladders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.5.1 Loads on Handrail and Guardrail Systems . . . . . . . . . . . . . . . . . . . . . 409

C4.5.2 Loads on Grab Bar Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.5.3 Loads on Vehicle Barrier Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.5.4 Loads on Fixed Ladders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.6 Impact Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409

C4.7 Reduction In Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

C4.7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

C4.7.3 Heavy Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

C4.7.4 Passenger Vehicle Garages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

C4.7.6 Limitations on One-Way Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

C4.8 Reduction In Roof Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

C4.8.2 Flat, Pitched, and Curved Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

C4.8.3 Special Purpose Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

C4.9 Crane Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

C5 Flood Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

C5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

C5.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

C5.3 Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

C5.3.1 Design Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

C5.3.2 Erosion and Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

C5.3.3 Loads on Breakaway Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

C5.4.1 Load Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

C5.4.2 Hydrostatic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

C5.4.3 Hydrodynamic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

C5.4.4 Wave Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

C5.4.4.2 Breaking Wave Loads on Vertical Walls . . . . . . . . . . . . . 418

C5.4.5 Impact Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

C7 Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

C7.0 Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

C7.2 Ground Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425

C7.3 Flat-Roof Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

C7.3.1 Exposure Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427

C7.3.2 Thermal Factor, C

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

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C7.3.3 Importance Factor, I

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

C7.3.4 Minimum Snow Load for Low-Slope Roofs, p

. . . . . . . . . . . . . . . . 429

C7.4 Sloped Roof Snow Loads, p

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

C7.4.3 Roof Slope Factor for Curved Roofs . . . . . . . . . . . . . . . . . . . . . . . . . 430

C7.4.4 Roof Slope Factor for Multiple Folded Plate, Sawtooth,

and Barrel Vault Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

C7.4.5 Ice Dams and Icicles Along Eaves . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

C7.5 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431

C7.6 Unbalanced Roof Snow Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431

C7.6.1 Unbalanced Snow Loads for Hip and Gable Roofs . . . . . . . . . . . . . . 431

C7.6.2 Unbalanced Snow Loads for Curved Roofs . . . . . . . . . . . . . . . . . . . . 431

C7.6.3 Unbalanced Snow Loads for Multiple Folded Plate, Sawtooth,

and Barrel Vault Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431

C7.6.4 Unbalanced Snow Loads for Dome Roofs . . . . . . . . . . . . . . . . . . . . . 432

C7.7 Drifts on Lower Roofs (Aerodynamic Shade) . . . . . . . . . . . . . . . . . . . . . . . . . . . 432

C7.7.2 Adjacent Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

C7.8 Roof Projections and Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

C7.9 Sliding Snow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433

C7.10 Rain-on-Snow Surcharge Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

C7.11 Ponding Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

C7.12 Existing Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

C7.13 Other Roofs and Sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437

C8 Rain Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

C8.1 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

C8.2 Roof Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

C8.3 Design Rain Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

C8.4 Ponding Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447

C8.5 Controlled Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448

C10 Ice Loads—Atmospheric Icing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455

C10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455

C10.1.1 Site-Speciﬁ c Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455

C10.1.2 Dynamic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456

C10.1.3 Exclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456

C10.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456

C10.4 Ice Loads Due to Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458

C10.4.1 Ice Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458

C10.4.2 Nominal Ice Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

C10.4.4 Importance Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

C10.4.6 Design Ice Thickness for Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . 461

C10.5 Wind on Ice-Covered Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461

C10.5.5 Wind on Ice-Covered Guys and Cables . . . . . . . . . . . . . . . . . . . . . . . 461

C10.6 Design Temperatures for Freezing Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462

C10.7 Partial Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462

Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462

C11 Seismic Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

C11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

C11.1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

C11.1.3 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

C11.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

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C11.4 Seismic Ground Motion Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

C11.7 Design Requirements for Seismic Design Category A . . . . . . . . . . . . . . . . . . . . 477

C11.8.2 Geotechnical Investigation Report Requirements for Seismic

Design Categories C through F . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

C11.8.3 Additional Geotechnical Investigation Report Requirements for

Seismic Design Categories D through F . . . . . . . . . . . . . . . . . . . . . . . 477

C12 Seismic Design Requirements for Building Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

C12.3.3.3 Elements Supporting Discontinuous Walls

or Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

C12.3.4 Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

C12.4.3 Seismic Load Effect Including Overstrength Factor . . . . . . . . . . . . . . 479

C12.6 Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

C12.7.1 Foundation Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

C12.8.4.1 Inherent Torsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

C12.11.2 Anchorage of Structural Walls and Transfer of Design Forces

into Diaphragms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481

C13 Seismic Design Requirements for Nonstructural Components . . . . . . . . . . . . . . . . . . . . . . 483

C13.0 Seismic Design Requirements for Nonstructural Components . . . . . . . . . . . . . . 483

C13.1.4 Exemptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483

C13.2.2 Special Certiﬁ cation Requirements for Designated Seismic

Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483

C13.3.2 Seismic Relative Displacements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

C13.4.2.3 Post-Installed Anchors in Concrete and Masonry . . . . . . 484

C13.4.6 Friction Clips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

C13.5.9 Glass in Glazed Curtain Walls, Glazed Storefronts, and

Glazed Partitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

C13.6 Mechanical and Electrical Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

C13.6.5.5 Additional Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 485

C13.6.5.6 Conduit, Cable Tray, and Other Electrical

Distribution Systems (Raceways) . . . . . . . . . . . . . . . . . . 486

C13.6.8 Piping Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486

C13.6.8.1 ASME Pressure Piping Systems . . . . . . . . . . . . . . . . . . . 488

C13.6.8.2 Fire Protection Sprinkler Piping Systems . . . . . . . . . . . . 488

C13.6.8.3 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

C14 Material-Speciﬁ c Seismic Design and Detailing Requirements . . . . . . . . . . . . . . . . . . . . . 489

C14.2 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.1 ACI 318, Section 7.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.4 Wall Piers and Wall Segments . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.6 Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

C14.2.2.7 Intermediate Precast Structural Walls . . . . . . . . . . . . . . . 489

C14.2.2.8 Detailed Plain Concrete Shear Walls . . . . . . . . . . . . . . . . 490

C14.2.2.9 Strength Requirements for Anchors . . . . . . . . . . . . . . . . . 490

C14.2.3 Additional Detailing Requirements for Concrete Piles . . . . . . . . . . . . 490

C14.4 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491

C15 Seismic Design Requirements for Nonbuilding Structures . . . . . . . . . . . . . . . . . . . . . . . . . 493

C15.0 Seismic Design Requirements for Nonbuilding Structures . . . . . . . . . . . . . . . . . 493

C15.1.3 Structural Analysis Procedure Selection . . . . . . . . . . . . . . . . . . . . . . . 493

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C15.2 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

C15.4.4 Fundamental Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

C15.4.9.3 Post-Installed Anchors in Concrete and Masonry . . . . . . 496

C15.6.5 Secondary Containment Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

C15.6.6 Telecommunication Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

C15.7 Tanks and Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

C15.7.2 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

C15.7.6 Ground-Supported Storage Tanks for Liquids . . . . . . . . . . . . . . . . . . 497

C15.7.8.2 Bolted Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498

C15.7.13 Refrigerated Gas Liquid Storage Tanks and Vessels . . . . . . . . . . . . . . 498

C19 Soil–Structure Interaction for Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

C19 Soil–Structure Interaction for Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . 501

C22 Seismic Ground Motion, Long-Period Transition and Risk Coefﬁ cient Maps . . . . . . . . . 503

C26 Wind Loads—General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505

C26.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505

C26.1.2 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505

C26.2 Deﬁ nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506

C26.3 Symbols and Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508

C26.4.3 Wind Pressures Acting on Opposite Faces of Each Building

Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508

C26.5.1 Basic Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508

C26.5.2 Special Wind Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512

C26.5.3 Estimation of Basic Wind Speeds from Regional Climatic Data . . . . 512

C26.5.4 Limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513

C26.6 Wind Directionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513

C26.7 Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514

C26.7.4 Exposure Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517

C26.8 Topographic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518

C26.9 Gust Effect Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519

C26.10 Enclosure Classiﬁ cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524

C26.11 Internal Pressure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526

Additional References of Interest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529

C27 Wind Loads on Buildings—MWFRS Directional Procedure . . . . . . . . . . . . . . . . . . . . . . . 547

Part 1: Enclosed, Partially Enclosed, and Open Buildings of All Heights . . . . . . . . . . . . . 547

C27.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 547

27.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550

C27.4.1 Enclosed and Partially Enclosed Rigid Buildings . . . . . . . . . . . . . . . . 550

C27.4.3 Open Buildings with Monoslope, Pitched, or Troughed

Free Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552

C27.4.6 Design Wind Load Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552

C27.4.7 Minimum Design Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553

Part 2: Enclosed Simple Diaphragm Buildings with h ≤ 160 ft . . . . . . . . . . . . . . . . . . . . . 553

C27.6.1 Wall and Roof Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

C27.6.2 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555

C27.6.3 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555

C28 Wind Loads on Buildings—MWFRS (Envelope Procedure) . . . . . . . . . . . . . . . . . . . . . . . 557

Part 1: Enclosed and Partially Enclosed Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . 557

C28.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 557

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CONTENTS

xlii

C28.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557

C28.4.4 Minimum Design Wind Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560

Part 2: Enclosed Simple Diaphragm Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . . . . 560

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

C29 Wind Loads (MWFRS)—Other Structures and Building Appurtenances . . . . . . . . . . . . . 563

C29.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 563

C29.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

C29.4.2 Solid Attached Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

C29.6 Rooftop Structures and Equipment for Buildings with h ≤ 60 ft . . . . . . . . . . . . 564

C29.7 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564

C29.9 Minimum Design Wind Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566

C30 Wind Loads—Components and Cladding (C&C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569

C30.1.5 Air-Permeable Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569

C30.3.1 Velocity Pressure Exposure Coefﬁ cient . . . . . . . . . . . . . . . . . . . . . . . 570

C30.3.2 Velocity Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570

Part 1: Low-Rise Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

Part 3: Buildings With h > 60 ft (18.3 m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

Part 4: Buildings with h ≤ 160 ft (Simpliﬁ ed) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

C30.7.1.2 Parapets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

C30.7.1.3 Roof Overhangs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

Part 5: Open Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573

C31 Wind Tunnel Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575

C31.4.1 Mean Recurrence Intervals of Load Effects . . . . . . . . . . . . . . . . . . . . 576

C31.4.2 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577

Commentary Appendix C Serviceability Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579

CC. Serviceability Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579

CC.1.1 Vertical Deﬂ ections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579

CC.1.2 Drift of Walls and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580

CC.1.3 Vibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580

CC.2 Design for Long-Term Deﬂ ection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581

CC.3 Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

CC.4 Expansion and Contraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

CC.5 Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

Commentary Chapter: Appendix D Buildings Exempted from Torsional Wind

Load Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

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Chapter 1

GENERAL

judged either to be no longer useful for its intended

function (serviceability limit state) or to be unsafe

(strength limit state).

LOAD EFFECTS: Forces and deformations

produced in structural members by the applied loads.

LOAD FACTOR: A factor that accounts for

deviations of the actual load from the nominal load,

for uncertainties in the analysis that transforms the

load into a load effect, and for the probability that

more than one extreme load will occur simultaneously.

LOADS: Forces or other actions that result from

the weight of all building materials, occupants and

their possessions, environmental effects, differential

movement, and restrained dimensional changes.

Permanent loads are those loads in which variations

over time are rare or of small magnitude. All other

loads are variable loads (see also “nominal loads”).

NOMINAL LOADS: The magnitudes of the

loads speciﬁ ed in this standard for dead, live, soil,

wind, snow, rain, ﬂ ood, and earthquake.

NOMINAL STRENGTH: The capacity of a

structure or member to resist the effects of loads, as

determined by computations using speciﬁ ed material

strengths and dimensions and formulas derived from

accepted principles of structural mechanics or by ﬁ eld

tests or laboratory tests of scaled models, allowing for

modeling effects and differences between laboratory

and ﬁ eld conditions.

OCCUPANCY: The purpose for which a

building or other structure, or part thereof, is used or

intended to be used.

OTHER STRUCTURES: Structures, other than

buildings, for which loads are speciﬁ ed in this standard.

P-DELTA EFFECT: The second order effect on

shears and moments of frame members induced by

axial loads on a laterally displaced building frame.

RESISTANCE FACTOR: A factor that

accounts for deviations of the actual strength from the

nominal strength and the manner and consequences of

failure (also called “strength reduction factor”).

RISK CATEGORY: A categorization of

buildings and other structures for determination of

ﬂ ood, wind, snow, ice, and earthquake loads based on

the risk associated with unacceptable performance.

See Table 1.5-1.

STRENGTH DESIGN: A method of proportion-

ing structural members such that the computed forces

produced in the members by the factored loads do not

1.1 SCOPE

This standard provides minimum load requirements

for the design of buildings and other structures that

are subject to building code requirements. Loads and

appropriate load combinations, which have been

developed to be used together, are set forth for

strength design and allowable stress design. For

design strengths and allowable stress limits, design

speciﬁ cations for conventional structural materials

used in buildings and modiﬁ cations contained in this

standard shall be followed.

1.2 DEFINITIONS AND NOTATIONS

1.2.1 Deﬁ nitions

The following deﬁ nitions apply to the provisions

of the entire standard.

ALLOWABLE STRESS DESIGN: A method of

proportioning structural members such that elastically

computed stresses produced in the members by

nominal loads do not exceed speciﬁ ed allowable

stresses (also called “working stress design”).

AUTHORITY HAVING JURISDICTION:

The organization, political subdivision, ofﬁ ce, or

individual charged with the responsibility of adminis-

tering and enforcing the provisions of this standard.

BUILDINGS: Structures, usually enclosed by

walls and a roof, constructed to provide support or

shelter for an intended occupancy.

DESIGN STRENGTH: The product of the

nominal strength and a resistance factor.

ESSENTIAL FACILITIES: Buildings and other

structures that are intended to remain operational in

the event of extreme environmental loading from

ﬂ ood, wind, snow, or earthquakes.

FACTORED LOAD: The product of the

nominal load and a load factor.

HIGHLY TOXIC SUBSTANCE: As deﬁ ned in

29 CFR 1910.1200 Appendix A with Amendments as

of February 1, 2000.

IMPORTANCE FACTOR: A factor that

accounts for the degree of risk to human life, health,

and welfare associated with damage to property or

loss of use or functionality.

LIMIT STATE: A condition beyond which a

structure or member becomes unﬁ t for service and is

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CHAPTER 1 GENERAL

exceed the member design strength (also called “load

and resistance factor design”).

TEMPORARY FACILITIES: Buildings or

other structures that are to be in service for a limited

time and have a limited exposure period for environ-

mental loadings.

TOXIC SUBSTANCE: As deﬁ ned in 29 CFR

1910.1200 Appendix A with Amendments as of

February 1, 2000.

1.1.2 Symbols and Notations

A minimum design lateral force applied to level

x of the structure and used for purposes of

evaluating structural integrity in accordance with

Section 1.4.2.

The portion of the total dead load of the struc-

ture, D, located or assigned to Level x.

D Dead load.

L Live load.

Roof live load.

N Notional load used to evaluate conformance with

minimum structural integrity criteria.

R Rain load.

S Snow load.

1.3 BASIC REQUIREMENTS

1.3.1 Strength and Stiffness

Buildings and other structures, and all parts

thereof, shall be designed and constructed with

adequate strength and stiffness to provide structural

stability, protect nonstructural components and

systems from unacceptable damage, and meet the

serviceability requirements of Section 1.3.2.

Acceptable strength shall be demonstrated using

one or more of the following procedures:

a. the Strength Procedures of Section 1.3.1.1,

b. the Allowable Stress Procedures of Section 1.3.1.2,

c. subject to the approval of the authority

having jurisdiction for individual projects,

the Performance-Based Procedures of Section

1.3.1.3.

Table 1.5-1 Risk Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake,

and Ice Loads

Use or Occupancy of Buildings and Structures Risk Category

Buildings and other structures that represent a low risk to human life in the event of failure I

All buildings and other structures except those listed in Risk Categories I, III, and IV II

Buildings and other structures, the failure of which could pose a substantial risk to human life.

Buildings and other structures, not included in Risk Category IV, with potential to cause a substantial

economic impact and/or mass disruption of day-to-day civilian life in the event of failure.

Buildings and other structures not included in Risk Category IV (including, but not limited to, facilities that

manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous

chemicals, hazardous waste, or explosives) containing toxic or explosive substances where their quantity

exceeds a threshold quantity established by the authority having jurisdiction and is sufﬁ cient to pose a threat

to the public if released.

III

Buildings and other structures designated as essential facilities.

Buildings and other structures, the failure of which could pose a substantial hazard to the community.

Buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, store,

use, or dispose of such substances as hazardous fuels, hazardous chemicals, or hazardous waste) containing

sufﬁ cient quantities of highly toxic substances where the quantity exceeds a threshold quantity established by

the authority having jurisdiction to be dangerous to the public if released and is sufﬁ cient to pose a threat to

the public if released.

Buildings and other structures required to maintain the functionality of other Risk Category IV structures.

Buildings and other structures containing toxic, highly toxic, or explosive substances shall be eligible for classiﬁ cation to a lower Risk Category

if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard assessment as described in Section 1.5.2 that a

release of the substances is commensurate with the risk associated with that Risk Category.

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MINIMUM DESIGN LOADS

It shall be permitted to use alternative procedures

for different parts of a structure and for different

load combinations, subject to the limitations of

Chapter 2. Where resistance to extraordinary events

is considered, the procedures of Section 2.5 shall

be used.

1.3.1.1 Strength Procedures

Structural and nonstructural components and their

connections shall have adequate strength to resist the

applicable load combinations of Section 2.3 of this

Standard without exceeding the applicable strength

limit states for the materials of construction.

1.3.1.2 Allowable Stress Procedures

Structural and nonstructural components and their

connections shall have adequate strength to resist the

applicable load combinations of Section 2.4 of this

Standard without exceeding the applicable allowable

stresses for the materials of construction.

1.3.1.3 Performance-Based Procedures

Structural and nonstructural components and their

connections shall be demonstrated by analysis or by a

combination of analysis and testing to provide a

reliability not less than that expected for similar

components designed in accordance with the Strength

Procedures of Section 1.3.1.1 when subject to the

inﬂ uence of dead, live, environmental, and other

loads. Consideration shall be given to uncertainties in

loading and resistance.

1.3.1.3.1 Analysis Analysis shall employ rational

methods based on accepted principles of engineering

mechanics and shall consider all signiﬁ cant sources of

deformation and resistance. Assumptions of stiffness,

strength, damping, and other properties of components

and connections incorporated in the analysis shall be

based on approved test data or referenced Standards.

1.3.1.3.2 Testing Testing used to substantiate the

performance capability of structural and nonstructural

components and their connections under load shall

accurately represent the materials, conﬁ guration,

construction, loading intensity, and boundary condi-

tions anticipated in the structure. Where an approved

industry standard or practice that governs the testing

of similar components exists, the test program and

determination of design values from the test program

shall be in accordance with those industry standards

and practices. Where such standards or practices do

not exist, specimens shall be constructed to a scale

similar to that of the intended application unless it can

be demonstrated that scale effects are not signiﬁ cant

to the indicated performance. Evaluation of test

results shall be made on the basis of the values

obtained from not less than 3 tests, provided that the

deviation of any value obtained from any single test

does not vary from the average value for all tests by

more than 15%. If such deviaton from the average

value for any test exceeds 15%, then additional tests

shall be performed until the deviation of any test from

the average value does not exceed 15% or a minimum

of 6 tests have been performed. No test shall be

eliminated unless a rationale for its exclusion is given.

Test reports shall document the location, the time and

date of the test, the characteristics of the tested

specimen, the laboratory facilities, the test conﬁ gura-

tion, the applied loading and deformation under load,

and the occurrence of any damage sustained by the

specimen, together with the loading and deformation

at which such damage occurred.

1.3.1.3.3 Documentation The procedures used to

demonstrate compliance with this section and the

results of analysis and testing shall be documented in

one or more reports submitted to the authority having

jurisdiction and to an independent peer review.

1.3.1.3.4 Peer Review The procedures and results of

analysis, testing, and calculation used to demonstrate

compliance with the requirements of this section shall

be subject to an independent peer review approved by

the authority having jurisdiction. The peer review

shall comprise one or more persons having the

necessary expertise and knowledge to evaluate

compliance, including knowledge of the expected

performance, the structural and component behavior,

the particular loads considered, structural analysis of

the type performed, the materials of construction, and

laboratory testing of elements and components to

determine structural resistance and performance

characteristics. The review shall include the assump-

tions, criteria, procedures, calculations, analytical

models, test setup, test data, ﬁ nal drawings, and

reports. Upon satisfactory completion, the peer review

shall submit a letter to the authority having jurisdic-

tion indicating the scope of their review and their

ﬁ ndings.

1.3.2 Serviceability

Structural systems, and members thereof, shall be

designed to have adequate stiffness to limit deﬂ ec-

tions, lateral drift, vibration, or any other deforma-

tions that adversely affect the intended use and

performance of buildings and other structures.

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CHAPTER 1 GENERAL

1.3.3 Self-Straining Forces

Provision shall be made for anticipated self-

straining forces arising from differential settlements of

foundations and from restrained dimensional changes

due to temperature, moisture, shrinkage, creep, and

similar effects.

1.3.4 Analysis

Load effects on individual structural members

shall be determined by methods of structural analysis

that take into account equilibrium, general stability,

geometric compatibility, and both short- and long-term

material properties. Members that tend to accumulate

residual deformations under repeated service loads

shall have included in their analysis the added eccen-

tricities expected to occur during their service life.

1.3.5 Counteracting Structural Actions

All structural members and systems, and all

components and cladding in a building or other

structure, shall be designed to resist forces due to

earthquake and wind, with consideration of overturn-

ing, sliding, and uplift, and continuous load paths

shall be provided for transmitting these forces to the

foundation. Where sliding is used to isolate the

elements, the effects of friction between sliding

elements shall be included as a force. Where all or a

portion of the resistance to these forces is provided by

dead load, the dead load shall be taken as the

minimum dead load likely to be in place during the

event causing the considered forces. Consideration

shall be given to the effects of vertical and horizontal

deﬂ ections resulting from such forces.

1.4 GENERAL STRUCTURAL INTEGRITY

All structures shall be provided with a continuous load

path in accordance with the requirements of Section

1.4.1 and shall have a complete lateral force-resisting

system with adequate strength to resist the forces

indicated in Section 1.4.2. All members of the

structural system shall be connected to their support-

ing members in accordance with Section 1.4.3.

Structural walls shall be anchored to diaphragms and

supports in accordance with Section 1.4.4. The effects

on the structure and its components due to the forces

stipulated in this section shall be taken as the notional

load, N, and combined with the effects of other loads

in accordance with the load combinations of Section

of Section 1.4.1. Where material resistance is depen-

dent on load duration, notional loads are permitted to

be taken as having a duration of 10 minutes. Structures

designed in conformance with the requirements of this

Standard for Seismic Design Categories B, C, D, E, or

F shall be deemed to comply with the requirements of

Sections 1.4.1, 1.4.2, 1.4.3, 1.4.4 and 1.4.5.

1.4.1 Load Combinations of Integrity Loads

The notional loads, N, speciﬁ ed in Sections 1.4.2

through 1.4.5 shall be combined with dead and live

loads in accordance with Section 1.4.1.1 for strength

design and 1.4.1.2 for allowable stress design.

1.4.1.1 Strength Design Notional Load Combinations

a. 1.2D + 1.0N + L + 0.2S

b. 0.9D + 1.0N

1.4.1.2 Allowable Stress Design Notional

Load Combinations

a. D 0.7N

b. D + 0.75(0.7N) + 0.75L+ 0.75(L

or S or R)

c. 0.6D + 0.7N

1.4.2 Load Path Connections

All parts of the structure between separation

joints shall be interconnected to form a continuous

path to the lateral force-resisting system, and the

connections shall be capable of transmitting the lateral

forces induced by the parts being connected. Any

smaller portion of the structure shall be tied to the

remainder of the structure with elements having

strength to resist a force of not less than 5% of the

portion’s weight.

1.4.3 Lateral Forces

Each structure shall be analyzed for the effects of

static lateral forces applied independently in each of

two orthogonal directions. In each direction, the static

lateral forces at all levels shall be applied simultane-

ously. For purposes of analysis, the force at each level

shall be determined using Eq. 1.4-1 as follows:

= 0.01 W

(1.4-1)

where

= the design lateral force applied at story x and

= the portion of the total dead load of the struc-

ture, D, located or assigned to level x.

Structures explicitly designed for stability,

including second-order effects, shall be deemed to

comply with the requirements of this section.

1.4.4 Connection to Supports

A positive connection for resisting a horizontal

force acting parallel to the member shall be provided

c01.indd 4 4/14/2010 11:00:34 AM

MINIMUM DESIGN LOADS

for each beam, girder, or truss either directly to its

supporting elements or to slabs designed to act as

diaphragms. Where the connection is through a

diaphragm, the member’s supporting element shall

also be connected to the diaphragm. The connection

shall have the strength to resist a force of 5 percent of

the unfactored dead load plus live load reaction

imposed by the supported member on the supporting

member.

1.4.5 Anchorage of Structural Walls

Walls that provide vertical load bearing or lateral

shear resistance for a portion of the structure shall be

anchored to the roof and all ﬂ oors and members that

provide lateral support for the wall or that are

supported by the wall. The anchorage shall provide a

direct connection between the walls and the roof or

ﬂ oor construction. The connections shall be capable

of resisting a strength level horizontal force perpen-

dicular to the plane of the wall equal to 0.2 times the

weight of the wall tributary to the connection, but not

less than 5 psf (0.24 kN/m

1.4.6 Extraordinary Loads and Events

When considered, design for resistance to

extraordinary loads and events shall be in accordance

with the procedures of Section 2.5.

1.5 CLASSIFICATION OF BUILDINGS AND

OTHER STRUCTURES

1.5.1 Risk Categorization

Buildings and other structures shall be classiﬁ ed,

based on the risk to human life, health, and welfare

associated with their damage or failure by nature of

their occupancy or use, according to Table 1.5-1 for

the purposes of applying ﬂ ood, wind, snow, earth-

quake, and ice provisions. Each building or other

structure shall be assigned to the highest applicable

risk category or categories. Minimum design loads for

structures shall incorporate the applicable importance

factors given in Table 1.5-2, as required by other

sections of this Standard. Assignment of a building or

other structure to multiple risk categories based on the

type of load condition being evaluated (e.g., snow or

seismic) shall be permitted.

When the building code or other referenced

standard speciﬁ es an Occupancy Category, the Risk

Category shall not be taken as lower than the Occu-

pancy Category speciﬁ ed therein.

1.5.2 Multiple Risk Categories

Where buildings or other structures are divided

into portions with independent structural systems, the

classiﬁ cation for each portion shall be permitted to be

determined independently. Where building systems,

such as required egress, HVAC, or electrical power,

for a portion with a higher risk category pass through

or depend on other portions of the building or other

structure having a lower risk category, those portions

shall be assigned to the higher risk category.

1.5.3 Toxic, Highly Toxic, and Explosive Substances

Buildings and other structures containing toxic,

highly toxic, or explosive substances are permitted to

be classiﬁ ed as Risk Category II structures if it can be

demonstrated to the satisfaction of the authority

having jurisdiction by a hazard assessment as part of

an overall risk management plan (RMP) that a release

of the toxic, highly toxic, or explosive substances is

not sufﬁ cient to pose a threat to the public.

To qualify for this reduced classiﬁ cation, the

owner or operator of the buildings or other structures

Table 1.5-2 Importance Factors by Risk Category of Buildings and Other Structures for Snow, Ice, and

Earthquake Loads

Risk Category

from

Table 1.5-1

Snow Importance

Factor,

Ice Importance

Factor—Thickness,

Ice Importance

Factor—Wind,

Seismic Importance

Factor,

I 0.80 0.80 1.00 1.00

II 1.00 1.00 1.00 1.00

III 1.10 1.25 1.00 1.25

IV 1.20 1.25 1.00 1.50

The component importance factor, I

, applicable to earthquake loads, is not included in this table because it is dependent on the importance of

the individual component rather than that of the building as a whole, or its occupancy. Refer to Section 13.1.3.

c01.indd 5 4/14/2010 11:00:34 AM

CHAPTER 1 GENERAL

containing the toxic, highly toxic, or explosive

substances shall have an RMP that incorporates three

elements as a minimum: a hazard assessment, a

prevention program, and an emergency response plan.

As a minimum, the hazard assessment shall

include the preparation and reporting of worst-case

release scenarios for each structure under consider-

ation, showing the potential effect on the public for

each. As a minimum, the worst-case event shall

include the complete failure (instantaneous release of

entire contents) of a vessel, piping system, or other

storage structure. A worst-case event includes (but is

not limited to) a release during the design wind or

design seismic event. In this assessment, the evalua-

tion of the effectiveness of subsequent measures for

accident mitigation shall be based on the assumption

that the complete failure of the primary storage

structure has occurred. The offsite impact shall be

deﬁ ned in terms of population within the potentially

affected area. To qualify for the reduced classiﬁ cation,

the hazard assessment shall demonstrate that a release

of the toxic, highly toxic, or explosive substances

from a worst-case event does not pose a threat to the

public outside the property boundary of the facility.

As a minimum, the prevention program shall

consist of the comprehensive elements of process

safety management, which is based upon accident

prevention through the application of management

controls in the key areas of design, construction,

operation, and maintenance. Secondary containment

of the toxic, highly toxic, or explosive substances

(including, but not limited to, double wall tank, dike

of sufﬁ cient size to contain a spill, or other means to

contain a release of the toxic, highly toxic, or explo-

sive substances within the property boundary of the

facility and prevent release of harmful quantities of

contaminants to the air, soil, ground water, or surface

water) are permitted to be used to mitigate the risk

of release. Where secondary containment is provided,

it shall be designed for all environmental loads and

is not eligible for this reduced classiﬁ cation. In

hurricane-prone regions, mandatory practices and

procedures that effectively diminish the effects of

wind on critical structural elements or that alterna-

tively protect against harmful releases during and after

hurricanes are permitted to be used to mitigate the

risk of release.

As a minimum, the emergency response plan

shall address public notiﬁ cation, emergency medical

treatment for accidental exposure to humans, and

procedures for emergency response to releases that

have consequences beyond the property boundary of

the facility. The emergency response plan shall

address the potential that resources for response could

be compromised by the event that has caused the

emergency.

1.6 ADDITIONS AND ALTERATIONS TO

EXISTING STRUCTURES

When an existing building or other structure is

enlarged or otherwise altered, structural members

affected shall be strengthened if necessary so that the

factored loads deﬁ ned in this document will be

supported without exceeding the speciﬁ ed design

strength for the materials of construction. When using

allowable stress design, strengthening is required when

the stresses due to nominal loads exceed the speciﬁ ed

allowable stresses for the materials of construction.

1.7 LOAD TESTS

A load test of any construction shall be conducted

when required by the authority having jurisdiction

whenever there is reason to question its safety for the

intended use.

1.8 CONSENSUS STANDARDS AND OTHER

REFERENCED DOCUMENTS

This section lists the consensus standards and other

documents that are adopted by reference within this

chapter:

OSHA

Occupational Safety and Health Administration

200 Constitution Avenue, NW

Washington, DC 20210

29 CFR 1910.1200 Appendix A with Amendments as

of February 1, 2000.

Section 1.2

OSHA Standards for General Industry, 29 CFR (Code

of Federal Regulations) Part 1910.1200

Appendix A, United States Department of Labor,

Occupational Safety and Health Administration,

Washington, DC, 2005

c01.indd 6 4/14/2010 11:00:34 AM

Chapter 2

COMBINATIONS OF LOADS

5. 1.2D + 1.0E + L + 0.2S

6. 0.9D + 1.0W

7. 0.9D + 1.0E

EXCEPTIONS:

1. The load factor on L in combinations 3, 4, and 5 is

permitted to equal 0.5 for all occupancies in which

in Table 4-1 is less than or equal to 100 psf,

with the exception of garages or areas occupied as

places of public assembly.

2. In combinations 2, 4, and 5, the companion load S

shall be taken as either the ﬂ at roof snow load (p

)

or the sloped roof snow load (p

Where ﬂ uid loads F are present, they shall be

included with the same load factor as dead load D in

combinations 1 through 5 and 7.

Where load H are present, they shall be included

as follows:

1. where the effect of H adds to the primary variable

load effect, include H with a load factor of 1.6;

2. where the effect of H resists the primary variable

load effect, include H with a load factor of 0.9

where the load is permanent or a load factor of 0

for all other conditions.

Effects of one or more loads not acting shall be

investigated. The most unfavorable effects from both

wind and earthquake loads shall be investigated,

where appropriate, but they need not be considered to

act simultaneously. Refer to Section 12.4 for speciﬁ c

deﬁ nition of the earthquake load effect E.

Each relevant strength limit state shall be

investigated.

2.3.3 Load Combinations Including Flood Load

When a structure is located in a ﬂ ood zone

(Section 5.3.1), the following load combinations shall

be considered in addition to the basic combinations in

Section 2.3.2:

1. In V-Zones or Coastal A-Zones, 1.0W in combina-

tions 4 and 6 shall be replaced by 1.0W + 2.0F

2. In noncoastal A-Zones, 1.0W in combinations 4

and 6 shall be replaced by 0.5W + 1.0F

2.1 GENERAL

Buildings and other structures shall be designed using

the provisions of either Section 2.3 or 2.4. Where

elements of a structure are designed by a particular

material standard or speciﬁ cation, they shall be

designed exclusively by either Section 2.3 or 2.4.

2.2 SYMBOLS

= load or load effect arising from extra ordinary

event A

D = dead load

= weight of ice

E = earthquake load

F = load due to ﬂ uids with well-deﬁ ned pressures

and maximum heights

= ﬂ ood load

H = load due to lateral earth pressure, ground water

pressure, or pressure of bulk materials

L = live load

= roof live load

R = rain load

S = snow load

T = self-straining load

W = wind load

wind-on-ice determined in accordance with

Chapter 10

2.3 COMBINING FACTORED LOADS USING

STRENGTH DESIGN

2.3.1 Applicability

The load combinations and load factors given in

Section 2.3.2 shall be used only in those cases in

which they are speciﬁ cally authorized by the appli-

cable material design standard.

2.3.2 Basic Combinations

Structures, components, and foundations shall be

designed so that their design strength equals or

exceeds the effects of the factored loads in the

following combinations:

1. 1.4D

2. 1.2D + 1.6L + 0.5(L

or S or R)

3. 1.2D + 1.6(L

or S or R) + (L or 0.5W)

4. 1.2D + 1.0W + L + 0.5(L

or S or R)

The same E from Sections 1.4 and 12.4 is used for both Sections

2.3.2 and 2.4.1. Refer to the Chapter 11 Commentary for the Seismic

Provisions.

c02.indd 7 4/14/2010 11:00:35 AM

CHAPTER 2 COMBINATIONS OF LOADS

2.3.4. Load Combinations Including Atmospheric

Ice Loads

When a structure is subjected to atmospheric ice

and wind-on-ice loads, the following load combina-

tions shall be considered:

1. 0.5(L

or S or R) in combination 2 shall be replaced

by 0.2D

+ 0.5S.

2. 1.0W + 0.5(L

or S or R) in combination 4 shall be

replaced by D

+ W

+ 0.5S.

3. 1.0W in combination 6 shall be replaced by

+ W

2.3.5 Load Combinations Including

Self-Straining Loads

Where applicable, the structural effects of load T

shall be considered in combination with other loads.

The load factor on load T shall be established consid-

ering the uncertainty associated with the likely

magnitude of the load, the probability that the

maximum effect of T will occur simultaneously with

other applied loadings, and the potential adverse

consequences if the effect of T is greater than

assumed. The load factor on T shall not have a value

less than 1.0.

2.3.6 Load Combinations for Nonspeciﬁ ed Loads

Where approved by the Authority Having

Jurisdiction, the Responsible Design Professional is

permitted to determine the combined load effect for

strength design using a method that is consistent with

the method on which the load combination require-

ments in Section 2.3.2 are based. Such a method must

be probability-based and must be accompanied by

documentation regarding the analysis and collection

of supporting data that is acceptable to the Authority

Having Jurisdiction.

2.4 COMBINING NOMINAL LOADS USING

ALLOWABLE STRESS DESIGN

2.4.1 Basic Combinations

Loads listed herein shall be considered to act in

the following combinations; whichever produces the

most unfavorable effect in the building, foundation, or

structural member being considered. Effects of one or

more loads not acting shall be considered.

1. D

2. D + L

3. D + (L

or S or R)

4. D + 0.75L + 0.75(L

or S or R)

5. D + (0.6W or 0.7E)

6a. D + 0.75L + 0.75(0.6W) + 0.75(L

or S or R)

6b. D + 0.75L + 0.75(0.7E) + 0.75S

7. 0.6D + 0.6W

8. 0.6D + 0.7E

EXCEPTIONS:

1. In combinations 4 and 6, the companion load S

shall be taken as either the ﬂ at roof snow load (p

)

or the sloped roof snow load (p

2. For nonbuilding structures, in which the wind load

is determined from force coefﬁ cients, C

, identiﬁ ed

in Figures 29.5-1, 29.5-2 and 29.5-3 and the

projected area contributing wind force to a founda-

tion element exceeds 1,000 square feet on either a

vertical or a horizontal plane, it shall be permitted

to replace W with 0.9W in combination 7 for

design of the foundation, excluding anchorage of

the structure to the foundation.

3. It shall be permitted to replace 0.6D with 0.9D in

combination 8 for the design of Special Reinforced

Masonry Shear Walls, where the walls satisfy the

requirement of Section 14.4.2.

Where ﬂ uid loads F are present, they shall be

included in combinations 1 through 6 and 8 with the

same factor as that used for dead load D.

Where load H is present, it shall be included as

follows:

1. where the effect of H adds to the primary variable

load effect, include H with a load factor of 1.0;

2. where the effect of H resists the primary variable

load effect, include H with a load factor of 0.6

where the load is permanent or a load factor of 0

for all other conditions.

The most unfavorable effects from both wind

and earthquake loads shall be considered, where

appropriate, but they need not be assumed to act

simultaneously. Refer to Section 1.4 and 12.4

for the speciﬁ c deﬁ nition of the earthquake load

effect E.

Increases in allowable stress shall not be used

with the loads or load combinations given in this

standard unless it can be demonstrated that such an

increase is justiﬁ ed by structural behavior caused by

rate or duration of load.

The same E from Sections 1.4 and 12.4 is used for both Sections

2.3.2 and 2.4.1. Refer to the Chapter 11 Commentary for the Seismic

Provisions.

c02.indd 8 4/14/2010 11:00:35 AM

MINIMUM DESIGN LOADS

2.4.2 Load Combinations Including Flood Load

When a structure is located in a ﬂ ood zone,

the following load combinations shall be

considered in addition to the basic combinations in

Section 2.4.1:

1. In V-Zones or Coastal A-Zones (Section 5.3.1),

1.5F

shall be added to other loads in combinations

5, 6, and 7, and E shall be set equal to zero in 5

and 6.

2. In non-coastal A-Zones, 0.75F

shall be added to

combinations 5, 6, and 7, and E shall be set equal

to zero in 5 and 6.

2.4.3 Load Combinations Including Atmospheric

Ice Loads

When a structure is subjected to atmospheric ice

and wind-on-ice loads, the following load combina-

tions shall be considered:

1. 0.7D

shall be added to combination 2.

2. (L

or S or R) in combination 3 shall be replaced

by 0.7D

+ 0.7W

+ S.

3. 0.6W in combination 7 shall be replaced by 0.7D

0.7W

2.4.4 Load Combinations Including

Self-Straining Loads

Where applicable, the structural effects of load T

shall be considered in combination with other loads.

Where the maximum effect of load T is unlikely to

occur simultaneously with the maximum effects of

other variable loads, it shall be permitted to reduce

the magnitude of T considered in combination with

these other loads. The fraction of T considered in

combination with other loads shall not be less than

0.75.

2.5 LOAD COMBINATIONS FOR

EXTRAORDINARY EVENTS

2.5.1 Applicability

Where required by the owner or applicable code,

strength and stability shall be checked to ensure that

structures are capable of withstanding the effects of

extraordinary (i.e., low-probability) events, such as

ﬁ res, explosions, and vehicular impact

without

disproportionate collapse.

2.5.2 Load Combinations

2.5.2.1 Capacity

For checking the capacity of a structure or structural

element to withstand the effect of an extraordinary

event, the following gravity load combination shall be

considered:

(0.9 or 1.2)D + A

+ 0.5L + 0.2S (2.5-1)

in which A

= the load or load effect resulting from

extraordinary event A.

2.5.2.2 Residual Capacity

For checking the residual load-carrying capacity

of a structure or structural element following the

occurrence of a damaging event, selected load-bearing

elements identiﬁ ed by the Responsible Design

Professional shall be notionally removed, and the

capacity of the damaged structure shall be evaluated

using the following gravity load combination:

(0.9 or 1.2)D + 0.5L + 0.2(L

or S or R) (2.5-2)

2.5.3 Stability Requirements

Stability shall be provided for the structure as a

whole and for each of its elements. Any method that

considers the inﬂ uence of second-order effects is

permitted.

c02.indd 9 4/14/2010 11:00:35 AM

c02.indd 10 4/14/2010 11:00:35 AM

Chapter 3

DEAD LOADS, SOIL LOADS,

AND HYDROSTATIC PRESSURE

3.1.3 Weight of Fixed Service Equipment

In determining dead loads for purposes of design, the

weight of ﬁ xed service equipment, such as plumbing

stacks and risers, electrical feeders, and heating,

ventilating, and air conditioning systems shall be

included.

3.2 SOIL LOADS AND

HYDROSTATIC PRESSURE

3.2.1 Lateral Pressures

In the design of structures below grade, provision

shall be made for the lateral pressure of adjacent soil.

If soil loads are not given in a soil investigation report

approved by the authority having jurisdiction, then the

soil loads speciﬁ ed in Table 3.2-1 shall be used as the

3.1 DEAD LOADS

3.1.1 Deﬁ nition

Dead loads consist of the weight of all materials

of construction incorporated into the building includ-

ing, but not limited to, walls, ﬂ oors, roofs, ceilings,

stairways, built-in partitions, ﬁ nishes, cladding, and

other similarly incorporated architectural and struc-

tural items, and ﬁ xed service equipment including the

weight of cranes.

3.1.2 Weights of Materials and Constructions

In determining dead loads for purposes of design,

the actual weights of materials and constructions shall

be used provided that in the absence of deﬁ nite

information, values approved by the authority having

jurisdiction shall be used.

Table 3.2-1 Design Lateral Soil Load

Description of Backﬁ ll Material

Uniﬁ ed Soil

Classiﬁ cation

Design Lateral Soil Load

psf per foot of depth (kN/m

per meter of depth)

Well-graded, clean gravels; gravel–sand mixes GW

35 (5.50)

Poorly graded clean gravels; gravel–sand mixes GP

35 (5.50)

Silty gravels, poorly graded gravel–sand mixes GM

35 (5.50)

Clayey gravels, poorly graded gravel-and-clay mixes GC

45 (7.07)

Well-graded, clean sands; gravelly–sand mixes SW

35 (5.50)

Poorly graded clean sands; sand–gravel mixes SP

35 (5.50)

Silty sands, poorly graded sand–silt mixes SM

45 (7.07)

Sand–silt clay mix with plastic ﬁ nes SM–SC

85 (13.35)

Clayey sands, poorly graded sand–clay mixes SC

85 (13.35)

Inorganic silts and clayey silts ML

85 (13.35)

Mixture of inorganic silt and clay ML–CL

85 (13.35)

Inorganic clays of low to medium plasticity CL 100 (15.71)

Organic silts and silt–clays, low plasticity OL

Inorganic clayey silts, elastic silts MH

Inorganic clays of high plasticity CH

Organic clays and silty clays OH

Design lateral soil loads are given for moist conditions for the speciﬁ ed soils at their optimum densities. Actual ﬁ eld conditions shall govern.

Submerged or saturated soil pressures shall include the weight of the buoyant soil plus the hydrostatic loads.

For relatively rigid walls, as when braced by ﬂ oors, the design lateral soil load shall be increased for sand and gravel type soils to 60 psf

(9.43 kN/m

) per foot (meter) of depth. Basement walls extending not more than 8 ft (2.44 m) below grade and supporting light ﬂ oor systems

are not considered as being relatively rigid walls.

For relatively rigid walls, as when braced by ﬂ oors, the design lateral load shall be increased for silt and clay type soils to 100 psf

(15.71 kN/m

) per foot (meter) of depth. Basement walls extending not more than 8 ft (2.44 m) below grade and supporting light ﬂ oor

systems are not considered as being relatively rigid walls.

Unsuitable as backﬁ ll material.

c03.indd 11 4/14/2010 11:00:36 AM

CHAPTER 3 DEAD LOADS, SOIL LOADS, AND HYDROSTATIC PRESSURE

minimum design lateral loads. Due allowance shall be

made for possible surcharge from ﬁ xed or moving

loads. When a portion or the whole of the adjacent

soil is below a free-water surface, computations shall

be based upon the weight of the soil diminished by

buoyancy, plus full hydrostatic pressure.

The lateral pressure shall be increased if soils

with expansion potential are present at the site as

determined by a geotechnical investigation.

3.2.2 Uplift on Floors and Foundations

In the design of basement ﬂ oors and similar

approximately horizontal elements below grade,

the upward pressure of water, where applicable,

shall be taken as the full hydrostatic pressure applied

over the entire area. The hydrostatic load shall be

measured from the underside of the construction.

Any other upward loads shall be included in the

design.

Where expansive soils are present under founda-

tions or slabs-on-ground, the foundations, slabs, and

other components shall be designed to tolerate the

movement or resist the upward loads caused by the

expansive soils, or the expansive soil shall be

removed or stabilized around and beneath the

structure.

c03.indd 12 4/14/2010 11:00:37 AM

Chapter 4

LIVE LOADS

with a method approved by the authority having

jurisdiction.

4.3 UNIFORMLY DISTRIBUTED LIVE LOADS

4.3.1 Required Live Loads

The live loads used in the design of buildings and

other structures shall be the maximum loads expected

by the intended use or occupancy, but shall in no case

be less than the minimum uniformly distributed unit

loads required by Table 4-1, including any permis-

sible reduction.

4.3.2 Provision for Partitions

In ofﬁ ce buildings or other buildings where

partitions will be erected or rearranged, provision for

partition weight shall be made, whether or not

partitions are shown on the plans. Partition load shall

not be less than 15 psf (0.72 kN/m

EXCEPTION: A partition live load is not

required where the minimum speciﬁ ed live load

exceeds 80 psf (3.83 kN/m

4.3.3 Partial Loading

The full intensity of the appropriately reduced

live load applied only to a portion of a structure

or member shall be accounted for if it produces

a more unfavorable load effect than the same

intensity applied over the full structure or member.

Roof live loads shall be distributed as speciﬁ ed in

Table 4-1.

4.4 CONCENTRATED LIVE LOADS

Floors, roofs, and other similar surfaces shall

be designed to support safely the uniformly

distributed live loads prescribed in Section 4.3 or

the concentrated load, in pounds or kilonewtons

(kN), given in Table 4-1, whichever produces

the greater load effects. Unless otherwise speciﬁ ed,

the indicated concentration shall be assumed to

be uniformly distributed over an area 2.5 ft

(762 mm) by 2.5 ft (762 mm) and shall be located

so as to produce the maximum load effects in the

members.

4.1 DEFINITIONS

FIXED LADDER: A ladder that is permanently

attached to a structure, building, or equipment.

GRAB BAR SYSTEM: A bar and associated

anchorages and attachments to the structural system,

for the support of body weight in locations such as

toilets, showers, and tub enclosures.

GUARDRAIL SYSTEM: A system of compo-

nents, including anchorages and attachments to the

structural system, near open sides of an elevated

surface for the purpose of minimizing the possibility

of a fall from the elevated surface by people, equip-

ment, or material.

HANDRAIL SYSTEM: A rail grasped by hand

for guidance and support, and associated anchorages

and attachments to the structural system.

HELIPAD: A structural surface that is used for

landing, taking off, taxiing, and parking of helicopters.

LIVE LOAD: A load produced by the use and

occupancy of the building or other structure that does

not include construction or environmental loads, such

as wind load, snow load, rain load, earthquake load,

ﬂ ood load, or dead load.

ROOF LIVE LOAD: A load on a roof produced

(1) during maintenance by workers, equipment, and

materials and (2) during the life of the structure by

movable objects, such as planters or other similar

small decorative appurtenances that are not occupancy

related.

SCREEN ENCLOSURE: A building or part

thereof, in whole or in part self-supporting, having

walls and a roof of insect or sun screening using

ﬁ berglass, aluminum, plastic, or similar lightweight

netting material, which enclose an occupancy or use

such as outdoor swimming pools, patios or decks, and

horticultural and agricultural production facilities.

VEHICLE BARRIER SYSTEM: A system of

components, including anchorages and attachments to

the structural system near open sides or walls of

garage ﬂ oors or ramps, that acts as a restraint for

vehicles.

4.2 LOADS NOT SPECIFIED

For occupancies or uses not designated in this chapter,

the live load shall be determined in accordance

c04.indd 13 4/14/2010 11:00:42 AM

CHAPTER 4 LIVE LOADS

4.5 LOADS ON HANDRAIL, GUARDRAIL,

GRAB BAR, VEHICLE BARRIER SYSTEMS,

AND FIXED LADDERS

4.5.1 Loads on Handrail and Guardrail Systems

All handrail and guardrail systems shall be

designed to resist a single concentrated load of 200 lb

(0.89 kN) applied in any direction at any point on the

handrail or top rail and to transfer this load through

the supports to the structure to produce the maximum

load effect on the element being considered.

Further, all handrail and guardrail systems shall

be designed to resist a load of 50 lb/ft (pound-force

per linear foot) (0.73 kN/m) applied in any direction

along the handrail or top rail. This load need not be

assumed to act concurrently with the load speciﬁ ed in

the preceding paragraph, and this load need not be

considered for the following occupancies:

1. One- and two-family dwellings.

2. Factory, industrial, and storage occupancies, in

areas that are not accessible to the public and that

serve an occupant load not greater than 50.

Intermediate rails (all those except the handrail),

and panel ﬁ llers shall be designed to withstand a

horizontally applied normal load of 50 lb (0.22 kN)

on an area not to exceed 12 in. by 12 in. (305 mm by

305 mm) including openings and space between rails

and located so as to produce the maximum load

effects. Reactions due to this loading are not required

to be superimposed with the loads speciﬁ ed in either

preceding paragraph.

4.5.2 Loads on Grab Bar Systems

Grab bar systems shall be designed to resist a

single concentrated load of 250 lb (1.11 kN) applied

in any direction at any point on the grab bar to

produce the maximum load effect.

4.5.3 Loads on Vehicle Barrier Systems

Vehicle barrier systems for passenger vehicles

shall be designed to resist a single load of 6,000 lb

(26.70 kN) applied horizontally in any direction to the

barrier system, and shall have anchorages or attach-

ments capable of transferring this load to the struc-

ture. For design of the system, the load shall be

assumed to act at heights between 1 ft 6 in. (460 mm)

and 2 ft 3 in. (686 mm) above the ﬂ oor or ramp

surface, selected to produce the maximum load effect.

The load shall be applied on an area not to exceed 12

in. by 12 in. (305 mm by 305 mm) and located so as

to produce the maximum load effects. This load is not

required to act concurrently with any handrail or

guardrail system loadings speciﬁ ed in Section 4.5.1.

Vehicle barrier systems in garages accommodating

trucks and buses shall be designed in accordance with

AASHTO LRFD Bridge Design Speciﬁ cations.

.5.4 Loads on Fixed Ladders

The minimum design live load on ﬁ xed ladders

with rungs shall be a single concentrated load of 300

lb (1.33 kN), and shall be applied at any point to

produce the maximum load effect on the element

being considered. The number and position of

additional concentrated live load units shall be a

minimum of 1 unit of 300 lb (1.33 kN) for every 10 ft

(3.05 m) of ladder height.

Where rails of ﬁ xed ladders extend above a

ﬂ oor or platform at the top of the ladder, each side

rail extension shall be designed to resist a single

concentrated live load of 100 lb (0.445 kN) in any

direction at any height up to the top of the side rail

extension. Ship ladders with treads instead of rungs

shall have minimum design loads as stairs, deﬁ ned in

Table 4-1.

4.6 IMPACT LOADS

4.6.1 General

The live loads speciﬁ ed in Sections 4.3 through

4.5 shall be assumed to include adequate allowance

for ordinary impact conditions. Provision shall be

made in the structural design for uses and loads that

involve unusual vibration and impact forces.

4.6.2 Elevators

All elements subject to dynamic loads from

elevators shall be designed for impact loads and

deﬂ ection limits prescribed by ASME A17.1.

4.6.3 Machinery

For the purpose of design, the weight of machin-

ery and moving loads shall be increased as follows to

allow for impact: (1) light machinery, shaft- or

motor-driven, 20 percent; and (2) reciprocating

machinery or power-driven units, 50 percent. All

percentages shall be increased where speciﬁ ed by the

manufacturer.

4.7 REDUCTION IN LIVE LOADS

4.7.1 General

Except for roof uniform live loads, all other

minimum uniformly distributed live loads, L

c04.indd 14 4/14/2010 11:00:42 AM

MINIMUM DESIGN LOADS

Table 4-1, shall be permitted to be reduced in

accordance with the requirements of Sections 4.7.2

through 4.7.6.

4.7.2 Reduction in Uniform Live Loads

Subject to the limitations of Sections 4.7.3 through

4.7.6, members for which a value of K

is 400 ft

(37.16 m

) or more are permitted to be designed for a

reduced live load in accordance with the following

formula:

LL T

⎛

⎝

⎜

⎞

⎠

⎟

025

(4.7-1)

In SI:

LL T

⎛

⎝

⎜

⎞

⎠

⎟

025

457

where

L = reduced design live load per ft

) of area

supported by the member

= unreduced design live load per ft

) of area

supported by the member (see Table 4-1)

= live load element factor (see Table 4-2)

= tributary area in ft

)

L shall not be less than 0.50L

for members

supporting one ﬂ oor and L shall not be less than

0.40L

for members supporting two or more

ﬂ oors.

EXCEPTION: For structural members in one-

and two-family dwellings supporting more than one

ﬂ oor load, the following ﬂ oor live load reduction shall

be permitted as an alternative to Eq. 4.7-1:

L = 0.7 × (L

+ L

+ …)

, L

, … are the unreduced ﬂ oor live loads appli-

cable to each of multiple supported story levels

regardless of tributary area. The reduced ﬂ oor live

load effect, L, shall not be less than that produced by

the effect of the largest unreduced ﬂ oor live load on a

given story level acting alone.

4.7.3 Heavy Live Loads

Live loads that exceed 100 lb/ft

(4.79 kN/m

) shall

not be reduced.

EXCEPTION: Live loads for members

supporting two or more ﬂ oors shall be permitted to be

reduced by 20 percent.

4.7.4 Passenger Vehicle Garages

The live loads shall not be reduced in passenger

vehicle garages.

EXCEPTION: Live loads for members

supporting two or more ﬂ oors shall be permitted to be

reduced by 20 percent.

4.7.5 Assembly Uses

Live loads shall not be reduced in assembly uses.

4.7.6 Limitations on One-Way Slabs

The tributary area, A

, for one-way slabs shall not

exceed an area deﬁ ned by the slab span times a width

normal to the span of 1.5 times the slab span.

4.8 REDUCTION IN ROOF LIVE LOADS

4.8.1 General

The minimum uniformly distributed roof live loads, L

in Table 4-1, are permitted to be reduced in accor-

dance with the requirements of Sections 4.8.2 and

4.8.3.

4.8.2 Flat, Pitched, and Curved Roofs

Ordinary ﬂ at, pitched, and curved roofs, and awning

and canopies other than those of fabric construction

supported by a skeleton structure, are permitted to be

designed for a reduced roof live load, as speciﬁ ed in

Eq. 4.8-1 or other controlling combinations of loads,

as speciﬁ ed in Chapter 2, whichever produces the

greater load effect. In structures such as greenhouses,

where special scaffolding is used as a work surface

for workers and materials during maintenance and

repair operations, a lower roof load than speciﬁ ed in

Eq. 4.8-1 shall not be used unless approved by the

authority having jurisdiction. On such structures, the

minimum roof live load shall be 12 psf (0.58 kN/m

= L

where 12 ≤ L

≤ 20 (4.8-1)

In SI:

= L

where 0.58 ≤ L

≤ 0.96

where

= reduced roof live load per ft

) of horizontal

projection supported by the member

= unreduced design roof live load per ft

) of

horizontal projection supported by the member

(see Table 4-1)

The reduction factors R

and R

shall be deter-

mined as follows:

1 for A

≤ 200 ft

= 1.2 − 0.001A

for 200 ft

< A

< 600 ft

0.6 for A

≥ 600 ft

c04.indd 15 4/14/2010 11:00:42 AM

CHAPTER 4 LIVE LOADS

in SI:

1 for A

≤ 18.58 m

= 1.2 − 0.011A

for 18.58 m

< A

< 55.74 m

0.6 for A

≥ 55.74 m

where A

= tributary area in ft

) supported by the

member and

1 for F ≤ 4

= 1.2 − 0.05F for 4 < F < 12

0.6 for F ≥ 12

where, for a pitched roof, F = number of inches of

rise per foot (in SI: F = 0.12 × slope, with slope

expressed in percentage points) and, for an arch or

dome, F = rise-to-span ratio multiplied by 32.

4.8.3 Special Purpose Roofs

Roofs that have an occupancy function, such as roof

gardens, assembly purposes, or other special purposes

are permitted to have their uniformly distributed live

load reduced in accordance with the requirements of

Section 4.7.

4.9 CRANE LOADS

4.9.1 General

The crane live load shall be the rated capacity

of the crane. Design loads for the runway beams,

including connections and support brackets, of

moving bridge cranes and monorail cranes shall

include the maximum wheel loads of the crane and

the vertical impact, lateral, and longitudinal forces

induced by the moving crane.

4.9.2 Maximum Wheel Load

The maximum wheel loads shall be the wheel

loads produced by the weight of the bridge, as

applicable, plus the sum of the rated capacity and the

weight of the trolley with the trolley positioned on its

runway at the location where the resulting load effect

is maximum.

4.9.3 Vertical Impact Force

The maximum wheel loads of the crane shall be

increased by the percentages shown in the following

text to determine the induced vertical impact or

vibration force:

Monorail cranes (powered) 25

Cab-operated or remotely operated

bridge cranes (powered) 25

Pendant-operated bridge cranes (powered) 10

Bridge cranes or monorail cranes with

hand-geared bridge, trolley, and hoist 0

4.9.4 Lateral Force

The lateral force on crane runway beams with

electrically powered trolleys shall be calculated as 20

percent of the sum of the rated capacity of the crane

and the weight of the hoist and trolley. The lateral

force shall be assumed to act horizontally at the

traction surface of a runway beam, in either direction

perpendicular to the beam, and shall be distributed

with due regard to the lateral stiffness of the runway

beam and supporting structure.

4.9.5 Longitudinal Force

The longitudinal force on crane runway beams,

except for bridge cranes with hand-geared bridges,

shall be calculated as 10 percent of the maximum

wheel loads of the crane. The longitudinal force shall

be assumed to act horizontally at the traction surface

of a runway beam in either direction parallel to the

beam.

4.10 CONSENSUS STANDARDS AND OTHER

REFERENCED DOCUMENTS

This section lists the consensus standards and other

documents that are adopted by reference within this

chapter:

AASHTO

American Association of State Highway and

Transportation Ofﬁ cials

444 North Capitol Street, NW, Suite 249

Washington, DC 20001

Sections 4.4.3, Table 4-1

AASHTO LRFD Bridge Design Speciﬁ cations, 4th

edition, 2007, with 2008 Interim Revisions

Sections 4.5.3, Table 4-1

ASME

American Society of Mechanical Engineers

Three Park Avenue

New York, NY 10016-5900

ASME A17.1

Section 4.6.2

American National Standard Safety Code for

Elevators and Escalators, 2007.

c04.indd 16 4/14/2010 11:00:42 AM

MINIMUM DESIGN LOADS

Table 4-1 Minimum Uniformly Distributed Live Loads, L

, and Minimum Concentrated Live Loads

Occupancy or Use Uniform psf (kN/m

) Conc. lb (kN)

Apartments (see Residential)

Access ﬂ oor systems

Ofﬁ ce use 50 (2.4) 2,000 (8.9)

Computer use 100 (4.79) 2,000 (8.9)

Armories and drill rooms

150 (7.18)

Assembly areas and theaters

Fixed seats (fastened to ﬂ oor)

60 (2.87)

Lobbies

100 (4.79)

Movable seats

100 (4.79)

Platforms (assembly)

100 (4.79)

Stage ﬂ oors

150 (7.18)

Balconies and decks 1.5 times the live load for the

occupancy served. Not required

to exceed 100 psf (4.79 kN/m

)

Catwalks for maintenance access 40 (1.92) 300 (1.33)

Corridors

First ﬂ oor 100 (4.79)

Other ﬂ oors, same as occupancy served except as indicated

Dining rooms and restaurants

100 (4.79)

Dwellings (see Residential)

Elevator machine room grating (on area of 2 in. by 2 in. (50 mm by

50 mm))

300 (1.33)

Finish light ﬂ oor plate construction (on area of 1 in. by 1 in. (25 mm

by 25 mm))

200 (0.89)

Fire escapes 100 (4.79)

On single-family dwellings only 40 (1.92)

Fixed ladders See Section 4.5

Garages

Passenger vehicles only

40 (1.92)

a,b,c

Trucks and buses

Handrails, guardrails, and grab bars See Section 4.5

Helipads

60 (2.87)

d,e

Nonreducible

e,f,g

Hospitals

Operating rooms, laboratories 60 (2.87) 1,000 (4.45)

Patient rooms 40 (1.92) 1,000 (4.45)

Corridors above ﬁ rst ﬂ oor 80 (3.83) 1,000 (4.45)

Hotels (see Residential)

Libraries

Reading rooms 60 (2.87) 1,000 (4.45)

Stack rooms

150 (7.18)

a,h

1,000 (4.45)

Corridors above ﬁ rst ﬂ oor 80 (3.83) 1,000 (4.45)

Manufacturing

Light

125 (6.00)

2,000 (8.90)

Heavy

250 (11.97)

3,000 (13.40)

Continued

c04.indd 17 4/14/2010 11:00:42 AM

CHAPTER 4 LIVE LOADS

Occupancy or Use Uniform psf (kN/m

) Conc. lb (kN)

Ofﬁ ce buildings

File and computer rooms shall be designed for heavier loads based

on anticipated occupancy

Lobbies and ﬁ rst-ﬂ oor corridors 100 (4.79) 2,000 (8.90)

Ofﬁ ces 50 (2.40) 2,000 (8.90)

Corridors above ﬁ rst ﬂ oor 80 (3.83) 2,000 (8.90)

Penal institutions

Cell blocks 40 (1.92)

Corridors 100 (4.79)

Recreational uses

Bowling alleys, poolrooms, and similar uses

Dance halls and ballrooms

Gymnasiums

Reviewing stands, grandstands, and bleachers

Stadiums and arenas with ﬁ xed seats (fastened to the ﬂ oor)

75 (3.59)

100 (4.79)

a,k

60 (2.87)

a,k

Residential

One- and two-family dwellings

Uninhabitable attics without storage

10 (0.48)

Uninhabitable attics with storage

20 (0.96)

Habitable attics and sleeping areas 30 (1.44)

All other areas except stairs 40 (1.92)

All other residential occupancies

Private rooms and corridors serving them 40 (1.92)

Public rooms

and corridors serving them

100 (4.79)

Roofs

Ordinary ﬂ at, pitched, and curved roofs

20 (0.96)

Roofs used for roof gardens 100 (4.79)

Roofs used for assembly purposes Same as occupancy served

Roofs used for other occupancies

Awnings and canopies

Fabric construction supported by a skeleton structure 5 (0.24) nonreducible 300 (1.33) applied to

skeleton structure

Screen enclosure support frame 5 (0.24) nonreducible and

applied to the roof frame

members only, not the screen

200 (0.89) applied to

supporting roof frame

members only

All other construction 20 (0.96)

Primary roof members, exposed to a work ﬂ oor

Single panel point of lower chord of roof trusses or any point

along primary structural members supporting roofs over

manufacturing, storage warehouses, and repair garages

2,000 (8.9)

All other primary roof members 300 (1.33)

All roof surfaces subject to maintenance workers 300 (1.33)

Schools

Classrooms 40 (1.92) 1,000 (4.45)

Corridors above ﬁ rst ﬂ oor 80 (3.83) 1,000 (4.45)

First-ﬂ oor corridors 100 (4.79) 1,000 (4.45)

Scuttles, skylight ribs, and accessible ceilings 200 (0.89)

Sidewalks, vehicular driveways, and yards subject to trucking

250 (11.97)

a,p

8,000 (35.60)

Stairs and exit ways 100 (4.79)

300

One- and two-family dwellings only 40 (1.92)

300

Table 4-1 (Continued)

c04.indd 18 4/14/2010 11:00:42 AM

MINIMUM DESIGN LOADS

Occupancy or Use Uniform psf (kN/m

) Conc. lb (kN)

Storage areas above ceilings 20 (0.96)

Storage warehouses (shall be designed for heavier loads if required

for anticipated storage)

Light

125 (6.00)

Heavy

250 (11.97)

Stores

Retail

First ﬂ oor 100 (4.79) 1,000 (4.45)

Upper ﬂ oors 75 (3.59) 1,000 (4.45)

Wholesale, all ﬂ oors

125 (6.00)

1,000 (4.45)

Vehicle barriers See Section 4.5

Walkways and elevated platforms (other than exit ways) 60 (2.87)

Yards and terraces, pedestrian

100 (4.79)

Live load reduction for this use is not permitted by Section 4.7 unless speciﬁ c exceptions apply.

Floors in garages or portions of a building used for the storage of motor vehicles shall be designed for the uniformly distributed live loads of

Table 4-1 or the following concentrated load: (1) for garages restricted to passenger vehicles accommodating not more than nine passengers,

3,000 lb (13.35 kN) acting on an area of 4.5 in. by 4.5 in. (114 mm by 114 mm); and (2) for mechanical parking structures without slab or deck

that are used for storing passenger vehicles only, 2,250 lb (10 kN) per wheel.

Design for trucks and buses shall be per AASHTO LRFD Bridge Design Speciﬁ cations; however, provisions for fatigue and dynamic load

allowance are not required to be applied.

Uniform load shall be 40 psf (1.92 kN/m

) where the design basis helicopter has a maximum take-off weight of 3,000 lbs (13.35 kN) or less.

This load shall not be reduced.

Labeling of helicopter capacity shall be as required by the authority having jurisdiction.

Two single concentrated loads, 8 ft (2.44 m) apart shall be applied on the landing area (representing the helicopter’s two main landing gear,

whether skid type or wheeled type), each having a magnitude of 0.75 times the maximum take-off weight of the helicopter and located to

produce the maximum load effect on the structural elements under consideration. The concentrated loads shall be applied over an area of 8 in. by

8 in. (200 mm by 200 mm) and shall not be concurrent with other uniform or concentrated live loads.

A single concentrated load of 3,000 lbs (13.35 kN) shall be applied over an area 4.5 in. by 4.5 in. (114 mm by 114 mm), located so as to

produce the maximum load effects on the structural elements under consideration. The concentrated load need not be assumed to act concurrently

with other uniform or concentrated live loads.

The loading applies to stack room ﬂ oors that support nonmobile, double-faced library book stacks subject to the following limitations: (1) The

nominal book stack unit height shall not exceed 90 in. (2,290 mm); (2) the nominal shelf depth shall not exceed 12 in. (305 mm) for each face;

and (3) parallel rows of double-faced book stacks shall be separated by aisles not less than 36 in. (914 mm) wide.

In addition to the vertical live loads, the design shall include horizontal swaying forces applied to each row of the seats as follows: 24 lb per

linear ft of seat applied in a direction parallel to each row of seats and 10 lb per linear ft of seat applied in a direction perpendicular to each row

of seats. The parallel and perpendicular horizontal swaying forces need not be applied simultaneously.

Uninhabitable attic areas without storage are those where the maximum clear height between the joist and rafter is less than 42 in. (1,067 mm),

or where there are not two or more adjacent trusses with web conﬁ gurations capable of accommodating an assumed rectangle 42 in. (1,067 mm)

in height by 24 in. (610 mm) in width, or greater, within the plane of the trusses. This live load need not be assumed to act concurrently with

any other live load requirement.

Uninhabitable attic areas with storage are those where the maximum clear height between the joist and rafter is 42 in. (1,067 mm) or greater, or

where there are two or more adjacent trusses with web conﬁ gurations capable of accommodating an assumed rectangle 42 in. (1,067 mm) in

height by 24 in. (610 mm) in width, or greater, within the plane of the trusses. At the trusses, the live load need only be applied to those portions

of the bottom chords where both of the following conditions are met:

i. The attic area is accessible from an opening not less than 20 in. (508 mm) in width by 30 in. (762 mm) in length that is located where the

clear height in the attic is a minimum of 30 in. (762 mm); and

ii. The slope of the truss bottom chord is no greater than 2 units vertical to 12 units horizontal (9.5% slope).

The remaining portions of the bottom chords shall be designed for a uniformly distributed nonconcurrent live load of not less than 10 lb/ft

(0.48 kN/m

Where uniform roof live loads are reduced to less than 20 lb/ft

(0.96 kN/m

) in accordance with Section 4.8.1 and are applied to the design of

structural members arranged so as to create continuity, the reduced roof live load shall be applied to adjacent spans or to alternate spans,

whichever produces the greatest unfavorable load effect.

Roofs used for other occupancies shall be designed for appropriate loads as approved by the authority having jurisdiction.

Other uniform loads in accordance with an approved method, which contains provisions for truck loadings, shall also be considered where appropriate.

The concentrated wheel load shall be applied on an area of 4.5 in. by 4.5 in. (114 mm by 114 mm).

Minimum concentrated load on stair treads (on area of 2 in. by 2 in. [50 mm by 50 mm]) is to be applied nonconcurrent with the uniform load.

Table 4-1 (Continued)

c04.indd 19 4/14/2010 11:00:43 AM

CHAPTER 4 LIVE LOADS

Table 4-2 Live Load Element Factor, K

Element K

Interior columns 4

Exterior columns without cantilever slabs 4

Edge columns with cantilever slabs 3

Corner columns with cantilever slabs 2

Edge beams without cantilever slabs 2

Interior beams 2

All other members not identiﬁ ed, including: 1

Edge beams with cantilever slabs

Cantilever beams

One-way slabs

Two-way slabs

Members without provisions for continuous shear transfer normal to

their span

In lieu of the preceding values, K

is permitted to be calculated.

c04.indd 20 4/14/2010 11:00:43 AM

Chapter 5

FLOOD LOADS

community’s FIRM; or (2) the ﬂ ood corresponding to

the area designated as a Flood Hazard Area on a

community’s Flood Hazard Map or otherwise legally

designated.

DESIGN FLOOD ELEVATION (DFE): The

elevation of the design ﬂ ood, including wave height,

relative to the datum speciﬁ ed on a community’s

ﬂ ood hazard map.

FLOOD HAZARD AREA: The area subject to

ﬂ ooding during the design ﬂ ood.

FLOOD HAZARD MAP: The map delineating

Flood Hazard Areas adopted by the authority having

jurisdiction.

FLOOD INSURANCE RATE MAP (FIRM):

An ofﬁ cial map of a community on which the Federal

Insurance and Mitigation Administration has delin-

eated both special ﬂ ood hazard areas and the risk

premium zones applicable to the community.

SPECIAL FLOOD HAZARD AREA (AREA

OF SPECIAL FLOOD HAZARD): The land in the

ﬂ oodplain subject to a 1 percent or greater chance of

ﬂ ooding in any given year. These areas are delineated

on a community’s FIRM as A-Zones (A, AE, A1-30,

A99, AR, AO, or AH) or V-Zones (V, VE, VO, or

V1-30).

5.3 DESIGN REQUIREMENTS

5.3.1 Design Loads

Structural systems of buildings or other structures

shall be designed, constructed, connected, and

anchored to resist ﬂ otation, collapse, and permanent

lateral displacement due to action of ﬂ ood loads

associated with the design ﬂ ood (see Section 5.3.3)

and other loads in accordance with the load combina-

tions of Chapter 2.

5.3.2 Erosion and Scour

The effects of erosion and scour shall be included

in the calculation of loads on buildings and other

structures in ﬂ ood hazard areas.

5.3.3 Loads on Breakaway Walls

Walls and partitions required by ASCE/SEI 24 to

break away, including their connections to the

structure, shall be designed for the largest of the

5.1 GENERAL

The provisions of this section apply to buildings and

other structures located in areas prone to ﬂ ooding as

deﬁ ned on a ﬂ ood hazard map.

5.2 DEFINITIONS

The following deﬁ nitions apply to the provisions of

this chapter:

APPROVED: Acceptable to the authority having

jurisdiction.

BASE FLOOD: The ﬂ ood having a 1 percent

chance of being equaled or exceeded in any given

year.

BASE FLOOD ELEVATION (BFE): The

elevation of ﬂ ooding, including wave height, having a

1 percent chance of being equaled or exceeded in any

given year.

BREAKAWAY WALL: Any type of wall

subject to ﬂ ooding that is not required to provide

structural support to a building or other structure and

that is designed and constructed such that, under base

ﬂ ood or lesser ﬂ ood conditions, it will collapse in

such a way that: (1) it allows the free passage of

ﬂ oodwaters, and (2) it does not damage the structure

or supporting foundation system.

COASTAL A-ZONE: An area within a special

ﬂ ood hazard area, landward of a V-Zone or landward

of an open coast without mapped V-Zones. To be

classiﬁ ed as a Coastal A-Zone, the principal source of

ﬂ ooding must be astronomical tides, storm surges,

seiches, or tsunamis, not riverine ﬂ ooding, and the

potential for breaking wave heights greater than or

equal to 1.5 ft (0.46 m) must exist during the base

ﬂ ood.

COASTAL HIGH HAZARD AREA

(V-ZONE): An area within a Special Flood Hazard

Area, extending from offshore to the inland limit of a

primary frontal dune along an open coast, and any

other area that is subject to high-velocity wave action

from storms or seismic sources. This area is desig-

nated on Flood Insurance Rate Maps (FIRMs) as V,

VE, VO, or V1-30.

DESIGN FLOOD:

The greater of the following

two ﬂ ood events: (1) the Base Flood, affecting those

areas identiﬁ ed as Special Flood Hazard Areas on the

c05.indd 21 4/14/2010 11:00:46 AM

CHAPTER 5 FLOOD LOADS

following loads acting perpendicular to the plane of

the wall:

1. The wind load speciﬁ ed in Chapter 26.

2. The earthquake load speciﬁ ed in Chapter 12.

3. 10 psf (0.48 kN/m

The loading at which breakaway walls are

intended to collapse shall not exceed 20 psf

(0.96 kN/m

) unless the design meets the following

conditions:

1. Breakaway wall collapse is designed to result from

a ﬂ ood load less than that which occurs during the

base ﬂ ood.

2. The supporting foundation and the elevated portion

of the building shall be designed against collapse,

permanent lateral displacement, and other struc-

tural damage due to the effects of ﬂ ood loads in

combination with other loads as speciﬁ ed in

Chapter 2.

5.4 LOADS DURING FLOODING

5.4.1 Load Basis

In ﬂ ood hazard areas, the structural design shall

be based on the design ﬂ ood.

5.4.2 Hydrostatic Loads

Hydrostatic loads caused by a depth of water to

the level of the DFE shall be applied over all surfaces

involved, both above and below ground level, except

that for surfaces exposed to free water, the design

depth shall be increased by 1 ft (0.30 m).

Reduced uplift and lateral loads on surfaces

of enclosed spaces below the DFE shall apply

only if provision is made for entry and exit of

ﬂ oodwater.

5.4.3 Hydrodynamic Loads

Dynamic effects of moving water shall be

determined by a detailed analysis utilizing basic

concepts of ﬂ uid mechanics.

EXCEPTION: Where water velocities do not

exceed 10 ft/s (3.05 m/s), dynamic effects of moving

water shall be permitted to be converted into

equivalent hydrostatic loads by increasing the DFE for

design purposes by an equivalent surcharge depth, d

on the headwater side and above the ground level

only, equal to

(5.4-1)

where

V = average velocity of water in ft/s (m/s)

g = acceleration due to gravity, 32.2 ft/s

(9.81 m/s

)

a = coefﬁ cient of drag or shape factor (not less than

1.25)

The equivalent surcharge depth shall be added to

the DFE design depth and the resultant hydrostatic

pressures applied to, and uniformly distributed across,

the vertical projected area of the building or structure

that is perpendicular to the ﬂ ow. Surfaces parallel to

the ﬂ ow or surfaces wetted by the tail water shall be

subject to the hydrostatic pressures for depths to the

DFE only.

5.4.4 Wave Loads

Wave loads shall be determined by one of the

following three methods: (1) by using the analytical

procedures outlined in this section, (2) by more

advanced numerical modeling procedures, or (3) by

laboratory test procedures (physical modeling).

Wave loads are those loads that result from

water waves propagating over the water surface and

striking a building or other structure. Design and

construction of buildings and other structures subject

to wave loads shall account for the following loads:

waves breaking on any portion of the building or

structure; uplift forces caused by shoaling waves

beneath a building or structure, or portion thereof;

wave runup striking any portion of the building or

structure; wave-induced drag and inertia forces; and

wave-induced scour at the base of a building or

structure, or its foundation. Wave loads shall be

included for both V-Zones and A-Zones. In V-Zones,

waves are 3 ft (0.91 m) high, or higher; in coastal

ﬂ oodplains landward of the V-Zone, waves are less

than 3 ft high (0.91 m).

Nonbreaking and broken wave loads shall be

calculated using the procedures described in Sections

5.4.2 and 5.4.3 that show how to calculate hydrostatic

and hydrodynamic loads.

Breaking wave loads shall be calculated using the

procedures described in Sections 5.4.4.1 through

5.4.4.4. Breaking wave heights used in the procedures

described in Sections 5.4.4.1 through 5.4.4.4 shall be

calculated for V-Zones and Coastal A-Zones using

Eqs. 5.4-2 and 5.4-3.

= 0.78d

(5.4-2)

where

= breaking wave height in ft (m)

= local still water depth in ft (m)

c05.indd 22 4/14/2010 11:00:46 AM

MINIMUM DESIGN LOADS

The local still water depth shall be calculated

using Eq. 5.4-3, unless more advanced procedures or

laboratory tests permitted by this section are used.

= 0.65(BFE – G) (5.4-3)

where

BFE = BFE in ft (m)

G = ground elevation in ft (m)

5.4.4.1 Breaking Wave Loads on Vertical Pilings

and Columns

The net force resulting from a breaking wave

acting on a rigid vertical pile or column shall be

assumed to act at the still water elevation and shall be

calculated by the following:

= 0.5γ

(5.4-4)

where

= net wave force, in lb (kN)

= unit weight of water, in lb per cubic ft (kN/m

= 62.4 pcf (9.80 kN/m

) for fresh water and

64.0 pcf (10.05 kN/m

) for salt water

= coefﬁ cient of drag for breaking waves, = 1.75

for round piles or columns and = 2.25 for square

piles or columns

D = pile or column diameter, in ft (m) for

circular sections, or for a square pile or

column, 1.4 times the width of the pile or

column in ft (m)

= breaking wave height, in ft (m)

5.4.4.2 Breaking Wave Loads on Vertical Walls

Maximum pressures and net forces resulting from

a normally incident breaking wave (depth-limited in

size, with H

= 0.78d

) acting on a rigid vertical wall

shall be calculated by the following:

max

= C

+ 1.2γ

(5.4-5)

and

= 1.1C

+ 2.4γ

(5.4-6)

where

max

= maximum combined dynamic (C

) and

static (1.2γ

) wave pressures, also referred to

as shock pressures in lb/ft

(kN/m

)

= net breaking wave force per unit length of

structure, also referred to as shock, impulse, or

wave impact force in lb/ft (kN/m), acting near

the still water elevation

= dynamic pressure coefﬁ cient (1.6 < C

< 3.5)

(see Table 5.4-1)

Table 5.4-1 Value of Dynamic Pressure

Coefﬁ cient, C

Risk Category

I 1.6

II 2.8

III 3.2

IV 3.5

For Risk Category, see Table 1.5-1.

= unit weight of water, in lb per cubic ft (kN/m

= 62.4 pcf (9.80 kN/m

) for fresh water and

64.0 pcf (10.05 kN/m

) for salt water

= still water depth in ft (m) at base of building or

other structure where the wave breaks

This procedure assumes the vertical wall causes a

reﬂ ected or standing wave against the waterward side

of the wall with the crest of the wave at a height of

1.2d

above the still water level. Thus, the dynamic

static and total pressure distributions against the wall

are as shown in Fig. 5.4-1.

This procedure also assumes the space behind the

vertical wall is dry, with no ﬂ uid balancing the static

component of the wave force on the outside of the

wall. If free water exists behind the wall, a portion of

the hydrostatic component of the wave pressure and

force disappears (see Fig. 5.4-2) and the net force

shall be computed by Eq. 5.4-7 (the maximum

combined wave pressure is still computed with

Eq. 5.4-5).

= 1.1C

+ 1.9γ

(5.4-7)

where

= net breaking wave force per unit length of

structure, also referred to as shock, impulse, or

wave impact force in lb/ft (kN/m), acting near

the still water elevation

= dynamic pressure coefﬁ cient (1.6 < C

< 3.5)

(see Table 5.4-1)

= unit weight of water, in lb per cubic ft (kN/m

= 62.4 pcf (9.80 kN/m

) for fresh water and

64.0 pcf (10.05 kN/m

) for salt water

= still water depth in ft (m) at base of building or

other structure where the wave breaks

5.4.4.3 Breaking Wave Loads on Nonvertical Walls

Breaking wave forces given by Eqs. 5.4-6 and

5.4-7 shall be modiﬁ ed in instances where the walls

or surfaces upon which the breaking waves act are

c05.indd 23 4/14/2010 11:00:46 AM

CHAPTER 5 FLOOD LOADS

nonvertical. The horizontal component of breaking

wave force shall be given by

= F

sin

α (5.4-8)

where

= horizontal component of breaking wave force in

lb/ft (kN/m)

= net breaking wave force acting on a vertical

surface in lb/ft (kN/m)

α = vertical angle between nonvertical surface and

the horizontal

5.4.4.4 Breaking Wave Loads from Obliquely

Incident Waves

Breaking wave forces given by Eqs. 5.4-6

and 5.4-7 shall be modiﬁ ed in instances where

waves are obliquely incident. Breaking wave

forces from non-normally incident waves shall be

given by

= F

sin

α (5.4-9)

where

= horizontal component of obliquely incident

breaking wave force in lb/ft (kN/m)

= net breaking wave force (normally incident

waves) acting on a vertical surface in lb/ft

(kN/m)

α = horizontal angle between the direction of wave

approach and the vertical surface

5.4.5 Impact Loads

Impact loads are those that result from debris,

ice, and any object transported by ﬂ oodwaters

striking against buildings and structures, or parts

thereof. Impact loads shall be determined using a

rational approach as concentrated loads acting

horizontally at the most critical location at or below

the DFE.

Vertical Wall

Crest of reflected wave

Dynamic pressure

1.2 d

Crest of incident wave

0.55 d

Stillwater level

Hydrostatic pressure

Ground elevation

FIGURE 5.4-1 Normally Incident Breaking Wave Pressures against a Vertical Wall (Space behind Vertical

Wall is Dry).

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MINIMUM DESIGN LOADS

Vertical Wall

Crest of reflected wave

Dynamic pressure

1.2 d

Crest of incident wave

0.55 d

Stillwater level

Net hydrostatic pressure

Ground elevation

FIGURE 5.4-2 Normally Incident Breaking Wave Pressures against a Vertical Wall (Still Water Level Equal

on Both Sides of Wall).

5.5 CONSENSUS STANDARDS AND OTHER

REFERENCED DOCUMENTS

This section lists the consensus standards and other

documents that are adopted by reference within this

chapter:

ASCE/SEI

American Society of Civil Engineers

Structural Engineering Institute

1801 Alexander Bell Drive

Reston, VA 20191-4400

ASCE/SEI 24

Section 5.3.3

Flood Resistant Design and Construction, 1998

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c05.indd 26 4/14/2010 11:00:46 AM

Chapter 6

RESERVED FOR FUTURE PROVISIONS

WLSC, the wind load provisions of ASCE 7 are

presented in Chapters 26 through 31 as opposed

to prior editions wherein the wind load provisions

were contained in a single section (previously

Chapter 6).

In preparing the wind load provisions contained

within this standard, the Wind Load Subcommittee

(WLSC) of ASCE 7 established as one of its

primary goals the improvement of the clarity and use

of the standard. As a result of the efforts of the

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c06.indd 28 4/14/2010 11:00:47 AM

Chapter 7

SNOW LOADS

designated CS in Fig. 7-1. Ground snow loads for

sites at elevations above the limits indicated in Fig.

7-1 and for all sites within the CS areas shall be

approved by the authority having jurisdiction. Ground

snow load determination for such sites shall be based

on an extreme value statistical analysis of data

available in the vicinity of the site using a value with

a 2 percent annual probability of being exceeded

(50-year mean recurrence interval).

Snow loads are zero for Hawaii, except in

mountainous regions as determined by the authority

having jurisdiction.

7.3 FLAT ROOF SNOW LOADS, p

The ﬂ at roof snow load, p

, shall be calculated in lb/ft

(kN/m

) using the following formula:

= 0.7C

(7.3-1)

7.3.1 Exposure Factor, C

The value for C

shall be determined from

Table 7-2.

7.3.2 Thermal Factor, C

The value for C

shall be determined from

Table 7-3.

7.3.3 Importance Factor, I

The value for I

shall be determined from Table

1.5-2 based on the Risk Category from Table 1.5-1.

7.3.4 Minimum Snow Load for Low-Slope Roofs, p

A minimum roof snow load, p

, shall only apply to

monoslope, hip and gable roofs with slopes less than

15°, and to curved roofs where the vertical angle from

the eaves to the crown is less than 10°. The minimum

roof snow load for low-slope roofs shall be obtained

using the following formula:

Where p

is 20 lb/ft

(0.96 kN/m

) or less:

= I

(Importance Factor times p

)

Where p

exceeds 20 lb/ft

(0.96 kN/m

= 20 (I

) (20 lb/ft

times Importance Factor)

This minimum roof snow load is a separate

uniform load case. It need not be used in determining

7.1 SYMBOLS

= exposure factor as determined from Table 7-2

= slope factor as determined from Fig. 7-2

= thermal factor as determined from Table 7-3

h = vertical separation distance in feet (m) between

the edge of a higher roof including any parapet

and the edge of a lower adjacent roof excluding

any parapet

= height of balanced snow load determined by

dividing p

by γ, in ft (m)

= clear height from top of balanced snow load to

(1) closest point on adjacent upper roof, (2) top

of parapet, or (3) top of a projection on the roof,

in ft (m)

= height of snow drift, in ft (m)

= height of obstruction above the surface of the

roof, in ft (m)

= importance factor as prescribed in Section 7.3.3

= length of the roof upwind of the drift, in ft (m)

= maximum intensity of drift surcharge load, in

lb/ft

(kN/m

)

= snow load on ﬂ at roofs (“ﬂ at” = roof slope ≤ 5°),

in lb/ft

(kN/m

)

= ground snow load as determined from Fig. 7-1

and Table 7-1; or a site-speciﬁ c analysis, in lb/ft

(kN/m

)

= minimum snow load for low-slope roofs, in lb/ft

(kN/m

)

= sloped roof (balanced) snow load, in lb/ft

(kN/m

)

s = horizontal separation distance in feet (m)

between the edges of two adjacent buildings

S = roof slope run for a rise of one

θ = roof slope on the leeward side, in degrees

w = width of snow drift, in ft (m)

W = horizontal distance from eave to ridge, in ft (m)

γ = snow density, in lb/ft

(kN/m

) as determined

from Eq. 7.7-1

7.2 GROUND SNOW LOADS, p

Ground snow loads, p

, to be used in the determina-

tion of design snow loads for roofs shall be as set

forth in Fig. 7-1 for the contiguous United States and

Table 7-1 for Alaska. Site-speciﬁ c case studies shall

be made to determine ground snow loads in areas

c07.indd 29 4/14/2010 11:00:51 AM

CHAPTER 7 SNOW LOADS

Table 7-1 Ground Snow Loads, p

, for Alaskan Locations

Location lb/ft

kN/m

Location lb/ft

kN/m

Location lb/ft

kN/m

Adak 30 1.4 Galena 60 2.9 Petersburg 150 7.2

Anchorage 50 2.4 Gulkana 70 3.4 St. Paul 40 1.9

Angoon 70 3.4 Homer 40 1.9 Seward 50 2.4

Barrow 25 1.2 Juneau 60 2.9 Shemya 25 1.2

Barter 35 1.7 Kenai 70 3.4 Sitka 50 2.4

Bethel 40 1.9 Kodiak 30 1.4 Talkeetna 120 5.8

Big Delta 50 2.4 Kotzebue 60 2.9 Unalakleet 50 2.4

Cold Bay 25 1.2 McGrath 70 3.4 Valdez 160 7.7

Cordova 100 4.8 Nenana 80 3.8 Whittier 300 14.4

Fairbanks 60 2.9 Nome 70 3.4 Wrangell 60 2.9

Fort Yukon 60 2.9 Palmer 50 2.4 Yakutat 150 7.2

Table 7-2 Exposure Factor, C

Terrain Category

Exposure of Roof

Fully Exposed Partially Exposed Sheltered

B (see Section 26.7) 0.9 1.0 1.2

C (see Section 26.7) 0.9 1.0 1.1

D (see Section 26.7) 0.8 0.9 1.0

Above the treeline in windswept mountainous areas. 0.7 0.8 N/A

In Alaska, in areas where trees do not exist within a 2-mile (3-km) radius of

the site.

0.7 0.8 N/A

The terrain category and roof exposure condition chosen shall be representative of the anticipated conditions during the life of the structure. An

exposure factor shall be determined for each roof of a structure.

Deﬁ nitions: Partially Exposed: All roofs except as indicated in the following text. Fully Exposed: Roofs exposed on all sides with no shelter

afforded by terrain, higher structures, or trees. Roofs that contain several large pieces of mechanical equipment, parapets that extend above the

height of the balanced snow load (h

), or other obstructions are not in this category. Sheltered: Roofs located tight in among conifers that qualify

as obstructions.

Obstructions within a distance of 10h

provide “shelter,” where h

is the height of the obstruction above the roof level. If the only obstructions

are a few deciduous trees that are leaﬂ ess in winter, the “fully exposed” category shall be used. Note that these are heights above the roof.

Heights used to establish the Exposure Category in Section 26.7 are heights above the ground.

Table 7-3 Thermal Factor, C

Thermal Condition

All structures except as indicated below 1.0

Structures kept just above freezing and others with cold, ventilated roofs in which the thermal resistance (R-value)

between the ventilated space and the heated space exceeds 25 °F × h × ft

/Btu (4.4 K × m

/W).

1.1

Unheated and open air structures 1.2

Structures intentionally kept below freezing 1.3

Continuously heated greenhouses

with a roof having a thermal resistance (R-value) less than 2.0 °F × h × ft

/Btu

(0.4 K × m

/W)

0.85

These conditions shall be representative of the anticipated conditions during winters for the life of the structure.

Greenhouses with a constantly maintained interior temperature of 50 °F (10 °C) or more at any point 3 ft above the ﬂ oor level during winters

and having either a maintenance attendant on duty at all times or a temperature alarm system to provide warning in the event of a heating failure.

c07.indd 30 4/14/2010 11:00:51 AM

MINIMUM DESIGN LOADS

or in combination with drift, sliding, unbalanced, or

partial loads.

7.4 SLOPED ROOF SNOW LOADS, p

Snow loads acting on a sloping surface shall be

assumed to act on the horizontal projection of that

surface. The sloped roof (balanced) snow load, p

shall be obtained by multiplying the ﬂ at roof snow

load, p

, by the roof slope factor, C

= C

(7.4-1)

Values of C

for warm roofs, cold roofs, curved roofs,

and multiple roofs are determined from Sections 7.4.1

through 7.4.4. The thermal factor, C

, from Table 7-3

determines if a roof is “cold” or “warm.” “Slippery

surface” values shall be used only where the roof’s

surface is unobstructed and sufﬁ cient space is avail-

able below the eaves to accept all the sliding snow. A

roof shall be considered unobstructed if no objects

exist on it that prevent snow on it from sliding.

Slippery surfaces shall include metal, slate, glass, and

bituminous, rubber, and plastic membranes with a

smooth surface. Membranes with an imbedded

aggregate or mineral granule surface shall not be

considered smooth. Asphalt shingles, wood shingles,

and shakes shall not be considered slippery.

7.4.1 Warm Roof Slope Factor, C

For warm roofs (C

≤ 1.0 as determined from

Table 7-3) with an unobstructed slippery surface that

will allow snow to slide off the eaves, the roof slope

factor C

shall be determined using the dashed line in

Fig. 7-2a, provided that for nonventilated warm roofs,

their thermal resistance (R-value) equals or exceeds

30 ft

hr °F/Btu (5.3 °C m

/W) and for warm venti-

lated roofs, their R-value equals or exceeds 20 ft

°F/Btu (3.5 °C m

/W). Exterior air shall be able to

circulate freely under a ventilated roof from its eaves

to its ridge. For warm roofs that do not meet the

aforementioned conditions, the solid line in Fig. 7-2a

shall be used to determine the roof slope factor C

7.4.2 Cold Roof Slope Factor, C

Cold roofs are those with a C

> 1.0 as deter-

mined from Table 7-3. For cold roofs with C

= 1.1

and an unobstructed slippery surface that will allow

snow to slide off the eaves, the roof slope factor C

shall be determined using the dashed line in Fig. 7-2b.

For all other cold roofs with C

= 1.1, the solid line in

Fig. 7-2b shall be used to determine the roof slope

factor C

. For cold roofs with C

= 1.2 and an unob-

structed slippery surface that will allow snow to

slide off the eaves, the roof slope factor C

shall be

determined using the dashed line on Fig. 7-2c. For

all other cold roofs with C

= 1.2, the solid line in

Fig. 7-2c shall be used to determine the roof slope

factor C

7.4.3 Roof Slope Factor for Curved Roofs

Portions of curved roofs having a slope exceeding

70° shall be considered free of snow load (i.e.,

= 0). Balanced loads shall be determined from the

balanced load diagrams in Fig. 7-3 with C

determined

from the appropriate curve in Fig. 7-2.

7.4.4 Roof Slope Factor for Multiple Folded Plate,

Sawtooth, and Barrel Vault Roofs

Multiple folded plate, sawtooth, or barrel vault

roofs shall have a C

= 1.0, with no reduction in snow

load because of slope (i.e., p

= p

7.4.5 Ice Dams and Icicles Along Eaves

Two types of warm roofs that drain water over

their eaves shall be capable of sustaining a uniformly

distributed load of 2p

on all overhanging portions:

those that are unventilated and have an R-value less

than 30 ft

hr °F/Btu (5.3 °C m

/W) and those that are

ventilated and have an R-value less than 20 ft

hr °F/

Btu (3.5 °C m

/W). The load on the overhang shall be

based upon the ﬂ at roof snow load for the heated

portion of the roof up-slope of the exterior wall. No

other loads except dead loads shall be present on the

roof when this uniformly distributed load is applied.

7.5 PARTIAL LOADING

The effect of having selected spans loaded with the

balanced snow load and remaining spans loaded with

half the balanced snow load shall be investigated as

follows:

7.5.1 Continuous Beam Systems

Continuous beam systems shall be investigated

for the effects of the three loadings shown in Fig. 7-4:

Case 1: Full balanced snow load on either exterior span

and half the balanced snow load on all other spans.

Case 2: Half the balanced snow load on either exterior

span and full balanced snow load on all other spans.

Case 3: All possible combinations of full balanced

snow load on any two adjacent spans and half the

balanced snow load on all other spans. For this

case there will be (n –1) possible combinations

where n equals the number of spans in the continu-

ous beam system.

c07.indd 31 4/14/2010 11:00:51 AM

CHAPTER 7 SNOW LOADS

If a cantilever is present in any of the above cases, it

shall be considered to be a span.

Partial load provisions need not be applied to

structural members that span perpendicular to the

ridgeline in gable roofs with slopes of 2.38˚ (½ on 12)

and greater.

7.5.2 Other Structural Systems

Areas sustaining only half the balanced snow load

shall be chosen so as to produce the greatest effects

on members being analyzed.

7.6 UNBALANCED ROOF SNOW LOADS

Balanced and unbalanced loads shall be analyzed

separately. Winds from all directions shall be

accounted for when establishing unbalanced loads.

7.6.1 Unbalanced Snow Loads for Hip and

Gable Roofs

For hip and gable roofs with a slope exceeding 7

on 12 (30.2°) or with a slope less than 2.38° (½ on

12) unbalanced snow loads are not required to be

applied. Roofs with an eave to ridge distance, W, of

20 ft (6.1 m) or less, having simply supported

prismatic members spanning from ridge to eave shall

be designed to resist an unbalanced uniform snow

load on the leeward side equal to Ip

. For these roofs

the windward side shall be unloaded. For all other

gable roofs, the unbalanced load shall consist of 0.3p

on the windward side, p

on the leeward side plus a

rectangular surcharge with magnitude h

γ/ S and

horizontal extent from the ridge

83Sh

where h

the drift height from Fig. 7-9 with l

equal to the eave

to ridge distance for the windward portion of the roof,

W. For W less than 20 ft (6.1 m), use W = l

= 20 ft in

Fig 7-9.

Balanced and unbalanced loading diagrams

are presented in Fig. 7-5.

7.6.2 Unbalanced Snow Loads for Curved Roofs

Portions of curved roofs having a slope exceeding

70° shall be considered free of snow load. If the slope

of a straight line from the eaves (or the 70° point, if

present) to the crown is less than 10° or greater than

60°, unbalanced snow loads shall not be taken into

account.

Unbalanced loads shall be determined according

to the loading diagrams in Fig. 7-3. In all cases the

windward side shall be considered free of snow. If the

ground or another roof abuts a Case II or Case III (see

Fig. 7-3) curved roof at or within 3 ft (0.91 m) of its

eaves, the snow load shall not be decreased between

the 30° point and the eaves, but shall remain constant

at the 30° point value. This distribution is shown as a

dashed line in Fig. 7-3.

7.6.3 Unbalanced Snow Loads for Multiple Folded

Plate, Sawtooth, and Barrel Vault Roofs

Unbalanced loads shall be applied to folded plate,

sawtooth, and barrel-vaulted multiple roofs with a

slope exceeding 3/8 in./ft (1.79°). According to

Section 7.4.4, C

= 1.0 for such roofs, and the

balanced snow load equals p

. The unbalanced snow

load shall increase from one-half the balanced load at

the ridge or crown (i.e., 0.5p

) to two times the

balanced load given in Section 7.4.4 divided by C

the valley (i.e., 2p

). Balanced and unbalanced

loading diagrams for a sawtooth roof are presented in

Fig. 7-6. However, the snow surface above the valley

shall not be at an elevation higher than the snow

above the ridge. Snow depths shall be determined by

dividing the snow load by the density of that snow

from Eq. 7.7-1, which is in Section 7.7.1.

7.6.4 Unbalanced Snow Loads for Dome Roofs

Unbalanced snow loads shall be applied to domes

and similar rounded structures. Snow loads, deter-

mined in the same manner as for curved roofs in

Section 7.6.2, shall be applied to the downwind 90°

sector in plan view. At both edges of this sector, the

load shall decrease linearly to zero over sectors of

22.5° each. There shall be no snow load on the

remaining 225° upwind sector.

7.7 DRIFTS ON LOWER ROOFS

(AERODYNAMIC SHADE)

Roofs shall be designed to sustain localized loads

from snowdrifts that form in the wind shadow of

(1) higher portions of the same structure and

(2) adjacent structures and terrain features.

7.7.1 Lower Roof of a Structure

Snow that forms drifts comes from a higher roof

or, with the wind from the opposite direction, from the

roof on which the drift is located. These two kinds of

drifts (“leeward” and “windward” respectively) are

shown in Fig. 7-7. The geometry of the surcharge load

due to snow drifting shall be approximated by a

triangle as shown in Fig. 7-8. Drift loads shall be

superimposed on the balanced snow load. If h

less than 0.2, drift loads are not required to be applied.

For leeward drifts, the drift height h

shall be

determined directly from Fig. 7-9 using the length of

the upper roof. For windward drifts, the drift height

shall be determined by substituting the length of the

c07.indd 32 4/14/2010 11:00:52 AM

MINIMUM DESIGN LOADS

lower roof for l

in Fig. 7-9 and using three-quarters of

as determined from Fig. 7-9 as the drift height. The

larger of these two heights shall be used in design. If

this height is equal to or less than h

, the drift width,

w, shall equal 4h

and the drift height shall equal h

. If

this height exceeds h

, the drift width, w, shall equal

and the drift height shall equal h

. However,

the drift width, w, shall not be greater than 8h

. If the

drift width, w, exceeds the width of the lower roof, the

drift shall be truncated at the far edge of the roof, not

reduced to zero there. The maximum intensity of the

drift surcharge load, p

, equals h

γ where snow

density, γ, is deﬁ ned in Eq. 7.7-1:

γ = 0.13p

+ 14 but not more than 30 pcf (7.7-1)

(in SI: γ = 0.426p

+ 2.2, but not more than 4.7 kN/m

)

This density shall also be used to determine h

dividing p

by γ (in SI: also multiply by 102 to get the

depth in m).

7.7.2 Adjacent Structures

If the horizontal separation distance between

adjacent structures, s, is less than 20 ft (6.1 m) and less

than six times the vertical separation distance (s < 6h),

then the requirements for the leeward drift of Section

7.7.1 shall be used to determine the drift load on the

lower structure. The height of the snow drift shall be

the smaller of h

, based upon the length of the adjacent

higher structure, and (6h – s)/6. The horizontal extent

of the drift shall be the smaller of 6h

or (6h – s).

For windward drifts, the requirements of Section

7.7.1 shall be used. The resulting drift is permitted to

be truncated.

7.8 ROOF PROJECTIONS AND PARAPETS

The method in Section 7.7.1 shall be used to calculate

drift loads on all sides of roof projections and at parapet

walls. The height of such drifts shall be taken as

three-quarters the drift height from Fig. 7-9 (i.e.,

0.75h

). For parapet walls, l

shall be taken equal to the

length of the roof upwind of the wall. For roof projec-

tions, l

shall be taken equal to the greater of the length

of the roof upwind or downwind of the projection. If the

side of a roof projection is less than 15 ft (4.6 m) long, a

drift load is not required to be applied to that side.

7.9 SLIDING SNOW

The load caused by snow sliding off a sloped roof

onto a lower roof shall be determined for slippery

upper roofs with slopes greater than ¼ on 12, and for

other (i.e., nonslippery) upper roofs with slopes

greater than 2 on 12. The total sliding load per unit

length of eave shall be 0.4p

W, where W is the

horizontal distance from the eave to ridge for the

sloped upper roof. The sliding load shall be distrib-

uted uniformly on the lower roof over a distance of

15 ft (4.6 m) from the upper roof eave. If the width of

the lower roof is less than 15 ft (4.6 m), the sliding

load shall be reduced proportionally.

The sliding snow load shall not be further

reduced unless a portion of the snow on the upper

roof is blocked from sliding onto the lower roof by

snow already on the lower roof.

For separated structures, sliding loads shall be

considered when h/s > 1 and s < 15 ft (4.6 m). The

horizontal extent of the sliding load on the lower roof

shall be 15 – s with s in feet (4.6 – s with s in meters),

and the load per unit length shall be 0.4 p

W (15 – s)/15

with s in feet (0.4p

W (4.6 – s)/4.6 with s in meters).

Sliding loads shall be superimposed on the

balanced snow load and need not be used in combina-

tion with drift, unbalanced, partial, or rain-on-snow

loads.

7.10 RAIN-ON-SNOW SURCHARGE LOAD

For locations where p

is 20 lb/ft

(0.96 kN/m

) or

less, but not zero, all roofs with slopes (in degrees)

less than W/50 with W in ft (in SI: W/15.2 with W in

m) shall include a 5 lb/ft

(0.24 kN/m

) rain-on-snow

surcharge load. This additional load applies only to

the sloped roof (balanced) load case and need not be

used in combination with drift, sliding, unbalanced,

minimum, or partial loads.

7.11 PONDING INSTABILITY

Roofs shall be designed to preclude ponding instabil-

ity. For roofs with a slope less than ¼ in./ft (1.19˚)

and roofs where water can be impounded, roof

deﬂ ections caused by full snow loads shall be evalu-

ated when determining the likelihood of ponding

instability (see Section 8.4).

7.12 EXISTING ROOFS

Existing roofs shall be evaluated for increased snow

loads caused by additions or alterations. Owners or

agents for owners of an existing lower roof shall be

advised of the potential for increased snow loads

where a higher roof is constructed within 20 ft

(6.1 m). See footnote to Table 7-2 and Section 7.7.2.

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CHAPTER 7 SNOW LOADS

FIGURE 7-1 Ground Snow Loads, P

, for the United States (Lb/Ft

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MINIMUM DESIGN LOADS

FIGURE 7-1. (Continued)

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CHAPTER 7 SNOW LOADS

FIGURE 7-2 Graphs for Determining Roof Slope Factor C

, for Warm and Cold Roofs (See Table 7-3 for C

Deﬁ nitions).

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MINIMUM DESIGN LOADS

FIGURE 7-3 Balanced and Unbalanced Loads for Curved Roofs.

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CHAPTER 7 SNOW LOADS

FIGURE 7-4 Partial Loading Diagrams for Continuous Beams.

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MINIMUM DESIGN LOADS

p decnalaB

Unbalanced

W < 20 ft with

roof rafter system

I * p

Unbalanced

Other

Sγh

0.3 p

Note: Unbalanced loads need not be considered

for θ > 30.2° (7 on 12) or for θ ≤ 2.38° (1/2 on 12).

FIGURE 7-5 Balanced and Unbalanced Snow Loads for Hip and Gable Roofs.

c07.indd 39 4/14/2010 11:00:55 AM

CHAPTER 7 SNOW LOADS

2 p

∗

0.5 p

Balanced

Load

Unbalanced

Load

* May be somewhat less; see Section 7.6.3

FIGURE 7-6 Balanced and Unbalanced Snow Loads for a Sawtooth Roof.

FIGURE 7-7 Drifts Formed at Windward and Leeward Steps.

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MINIMUM DESIGN LOADS

FIGURE 7-8 Conﬁ guration of Snow Drifts on Lower Roofs.

FIGURE 7-9 Graph and Equation for Determining Drift Height, h

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c07.indd 42 4/14/2010 11:00:56 AM

Chapter 8

RAIN LOADS

If the secondary drainage systems contain drain

lines, such lines and their point of discharge shall be

separate from the primary drain lines.

8.4 PONDING INSTABILITY

“Ponding” refers to the retention of water due solely

to the deﬂ ection of relatively ﬂ at roofs. Susceptible

bays shall be investigated by structural analysis to

assure that they possess adequate stiffness to preclude

progressive deﬂ ection (i.e., instability) as rain falls on

them or meltwater is created from snow on them.

Bays with a roof slope less than 1/4 in./ft., or on

which water is impounded upon them (in whole or in

part) when the primary drain system is blocked, but

the secondary drain system is functional, shall be

designated as susceptible bays. Roof surfaces with a

slope of at least 1/4 in. per ft (1.19º) towards points of

free drainage need not be considered a susceptible

bay.

The larger of the snow load or the rain load

equal to the design condition for a blocked primary

drain system shall be used in this analysis.

8.5 CONTROLLED DRAINAGE

Roofs equipped with hardware to control the rate of

drainage shall be equipped with a secondary drainage

system at a higher elevation that limits accumulation

of water on the roof above that elevation. Such roofs

shall be designed to sustain the load of all rainwater

that will accumulate on them to the elevation of the

secondary drainage system plus the uniform load

caused by water that rises above the inlet of the

secondary drainage system at its design ﬂ ow (deter-

mined from Section 8.3).

Such roofs shall also be checked for ponding

instability (determined from Section 8.4).

8.1 SYMBOLS

R = rain load on the undeﬂ ected roof, in lb/ft

(kN/m

). When the phrase “undeﬂ ected roof” is

used, deﬂ ections from loads (including dead

loads) shall not be considered when determining

the amount of rain on the roof.

= depth of water on the undeﬂ ected roof up to the

inlet of the secondary drainage system when the

primary drainage system is blocked (i.e., the

static head), in in. (mm).

= additional depth of water on the undeﬂ ected roof

above the inlet of the secondary drainage system

at its design ﬂ ow (i.e., the hydraulic head), in in.

(mm).

8.2 ROOF DRAINAGE

Roof drainage systems shall be designed in accor-

dance with the provisions of the code having jurisdic-

tion. The ﬂ ow capacity of secondary (overﬂ ow) drains

or scuppers shall not be less than that of the primary

drains or scuppers.

8.3 DESIGN RAIN LOADS

Each portion of a roof shall be designed to sustain the

load of all rainwater that will accumulate on it if the

primary drainage system for that portion is blocked

plus the uniform load caused by water that rises above

the inlet of the secondary drainage system at its

design ﬂ ow.

R = 5.2(d

+ d

) (8.3-1)

In SI: R = 0.0098(d

+ d

)

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c08.indd 44 4/14/2010 11:00:57 AM

Chapter 9

RESERVED FOR FUTURE PROVISIONS

separate sections and to relocate provisions into their

most logical new sections.

The provisions for buildings and nonbuilding

structures are now distinctly separate as are the

provisions for nonstructural components. Less

commonly used provisions, such as those for seismi-

cally isolated structures, have also been located in

their own distinct chapter. We hope that the users of

ASCE 7 will ﬁ nd the reformatted seismic provisions

to be a signiﬁ cant improvement in organization and

presentation over prior editions and will be able to

more quickly locate applicable provisions. Table

C11-1, located in Commentary Chapter C11 of the

2005 edition of ASCE 7 was provided to assist users

in locating provisions between the 2002 and 2005

editions of the standard. Table C11-1 is not included

in this edition of the standard.

In preparing the seismic provisions contained within

this standard, the Seismic Task Committee of ASCE 7

established a Scope and Format Subcommittee to

review the layout and presentation of the seismic

provisions and to make recommendations to improve

the clarity and use of the standard. As a result of the

efforts of this subcommittee, the seismic provisions

of ASCE 7 are presented in Chapters 11 through 23

and Appendices 11A and 11B, as opposed to prior

editions wherein the seismic provisions were pre-

sented in a single section (previously Section 9).

Of foremost concern in the reformat effort was

the organization of the seismic provisions in a logical

sequence for the general structural design community

and the clariﬁ cation of the various headings to more

accurately reﬂ ect their content. Accomplishing these

two primary goals led to the decision to create 13

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c09.indd 46 4/14/2010 11:01:06 AM

Chapter 10

ICE LOADS—ATMOSPHERIC ICING

caused or enhanced by an ice accretion on a ﬂ exible

structural member, component, or appurtenance are

not covered in this section.

10.1.3 Exclusions

Electric transmission systems, communications

towers and masts, and other structures for which

national standards exist are excluded from the

requirements of this section. Applicable standards and

guidelines include the NESC, ASCE Manual 74, and

ANSI/EIA/TIA-222.

10.2 DEFINITIONS

The following deﬁ nitions apply only to the provisions

of this chapter.

COMPONENTS AND APPURTENANCES:

Nonstructural elements that may be exposed to

atmospheric icing. Examples are ladders, handrails,

antennas, waveguides, Radio Frequency (RF) trans-

mission lines, pipes, electrical conduits, and cable

trays.

FREEZING RAIN: Rain or drizzle that falls

into a layer of subfreezing air at the earth’s surface

and freezes on contact with the ground or an object to

form glaze ice.

GLAZE: Clear high-density ice.

HOARFROST: An accumulation of ice crystals

formed by direct deposition of water vapor from the

air onto an object.

ICE-SENSITIVE STRUCTURES: Structures

for which the effect of an atmospheric icing load

governs the design of part or all of the structure.

This includes, but is not limited to, lattice structures,

guyed masts, overhead lines, light suspension and

cable-stayed bridges, aerial cable systems (e.g.,

for ski lifts and logging operations), amusement

rides, open catwalks and platforms, ﬂ agpoles, and

signs.

IN-CLOUD ICING: Occurs when supercooled

cloud or fog droplets carried by the wind freeze on

impact with objects. In-cloud icing usually forms

rime, but may also form glaze.

RIME: White or opaque ice with entrapped air.

SNOW: Snow that adheres to objects by some

combination of capillary forces, freezing, and

sintering.

10.1 GENERAL

Atmospheric ice loads due to freezing rain, snow, and

in-cloud icing shall be considered in the design of

ice-sensitive structures. In areas where records or

experience indicate that snow or in-cloud icing

produces larger loads than freezing rain, site-speciﬁ c

studies shall be used. Structural loads due to hoarfrost

are not a design consideration. Roof snow loads are

covered in Chapter 7.

10.1.1 Site-Speciﬁ c Studies

Mountainous terrain and gorges shall be exam-

ined for unusual icing conditions. Site-speciﬁ c studies

shall be used to determine the 50-year mean recur-

rence interval ice thickness, concurrent wind speed,

and concurrent temperature in

1. Alaska.

2. Areas where records or experience indicate that

snow or in-cloud icing produces larger loads than

freezing rain.

3. Special icing regions shown in Figs. 10-2, 10-4,

and 10-5.

4. Mountainous terrain and gorges where examination

indicates unusual icing conditions exist.

Site-speciﬁ c studies shall be subject to review

and approval by the authority having jurisdiction.

In lieu of using the mapped values, it shall be

permitted to determine the ice thickness, the concur-

rent wind speed, and the concurrent temperature for a

structure from local meteorological data based on a

50-year mean recurrence interval provided that

1. The quality of the data for wind and type and

amount of precipitation has been taken into account.

2. A robust ice accretion algorithm has been used to

estimate uniform ice thicknesses and concurrent

wind speeds from these data.

3. Extreme-value statistical analysis procedures

acceptable to the authority having jurisdiction have

been employed in analyzing the ice thickness and

concurrent wind speed data.

4. The length of record and sampling error have been

taken into account.

10.1.2 Dynamic Loads

Dynamic loads, such as those resulting from gallop-

ing, ice shedding, and aeolian vibrations, that are

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CHAPTER 10 ICE LOADS—ATMOSPHERIC ICING

10.3 SYMBOLS

= surface area of one side of a ﬂ at plate or the

projected area of complex shapes

= cross-sectional area of ice

D = diameter of a circular structure or member as

deﬁ ned in Chapter 29, in ft (m)

= diameter of the cylinder circumscribing an object

= factor to account for the increase in ice thick-

ness with height

= importance factor for ice thickness from Table

1.5-2 based on the Risk Category from Table 1.5-1

= importance factor for concurrent wind pressure

from Table 1.5-2 based on the Risk Category

from Table 1.5-1

= topographic factor as deﬁ ned in Chapter 26

= velocity pressure evaluated at height z above

ground, in lb/ft

(N/m

) as deﬁ ned in Chapter 29

r = radius of the maximum cross-section of a dome

or radius of a sphere

t = nominal ice thickness due to freezing rain at a

height of 33 ft (10 m) from Figs. 10-2 through

10-6 in inches (mm)

= design ice thickness in in. (mm) from Eq. 10.4-5

= concurrent wind speed mph (m/s) from Figs.

10-2 through 10-6

= volume of ice

z = height above ground in ft (m)

∈ = solidity ratio as deﬁ ned in Chapter 29

10.4 ICE LOADS DUE TO FREEZING RAIN

10.4.1 Ice Weight

The ice load shall be determined using the weight

of glaze ice formed on all exposed surfaces of

structural members, guys, components, appurtenances,

and cable systems. On structural shapes, prismatic

members, and other similar shapes, the cross-sectional

area of ice shall be determined by

= πt

+ t

) (10.4-1)

is shown for a variety of cross-sectional shapes in

Fig. 10-1.

On ﬂ at plates and large three-dimensional objects

such as domes and spheres, the volume of ice shall be

determined by

= πt

(10.4-2)

For a ﬂ at plate A

shall be the area of one side of

the plate, for domes and spheres A

shall be deter-

mined by

= πr

(10.4-3)

It is acceptable to multiply V

by 0.8 for vertical

plates and 0.6 for horizontal plates.

The ice density shall be not less than 56 pcf

(900 kg/m

10.4.2 Nominal Ice Thickness

Figs. 10-2 through 10-6 show the equivalent

uniform radial thicknesses t of ice due to freezing rain

at a height of 33 ft (10 m) over the contiguous 48

states and Alaska for a 50-year mean recurrence

interval. Also shown are concurrent 3-s gust wind

speeds. Thicknesses for Hawaii, and for ice accretions

due to other sources in all regions, shall be obtained

from local meteorological studies.

10.4.3 Height Factor

The height factor f

used to increase the radial

thickness of ice for height above ground z shall be

determined by

010

⎛

⎝

⎜

⎞

⎠

⎟

for 0 ft < z ≤ 900 ft

(10.4-4)

= 1.4 for z > 900 ft

In SI:

010

⎛

⎝

⎜

⎞

⎠

⎟

for 0 m < z ≤ 275 m

= 1.4 for z > 275 m

10.4.4 Importance Factors

Importance factors to be applied to the radial

ice thickness and wind pressure shall be determined

from Table 1.5-2 based on the Risk Category from

Table 1.5-1. The importance factor I

shall be

applied to the ice thickness, not the ice weight,

because the ice weight is not a linear function of

thickness.

10.4.5 Topographic Factor

Both the ice thickness and concurrent wind speed

for structures on hills, ridges, and escarpments are

higher than those on level terrain because of wind

speed-up effects. The topographic factor for the

concurrent wind pressure is K

and the topographic

factor for ice thickness is (K

)

0.35

, where K

obtained from Eq. 26.8-1.

10.4.6 Design Ice Thickness for Freezing Rain

The design ice thickness t

shall be calculated

from Eq. 10.4-5.

= 2.0tI

)

0.35

(10.4-5)

c10.indd 48 4/14/2010 11:01:02 AM

MINIMUM DESIGN LOADS

10.5 WIND ON ICE-COVERED STRUCTURES

Ice accreted on structural members, components, and

appurtenances increases the projected area of the

structure exposed to wind. The projected area shall be

increased by adding t

to all free edges of the projected

area. Wind loads on this increased projected area

shall be used in the design of ice-sensitive structures.

Figs. 10-2 to 10-6 include 3-s gust wind speeds at

33 ft (10 m) above grade that are concurrent with the

ice loads due to freezing rain. Wind loads shall be

calculated in accordance with Chapters 26 through 31

as modiﬁ ed by Sections 10.5.1 through 10.5.5.

10.5.1 Wind on Ice-Covered Chimneys, Tanks, and

Similar Structures

Force coefﬁ cients C

for structures with square,

hexagonal, and octagonal cross-sections shall be as

given in Fig. 29.5-1. Force coefﬁ cients C

for struc-

tures with round cross-sections shall be as given in

Fig. 29.5-1 for round cross-sections with D√q

≤ 2.5

for all ice thicknesses, wind speeds, and structure

diameters.

10.5.2 Wind on Ice-Covered Solid Freestanding

Walls and Solid Signs

Force coefﬁ cients C

shall be as given in Fig.

29.4 based on the dimensions of the wall or sign

including ice.

10.5.3 Wind on Ice-Covered Open Signs and

Lattice Frameworks

The solidity ratio ∈ shall be based on the

projected area including ice. The force coefﬁ cient C

for the projected area of ﬂ at members shall be as

given in Fig. 29.5-2. The force coefﬁ cient C

for

rounded members and for the additional projected

area due to ice on both ﬂ at and rounded members

shall be as given in Fig. 29.5-2 for rounded members

with D√q

≤ 2.5 for all ice thicknesses, wind speeds,

and member diameters.

10.5.4 Wind on Ice-Covered Trussed Towers

The solidity ratio ∈ shall be based on the projected

area including ice. The force coefﬁ cients C

shall be as

given in Fig. 29.5-3. It is acceptable to reduce the force

coefﬁ cients C

for the additional projected area due to

ice on both round and ﬂ at members by the factor for

rounded members in Note 3 of Fig. 29.5-3.

10.5.5 Wind on Ice-Covered Guys and Cables

The force coefﬁ cient C

(as deﬁ ned in Chapter

29) for ice-covered guys and cables shall be 1.2.

10.6 Design Temperatures for Freezing Rain

The design temperatures for ice and wind-on-ice due

to freezing rain shall be either the temperature for

the site shown in Figs. 10-7 and 10-8 or 32°F (0°C),

whichever gives the maximum load effect. The

temperature for Hawaii shall be 32°F (0°C). For

temperature sensitive structures, the load shall include

the effect of temperature change from everyday

conditions to the design temperature for ice and

wind-on-ice. These temperatures are to be used with

ice thicknesses for all mean recurrence intervals. The

design temperatures are considered to be concurrent

with the design ice load and the concurrent wind load.

10.7 PARTIAL LOADING

The effects of a partial ice load shall be considered

when this condition is critical for the type of structure

under consideration. It is permitted to consider this to

be a static load.

10.8 DESIGN PROCEDURE

1. The nominal ice thickness, t, the concurrent wind

speed, V

, and the concurrent temperature for the

site shall be determined from Figs. 10-2 to 10-8

or a site-speciﬁ c study.

2. The topographic factor for the site, K

shall be determined in accordance with

Section 10.4.5.

3. The importance factor for ice thickness, I

shall be determined in accordance with

Section 10.4.4.

4. The height factor, f

, shall be determined in

accordance with Section 10.4.3 for each design

segment of the structure.

5. The design ice thickness, t

, shall be determined

in accordance with Section 10.4.6, Eq. 10.4-5.

6. The weight of ice shall be calculated for the

design ice thickness, t

, in accordance with

Section 10.4.1.

7. The velocity pressure q

for wind speed V

shall

be determined in accordance with Section 29.3

using the importance factor for concurrent wind

pressure I

determined in accordance with Section

10.4.4.

8. The wind force coefﬁ cients C

shall be deter-

mined in accordance with Section 10.5.

9. The gust effect factor shall be determined in

accordance with Section 26.9.

c10.indd 49 4/14/2010 11:01:02 AM

CHAPTER 10 ICE LOADS—ATMOSPHERIC ICING

10. The design wind force shall be determined in

accordance with Chapter 29.

11. The iced structure shall be analyzed for the load

combinations in either Section 2.3 or 2.4.

10.9 CONSENSUS STANDARDS AND OTHER

REFERENCED DOCUMENTS

This section lists the consensus standards and other

documents that are adopted by reference within this

chapter:

ASCE

American Society of Civil Engineers

1801 Alexander Bell Drive

Reston, VA 20191

ASCE Manual 74

Section 10.1.3

Guidelines for Electrical Transmission Line Structural

Loading, 1991

ANSI

American National Standards Institute

25 West 43rd Street, 4th Floor

New York, NY 10036

ANSI/EIA/TIA-222

Section 10.1.3

Structural Standards for Steel Antenna Towers and

Antenna Supporting Structures, 1996

IEEE

445 Hoes Lane

Piscataway, NJ 08854-1331

NESC

Section 10.1.3

National Electrical Safety Code, 2001

c10.indd 50 4/14/2010 11:01:02 AM

MINIMUM DESIGN LOADS

FIGURE 10-1 Characteristic Dimension D

for Calculating the Ice Area for a Variety of Cross-Sectional

Shapes.

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CHAPTER 10 ICE LOADS—ATMOSPHERIC ICING

FIGURE 10-2 Equivalent Radial Ice Thicknesses Due to Freezing Rain with Concurrent 3-Second Gust

Speeds, for a 50-Year Mean Recurrence Interval.

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MINIMUM DESIGN LOADS

FIGURE 10-2 (Continued)

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CHAPTER 10 ICE LOADS—ATMOSPHERIC ICING

FIGURE 10-3 Lake Superior Detail.

FIGURE 10-4 Fraser Valley Detail.

c10.indd 54 4/14/2010 11:01:04 AM

FIGURE 10-5 Columbia River Gorge Detail.

FIGURE 10-6 50-Yr Mean Recurrence Interval Uniform Ice Thicknesses Due to Freezing Rain with

Concurrent 3-Second Gust Speeds: Alaska.

c10.indd 55 4/14/2010 11:01:04 AM

FIGURE 10-7 Temperatures Concurrent with Ice Thicknesses Due to Freezing Rain: Contiguous 48 States.

FIGURE 10-8 Temperatures Concurrent with Ice Thicknesses Due to Freezing Rain: Alaska.

c10.indd 56 4/14/2010 11:01:04 AM

Chapter 11

SEISMIC DESIGN CRITERIA

vehicular bridges, electrical transmission towers,

hydraulic structures, buried utility lines and their

appurtenances, and nuclear reactors.

5. Piers and wharves that are not accessible to the

general public.

11.1.3 Applicability

Structures and their nonstructural components

shall be designed and constructed in accordance with

the requirement of the following sections based on the

type of structure or component:

a. Buildings: Chapter 12

b. Nonbuilding Structures: Chapter 15

c. Nonstructural Components: Chapter 13

d. Seismically Isolated Structures: Chapter 17

e. Structures with Damping Systems: Chapter 18

Buildings whose purpose is to enclose equipment or

machinery and whose occupants are engaged in

maintenance or monitoring of that equipment,

machinery or their associated processes shall be

permitted to be classiﬁ ed as nonbuilding structures

designed and detailed in accordance with Section 15.5

of this standard.

11.1.4 Alternate Materials and Methods

of Construction

Alternate materials and methods of construction

to those prescribed in the seismic requirements of this

standard shall not be used unless approved by the

authority having jurisdiction. Substantiating evidence

shall be submitted demonstrating that the proposed

alternate, for the purpose intended, will be at least

equal in strength, durability, and seismic resistance.

11.2 DEFINITIONS

The following deﬁ nitions apply only to the seismic

requirements of this standard.

ACTIVE FAULT: A fault determined to be

active by the authority having jurisdiction from

properly substantiated data (e.g., most recent mapping

of active faults by the United States Geological

Survey).

ADDITION: An increase in building area,

aggregate ﬂ oor area, height, or number of stories of a

structure.

11.1 GENERAL

11.1.1 Purpose

Chapter 11 presents criteria for the design and

construction of buildings and other structures subject

to earthquake ground motions. The speciﬁ ed earth-

quake loads are based upon post-elastic energy

dissipation in the structure, and because of this fact,

the requirements for design, detailing, and construc-

tion shall be satisﬁ ed even for structures and members

for which load combinations that do not contain

earthquake loads indicate larger demands than

combinations that include earthquake loads. Minimum

requirements for quality assurance for seismic

force-resisting systems are set forth in Appendix 11A.

11.1.2 Scope

Every structure, and portion thereof, including

nonstructural components, shall be designed and

constructed to resist the effects of earthquake motions

as prescribed by the seismic requirements of this

standard. Certain nonbuilding structures, as described

in Chapter 15, are also within the scope and shall be

designed and constructed in accordance with the

requirements of Chapter 15. Requirements concerning

alterations, additions, and change of use are set forth

in Appendix 11B. Existing structures and alterations to

existing structures need only comply with the seismic

requirements of this standard where required by

Appendix 11B. The following structures are exempt

from the seismic requirements of this standard:

1. Detached one- and two-family dwellings that are

located where the mapped, short period, spectral

response acceleration parameter, S

, is less than 0.4

or where the Seismic Design Category determined

in accordance with Section 11.6 is A, B, or C.

2. Detached one- and two-family wood-frame

dwellings not included in Exception 1 with not

more than two stories above grade plane, satisfying

the limitations of and constructed in accordance

with the IRC.

3. Agricultural storage structures that are intended

only for incidental human occupancy.

4. Structures that require special consideration of their

response characteristics and environment that are

not addressed in Chapter 15 and for which other

regulations provide seismic criteria, such as

c11.indd 57 4/14/2010 11:01:13 AM

CHAPTER 11 SEISMIC DESIGN CRITERIA

ALTERATION: Any construction or renovation

to an existing structure other than an addition.

APPENDAGE: An architectural component such

as a canopy, marquee, ornamental balcony, or

statuary.

APPROVAL: The written acceptance by the

authority having jurisdiction of documentation

that establishes the qualiﬁ cation of a material,

system, component, procedure, or person to fulﬁ ll

the requirements of this standard for the intended

use.

ATTACHMENTS: Means by which nonstruc-

tural components or supports of nonstructural compo-

nents are secured or connected to the seismic

force-resisting system of the structure. Such attach-

ments include anchor bolts, welded connections, and

mechanical fasteners.

BASE: The level at which the horizontal seismic

ground motions are considered to be imparted to the

structure.

BASE SHEAR: Total design lateral force or

shear at the base.

BOUNDARY ELEMENTS: Diaphragm and

shear wall boundary members to which the diaphragm

transfers forces. Boundary members include chords

and drag struts at diaphragm and shear wall perim-

eters, interior openings, discontinuities, and reentrant

corners.

BOUNDARY MEMBERS: Portions along wall

and diaphragm edges strengthened by longitudinal and

transverse reinforcement. Boundary members include

chords and drag struts at diaphragm and shear wall

perimeters, interior openings, discontinuities, and

reentrant corners.

BUILDING: Any structure whose intended use

includes shelter of human occupants.

CANTILEVERED COLUMN SYSTEM: A

seismic force-resisting system in which lateral forces

are resisted entirely by columns acting as cantilevers

from the base.

CHARACTERISTIC EARTHQUAKE: An

earthquake assessed for an active fault having a

magnitude equal to the best estimate of the maximum

magnitude capable of occurring on the fault, but not

less than the largest magnitude that has occurred

historically on the fault.

COMPONENT: A part of an architectural,

electrical, or mechanical system.

Component, Nonstructural: A part of an

architectural, mechanical, or electrical system

within or without a building or nonbuilding

structure.

Component, Flexible: Nonstructural component

having a fundamental period greater than

0.06 s.

Component, Rigid: Nonstructural component

having a fundamental period less than or equal

to 0.06 s.

CONCRETE, PLAIN: Concrete that is either

unreinforced or contains less reinforcement than the

minimum amount speciﬁ ed in ACI 318 for reinforced

concrete.

CONCRETE, REINFORCED: Concrete

reinforced with no less reinforcement than the

minimum amount required by ACI 318 prestressed

or nonprestressed, and designed on the assumption

that the two materials act together in resisting

forces.

CONSTRUCTION DOCUMENTS: The

written, graphic, electronic, and pictorial documents

describing the design, locations, and physical charac-

teristics of the project required to verify compliance

with this standard.

COUPLING BEAM: A beam that is used to

connect adjacent concrete wall elements to make them

act together as a unit to resist lateral loads.

DEFORMABILITY: The ratio of the ultimate

deformation to the limit deformation.

High-Deformability Element: An element

whose deformability is not less than 3.5 where

subjected to four fully reversed cycles at the

limit deformation.

Limited-Deformability Element: An element

that is neither a low-deformability nor a

high-deformability element.

Low-Deformability Element: An element whose

deformability is 1.5 or less.

DEFORMATION:

Limit Deformation: Two times the initial

deformation that occurs at a load equal to 40

percent of the maximum strength.

Ultimate Deformation: The deformation at

which failure occurs and that shall be deemed

to occur if the sustainable load reduces to 80

percent or less of the maximum strength.

DESIGNATED SEISMIC SYSTEMS: Those

nonstructural components that require design in

accordance with Chapter 13 and for which the

component importance factor, I

, is greater than 1.0.

DESIGN EARTHQUAKE: The earthquake

effects that are two-thirds of the corresponding

Maximum Considered Earthquake (MCE

) effects.

c11.indd 58 4/14/2010 11:01:14 AM

MINIMUM DESIGN LOADS

DESIGN EARTHQUAKE GROUND

MOTION: The earthquake ground motions that are

two-thirds of the corresponding MCE

ground

motions.

DIAPHRAGM: Roof, ﬂ oor, or other membrane

or bracing system acting to transfer the lateral forces

to the vertical resisting elements.

DIAPHRAGM BOUNDARY: A location where

shear is transferred into or out of the diaphragm

element. Transfer is either to a boundary element or

to another force-resisting element.

DIAPHRAGM CHORD: A diaphragm bound-

ary element perpendicular to the applied load that is

assumed to take axial stresses due to the diaphragm

moment.

DRAG STRUT (COLLECTOR, TIE, DIA-

PHRAGM STRUT): A diaphragm or shear wall

boundary element parallel to the applied load that

collects and transfers diaphragm shear forces to the

vertical force-resisting elements or distributes forces

within the diaphragm or shear wall.

ENCLOSURE: An interior space surrounded by

walls.

EQUIPMENT SUPPORT: Those structural

members or assemblies of members or manufactured

elements, including braces, frames, legs, lugs,

snuggers, hangers, or saddles that transmit gravity

loads and operating loads between the equipment and

the structure.

FLEXIBLE CONNECTIONS: Those connec-

tions between equipment components that permit

rotational and/or translational movement without

degradation of performance. Examples include

universal joints, bellows expansion joints, and ﬂ exible

metal hose.

FRAME:

Braced Frame: An essentially vertical truss, or

its equivalent, of the concentric or eccentric

type that is provided in a building frame

system or dual system to resist seismic

forces.

Concentrically Braced Frame (CBF): A

braced frame in which the members are

subjected primarily to axial forces. CBFs are

categorized as ordinary concentrically braced

frames (OCBFs) or special concentrically

braced frames (SCBFs).

Eccentrically Braced Frame (EBF): A

diagonally braced frame in which at least

one end of each brace frames into a beam a

short distance from a beam-column or from

another diagonal brace.

Moment Frame: A frame in which members and

joints resist lateral forces by ﬂ exure as well as

along the axis of the members. Moment frames

are categorized as intermediate moment frames

(IMF), ordinary moment frames (OMF), and

special moment frames (SMF).

Structural System:

Building Frame System: A structural system

with an essentially complete space frame

providing support for vertical loads. Seismic

force resistance is provided by shear walls or

braced frames.

Dual System: A structural system with an

essentially complete space frame providing

support for vertical loads. Seismic force

resistance is provided by moment-resisting

frames and shear walls or braced frames as

prescribed in Section 12.2.5.1.

Shear Wall-Frame Interactive System: A

structural system that uses combinations of

ordinary reinforced concrete shear walls and

ordinary reinforced concrete moment frames

designed to resist lateral forces in proportion to

their rigidities considering interaction between

shear walls and frames on all levels.

Space Frame System: A 3-D structural system

composed of interconnected members, other

than bearing walls, that is capable of support-

ing vertical loads and, where designed for such

an application, is capable of providing resis-

tance to seismic forces.

FRICTION CLIP: A device that relies on

friction to resist applied loads in one or more direc-

tions to anchor a nonstructural component. Friction is

provided mechanically and is not due to gravity loads.

GLAZED CURTAIN WALL: A nonbearing

wall that extends beyond the edges of building ﬂ oor

slabs, and includes a glazing material installed in the

curtain wall framing.

GLAZED STOREFRONT: A nonbearing wall

that is installed between ﬂ oor slabs, typically includ-

ing entrances, and includes a glazing material installed

in the storefront framing.

GRADE PLANE: A horizontal reference plane

representing the average of ﬁ nished ground level

adjoining the structure at all exterior walls. Where the

ﬁ nished ground level slopes away from the exterior

walls, the grade plane is established by the lowest

points within the area between the structure and the

property line or, where the property line is more than 6

ft (1,829 mm) from the structure, between the structure

and points 6 ft (1,829 mm) from the structure.

c11.indd 59 4/14/2010 11:01:14 AM

CHAPTER 11 SEISMIC DESIGN CRITERIA

INSPECTION, SPECIAL: The observation of

the work by a special inspector to determine compli-

ance with the approved construction documents and

these standards in accordance with the quality

assurance plan.

Continuous Special Inspection: The full-time

observation of the work by a special inspector

who is present in the area where work is being

performed.

Periodic Special Inspection: The part-time or

intermittent observation of the work by a

special inspector who is present in the area

where work has been or is being performed.

INSPECTOR, SPECIAL (who shall be identi-

ﬁ ed as the owner’s inspector): A person approved

by the authority having jurisdiction to perform special

inspection.

INVERTED PENDULUM-TYPE STRUC-

TURES: Structures in which more than 50 percent of

the structure’s mass is concentrated at the top of a

slender, cantilevered structure and in which stability

of the mass at the top of the structure relies on

rotational restraint to the top of the cantilevered

element.

JOINT: The geometric volume common to

intersecting members.

LIGHT-FRAME CONSTRUCTION: A method

of construction where the structural assemblies (e.g.,

walls, ﬂ oors, ceilings, and roofs) are primarily formed

by a system of repetitive wood or cold-formed steel

framing members or subassemblies of these members

(e.g., trusses).

LONGITUDINAL REINFORCEMENT

RATIO: Area of longitudinal reinforcement divided

by the cross-sectional area of the concrete.

MAXIMUM CONSIDERED EARTHQUAKE

(MCE) GROUND MOTION: The most severe

earthquake effects considered by this standard more

speciﬁ cally deﬁ ned in the following two terms.

MAXIMUM CONSIDERED EARTHQUAKE

GEOMETRIC MEAN (MCE

) PEAK GROUND

ACCELERATION: The most severe earthquake

effects considered by this standard determined for

geometric mean peak ground acceleration and

without adjustment for targeted risk. The MCE

peak ground acceleration adjusted for site effects

(PGA

) is used in this standard for evaluation of

liquefaction, lateral spreading, seismic settlements,

and other soil related issues. In this standard, general

procedures for determining PGA

are provided in

Section 11.8.3; site-speciﬁ c procedures are provided

in Section 21.5.

RISK-TARGETED MAXIMUM CONSID-

ERED EARTHQUAKE (MCE

) GROUND

MOTION RESPONSE ACCELERATION: The

most severe earthquake effects considered by this

standard determined for the orientation that results in

the largest maximum response to horizontal ground

motions and with adjustment for targeted risk. In

this standard, general procedures for determining

the MCE

Ground Motion values are provided in

Section 11.4.3; site-speciﬁ c procedures are provided

in Sections 21.1 and 21.2.

MECHANICALLY ANCHORED TANKS OR

VESSELS: Tanks or vessels provided with mechani-

cal anchors to resist overturning moments.

NONBUILDING STRUCTURE: A structure,

other than a building, constructed of a type included

in Chapter 15 and within the limits of Section 15.1.1.

NONBUILDING STRUCTURE SIMILAR TO

A BUILDING: A nonbuilding structure that is

designed and constructed in a manner similar to

buildings, will respond to strong ground motion in a

fashion similar to buildings, and has a basic lateral

and vertical seismic force-resisting system conforming

to one of the types indicated in Tables 12.2-1 or

15.4-1.

ORTHOGONAL: To be in two horizontal

directions, at 90° to each other.

OWNER: Any person, agent, ﬁ rm, or corporation

having a legal or equitable interest in the property.

PARTITION: A nonstructural interior wall that

spans horizontally or vertically from support to

support. The supports may be the basic building

frame, subsidiary structural members, or other

portions of the partition system.

P-DELTA EFFECT: The secondary effect on

shears and moments of structural members due to the

action of the vertical loads induced by horizontal

displacement of the structure resulting from various

loading conditions.

PILE: Deep foundation element, which includes

piers, caissons, and piles.

PILE CAP: Foundation elements to which piles

are connected including grade beams and mats.

REGISTERED DESIGN PROFESSIONAL:

An architect or engineer, registered or licensed to

practice professional architecture or engineering, as

deﬁ ned by the statutory requirements of the profes-

sional registrations laws of the state in which the

project is to be constructed.

SEISMIC DESIGN CATEGORY: A classiﬁ ca-

tion assigned to a structure based on its Risk Category

and the severity of the design earthquake ground

motion at the site as deﬁ ned in Section 11.4.

c11.indd 60 4/14/2010 11:01:14 AM

MINIMUM DESIGN LOADS

SEISMIC FORCE-RESISTING SYSTEM:

That part of the structural system that has been

considered in the design to provide the required

resistance to the seismic forces prescribed herein.

SEISMIC FORCES: The assumed forces

prescribed herein, related to the response of the

structure to earthquake motions, to be used in the

design of the structure and its components.

SELF-ANCHORED TANKS OR VESSELS:

Tanks or vessels that are stable under design overturn-

ing moment without the need for mechanical anchors

to resist uplift.

SHEAR PANEL: A ﬂ oor, roof, or wall element

sheathed to act as a shear wall or diaphragm.

SITE CLASS: A classiﬁ cation assigned to a site

based on the types of soils present and their engineer-

ing properties as deﬁ ned in Chapter 20.

STORAGE RACKS: Include industrial pallet

racks, moveable shelf racks, and stacker racks made

of cold-formed or hot-rolled structural members. Does

not include other types of racks such as drive-in and

drive-through racks, cantilever racks, portable racks,

or racks made of materials other than steel.

STORY: The portion of a structure between the

tops of two successive ﬂ oor surfaces and, for the

topmost story, from the top of the ﬂ oor surface to the

top of the roof surface.

STORY ABOVE GRADE PLANE: A story in

which the ﬂ oor or roof surface at the top of the story

is more than 6 ft (1,828 mm) above grade plane or is

more than 12 ft (3,658 mm) above the ﬁ nished ground

level at any point on the perimeter of the structure.

STORY DRIFT: The horizontal deﬂ ection at the

top of the story relative to the bottom of the story as

determined in Section 12.8.6.

STORY DRIFT RATIO: The story drift, as

determined in Section 12.8.6, divided by the story

height, h

STORY SHEAR: The summation of design

lateral seismic forces at levels above the story under

consideration.

STRENGTH:

Design Strength: Nominal strength multiplied by

a strength reduction factor, ϕ.

Nominal Strength: Strength of a member or

cross-section calculated in accordance with the

requirements and assumptions of the strength

design methods of this standard (or the

reference documents) before application of any

strength-reduction factors.

Required Strength: Strength of a member,

cross-section, or connection required to resist

factored loads or related internal moments and

forces in such combinations as stipulated by

this standard.

STRUCTURAL HEIGHT: The vertical distance

from the base to the highest level of the seismic

force-resisting system of the structure. For pitched or

sloped roofs, the structural height is from the base to

the average height of the roof.

STRUCTURAL OBSERVATIONS: The

visual observations to determine that the seismic

force-resisting system is constructed in general

conformance with the construction documents.

STRUCTURE: That which is built or con-

structed and limited to buildings and nonbuilding

structures as deﬁ ned herein.

SUBDIAPHRAGM: A portion of a diaphragm

used to transfer wall anchorage forces to diaphragm

cross ties.

SUPPORTS: Those members, assemblies of

members, or manufactured elements, including braces,

frames, legs, lugs, snubbers, hangers, saddles, or

struts, and associated fasteners that transmit loads

between nonstructural components and their attach-

ments to the structure.

TESTING AGENCY: A company or

corporation that provides testing and/or inspection

services.

VENEERS: Facings or ornamentation of brick,

concrete, stone, tile, or similar materials attached to a

backing.

WALL: A component that has a slope of 60° or

greater with the horizontal plane used to enclose or

divide space.

Bearing Wall: Any wall meeting either of the

following classiﬁ cations:

1. Any metal or wood stud wall that supports

more than 100 lb/linear ft (1,459 N/m) of

vertical load in addition to its own weight.

2. Any concrete or masonry wall that supports

more than 200 lb/linear ft (2,919 N/m) of

vertical load in addition to its own weight.

Light Frame Wall: A wall with wood or steel

studs.

Light Frame Wood Shear Wall: A wall

constructed with wood studs and sheathed with

material rated for shear resistance.

Nonbearing Wall: Any wall that is not a bearing

wall.

Nonstructural Wall: All walls other than bearing

walls or shear walls.

Shear Wall (Vertical Diaphragm): A wall,

bearing or nonbearing, designed to resist lateral

c11.indd 61 4/14/2010 11:01:14 AM

CHAPTER 11 SEISMIC DESIGN CRITERIA

forces acting in the plane of the wall (some-

times referred to as a “vertical diaphragm”).

Structural Wall: Walls that meet the deﬁ nition

for bearing walls or shear walls.

WALL SYSTEM, BEARING: A structural

system with bearing walls providing support for all or

major portions of the vertical loads. Shear walls or

braced frames provide seismic force resistance.

WOOD STRUCTURAL PANEL: A wood-

based panel product that meets the requirements of

DOC PS1 or DOC PS2 and is bonded with a water-

proof adhesive. Included under this designation are

plywood, oriented strand board, and composite

panels.

11.3 SYMBOLS

The unit dimensions used with the items covered by

the symbols shall be consistent throughout except

where speciﬁ cally noted. Symbols presented in this

section apply only to the seismic requirements in this

standard as indicated.

= cross-sectional area (in.

or mm

) of a

structural member measured out-to-out of

transverse reinforcement

= area of the load-carrying foundation

(ft

or m

)

= total cross-sectional area of hoop rein-

forcement (in.

or mm

), including

supplementary cross-ties, having a

spacing of s

and crossing a section with

a core dimension of h

= required area of leg (in.

or mm

) of

diagonal reinforcement

= torsional ampliﬁ cation factor (Section

12.8.4.3)

= the acceleration at level i obtained from a

modal analysis (Section 13.3.1)

= the ampliﬁ cation factor related to the

response of a system or component as

affected by the type of seismic attach-

ment, determined in Section 13.3.1

= the width of the rectangular glass panel

= deﬂ ection ampliﬁ cation factor as given in

Tables 12.2-1, 15.4-1, or 15.4-2

= site-speciﬁ c risk coefﬁ cient at any period;

see Section 21.2.1.1

= mapped value of the risk coefﬁ cient at

short periods as given by Fig. 22-17

= mapped value of the risk coefﬁ cient at a

period of 1 s as given by Fig. 22-18

= seismic response coefﬁ cient determined in

Section 12.8.1.1 and 19.3.1 (dimensionless)

= building period coefﬁ cient in Section

12.8.2.1

= vertical distribution factor as determined

in Section 12.8.3

c = distance from the neutral axis of a

ﬂ exural member to the ﬁ ber of maximum

compressive strain (in. or mm)

D = the effect of dead load

clear

= relative horizontal (drift) displacement,

measured over the height of the glass

panel under consideration, which causes

initial glass-to-frame contact. For rectan-

gular glass panels within a rectangular

wall frame, D

clear

is set forth in Section

13.5.9.1

= seismic relative displacement; see Section

13.3.2

= the total depth of stratum in Eq. 19.2-12

(ft or m)

= The total thickness of cohesive soil layers

in the top 100 ft (30 m); see Section

20.4.3 (ft or m)

= The thickness of any soil or rock layer i

(between 0 and 100 ft [30 m]); see

Section 20.4.1 (ft or m)

= The total thickness of cohesionless soil

layers in the top 100 ft (30 m); see

Section 20.4.2 (ft or m)

E = effect of horizontal and vertical earth-

quake-induced forces (Section 12.4)

= short-period site coefﬁ cient (at 0.2

s-period); see Section 11.4.3

, F

= portion of the seismic base shear, V,

induced at Level i, n, or x, respectively,

as determined in Section 12.8.3

= the seismic force acting on a component

of a structure as determined in Sections

12.11.1 and 13.3.1

PGA

= site coefﬁ cient for PGA; see Section 11.8.3

= long-period site coefﬁ cient (at 1.0

s-period); see Section 11.4.3

′ = speciﬁ ed compressive strength of concrete

used in design

′ = ultimate tensile strength (psi or MPa) of the

bolt, stud, or insert leg wires. For ASTM

A307 bolts or A108 studs, it is permitted to

be assumed to be 60,000 psi (415 MPa)

= speciﬁ ed yield strength of reinforcement

(psi or MPa)

= speciﬁ ed yield strength of the special

lateral reinforcement (psi or kPa)

c11.indd 62 4/14/2010 11:01:14 AM

MINIMUM DESIGN LOADS

G = γυ

/g = the average shear modulus for the

soils beneath the foundation at

large strain levels (psf or Pa)

= γυ

/g = the average shear modulus for

the soils beneath the foundation

at small strain levels (psf or Pa)

g = acceleration due to gravity

H = thickness of soil

h = height of a shear wall measured as the

maximum clear height from top of

foundation to bottom of diaphragm

framing above, or the maximum clear

height from top of diaphragm to bottom

of diaphragm framing above

h = average roof height of structure with

respect to the base; see Chapter 13

= effective height of the building as

determined in Section 19.2.1.1 or 19.3.1

(ft or m)

= core dimension of a component measured

to the outside of the special lateral

reinforcement (in. or mm)

, h

= the height above the base to Level i or x,

respectively

= structural height as deﬁ ned in Section 11.2

= the height of the rectangular glass panel

= the story height below Level

x = (h

– h

x–1

)

= the importance factor as prescribed in

Section 11.5.1

= the static moment of inertia of the

load-carrying foundation; see Section

19.2.1.1 (in.

or mm

)

= the component importance factor as

prescribed in Section 13.3.1

i = the building level referred to by the

subscript i; i = 1 designates the ﬁ rst level

above the base

= the stiffness of the component or attach-

ment, Section 13.6.2

= the lateral stiffness of the foundation as

deﬁ ned in Section 19.2.1.1 (lb/in. or N/m)

= the rocking stiffness of the foundation as

deﬁ ned in Section 19.2.1.1 (ft-lb/degree

or N-m/rad)

KL/r = the lateral slenderness ratio of a compres-

sion member measured in terms of its

effective length, KL, and the least radius

of gyration of the member cross section, r

k = distribution exponent given in Section

12.8.3

= stiffness of the building as determined in

Section 19.2.1.1 (lb/ft or N/m)

= coefﬁ cient deﬁ ned in Sections 12.11.2

and 12.14.7.5

L = overall length of the building (ft or m) at

the base in the direction being analyzed

= overall length of the side of the founda-

tion in the direction being analyzed,

Section 19.2.1.2 (ft or m)

, M

= the overturning moment at the founda-

tion–soil interface as determined in

Sections 19.2.3 and 19.3.2 (ft-lb or N-m)

= torsional moment resulting from eccen-

tricity between the locations of center of

mass and the center of rigidity (Section

12.8.4.1)

= accidental torsional moment as deter-

mined in Section 12.8.4.2

m = a subscript denoting the mode of vibra-

tion under consideration; that is, m = 1

for the fundamental mode

N = standard penetration resistance, ASTM

D-1586

N = number of stories above the base (Section

12.8.2.1)

= average ﬁ eld standard penetration

resistance for the top 100 ft (30 m); see

Sections 20.3.3 and 20.4.2

= average standard penetration resistance

for cohesionless soil layers for the top

100 ft (30 m); see Sections 20.3.3 and

20.4.2

= standard penetration resistance of any

soil or rock layer i (between 0 and 100 ft

[30 m]); see Section 20.4.2

n = designation for the level that is uppermost

in the main portion of the building

PGA = mapped MCE

peak ground acceleration

shown in Figs. 22-6 through 22-10

PGA

= MCE

peak ground acceleration adjusted

for Site Class effects; see Section 11.8.3

= total unfactored vertical design load at and

above level x, for use in Section 12.8.7

PI = plasticity index, ASTM D4318

= effect of horizontal seismic (earthquake-

induced) forces

R = response modiﬁ cation coefﬁ cient as given

in Tables 12.2-1, 12.14-1, 15.4-1, or

15.4-2

= component response modiﬁ cation factor

as deﬁ ned in Section 13.3.1

r = a characteristic length of the foundation

as deﬁ ned in Section 19.2.1.2

= characteristic foundation length as deﬁ ned

by Eq. 19.2-7 (ft or m)

c11.indd 63 4/14/2010 11:01:14 AM

CHAPTER 11 SEISMIC DESIGN CRITERIA

= characteristic foundation length as deﬁ ned

by Eq. 19.2-8 (ft or m)

= mapped MCE

, 5 percent damped,

spectral response acceleration parameter

at short periods as deﬁ ned in Section

11.4.1

= mapped MCE

, 5 percent damped,

spectral response acceleration parameter

at a period of 1 s as deﬁ ned in Section

11.4.1

= the site-speciﬁ c MCE

spectral response

acceleration parameter at any period

= design, 5 percent damped, spectral

response acceleration parameter at short

periods as deﬁ ned in Section 11.4.4

= design, 5 percent damped, spectral

response acceleration parameter at a

period of 1 s as deﬁ ned in Section 11.4.4

= the MCE

, 5 percent damped, spectral

response acceleration parameter at short

periods adjusted for site class effects as

deﬁ ned in Section 11.4.3

= the MCE

, 5 percent damped, spectral

response acceleration parameter at a

period of 1 s adjusted for site class effects

as deﬁ ned in Section 11.4.3

= undrained shear strength; see Section

20.4.3

= average undrained shear strength in top

100 ft (30 m); see Sections 20.3.3 and

20.4.3, ASTM D2166 or ASTM D2850

= undrained shear strength of any cohesive

soil layer i (between 0 and 100 ft [30 m]);

see Section 20.4.3

= spacing of special lateral reinforcement

(in. or mm)

T = the fundamental period of the building

, T

= the effective fundamental period(s) of the

building as determined in Sections

19.2.1.1 and 19.3.1

= approximate fundamental period of the

building as determined in Section 12.8.2

= long-period transition period as deﬁ ned in

Section 11.4.5

= fundamental period of the component and

its attachment, Section 13.6.2

= 0.2S

= S

= net tension in steel cable due to dead

load, prestress, live load, and seismic load

(Section 14.1.7)

V = total design lateral force or shear at the

base

= design value of the seismic base shear as

determined in Section 12.9.4

= seismic design shear in story x as deter-

mined in Section 12.8.4 or 12.9.4

= reduced base shear accounting for the

effects of soil structure interaction as

determined in Section 19.3.1

= portion of the reduced base shear, V

contributed by the fundamental mode,

Section 19.3 (kip or kN)

ΔV = reduction in V as determined in Section

19.3.1 (kip or kN)

ΔV

= reduction in V

as determined in Section

19.3.1 (kip or kN)

= shear wave velocity at small shear strains

(greater than 10

–3

percent strain); see

Section 19.2.1 (ft/s or m/s)

= average shear wave velocity at small

shear strains in top 100 ft (30 m); see

Sections 20.3.3 and 20.4.1

= the shear wave velocity of any soil

or rock layer i (between 0 and 100 ft

[30 m]); see Section 20.4.1

= average shear wave velocity for the

soils beneath the foundation at small

strain levels, Section 19.2.1.1

(ft/s or m/s)

W = effective seismic weight of the building

as deﬁ ned in Section 12.7.2. For calcula-

tion of seismic-isolated building period,

W is the total effective seismic weight of

the building as deﬁ ned in Sections 19.2

and 19.3 (kip or kN)

= effective seismic weight of the building

as deﬁ ned in Sections 19.2 and 19.3 (kip

or kN)

= gravity load of a component of the

building

= component operating weight (lb or N)

w = moisture content (in percent), ASTM

D2216

, w

= portion of W that is located at or assigned

to Level i, n, or x, respectively

x = level under consideration, 1 designates

the ﬁ rst level above the base

z = height in structure of point of attachment

of component with respect to the base;

see Section 13.3.1

β = ratio of shear demand to shear capacity

for the story between Level x and x – 1

= fraction of critical damping for the

coupled structure-foundation system,

determined in Section 19.2.1

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MINIMUM DESIGN LOADS

= foundation damping factor as speciﬁ ed in

Section 19.2.1.2

γ = average unit weight of soil (lb/ft

or N/m

)

Δ = design story drift as determined in

Section 12.8.6

fallout

= the relative seismic displacement (drift) at

which glass fallout from the curtain wall,

storefront, or partition occurs

= allowable story drift as speciﬁ ed in

Section 12.12.1

max

= maximum displacement at Level x,

considering torsion, Section 12.8.4.3

= maximum inelastic response displace-

ment, considering torsion, Section 12.12.3

= total separation distance between adjacent

structures on the same property, Section

12.12.3

avg

= the average of the displacements at the

extreme points of the structure at Level x,

Section 12.8.4.3

= deﬂ ection of Level x at the center of the

mass at and above Level x, Eq. 12.8-15

= deﬂ ection of Level x at the center of the

mass at and above Level x determined by

an elastic analysis, Section 12.8-6

= modal deﬂ ection of Level x at the center

of the mass at and above Level x as

determined by Section 19.3.2

, δ

= deﬂ ection of Level x at the center of the

mass at and above Level x, Eqs. 19.2-13

and 19.3-3 (in. or mm)

θ = stability coefﬁ cient for P-delta effects as

determined in Section 12.8.7

ρ = a redundancy factor based on the extent

of structural redundancy present in a

building as deﬁ ned in Section 12.3.4

= spiral reinforcement ratio for precast,

prestressed piles in Section 14.2.3.2.6

λ = time effect factor

= overstrength factor as deﬁ ned in Tables

12.2-1, 15.4-1, and 15.4-2

11.4 SEISMIC GROUND MOTION VALUES

11.4.1 Mapped Acceleration Parameters

The parameters S

and S

shall be determined from

the 0.2 and 1 s spectral response accelerations shown on

Figs. 22-1, 22-3, 22-5, and 22-6 for S

and Figs. 22-2,

22-4, 22-5, and 22-6 for S

. Where S

is less than or equal

to 0.04 and S

is less than or equal to 0.15, the structure is

permitted to be assigned to Seismic Design Category A

and is only required to comply with Section 11.7.

User Note: Electronic values of mapped

acceleration parameters, and other seismic design

parameters, are provided at the USGS Web site at

http://earthquake.usgs.gov/designmaps, or through

the SEI Web site at http://content.seinstitute.org.

11.4.2 Site Class

Based on the site soil properties, the site shall be

classiﬁ ed as Site Class A, B, C, D, E, or F in accor-

dance with Chapter 20. Where the soil properties are

not known in sufﬁ cient detail to determine the site

class, Site Class D shall be used unless the authority

having jurisdiction or geotechnical data determines

Site Class E or F soils are present at the site.

11.4.3 Site Coefﬁ cients and Risk-Targeted

Maximum Considered Earthquake (MCE

)

Spectral Response Acceleration Parameters

The MCE

spectral response acceleration

parameter for short periods (S

) and at 1 s (S

adjusted for Site Class effects, shall be determined

by Eqs. 11.4-1 and 11.4-2, respectively.

= F

(11.4-1)

= F

(11.4-2)

where

= the mapped MCE

spectral response acceleration

parameter at short periods as determined in

accordance with Section 11.4.1, and

= the mapped MCE

spectral response acceleration

parameter at a period of 1 s as determined in

accordance with Section 11.4.1

where site coefﬁ cients F

and F

are deﬁ ned in Tables

11.4-1 and 11.4-2, respectively. Where the simpliﬁ ed

design procedure of Section 12.14 is used, the value

of F

shall be determined in accordance with Section

12.14.8.1, and the values for F

, S

, and S

need not

be determined.

11.4.4 Design Spectral Acceleration Parameters

Design earthquake spectral response acceleration

parameter at short period, S

, and at 1 s period, S

shall be determined from Eqs. 11.4-3 and 11.4-4,

respectively. Where the alternate simpliﬁ ed design

procedure of Section 12.14 is used, the value of S

shall be determined in accordance with Section

12.14.8.1, and the value for S

need not be determined.

DS MS

(11.4-3)

DM11

= (11.4-4)

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CHAPTER 11 SEISMIC DESIGN CRITERIA

11.4.5 Design Response Spectrum

Where a design response spectrum is required by

this standard and site-speciﬁ c ground motion proce-

dures are not used, the design response spectrum

curve shall be developed as indicated in Fig. 11.4-1

and as follows:

1.0

Period, T (sec)

Spectral Response Acceleration,

(g)

SDS

SD1

⋅T

FIGURE 11.4-1 Design Response Spectrum.

Table 11.4-1 Site Coefﬁ cient, F

Site Class

Mapped Risk-Targeted Maximum Considered Earthquake (MCE

) Spectral Response Acceleration

Parameter at Short Period

≤ 0.25 S

= 0.5 S

= 0.75 S

= 1.0 S

≥ 1.25

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F See Section 11.4.7

Note: Use straight-line interpolation for intermediate values of S

Table 11.4-2 Site Coefﬁ cient, F

Site Class

Mapped Risk-Targeted Maximum Considered Earthquake (MCE

) Spectral Response Acceleration

Parameter at 1-s Period

≤ 0.1 S

= 0.2 S

= 0.3 S

= 0.4 S

≥ 0.5

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.7 1.6 1.5 1.4 1.3

D 2.4 2.0 1.8 1.6 1.5

E 3.5 3.2 2.8 2.4 2.4

F See Section 11.4.7

Note: Use straight-line interpolation for intermediate values of S

1. For periods less than T

, the design spectral

response acceleration, S

, shall be taken as given

by Eq. 11.4-5:

aDS

⎛

⎝

⎜

⎞

⎠

⎟

04 06

. . (11.4-5)

2. For periods greater than or equal to T

and less

than or equal to T

, the design spectral response

acceleration, S

, shall be taken equal to S

3. For periods greater than T

, and less than or equal

to T

, the design spectral response acceleration, S

shall be taken as given by Eq. 11.4-6:

(11.4-6)

4. For periods greater than T

, S

shall be taken as

given by Eq. 11.4-7:

(11.4-7)

where

= the design spectral response acceleration

parameter at short periods

c11.indd 66 4/14/2010 11:01:14 AM

MINIMUM DESIGN LOADS

= the design spectral response acceleration

parameter at 1-s period

T = the fundamental period of the structure, s

= 0.2

and

= long-period transition period (s) shown in

Figs. 22-12 through 22-16.

11.4.6 Risk-Targeted Maximum Considered

(MCE

) Response Spectrum

Where an MCE

response spectrum is required, it

shall be determined by multiplying the design

response spectrum by 1.5.

11.4.7 Site-Speciﬁ c Ground Motion Procedures

The site-speciﬁ c ground motion procedures set

forth in Chapter 21 are permitted to be used to

determine ground motions for any structure. A site

response analysis shall be performed in accordance

with Section 21.1 for structures on Site Class F sites,

unless the exception to Section 20.3.1 is applicable.

For seismically isolated structures and for structures

with damping systems on sites with S

greater than or

equal to 0.6, a ground motion hazard analysis shall be

performed in accordance with Section 21.2.

11.5 IMPORTANCE FACTOR AND

RISK CATEGORY

11.5.1 Importance Factor

An importance factor, I

, shall be assigned to

each structure in accordance with Table 1.5-2.

11.5.2 Protected Access for Risk Category IV

Where operational access to a Risk Category IV

structure is required through an adjacent structure, the

adjacent structure shall conform to the requirements

for Risk Category IV structures. Where operational

access is less than 10 ft from an interior lot line or

another structure on the same lot, protection from

potential falling debris from adjacent structures shall

be provided by the owner of the Risk Category IV

structure.

11.6 SEISMIC DESIGN CATEGORY

Structures shall be assigned a Seismic Design

Category in accordance with this section.

Risk Category I, II, or III structures located

where the mapped spectral response acceleration

parameter at 1-s period, S

, is greater than or equal to

0.75 shall be assigned to Seismic Design Category E.

Risk Category IV structures located where the

mapped spectral response acceleration parameter at

1-s period, S

, is greater than or equal to 0.75 shall be

assigned to Seismic Design Category F. All other

structures shall be assigned to a Seismic Design

Category based on their Risk Category and the design

spectral response acceleration parameters, S

and S

determined in accordance with Section 11.4.4. Each

building and structure shall be assigned to the more

severe Seismic Design Category in accordance with

Table 11.6-1 or 11.6-2, irrespective of the fundamen-

tal period of vibration of the structure, T.

Where S

is less than 0.75, the Seismic Design

Category is permitted to be determined from Table

11.6-1 alone where all of the following apply:

1. In each of the two orthogonal directions, the

approximate fundamental period of the structure,

, determined in accordance with Section 12.8.2.1

is less than 0.8T

, where T

is determined in

accordance with Section 11.4.5.

2. In each of two orthogonal directions, the funda-

mental period of the structure used to calculate the

story drift is less than T

3. Eq. 12.8-2 is used to determine the seismic

response coefﬁ cient C

Table 11.6-1 Seismic Design Category Based on

Short Period Response Acceleration Parameter

Value of S

Risk Category

I or II or III IV

< 0.167

0.167 ≤ S

< 0.33

0.33 ≤ S

< 0.50

0.50 ≤ S

Table 11.6-2 Seismic Design Category Based on

1-S Period Response Acceleration Parameter

Value of S

Risk Category

I or II or III IV

< 0.067

0.067 ≤ S

< 0.133

0.133 ≤ S

< 0.20

0.20 ≤ S

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CHAPTER 11 SEISMIC DESIGN CRITERIA

Table 11.8-1 Site Coefﬁ cient F

PGA

Site Class

Mapped Maximum Considered Geometric Mean (MCE

) Peak Ground Acceleration, PGA

PGA ≤ 0.1 PGA = 0.2 PGA = 0.3 PGA = 0.4 PGA ≥ 0.5

A 0.8 0.8 0.8 0.8 0.8

B 1.0 1.0 1.0 1.0 1.0

C 1.2 1.2 1.1 1.0 1.0

D 1.6 1.4 1.2 1.1 1.0

E 2.5 1.7 1.2 0.9 0.9

F See Section 11.4.7

Note: Use straight-line interpolation for intermediate values of PGA.

4. The diaphragms are rigid as deﬁ ned in Section

12.3.1 or for diaphragms that are ﬂ exible, the

distance between vertical elements of the seismic

force-resisting system does not exceed 40 ft.

Where the alternate simpliﬁ ed design procedure of

Section 12.14 is used, the Seismic Design Category is

permitted to be determined from Table 11.6-1 alone,

using the value of S

determined in Section 12.14.8.1.

11.7 DESIGN REQUIREMENTS FOR SEISMIC

DESIGN CATEGORY A

Buildings and other structures assigned to Seismic

Design Category A need only comply with the

requirements of Section 1.4. Nonstructural compo-

nents in SDC A are exempt from seismic design

requirements. In addition, tanks assigned to Risk

Category IV shall satisfy the freeboard requirement in

Section 15.7.6.1.2.

11.8 GEOLOGIC HAZARDS AND

GEOTECHNICAL INVESTIGATION

11.8.1 Site Limitation for Seismic Design

Categories E and F

A structure assigned to Seismic Design Category

E or F shall not be located where there is a known

potential for an active fault to cause rupture of the

ground surface at the structure.

11.8.2 Geotechnical Investigation Report

Requirements for Seismic Design Categories C

through F

A geotechnical investigation report shall be

provided for a structure assigned to Seismic Design

Category C, D, E, or F in accordance with this

section. An investigation shall be conducted and a

report shall be submitted that includes an evaluation

of the following potential geologic and seismic

hazards:

a. Slope instability,

b. Liquefaction,

c. Total and differential settlement, and

d. Surface displacement due to faulting or seismically

induced lateral spreading or lateral ﬂ ow.

The report shall contain recommendations for

foundation designs or other measures to mitigate the

effects of the previously mentioned hazards.

EXCEPTION: Where approved by the authority

having jurisdiction, a site-speciﬁ c geotechnical report

is not required where prior evaluations of nearby sites

with similar soil conditions provide direction relative

to the proposed construction.

11.8.3 Additional Geotechnical Investigation

Report Requirements for Seismic Design

Categories D through F

The geotechnical investigation report for a

structure assigned to Seismic Design Category

D, E, or F shall include all of the following, as

applicable:

1. The determination of dynamic seismic lateral earth

pressures on basement and retaining walls due to

design earthquake ground motions.

2. The potential for liquefaction and soil strength loss

evaluated for site peak ground acceleration,

earthquake magnitude, and source characteristics

consistent with the MCE

peak ground accelera-

tion. Peak ground acceleration shall be determined

based on either (1) a site-speciﬁ c study taking into

account soil ampliﬁ cation effects as speciﬁ ed in

c11.indd 68 4/14/2010 11:01:15 AM

MINIMUM DESIGN LOADS

Section 11.4.7 or (2) the peak ground acceleration

PGA

, from Eq. 11.8-1.

PGA

= F

PGA

PGA (Eq. 11.8-1)

where

PGA

= MCE

peak ground acceleration adjusted for

Site Class effects.

PGA = Mapped MCE

peak ground acceleration

shown in Figs. 22-6 through 22-10.

PGA

= Site coefﬁ cient from Table 11.8-1.

3. Assessment of potential consequences of liquefac-

tion and soil strength loss, including, but not

limited to, estimation of total and differential

settlement, lateral soil movement, lateral soil

loads on foundations, reduction in foundation

soil-

bearing capacity and lateral soil reaction, soil

downdrag and reduction in axial and lateral soil

reaction for pile foundations, increases in soil

lateral pressures on retaining walls, and ﬂ otation of

buried structures.

4. Discussion of mitigation measures such as, but

not limited to, selection of appropriate foundation

type and depths, selection of appropriate structural

systems to accommodate anticipated displacements

and forces, ground stabilization, or any combina-

tion of these measures and how they shall be

considered in the design of the structure.

c11.indd 69 4/14/2010 11:01:15 AM

c11.indd 70 4/14/2010 11:01:15 AM

Chapter 12

SEISMIC DESIGN REQUIREMENTS FOR

BUILDING STRUCTURES

12.1.3 Continuous Load Path and Interconnection

A continuous load path, or paths, with adequate

strength and stiffness shall be provided to transfer all

forces from the point of application to the ﬁ nal point

of resistance. All parts of the structure between

separation joints shall be interconnected to form a

continuous path to the seismic force-resisting system,

and the connections shall be capable of transmitting

the seismic force (F

) induced by the parts being

connected. Any smaller portion of the structure

shall be tied to the remainder of the structure with

elements having a design strength capable of transmit-

ting a seismic force of 0.133 times the short period

design spectral response acceleration parameter, S

times the weight of the smaller portion or 5 percent

of the portion’s weight, whichever is greater. This

connection force does not apply to the overall design

of the seismic force-resisting system. Connection

design forces need not exceed the maximum

forces that the structural system can deliver to the

connection.

12.1.4 Connection to Supports

A positive connection for resisting a horizontal

force acting parallel to the member shall be

provided for each beam, girder, or truss either

directly to its supporting elements, or to slabs

designed to act as diaphragms. Where the connection

is through a diaphragm, then the member’s

supporting element must also be connected to the

diaphragm. The connection shall have a minimum

design strength of 5 percent of the dead plus live load

reaction.

12.1.5 Foundation Design

The foundation shall be designed to resist the

forces developed and accommodate the movements

imparted to the structure by the design ground

motions. The dynamic nature of the forces, the

expected ground motion, the design basis for strength

and energy dissipation capacity of the structure, and

the dynamic properties of the soil shall be included in

the determination of the foundation design criteria.

The design and construction of foundations shall

comply with Section 12.13.

12.1 STRUCTURAL DESIGN BASIS

12.1.1 Basic Requirements

The seismic analysis and design procedures to be

used in the design of building structures and their

members shall be as prescribed in this section. The

building structure shall include complete lateral and

vertical force-resisting systems capable of providing

adequate strength, stiffness, and energy dissipation

capacity to withstand the design ground motions

within the prescribed limits of deformation and

strength demand. The design ground motions shall be

assumed to occur along any horizontal direction of a

building structure. The adequacy of the structural

systems shall be demonstrated through the construc-

tion of a mathematical model and evaluation of this

model for the effects of design ground motions. The

design seismic forces, and their distribution over the

height of the building structure, shall be established in

accordance with one of the applicable procedures

indicated in Section 12.6 and the corresponding

internal forces and deformations in the members of

the structure shall be determined. An approved

alternative procedure shall not be used to establish the

seismic forces and their distribution unless the

corresponding internal forces and deformations in the

members are determined using a model consistent

with the procedure adopted.

EXCEPTION: As an alternative, the simpliﬁ ed

design procedures of Section 12.14 is permitted to be

used in lieu of the requirements of Sections 12.1

through 12.12, subject to all of the limitations

contained in Section 12.14.

12.1.2 Member Design, Connection Design, and

Deformation Limit

Individual members, including those not part of

the seismic force–resisting system, shall be provided

with adequate strength to resist the shears, axial

forces, and moments determined in accordance with

this standard, and connections shall develop the

strength of the connected members or the forces

indicated in Section 12.1.1. The deformation of

the structure shall not exceed the prescribed limits

where the structure is subjected to the design seismic

forces.

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.1.6 Material Design and Detailing Requirements

Structural elements including foundation elements

shall conform to the material design and detailing

requirements set forth in Chapter 14.

12.2 STRUCTURAL SYSTEM SELECTION

12.2.1 Selection and Limitations

The basic lateral and vertical seismic force-resist-

ing system shall conform to one of the types indicated

in Table 12.2-1 or a combination of systems as

permitted in Sections 12.2.2, 12.2.3, and 12.2.4. Each

type is subdivided by the types of vertical elements

used to resist lateral seismic forces. The structural

system used shall be in accordance with the structural

system limitations and the limits on structural height,

, contained in Table 12.2-1. The appropriate

response modiﬁ cation coefﬁ cient, R, overstrength

factor, Ω

, and the deﬂ ection ampliﬁ cation factor, C

indicated in Table 12.2-1 shall be used in determining

the base shear, element design forces, and design

story drift.

Each selected seismic force-resisting system shall

be designed and detailed in accordance with the

speciﬁ c requirements for the system as set forth in the

applicable reference document listed in Table 12.2-1

and the additional requirements set forth in Chapter 14.

Seismic force-resisting systems not contained in

Table 12.2-1 are permitted provided analytical and

test data are submitted to the authority having

jurisdiction for approval that establish their dynamic

characteristics and demonstrate their lateral force

resistance and energy dissipation capacity to be

equivalent to the structural systems listed in Table

12.2-1 for equivalent values of response modiﬁ cation

coefﬁ cient, R, overstrength factor, Ω

, and deﬂ ection

ampliﬁ cation factor, C

12.2.2 Combinations of Framing Systems in

Different Directions

Different seismic force-resisting systems are

permitted to be used to resist seismic forces along

each of the two orthogonal axes of the structure.

Where different systems are used, the respective R,

, and Ω

coefﬁ cients shall apply to each system,

including the structural system limitations contained

in Table 12.2-1.

12.2.3 Combinations of Framing Systems in the

Same Direction

Where different seismic force-resisting systems

are used in combination to resist seismic forces in the

same direction, other than those combinations

considered as dual systems, the most stringent

applicable structural system limitations contained in

Table 12.2-1 shall apply and the design shall comply

with the requirements of this section.

12.2.3.1 R, C

, and Ω

Values for

Vertical Combinations

Where a structure has a vertical combination in

the same direction, the following requirements shall

apply:

1. Where the lower system has a lower Response

Modiﬁ cation Coefﬁ cient, R, the design coefﬁ cients

(R, Ω

, and C

) for the upper system are permitted

to be used to calculate the forces and drifts of the

upper system. For the design of the lower system,

the design coefﬁ cients (R, Ω

, and C

) for the

lower system shall be used. Forces transferred from

the upper system to the lower system shall be

increased by multiplying by the ratio of the higher

response modiﬁ cation coefﬁ cient to the lower

response modiﬁ cation coefﬁ cient.

2. Where the upper system has a lower Response

Modiﬁ cation Coefﬁ cient, the Design Coefﬁ cients

(R, Ω

, and C

) for the upper system shall be used

for both systems.

EXCEPTIONS:

1. Rooftop structures not exceeding two stories

in height and 10 percent of the total structure

weight.

2. Other supported structural systems with a weight

equal to or less than 10 percent of the weight of

the structure.

3. Detached one- and two-family dwellings of

light-frame construction.

12.2.3.2 Two Stage Analysis Procedure

A two-stage equivalent lateral force procedure is

permitted to be used for structures having a ﬂ exible

upper portion above a rigid lower portion, provided

the design of the structure complies with all of the

following:

a. The stiffness of the lower portion shall be at least

10 times the stiffness of the upper portion.

b. The period of the entire structure shall not be

greater than 1.1 times the period of the upper

portion considered as a separate structure supported

at the transition from the upper to the lower

portion.

c. The upper portion shall be designed as a separate

structure using the appropriate values of R and ρ.

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MINIMUM DESIGN LOADS

Table 12.2-1 Design Coefﬁ cients and Factors for Seismic Force-Resisting Systems

Seismic Force-Resisting System

ASCE 7

Section

Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Overstrength

Factor, Ω

Deﬂ ection

Ampliﬁ cation

Factor, C

Structural System

Limitations Including

Structural Height, h

(ft)

Limits

Seismic Design Category

BCD

A. BEARING WALL SYSTEMS

1. Special reinforced concrete shear

walls

l, m

14.2 5 2½ 5 NL NL 160 160 100

2. Ordinary reinforced concrete shear

walls

14.2 4 2½ 4 NL NL NP NP NP

3. Detailed plain concrete shear walls

14.2 2 2½ 2 NL NP NP NP NP

4. Ordinary plain concrete shear walls

14.2 1½ 2½ 1½ NL NP NP NP NP

5. Intermediate precast shear walls

14.2 4 2½ 4 NL NL

6. Ordinary precast shear walls

14.2 3 2½ 3 NL NP NP NP NP

7. Special reinforced masonry shear walls 14.4 5 2½ 3½ NL NL 160 160 100

8. Intermediate reinforced masonry shear

walls

14.4 3½ 2½ 2¼ NL NL NP NP NP

9. Ordinary reinforced masonry shear

walls

14.4 2 2½ 1¾ NL 160 NP NP NP

10. Detailed plain masonry shear walls 14.4 2 2½ 1¾ NL NP NP NP NP

11. Ordinary plain masonry shear walls 14.4 1½ 2½ 1¼ NL NP NP NP NP

12. Prestressed masonry shear walls 14.4 1½ 2½ 1¾ NL NP NP NP NP

13. Ordinary reinforced AAC masonry

shear walls

14.4 2 2½ 2 NL 35 NP NP NP

14. Ordinary plain AAC masonry shear

walls

14.4 1½ 2½ 1½ NL NP NP NP NP

15. Light-frame (wood) walls sheathed

with wood structural panels rated for

shear resistance or steel sheets

14.1 and 14.5 6½ 3 4 NL NL 65 65 65

16. Light-frame (cold-formed steel) walls

sheathed with wood structural panels

rated for shear resistance or steel

sheets

14.1 6½ 3 4 NL NL 65 65 65

17. Light-frame walls with shear panels of

all other materials

14.1 and 14.5 2 2½ 2 NL NL 35 NP NP

18. Light-frame (cold-formed steel) wall

systems using ﬂ at strap bracing

14.1 4 2 3½ NL NL 65 65 65

B. BUILDING FRAME SYSTEMS

1. Steel eccentrically braced frames 14.1 8 2 4 NL NL 160 160 100

2. Steel special concentrically braced

frames

14.1 6 2 5 NL NL 160 160 100

3. Steel ordinary concentrically braced

frames

14.1 3¼ 2 3¼ NL NL

Continued

c12.indd 73 4/14/2010 11:02:03 AM

CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

Seismic Force-Resisting System

ASCE 7

Section

Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Overstrength

Factor, Ω

Deﬂ ection

Ampliﬁ cation

Factor, C

Structural System

Limitations Including

Structural Height, h

(ft)

Limits

Seismic Design Category

BCD

4. Special reinforced concrete shear

walls

l,m

14.2 6 2½ 5 NL NL 160 160 100

5. Ordinary reinforced concrete shear walls

14.2 5 2½ 4½ NL NL NP NP NP

6. Detailed plain concrete shear walls

14.2 and

14.2.2.8

2 2½ 2 NL NP NP NP NP

7. Ordinary plain concrete shear walls

14.2 1½ 2½ 1½ NL NP NP NP NP

8. Intermediate precast shear walls

14.2 5 2½ 4½ NL NL

9. Ordinary precast shear walls

14.2 4 2½ 4 NL NP NP NP NP

10. Steel and concrete composite

eccentrically braced frames

14.3 8 2 ½ 4 NL NL 160 160 100

11. Steel and concrete composite special

concentrically braced frames

14.3 5 2 4½ NL NL 160 160 100

12. Steel and concrete composite ordinary

braced frames

14.3 3 2 3 NL NL NP NP NP

13. Steel and concrete composite plate

shear walls

14.3 6½ 2½ 5½ NL NL 160 160 100

14. Steel and concrete composite special

shear walls

14.3 6 2½ 5 NL NL 160 160 100

15. Steel and concrete composite ordinary

shear walls

14.3 5 2½ 4½ NL NL NP NP NP

16. Special reinforced masonry shear walls 14.4 5½ 2½ 4 NL NL 160 160 100

17. Intermediate reinforced masonry shear

walls

14.4 4 2½ 4 NL NL NP NP NP

18. Ordinary reinforced masonry shear

walls

14.4 2 2½ 2 NL 160 NP NP NP

19. Detailed plain masonry shear walls 14.4 2 2½ 2 NL NP NP NP NP

20. Ordinary plain masonry shear walls 14.4 1½ 2½ 1¼ NL NP NP NP NP

21. Prestressed masonry shear walls 14.4 1½ 2½ 1¾ NL NP NP NP NP

22. Light-frame (wood) walls sheathed

with wood structural panels rated for

shear resistance

14.5 7 2½ 4½ NL NL 65 65 65

23. Light-frame (cold-formed steel) walls

sheathed with wood structural panels

rated for shear resistance or steel sheets

14.1 7 2½ 4½ NL NL 65 65 65

24. Light-frame walls with shear panels of

all other materials

14.1and 14.5 2½ 2½ 2½ NL NL 35 NP NP

25. Steel buckling-restrained braced

frames

14.1 8 2½ 5 NL NL 160 160 100

26. Steel special plate shear walls 14.1 7 2 6 NL NL 160 160 100

Table 12.2-1 (Continued)

c12.indd 74 4/14/2010 11:02:03 AM

MINIMUM DESIGN LOADS

Continued

Seismic Force-Resisting System

ASCE 7

Section

Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Overstrength

Factor, Ω

Deﬂ ection

Ampliﬁ cation

Factor, C

Structural System

Limitations Including

Structural Height, h

(ft)

Limits

Seismic Design Category

BCD

C. MOMENT-RESISTING FRAME

SYSTEMS

1. Steel special moment frames 14.1 and

12.2.5.5

8 3 5½ NL NL NL NL NL

2. Steel special truss moment frames 14.1 7 3 5½ NL NL 160 100 NP

3. Steel intermediate moment frames 12.2.5.7 and

14.1

4½ 3 4 NL NL

4. Steel ordinary moment frames 12.2.5.6 and

14.1

3½ 3 3 NL NL

5. Special reinforced concrete moment

frames

12.2.5.5 and

14.2

8 3 5½ NL NL NL NL NL

6. Intermediate reinforced concrete

moment frames

14.2 5 3 4½ NL NL NP NP NP

7. Ordinary reinforced concrete moment

frames

14.2 3 3 2½ NL NP NP NP NP

8. Steel and concrete composite special

moment frames

12.2.5.5 and

14.3

8 3 5½ NL NL NL NL NL

9. Steel and concrete composite

intermediate moment frames

14.3 5 3 4½ NL NL NP NP NP

10. Steel and concrete composite partially

restrained moment frames

14.3 6 3 5½ 160 160 100 NP NP

11. Steel and concrete composite ordinary

moment frames

14.3 3 3 2½ NL NP NP NP NP

12. Cold-formed steel—special bolted

moment frame

14.1 3½ 3

3½ 35 35 35 35 35

D. DUAL SYSTEMS WITH SPECIAL

MOMENT FRAMES CAPABLE OF

RESISTING AT LEAST 25% OF

PRESCRIBED SEISMIC FORCES

12.2.5.1

1. Steel eccentrically braced frames 14.1 8 2½ 4 NL NL NL NL NL

2. Steel special concentrically braced

frames

14.1 7 2½ 5½ NL NL NL NL NL

3. Special reinforced concrete shear walls

14.2 7 2½ 5½ NL NL NL NL NL

4. Ordinary reinforced concrete shear

walls

14.2 6 2½ 5 NL NL NP NP NP

5. Steel and concrete composite

eccentrically braced frames

14.3 8 2½ 4 NL NL NL NL NL

6. Steel and concrete composite special

concentrically braced frames

14.3 6 2½ 5 NL NL NL NL NL

Table 12.2-1 (Continued)

c12.indd 75 4/14/2010 11:02:03 AM

CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

Seismic Force-Resisting System

ASCE 7

Section

Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Overstrength

Factor, Ω

Deﬂ ection

Ampliﬁ cation

Factor, C

Structural System

Limitations Including

Structural Height, h

(ft)

Limits

Seismic Design Category

BCD

7. Steel and concrete composite plate

shear walls

14.3 7½ 2½ 6 NL NL NL NL NL

8. Steel and concrete composite special

shear walls

14.3 7 2½ 6 NL NL NL NL NL

9. Steel and concrete composite ordinary

shear walls

14.3 6 2½ 5 NL NL NP NP NP

10. Special reinforced masonry shear walls 14.4 5½ 3 5 NL NL NL NL NL

11. Intermediate reinforced masonry shear

walls

14.4 4 3 3½ NL NL NP NP NP

12. Steel buckling-restrained braced

frames

14.1 8 2½ 5 NL NL NL NL NL

13. Steel special plate shear walls 14.1 8 2½ 6½ NL NL NL NL NL

E. DUAL SYSTEMS WITH

INTERMEDIATE MOMENT

FRAMES CAPABLE OF

RESISTING AT LEAST 25% OF

PRESCRIBED SEISMIC FORCES

12.2.5.1

1. Steel special concentrically braced

frames

14.1 6 2½ 5 NL NL 35 NP NP

2. Special reinforced concrete shear walls

14.2 6½ 2½ 5 NL NL 160 100 100

3. Ordinary reinforced masonry shear

walls

14.4 3 3 2½ NL 160 NP NP NP

4. Intermediate reinforced masonry shear

walls

14.4 3½ 3 3 NL NL NP NP NP

5. Steel and concrete composite special

concentrically braced frames

14.3 5½ 2½ 4½ NL NL 160 100 NP

6. Steel and concrete composite ordinary

braced frames

14.3 3½ 2½ 3 NL NL NP NP NP

7. Steel and concrete composite ordinary

shear walls

14.3 5 3 4½ NL NL NP NP NP

8. Ordinary reinforced concrete shear

walls

14.2 5½ 2½ 4½ NL NL NP NP NP

F. SHEAR WALL-FRAME

INTERACTIVE SYSTEM WITH

ORDINARY REINFORCED

CONCRETE MOMENT FRAMES

AND ORDINARY REINFORCED

CONCRETE SHEAR WALLS

12.2.5.8 and

14.2

4½ 2½ 4 NL NP NP NP NP

Table 12.2-1 (Continued)

c12.indd 76 4/14/2010 11:02:03 AM

MINIMUM DESIGN LOADS

Seismic Force-Resisting System

ASCE 7

Section

Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Overstrength

Factor, Ω

Deﬂ ection

Ampliﬁ cation

Factor, C

Structural System

Limitations Including

Structural Height, h

(ft)

Limits

Seismic Design Category

BCD

G. CANTILEVERED COLUMN

SYSTEMS DETAILED TO

CONFORM TO THE

REQUIREMENTS FOR:

12.2.5.2

1. Steel special cantilever column

systems

14.1 2½ 1¼ 2½ 35 35 35 35 35

2. Steel ordinary cantilever column

systems

14.1 1¼ 1¼ 1¼ 35 35

3. Special reinforced concrete moment

frames

12.2.5.5 and

14.2

2½ 1¼ 2½ 35 35 35 35 35

4. Intermediate reinforced concrete

moment frames

14.2 1½ 1¼ 1½ 35 35 NP NP NP

5. Ordinary reinforced concrete moment

frames

14.2 1 1¼ 1 35 NP NP NP NP

6. Timber frames 14.5 1½ 1½ 1½ 35 35 35 NP NP

H. STEEL SYSTEMS NOT

SPECIFICALLY DETAILED FOR

SEISMIC RESISTANCE,

EXCLUDING CANTILEVER

COLUMN SYSTEMS

14.1 3 3 3 NL NL NP NP NP

Response modiﬁ cation coefﬁ cient, R, for use throughout the standard. Note R reduces forces to a strength level, not an allowable stress level.

Deﬂ ection ampliﬁ cation factor, C

, for use in Sections 12.8.6, 12.8.7, and 12.9.2.

NL = Not Limited and NP = Not Permitted. For metric units use 30.5 m for 100 ft and use 48.8 m for 160 ft.

See Section 12.2.5.4 for a description of seismic force-resisting systems limited to buildings with a structural height, h

, of 240 ft (73.2 m) or less.

See Section 12.2.5.4 for seismic force-resisting systems limited to buildings with a structural height, h

, of 160 ft (48.8 m) or less.

Ordinary moment frame is permitted to be used in lieu of intermediate moment frame for Seismic Design Categories B or C.

Where the tabulated value of the overstrength factor, Ω

, is greater than or equal to 2½, Ω

is permitted to be reduced by subtracting the value of 1/2

for structures with ﬂ exible diaphragms.

See Section 12.2.5.7 for limitations in structures assigned to Seismic Design Categories D, E, or F.

See Section 12.2.5.6 for limitations in structures assigned to Seismic Design Categories D, E, or F.

Steel ordinary concentrically braced frames are permitted in single-story buildings up to a structural height, h

, of 60 ft (18.3 m) where the dead load of

the roof does not exceed 20 psf

(0.96 kN/m

) and in penthouse structures.

An increase in structural height, h

, to 45 ft (13.7 m) is permitted for single story storage warehouse facilities.

In Section 2.2 of ACI 318. A shear wall is deﬁ ned as a structural wall.

In Section 2.2 of ACI 318. The deﬁ nition of “special structural wall” includes precast and cast-in-place construction.

In Section 2.2 of ACI 318. The deﬁ nition of “special moment frame” includes precast and cast-in-place construction.

Alternately, the seismic load effect with overstrength, E

, is permitted to be based on the expected strength determined in accordance with AISI S110.

Cold-formed steel – special bolted moment frames shall be limited to one-story in height in accordance with AISI S110.

Table 12.2-1 (Continued)

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

d. The lower portion shall be designed as a separate

structure using the appropriate values of R and ρ.

The reactions from the upper portion shall be those

determined from the analysis of the upper portion

ampliﬁ ed by the ratio of the R/ρ of the upper

portion over R/ρ of the lower portion. This ratio

shall not be less than 1.0.

e. The upper portion is analyzed with the equivalent

lateral force or modal response spectrum proce-

dure, and the lower portion is analyzed with the

equivalent lateral force procedure.

12.2.3.3 R, C

, and Ω

Values for Horizontal

Combinations

The value of the response modiﬁ cation coefﬁ -

cient, R, used for design in the direction under

consideration shall not be greater than the least value

of R for any of the systems utilized in that direction.

The deﬂ ection ampliﬁ cation factor, C

, and the

overstrength factor, Ω

, shall be consistent with R

required in that direction.

EXCEPTION: Resisting elements are permitted

to be designed using the least value of R for the

different structural systems found in each independent

line of resistance if the following three conditions are

met: (1) Risk Category I or II building, (2) two stories

or less above grade plane, and (3) use of light-frame

construction or ﬂ exible diaphragms. The value of R

used for design of diaphragms in such structures shall

not be greater than the least value of R for any of the

systems utilized in that same direction.

12.2.4 Combination Framing

Detailing Requirements

Structural members common to different framing

systems used to resist seismic forces in any direction

shall be designed using the detailing requirements

of Chapter 12 required by the highest response

modiﬁ cation coefﬁ cient, R, of the connected framing

systems.

12.2.5 System Speciﬁ c Requirements

The structural framing system shall also comply

with the following system speciﬁ c requirements of

this section.

12.2.5.1 Dual System

For a dual system, the moment frames shall be

capable of resisting at least 25 percent of the design

seismic forces. The total seismic force resistance is to

be provided by the combination of the moment frames

and the shear walls or braced frames in proportion to

their rigidities.

12.2.5.2 Cantilever Column Systems

Cantilever column systems are permitted as

indicated in Table 12.2-1 and as follows. The required

axial strength of individual cantilever column ele-

ments, considering only the load combinations that

include seismic load effects, shall not exceed 15

percent of the available axial strength, including

slenderness effects.

Foundation and other elements used to provide

overturning resistance at the base of cantilever column

elements shall be designed to resist the seismic load

effects including overstrength factor of Section 12.4.3.

12.2.5.3 Inverted Pendulum-Type Structures

Regardless of the structural system selected,

inverted pendulums as deﬁ ned in Section 11.2, shall

comply with this section. Supporting columns or piers

of inverted pendulum-type structures shall be

designed for the bending moment calculated at the

base determined using the procedures given in Section

12.8 and varying uniformly to a moment at the top

equal to one-half the calculated bending moment at

the base.

12.2.5.4 Increased Structural Height Limit for

Steel Eccentrically Braced Frames, Steel Special

Concentrically Braced Frames, Steel

Buckling-restrained Braced Frames, Steel Special

Plate Shear Walls and Special Reinforced Concrete

Shear Walls

The limits on structural height, h

, in Table

12.2-1 are permitted to be increased from 160 ft (50

m) to 240 ft (75 m) for structures assigned to Seismic

Design Categories D or E and from 100 ft (30 m) to

160 ft (50 m) for structures assigned to Seismic

Design Category F provided the seismic force-

resisting systems are limited to steel eccentrically

braced frames, steel special concentrically braced

frames, steel buckling-restrained braced frames, steel

special plate shear walls, or special reinforced

concrete cast-in-place shear walls and both of the

following requirements are met:

1. The structure shall not have an extreme torsional

irregularity as deﬁ ned in Table 12.2-1 (horizontal

structural irregularity Type 1b).

2. The steel eccentrically braced frames, steel special

concentrically braced frames, steel buckling-

restrained braced frames, steel special plate shear

walls or special reinforced cast-in-place concrete

shear walls in any one plane shall resist no more

than 60 percent of the total seismic forces in each

direction, neglecting accidental torsional effects.

c12.indd 78 4/14/2010 11:02:04 AM

MINIMUM DESIGN LOADS

12.2.5.5 Special Moment Frames in Structures

Assigned to Seismic Design Categories D through F

For structures assigned to Seismic Design

Categories D, E, or F, a special moment frame that is

used but not required by Table 12.2-1 shall not be

discontinued and supported by a more rigid system

with a lower response modiﬁ cation coefﬁ cient, R,

unless the requirements of Sections 12.3.3.2 and

12.3.3.4 are met. Where a special moment frame is

required by Table 12.2-1, the frame shall be continu-

ous to the base.

12.2.5.6 Steel Ordinary Moment Frames

12.2.5.6.1 Seismic Design Category D or E.

a. Single-story steel ordinary moment frames in

structures assigned to Seismic Design Category D

or E are permitted up to a structural height, h

, of

65 ft (20 m) where the dead load supported by

and tributary to the roof does not exceed 20 psf

(0.96 kN/m

). In addition, the dead load of the

exterior walls more than 35 ft (10.6 m) above the

base tributary to the moment frames shall not

exceed 20 psf (0.96 kN/m

EXCEPTION: Single-story structures with

steel ordinary moment frames whose purpose is to

enclose equipment or machinery and whose

occupants are engaged in maintenance or

monitoring of that equipment, machinery, or their

associated processes shall be permitted to be of

unlimited height where the sum of the dead and

equipment loads supported by and tributary to the

roof does not exceed 20 psf (0.96 kN/m

). In

addition, the dead load of the exterior wall system

including exterior columns more than 35 ft

(10.6 m) above the base shall not exceed 20 psf

(0.96 kN/m

). For determining compliance with

the exterior wall or roof load limits, the weight

of equipment or machinery, including cranes, not

self-supporting for all loads shall be assumed fully

tributary to the area of the adjacent exterior wall or

roof not to exceed 600 ft

(55.8 m

) regardless of

their height above the base of the structure.

b. Steel ordinary moment frames in structures

assigned to Seismic Design Category D or E not

meeting the limitations set forth in Section

12.2.5.6.1.a are permitted within light-frame

construction up to a structural height, h

, of 35 ft

(10.6 m) where neither the roof dead load nor the

dead load of any ﬂ oor above the base supported by

and tributary to the moment frames exceeds 35 psf

(1.68 kN/m

). In addition, the dead load of the

exterior walls tributary to the moment frames shall

not exceed 20 psf (0.96 kN/m

12.2.5.6.2 Seismic Design Category F. Single-story

steel ordinary moment frames in structures assigned to

Seismic Design Category F are permitted up to a

structural height, h

, of 65 ft (20 m) where the dead

load supported by and tributary to the roof does not

exceed 20 psf (0.96 kN/m

). In addition, the dead load

of the exterior walls tributary to the moment frames

shall not exceed 20 psf (0.96 kN/m

12.2.5.7 Steel Intermediate Moment Frames

12.2.5.7.1 Seismic Design Category D

a. Single-story steel intermediate moment frames in

structures assigned to Seismic Design Category D

are permitted up to a structural height, h

, of 65 ft

(20 m) where the dead load supported by and

tributary to the roof does not exceed 20 psf

(0.96 kN/m

). In addition, the dead load of the

exterior walls more than 35 ft (10.6 m) above the

base tributary to the moment frames shall not

exceed 20 psf (0.96 kN/m

EXCEPTION: Single-story structures

with steel intermediate moment frames whose

purpose is to enclose equipment or machinery

and whose occupants are engaged in maintenance

or monitoring of that equipment, machinery, or

their associated processes shall be permitted to

be of unlimited height where the sum of the

dead and equipment loads supported by and

tributary to the roof does not exceed 20 psf

(0.96 kN/m

). In addition, the dead load of the

exterior wall system including exterior columns

more than 35 ft (10.6 m) above the base shall not

exceed 20 psf (0.96 kN/m

). For determining

compliance with the exterior wall or roof load

limits, the weight of equipment or machinery,

including cranes, not self-supporting for all loads

shall be assumed fully tributary to the area of the

adjacent exterior wall or roof not to exceed 600 ft

(55.8 m

) regardless of their height above the base

of the structure.

b. Steel intermediate moment frames in structures

assigned to Seismic Design Category D not

meeting the limitations set forth in Section

12.2.5.7.1.a are permitted up to a structural height,

, of 35 ft (10.6 m).

c12.indd 79 4/14/2010 11:02:04 AM

CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.2.5.7.2 Seismic Design Category E.

a. Single-story steel intermediate moment frames in

structures assigned to Seismic Design Category E

are permitted up to a structural height, h

, of 65 ft

(20 m) where the dead load supported by and

tributary to the roof does not exceed 20 psf

(0.96 kN/m

). In addition, the dead load of the

exterior walls more than 35 ft (10.6 m) above the

base tributary to the moment frames shall not

exceed 20 psf (0.96 kN/m

EXCEPTION: Single-story structures with

steel intermediate moment frames whose purpose

is to enclose equipment or machinery and whose

occupants are engaged in maintenance or

monitoring of that equipment, machinery, or their

associated processes shall be permitted to be of

unlimited height where the sum of the dead and

equipment loads supported by and tributary to the

roof does not exceed 20 psf (0.96 kN/m

). In

addition, the dead load of the exterior wall system

including exterior columns more than 35 ft

(10.6 m) above the base shall not exceed 20 psf

(0.96 kN/m

). For determining compliance with

the exterior wall or roof load limits, the weight

of equipment or machinery, including cranes, not

self-supporting for all loads shall be assumed fully

tributary to the area of the adjacent exterior wall or

roof not to exceed 600 ft

(55.8 m

) regardless of

their height above the base of the structure.

b. Steel intermediate moment frames in structures

assigned to Seismic Design Category E not

meeting the limitations set forth in Section

12.2.5.7.2.a are permitted up to a structural height,

, of 35 ft (10.6 m) where neither the roof dead

load nor the dead load of any ﬂ oor above the base

supported by and tributary to the moment frames

exceeds 35 psf (1.68 kN/m

). In addition, the dead

load of the exterior walls tributary to the moment

frames shall not exceed 20 psf (0.96 kN/m

12.2.5.7.3 Seismic Design Category F.

a. Single-story steel intermediate moment frames in

structures assigned to Seismic Design Category F

are permitted up to a structural height, h

, of 65 ft

(20 m) where the dead load supported by and

tributary to the roof does not exceed 20 psf (0.96

kN/m

). In addition, the dead load of the exterior

walls tributary to the moment frames shall not

exceed 20 psf (0.96 kN/m

b. Steel intermediate moment frames in structures

assigned to Seismic Design Category F not

meeting the limitations set forth in Section

12.2.5.7.3.a are permitted within light-frame

construction up to a structural height, h

, of 35 ft

(10.6 m) where neither the roof dead load nor the

dead load of any ﬂ oor above the base supported by

and tributary to the moment frames exceeds 35 psf

(1.68 kN/m

). In addition, the dead load of the

exterior walls tributary to the moment frames shall

not exceed 20 psf (0.96 kN/m

12.2.5.8 Shear Wall-Frame Interactive Systems

The shear strength of the shear walls of the shear

wall-frame interactive system shall be at least 75

percent of the design story shear at each story. The

frames of the shear wall-frame interactive system

shall be capable of resisting at least 25 percent of the

design story shear in every story.

12.3 DIAPHRAGM FLEXIBILITY,

CONFIGURATION IRREGULARITIES,

AND REDUNDANCY

12.3.1 Diaphragm Flexibility

The structural analysis shall consider the relative

stiffnesses of diaphragms and the vertical elements of

the seismic force-resisting system. Unless a dia-

phragm can be idealized as either ﬂ exible or rigid in

accordance with Sections 12.3.1.1, 12.3.1.2, or

12.3.1.3, the structural analysis shall explicitly include

consideration of the stiffness of the diaphragm (i.e.,

semirigid modeling assumption).

12.3.1.1 Flexible Diaphragm Condition

Diaphragms constructed of untopped steel

decking or wood structural panels are permitted to be

idealized as ﬂ exible if any of the following conditions

exist:

a. In structures where the vertical elements are steel

braced frames, steel and concrete composite braced

frames or concrete, masonry, steel, or steel and

concrete composite shear walls.

b. In one- and two-family dwellings.

c. In structures of light-frame construction where all

of the following conditions are met:

1. Topping of concrete or similar materials is not

placed over wood structural panel diaphragms

except for nonstructural topping no greater than

1 1/2 in. (38 mm) thick.

2. Each line of vertical elements of the seismic

force-resisting system complies with the

allowable story drift of Table 12.12-1.

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MINIMUM DESIGN LOADS

12.3.1.2 Rigid Diaphragm Condition

Diaphragms of concrete slabs or concrete ﬁ lled

metal deck with span-to-depth ratios of 3 or less in

structures that have no horizontal irregularities are

permitted to be idealized as rigid.

12.3.1.3 Calculated Flexible Diaphragm Condition

Diaphragms not satisfying the conditions of

Sections 12.3.1.1 or 12.3.1.2 are permitted to be

idealized as ﬂ exible where the computed maximum

in-plane deﬂ ection of the diaphragm under lateral

load is more than two times the average story drift

of adjoining vertical elements of the seismic force-

resisting system of the associated story under equiva-

lent tributary lateral load as shown in Fig. 12.3-1. The

loadings used for this calculation shall be those

prescribed by Section 12.8.

12.3.2 Irregular and Regular Classiﬁ cation

Structures shall be classiﬁ ed as having a struc-

tural irregularity based upon the criteria in this

section. Such classiﬁ cation shall be based on their

structural conﬁ gurations.

12.3.2.1 Horizontal Irregularity

Structures having one or more of the irregularity

types listed in Table 12.3-1 shall be designated as

having a horizontal structural irregularity. Such

structures assigned to the seismic design categories

listed in Table 12.3-1 shall comply with the require-

ments in the sections referenced in that table.

12.3.2.2 Vertical Irregularity

Structures having one or more of the irregularity

types listed in Table 12.3-2 shall be designated as

having a vertical structural irregularity. Such struc-

tures assigned to the seismic design categories listed

in Table 12.3-2 shall comply with the requirements in

the sections referenced in that table.

EXCEPTIONS:

1. Vertical structural irregularities of Types 1a, 1b,

and 2 in Table 12.3-2 do not apply where no story

drift ratio under design lateral seismic force is

greater than 130 percent of the story drift ratio

of the next story above. Torsional effects need

not be considered in the calculation of story drifts.

The story drift ratio relationship for the top two

stories of the structure are not required to be

evaluated.

2. Vertical structural irregularities of Types 1a, 1b,

and 2 in Table 12.3-2 are not required to be

considered for one-story buildings in any seismic

design category or for two-story buildings assigned

to Seismic Design Categories B, C, or D.

12.3.3 Limitations and Additional Requirements

for Systems with Structural Irregularities

12.3.3.1 Prohibited Horizontal and Vertical

Irregularities for Seismic Design Categories

D through F

Structures assigned to Seismic Design Category E

or F having horizontal irregularity Type 1b of Table

12.3-1 or vertical irregularities Type 1b, 5a, or 5b of

Table 12.3-2 shall not be permitted. Structures

assigned to Seismic Design Category D having

vertical irregularity Type 5b of Table 12.3-2 shall not

be permitted.

12.3.3.2 Extreme Weak Stories

Structures with a vertical irregularity Type 5b as

deﬁ ned in Table 12.3-2, shall not be over two stories

or 30 ft (9 m) in structural height, h

MAXIMUM DIAPHRAGM

(ADVE)

AVERAGE DRIFT OF VERTICAL ELEMENT

Note: Diaphragm is flexible if MDD > 2(ADVE).

DEFLECTION (MDD)

SEISMIC LOADING

FIGURE 12.3-1 Flexible Diaphragm

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

Table 12.3-1 Horizontal Structural Irregularities

Type Description Reference Section

Seismic Design

Category Application

1a. Torsional Irregularity: Torsional irregularity is deﬁ ned to exist where the

maximum story drift, computed including accidental torsion with A

= 1.0,

at one end of the structure transverse to an axis is more than 1.2 times the

average of the story drifts at the two ends of the structure. Torsional

irregularity requirements in the reference sections apply only to structures

in which the diaphragms are rigid or semirigid.

12.3.3.4

12.7.3

12.8.4.3

12.12.1

Table 12.6-1

Section 16.2.2

D, E, and F

B, C, D, E, and F

C, D, E, and F

D, E, and F

B, C, D, E, and F

1b. Extreme Torsional Irregularity: Extreme torsional irregularity is deﬁ ned

to exist where the maximum story drift, computed including accidental

torsion with A

= 1.0, at one end of the structure transverse to an axis is

more than 1.4 times the average of the story drifts at the two ends of the

structure. Extreme torsional irregularity requirements in the reference

sections apply only to structures in which the diaphragms are rigid or

semirigid.

12.3.3.1

12.3.3.4

12.7.3

12.8.4.3

12.12.1

Table 12.6-1

Section 16.2.2

E and F

B, C, and D

C and D

B, C, and D

2. Reentrant Corner Irregularity: Reentrant corner irregularity is deﬁ ned to

exist where both plan projections of the structure beyond a reentrant corner

are greater than 15% of the plan dimension of the structure in the given

direction.

12.3.3.4

Table 12.6-1

D, E, and F

3. Diaphragm Discontinuity Irregularity: Diaphragm discontinuity

irregularity is deﬁ ned to exist where there is a diaphragm with an abrupt

discontinuity or variation in stiffness, including one having a cutout or open

area greater than 50% of the gross enclosed diaphragm area, or a change in

effective diaphragm stiffness of more than 50% from one story to the next.

12.3.3.4

Table 12.6-1

D, E, and F

4. Out-of-Plane Offset Irregularity: Out-of-plane offset irregularity is

deﬁ ned to exist where there is a discontinuity in a lateral force-resistance

path, such as an out-of-plane offset of at least one of the vertical elements.

12.3.3.3

12.3.3.4

12.7.3

Table 12.6-1

Section 16.2.2

B, C, D, E, and F

D, E, and F

B, C, D, E, and F

D, E, and F

B, C, D, E, and F

5. Nonparallel System Irregularity: Nonparallel system irregularity is

deﬁ ned to exist where vertical lateral force-resisting elements are not

parallel to the major orthogonal axes of the seismic force-resisting system.

12.5.3

12.7.3

Table 12.6-1

Section 16.2.2

C, D, E, and F

B, C, D, E, and F

D, E, and F

B, C, D, E, and F

EXCEPTION: The limit does not apply where

the “weak” story is capable of resisting a total seismic

force equal to Ω

times the design force prescribed in

Section 12.8.

12.3.3.3 Elements Supporting Discontinuous Walls

or Frames

Columns, beams, trusses, or slabs supporting

discontinuous walls or frames of structures having

horizontal irregularity Type 4 of Table 12.3-1 or vertical

irregularity Type 4 of Table 12.3-2 shall be designed to

resist the seismic load effects including overstrength

factor of Section 12.4.3. The connections of such

discontinuous elements to the supporting members shall

be adequate to transmit the forces for which the discon-

tinuous elements were required to be designed.

12.3.3.4 Increase in Forces Due to Irregularities for

Seismic Design Categories D through F

For structures assigned to Seismic Design

Category D, E, or F and having a horizontal structural

irregularity of Type 1a, 1b, 2, 3, or 4 in Table 12.3-1

or a vertical structural irregularity of Type 4 in Table

12.3-2, the design forces determined from Section

12.10.1.1 shall be increased 25 percent for the

following elements of the seismic force-resisting

system:

1. Connections of diaphragms to vertical elements

and to collectors.

2. Collectors and their connections, including

connections to vertical elements, of the seismic

force-resisting system.

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MINIMUM DESIGN LOADS

EXCEPTION:

Forces calculated using the seismic load effects

including overstrength factor of Section 12.4.3 need

not be increased.

12.3.4 Redundancy

A redundancy factor, ρ, shall be assigned to the

seismic force-resisting system in each of two orthogo-

nal directions for all structures in accordance with this

section.

12.3.4.1 Conditions Where Value of ρ is 1.0

The value of ρ is permitted to equal 1.0 for the

following:

1. Structures assigned to Seismic Design Category B

or C.

2. Drift calculation and P-delta effects.

3. Design of nonstructural components.

4. Design of nonbuilding structures that are not

similar to buildings.

5. Design of collector elements, splices, and their

connections for which the seismic load effects

including overstrength factor of Section 12.4.3 are

used.

6. Design of members or connections where the

seismic load effects including overstrength factor

of Section 12.4.3 are required for design.

7. Diaphragm loads determined using Eq. 12.10-1.

8. Structures with damping systems designed in

accordance with Chapter 18.

9. Design of structural walls for out-of-plane forces,

including their anchorage.

Table 12.3-2 Vertical Structural Irregularities

Type Description Reference Section

Seismic Design

Category Application

1a. Stiffness-Soft Story Irregularity: Stiffness-soft story irregularity is

deﬁ ned to exist where there is a story in which the lateral stiffness is less

than 70% of that in the story above or less than 80% of the average

stiffness of the three stories above.

Table 12.6-1 D, E, and F

1b. Stiffness-Extreme Soft Story Irregularity: Stiffness-extreme soft story

irregularity is deﬁ ned to exist where there is a story in which the lateral

stiffness is less than 60% of that in the story above or less than 70% of the

average stiffness of the three stories above.

12.3.3.1

Table 12.6-1

E and F

D, E, and F

2. Weight (Mass) Irregularity: Weight (mass) irregularity is deﬁ ned to exist

where the effective mass of any story is more than 150% of the effective

mass of an adjacent story. A roof that is lighter than the ﬂ oor below need

not be considered.

Table 12.6-1 D, E, and F

3. Vertical Geometric Irregularity: Vertical geometric irregularity is deﬁ ned

to exist where the horizontal dimension of the seismic force-resisting

system in any story is more than 130% of that in an adjacent story.

Table 12.6-1 D, E, and F

4. In-Plane Discontinuity in Vertical Lateral Force-Resisting Element

Irregularity: In-plane discontinuity in vertical lateral force-resisting

elements irregularity is deﬁ ned to exist where there is an in-plane offset of

a vertical seismic force-resisting element resulting in overturning demands

on a supporting beam, column, truss, or slab.

12.3.3.3

12.3.3.4

Table 12.6-1

B, C, D, E, and F

D, E, and F

5a. Discontinuity in Lateral Strength–Weak Story Irregularity:

Discontinuity in lateral strength–weak story irregularity is deﬁ ned to exist

where the story lateral strength is less than 80% of that in the story above.

The story lateral strength is the total lateral strength of all seismic-resisting

elements sharing the story shear for the direction under consideration.

12.3.3.1

Table 12.6-1

E and F

D, E, and F

5b. Discontinuity in Lateral Strength–Extreme Weak Story Irregularity:

Discontinuity in lateral strength–extreme weak story irregularity is deﬁ ned

to exist where the story lateral strength is less than 65% of that in the story

above. The story strength is the total strength of all seismic-resisting

elements sharing the story shear for the direction under consideration.

12.3.3.1

12.3.3.2

Table 12.6-1

D, E, and F

B and C

D, E, and F

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.3.4.2 Redundancy Factor, ρ, for Seismic Design

Categories D through F

For structures assigned to Seismic Design

Category D, E, or F, ρ shall equal 1.3 unless one of

the following two conditions is met, whereby ρ is

permitted to be taken as 1.0:

a. Each story resisting more than 35 percent of the

base shear in the direction of interest shall comply

with Table 12.3-3.

b. Structures that are regular in plan at all levels

provided that the seismic force-resisting systems

consist of at least two bays of seismic force-resisting

perimeter framing on each side of the structure in

each orthogonal direction at each story resisting

more than 35 percent of the base shear. The number

of bays for a shear wall shall be calculated as the

length of shear wall divided by the story height or

two times the length of shear wall divided by the

story height, h

, for light-frame construction.

12.4 SEISMIC LOAD EFFECTS

AND COMBINATIONS

12.4.1 Applicability

All members of the structure, including those not

part of the seismic force-resisting system, shall be

designed using the seismic load effects of Section

12.4 unless otherwise exempted by this standard.

Seismic load effects are the axial, shear, and ﬂ exural

member forces resulting from application of horizon-

tal and vertical seismic forces as set forth in Section

12.4.2. Where speciﬁ cally required, seismic load

effects shall be modiﬁ ed to account for overstrength,

as set forth in Section 12.4.3.

12.4.2 Seismic Load Effect

The seismic load effect, E, shall be determined in

accordance with the following:

1. For use in load combination 5 in Section 2.3.2 or

load combinations 5 and 6 in Section 2.4.1, E shall

be determined in accordance with Eq. 12.4-1 as

follows:

E = E

+ E

(12.4-1)

2. For use in load combination 7 in Section 2.3.2 or

load combination 8 in Section 2.4.1, E shall be

determined in accordance with Eq. 12.4-2 as follows:

E = E

– E

(12.4-2)

where

E = seismic load effect

= effect of horizontal seismic forces as deﬁ ned in

Section 12.4.2.1

= effect of vertical seismic forces as deﬁ ned in

Section 12.4.2.2

12.4.2.1 Horizontal Seismic Load Effect

The horizontal seismic load effect, E

, shall be

determined in accordance with Eq. 12.4-3 as follows:

= ρQ

(12.4-3)

Table 12.3-3 Requirements for Each Story Resisting More than 35% of the Base Shear

Lateral Force-Resisting Element Requirement

Braced frames Removal of an individual brace, or connection thereto, would not result in more than a 33%

reduction in story strength, nor does the resulting system have an extreme torsional

irregularity (horizontal structural irregularity Type 1b).

Moment frames Loss of moment resistance at the beam-to-column connections at both ends of a single beam

would not result in more than a 33% reduction in story strength, nor does the resulting

system have an extreme torsional irregularity (horizontal structural irregularity Type 1b).

Shear walls or wall piers with

a height-to-length ratio greater

than 1.0

Removal of a shear wall or wall pier with a height-to-length ratio greater than 1.0 within

any story, or collector connections thereto, would not result in more than a 33% reduction

in story strength, nor does the resulting system have an extreme torsional irregularity

(horizontal structural irregularity Type 1b). The shear wall and wall pier height-to-length

ratios are determined as shown in Figure 12.3-2.

Cantilever columns Loss of moment resistance at the base connections of any single cantilever column would

not result in more than a 33% reduction in story strength, nor does the resulting system

have an extreme torsional irregularity (horizontal structural irregularity Type 1b).

Other No requirements

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MINIMUM DESIGN LOADS

Shear wall height-to-length-

ratio = h

wall

Wall pier height-to-length-

ratio = h

wall

= height of shear wall

= height of wall pier

wall

= height of shear wall

= height of wall pier

Story Level

wall

FIGURE 12.3-2 Shear Wall and Wall Pier Height-To-Length Ratio Determination

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

where

= effects of horizontal seismic forces from V or F

Where required by Section 12.5.3 or 12.5.4,

such effects shall result from application of

horizontal forces simultaneously in two direc-

tions at right angles to each other

ρ = redundancy factor, as deﬁ ned in Section 12.3.4

12.4.2.2 Vertical Seismic Load Effect

The vertical seismic load effect, E

, shall be

determined in accordance with Eq. 12.4-4 as follows:

= 0.2S

D (12.4-4)

where

= design spectral response acceleration parameter

at short periods obtained from Section 11.4.4

D = effect of dead load

EXCEPTIONS: The vertical seismic load effect,

, is permitted to be taken as zero for either of the

following conditions:

1. In Eqs. 12.4-1, 12.4-2, 12.4-5, and 12.4-6 where

is equal to or less than 0.125.

2. In Eq. 12.4-2 where determining demands on the

soil–structure interface of foundations.

12.4.2.3 Seismic Load Combinations

Where the prescribed seismic load effect, E,

deﬁ ned in Section 12.4.2 is combined with the effects

of other loads as set forth in Chapter 2, the following

seismic load combinations for structures not subject to

ﬂ ood or atmospheric ice loads shall be used in lieu of

the seismic load combinations in either Section 2.3.2

or 2.4.1:

Basic Combinations for Strength Design (see

Sections 2.3.2 and 2.2 for notation).

5. (1.2 + 0.2S

)D + ρQ

+ L + 0.2S

6. (0.9 – 0.2S

)D + ρQ

+ 1.6H

NOTES:

1. The load factor on L in combination 5 is permitted

to equal 0.5 for all occupancies in which L

Table 4-1 is less than or equal to 100 psf

(4.79 kN/m

), with the exception of garages or

areas occupied as places of public assembly.

2. The load factor on H shall be set equal to zero in

combination 7 if the structural action due to H

counteracts that due to E. Where lateral earth

pressure provides resistance to structural actions

from other forces, it shall not be included in H but

shall be included in the design resistance.

Basic Combinations for Allowable Stress Design

(see Sections 2.4.1 and 2.2 for notation).

5. (1.0 + 0.14S

)D + H + F + 0.7ρQ

6. (1.0 + 0.10S

)D + H + F + 0.525ρQ

+ 0.75L +

0.75(L

or S or R)

8. (0.6 – 0.14S

)D + 0.7ρQ

+ H

12.4.3 Seismic Load Effect Including

Overstrength Factor

Where speciﬁ cally required, conditions requiring

overstrength factor applications shall be determined in

accordance with the following:

1. For use in load combination 5 in Section 2.3.2 or

load combinations 5 and 6 in Section 2.4.1, E shall

be taken equal to E

as determined in accordance

with Eq. 12.4-5 as follows:

= E

+ E

(12.4-5)

2. For use in load combination 7 in Section 2.3.2 or

load combination 8 in Section 2.4.1, E shall be

taken equal to E

as determined in accordance with

Eq. 12.4-6 as follows:

= E

– E

(12.4-6)

where

= seismic load effect including overstrength factor

= effect of horizontal seismic forces including

overstrength factor as deﬁ ned in Section

12.4.3.1

= vertical seismic load effect as deﬁ ned in Section

12.4.2.2

12.4.3.1 Horizontal Seismic Load Effect with

Overstrength Factor

The horizontal seismic load effect with over-

strength factor, E

, shall be determined in accordance

with Eq. 12.4-7 as follows:

= Ω

(12.4-7)

where

= effects of horizontal seismic forces from V, F

or F

as speciﬁ ed in Sections 12.8.1, 12.10, or

13.3.1. Where required by Section 12.5.3 or

12.5.4, such effects shall result from application

of horizontal forces simultaneously in two

directions at right angles to each other.

= overstrength factor

EXCEPTION: The value of E

need not exceed

the maximum force that can develop in the element as

determined by a rational, plastic mechanism analysis

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MINIMUM DESIGN LOADS

or nonlinear response analysis utilizing realistic

expected values of material strengths.

12.4.3.2 Load Combinations with

Overstrength Factor

Where the seismic load effect with overstrength

factor, E

, deﬁ ned in Section 12.4.3, is combined with

the effects of other loads as set forth in Chapter 2, the

following seismic load combination for structures not

subject to ﬂ ood or atmospheric ice loads shall be used

in lieu of the seismic load combinations in either

Section 2.3.2 or 2.4.1:

Basic Combinations for Strength Design with

Overstrength Factor (see Sections 2.3.2 and 2.2 for

notation).

5. (1.2 + 0.2S

)D + Ω

+ L + 0.2S

7. (0.9 – 0.2S

)D + Ω

+ 1.6H

NOTES:

1. The load factor on L in combination 5 is permitted

to equal 0.5 for all occupancies in which L

Table 4-1 is less than or equal to 100 psf (4.79 kN/

), with the exception of garages or areas

occupied as places of public assembly.

2. The load factor on H shall be set equal to zero in

combination 7 if the structural action due to H

counteracts that due to E. Where lateral earth

pressure provides resistance to structural actions

from other forces, it shall not be included in H but

shall be included in the design resistance.

Basic Combinations for Allowable Stress Design

with Overstrength Factor (see Sections 2.4.1 and

2.2 for notation).

5. (1.0 + 0.14S

)D + H + F + 0.7Ω

6. (1.0 + 0.105S

)D + H + F + 0.525Ω

+ 0.75L +

0.75(L

or S or R)

8. (0.6 – 0.14S

)D + 0.7Ω

+ H

12.4.3.3 Allowable Stress Increase for Load

Combinations with Overstrength

Where allowable stress design methodologies are

used with the seismic load effect deﬁ ned in Section

12.4.3 applied in load combinations 5, 6, or 8 of

Section 2.4.1, allowable stresses are permitted to

be determined using an allowable stress increase of

1.2. This increase shall not be combined with

increases in allowable stresses or load combination

reductions otherwise permitted by this standard or

the material reference document except for increases

due to adjustment factors in accordance with AF&PA

NDS.

12.4.4 Minimum Upward Force for Horizontal

Cantilevers for Seismic Design Categories

D through F

In structures assigned to Seismic Design Category

D, E, or F, horizontal cantilever structural members

shall be designed for a minimum net upward force of

0.2 times the dead load in addition to the applicable

load combinations of Section 12.4.

12.5 DIRECTION OF LOADING

12.5.1 Direction of Loading Criteria

The directions of application of seismic forces

used in the design shall be those which will produce

the most critical load effects. It is permitted to satisfy

this requirement using the procedures of Section

12.5.2 for Seismic Design Category B, Section 12.5.3

for Seismic Design Category C, and Section 12.5.4

for Seismic Design Categories D, E, and F.

12.5.2 Seismic Design Category B

For structures assigned to Seismic Design

Category B, the design seismic forces are permitted to

be applied independently in each of two orthogonal

directions and orthogonal interaction effects are

permitted to be neglected.

12.5.3 Seismic Design Category C

Loading applied to structures assigned to Seismic

Design Category C shall, as a minimum, conform to

the requirements of Section 12.5.2 for Seismic Design

Category B and the requirements of this section.

Structures that have horizontal structural irregularity

Type 5 in Table 12.3-1 shall use one of the following

procedures:

a. Orthogonal Combination Procedure. The

structure shall be analyzed using the equivalent

lateral force analysis procedure of Section 12.8, the

modal response spectrum analysis procedure of

Section 12.9, or the linear response history

procedure of Section 16.1, as permitted under

Section 12.6, with the loading applied indepen-

dently in any two orthogonal directions. The

requirement of Section 12.5.1 is deemed satisﬁ ed if

members and their foundations are designed for

100 percent of the forces for one direction plus 30

percent of the forces for the perpendicular direc-

tion. The combination requiring the maximum

component strength shall be used.

b. Simultaneous Application of Orthogonal

Ground Motion. The structure shall be analyzed

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

using the linear response history procedure of

Section 16.1 or the nonlinear response history

procedure of Section 16.2, as permitted by Section

12.6, with orthogonal pairs of ground motion

acceleration histories applied simultaneously.

12.5.4 Seismic Design Categories D through F

Structures assigned to Seismic Design Category

D, E, or F shall, as a minimum, conform to the

requirements of Section 12.5.3. In addition, any

column or wall that forms part of two or more

intersecting seismic force-resisting systems and is

subjected to axial load due to seismic forces acting

along either principal plan axis equaling or exceeding

20 percent of the axial design strength of the column

or wall shall be designed for the most critical load

effect due to application of seismic forces in any

direction. Either of the procedures of Section 12.5.3 a

or b are permitted to be used to satisfy this require-

ment. Except as required by Section 12.7.3, 2-D

analyses are permitted for structures with ﬂ exible

diaphragms.

12.6 ANALYSIS PROCEDURE SELECTION

The structural analysis required by Chapter 12 shall

consist of one of the types permitted in Table 12.6-1,

based on the structure’s seismic design category,

structural system, dynamic properties, and regularity,

or with the approval of the authority having jurisdic-

tion, an alternative generally accepted procedure is

permitted to be used. The analysis procedure selected

shall be completed in accordance with the require-

ments of the corresponding section referenced in

Table 12.6-1.

12.7 MODELING CRITERIA

12.7.1 Foundation Modeling

For purposes of determining seismic loads, it is

permitted to consider the structure to be ﬁ xed at the

base. Alternatively, where foundation ﬂ exibility is

considered, it shall be in accordance with Section

12.13.3 or Chapter 19.

12.7.2 Effective Seismic Weight

The effective seismic weight, W, of a structure

shall include the dead load, as deﬁ ned in Section 3.1,

above the base and other loads above the base as

listed below:

1. In areas used for storage, a minimum of 25 percent

of the ﬂ oor live load shall be included.

EXCEPTIONS:

a. Where the inclusion of storage loads adds no

more than 5% to the effective seismic weight at

that level, it need not be included in the

effective seismic weight.

b. Floor live load in public garages and open

parking structures need not be included.

Table 12.6-1 Permitted Analytical Procedures

Seismic

Design

Category Structural Characteristics

Equivalent Lateral

Force Analysis,

Section 12.8

Modal Response

Spectrum Analysis,

Section 12.9

Seismic Response

History Procedures,

Chapter 16

B, C All structures P P P

D, E, F Risk Category I or II buildings not exceeding 2

stories above the base

PP P

Structures of light frame construction P P P

Structures with no structural irregularities and not

exceeding 160 ft in structural height

PP P

Structures exceeding 160 ft in structural height

with no structural irregularities and with T < 3.5T

PP P

Structures not exceeding 160 ft in structural

height and having only horizontal irregularities of

Type 2, 3, 4, or 5 in Table 12.3-1 or vertical

irregularities of Type 4, 5a, or 5b in Table 12.3-2

PP P

All other structures NP P P

P: Permitted; NP: Not Permitted; T

= S

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MINIMUM DESIGN LOADS

2. Where provision for partitions is required by

Section 4.2.2 in the ﬂ oor load design, the

actual partition weight or a minimum weight

of 10 psf (0.48 kN/m

) of ﬂ oor area, whichever is

greater.

3. Total operating weight of permanent equipment.

4. Where the ﬂ at roof snow load, P

, exceeds 30 psf

(1.44 kN/m

), 20 percent of the uniform design

snow load, regardless of actual roof slope.

5. Weight of landscaping and other materials at roof

gardens and similar areas.

12.7.3 Structural Modeling

A mathematical model of the structure shall be

constructed for the purpose of determining member

forces and structure displacements resulting from

applied loads and any imposed displacements or

P-delta effects. The model shall include the stiffness

and strength of elements that are signiﬁ cant to the

distribution of forces and deformations in the structure

and represent the spatial distribution of mass and

stiffness throughout the structure.

In addition, the model shall comply with the

following:

a. Stiffness properties of concrete and masonry

elements shall consider the effects of cracked

sections.

b. For steel moment frame systems, the contribution

of panel zone deformations to overall story drift

shall be included.

Structures that have horizontal structural irregu-

larity Type 1a, 1b, 4, or 5 of Table 12.3-1 shall be

analyzed using a 3-D representation. Where a 3-D

model is used, a minimum of three dynamic degrees

of freedom consisting of translation in two orthogonal

plan directions and rotation about the vertical axis

shall be included at each level of the structure. Where

the diaphragms have not been classiﬁ ed as rigid or

ﬂ exible in accordance with Section 12.3.1, the model

shall include representation of the diaphragm’s

stiffness characteristics and such additional dynamic

degrees of freedom as are required to account for the

participation of the diaphragm in the structure’s

dynamic response.

EXCEPTION: Analysis using a 3-D

representation is not required for structures with

ﬂ exible diaphragms that have Type 4 horizontal

structural irregularities.

12.7.4 Interaction Effects

Moment-resisting frames that are enclosed or

adjoined by elements that are more rigid and not

considered to be part of the seismic force-resisting

system shall be designed so that the action or

failure of those elements will not impair the vertical

load and seismic force-resisting capability of the

frame. The design shall provide for the effect of

these rigid elements on the structural system at

structural deformations corresponding to the design

story drift (Δ) as determined in Section 12.8.6. In

addition, the effects of these elements shall be

considered where determining whether a structure

has one or more of the irregularities deﬁ ned in

Section 12.3.2.

12.8 EQUIVALENT LATERAL

FORCE PROCEDURE

12.8.1 Seismic Base Shear

The seismic base shear, V, in a given direction

shall be determined in accordance with the following

equation:

V = C

W (12.8-1)

where

= the seismic response coefﬁ cient determined in

accordance with Section 12.8.1.1

W = the effective seismic weight per Section 12.7.2

12.8.1.1 Calculation of Seismic Response Coefﬁ cient

The seismic response coefﬁ cient, C

, shall be

determined in accordance with Eq. 12.8-2.

⎛

⎝

⎜

⎞

⎠

⎟

(12.8-2)

where

= the design spectral response acceleration

parameter in the short period range as deter-

mined from Section 11.4.4 or 11.4.7

R = the response modiﬁ cation factor in Table 12.2-1

= the importance factor determined in accordance

with Section 11.5.1

The value of C

computed in accordance with Eq.

12.8-2 need not exceed the following:

⎛

⎝

⎜

⎞

⎠

⎟

for T ≤ T

(12.8-3)

⎛

⎝

⎜

⎞

⎠

⎟

for T > T

(12.8-4)

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

shall not be less than

= 0.044S

≥ 0.01 (12.8-5)

In addition, for structures located where S

is equal to

or greater than 0.6g, C

shall not be less than

= 0.5S

/(R/I

) (12.8-6)

where I

and R are as deﬁ ned in Section 12.8.1.1 and

= the design spectral response acceleration

parameter at a period of 1.0 s, as determined

from Section 11.4.4 or 11.4.7

T = the fundamental period of the structure(s)

determined in Section 12.8.2

= long-period transition period(s) determined in

Section 11.4.5

= the mapped maximum considered earthquake

spectral response acceleration parameter

determined in accordance with Section 11.4.1

or 11.4.7

12.8.1.2 Soil Structure Interaction Reduction

A soil structure interaction reduction is permitted

where determined using Chapter 19 or other generally

accepted procedures approved by the authority having

jurisdiction.

12.8.1.3 Maximum S

Value in Determination of C

For regular structures ﬁ ve stories or less above

the base as deﬁ ned in Section 11.2 and with a period,

T, of 0.5 s or less, C

is permitted to be calculated

using a value of 1.5 for S

12.8.2 Period Determination

The fundamental period of the structure, T, in the

direction under consideration shall be established

using the structural properties and deformational

characteristics of the resisting elements in a properly

substantiated analysis. The fundamental period, T,

shall not exceed the product of the coefﬁ cient for

upper limit on calculated period (C

) from Table

12.8-1 and the approximate fundamental period, T

determined in accordance with Section 12.8.2.1. As an

alternative to performing an analysis to determine the

fundamental period, T, it is permitted to use the

approximate building period, T

, calculated in accor-

dance with Section 12.8.2.1, directly.

12.8.2.1 Approximate Fundamental Period

The approximate fundamental period (T

), in s,

shall be determined from the following equation:

= C

(12.8-7)

where h

is the structural height as deﬁ ned in Section

11.2 and the coefﬁ cients C

and x are determined from

Table 12.8-2.

Alternatively, it is permitted to determine the

approximate fundamental period (T

), in s, from the

following equation for structures not exceeding 12

stories above the base as deﬁ ned in Section 11.2

where the seismic force-resisting system consists

Table 12.8-1 Coefﬁ cient for Upper Limit on

Calculated Period

Design Spectral Response Acceleration

Parameter at 1 s, S

Coefﬁ cient C

≥ 0.4 1.4

0.3 1.4

0.2 1.5

0.15 1.6

≤ 0.1 1.7

Table 12.8-2 Values of Approximate Period Parameters C

and x

Structure Type C

Moment-resisting frame systems in which the frames resist 100% of the required seismic force

and are not enclosed or adjoined by components that are more rigid and will prevent the frames

from deﬂ ecting where subjected to seismic forces:

Steel moment-resisting frames

0.028 (0.0724)

0.8

Concrete moment-resisting frames

0.016 (0.0466)

0.9

Steel eccentrically braced frames in accordance with Table 12.2-1 lines B1 or D1

0.03 (0.0731)

0.75

Steel buckling-restrained braced frames

0.03 (0.0731)

0.75

All other structural systems

0.02 (0.0488)

0.75

Metric equivalents are shown in parentheses.

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MINIMUM DESIGN LOADS

entirely of concrete or steel moment resisting frames

and the average story height is at least 10 ft (3 m):

= 0.1N (12.8-8)

where N = number of stories above the base.

The approximate fundamental period, T

, in s for

masonry or concrete shear wall structures is permitted

to be determined from Eq. 12.8-9 as follows:

0 0019.

(12.8-9)

where C

is calculated from Eq. 12.8-10 as follows:

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

∑

100

1083

(12.8-10)

where

= area of base of structure, ft

= web area of shear wall i in ft

= length of shear wall i in ft

= height of shear wall i in ft

x = number of shear walls in the building effective

in resisting lateral forces in the direction under

consideration

12.8.3 Vertical Distribution of Seismic Forces

The lateral seismic force (F

) (kip or kN) induced

at any level shall be determined from the following

equations:

= C

V (12.8-11)

and

∑

(12.8-12)

where

= vertical distribution factor

V = total design lateral force or shear at the

base of the structure (kip or kN)

and w

= the portion of the total effective seismic

weight of the structure (W) located or

assigned to Level i or x

and h

= the height (ft or m) from the base to

Level i or x

k = an exponent related to the structure period

as follows:

for structures having a period of 0.5 s or

less, k = 1

for structures having a period of 2.5 s or

more, k = 2

for structures having a period between 0.5

and 2.5 s, k shall be 2 or shall be

determined by linear interpolation

between 1 and 2

12.8.4 Horizontal Distribution of Forces

The seismic design story shear in any story (V

)

(kip or kN) shall be determined from the following

equation:

∑

(12.8-13)

where F

= the portion of the seismic base shear (V)

(kip or kN) induced at Level i.

The seismic design story shear (V

) (kip or kN)

shall be distributed to the various vertical elements of

the seismic force-resisting system in the story under

consideration based on the relative lateral stiffness of

the vertical resisting elements and the diaphragm.

12.8.4.1 Inherent Torsion

For diaphragms that are not ﬂ exible, the distribu-

tion of lateral forces at each level shall consider the

effect of the inherent torsional moment, M

, resulting

from eccentricity between the locations of the center

of mass and the center of rigidity. For ﬂ exible

diaphragms, the distribution of forces to the vertical

elements shall account for the position and distribu-

tion of the masses supported.

12.8.4.2 Accidental Torsion

Where diaphragms are not ﬂ exible, the design

shall include the inherent torsional moment (M

)

resulting from the location of the structure masses

plus the accidental torsional moments (M

) caused by

assumed displacement of the center of mass each way

from its actual location by a distance equal to 5

percent of the dimension of the structure perpendicu-

lar to the direction of the applied forces.

Where earthquake forces are applied concurrently

in two orthogonal directions, the required 5 percent

displacement of the center of mass need not be

applied in both of the orthogonal directions at the

same time, but shall be applied in the direction that

produces the greater effect.

12.8.4.3 Ampliﬁ cation of Accidental

Torsional Moment

Structures assigned to Seismic Design Category

C, D, E, or F, where Type 1a or 1b torsional irregu-

larity exists as deﬁ ned in Table 12.3-1 shall have the

effects accounted for by multiplying M

at each level

by a torsional ampliﬁ cation factor (A

) as illustrated in

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

Fig. 12.8-1 and determined from the following

equation:

⎛

⎝

⎜

⎞

⎠

⎟

max

.12

avg

(12.8-14)

where

max

= the maximum displacement at Level x com-

puted assuming A

= 1 (in. or mm)

avg

= the average of the displacements at the extreme

points of the structure at Level x computed

assuming A

= 1 (in. or mm)

The torsional ampliﬁ cation factor (A

) shall not

be less than 1 and is not required to exceed 3.0. The

more severe loading for each element shall be

considered for design.

12.8.5 Overturning

The structure shall be designed to resist overturn-

ing effects caused by the seismic forces determined in

Section 12.8.3.

12.8.6 Story Drift Determination

The design story drift (Δ) shall be computed as

the difference of the deﬂ ections at the centers of mass

at the top and bottom of the story under consideration.

See Fig. 12.8-2. Where centers of mass do not align

vertically, it is permitted to compute the deﬂ ection at

the bottom of the story based on the vertical projec-

tion of the center of mass at the top of the story.

Where allowable stress design is used, Δ shall be

computed using the strength level seismic forces

speciﬁ ed in Section 12.8 without reduction for

allowable stress design.

For structures assigned to Seismic Design

Category C, D, E, or F having horizontal irregularity

Type 1a or 1b of Table 12.3-1, the design story drift,

Δ, shall be computed as the largest difference of the

deﬂ ections of vertically aligned points at the top and

bottom of the story under consideration along any of

the edges of the structure.

The deﬂ ection at Level x (δ

) (in. or mm) used to

compute the design story drift, Δ, shall be determined

in accordance with the following equation:

dxe

(12.8-15)

where

= the deﬂ ection ampliﬁ cation factor in Table

12.2-1

= the deﬂ ection at the location required by this

section determined by an elastic analysis

= the importance factor determined in accordance

with Section 11.5.1

12.8.6.1 Minimum Base Shear for Computing Drift

The elastic analysis of the seismic force-resisting

system for computing drift shall be made using the

prescribed seismic design forces of Section 12.8.

EXCEPTION: Eq. 12.8-5 need not be

considered for computing drift.

xavg

⎥

⎦

⎤

⎢

⎣

⎡

avg

max

xavg

1.2

⎥

⎦

⎤

⎢

⎣

⎡

δδ

FIGURE 12.8-1 Torsional Ampliﬁ cation Factor, A

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MINIMUM DESIGN LOADS

12.8.6.2 Period for Computing Drift

For determining compliance with the story drift

limits of Section 12.12.1, it is permitted to determine

the elastic drifts, (δ

), using seismic design forces

based on the computed fundamental period of the

structure without the upper limit (C

) speciﬁ ed in

Section 12.8.2.

12.8.7 P-Delta Effects

P-delta effects on story shears and moments, the

resulting member forces and moments, and the story

drifts induced by these effects are not required to be

considered where the stability coefﬁ cient (θ) as

determined by the following equation is equal to or

less than 0.10:

θ=

ΔPI

Vh C

xsx d

(12.8-16)

where

= the total vertical design load at and above Level

x (kip or kN); where computing P

, no individual

load factor need exceed 1.0

Δ = the design story drift as deﬁ ned in Section 12.8.6

occurring simultaneously with V

(in. or mm)

= the importance factor determined in accordance

with Section 11.5.1

= the seismic shear force acting between Levels x

and x – 1 (kip or kN)

= the story height below Level x (in. or mm)

= the deﬂ ection ampliﬁ cation factor in Table

12.2-1

The stability coefﬁ cient (θ) shall not exceed θ

max

determined as follows:

max

.=≤

025

(12.8-17)

where β is the ratio of shear demand to shear capacity

for the story between Levels x and x – 1. This ratio is

permitted to be conservatively taken as 1.0.

Where the stability coefﬁ cient (θ) is greater than

0.10 but less than or equal to θ

max

, the incremental

factor related to P-delta effects on displacements and

member forces shall be determined by rational

analysis. Alternatively, it is permitted to multiply

displacements and member forces by 1.0/(1 – θ).

Where θ is greater than θ

max

, the structure is

potentially unstable and shall be redesigned.

Where the P-delta effect is included in an

automated analysis, Eq. 12.8-17 shall still be satisﬁ ed,

however, the value of θ computed from Eq. 12.8-16

using the results of the P-delta analysis is permitted to

be divided by (1 + θ) before checking Eq. 12.8-17.

Story Level 2

= strength-level design earthquake force

δδ

= elastic displacement computed under

strength-level design earthquake forces

δδ

= Cd δe2/IE = amplified displacement

ΔΔ

(δ(δ

(δ

δδ

≤

≤≤

≤Δ

ΔΔ

(Table 12.12-1)

Story Level 1

= strength-level design earthquake force

δδ

= elastic displacement computed under

strength-level design earthquake forces

δδ

= C

δ δ

= amplified displacement

ΔΔ

δδ

≤

≤≤

≤Δ

ΔΔ

(Table 12.12-1)

ΔΔ

= Story Drift

ΔΔ

= Story Drift Ratio

δδ

= Total Displacement

FIGURE 12.8-2 Story Drift Determination

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.9 MODAL RESPONSE

SPECTRUM ANALYSIS

12.9.1 Number of Modes

An analysis shall be conducted to determine the

natural modes of vibration for the structure. The

analysis shall include a sufﬁ cient number of modes to

obtain a combined modal mass participation of at

least 90 percent of the actual mass in each of the

orthogonal horizontal directions of response consid-

ered by the model.

12.9.2 Modal Response Parameters

The value for each force-related design parameter

of interest, including story drifts, support forces, and

individual member forces for each mode of response

shall be computed using the properties of each mode

and the response spectra deﬁ ned in either Section

11.4.5 or 21.2 divided by the quantity R/I

. The value

for displacement and drift quantities shall be multi-

plied by the quantity C

12.9.3 Combined Response Parameters

The value for each parameter of interest calcu-

lated for the various modes shall be combined using

the square root of the sum of the squares (SRSS)

method, the complete quadratic combination (CQC)

method, the complete quadratic combination method

as modiﬁ ed by ASCE 4 (CQC-4), or an approved

equivalent approach. The CQC or the CQC-4 method

shall be used for each of the modal values where

closely spaced modes have signiﬁ cant cross-

correlation of translational and torsional response.

12.9.4 Scaling Design Values of

Combined Response

A base shear (V) shall be calculated in each of

the two orthogonal horizontal directions using the

calculated fundamental period of the structure T in

each direction and the procedures of Section 12.8.

12.9.4.1 Scaling of Forces

Where the calculated fundamental period exceeds

in a given direction, C

shall be used in lieu of

T in that direction. Where the combined response for

the modal base shear (V

) is less than 85 percent of

the calculated base shear (V) using the equivalent

lateral force procedure, the forces shall be multiplied

by 0.85

−

where

V = the equivalent lateral force procedure base shear,

calculated in accordance with this section and

Section 12.8

= the base shear from the required modal

combination

12.9.4.2 Scaling of Drifts

Where the combined response for the modal base

shear (V

) is less than 0.85C

W, and where C

determined in accordance with Eq. 12.8-6, drifts shall

be multiplied by

085.

12.9.5 Horizontal Shear Distribution

The distribution of horizontal shear shall be in

accordance with Section 12.8.4 except that ampliﬁ ca-

tion of torsion in accordance with Section 12.8.4.3 is

not required where accidental torsion effects are

included in the dynamic analysis model.

12.9.6 P-Delta Effects

The P-delta effects shall be determined in

accordance with Section 12.8.7. The base shear

used to determine the story shears and the story

drifts shall be determined in accordance with

Section 12.8.6.

12.9.7 Soil Structure Interaction Reduction

A soil structure interaction reduction is permitted

where determined using Chapter 19 or other generally

accepted procedures approved by the authority having

jurisdiction.

12.10 DIAPHRAGMS, CHORDS,

AND COLLECTORS

12.10.1 Diaphragm Design

Diaphragms shall be designed for both the shear

and bending stresses resulting from design forces. At

diaphragm discontinuities, such as openings and

reentrant corners, the design shall assure that the

dissipation or transfer of edge (chord) forces com-

bined with other forces in the diaphragm is within

shear and tension capacity of the diaphragm.

12.10.1.1 Diaphragm Design Forces

Floor and roof diaphragms shall be designed to

resist design seismic forces from the structural

analysis, but shall not be less than that determined in

accordance with Eq. 12.10-1 as follows:

∑

(12.10-1)

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MINIMUM DESIGN LOADS

where

= the diaphragm design force

= the design force applied to Level i

= the weight tributary to Level i

= the weight tributary to the diaphragm at Level x

The force determined from Eq. 12.10-1 shall not

be less than

= 0.2S

(12.10-2)

The force determined from Eq. 12.10-1 need not

exceed

= 0.4S

(12.10-3)

Where the diaphragm is required to transfer

design seismic force from the vertical resisting

elements above the diaphragm to other vertical

resisting elements below the diaphragm due to offsets

in the placement of the elements or to changes in

relative lateral stiffness in the vertical elements, these

forces shall be added to those determined from Eq.

12.10-1. The redundancy factor, ρ, applies to the

design of diaphragms in structures assigned to

Seismic Design Category D, E, or F. For inertial

forces calculated in accordance with Eq. 12.10-1, the

redundancy factor shall equal 1.0. For transfer forces,

the redundancy factor, ρ, shall be the same as that

used for the structure. For structures having horizontal

or vertical structural irregularities of the types

indicated in Section 12.3.3.4, the requirements of that

section shall also apply.

12.10.2 Collector Elements

Collector elements shall be provided that are

capable of transferring the seismic forces originating

in other portions of the structure to the element

providing the resistance to those forces.

12.10.2.1 Collector Elements Requiring Load

Combinations with Overstrength Factor for Seismic

Design Categories C through F

In structures assigned to Seismic Design Category

C, D, E, or F, collector elements (see Fig. 12.10-1)

and their connections including connections to vertical

elements shall be designed to resist the maximum of

the following:

1. Forces calculated using the seismic load effects

including overstrength factor of Section 12.4.3 with

seismic forces determined by the Equivalent

Lateral Force procedure of Section 12.8 or the

Modal Response Spectrum Analysis procedure of

Section 12.9.

2. Forces calculated using the seismic load effects

including overstrength factor of Section 12.4.3

with seismic forces determined by Equation

12.10-1.

3. Forces calculated using the load combinations of

Section 12.4.2.3 with seismic forces determined by

Equation 12.10-2.

Transfer forces as described in Section 12.10.1.1

shall be considered.

EXCEPTIONS:

1. The forces calculated above need not exceed those

calculated using the load combinations of Section

12.4.2.3 with seismic forces determined by

Equation 12.10-3.

2. In structures or portions thereof braced entirely by

light-frame shear walls, collector elements and

their connections including connections to vertical

elements need only be designed to resist forces

using the load combinations of Section 12.4.2.3

with seismic forces determined in accordance with

Section 12.10.1.1.

FULL LENGTH SHEAR WALL

(NO COLLECTOR REQUIRED)

COLLECTOR ELEMENT TO

TRANSFER FORCE BETWEEN

DIAPHRAGM AND SHEAR WALL

SHEAR WALL AT

STAIRWELL

FIGURE 12.10-1 Collectors

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.11 STRUCTURAL WALLS AND

THEIR ANCHORAGE

12.11.1 Design for Out-of-Plane Forces

Structural walls and their anchorage shall be

designed for a force normal to the surface equal to F

= 0.4S

times the weight of the structural wall with

a minimum force of 10 percent of the weight of the

structural wall. Interconnection of structural wall

elements and connections to supporting framing

systems shall have sufﬁ cient ductility, rotational

capacity, or sufﬁ cient strength to resist shrinkage,

thermal changes, and differential foundation settle-

ment when combined with seismic forces.

12.11.2 Anchorage of Structural Walls and

Transfer of Design Forces into Diaphragms.

12.11.2.1 Wall Anchorage Forces

The anchorage of structural walls to supporting

construction shall provide a direct connection capable

of resisting the following:

= 0.4S

(12.11-1)

shall not be taken less than 0.2k

=+10

100

. (12.11-2)

need not be taken larger than 2.0.

where

= the design force in the individual anchors

= the design spectral response acceleration

parameter at short periods per Section 11.4.4

= the importance factor determined in accordance

with Section 11.5.1

= ampliﬁ cation factor for diaphragm ﬂ exibility

= the span, in feet, of a ﬂ exible diaphragm that

provides the lateral support for the wall; the span is

measured between vertical elements that provide

lateral support to the diaphragm in the direction

considered; use zero for rigid diaphragms

= the weight of the wall tributary to the anchor

Where the anchorage is not located at the roof

and all diaphragms are not ﬂ exible, the value from

Eq. 12.11-1 is permitted to be multiplied by the factor

(1 + 2z/h)/3, where z is the height of the anchor above

the base of the structure and h is the height of the roof

above the base.

Structural walls shall be designed to resist

bending between anchors where the anchor spacing

exceeds 4 ft (1,219 mm).

12.11.2.2 Additional Requirements for Diaphragms

in Structures Assigned to Seismic Design Categories

C through F

12.11.2.2.1 Transfer of Anchorage Forces into

Diaphragm Diaphragms shall be provided with

continuous ties or struts between diaphragm chords to

distribute these anchorage forces into the diaphragms.

Diaphragm connections shall be positive, mechanical,

or welded. Added chords are permitted to be used to

form subdiaphragms to transmit the anchorage forces

to the main continuous cross-ties. The maximum

length-to-width ratio of the structural subdiaphragm

shall be 2.5 to 1. Connections and anchorages capable

of resisting the prescribed forces shall be provided

between the diaphragm and the attached components.

Connections shall extend into the diaphragm a

sufﬁ cient distance to develop the force transferred into

the diaphragm.

12.11.2.2.2 Steel Elements of Structural Wall Anchor-

age System The strength design forces for steel

elements of the structural wall anchorage system, with

the exception of anchor bolts and reinforcing steel,

shall be increased by 1.4 times the forces otherwise

required by this section.

12.11.2.2.3 Wood Diaphragms In wood diaphragms,

the continuous ties shall be in addition to the dia-

phragm sheathing. Anchorage shall not be accom-

plished by use of toenails or nails subject to

withdrawal nor shall wood ledgers or framing be

used in cross-grain bending or cross-grain tension.

The diaphragm sheathing shall not be considered

effective as providing the ties or struts required by

this section.

12.11.2.2.4 Metal Deck Diaphragms In metal deck

diaphragms, the metal deck shall not be used as the

continuous ties required by this section in the direc-

tion perpendicular to the deck span.

12.11.2.2.5 Embedded Straps Diaphragm to structural

wall anchorage using embedded straps shall be

attached to, or hooked around, the reinforcing steel or

otherwise terminated so as to effectively transfer

forces to the reinforcing steel.

12.11.2.2.6 Eccentrically Loaded Anchorage System

Where elements of the wall anchorage system are

loaded eccentrically or are not perpendicular to the

wall, the system shall be designed to resist all

components of the forces induced by the eccentricity.

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MINIMUM DESIGN LOADS

12.11.2.2.7 Walls with Pilasters Where pilasters are

present in the wall, the anchorage force at the pilas-

ters shall be calculated considering the additional load

transferred from the wall panels to the pilasters.

However, the minimum anchorage force at a ﬂ oor or

roof shall not be reduced.

12.12 DRIFT AND DEFORMATION

12.12.1 Story Drift Limit

The design story drift (Δ) as determined in

Sections 12.8.6, 12.9.2, or 16.1, shall not exceed the

allowable story drift (Δ

) as obtained from Table

12.12-1 for any story.

12.12.1.1 Moment Frames in Structures Assigned to

Seismic Design Categories D through F

For seismic force-resisting systems comprised

solely of moment frames in structures assigned to

Seismic Design Categories D, E, or F, the design

story drift (Δ) shall not exceed Δ

/ρ for any story.

ρ shall be determined in accordance with Section

12.3.4.2.

12.12.2 Diaphragm Deﬂ ection

The deﬂ ection in the plane of the diaphragm, as

determined by engineering analysis, shall not exceed

the permissible deﬂ ection of the attached elements.

Permissible deﬂ ection shall be that deﬂ ection that will

permit the attached element to maintain its structural

integrity under the individual loading and continue to

support the prescribed loads.

12.12.3 Structural Separation

All portions of the structure shall be designed and

constructed to act as an integral unit in resisting

seismic forces unless separated structurally by a

distance sufﬁ cient to avoid damaging contact as set

forth in this section.

Separations shall allow for the maximum inelastic

response displacement (δ

). δ

shall be determined at

critical locations with consideration for translational

and torsional displacements of the structure including

torsional ampliﬁ cations, where applicable, using the

following equation:

max

(12.12-1)

Where δ

max

= maximum elastic displacement at the

critical location.

Adjacent structures on the same property shall be

separated by at least δ

, determined as follows:

δδδ

MT M M

()

(12.12-2)

where δ

and δ

are the maximum inelastic response

displacements of the adjacent structures at their

adjacent edges.

Where a structure adjoins a property line not

common to a public way, the structure shall be set

back from the property line by at least the displace-

ment δ

of that structure.

EXCEPTION: Smaller separations or property

line setbacks are permitted where justiﬁ ed by rational

analysis based on inelastic response to design ground

motions.

Table 12.12-1 Allowable Story Drift, Δ

a,b

Structure

Risk Category

I or II III IV

Structures, other than masonry shear wall structures, 4 stories or less above the base as

deﬁ ned in Section 11.2, with interior walls, partitions, ceilings, and exterior wall systems

that have been designed to accommodate the story drifts.

0.025h

0.020h

0.015h

Masonry cantilever shear wall structures

0.010h

Other masonry shear wall structures

0.007h

All other structures

0.020h

0.015h

0.010h

is the story height below Level x.

For seismic force-resisting systems comprised solely of moment frames in Seismic Design Categories D, E, and F, the allowable story drift shall

comply with the requirements of Section 12.12.1.1.

There shall be no drift limit for single-story structures with interior walls, partitions, ceilings, and exterior wall systems that have been designed

to accommodate the story drifts. The structure separation requirement of Section 12.12.3 is not waived.

Structures in which the basic structural system consists of masonry shear walls designed as vertical elements cantilevered from their base or

foundation support which are so constructed that moment transfer between shear walls (coupling) is negligible.

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

12.12.4 Members Spanning between Structures

Gravity connections or supports for members

spanning between structures or seismically separate

portions of structures shall be designed for the

maximum anticipated relative displacements. These

displacements shall be calculated:

1. Using the deﬂ ection calculated at the locations of

support, per Eq. 12.8-15 multiplied by 1.5R/C

, and

2. Considering additional deﬂ ection due to diaphragm

rotation including the torsional ampliﬁ cation factor

calculated per Section 12.8.4.3 where either

structure is torsionally irregular, and

3. Considering diaphragm deformations, and

4. Assuming the two structures are moving in

opposite directions and using the absolute sum of

the displacements.

12.12.5 Deformation Compatibility for Seismic

Design Categories D through F

For structures assigned to Seismic Design

Category D, E, or F, every structural component not

included in the seismic force-resisting system in the

direction under consideration shall be designed to be

adequate for the gravity load effects and the seismic

forces resulting from displacement due to the design

story drift (Δ) as determined in accordance with

Section 12.8.6 (see also Section 12.12.1).

EXCEPTION: Reinforced concrete frame

members not designed as part of the seismic force-

resisting system shall comply with Section 21.11 of

ACI 318.

Where determining the moments and shears

induced in components that are not included in the

seismic force-resisting system in the direction under

consideration, the stiffening effects of adjoining rigid

structural and nonstructural elements shall be consid-

ered and a rational value of member and restraint

stiffness shall be used.

12.13 FOUNDATION DESIGN

12.13.1 Design Basis

The design basis for foundations shall be as set

forth in Section 12.1.5.

12.13.2 Materials of Construction

Materials used for the design and construction of

foundations shall comply with the requirements of

Chapter 14. Design and detailing of steel piles shall

comply with Section 14.1.7 Design and detailing of

concrete piles shall comply with Section 14.2.3.

12.13.3 Foundation Load-Deformation

Characteristics

Where foundation ﬂ exibility is included for the

linear analysis procedures in Chapters 12 and 16, the

load-deformation characteristics of the foundation–soil

system (foundation stiffness) shall be modeled in

accordance with the requirements of this section.

The linear load-deformation behavior of foundations

shall be represented by an equivalent linear stiffness

using soil properties that are compatible with the

soil strain levels associated with the design

earthquake motion. The strain-compatible shear

modulus, G, and the associated strain-compatible

shear wave velocity, v

, needed for the evaluation

of equivalent linear stiffness shall be determined

using the criteria in Section 19.2.1.1 or based on a

site-speciﬁ c study. A 50 percent increase and

decrease in stiffness shall be incorporated in dynamic

analyses unless smaller variations can be justiﬁ ed

based on ﬁ eld measurements of dynamic soil proper-

ties or direct measurements of dynamic foundation

stiffness. The largest values of response shall be used

in design.

12.13.4 Reduction of Foundation Overturning

Overturning effects at the soil–foundation

interface are permitted to be reduced by 25 percent

for foundations of structures that satisfy both of the

following conditions:

a. The structure is designed in accordance with the

Equivalent Lateral Force Analysis as set forth in

Section 12.8.

b. The structure is not an inverted pendulum or

cantilevered column type structure.

Overturning effects at the soil–foundation

interface are permitted to be reduced by 10 percent

for foundations of structures designed in accordance

with the modal analysis requirements of Section 12.9.

12.13.5 Requirements for Structures Assigned to

Seismic Design Category C

In addition to the requirements of Section 11.8.2,

the following foundation design requirements shall

apply to structures assigned to Seismic Design

Category C.

12.13.5.1 Pole-Type Structures

Where construction employing posts or poles as

columns embedded in earth or embedded in concrete

footings in the earth is used to resist lateral loads, the

depth of embedment required for posts or poles to

resist seismic forces shall be determined by means of

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MINIMUM DESIGN LOADS

the design criteria established in the foundation

investigation report.

12.13.5.2 Foundation Ties

Individual pile caps, drilled piers, or caissons

shall be interconnected by ties. All ties shall have a

design strength in tension or compression at least

equal to a force equal to 10 percent of S

times the

larger pile cap or column factored dead plus factored

live load unless it is demonstrated that equivalent

restraint will be provided by reinforced concrete

beams within slabs on grade or reinforced concrete

slabs on grade or conﬁ nement by competent rock,

hard cohesive soils, very dense granular soils, or other

approved means.

12.13.5.3 Pile Anchorage Requirements

In addition to the requirements of Section

14.2.3.1, anchorage of piles shall comply with this

section. Where required for resistance to uplift forces,

anchorage of steel pipe (round HSS sections),

concrete-ﬁ lled steel pipe or H piles to the pile cap

shall be made by means other than concrete bond to

the bare steel section.

EXCEPTION: Anchorage of concrete-ﬁ lled steel

pipe piles is permitted to be accomplished using

deformed bars developed into the concrete portion of

the pile.

12.13.6 Requirements for Structures Assigned to

Seismic Design Categories D through F

In addition to the requirements of Sections 11.8.2,

11.8.3, 14.1.8, and 14.2.3.2, the following foundation

design requirements shall apply to structures assigned

to Seismic Design Category D, E, or F. Design and

construction of concrete foundation elements shall

conform to the requirements of ACI 318, Section

21.8, except as modiﬁ ed by the requirements of this

section.

EXCEPTION: Detached one- and two-family

dwellings of light-frame construction not exceeding

two stories above grade plane need only comply with

the requirements for Sections 11.8.2, 11.8.3 (Items 2

through 4), 12.13.2, and 12.13.5.

12.13.6.1 Pole-Type Structures

Where construction employing posts or poles as

columns embedded in earth or embedded in concrete

footings in the earth is used to resist lateral loads, the

depth of embedment required for posts or poles to

resist seismic forces shall be determined by means of

the design criteria established in the foundation

investigation report.

12.13.6.2 Foundation Ties

Individual pile caps, drilled piers, or caissons

shall be interconnected by ties. In addition, individual

spread footings founded on soil deﬁ ned in Chapter 20

as Site Class E or F shall be interconnected by ties.

All ties shall have a design strength in tension or

compression at least equal to a force equal to 10

percent of S

times the larger pile cap or column

factored dead plus factored live load unless it is

demonstrated that equivalent restraint will be provided

by reinforced concrete beams within slabs on grade or

reinforced concrete slabs on grade or conﬁ nement by

competent rock, hard cohesive soils, very dense

granular soils, or other approved means.

12.13.6.3 General Pile Design Requirement

Piling shall be designed and constructed to

withstand deformations from earthquake ground

motions and structure response. Deformations shall

include both free-ﬁ eld soil strains (without the

structure) and deformations induced by lateral pile

resistance to structure seismic forces, all as modiﬁ ed

by soil–pile interaction.

12.13.6.4 Batter Piles

Batter piles and their connections shall be capable

of resisting forces and moments from the load

combinations with overstrength factor of Section

12.4.3.2 or 12.14.3.2.2. Where vertical and batter piles

act jointly to resist foundation forces as a group, these

forces shall be distributed to the individual piles in

accordance with their relative horizontal and vertical

rigidities and the geometric distribution of the piles

within the group.

12.13.6.5 Pile Anchorage Requirements

In addition to the requirements of Section

12.13.5.3, anchorage of piles shall comply with this

section. Design of anchorage of piles into the pile cap

shall consider the combined effect of axial forces due

to uplift and bending moments due to ﬁ xity to the pile

cap. For piles required to resist uplift forces or

provide rotational restraint, anchorage into the pile

cap shall comply with the following:

1. In the case of uplift, the anchorage shall be capable

of developing the least of the nominal tensile

strength of the longitudinal reinforcement in a

concrete pile, the nominal tensile strength of a steel

pile, and 1.3 times the pile pullout resistance, or

shall be designed to resist the axial tension force

resulting from the seismic load effects including

overstrength factor of Section 12.4.3 or 12.14.3.2.

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

100

The pile pullout resistance shall be taken as the

ultimate frictional or adhesive force that can be

developed between the soil and the pile plus the

pile and pile cap weight.

2. In the case of rotational restraint, the anchorage

shall be designed to resist the axial and shear

forces and moments resulting from the seismic

load effects including overstrength factor of

Section 12.4.3 or 12.14.3.2 or shall be capable of

developing the full axial, bending, and shear

nominal strength of the pile.

12.13.6.6 Splices of Pile Segments

Splices of pile segments shall develop the

nominal strength of the pile section.

EXCEPTION: Splices designed to resist the

axial and shear forces and moments from the seismic

load effects including overstrength factor of Section

12.4.3 or 12.14.3.2.

12.13.6.7 Pile Soil Interaction

Pile moments, shears, and lateral deﬂ ections used

for design shall be established considering the interac-

tion of the shaft and soil. Where the ratio of the depth

of embedment of the pile to the pile diameter or width

is less than or equal to 6, the pile is permitted to be

assumed to be ﬂ exurally rigid with respect to the soil.

12.13.6.8 Pile Group Effects

Pile group effects from soil on lateral pile

nominal strength shall be included where pile center-

to-center spacing in the direction of lateral force is

less than eight pile diameters or widths. Pile group

effects on vertical nominal strength shall be included

where pile center-to-center spacing is less than three

pile diameters or widths.

12.14 SIMPLIFIED ALTERNATIVE

STRUCTURAL DESIGN CRITERIA FOR

SIMPLE BEARING WALL OR BUILDING

FRAME SYSTEMS

12.14.1 General

12.14.1.1 Simpliﬁ ed Design Procedure

The procedures of this section are permitted to be

used in lieu of other analytical procedures in Chapter

12 for the analysis and design of simple buildings

with bearing wall or building frame systems, subject

to all of the limitations listed in this section. Where

these procedures are used, the seismic design category

shall be determined from Table 11.6-1 using the value

of S

from Section 12.14.8.1. The simpliﬁ ed design

procedure is permitted to be used if the following

limitations are met:

1. The structure shall qualify for Risk Category I or

II in accordance with Table 1.5-1.

2. The site class, deﬁ ned in Chapter 20, shall not be

class E or F.

3. The structure shall not exceed three stories above

grade plane.

4. The seismic force-resisting system shall be either

a bearing wall system or building frame system,

as indicated in Table 12.14-1.

5. The structure shall have at least two lines of

lateral resistance in each of two major axis

directions.

6. At least one line of resistance shall be provided

on each side of the center of mass in each

direction.

7. For structures with ﬂ exible diaphragms, over-

hangs beyond the outside line of shear walls or

braced frames shall satisfy the following:

a ≤ d/5 (12.14-1)

where

a = the distance perpendicular to the forces being

considered from the extreme edge of the

diaphragm to the line of vertical resistance

closest to that edge

d = the depth of the diaphragm parallel to the

forces being considered at the line of vertical

resistance closest to the edge

8. For buildings with a diaphragm that is not

ﬂ exible, the distance between the center of

rigidity and the center of mass parallel to each

major axis shall not exceed 15 percent of the

greatest width of the diaphragm parallel to that

axis. In addition, the following two equations

shall be satisﬁ ed:

kd k d

25 005

== =

∑∑ ∑

+≥+

⎛

⎝

⎜

⎞

⎠

⎟

(Eq. 12.14-2A)

kd k d

25 005

== =

∑∑ ∑

+≥+

⎛

⎝

⎜

⎞

⎠

⎟

(Eq. 12.14-2B)

where (see Fig. 12.14-1)

= the lateral load stiffness of wall i or braced

frame i parallel to major axis 1

= the lateral load stiffness of wall j or braced

frame j parallel to major axis 2

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MINIMUM DESIGN LOADS

101

Table 12.14-1 Design Coefﬁ cients and Factors for Seismic Force-Resisting Systems for Simpliﬁ ed

Design Procedure

Seismic Force-Resisting System

ASCE 7

Section Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Limitations

Seismic Design Category

B C D, E

A. BEARING WALL SYSTEMS

1. Special reinforced concrete shear walls 14.2 5 P P P

2. Ordinary reinforced concrete shear walls 14.2 4 P P NP

3. Detailed plain concrete shear walls 14.2 2 P NP NP

4. Ordinary plain concrete shear walls 14.2 1½ P NP NP

5. Intermediate precast shear walls 14.2 4 P P

6. Ordinary precast shear walls 14.2 3 P NP NP

7. Special reinforced masonry shear walls 14.4 5 P P P

8. Intermediate reinforced masonry shear walls 14.4 3½ P P NP

9. Ordinary reinforced masonry shear walls 14.4 2 P NP NP

10. Detailed plain masonry shear walls 14.4 2 P NP NP

11. Ordinary plain masonry shear walls 14.4 1½ P NP NP

12. Prestressed masonry shear walls 14.4 1½ P NP NP

13. Light-frame (wood) walls sheathed with wood structural panels

rated for shear resistance

14.5 6½ P P P

14. Light-frame (cold-formed steel) walls sheathed with wood

structural panels rated for shear resistance or steel sheets

14.1 6½ P P P

15. Light-frame walls with shear panels of all other materials 14.1 and 14.5 2 P P

16. Light-frame (cold-formed steel) wall systems using ﬂ at strap

bracing

14.1 and 14.5 4 P P P

B. BUILDING FRAME SYSTEMS

1. Steel eccentrically braced frames 14.1 8 P P P

2. Steel special concentrically braced frames 14.1 6 P P P

3. Steel ordinary concentrically braced frames 14.1 3¼ P P P

4. Special reinforced concrete shear walls 14.2 6 P P P

5. Ordinary reinforced concrete shear walls 14.2 5 P P NP

6. Detailed plain concrete shear walls 14.2 and

14.2.2.8

2 P NP NP

7. Ordinary plain concrete shear walls 14.2 1½ P NP NP

8. Intermediate precast shear walls 14.2 5 P P

9. Ordinary precast shear walls 14.2 4 P NP NP

10. Steel and concrete composite eccentrically braced frames 14.3 8 P P P

11. Steel and concrete composite special concentrically braced frames 14.3 5 P P P

12. Steel and concrete composite ordinary braced frames 14.3 3 P P NP

13. Steel and concrete composite plate shear walls 14.3 6½ P P P

14. Steel and concrete composite special shear walls 14.3 6 P P P

15. Steel and concrete composite ordinary shear walls 14.3 5 P P NP

16. Special reinforced masonry shear walls 14.4 5½ P P P

Continued

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

102

= the distance from the wall i or braced frame

i to the center of rigidity, perpendicular to

major axis 1

= the distance from the wall j or braced frame

j to the center of rigidity, perpendicular to

major axis 2

= the distance perpendicular to major axis 1

between the center of rigidity and the center

of mass

= the width of the diaphragm perpendicular to

major axis 1

= the distance perpendicular to major axis 2

between the center of rigidity and the center

of mass

= the width of the diaphragm perpendicular to

major axis 2

m = the number of walls and braced frames

resisting lateral force in direction 1

n = the number of walls and braced frames

resisting lateral force in direction 2

Eq. 12.14-2 A and B need not be checked

where a structure fulﬁ lls all the following

limitations:

1. The arrangement of walls or braced frames is

symmetric about each major axis direction.

2. The distance between the two most separated

lines of walls or braced frames is at least 90

percent of the dimension of the structure

perpendicular to that axis direction.

3. The stiffness along each of the lines considered

for item 2 above is at least 33 percent of the

total stiffness in that axis direction.

9. Lines of resistance of the seismic force-resisting

system shall be oriented at angles of no more than

15° from alignment with the major orthogonal

horizontal axes of the building.

10. The simpliﬁ ed design procedure shall be used for

each major orthogonal horizontal axis direction of

the building.

11. System irregularities caused by in-plane or

out-of-plane offsets of lateral force-resisting

elements shall not be permitted.

EXCEPTION: Out-of-plane and in-plane

offsets of shear walls are permitted in two-story

buildings of light-frame construction provided that

the framing supporting the upper wall is designed

for seismic force effects from overturning of the

wall ampliﬁ ed by a factor of 2.5.

12. The lateral load resistance of any story shall not

be less than 80 percent of the story above.

Seismic Force-Resisting System

ASCE 7

Section Where

Detailing

Requirements

Are Speciﬁ ed

Response

Modiﬁ cation

Coefﬁ cient,

Limitations

Seismic Design Category

B C D, E

17. Intermediate reinforced masonry shear walls 14.4 4 P P NP

18. Ordinary reinforced masonry shear walls 14.4 2 P NP NP

19. Detailed plain masonry shear walls 14.4 2 P NP NP

20. Ordinary plain masonry shear walls 14.4 1½ P NP NP

21. Prestressed masonry shear walls 14.4 1½ P NP NP

22. Light-frame (wood) walls sheathed with wood structural panels

rated for shear resistance or steel sheets

14.5 7 P P P

23. Light-frame (cold-formed steel) walls sheathed with wood

structural panels rated for shear resistance or steel sheets

14.1 7 P P P

24. Light-frame walls with shear panels of all other materials 14.1and 14.5 2½ P P

25. Steel buckling-restrained braced frames 14.1 8 P P P

26. Steel special plate shear walls 14.1 7 P P P

Response modiﬁ cation coefﬁ cient, R, for use throughout the standard.

P = permitted; NP = not permitted.

Light-frame walls with shear panels of all other materials are not permitted in Seismic Design Category E.

Light-frame walls with shear panels of all other materials are permitted up to 35 ft (10.6 m) in structural height, h

, in Seismic Design Category

D and are not permitted in Seismic Design Category E.

Table 12.14-1 (Continued)

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103

12.14.1.2 Reference Documents

The reference documents listed in Chapter 23

shall be used as indicated in Section 12.14.

12.14.1.3 Deﬁ nitions

The deﬁ nitions listed in Section 11.2 shall be

used in addition to the following:

PRINCIPAL ORTHOGONAL HORIZON-

TAL DIRECTIONS: The orthogonal directions that

overlay the majority of lateral force-resisting

elements.

12.14.1.4 Notation

D = The effect of dead load

E = The effect of horizontal and vertical

earthquake-induced forces

= Acceleration-based site coefﬁ cient, see

Section 12.14.8.1

= The portion of the seismic base shear, V,

induced at Level i

= The seismic design force applicable to a

particular structural component

= See Section 12.14.8.2

= The height above the base to Level i

= The height above the base to Level x

Level i = The building level referred to by the

subscript i; i = 1 designates the ﬁ rst level

above the base

Level n = The level that is uppermost in the main

portion of the building

Level x = See “Level i”

= The effect of horizontal seismic forces

R = The response modiﬁ cation coefﬁ cient as

given in Table 12.14-1

= See Section 12.14.8.1

= See Section 11.4.1

Y-axis

= d

Axis 2

Center of

Rigidity

Center of

Mass

Wall 2

Wall 1

Axis 1

X - axis

FIGURE 12.14-1 Notation Used in Torsion Check for Nonﬂ exible Diaphragms

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

104

V = The total design shear at the base of the

structure in the direction of interest, as

determined using the procedure of

12.14.8.1

= The seismic design shear in Story x. See

Section 12.14.8.3

W = See Section 12.14.8.1

= Weight of wall

= Weight of structural component

= The portion of the effective seismic weight,

W, located at or assigned to Level i

= See Section 12.14.8.2

12.14.2 Design Basis

The structure shall include complete lateral and

vertical force-resisting systems with adequate strength

to resist the design seismic forces, speciﬁ ed in this

section, in combination with other loads. Design

seismic forces shall be distributed to the various

elements of the structure and their connections

using a linear elastic analysis in accordance with the

procedures of Section 12.14.8. The members of the

seismic force-resisting system and their connections

shall be detailed to conform with the applicable

requirements for the selected structural system as

indicated in Section 12.14.4.1. A continuous load

path, or paths, with adequate strength and stiffness

shall be provided to transfer all forces from the point

of application to the ﬁ nal point of resistance. The

foundation shall be designed to accommodate the

forces developed.

12.14.3 Seismic Load Effects and Combinations

All members of the structure, including those not

part of the seismic force-resisting system, shall be

designed using the seismic load effects of Section

12.14.3 unless otherwise exempted by this standard.

Seismic load effects are the axial, shear, and ﬂ exural

member forces resulting from application of horizon-

tal and vertical seismic forces as set forth in Section

12.14.3.1. Where speciﬁ cally required, seismic load

effects shall be modiﬁ ed to account for overstrength,

as set forth in Section 12.14.3.2.

12.14.3.1 Seismic Load Effect

The seismic load effect, E, shall be determined in

accordance with the following:

1. For use in load combination 5 in Section 2.3.2 or

load combinations 5 and 6 in Section 2.4.1, E shall

be determined in accordance with Eq. 12.14-3 as

follows:

E = E

+ E

(12.14-3)

2. For use in load combination 7 in Section 2.3.2 or

load combination 8 in Section 2.4.1, E shall be

determined in accordance with Eq. 12.14-4 as

follows:

E = E

– E

(12.14-4)

where

E = seismic load effect

= effect of horizontal seismic forces as deﬁ ned in

Section 12.14.3.1.1

= effect of vertical seismic forces as deﬁ ned in

Section 12.14.3.1.2

12.14.3.1.1 Horizontal Seismic Load Effect The

horizontal seismic load effect, E

, shall be determined

in accordance with Eq. 12.14-5 as follows:

= Q

(12.14-5)

where

= effects of horizontal seismic forces from V or F

as speciﬁ ed in Sections 12.14.7.5, 12.14.8.1, and

13.3.1.

12.14.3.1.2 Vertical Seismic Load Effect The vertical

seismic load effect, E

, shall be determined in accor-

dance with Eq. 12.14-6 as follows:

= 0.2S

D (12.14-6)

where

= design spectral response acceleration parameter

at short periods obtained from Section 11.4.4

D = effect of dead load

EXCEPTION: The vertical seismic load effect,

, is permitted to be taken as zero for either of the

following conditions:

1. In Eqs. 12.4-3, 12.4-4, 12.4-7, and 12.14-8 where

is equal to or less than 0.125.

2. In Eq. 12.14-4 where determining demands on the

soil–structure interface of foundations.

12.14.3.1.3 Seismic Load Combinations Where the

prescribed seismic load effect, E, deﬁ ned in Section

12.14.3.1 is combined with the effects of other

loads as set forth in Chapter 2, the following

seismic load combinations for structures not subject

to ﬂ ood or atmospheric ice loads shall be used in lieu

of the seismic load combinations in Sections 2.3.2 or

2.4.1:

Basic Combinations for Strength Design (see

Sections 2.3.2 and 2.2 for notation).

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105

5. (1.2 + 0.2S

)D + Q

+ L + 0.2S

7. (0.9 – 0.2S

)D + Q

+ 1.6H

NOTES:

1. The load factor on L in combination 5 is permitted

to equal 0.5 for all occupancies in which L

Table 4-1 is less than or equal to 100 psf

(4.79 kN/m

), with the exception of garages or

areas occupied as places of public assembly.

2. The load factor on H shall be set equal to zero in

combination 7 if the structural action due to H

counteracts that due to E. Where lateral earth

pressure provides resistance to structural actions

from other forces, it shall not be included in H but

shall be included in the design resistance.

Basic Combinations for Allowable Stress Design

(see Sections 2.4.1 and 2.2 for notation).

5. (1.0 + 0.14S

)D + H + F + 0.7Q

6. (1.0 + 0.105S

)D + H + F + 0.525Q

+ 0.75L +

0.75(L

or S or R)

8. (0.6 – 0.14S

)D + 0.7Q

+ H

12.14.3.2 Seismic Load Effect Including a 2.5

Overstrength Factor

Where speciﬁ cally required, conditions requiring

overstrength factor applications shall be determined in

accordance with the following:

1. For use in load combination 5 in Section 2.3.2 or

load combinations 5 and 6 in Section 2.4.1, E shall

be taken equal to E

as determined in accordance

with Eq. 12.14-7 as follows:

= E

+ E

(12.14-7)

2. For use in load combination 7 in Section 2.3.2 or

load combination 8 in Section 2.4.1, E shall be

taken equal to E

as determined in accordance with

Eq. 12.14-8 as follows:

= E

– E

(12.14-8)

where

= seismic load effect including overstrength factor

= effect of horizontal seismic forces including

overstrength factor as deﬁ ned in Section

12.14.3.2.1

= vertical seismic load effect as deﬁ ned in Section

12.14.3.1.2

12.14.3.2.1 Horizontal Seismic Load Effect with a 2.5

Overstrength Factor The horizontal seismic load

effect with overstrength factor, E

, shall be deter-

mined in accordance with Eq. 12.14-9 as follows:

= 2.5Q

(12.14-9)

where

= effects of horizontal seismic forces from V or F

as speciﬁ ed in Sections 12.14.7.5, 12.14.8.1, and

13.3.1

EXCEPTION: The value of E

need not exceed

the maximum force that can develop in the element as

determined by a rational, plastic mechanism analysis

or nonlinear response analysis utilizing realistic

expected values of material strengths.

12.14.3.2.2 Load Combinations with Overstrength

Factor Where the seismic load effect with over-

strength factor, E

, deﬁ ned in Section 12.14.3.2, is

combined with the effects of other loads as set forth

in Chapter 2, the following seismic load combinations

for structures not subject to ﬂ ood or atmospheric ice

loads shall be used in lieu of the seismic load combi-

nations in Section 2.3.2 or 2.4.1:

Basic Combinations for Strength Design with

Overstrength Factor (see Sections 2.3.2 and 2.2 for

notation).

5. (1.2 + 0.2S

)D + 2.5Q

+ L + 0.2S

7. (0.9 – 0.2S

)D + 2.5Q

+ 1.6H

NOTES:

1. The load factor on L in combination 5 is permitted

to equal 0.5 for all occupancies in which L

Table 4-1 is less than or equal to 100 psf (4.79 kN/

), with the exception of garages or areas

occupied as places of public assembly.

2. The load factor on H shall be set equal to zero in

combination 7 if the structural action due to H

counteracts that due to E. Where lateral earth

pressure provides resistance to structural actions

from other forces, it shall not be included in H, but

shall be included in the design resistance.

Basic Combinations for Allowable Stress Design

with Overstrength Factor (see Sections 2.4.1 and

2.2 for notation).

5. (1.0 + 0.14S

)D + H + F + 1.75Q

6. (1.0 + 0.105S

)D + H + F + 1.313Q

+ 0.75L +

0.75(L

or S or R)

8. (0.6 – 0.14S

)D + 1.75Q

+ H

12.14.3.2.3 Allowable Stress Increase for Load

Combinations with Overstrength Where allowable

stress design methodologies are used with the seismic

load effect deﬁ ned in Section 12.14.3.2 applied in load

combinations 5, 6, or 8 of Section 2.4.1, allowable

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

106

stresses are permitted to be determined using an

allowable stress increase of 1.2. This increase shall not

be combined with increases in allowable stresses or

load combination reductions otherwise permitted by

this standard or the material reference document

except that combination with the duration of load

increases permitted in AF&PA NDS is permitted.

12.14.4 Seismic Force-Resisting System

12.14.4.1 Selection and Limitations

The basic lateral and vertical seismic force-resist-

ing system shall conform to one of the types indicated

in Table 12.14-1 and shall conform to all of the

detailing requirements referenced in the table. The

appropriate response modiﬁ cation coefﬁ cient, R,

indicated in Table 12.14-1 shall be used in determin-

ing the base shear and element design forces as set

forth in the seismic requirements of this standard.

Special framing and detailing requirements are

indicated in Section 12.14.7 and in Sections 14.1,

14.2, 14.3, 14.4, and 14.5 for structures assigned to

the various seismic design categories.

12.14.4.2 Combinations of Framing Systems

12.14.4.2.1 Horizontal Combinations Different

seismic force-resisting systems are permitted to be

used in each of the two principal orthogonal building

directions. Where a combination of different structural

systems is utilized to resist lateral forces in the same

direction, the value of R used for design in that

direction shall not be greater than the least value of R

for any of the systems utilized in that direction.

EXCEPTION: For buildings of light-frame

construction or having ﬂ exible diaphragms and that

are two stories or less above grade plane, resisting

elements are permitted to be designed using the least

value of R of the different seismic force-resisting

systems found in each independent line of framing.

The value of R used for design of diaphragms in such

structures shall not be greater than the least value for

any of the systems utilized in that same direction.

12.14.4.2.2 Vertical Combinations Different seismic

force-resisting systems are permitted to be used in

different stories. The value of R used in a given

direction shall not be greater than the least value of

any of the systems used in that direction.

12.14.4.2.3 Combination Framing Detailing Require-

ments The detailing requirements of Section 12.14.7

required by the higher response modiﬁ cation coefﬁ -

cient, R, shall be used for structural members common

to systems having different response modiﬁ cation

coefﬁ cients.

12.14.5 Diaphragm Flexibility

Diaphragms constructed of steel decking

(untopped), wood structural panels, or similar panel-

ized construction are permitted to be considered

ﬂ exible.

12.14.6 Application of Loading

The effects of the combination of loads shall be

considered as prescribed in Section 12.14.3. The

design seismic forces are permitted to be applied

separately in each orthogonal direction and the combi-

nation of effects from the two directions need not be

considered. Reversal of load shall be considered.

12.14.7 Design and Detailing Requirements

The design and detailing of the members of the

seismic force-resisting system shall comply with the

requirements of this section. The foundation shall

be designed to resist the forces developed and

accommodate the movements imparted to the

structure by the design ground motions. The

dynamic nature of the forces, the expected ground

motion, the design basis for strength and energy

dissipation capacity of the structure, and the dynamic

properties of the soil shall be included in the

determination of the foundation design criteria. The

design and construction of foundations shall comply

with Section 12.13. Structural elements including

foundation elements shall conform to the material

design and detailing requirements set forth in

Chapter 14.

12.14.7.1 Connections

All parts of the structure between separation

joints shall be interconnected, and the connection

shall be capable of transmitting the seismic force, F

induced by the parts being connected. Any smaller

portion of the structure shall be tied to the remainder

of the structure with elements having a strength of

0.20 times the short period design spectral response

acceleration coefﬁ cient, S

, times the weight of the

smaller portion or 5 percent of the portion’s weight,

whichever is greater.

A positive connection for resisting a horizontal

force acting parallel to the member shall be provided

for each beam, girder, or truss either directly to its

supporting elements, or to slabs designed to act as

diaphragms. Where the connection is through a

diaphragm, then the member’s supporting element

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MINIMUM DESIGN LOADS

107

must also be connected to the diaphragm. The

connection shall have minimum design strength of 5

percent of the dead plus live load reaction.

12.14.7.2 Openings or Reentrant Building Corners

Except where as otherwise speciﬁ cally provided

for in this standard, openings in shear walls, dia-

phragms, or other plate-type elements, shall be

provided with reinforcement at the edges of the

openings or reentrant corners designed to transfer the

stresses into the structure. The edge reinforcement

shall extend into the body of the wall or diaphragm a

distance sufﬁ cient to develop the force in the

reinforcement.

EXCEPTION: Shear walls of wood structural

panels are permitted where designed in accordance

with AF&PA SDPWS for perforated shear walls or

AISI S213 for Type II shear walls.

12.14.7.3 Collector Elements

Collector elements shall be provided with

adequate strength to transfer the seismic forces

originating in other portions of the structure to the

element providing the resistance to those forces (see

Fig. 12.10-1). Collector elements, splices, and their

connections to resisting elements shall be designed to

resist the forces deﬁ ned in Section 12.14.3.2.

EXCEPTION: In structures, or portions thereof,

braced entirely by light-frame shear walls, collector

elements, splices, and connections to resisting

elements are permitted to be designed to resist forces

in accordance with Section 12.14.7.4.

12.14.7.4 Diaphragms

Floor and roof diaphragms shall be designed to

resist the design seismic forces at each level, F

calculated in accordance with Section 12.14.8.2. Where

the diaphragm is required to transfer design seismic

forces from the vertical-resisting elements above the

diaphragm to other vertical-resisting elements below

the diaphragm due to changes in relative lateral

stiffness in the vertical elements, the transferred portion

of the seismic shear force at that level, V

, shall be

added to the diaphragm design force. Diaphragms shall

provide for both the shear and bending stresses

resulting from these forces. Diaphragms shall have ties

or struts to distribute the wall anchorage forces into the

diaphragm. Diaphragm connections shall be positive,

mechanical, or welded type connections.

12.14.7.5 Anchorage of Structural Walls

Structural walls shall be anchored to all ﬂ oors,

roofs, and members that provide out-of-plane lateral

support for the wall or that are supported by the wall.

The anchorage shall provide a positive direct connec-

tion between the wall and ﬂ oor, roof, or supporting

member with the strength to resist the out-of-plane

force given by Eq. 12.14-10:

=0.4k

(12.14-10)

shall not be taken less than 0.2k

=+10

100

(12.14-11)

need not be taken larger than 2.0 where

= the design force in the individual anchors

= ampliﬁ cation factor for diaphragm ﬂ exibility

= the span, in feet, of a ﬂ exible diaphragm that

provides the lateral support for the wall; the

span is measured between vertical elements

that provide lateral support to the diaphragm in

the direction considered; use zero for rigid

diaphragms

= the design spectral response acceleration at short

periods per Section 12.14.8.1

= the weight of the wall tributary to the anchor

12.14.7.5.1 Transfer of Anchorage Forces into

Diaphragms Diaphragms shall be provided with

continuous ties or struts between diaphragm chords to

distribute these anchorage forces into the diaphragms.

Added chords are permitted to be used to form

subdiaphragms to transmit the anchorage forces to the

main continuous cross-ties. The maximum length-to-

width ratio of the structural subdiaphragm shall be 2.5

to 1. Connections and anchorages capable of resisting

the prescribed forces shall be provided between the

diaphragm and the attached components. Connections

shall extend into the diaphragm a sufﬁ cient distance

to develop the force transferred into the diaphragm.

12.14.7.5.2 Wood Diaphragms In wood diaphragms,

the continuous ties shall be in addition to the dia-

phragm sheathing. Anchorage shall not be accom-

plished by use of toenails or nails subject to

withdrawal nor shall wood ledgers or framing be used

in cross-grain bending or cross-grain tension. The

diaphragm sheathing shall not be considered effective

as providing the ties or struts required by this section.

12.14.7.5.3 Metal Deck Diaphragms In metal deck

diaphragms, the metal deck shall not be used as the

continuous ties required by this section in the direc-

tion perpendicular to the deck span.

12.14.7.5.4 Embedded Straps Diaphragm to wall

anchorage using embedded straps shall be attached to

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CHAPTER 12 SEISMIC DESIGN REQUIREMENTS FOR BUILDING STRUCTURES

108

or hooked around the reinforcing steel or otherwise

terminated so as to effectively transfer forces to the

reinforcing steel.

12.14.7.6 Bearing Walls and Shear Walls

Exterior and interior bearing walls and shear

walls and their anchorage shall be designed for a

force equal to 40 percent of the short period design

spectral response acceleration S

times the weight

of wall, W

, normal to the surface, with a minimum

force of 10 percent of the weight of the wall. Inter-

connection of wall elements and connections to

supporting framing systems shall have sufﬁ cient

ductility, rotational capacity, or sufﬁ cient strength to

resist shrinkage, thermal changes, and differential

foundation settlement where combined with seismic

forces.

12.14.7.7 Anchorage of Nonstructural Systems

Where required by Chapter 13, all portions or

components of the structure shall be anchored for the

seismic force, F

, prescribed therein.

12.14.8 Simpliﬁ ed Lateral Force

Analysis Procedure

An equivalent lateral force analysis shall consist

of the application of equivalent static lateral forces to

a linear mathematical model of the structure. The

lateral forces applied in each direction shall sum to a

total seismic base shear given by Section 12.14.8.1

and shall be distributed vertically in accordance with

Section 12.14.8.2. For purposes of analysis, the

structure shall be considered ﬁ xed at the base.

12.14.8.1 Seismic Base Shear

The seismic base shear, V, in a given direction

shall be determined in accordance with Eq. 12.14-11:

(12.14-11)

where

SFS

DS a s

where F

is permitted to be taken as 1.0 for rock sites,

1.4 for soil sites, or determined in accordance with

Section 11.4.3. For the purpose of this section, sites

are permitted to be considered to be rock if there

is no more than 10 ft (3 m) of soil between the rock

surface and the bottom of spread footing or mat

foundation. In calculating S

, S

shall be in accor-

dance with Section 11.4.1, but need not be taken

larger than 1.5.

F = 1.0 for buildings that are one story above grade

plane

F = 1.1 for buildings that are two stories above grade

plane

F = 1.2 for buildings that are three stories above

grade plane

R = the response modiﬁ cation factor from Table

12.14-1

W = effective seismic weight of the structure that

includes the dead load, as deﬁ ned in Section 3.1,

above grade plane and other loads above grade

plane as listed in the following text:

1. In areas used for storage, a minimum of 25 percent

of the ﬂ oor live load shall be included.

EXCEPTIONS:

a. Where the inclusion of storage loads adds no

more than 5% to the effective seismic weight at

that level, it need not be included in the

effective seismic weight.

b. Floor live load in public garages and open

parking structures need not be included.

2. Where provision for partitions is required by

Section 4.2.2 in the ﬂ oor load design, the actual

partition weight, or a minimum weight of

10 psf (0.48 kN/m

) of ﬂ oor area, whichever is

greater.

3. Total operating weight of permanent equipment.

4. Where the ﬂ at roof snow load, P

, exceeds

30 psf (1.44 kN/m

), 20 percent of the uniform

design snow load, regardless of actual roof

slope.

5. Weight of landscaping and other materials at roof

gardens and similar areas.

12.14.8.2 Vertical Distribution

The forces at each level shall be calculated using

the following equation:

= (12.14-12)

where w

= the portion of the effective seismic weight

of the structure, W, at level x.

12.14.8.3 Horizontal Shear Distribution

The seismic design story shear in any story, V

(kip or kN), shall be determined from the following

equation:

∑

(12.14-13)

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MINIMUM DESIGN LOADS

109

where F

= the portion of the seismic base shear, V

(kip or kN) induced at Level i.

12.14.8.3.1 Flexible Diaphragm Structures The

seismic design story shear in stories of structures with

ﬂ exible diaphragms, as deﬁ ned in Section 12.14.5,

shall be distributed to the vertical elements of the

seismic force-resisting system using tributary area

rules. Two-dimensional analysis is permitted where

diaphragms are ﬂ exible.

12.14.8.3.2 Structures with Diaphragms That Are Not

Flexible For structures with diaphragms that are not

ﬂ exible, as deﬁ ned in Section 12.14.5, the seismic

design story shear, V

(kip or kN), shall be distributed

to the various vertical elements of the seismic

force-resisting system in the story under consideration

based on the relative lateral stiffnesses of the vertical

elements and the diaphragm.

12.14.8.3.2.1 Torsion The design of structures

with diaphragms that are not ﬂ exible shall include the

torsional moment, M

(kip-ft or KN-m) resulting from

eccentricity between the locations of center of mass

and the center of rigidity.

12.14.8.4 Overturning

The structure shall be designed to resist overturn-

ing effects caused by the seismic forces determined in

Section 12.14.8.2. The foundations of structures shall

be designed for not less than 75 percent of the

foundation overturning design moment, M

(kip-ft or

kN-m) at the foundation–soil interface.

12.14.8.5 Drift Limits and Building Separation

Structural drift need not be calculated. Where

a drift value is needed for use in material standards,

to determine structural separations between buildings

or from property lines, for design of cladding, or for

other design requirements, it shall be taken as 1

percent of structural height, h

, unless computed

to be less. All portions of the structure shall be

designed to act as an integral unit in resisting seismic

forces unless separated structurally by a distance

sufﬁ cient to avoid damaging contact under the total

deﬂ ection.

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111

Chapter 13

SEISMIC DESIGN REQUIREMENTS FOR

NONSTRUCTURAL COMPONENTS

13.1.4 Exemptions

The following nonstructural components are

exempt from the requirements of this section:

1. Furniture (except storage cabinets as noted in

Table 13.5-1).

2. Temporary or movable equipment.

3. Architectural components in Seismic Design

Category B other than parapets supported by

bearing walls or shear walls provided that the

component importance factor, I

, is equal to 1.0.

4. Mechanical and electrical components in Seismic

Design Category B.

5. Mechanical and electrical components in Seismic

Design Category C provided that the component

importance factor, I

, is equal to 1.0.

6. Mechanical and electrical components in Seismic

Design Categories D, E, or F where all of the

following apply:

a. The component importance factor, I

, is equal to

1.0;

b. The component is positively attached to the

structure;

c. Flexible connections are provided between the

component and associated ductwork, piping, and

conduit; and either

i. The component weighs 400 lb (1,780 N) or

less and has a center of mass located 4 ft

(1.22 m) or less above the adjacent ﬂ oor

level; or

ii. The component weighs 20 lb (89 N) or less

or, in the case of a distributed system, 5 lb/ft

(73 N/m) or less.

13.1.5 Application of Nonstructural Component

Requirements to Nonbuilding Structures

Nonbuilding structures (including storage racks

and tanks) that are supported by other structures

shall be designed in accordance with Chapter 15.

Where Section 15.3 requires that seismic forces be

determined in accordance with Chapter 13 and

values for R

are not provided in Table 13.5-1 or

13.6-1, R

shall be taken as equal to the value of R

listed in Section 15. The value of a

shall be deter-

mined in accordance with footnote a of Table 13.5-1

or 13.6-1.

13.1 GENERAL

13.1.1 Scope

This chapter establishes minimum design criteria

for nonstructural components that are permanently

attached to structures and for their supports and

attachments. Where the weight of a nonstructural

component is greater than or equal to 25 percent of

the effective seismic weight, W, of the structure as

deﬁ ned in Section 12.7.2, the component shall be

classiﬁ ed as a nonbuilding structure and shall be

designed in accordance with Section 15.3.2.

13.1.2 Seismic Design Category

For the purposes of this chapter, nonstructural

components shall be assigned to the same seismic

design category as the structure that they occupy or to

which they are attached.

13.1.3 Component Importance Factor

All components shall be assigned a component

importance factor as indicated in this section. The

component importance factor, I

, shall be taken as 1.5

if any of the following conditions apply:

1. The component is required to function for

life-safety purposes after an earthquake, including

ﬁ re protection sprinkler systems and egress

stairways.

2. The component conveys, supports, or otherwise

contains toxic, highly toxic, or explosive sub-

stances where the quantity of the material exceeds

a threshold quantity established by the authority

having jurisdiction and is sufﬁ cient to pose a threat

to the public if released.

3. The component is in or attached to a Risk Cat-

egory IV structure and it is needed for continued

operation of the facility or its failure could impair

the continued operation of the facility.

4. The component conveys, supports, or otherwise

contains hazardous substances and is attached to a

structure or portion thereof classiﬁ ed by the

authority having jurisdiction as a hazardous

occupancy.

All other components shall be assigned a component

importance factor, I

, equal to 1.0.

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CHAPTER 13 SEISMIC DESIGN REQUIREMENTS FOR NONSTRUCTURAL COMPONENTS

112

13.1.6 Reference Documents

Where a reference document provides a basis for

the earthquake-resistant design of a particular type of

nonstructural component, that document is permitted

to be used, subject to the approval of the authority

having jurisdiction and the following conditions:

a. The design earthquake forces shall not be less than

those determined in accordance with Section

13.3.1.

b. Each nonstructural component’s seismic interac-

tions with all other connected components and with

the supporting structure shall be accounted for in

the design. The component shall accommodate

drifts, deﬂ ections, and relative displacements

determined in accordance with the applicable

seismic requirements of this standard.

c. Nonstructural component anchorage requirements

shall not be less than those speciﬁ ed in Section

13.4.

13.1.7 Reference Documents Using Allowable

Stress Design

Where a reference document provides a basis for

the earthquake-resistant design of a particular type of

component, and the same reference document deﬁ nes

acceptance criteria in terms of allowable stresses

rather than strengths, that reference document is

permitted to be used. The allowable stress load

combination shall consider dead, live, operating, and

earthquake loads in addition to those in the reference

document. The earthquake loads determined in

accordance with Section 13.3.1 shall be multiplied by

a factor of 0.7. The allowable stress design load

combinations of Section 2.4 need not be used. The

component shall also accommodate the relative

displacements speciﬁ ed in Section 13.3.2.

13.2 GENERAL DESIGN REQUIREMENTS

13.2.1 Applicable Requirements for Architectural,

Mechanical, and Electrical Components, Supports,

and Attachments

Architectural, mechanical, and electrical compo-

nents, supports, and attachments shall comply with the

sections referenced in Table 13.2-1. These requirements

shall be satisﬁ ed by one of the following methods:

1. Project-speciﬁ c design and documentation submit-

ted for approval to the authority having jurisdiction

after review and acceptance by a registered design

professional.

2. Submittal of the manufacturer’s certiﬁ cation that

the component is seismically qualiﬁ ed by at least

one of the following:

a. Analysis, or

b. Testing in accordance with the alternative set

forth in Section 13.2.5, or

c. Experience data in accordance with the alterna-

tive set forth in Section 13.2.6.

13.2.2 Special Certiﬁ cation Requirements for

Designated Seismic Systems

Certiﬁ cations shall be provided for designated

seismic systems assigned to Seismic Design Catego-

ries C through F as follows:

1. Active mechanical and electrical equipment that

must remain operable following the design earth-

quake ground motion shall be certiﬁ ed by the

manufacturer as operable whereby active parts or

energized components shall be certiﬁ ed exclusively

on the basis of approved shake table testing in

accordance with Section 13.2.5 or experience data

in accordance with Section 13.2.6 unless it can be

Table 13.2-1 Applicable Requirements for Architectural, Mechanical, and Electrical Components:

Supports and Attachments

Nonstructural Element (i.e.,

Component, Support, Attachment)

General

Design

Requirements

(Section 13.2)

Force and

Displacement

Requirements

(Section 13.3)

Attachment

Requirements

(Section 13.4)

Architectural

Component

Requirements

(Section 13.5)

Mechanical and

Electrical Component

Requirements

(Section 13.6)

Architectural components and

supports and attachments for

architectural components

XXXX

Mechanical and electrical components

with I

> 1

XXX X

Supports and attachments for

mechanical and electrical components

XXX X

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MINIMUM DESIGN LOADS

113

shown that the component is inherently rugged by

comparison with similar seismically qualiﬁ ed

components. Evidence demonstrating compliance

with this requirement shall be submitted for

approval to the authority having jurisdiction after

review and acceptance by a registered design

professional.

2. Components with hazardous substances and

assigned a component importance factor, I

, of 1.5

in accordance with Section 13.1.3 shall be certiﬁ ed

by the manufacturer as maintaining containment

following the design earthquake ground motion by

(1) analysis, (2) approved shake table testing in

accordance with Section 13.2.5, or (3) experience

data in accordance with Section 13.2.6. Evidence

demonstrating compliance with this requirement

shall be submitted for approval to the authority

having jurisdiction after review and acceptance by

a registered design professional.

13.2.3 Consequential Damage

The functional and physical interrelationship of

components, their supports, and their effect on each

other shall be considered so that the failure of an

essential or nonessential architectural, mechanical, or

electrical component shall not cause the failure of an

essential architectural, mechanical, or electrical

component.

13.2.4 Flexibility

The design and evaluation of components, their

supports, and their attachments shall consider their

ﬂ exibility as well as their strength.

13.2.5 Testing Alternative for Seismic

Capacity Determination

As an alternative to the analytical requirements of

Sections 13.2 through 13.6, testing shall be deemed as

an acceptable method to determine the seismic

capacity of components and their supports and

attachments. Seismic qualiﬁ cation by testing based

upon a nationally recognized testing standard proce-

dure, such as ICC-ES AC 156, acceptable to the

authority having jurisdiction shall be deemed to

satisfy the design and evaluation requirements

provided that the substantiated seismic capacities

equal or exceed the seismic demands determined in

accordance with Sections 13.3.1 and 13.3.2.

13.2.6 Experience Data Alternative for Seismic

Capacity Determination

As an alternative to the analytical requirements of

Sections 13.2 through 13.6, use of experience data

shall be deemed as an acceptable method to

determine the seismic capacity of components and

their supports and attachments. Seismic qualiﬁ cation

by experience data based upon nationally recognized

procedures acceptable to the authority having jurisdic-

tion shall be deemed to satisfy the design and evalua-

tion requirements provided that the substantiated

seismic capacities equal or exceed the seismic

demands determined in accordance with Sections

13.3.1 and 13.3.2.

13.2.7 Construction Documents

Where design of nonstructural components or

their supports and attachments is required by Table

13.2-1, such design shall be shown in construction

documents prepared by a registered design profes-

sional for use by the owner, authorities having

jurisdiction, contractors, and inspectors. Such docu-

ments shall include a quality assurance plan if

required by Appendix 11A.

13.3 SEISMIC DEMANDS ON

NONSTRUCTURAL COMPONENTS

13.3.1 Seismic Design Force

The horizontal seismic design force (F

) shall be

applied at the component’s center of gravity and

distributed relative to the component’s mass distribu-

tion and shall be determined in accordance with

Eq. 13.3-1:

aS W

pDS p

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

(13.3-1)

is not required to be taken as greater than

= 1.6S

(13.3-2)

and F

shall not be taken as less than

= 0.3S

(13.3-3)

where

= seismic design force

= spectral acceleration, short period, as determined

from Section 11.4.4

= component ampliﬁ cation factor that varies from

1.00 to 2.50 (select appropriate value from

Table 13.5-1 or 13.6-1)

= component importance factor that varies from

1.00 to 1.50 (see Section 13.1.3)

= component operating weight

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CHAPTER 13 SEISMIC DESIGN REQUIREMENTS FOR NONSTRUCTURAL COMPONENTS

114

= component response modiﬁ cation factor that

varies from 1.00 to 12 (select appropriate value

from Table 13.5-1 or 13.6-1)

z = height in structure of point of attachment of

component with respect to the base. For items at

or below the base, z shall be taken as 0. The

value of z/h need not exceed 1.0

h = average roof height of structure with respect to

the base

The force (F

) shall be applied independently in

at least two orthogonal horizontal directions in

combination with service loads associated with the

component, as appropriate. For vertically cantilevered

systems, however, the force F

shall be assumed to

act in any horizontal direction. In addition, the

component shall be designed for a concurrent vertical

force ±0.2S

. The redundancy factor, ρ, is permit-

ted to be taken equal to 1 and the overstrength factor,

, does not apply.

EXCEPTION: The concurrent vertical seismic

force need not be considered for lay-in access ﬂ oor

panels and lay-in ceiling panels.

Where nonseismic loads on nonstructural

components exceed F

, such loads shall govern

the strength design, but the detailing requirements

and limitations prescribed in this chapter shall

apply.

In lieu of the forces determined in accordance

with Eq. 13.3-1, accelerations at any level are

permitted to be determined by the modal

analysis procedures of Section 12.9 with R = 1.0.

Seismic forces shall be in accordance with

Eq. 13.3-4:

aa W

ip p

⎛

⎝

⎜

⎞

⎠

⎟

(13.3-4)

where a

is the acceleration at level i obtained from

the modal analysis and where A

is the torsional

ampliﬁ cation factor determined by Eq.12.8-14. Upper

and lower limits of F

determined by Eqs. 13.3-2 and

13.3-3 shall apply.

13.3.2 Seismic Relative Displacements

The effects of seismic relative displacements shall

be considered in combination with displacements

caused by other loads as appropriate. Seismic relative

displacements, D

, shall be determined in accordance

with with Eq. 13.3-5 as:

= D

(13.3-5)

where

= the importance factor in Section 11.5.1

= displacement determined in accordance with the

equations set forth in Sections 13.3.2.1 and

13.3.2.2.

13.3.2.1 Displacements within Structures

For two connection points on the same Structure

A or the same structural system, one at a height h

and the other at a height h

, D

shall be determined as

= Δ

– Δ

(13.3-6)

Alternatively, D

is permitted to be determined

using modal procedures described in Section 12.9,

using the difference in story deﬂ ections calculated for

each mode and then combined using appropriate

modal combination procedures. D

is not required to

be taken as greater than

xyaA

−

()

(13.3-7)

13.3.2.2 Displacements between Structures

For two connection points on separate Structures

A and B or separate structural systems, one at a

height h

and the other at a height h

, D

shall be

determined as

= |δ

| + |δ

| (13.3-8)

is not required to be taken as greater than

xaA

yaB

(13.3-9)

where

= relative seismic displacement that the compo-

nent must be designed to accommodate

= deﬂ ection at building Level x of Structure A,

determined in accordance with Eq. (12.8-15)

= deﬂ ection at building Level y of Structure A,

determined in accordance with Eq. (12.8-15).

= deﬂ ection at building Level y of Structure B,

determined in accordance with Eq. (12.8-15).

= height of Level x to which upper connection

point is attached

= height of Level y to which lower connection

point is attached

= allowable story drift for Structure A as deﬁ ned

in Table 12.12-1

= allowable story drift for Structure B as deﬁ ned

in Table 12.12-1

= story height used in the deﬁ nition of the

allowable drift Δ

in Table12.12-1. Note that

= the drift index.

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MINIMUM DESIGN LOADS

115

The effects of seismic relative displacements shall

be considered in combination with displacements

caused by other loads as appropriate.

13.4 NONSTRUCTURAL

COMPONENT ANCHORAGE

Nonstructural components and their supports shall be

attached (or anchored) to the structure in accordance

with the requirements of this section and the attach-

ment shall satisfy the requirements for the parent

material as set forth elsewhere in this standard.

Component attachments shall be bolted, welded,

or otherwise positively fastened without consideration

of frictional resistance produced by the effects of

gravity. A continuous load path of sufﬁ cient strength

and stiffness between the component and the support-

ing structure shall be provided. Local elements of

the structure including connections shall be designed

and constructed for the component forces where

they control the design of the elements or their

connections. The component forces shall be those

determined in Section 13.3.1, except that modiﬁ ca-

tions to F

and R

due to anchorage conditions need

not be considered. The design documents shall

include sufﬁ cient information relating to the attach-

ments to verify compliance with the requirements of

this section.

13.4.1 Design Force in the Attachment

The force in the attachment shall be determined

based on the prescribed forces and displacements for

the component as determined in Sections 13.3.1 and

13.3.2, except that R

shall not be taken as larger

than 6.

13.4.2 Anchors in Concrete or Masonry.

13.4.2.1 Anchors in Concrete

Anchors in concrete shall be designed in accor-

dance with Appendix D of ACI 318.

13.4.2.2 Anchors in Masonry

Anchors in masonry shall be designed in accor-

dance with TMS 402/ACI 503/ASCE 5. Anchors shall

be designed to be governed by the tensile or shear

strength of a ductile steel element.

EXCEPTION: Anchors shall be permitted to be

designed so that the attachment that the anchor is

connecting to the structure undergoes ductile yielding

at a load level corresponding to anchor forces not

greater than their design strength, or the minimum

design strength of the anchors shall be at least 2.5

times the factored forces transmitted by the

component.

13.4.2.3 Post-Installed Anchors in Concrete

and Masonry

Post-installed anchors in concrete shall be

prequaliﬁ ed for seismic applications in accordance

with ACI 355.2 or other approved qualiﬁ cation

procedures. Post-installed anchors in masonry shall be

prequaliﬁ ed for seismic applications in accordance

with approved qualiﬁ cation procedures.

13.4.3 Installation Conditions

Determination of forces in attachments shall take

into account the expected conditions of installation

including eccentricities and prying effects.

13.4.4 Multiple Attachments

Determination of force distribution of multiple

attachments at one location shall take into account the

stiffness and ductility of the component, component

supports, attachments, and structure and the ability to

redistribute loads to other attachments in the group.

Designs of anchorage in concrete in accordance with

Appendix D of ACI 318 shall be considered to satisfy

this requirement.

13.4.5 Power Actuated Fasteners

Power actuated fasteners in concrete or steel shall

not be used for sustained tension loads or for brace

applications in Seismic Design Categories D, E, or F

unless approved for seismic loading. Power actuated

fasteners in masonry are not permitted unless

approved for seismic loading.

EXCEPTION: Power actuated fasteners in

concrete used for support of acoustical tile or lay-in

panel suspended ceiling applications and distributed

systems where the service load on any individual

fastener does not exceed 90 lb (400 N). Power

actuated fasteners in steel where the service load on

any individual fastener does not exceed 250 lb

(1,112 N).

13.4.6 Friction Clips

Friction clips in Seismic Design Categories D, E,

or F shall not be used for supporting sustained loads

in addition to resisting seismic forces. C-type beam

and large ﬂ ange clamps are permitted for hangers

provided they are equipped with restraining straps

equivalent to those speciﬁ ed in NFPA 13, Section

9.3.7. Lock nuts or equivalent shall be provided to

prevent loosening of threaded connections.

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CHAPTER 13 SEISMIC DESIGN REQUIREMENTS FOR NONSTRUCTURAL COMPONENTS

116

13.5 ARCHITECTURAL COMPONENTS

13.5.1 General

Architectural components, and their supports and

attachments, shall satisfy the requirements of this

section. Appropriate coefﬁ cients shall be selected

from Table 13.5-1.

EXCEPTION: Components supported by chains

or otherwise suspended from the structure are not

required to satisfy the seismic force and relative

displacement requirements provided they meet all of

the following criteria:

1. The design load for such items shall be equal to

1.4 times the operating weight acting down with a

simultaneous horizontal load equal to 1.4 times the

operating weight. The horizontal load shall be

applied in the direction that results in the most

critical loading for design.

2. Seismic interaction effects shall be considered in

accordance with Section 13.2.3.

3. The connection to the structure shall allow a 360°

range of motion in the horizontal plane.

13.5.2 Forces and Displacements

All architectural components, and their supports

and attachments, shall be designed for the seismic

forces deﬁ ned in Section 13.3.1.

Architectural components that could pose a

life-safety hazard shall be designed to accommodate

the seismic relative displacement requirements of

Section 13.3.2. Architectural components shall be

designed considering vertical deﬂ ection due to joint

rotation of cantilever structural members.

13.5.3 Exterior Nonstructural Wall Elements

and Connections

Exterior nonstructural wall panels or elements

that are attached to or enclose the structure shall be

designed to accommodate the seismic relative dis-

placements deﬁ ned in Section 13.3.2 and movements

due to temperature changes. Such elements shall be

supported by means of positive and direct structural

supports or by mechanical connections and fasteners

in accordance with the following requirements:

a. Connections and panel joints shall allow for the

story drift caused by relative seismic displacements

) determined in Section 13.3.2, or 0.5 in. (13

mm), whichever is greatest.

b. Connections to permit movement in the plane of

the panel for story drift shall be sliding connections

using slotted or oversize holes, connections that

permit movement by bending of steel, or other

connections that provide equivalent sliding or

ductile capacity.

c. The connecting member itself shall have sufﬁ cient

ductility and rotation capacity to preclude fracture

of the concrete or brittle failures at or near welds.

d. All fasteners in the connecting system such as

bolts, inserts, welds, and dowels and the body of

the connectors shall be designed for the force (F

)

determined by Section 13.3.1 with values of R

and

taken from Table 13.5-1 applied at the center of

mass of the panel.

e. Where anchorage is achieved using ﬂ at straps

embedded in concrete or masonry, such straps shall

be attached to or hooked around reinforcing steel

or otherwise terminated so as to effectively transfer

forces to the reinforcing steel or to assure that

pullout of anchorage is not the initial failure

mechanism.

13.5.4 Glass

Glass in glazed curtain walls and storefronts

shall be designed and installed in accordance with

Section 13.5.9.

13.5.5 Out-of-Plane Bending

Transverse or out-of-plane bending or deforma-

tion of a component or system that is subjected to

forces as determined in Section 13.5.2 shall not exceed

the deﬂ ection capability of the component or system.

13.5.6 Suspended Ceilings

Suspended ceilings shall be in accordance with

this section.

EXCEPTIONS:

1. Suspended ceilings with areas less than or equal to

144 ft

(13.4 m

) that are surrounded by walls or

sofﬁ ts that are laterally braced to the structure

above are exempt from the requirements of this

section.

2. Suspended ceilings constructed of screw- or

nail-attached gypsum board on one level that are

surrounded by and connected to walls or sofﬁ ts

that are laterally braced to the structure above are

exempt from the requirements of this section.

13.5.6.1 Seismic Forces

The weight of the ceiling, W

, shall include the

ceiling grid; ceiling tiles or panels; light ﬁ xtures if

attached to, clipped to, or laterally supported by the

ceiling grid; and other components that are laterally

supported by the ceiling. W

shall be taken as not less

than 4 psf (192 N/m

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MINIMUM DESIGN LOADS

117

The seismic force, F

, shall be transmitted

through the ceiling attachments to the building

structural elements or the ceiling–structure

boundary.

13.5.6.2 Industry Standard Construction for Acousti-

cal Tile or Lay-in Panel Ceilings

Unless designed in accordance with Section

13.5.6.3, or seismically qualiﬁ ed in accordance with

Table 13.5-1 Coefﬁ cients for Architectural Components

Architectural Component a

Interior nonstructural walls and partitions

Plain (unreinforced) masonry walls 1.0 1.5

All other walls and partitions 1.0 2.5

Cantilever elements (Unbraced or braced to structural frame below its center of mass)

Parapets and cantilever interior nonstructural walls 2.5 2.5

Chimneys where laterally braced or supported by the structural frame 2.5 2.5

Cantilever elements (Braced to structural frame above its center of mass)

Parapets 1.0 2.5

Chimneys 1.0 2.5

Exterior nonstructural walls

1.0

2.5

Exterior nonstructural wall elements and connections

Wall element 1.0 2.5

Body of wall panel connections 1.0 2.5

Fasteners of the connecting system 1.25 1.0

Veneer

Limited deformability elements and attachments 1.0 2.5

Low deformability elements and attachments 1.0 1.5

Penthouses (except where framed by an extension of the building frame) 2.5 3.5

Ceilings

All 1.0 2.5

Cabinets

Permanent ﬂ oor-supported storage cabinets over 6 ft (1,829 mm) tall, including contents

Permanent ﬂ oor-supported library shelving, book stacks, and bookshelves over 6 ft (1,829 mm) tall,

including contents

1.0

2.5

Laboratory equipment 1.0 2.5

Access ﬂ oors

Special access ﬂ oors (designed in accordance with Section 13.5.7.2) 1.0 2.5

All other 1.0 1.5

Appendages and ornamentations 2.5 2.5

Signs and billboards 2.5 3.0

Other rigid components

High deformability elements and attachments 1.0 3.5

Limited deformability elements and attachments 1.0 2.5

Low deformability materials and attachments 1.0 1.5

Other ﬂ exible components

High deformability elements and attachments 2.5 3.5

Limited deformability elements and attachments 2.5 2.5

Low deformability materials and attachments 2.5 1.5

Egress stairways not part of the building structure 1.0 2.5

A lower value for a

shall not be used unless justiﬁ ed by detailed dynamic analysis. The value for a

shall not be less than 1.00. The value of

= 1 is for rigid components and rigidly attached components. The value of a

= 2.5 is for ﬂ exible components and ﬂ exibly attached components.

Where ﬂ exible diaphragms provide lateral support for concrete or masonry walls and partitions, the design forces for anchorage to the

diaphragm shall be as speciﬁ ed in Section 12.11.2.

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CHAPTER 13 SEISMIC DESIGN REQUIREMENTS FOR NONSTRUCTURAL COMPONENTS

118

Section 13.2.5 or 13.2.6, acoustical tile or lay-in panel

ceilings shall be designed and constructed in accor-

dance with this section.

13.5.6.2.1 Seismic Design Category C Acoustical tile

or lay-in panel ceilings in structures assigned to

Seismic Design Category C shall be designed and

installed in accordance with ASTM C635, ASTM

C636, and ASTM E580, Section 4—Seismic Design

Category C.

13.5.6.2.2 Seismic Design Categories D through F

Acoustical tile or lay-in panel ceilings in Seismic

Design Categories D, E, and F shall be designed and

installed in accordance with ASTM C635, ASTM

C636, and ASTM E580, Section 5—Seismic Design

Categories D, E, and F as modiﬁ ed by this section.

Acoustical tile or lay-in panel ceilings shall also

comply with the following:

a. The width of the perimeter supporting closure

angle or channel shall be not less than 2.0 in. (50

mm). Where perimeter supporting clips are used,

they shall be qualiﬁ ed in accordance with approved

test criteria. In each orthogonal horizontal direc-

tion, one end of the ceiling grid shall be attached

to the closure angle or channel. The other end in

each horizontal direction shall have a 0.75 in. (19

mm) clearance from the wall and shall rest upon

and be free to slide on a closure angle or channel.

b. For ceiling areas exceeding 2,500 ft

(232 m

), a

seismic separation joint or full height partition that

breaks the ceiling up into areas not exceeding

2,500 ft

(232 m

), each with a ratio of the long to

short dimension less than or equal to 4, shall be

provided unless structural analyses are performed

of the ceiling bracing system for the prescribed

seismic forces that demonstrate ceiling penetrations

and closure angles or channels provide sufﬁ cient

clearance to accommodate the anticipated lateral

displacement. Each area shall be provided with

closure angles or channels in accordance with

Section 13.5.6.2.2.a and horizontal restraints or

bracing.

13.5.6.3 Integral Construction

As an alternate to providing large clearances

around sprinkler system penetrations through ceilings,

the sprinkler system and ceiling grid are permitted to

be designed and tied together as an integral unit. Such

a design shall consider the mass and ﬂ exibility of all

elements involved, including the ceiling, sprinkler

system, light ﬁ xtures, and mechanical (HVAC)

appurtenances. Such design shall be performed by a

registered design professional.

13.5.7 Access Floors

13.5.7.1 General

The weight of the access ﬂ oor, W

, shall include

the weight of the ﬂ oor system, 100 percent of the

weight of all equipment fastened to the ﬂ oor, and 25

percent of the weight of all equipment supported by

but not fastened to the ﬂ oor. The seismic force, F

shall be transmitted from the top surface of the access

ﬂ oor to the supporting structure.

Overturning effects of equipment fastened to the

access ﬂ oor panels also shall be considered. The

ability of “slip on” heads for pedestals shall be

evaluated for suitability to transfer overturning effects

of equipment.

Where checking individual pedestals for overturn-

ing effects, the maximum concurrent axial load shall

not exceed the portion of W

assigned to the pedestal

under consideration.

13.5.7.2 Special Access Floors

Access ﬂ oors shall be considered to be “special

access ﬂ oors” if they are designed to comply with the

following considerations:

1. Connections transmitting seismic loads consist of

mechanical fasteners, anchors satisfying the

requirements of Appendix D of ACI 318, welding,

or bearing. Design load capacities comply with

recognized design codes and/or certiﬁ ed test

results.

2. Seismic loads are not transmitted by friction,

power actuated fasteners, adhesives, or by friction

produced solely by the effects of gravity.

3. The design analysis of the bracing system includes

the destabilizing effects of individual members

buckling in compression.

4. Bracing and pedestals are of structural or mechani-

cal shapes produced to ASTM speciﬁ cations that

specify minimum mechanical properties. Electrical

tubing shall not be used.

5. Floor stringers that are designed to carry axial

seismic loads and that are mechanically fastened to

the supporting pedestals are used.

13.5.8 Partitions

13.5.8.1 General

Partitions that are tied to the ceiling and all

partitions greater than 6 ft (1.8 m) in height shall be

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MINIMUM DESIGN LOADS

119

laterally braced to the building structure. Such

bracing shall be independent of any ceiling lateral

force bracing. Bracing shall be spaced to limit

horizontal deﬂ ection at the partition head to be

compatible with ceiling deﬂ ection requirements

as determined in Section 13.5.6 for suspended

ceilings and elsewhere in this section for other

systems.

EXCEPTION: Partitions that meet all of the

following conditions:

1. The partition height does not exceed 9 ft

(2,740 mm).

2. The linear weight of the partition does not exceed

the product of 10 lb (0.479 kN) times the height

(ft or m) of the partition.

3. The partition horizontal seismic load does not

exceed 5 psf (0.24 kN/m

13.5.8.2 Glass

Glass in glazed partitions shall be designed and

installed in accordance with Section 13.5.9.

13.5.9 Glass in Glazed Curtain Walls, Glazed

Storefronts, and Glazed Partitions

13.5.9.1 General

Glass in glazed curtain walls, glazed storefronts,

and glazed partitions shall meet the relative displace-

ment requirement of Eq. 13.5-1:

fallout

≥ 1.25I

(13.5-1)

or 0.5 in. (13 mm), whichever is greater where:

fallout

= the relative seismic displacement (drift) at

which glass fallout from the curtain wall,

storefront wall, or partition occurs

(Section 13.5.9.2)

= the relative seismic displacement that the

component must be designed to accommodate

(Section 13.3.2.1). D

shall be applied over

the height of the glass component under

consideration

= the importance factor determined in accor-

dance with Section 11.5.1

EXCEPTION:

1. Glass with sufﬁ cient clearances from its frame

such that physical contact between the glass and

frame will not occur at the design drift, as demon-

strated by Eq. 13.5-2, need not comply with this

requirement:

clear

≥ 1.25D

(13.5-2)

where

clear

= relative horizontal (drift) displacement,

measured over the height of the glass panel

under consideration, which causes initial

glass-to-frame contact. For rectangular

glass panels within a rectangular wall frame

clear

= 21

⎛

⎝

⎜

⎞

⎠

⎟

where

= the height of the rectangular glass panel

= the width of the rectangular glass panel

= the average of the clearances (gaps) on both

sides between the vertical glass edges and

the frame

= the average of the clearances (gaps) top and

bottom between the horizontal glass edges

and the frame

2. Fully tempered monolithic glass in Risk Categories

I, II, and III located no more than 10 ft (3 m)

above a walking surface need not comply with this

requirement.

3. Annealed or heat-strengthened laminated glass in

single thickness with interlayer no less than 0.030

in. (0.76 mm) that is captured mechanically in a

wall system glazing pocket, and whose perimeter is

secured to the frame by a wet glazed gunable

curing elastomeric sealant perimeter bead of 0.5 in.

(13 mm) minimum glass contact width, or other

approved anchorage system need not comply with

this requirement.

13.5.9.2 Seismic Drift Limits for Glass Components

fallout

, the drift causing glass fallout from the

curtain wall, storefront, or partition shall be deter-

mined in accordance with AAMA 501.6 or by

engineering analysis.

13.6 MECHANICAL AND

ELECTRICAL COMPONENTS

13.6.1 General

Mechanical and electrical components and their

supports shall satisfy the requirements of this section.

The attachment of mechanical and electrical compo-

nents and their supports to the structure shall meet the

requirements of Section 13.4. Appropriate coefﬁ cients

shall be selected from Table 13.6-1.

EXCEPTION: Light ﬁ xtures, lighted signs, and

ceiling fans not connected to ducts or piping, which

are supported by chains or otherwise suspended from

the structure, are not required to satisfy the seismic

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120

Table 13.6-1 Seismic Coefﬁ cients for Mechanical and Electrical Components

Mechanical and Electrical Components a

Air-side HVAC, fans, air handlers, air conditioning units, cabinet heaters, air distribution boxes, and other

mechanical components constructed of sheet metal framing

2.5 6.0

Wet-side HVAC, boilers, furnaces, atmospheric tanks and bins, chillers, water heaters, heat exchangers,

evaporators, air separators, manufacturing or process equipment, and other mechanical components

constructed of high-deformability materials

1.0 2.5

Engines, turbines, pumps, compressors, and pressure vessels not supported on skirts and not within the scope

of Chapter 15

1.0 2.5

Skirt-supported pressure vessels not within the scope of Chapter 15 2.5 2.5

Elevator and escalator components 1.0 2.5

Generators, batteries, inverters, motors, transformers, and other electrical components constructed of high

deformability materials

1.0 2.5

Motor control centers, panel boards, switch gear, instrumentation cabinets, and other components constructed

of sheet metal framing

2.5 6.0

Communication equipment, computers, instrumentation, and controls 1.0 2.5

Roof-mounted stacks, cooling and electrical towers laterally braced below their center of mass 2.5 3.0

Roof-mounted stacks, cooling and electrical towers laterally braced above their center of mass 1.0 2.5

Lighting ﬁ xtures 1.0 1.5

Other mechanical or electrical components 1.0 1.5

Vibration Isolated Components and Systems

Components and systems isolated using neoprene elements and neoprene isolated ﬂ oors with built-in or

separate elastomeric snubbing devices or resilient perimeter stops

2.5 2.5

Spring isolated components and systems and vibration isolated ﬂ oors closely restrained using built-in or

separate elastomeric snubbing devices or resilient perimeter stops

2.5 2.0

Internally isolated components and systems 2.5 2.0

Suspended vibration isolated equipment including in-line duct devices and suspended internally isolated

components

2.5 2.5

Distribution Systems

Piping in accordance with ASME B31, including in-line components with joints made by welding or brazing 2.5 12.0

Piping in accordance with ASME B31, including in-line components, constructed of high or limited

deformability materials, with joints made by threading, bonding, compression couplings, or grooved

couplings

2.5 6.0

Piping and tubing not in accordance with ASME B31, including in-line components, constructed of

high-deformability materials, with joints made by welding or brazing

2.5 9.0

Piping and tubing not in accordance with ASME B31, including in-line components, constructed of high- or

limited-deformability materials, with joints made by threading, bonding, compression couplings, or grooved

couplings

2.5 4.5

Piping and tubing constructed of low-deformability materials, such as cast iron, glass, and nonductile plastics 2.5 3.0

Ductwork, including in-line components, constructed of high-deformability materials, with joints made by

welding or brazing

2.5 9.0

Ductwork, including in-line components, constructed of high- or limited-deformability materials with joints

made by means other than welding or brazing

2.5 6.0

Ductwork, including in-line components, constructed of low-deformability materials, such as cast iron, glass,

and nonductile plastics

2.5 3.0

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121

force and relative displacement requirements provided

they meet all of the following criteria:

1. The design load for such items shall be equal to

1.4 times the operating weight acting down with a

simultaneous horizontal load equal to 1.4 times the

operating weight. The horizontal load shall be

applied in the direction that results in the most

critical loading for the design.

2. Seismic interaction effects shall be considered in

accordance with Section 13.2.3.

3. The connection to the structure shall allow a 360°

range of motion in the horizontal plane.

Where design of mechanical and electrical

components for seismic effects is required, consider-

ation shall be given to the dynamic effects of the

components, their contents, and where appropriate,

their supports and attachments. In such cases, the

interaction between the components and the support-

ing structures, including other mechanical and

electrical components, shall also be considered.

13.6.2 Component Period

The fundamental period of the nonstructural

component (including its supports and attachment to

the structure), T

, shall be determined by the follow-

ing equation provided that the component, supports,

and attachment can be reasonably represented

analytically by a simple spring and mass single

degree-of-freedom system:

= 2π

(13.6-1)

where

= component fundamental period

= component operating weight

g = gravitational acceleration

= combined stiffness of the component, supports

and attachments, determined in terms of load per

unit deﬂ ection at the center of gravity of the

component

Alternatively, the fundamental period of the

component, T

, in seconds is permitted to be deter-

mined from experimental test data or by a properly

substantiated analysis.

13.6.3 Mechanical Components

HVAC ductwork shall meet the requirements of

Section 13.6.7. Piping systems shall meet the require-

ments of Section 13.6.8. Boilers and vessels shall

meet the requirements of Section 13.6.9. Elevators

shall meet the requirements of Section 13.6.10. All

other mechanical components shall meet the require-

ments of Section 13.6.11. Mechanical components

with I

greater than 1.0 shall be designed for the

seismic forces and relative displacements deﬁ ned in

Sections 13.3.1 and 13.3.2 and shall satisfy the

following additional requirements:

1. Provision shall be made to eliminate seismic

impact for components vulnerable to impact, for

components constructed of nonductile materials,

and in cases where material ductility will be

reduced due to service conditions (e.g., low

temperature applications).

2. The possibility of loads imposed on components by

attached utility or service lines, due to differential

movement of support points on separate structures,

shall be evaluated.

3. Where piping or HVAC ductwork components are

attached to structures that could displace relative to

one another and for isolated structures where such

components cross the isolation interface, the

Distribution Systems

Electrical conduit and cable trays 2.5 6.0

Bus ducts 1.0 2.5

Plumbing 1.0 2.5

Manufacturing or process conveyors (nonpersonnel) 2.5 3.0

A lower value for a

is permitted where justiﬁ ed by detailed dynamic analyses. The value for a

shall not be less than 1.0. The value of a

equal

to 1.0 is for rigid components and rigidly attached components. The value of a

equal to 2.5 is for ﬂ exible components and ﬂ exibly attached

components.

Components mounted on vibration isolators shall have a bumper restraint or snubber in each horizontal direction. The design force shall be

taken as 2F

if the nominal clearance (air gap) between the equipment support frame and restraint is greater than 0.25 in. (6 mm). If the nominal

clearance speciﬁ ed on the construction documents is not greater than 0.25 in. (6 mm), the design force is permitted to be taken as F

Table 13.6-1 (Continued)

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122

components shall be designed to accommodate the

seismic relative displacements deﬁ ned in Section

13.3.2.

13.6.4 Electrical Components

Electrical components with I

greater than 1.0

shall be designed for the seismic forces and relative

displacements deﬁ ned in Sections 13.3.1 and 13.3.2

and shall satisfy the following additional

requirements:

1. Provision shall be made to eliminate seismic

impact between components.

2. Loads imposed on the components by attached

utility or service lines that are attached to separate

structures shall be evaluated.

3. Batteries on racks shall have wrap-around restraints

to ensure that the batteries will not fall from the

racks. Spacers shall be used between restraints and

cells to prevent damage to cases. Racks shall be

evaluated for sufﬁ cient lateral load capacity.

4. Internal coils of dry type transformers shall be

positively attached to their supporting substructure

within the transformer enclosure.

5. Electrical control panels, computer equipment, and

other items with slide-out components shall have a

latching mechanism to hold the components in

place.

6. Electrical cabinet design shall comply with the

applicable National Electrical Manufacturers

Association (NEMA) standards. Cutouts in the

lower shear panel that have not been made by the

manufacturer and reduce signiﬁ cantly the strength

of the cabinet shall be speciﬁ cally evaluated.

7. The attachments for additional external items

weighing more than 100 lb (445 N) shall be

speciﬁ cally evaluated if not provided by the

manufacturer.

8. Where conduit, cable trays, or similar electrical

distribution components are attached to structures

that could displace relative to one another and for

isolated structures where such components cross

the isolation interface, the components shall be

designed to accommodate the seismic relative

displacements deﬁ ned in Section 13.3.2.

13.6.5 Component Supports

Mechanical and electrical component supports

(including those with I

= 1.0) and the means by

which they are attached to the component shall be

designed for the forces and displacements determined

in Sections 13.3.1 and 13.3.2. Such supports include

structural members, braces, frames, skirts, legs,

saddles, pedestals, cables, guys, stays, snubbers, and

tethers, as well as elements forged or cast as a part of

the mechanical or electrical component.

13.6.5.1 Design Basis

If standard supports, for example, ASME B31,

NFPA 13, or MSS SP-58, or proprietary supports are

used, they shall be designed by either load rating (i.e.,

testing) or for the calculated seismic forces. In

addition, the stiffness of the support, where appropri-

ate, shall be designed such that the seismic load path

for the component performs its intended function.

13.6.5.2 Design for Relative Displacement

Component supports shall be designed to accom-

modate the seismic relative displacements between

points of support determined in accordance with

Section 13.3.2.

13.6.5.3 Support Attachment to Component

The means by which supports are attached to the

component, except where integral (i.e., cast or

forged), shall be designed to accommodate both the

forces and displacements determined in accordance

with Sections 13.3.1 and 13.3.2. If the value of I

1.5 for the component, the local region of the support

attachment point to the component shall be evaluated

for the effect of the load transfer on the component

wall.

13.6.5.4 Material Detailing Requirements

The materials comprising supports and the means

of attachment to the component shall be constructed

of materials suitable for the application, including the

effects of service conditions, for example, low

temperature applications. Materials shall be in

conformance with a nationally recognized standard.

13.6.5.5 Additional Requirements

The following additional requirements shall apply

to mechanical and electrical component supports:

1. Seismic supports shall be constructed so that

support engagement is maintained.

2. Reinforcement (e.g., stiffeners or Belleville

washers) shall be provided at bolted connections

through sheet metal equipment housings as required

to transfer the equipment seismic loads speciﬁ ed in

this section from the equipment to the structure.

Where equipment has been certiﬁ ed per Section

13.2.2, 13.2.5, or 13.2.6, anchor bolts or other

fasteners and associated hardware as included in

the certiﬁ cation shall be installed in conformance

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123

with the manufacturer’s instructions. For those

cases where no certiﬁ cation exists or where

instructions for such reinforcement are not pro-

vided, reinforcement methods shall be as speciﬁ ed

by a registered design professional or as approved

by the authority having jurisdiction.

3. Where weak-axis bending of cold-formed steel

supports is relied on for the seismic load path, such

supports shall be speciﬁ cally evaluated.

4. Components mounted on vibration isolators shall

have a bumper restraint or snubber in each hori-

zontal direction, and vertical restraints shall be

provided where required to resist overturning.

Isolator housings and restraints shall be constructed

of ductile materials. (See additional design force

requirements in footnote b to Table 13.6-1.) A

viscoelastic pad or similar material of appropriate

thickness shall be used between the bumper and

components to limit the impact load.

5. Where post-installed mechanical anchors are used

for non-vibration isolated mechanical equipment

rated over 10 hp (7.45 kW), they shall be qualiﬁ ed

in accordance with ACI 355.2.

6. For piping, boilers, and pressure vessels,

attachments to concrete shall be suitable for

cyclic loads.

7. For mechanical equipment, drilled and grouted-in-

place anchors for tensile load applications shall

use either expansive cement or expansive epoxy

grout.

13.6.5.6 Conduit, Cable Tray, and Other Electrical

Distribution Systems (Raceways)

Raceways shall be designed for seismic forces

and seismic relative displacements as required in

Section 13.3. Conduit greater than 2.5 in. (64 mm)

trade size and attached to panels, cabinets, or other

equipment subject to seismic relative displacement,

, shall be provided with ﬂ exible connections or

designed for seismic forces and seismic relative

displacements as required in Section 13.3.

EXCEPTIONS:

1. Design for the seismic forces and relative displace-

ments of Section 13.3 shall not be required for

raceways where either:

a. Trapeze assemblies are used to support race-

ways and the total weight of the raceway

supported by trapeze assemblies is less than 10

lb/ft (146 N/m), or

b. The raceway is supported by hangers and each

hanger in the raceway run is 12 in. (305 mm) or

less in length from the raceway support point to

the supporting structure. Where rod hangers are

used, they shall be equipped with swivels to

prevent inelastic bending in the rod.

2. Design for the seismic forces and relative displace-

ments of Section 13.3 shall not be required for

conduit, regardless of the value of I

, where the

conduit is less than 2.5 in. (64 mm) trade size.

13.6.6 Utility and Service Lines

At the interface of adjacent structures or portions

of the same structure that may move independently,

utility lines shall be provided with adequate ﬂ exibility

to accommodate the anticipated differential movement

between the portions that move independently.

Differential displacement calculations shall be

determined in accordance with Section 13.3.2.

The possible interruption of utility service shall

be considered in relation to designated seismic

systems in Risk Category IV as deﬁ ned in Table 1.5-1.

Speciﬁ c attention shall be given to the vulnerability of

underground utilities and utility interfaces between the

structure and the ground where Site Class E or F soil

is present, and where the seismic coefﬁ cient S

at the

underground utility or at the base of the structure is

equal to or greater than 0.33.

13.6.7 Ductwork

HVAC and other ductwork shall be designed for

seismic forces and seismic relative displacements as

required in Section 13.3. Design for the displacements

across seismic joints shall be required for ductwork

with I

= 1.5 without consideration of the exceptions

below.

EXCEPTIONS: The following exceptions

pertain to ductwork not designed to carry toxic, highly

toxic, or ﬂ ammable gases or used for smoke control:

1. Design for the seismic forces and relative displace-

ments of Section 13.3 shall not be required for

ductwork where either:

a. Trapeze assemblies are used to support duct-

work and the total weight of the ductwork

supported by trapeze assemblies is less than 10

lb/ft (146 N/m); or

b. The ductwork is supported by hangers and each

hanger in the duct run is 12 in. (305 mm) or

less in length from the duct support point to the

supporting structure. Where rod hangers are

used, they shall be equipped with swivels to

prevent inelastic bending in the rod.

2. Design for the seismic forces and relative displace-

ments of Section 13.3 shall not be required where

provisions are made to avoid impact with larger

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124

ducts or mechanical components or to protect the

ducts in the event of such impact; and HVAC

ducts have a cross-sectional area of less than 6 ft

(0.557 m

), or weigh 17 lb/ft (248 N/m) or less.

HVAC duct systems fabricated and installed in

accordance with standards approved by the authority

having jurisdiction shall be deemed to meet the lateral

bracing requirements of this section.

Components that are installed in-line with the

duct system and have an operating weight greater than

75 lb (334 N), such as fans, heat exchangers, and

humidiﬁ ers, shall be supported and laterally braced

independent of the duct system and such braces shall

meet the force requirements of Section 13.3.1.

Appurtenances such as dampers, louvers, and diffus-

ers shall be positively attached with mechanical

fasteners. Unbraced piping attached to in-line equip-

ment shall be provided with adequate ﬂ exibility to

accommodate the seismic relative displacements of

Section 13.3.2.

13.6.8 Piping Systems

Unless otherwise noted in this section, piping

systems shall be designed for the seismic forces and

seismic relative displacements of Section 13.3. ASME

pressure piping systems shall satisfy the requirements

of Section 13.6.8.1. Fire protection sprinkler piping

shall satisfy the requirements of Section 13.6.8.2.

Elevator system piping shall satisfy the requirements

of Section 13.6.10.

Where other applicable material standards or

recognized design bases are not used, piping design

including consideration of service loads shall be based

on the following allowable stresses:

a. For piping constructed with ductile materials (e.g.,

steel, aluminum, or copper), 90 percent of the

minimum speciﬁ ed yield strength.

b. For threaded connections in piping constructed

with ductile materials, 70 percent of the minimum

speciﬁ ed yield strength.

c. For piping constructed with nonductile materials

(e.g., cast iron or ceramics), 10 percent of the

material minimum speciﬁ ed tensile strength.

d. For threaded connections in piping constructed

with nonductile materials, 8 percent of the material

minimum speciﬁ ed tensile strength.

Piping not detailed to accommodate the seismic

relative displacements at connections to other compo-

nents shall be provided with connections having

sufﬁ cient ﬂ exibility to avoid failure of the connection

between the components.

13.6.8.1 ASME Pressure Piping Systems

Pressure piping systems, including their supports,

designed and constructed in accordance with ASME

B31 shall be deemed to meet the force, displacement,

and other requirements of this section. In lieu of

speciﬁ c force and displacement requirements provided

in ASME B31, the force and displacement require-

ments of Section 13.3 shall be used. Materials

meeting the toughness requirements of ASME B31

shall be considered high-deformability materials.

13.6.8.2 Fire Protection Sprinkler Piping Systems

Fire protection sprinkler piping, pipe hangers, and

bracing designed and constructed in accordance with

NFPA 13 shall be deemed to meet the force and

displacement requirements of this section. The

exceptions of Section 13.6.8.3 shall not apply.

13.6.8.3 Exceptions

Design of piping systems and attachments for the

seismic forces and relative displacements of Section

13.3 shall not be required where one of the following

conditions apply:

1. Trapeze assemblies are used to support piping

whereby no single pipe exceeds the limits set forth

in 3a, 3b, or 3c below and the total weight of the

piping supported by the trapeze assemblies is less

than 10 lb/ft (146 N/m).

2. The piping is supported by hangers and each

hanger in the piping run is 12 in. (305 mm) or less

in length from the top of the pipe to the supporting

structure. Where pipes are supported on a trapeze,

the trapeze shall be supported by hangers having a

length of 12 in. (305 mm) or less. Where rod

hangers are used, they shall be equipped with

swivels, eye nuts, or other devices to prevent

bending in the rod.

3. Piping having an R

in Table 13.6-1 of 4.5 or

greater is used and provisions are made to avoid

impact with other structural or nonstructural

components or to protect the piping in the event of

such impact and where the following size require-

ments are satisﬁ ed:

a. For Seismic Design Category C where I

greater than 1.0, the nominal pipe size shall be

2 in. (50 mm) or less.

b. For Seismic Design Categories D, E, or F and

values of I

are greater than 1.0, the nominal

pipe size shall be 1 in. (25 mm) or less.

c. For Seismic Design Categories D, E, or F where

= 1.0, the nominal pipe size shall be 3 in.

(80 mm) or less.

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125

13.6.9 Boilers and Pressure Vessels

Boilers or pressure vessels designed and con-

structed in accordance with ASME BPVC shall be

deemed to meet the force, displacement, and other

requirements of this section. In lieu of the speciﬁ c force

and displacement requirements provided in the ASME

BPVC, the force and displacement requirements of

Sections 13.3.1 and 13.3.2 shall be used. Materials

meeting the toughness requirements of ASME BPVC

shall be considered high-deformability materials. Other

boilers and pressure vessels designated as having an I

= 1.5, but not designed and constructed in accordance

with the requirements of ASME BPVC, shall comply

with the requirements of Section 13.6.11.

13.6.10 Elevator and Escalator Design

Requirements

Elevators and escalators designed in accordance

with the seismic requirements of ASME A17.1 shall

be deemed to meet the seismic force requirements of

this section, except as modiﬁ ed in the following text.

The exceptions of Section 13.6.8.3 shall not apply to

elevator piping.

13.6.10.1 Escalators, Elevators, and Hoistway

Structural System

Escalators, elevators, and hoistway structural

systems shall be designed to meet the force and dis-

placement requirements of Sections 13.3.1 and 13.3.2.

13.6.10.2 Elevator Equipment and Controller

Supports and Attachments

Elevator equipment and controller supports and

attachments shall be designed to meet the force and

displacement requirements of Sections 13.3.1 and

13.3.2.

13.6.10.3 Seismic Controls for Elevators

Elevators operating with a speed of 150 ft/min

(46 m/min) or greater shall be provided with seismic

switches. Seismic switches shall provide an electric

signal indicating that structural motions are of such a

magnitude that the operation of the elevators may be

impaired. Seismic switches in accordance with

Section 8.4.10.1.2 of ASME A17.1 shall be deemed to

meet the requirements of this section.

EXCEPTION: In cases where seismic switches

cannot be located near a column in accordance with

ASME A17.1, they shall have two horizontal axes of

sensitivity and have a trigger level set to 20 percent of

the acceleration of gravity where located at or near

the base of the structure and 50 percent of the

acceleration of gravity in all other locations.

Upon activation of the seismic switch, elevator

operations shall conform to requirements of ASME

A17.1, except as noted in the following text.

In facilities where the loss of the use of an elevator

is a life-safety issue, the elevator shall only be used

after the seismic switch has triggered provided that:

1. The elevator shall operate no faster than the service

speed.

2. Before the elevator is occupied, it is operated from

top to bottom and back to top to verify that it is

operable.

13.6.10.4 Retainer Plates

Retainer plates are required at the top and bottom

of the car and counterweight.

13.6.11 Other Mechanical and

Electrical Components

Mechanical and electrical components, including

conveyor systems, not designed and constructed in

accordance with the reference documents in Chapter

23 shall meet the following:

1. Components, their supports and attachments shall

comply with the requirements of Sections 13.4,

13.6.3, 13.6.4, and 13.6.5.

2. For mechanical components with hazardous

substances and assigned a component importance

factor, I

, of 1.5 in accordance with Section 13.1.3,

and for boilers and pressure vessels not designed in

accordance with ASME BPVC, the design strength

for seismic loads in combination with other service

loads and appropriate environmental effects shall

be based on the following material properties:

a. For mechanical components constructed with

ductile materials (e.g., steel, aluminum, or

copper), 90 percent of the minimum speciﬁ ed

yield strength.

b. For threaded connections in components

constructed with ductile materials, 70 percent of

the minimum speciﬁ ed yield strength.

c. For mechanical components constructed with

nonductile materials (e.g., plastic, cast iron, or

ceramics), 10 percent of the material minimum

speciﬁ ed tensile strength.

d. For threaded connections in components

constructed with nonductile materials,

8 percent of the material minimum speciﬁ ed

tensile strength.

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127

Chapter 14

MATERIAL SPECIFIC SEISMIC DESIGN AND

DETAILING REQUIREMENTS

14.1.2.2 Seismic Requirements for Structural

Steel Structures

The design of structural steel structures to resist

seismic forces shall be in accordance with the provi-

sions of Section 14.1.2.2.1 or 14.1.2.2.2, as applicable.

14.1.2.2.1 Seismic Design Categories B and C

Structural steel structures assigned to Seismic Design

Category B or C shall be of any construction permit-

ted by the applicable reference documents in Section

14.1.1. Where a response modiﬁ cation coefﬁ cient, R,

in accordance with Table 12.2-1 is used for the design

of structural steel structures assigned to Seismic

Design Category B or C, the structures shall be

designed and detailed in accordance with the require-

ments of AISC 341.

EXCEPTION: The response modiﬁ cation

coefﬁ cient, R, designated for “Steel systems not

speciﬁ cally detailed for seismic resistance, excluding

cantilever column systems” in Table 12.2-1 shall be

permitted for systems designed and detailed in

accordance with AISC 360 and need not be designed

and detailed in accordance with AISC 341.

14.1.2.2.2 Seismic Design Categories D through F

Structural steel structures assigned to Seismic Design

Category D, E, or F shall be designed and detailed in

accordance with AISC 341, except as permitted in

Table 15.4-1.

14.1.3 Cold-Formed Steel

14.1.3.1 General

The design of cold-formed carbon or low-alloy

steel structural members shall be in accordance with

the requirements of AISI S100 and the design of

cold-formed stainless steel structural members shall

be in accordance with the requirements of ASCE 8.

Where required, the seismic design of cold-formed

steel structures shall be in accordance with the

additional provisions of Section 14.1.3.2.

14.1.3.2 Seismic Requirements for Cold-Formed

Steel Structures

Where a response modiﬁ cation coefﬁ cient, R, in

accordance with Table 12.2-1 is used for the design of

14.0 SCOPE

Structural elements including foundation elements

shall conform to the material design and detailing

requirements set forth in this chapter or as otherwise

speciﬁ ed for non-building structures in Tables 15.4-1

and 15.4-2.

14.1 STEEL

Structures, including foundations, constructed of steel

to resist seismic loads shall be designed and detailed

in accordance with this standard including the

reference documents and additional requirements

provided in this section.

14.1.1 Reference Documents

The design, construction, and quality of steel

members that resist seismic forces shall conform to

the applicable requirements, as amended herein, of the

following:

1. AISC 360

2. AISC 341

3. AISI S100

4. AISI S110

5. AISI S230

6. AISI S213

7. ASCE 19

8. ASCE 8

9. SJI-K-1.1

10. SJI-LH/DLH-1.1

11. SJI-JG-1.1

12. SJI-CJ-1.0

14.1.2 Structural Steel

14.1.2.1 General

The design of structural steel for buildings and

structures shall be in accordance with AISC 360.

Where required, the seismic design of structural steel

structures shall be in accordance with the additional

provisions of Section 14.1.2.2.

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128

cold-

formed steel structures, the structures shall be

designed and detailed in accordance with the require-

ments of AISI S100, ASCE 8, and AISI S110 as

modiﬁ ed in Section 14.1.3.3.

14.1.3.3 Modiﬁ cations to AISI S110

The text of AISI S110 shall be modiﬁ ed as

indicated in Sections 14.1.3.3.1 through 14.1.3.3.5.

Italics are used for text within Sections 14.1.3.3.1

through 14.1.3.3.5 to indicate requirements that differ

from AISI S110.

14.1.3.3.1 AISI S110, Section D1 Modify Section D1

to read as follows:

D1 Cold-Formed Steel Special Bolted Moment

Frames (CFS-SBMF)

Cold-formed steel–special bolted moment frame

(CFS-SBMF) systems shall withstand signiﬁ cant

inelastic deformations through friction and bearing at

their bolted connections. Beams, columns, and

connections shall satisfy the requirements in this

section. CFS-SBMF systems shall be limited to one-

story structures, no greater than 35 feet in height,

without column splices and satisfying the

requirements in this section. The CFS-SBMF shall

engage all columns supporting the roof or ﬂ oor

above. The single size beam and single size column

with the same bolted moment connection detail shall

be used for each frame. The frame shall be supported

on a level ﬂ oor or foundation.

14.1.3.3.2 AISI S110, Section D1.1.1 Modify Section

D1.1.1 to read as follows:

D1.1.1 Connection Limitations

Beam-to-column connections in CFS-SBMF

systems shall be bolted connections with snug-tight

high-strength bolts. The bolt spacing and edge

distance shall be in accordance with the limits of AISI

S100, Section E3. The 8-bolt conﬁ guration shown in

Table D1-1 shall be used. The faying surfaces of the

beam and column in the bolted moment connection

region shall be free of lubricants or debris.

14.1.3.3.3 AISI S110, Section D1.2.1 Modify

Section D1.2.1 and add new Section D1.2.1.1 to

read as follows:

D1.2.1 Beam Limitations

In addition to the requirements of Section D1.2.3,

beams in CFS-SBMF systems shall be ASTM A653

galvanized 55 ksi (374 MPa) yield stress cold-formed

steel C-section members with lips, and designed in

accordance with Chapter C of AISI S100. The beams

shall have a minimum design thickness of 0.105 in.

(2.67 mm). The beam depth shall be not less than 12

in. (305 mm) or greater than 20 in. (508 mm). The

ﬂ at depth-to-thickness ratio of the web shall not

exceed 6.18

D1.2.1.1 Single-Channel Beam Limitations

When single-channel beams are used, torsional

effects shall be accounted for in the design.

14.1.3.3.4 AISI S110, Section D1.2.2 Modify Section

D1.2.2 to read as follows:

D1.2.2 Column Limitations

In addition to the requirements of D1.2.3,

columns in CFS-SBMF systems shall be ASTM A500

Grade B cold-formed steel hollow structural section

(HSS) members painted with a standard industrial

ﬁ nished surface, and designed in accordance with

Chapter C of AISI S100. The column depth shall be

not less than 8 in. (203 mm) or greater than 12 in.

(305 mm). The ﬂ at depth-to-thickness ratio shall not

exceed 1.40

14.1.3.3.5 AISI S110, Section D1.3 Delete text in

Section D1.3 to read as follows:

D1.3 Design Story Drift

Where the applicable building code does not

contain design coefﬁ cients for CSF-SBMF systems,

the provisions of Appendix 1 shall apply.

For structures having a period less than T

, as

deﬁ ned in the applicable building code, alternate

methods of computing Δ shall be permitted, provided

such alternate methods are acceptable to the authority

having jurisdiction.

14.1.4 Cold-Formed Steel

Light-Frame Construction

14.1.4.1 General

Cold-formed steel light-frame construction shall

be designed in accordance with AISI S100, Section

D4. Where required, the seismic design of cold-

formed steel light-frame construction shall be in

accordance with the additional provisions of Section

14.1.4.2.

14.1.4.2 Seismic Requirements for Cold-Formed

Steel Light-Frame Construction

Where a response modiﬁ cation coefﬁ cient, R, in

accordance with Table 12.2-1 is used for the design of

cold-formed steel light-frame construction, the

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MINIMUM DESIGN LOADS

129

structures shall be designed and detailed in accor-

dance with the requirements of AISI S213.

14.1.4.3 Prescriptive Cold-Formed Steel

Light-Frame Construction

Cold-formed steel light-frame construction for

one- and two-family dwellings is permitted to be

designed and constructed in accordance with the

requirements of AISI S230 subject to the limitations

therein.

14.1.5 Steel Deck Diaphragms

Steel deck diaphragms shall be made from

materials conforming to the requirements of AISI

S100 or ASCE 8. Nominal strengths shall be deter-

mined in accordance with approved analytical

procedures or with test procedures prepared by a

registered design professional experienced in testing

of cold-formed steel assemblies and approved by the

authority having jurisdiction. The required strength of

diaphragms, including bracing members that form part

of the diaphragm, shall be determined in accordance

with Section 12.10.1. The steel deck installation for

the building, including fasteners, shall comply with

the test assembly arrangement. Quality standards

established for the nominal strength test shall be the

minimum standards required for the steel deck

installation, including fasteners.

14.1.6 Steel Cables

The design strength of steel cables shall be

determined by the requirements of ASCE 19 except as

modiﬁ ed by this chapter. ASCE 19, Section 3.1.2(d),

shall be modiﬁ ed by substituting 1.5(T

) where T

the net tension in cable due to dead load, prestress,

live load, and seismic load. A load factor of 1.1 shall

be applied to the prestress force to be added to the

load combination of Section 3.1.2 of ASCE 19.

14.1.7 Additional Detailing Requirements for Steel

Piles in Seismic Design Categories D through F

In addition to the foundation requirements set

forth in Sections 12.1.5 and 12.13, design and

detailing of H-piles shall conform to the requirements

of AISC 341, and the connection between the pile cap

and steel piles or unﬁ lled steel pipe piles in structures

assigned to Seismic Design Category D, E, or F shall

be designed for a tensile force not less than 10 percent

of the pile compression capacity.

EXCEPTION: Connection tensile capacity need

not exceed the strength required to resist seismic load

effects including overstrength factor of Section

12.4.3.2 or Section 12.14.2.2.2. Connections need not

be provided where the foundation or supported

structure does not rely on the tensile capacity of the

piles for stability under the design seismic forces.

14.2 CONCRETE

Structures, including foundations, constructed of

concrete to resist seismic loads shall be designed and

detailed in accordance with this standard including the

reference documents and additional requirements

provided in this section.

14.2.1 Reference Documents

The quality and testing of concrete materials and

the design and construction of structural concrete

members that resist seismic forces shall conform to

the requirements of ACI 318, except as modiﬁ ed in

Section 14.2.2.

14.2.2 Modiﬁ cations to ACI 318

The text of ACI 318 shall be modiﬁ ed as indi-

cated in Sections 14.2.2.1 through 14.2.2.9. Italics

are used for text within Sections 14.2.2.1 through

14.2.2.9 to indicate requirements that differ from

ACI 318.

14.2.2.1 Deﬁ nitions

Add the following deﬁ nitions to Section 2.2.

DETAILED PLAIN CONCRETE

STRUCTURAL WALL: A wall complying with the

requirements of Chapter 22.

ORDINARY PRECAST STRUCTURAL WALL:

A precast wall complying with the requirements of

Chapters 1 through 18.

WALL PIER: A wall segment with a horizontal

length-to-thickness ratio of at least 2.5, but not

exceeding 6, whose clear height is at least two times

its horizontal length.

14.2.2.2 ACI 318, Section 7.10

Modify Section 7.10 by revising Section 7.10.5.6

to read as follows:

7.10.5.6 Where anchor bolts are placed in the top

of columns or pedestals, the bolts shall be enclosed by

lateral reinforcement that also surrounds at least four

vertical bars of the column or pedestal. The lateral

reinforcement shall be distributed within 5 in. of the

top of the column or pedestal, and shall consist of at

least two No. 4 or three No. 3 bars. In structures

assigned to Seismic Design Categories C, D, E, or F,

the ties shall have a hook on each free end that

complies with 7.1.4.

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CHAPTER 14 MATERIAL SPECIFIC SEISMIC DESIGN AND DETAILING REQUIREMENTS

130

14.2.2.3 Scope

Modify Section

21.1.1.3 to read as follows:

21.1.1.3 All members shall satisfy requirements

of Chapters 1 to 19 and 22. Structures assigned to

SDC B, C, D, E, or F also shall satisfy 21.1.1.4 through

21.1.1.8, as applicable, except as modiﬁ ed by the

requirements of Chapters 14 and 15 of this standard.

14.2.2.4 Intermediate Precast Structural Walls

Modify Section 21.4 by renumbering Section

21.4.3 to Section 21.4.4 and adding new Sections

21.4.3, 21.4.5, and 21.4.6 to read as follows:

21.4.3 Connections that are designed to yield

shall be capable of maintaining 80 percent of their

design strength at the deformation induced by design

displacement, or shall use type 2 mechanical splices.

21.4.4 Elements of the connection that are not

designed to yield shall develop at least 1.5 S

21.4.5 Wall piers in structures assigned to SDC

D, E, or F shall comply with Section 14.2.2.4 of this

standard.

21.4.6 Wall piers not designed as part of a

moment frame in SDC C shall have transverse

reinforcement designed to resist the shear forces

determined from Section 21.3.3. Spacing of transverse

reinforcement shall not exceed 8 in. Transverse

reinforcement shall be extended beyond the pier clear

height for at least 12 in.

EXCEPTIONS: The preceding requirement need

not apply in the following situations:

1. Wall piers that satisfy Section 21,13.

2. Wall piers along a wall line within a story where

other shear wall segments provide lateral support

to the wall piers and such segments have a total

stiffness of at least six times the sum of the

stiffnesses of all the wall piers.

Wall segments with a horizontal length-to-thickness

ratio less than 2.5 shall be designed as columns.

14.2.2.5 Wall Piers and Wall Segments

Modify Section 21.9 by adding a new Section

21.9.10 to read as follows:

21.9.10 Wall Piers and Wall Segments.

21.9.10.1 Wall piers not designed as a part of a

special moment-resisting frame shall have transverse

reinforcement designed to satisfy the requirements in

Section 21.9.10.2.

EXCEPTIONS:

1. Wall piers that satisfy Section 21.13.

2. Wall piers along a wall line within a story where

other shear wall segments provide lateral support

to the wall piers, and such segments have a total

stiffness of at least six times the sum of the

in-plane stiffnesses of all the wall piers.

21.9.10.2 Transverse reinforcement with seismic

hooks at both ends shall be designed to resist the

shear forces determined from Section 21.6.5.1.

Spacing of transverse reinforcement shall not exceed

6 in. (152 mm). Transverse reinforcement shall be

extended beyond the pier clear height for at least 12

in. (304 mm).

21.9.10.3 Wall segments with a horizontal length-

to-thickness ratio less than 2.5 shall be designed as

columns.

14.2.2.6 Special Precast Structural Walls

Modify Section 21.10.2 to read as follows:

21.10.2 Special structural walls constructed using

precast concrete shall satisfy all requirements of

Section 21.9 in addition to Section 21.4 as modiﬁ ed

by Section 14.2.2.

14.2.2.7 Foundations

Modify Section 21.12.1.1 to read as follows:

21.12.1.1 Foundations resisting earthquake-

induced forces or transferring earthquake-induced

forces between structure and ground in structures

assigned to SDC D, E, or F shall comply with

requirements of Section 21.12 and other applicable

code provisions unless modiﬁ ed by Sections 12.1.5,

12.13, or 14.2 of ASCE 7.

14.2.2.8 Detailed Plain Concrete Shear Walls

Modify Section 22.6 by adding a new Section

22.6.7 to read

22.6.7 Detailed Plain Concrete Shear Walls.

22.6.7.1 Detailed plain concrete shear walls are

walls conforming to the requirements for ordinary

plain concrete shear walls and Section 22.6.7.2.

22.6.7.2 Reinforcement shall be provided as

follows:

a. Vertical reinforcement of at least 0.20 in.

(129

) in cross-sectional area shall be provided

continuously from support to support at each

corner, at each side of each opening, and at the

ends of walls. The continuous vertical bar required

beside an opening is permitted to substitute for the

No. 5 bar required by Section 22.6.6.5.

b. Horizontal reinforcement at least 0.20 in.

(129

) in cross-sectional area shall be provided:

1. Continuously at structurally connected roof and

ﬂ oor levels and at the top of walls.

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MINIMUM DESIGN LOADS

131

2. At the bottom of load-bearing walls or in the

top of foundations where doweled to the wall.

3. At a maximum spacing of 120 in. (3,048 mm).

Reinforcement at the top and bottom of openings,

where used in determining the maximum spacing

speciﬁ ed in Item 3 in the preceding text, shall be

continuous in the wall.

14.2.2.9 Strength Requirements for Anchors

Modify Section D.4 by adding a new exception at

the end of Section D.4.2.2 to read as follows:

EXCEPTION: If N

is determined using Eq.

D-7, the concrete breakout strength of Section D.4.2

shall be considered satisﬁ ed by the design procedure

of Sections D.5.2 and D.6.2 without the need for

testing regardless of anchor bolt diameter and tensile

embedment.

14.2.3 Additional Detailing Requirements for

Concrete Piles

In addition to the foundation requirements set

forth in Sections 12.1.5 and 12.13 of this standard and

in Section 21.12 of ACI 318, design, detailing, and

construction of concrete piles shall conform to the

requirements of this section.

14.2.3.1 Concrete Pile Requirements for Seismic

Design Category C

Concrete piles in structures assigned to Seismic

Design Category C shall comply with the require-

ments of this section.

14.2.3.1.1 Anchorage of Piles All concrete piles and

concrete-ﬁ lled pipe piles shall be connected to the pile

cap by embedding the pile reinforcement in the pile

cap for a distance equal to the development length as

speciﬁ ed in ACI 318 as modiﬁ ed by Section 14.2.2 of

this standard or by the use of ﬁ eld-placed dowels

anchored in the concrete pile. For deformed bars, the

development length is the full development length for

compression or tension, in the case of uplift, without

reduction in length for excess area.

Hoops, spirals, and ties shall be terminated with

seismic hooks as deﬁ ned in Section 2.2 of ACI 318.

Where a minimum length for reinforcement or

the extent of closely spaced conﬁ nement reinforce-

ment is speciﬁ ed at the top of the pile, provisions

shall be made so that those speciﬁ ed lengths or

extents are maintained after pile cutoff.

14.2.3.1.2 Reinforcement for Uncased Concrete Piles

(SDC C) Reinforcement shall be provided where

required by analysis. For uncased cast-in-place drilled

or augered concrete piles, a minimum of four longitu-

dinal bars, with a minimum longitudinal reinforce-

ment ratio of 0.0025, and transverse reinforcement, as

deﬁ ned below, shall be provided throughout the

minimum reinforced length of the pile as deﬁ ned

below starting at the top of the pile. The longitudinal

reinforcement shall extend beyond the minimum

reinforced length of the pile by the tension develop-

ment length. Transverse reinforcement shall consist of

closed ties (or equivalent spirals) with a minimum 3/8

in. (9 mm) diameter. Spacing of transverse reinforcing

shall not exceed 6 in. (150 mm) or 8 longitudinal-bar

diameters within a distance of three times the pile

diameter from the bottom of the pile cap. Spacing of

transverse reinforcing shall not exceed 16 longitudi-

nal-bar diameters throughout the remainder of the

minimum reinforced length.

The minimum reinforced length of the pile shall

be taken as the greater of

1. One-third of the pile length.

2. A distance of 10 ft (3 m).

3. Three times the pile diameter.

4. The ﬂ exural length of the pile, which shall be

taken as the length from the bottom of the pile cap

to a point where the concrete section cracking

moment multiplied by a resistance factor 0.4

exceeds the required factored moment at that point.

14.2.3.1.3 Reinforcement for Metal-Cased Concrete

Piles (SDC C) Reinforcement requirements are the

same as for uncased concrete piles.

EXCEPTION: Spiral-welded metal casing of a

thickness not less than No. 14 gauge can be

considered as providing concrete conﬁ nement

equivalent to the closed ties or equivalent spirals

required in an uncased concrete pile, provided that the

metal casing is adequately protected against possible

deleterious action due to soil constituents, changing

water levels, or other factors indicated by boring

records of site conditions.

14.2.3.1.4 Reinforcement for Concrete-Filled Pipe

Piles (SDC C) Minimum reinforcement 0.01 times the

cross-sectional area of the pile concrete shall be

provided in the top of the pile with a length equal to

two times the required cap embedment anchorage into

the pile cap.

14.2.3.1.5 Reinforcement for Precast Nonprestressed

Concrete Piles (SDC C) A minimum longitudinal

steel reinforcement ratio of 0.01 shall be provided for

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CHAPTER 14 MATERIAL SPECIFIC SEISMIC DESIGN AND DETAILING REQUIREMENTS

132

precast nonprestressed concrete piles. The longitudinal

reinforcing shall be conﬁ ned with closed ties or

equivalent spirals of a minimum 3/8 in. (10 mm)

diameter. Transverse conﬁ nement reinforcing shall be

provided at a maximum spacing of eight times the

diameter of the smallest longitudinal bar, but not to

exceed 6 in. (152 mm), within three pile diameters of

the bottom of the pile cap. Outside of the conﬁ nement

region, closed ties or equivalent spirals shall be

provided at a 16 longitudinal-bar-diameter maximum

spacing, but not greater than 8 in. (200 mm). Rein-

forcement shall be full length.

14.2.3.1.6 Reinforcement for Precast Prestressed Piles

(SDC C) For the upper 20 ft (6 m) of precast pre-

stressed piles, the minimum volumetric ratio of spiral

reinforcement shall not be less than 0.007 or the

amount required by the following equation:

′

012.

(14.2-1)

where

= volumetric ratio (vol. spiral/vol. core)

′ = speciﬁ ed compressive strength of concrete, psi

(MPa)

= speciﬁ ed yield strength of spiral reinforcement,

which shall not be taken greater than 85,000 psi

(586 MPa)

A minimum of one-half of the volumetric ratio of

spiral reinforcement required by Eq. 14.2-1 shall be

provided for the remaining length of the pile.

14.2.3.2 Concrete Pile Requirements for Seismic

Design Categories D through F

Concrete piles in structures assigned to Seismic

Design Category D, E, or F shall comply with the

requirements of this section.

14.2.3.2.1 Site Class E or F Soil Where concrete piles

are used in Site Class E or F, they shall have trans-

verse reinforcement in accordance with Sections

21.6.4.2 through 21.6.4.4 of ACI 318 within seven

pile diameters of the pile cap and of the interfaces

between strata that are hard or stiff and strata that are

liqueﬁ able or are composed of soft to medium stiff

clay.

14.2.3.2.2 Nonapplicable ACI 318 Sections for Grade

Beam and Piles Section 21.12.3.3 of ACI 318 need

not apply to grade beams designed to resist the

seismic load effects including overstrength factor of

Section 12.4.3 or 12.14.3.2. Section 21.12.4.4(a) of

ACI 318 need not apply to concrete piles. Section

21.12.4.4(b) of ACI 318 need not apply to precast,

prestressed concrete piles.

14.2.3.2.3 Reinforcement for Uncased Concrete Piles

(SDC D through F) Reinforcement shall be provided

where required by analysis. For uncased cast-in-place

drilled or augered concrete piles, a minimum of four

longitudinal bars with a minimum longitudinal

reinforcement ratio of 0.005 and transverse conﬁ ne-

ment reinforcement in accordance with Sections

21.6.4.2 through 21.6.4.4 of ACI 318 shall be pro-

vided throughout the minimum reinforced length of

the pile as deﬁ ned below starting at the top of the

pile. The longitudinal reinforcement shall extend

beyond the minimum reinforced length of the pile by

the tension development length.

The minimum reinforced length of the pile shall

be taken as the greater of

1. One-half of the pile length.

2. A distance of 10 ft (3 m).

3. Three times the pile diameter.

4. The ﬂ exural length of the pile, which shall be

taken as the length from the bottom of the pile cap

to a point where the concrete section cracking

moment multiplied by a resistance factor 0.4

exceeds the required factored moment at that point.

In addition, for piles located in Site Classes E or

F, longitudinal reinforcement and transverse conﬁ ne-

ment reinforcement, as described above, shall extend

the full length of the pile.

Where transverse reinforcing is required, trans-

verse reinforcing ties shall be a minimum of No. 3

bars for up to 20-in.-diameter (500 mm) piles and No.

4 bars for piles of larger diameter.

In Site Classes A through D, longitudinal

reinforcement and transverse conﬁ nement reinforce-

ment, as deﬁ ned above, shall also extend a minimum

of seven times the pile diameter above and below the

interfaces of soft to medium stiff clay or liqueﬁ able

strata except that transverse reinforcing not located

within the minimum reinforced length shall be

permitted to use a transverse spiral reinforcement ratio

of not less than one-half of that required in Section

21.6.4.4(a) of ACI 318. Spacing of transverse rein-

forcing not located within the minimum reinforced

length is permitted to be increased, but shall not

exceed the least of the following:

1. 12 longitudinal bar diameters.

2. One-half the pile diameter.

3. 12 in. (300 mm).

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MINIMUM DESIGN LOADS

133

14.2.3.2.4 Reinforcement for Metal-Cased Concrete

Piles (SDC D through F) Reinforcement requirements

are the same as for uncased concrete piles.

EXCEPTION: Spiral-welded metal casing of a

thickness not less than No. 14 gauge can be

considered as providing concrete conﬁ nement

equivalent to the closed ties or equivalent spirals

required in an uncased concrete pile, provided that the

metal casing is adequately protected against possible

deleterious action due to soil constituents, changing

water levels, or other factors indicated by boring

records of site conditions.

14.2.3.2.5 Reinforcement for Precast Concrete Piles

(SDC D through F) Transverse conﬁ nement reinforce-

ment consisting of closed ties or equivalent spirals

shall be provided in accordance with Sections 21.6.4.2

through 21.6.4.4 of ACI 318 for the full length of the

pile.

EXCEPTION: In other than Site Classes E or F,

the speciﬁ ed transverse conﬁ nement reinforcement

shall be provided within three pile diameters below

the bottom of the pile cap, but it is permitted to use a

transverse reinforcing ratio of not less than one-half

of that required in Section 21.6.4.4(a) of ACI 318

throughout the remainder of the pile length.

14.2.3.2.6 Reinforcement for Precast Prestressed Piles

(SDC D through F) In addition to the requirements

for Seismic Design Category C, the following

requirements shall be met:

1. Requirements of ACI 318, Chapter 21, need not

apply.

2. Where the total pile length in the soil is 35 ft

(10,668 mm) or less, the ductile pile region shall

be taken as the entire length of the pile. Where the

pile length exceeds 35 ft (10,668 mm), the ductile

pile region shall be taken as the greater of 35 ft

(10,668 mm) or the distance from the underside of

the pile cap to the point of zero curvature plus

three times the least pile dimension.

3. In the ductile pile region, the center to center

spacing of the spirals or hoop reinforcement shall

not exceed one-ﬁ fth of the least pile dimension, six

times the diameter of the longitudinal strand, or 8

in. (203 mm), whichever is smaller.

4. Spiral reinforcement shall be spliced by lapping

one full turn, by welding, or by the use of a

mechanical connector. Where spiral reinforcement

is lap spliced, the ends of the spiral shall terminate

in a seismic hook in accordance with ACI 318,

except that the bend shall be not less than 135°.

Welded splices and mechanical connectors shall

comply with Section 12.14.3 of ACI 318.

5. Where the transverse reinforcement consists of

spirals or circular hoops, the volumetric ratio of

spiral transverse reinforcement in the ductile pile

region shall comply with

ch c g

′

⎛

⎝

⎜

⎞

⎠

⎟

−

⎛

⎝

⎜

⎞

⎠

⎟

′

⎡

⎣

⎢

⎤

⎦

⎥

025 10 05

...

but not less than

yh c g

′

⎛

⎝

⎜

⎞

⎠

⎟

′

⎡

⎣

⎢

⎤

⎦

⎥

012 05

and ρ

need not exceed 0.021 where

= volumetric ratio (vol. of spiral/vol. of core)

′ ≤ 6,000 psi (41.4 MPa)

= yield strength of spiral reinforcement ≤ 85

ksi (586 MPa)

= pile cross-sectional area, in.

(mm

)

= core area deﬁ ned by spiral outside diameter,

in.

(mm

)

P = axial load on pile resulting from the load

combination 1.2D + 0.5L + 1.0E, lb (kN)

This required amount of spiral reinforcement is

permitted to be obtained by providing an inner and

outer spiral.

6. Where transverse reinforcement consists of

rectangular hoops and cross ties, the total cross-

sectional area of lateral transverse reinforcement in

the ductile region with spacing, s, and perpendicu-

lar to dimension, h

, shall conform to

Ash

sh c

ch c g

′

⎛

⎝

⎜

⎞

⎠

⎟

−

⎛

⎝

⎜

⎞

⎠

⎟

′

⎡

⎣

⎢

⎤

⎦

⎥

03 10 05

...

but not less than

Ash

sh c

yh c g

′

⎛

⎝

⎜

⎞

⎠

⎟

′

⎡

⎣

⎢

⎤

⎦

⎥

012 05

where

s = spacing of transverse reinforcement measured

along length of pile, in. (mm)

= cross-sectional dimension of pile core mea-

sured center to center of hoop reinforcement,

in. (mm)

≤ 70 ksi (483 MPa)

The hoops and cross ties shall be equivalent to

deformed bars not less than No. 3 in size. Rectan-

gular hoop ends shall terminate at a corner with

seismic hooks.

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CHAPTER 14 MATERIAL SPECIFIC SEISMIC DESIGN AND DETAILING REQUIREMENTS

134

7. Outside of the ductile pile region, the spiral or

hoop reinforcement with a volumetric ratio not less

than one-half of that required for transverse

conﬁ nement reinforcement shall be provided.

14.3 COMPOSITE STEEL AND

CONCRETE STRUCTURES

Structures, including foundations, constructed of

composite steel and concrete to resist seismic loads

shall be designed and detailed in accordance with this

standard, including the reference documents and

additional requirements provided in this section.

14.3.1 Reference Documents

The design, construction, and quality of compos-

ite steel and concrete members that resist seismic

forces shall conform to the applicable requirements of

the following:

1. AISC 341

2. AISC 360

3. ACI 318, excluding Chapter 22

14.3.2 General

Systems of structural steel acting compositely

with reinforced concrete shall be designed in accor-

dance with AISC 360 and ACI 318, excluding

Chapter 22. Where required, the seismic design of

composite steel and concrete systems shall be in

accordance with the additional provisions of Section

14.3.3.

14.3.3 Seismic Requirements for Composite Steel

and Concrete Structures

Where a response modiﬁ cation coefﬁ cient, R, in

accordance with Table 12.2-1 is used for the design of

systems of structural steel acting compositely with

reinforced concrete, the structures shall be designed

and detailed in accordance with the requirements of

AISC 341.

14.3.4 Metal-Cased Concrete Piles

Metal-cased concrete piles shall be designed and

detailed in accordance with Section 14.2.3.2.4.

14.4 MASONRY

Structures, including foundations, constructed of

masonry to resist seismic loads shall be designed and

detailed in accordance with this standard, including

the references and additional requirements provided in

this section.

14.4.1 Reference Documents

The design, construction, and quality assurance of

masonry members that resist seismic forces shall

conform to the requirements of TMS 402/ACI 530/

ASCE 5 and TMS 602/ACI 530.1/ASCE 6, except as

modiﬁ ed by Section 14.4.

14.4.2 R factors

To qualify for the response modiﬁ cation coefﬁ -

cients, R, set forth in this standard, the requirements

of TMS 402/ACI 530/ASCE 5 and TMS 602/ACI

530.1/ASCE 6, as amended in subsequent sections,

shall be satisﬁ ed.

Intermediate and special reinforced masonry

shear walls designed in accordance with Section 2.3

of TMS 402/ACI 530/ASCE 5 shall also comply with

the additional requirements contained in Section

14.4.4.

14.4.3 Modiﬁ cations to Chapter 1 of TMS 402/ACI

530/ASCE 5

14.4.3.1 Separation Joints

Add the following new Section 1.19.3 to TMS

402/ACI 530/ASCE 5:

1.19.3 Separation Joints. Where concrete abuts

structural masonry and the joint between the

materials is not designed as a separation joint, the

concrete shall be roughened so that the average

height of aggregate exposure is 1/8 in. (3 mm) and

shall be bonded to the masonry in accordance with

these requirements as if it were masonry. Vertical

joints not intended to act as separation joints shall be

crossed by horizontal reinforcement as required by

Section 1.9.4.2.

14.4.4 Modiﬁ cations to Chapter 2 of TMS

402/ACI 530/ASCE 5

14.4.4.1 Stress Increase

If the increase in stress given in Section 2.1.2.3

of TMS 402/ACI 530/ASCE 5 is used, the restriction

on load reduction in Section 2.4.1 of this standard

shall be observed.

14.4.4.2 Reinforcement Requirements and Details

14.4.4.2.1 Reinforcing Bar Size Limitations Reinforc-

ing bars used in masonry shall not be larger than No.

9 (M#29). The nominal bar diameter shall not exceed

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MINIMUM DESIGN LOADS

135

one-eighth of the nominal member thickness and shall

not exceed one-quarter of the least clear dimension of

the cell, course, or collar joint in which it is placed.

The area of reinforcing bars placed in a cell or in a

course of hollow unit construction shall not exceed 4

percent of the cell area.

14.4.4.2.2 Splices Lap splices shall not be used in

plastic hinge zones of special reinforced masonry

shear walls. The length of the plastic hinge zone shall

be taken as at least 0.15 times the distance between

the point of zero moment and the point of maximum

moment. Reinforcement splices shall comply with

TMS 402/ACI 530/ASCE 5 except paragraphs

2.1.9.7.2 and 2.1.9.7.3 shall be modiﬁ ed as follows:

2.1.9.7.2 Welded Splices: A welded splice shall

be capable of developing in tension at least 125

percent of the speciﬁ ed yield strength, f

, of the bar.

Welded splices shall only be permitted for ASTM

A706 steel reinforcement. Welded splices shall not be

permitted in plastic hinge zones of intermediate or

special reinforced walls of masonry.

2.1.9.7.3 Mechanical Connections: Mechanical

splices shall be classiﬁ ed as Type 1 or Type 2

according to Section 21.1.6.1 of ACI 318. Type 1

mechanical splices shall not be used within a plastic

hinge zone or within a beam-wall joint of intermediate

or special reinforced masonry shear wall system.

Type 2 mechanical splices shall be permitted in any

location within a member.

14.4.5 Modiﬁ cations to Chapter 3 of TMS 402/ACI

530/ASCE 5

14.4.5.1 Anchoring to Masonry

Add the following as the ﬁ rst paragraph in

Section 3.1.6 to TMS 402/ACI 530/ASCE 5:

3.1.6 Anchor Bolts Embedded in Grout.

Anchorage assemblies connecting masonry elements

that are part of the seismic force-resisting system to

diaphragms and chords shall be designed so that the

strength of the anchor is governed by steel tensile or

shear yielding. Alternatively, the anchorage assembly

is permitted to be designed so that it is governed by

masonry breakout or anchor pullout provided that the

anchorage assembly is designed to resist not less than

2.5 times the factored forces transmitted by the

assembly.

14.4.5.2 Splices in Reinforcement

Replace Sections 3.3.3.4(b) and 3.3.3.4(c) of

TMS 402/ACI 530/ASCE 5 with the following:

(b) A welded splice shall be capable of developing in

tension at least 125 percent of the speciﬁ ed yield

strength, f

, of the bar. Welded splices shall only

be permitted for ASTM A706 steel reinforcement.

Welded splices shall not be permitted in plastic

hinge zones of intermediate or special reinforced

walls of masonry.

or Type 2 according to Section 21.1.6.1 of ACI

318. Type 1 mechanical splices shall not be

used within a plastic hinge zone or within a

beam-column joint of intermediate or special

reinforced masonry shear walls. Type 2 mechani-

cal splices are permitted in any location within a

member.

Add the following new Section 3.3.3.4.1 to TMS

402/ACI 530/ASCE 5:

3.3.3.4.1 Lap splices shall not be used in plastic

hinge zones of special reinforced masonry shear

walls. The length of the plastic hinge zone shall be

taken as at least 0.15 times the distance between the

point of zero moment and the point of maximum

moment.

14.4.5.3 Coupling Beams

Add the following new Section 3.3.4.2.6 to TMS

402/ACI 530/ASCE 5:

3.3.4.2.6 Coupling Beams. Structural members

that provide coupling between shear walls shall be

designed to reach their moment or shear nominal

strength before either shear wall reaches its moment

or shear nominal strength. Analysis of coupled shear

walls shall comply with accepted principles of

mechanics.

The design shear strength, φV

, of the coupling

beams shall satisfy the following criterion:

φV

≥

()

125

where

and M

= nominal moment strength at the ends of

the beam

= length of the beam between the shear

walls

= unfactored shear force due to gravity

loads

The calculation of the nominal ﬂ exural moment

shall include the reinforcement in reinforced concrete

roof and ﬂ oor systems. The width of the reinforced

concrete used for calculations of reinforcement shall

be six times the ﬂ oor or roof slab thickness.

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CHAPTER 14 MATERIAL SPECIFIC SEISMIC DESIGN AND DETAILING REQUIREMENTS

136

14.4.5.4 Deep Flexural Members

Add the following new Section 3.3.4.2.7 to TMS

402/ACI 530/ASCE 5:

3.3.4.2.7 Deep Flexural Member Detailing.

Flexural members with overall-depth-to-clear-span

ratio greater than 2/5 for continuous spans or 4/5 for

simple spans shall be detailed in accordance with this

section.

3.3.4.2.7.1 Minimum ﬂ exural tension

reinforcement shall conform to Section 3.3.4.3.2.

3.3.4.2.7.2 Uniformly distributed horizontal and

vertical reinforcement shall be provided throughout

the length and depth of deep ﬂ exural members such

that the reinforcement ratios in both directions are at

least 0.001. Distributed ﬂ exural reinforcement is to be

included in the determination of the actual

reinforcement ratios.

14.4.5.5 Walls with Factored Axial Stress Greater

Than 0.05 f

′

Add the following exception following the second

paragraph of Section 3.3.5.3 of TMS 402/ACI 530/

ASCE 5:

EXCEPTION: A nominal thickness of 4 in. (102

mm) is permitted where load-bearing reinforced

hollow clay unit masonry walls satisfy all of the

following conditions.

1. The maximum unsupported height-to-thickness or

length-to-thickness ratios do not exceed 27.

2. The net area unit strength exceeds 8,000 psi (55

MPa).

3. Units are laid in running bond.

4. Bar sizes do not exceed No. 4 (13 mm).

5. There are no more than two bars or one splice in a

cell.

6. Joints are not raked.

14.4.5.6 Shear Keys

Add the following new Section 3.3.6.6 to TMS

402/ACI 530/ASCE 5:

3.3.6.11 Shear Keys. The surface of concrete

upon which a special reinforced masonry shear wall

is constructed shall have a minimum surface

roughness of 1/8 in. (3 mm). Shear keys are required

where the calculated tensile strain in vertical

reinforcement from in-plane loads exceeds the yield

strain under load combinations that include seismic

forces based on an R factor equal to 1.5. Shear keys

that satisfy the following requirements shall be placed

at the interface between the wall and the foundation.

1. The width of the keys shall be at least equal to the

width of the grout space.

2. The depth of the keys shall be at least 1.5 in.

(38 mm).

3. The length of the key shall be at least 6 in.

(152 mm).

4. The spacing between keys shall be at least equal to

the length of the key.

5. The cumulative length of all keys at each end of

the shear wall shall be at least 10 percent of the

length of the shear wall (20 percent total).

6. At least 6 in. (150 mm) of a shear key shall be

placed within 16 in. (406 mm) of each end of the

wall.

7. Each key and the grout space above each key in

the ﬁ rst course of masonry shall be grouted solid.

14.4.6 Modiﬁ cations to Chapter 6 of TMS 402/ACI

530/ASCE 5

14.4.6.1 Corrugated Sheet Metal Anchors

Add Section 6.2.2.10.1 to TMS 402/ACI 530/

ASCE 5 as follows:

6.2.2.10.1 Provide continuous single wire joint

reinforcement of wire size W1.7 (MW11) at a

maximum spacing of 18 in. (457 mm) on center

vertically. Mechanically attach anchors to the joint

reinforcement with clips or hooks. Corrugated sheet

metal anchors shall not be used.

14.4.7 Modiﬁ cations to TMS 602/ACI 530.1/ASCE 6

14.4.7.1 Construction Procedures

Add the following new Article 3.5 I to TMS 602/

ACI 530.1/ASCE 6:

3.5 I. Construction procedures or admixtures

shall be used to facilitate placement and control

shrinkage of grout.

14.5 WOOD

Structures, including foundations, constructed of wood

to resist seismic loads shall be designed and detailed

in accordance with this standard including the

references and additional requirements provided in

this section.

14.5.1 Reference Documents

The quality, testing, design, and construction of

members and their fastenings in wood systems that

resist seismic forces shall conform to the requirements

of the applicable following reference documents,:

1. AF&PA NDS

2. AF&PA SDPWS

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137

14.5.2 Framing

All wood columns and posts shall be framed to

provide full end bearing. Alternatively, column and

post end connections shall be designed to resist the

full compressive loads, neglecting all end-bearing

capacity. Continuity of wall top plates or provision

for transfer of induced axial load forces shall be

provided. Where offsets occur in the wall line,

portions of the shear wall on each side of the offset

shall be considered as separate shear walls unless

provisions for force transfer around the offset are

provided.

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139

Chapter 15

SEISMIC DESIGN REQUIREMENTS FOR

NONBUILDING STRUCTURES

selected in accordance with Section 12.6. Nonbuilding

structures that are not similar to buildings shall be

designed using either the equivalent lateral force

procedure in accordance with Section 12.8, the modal

analysis procedure in accordance with Section 12.9,

the linear response history analysis procedure in

accordance with Section 16.1, the nonlinear response

history analysis procedure in accordance with Section

16.2, or the procedure prescribed in the speciﬁ c

reference document.

15.2 REFERENCE DOCUMENTS

Reference documents referred to in Chapter 15 are

listed in Chapter 23 and have seismic requirements

based on the same force and displacement levels used

in this standard or have seismic requirements that are

speciﬁ cally modiﬁ ed by Chapter 15.

15.3 NONBUILDING STRUCTURES

SUPPORTED BY OTHER STRUCTURES

Where nonbuilding structures identiﬁ ed in Table

15.4-2 are supported by other structures, and the

nonbuilding structures are not part of the primary

seismic force-resisting system, one of the following

methods shall be used.

15.3.1 Less Than 25 percent Combined

Weight Condition

For the condition where the weight of the

nonbuilding structure is less than 25 percent of

the combined effective seismic weights of the

nonbuilding structure and supporting structure, the

design seismic forces of the nonbuilding structure

shall be determined in accordance with Chapter 13

where the values of R

and a

shall be determined

in accordance to Section 13.1.5. The supporting

structure shall be designed in accordance with the

requirements of Chapter 12 or Section 15.5 as

appropriate with the weight of the nonbuilding

structure considered in the determination of the

effective seismic weight, W.

15.1 GENERAL

15.1.1 Nonbuilding Structures

Nonbuilding structures include all self-supporting

structures that carry gravity loads and that may be

required to resist the effects of earthquake, with the

exception of building structures speciﬁ cally excluded

in Section 11.1.2, and other nonbuilding structures

where speciﬁ c seismic provisions have yet to be

developed, and therefore, are not set forth in Chapter

15. Nonbuilding structures supported by the earth or

supported by other structures shall be designed and

detailed to resist the minimum lateral forces speciﬁ ed

in this section. Design shall conform to the applicable

requirements of other sections as modiﬁ ed by this

section. Foundation design shall comply with the

requirements of Sections 12.1.5, 12.13, and

Chapter 14.

15.1.2 Design

The design of nonbuilding structures shall

provide sufﬁ cient stiffness, strength, and ductility

consistent with the requirements speciﬁ ed herein for

buildings to resist the effects of seismic ground

motions as represented by these design forces:

a. Applicable strength and other design criteria shall

be obtained from other portions of the seismic

requirements of this standard or its reference

documents.

b. Where applicable strength and other design criteria

are not contained in, or referenced by the seismic

requirements of this standard, such criteria shall be

obtained from reference documents. Where

reference documents deﬁ ne acceptance criteria in

terms of allowable stresses as opposed to strength,

the design seismic forces shall be obtained from

this section and used in combination with other

loads as speciﬁ ed in Section 2.4 of this standard

and used directly with allowable stresses speciﬁ ed

in the reference documents. Detailing shall be in

accordance with the reference documents.

15.1.3 Structural Analysis Procedure Selection

Structural analysis procedures for nonbuilding

structures that are similar to buildings shall be

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

140

15.3.2 Greater Than or Equal to 25 Percent

Combined Weight Condition

For the condition where the weight of the

nonbuilding structure is equal to or greater than 25

percent of the combined effective seismic weights of

the nonbuilding structure and supporting structure, an

analysis combining the structural characteristics of

both the nonbuilding structure and the supporting

structures shall be performed to determine the seismic

design forces as follows:

1. Where the fundamental period, T, of the nonbuild-

ing structure is less than 0.06 s, the nonbuilding

structure shall be considered a rigid element with

appropriate distribution of its effective seismic

weight. The supporting structure shall be designed

in accordance with the requirements of Chapter 12

or Section 15.5 as appropriate, and the R value of

the combined system is permitted to be taken as

the R value of the supporting structural system.

The nonbuilding structure and attachments shall be

designed for the forces using the procedures of

Chapter 13 where the value of R

shall be taken as

equal to the R value of the nonbuilding structure as

set forth in Table 15.4-2, and a

shall be taken as

1.0.

2. Where the fundamental period, T, of the nonbuild-

ing structure is 0.06 s or greater, the nonbuilding

structure and supporting structure shall be modeled

together in a combined model with appropriate

stiffness and effective seismic weight distributions.

The combined structure shall be designed in

accordance with Section 15.5 with the R value of

the combined system taken as the lesser R value of

the nonbuilding structure or the supporting struc-

ture. The nonbuilding structure and attachments

shall be designed for the forces determined for the

nonbuilding structure in the combined analysis.

15.3.3 Architectural, Mechanical,

and Electrical Components

Architectural, mechanical, and electrical

components supported by nonbuilding structures shall

be designed in accordance with Chapter 13 of this

standard.

15.4 STRUCTURAL DESIGN REQUIREMENTS

15.4.1 Design Basis

Nonbuilding structures having speciﬁ c seismic

design criteria established in reference documents

shall be designed using the standards as amended

herein. Where reference documents are not cited

herein, nonbuilding structures shall be designed in

compliance with Sections 15.5 and 15.6 to resist

minimum seismic lateral forces that are not less than

the requirements of Section 12.8 with the following

additions and exceptions:

1. The seismic force-resisting system shall be selected

as follows:

a. For nonbuilding structures similar to buildings,

a system shall be selected from among the types

indicated in Table 12.2-1 or Table 15.4-1

subject to the system limitations and limits on

structural height, h

, based on the seismic design

category indicated in the table. The appropriate

values of R, Ω

, and C

indicated in the selected

table shall be used in determining the base

shear, element design forces, and design story

drift as indicated in this standard. Design and

detailing requirements shall comply with the

sections referenced in the selected table.

b. For nonbuilding structures not similar to

buildings, a system shall be selected from

among the types indicated in Table 15.4-2

subject to the system limitations and limits on

structural height, h

, based on seismic design

category indicated in the table. The appropriate

values of R, Ω

, and C

indicated in Table

15.4-2 shall be used in determining the base

shear, element design forces, and design story

drift as indicated in this standard. Design and

detailing requirements shall comply with the

sections referenced in Table 15.4-2.

c. Where neither Table 15.4-1 nor Table 15.4-2

contains an appropriate entry, applicable

strength and other design criteria shall be

obtained from a reference document that is

applicable to the speciﬁ c type of nonbuilding

structure. Design and detailing requirements

shall comply with the reference document.

2. For nonbuilding systems that have an R value

provided in Table 15.4-2, the minimum speciﬁ ed

value in Eq. 12.8-5 shall be replaced by

= 0.044S

(15.4-1)

The value of C

shall not be taken as less than 0.03.

And for nonbuilding structures located where

≥ 0.6g, the minimum speciﬁ ed value in Eq. 12.8-6

shall be replaced by

= 0.8S

/(R/I

) (15.4-2)

EXCEPTION: Tanks and vessels that are

designed to AWWA D100, AWWA D103, API

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MINIMUM DESIGN LOADS

141

Table 15.4-1 Seismic Coefﬁ cients for Nonbuilding Structures Similar to Buildings

Nonbuilding Structure Type Detailing Requirements R Ω

Structural System and Structural

Height, h

, Limits (ft)

BC D E F

Steel storage racks 15.5.3 4 2 3.5 NL NL NL NL NL

Building frame systems:

Steel special concentrically braced

frames

AISC 341 6 2 5 NL NL 160 160 100

Steel ordinary concentrically braced

frame

AISC 341 3¼ 2 3¼ NL NL

With permitted height increase AISC 341 2½ 2 2½ NL NL 160 160 100

With unlimited height AISC 360 1.5 1 1.5 NL NL NL NL NL

Moment-resisting frame systems:

Steel special moment frames AISC 341 8 3 5.5 NL NL NL NL NL

Special reinforced concrete moment

frames

14.2.2.6 & ACI 318,

including Chapter 21

8 3 5.5 NL NL NL NL NL

Steel intermediate moment frames AISC 341 4.5 3 4 NL NL

c,d

With permitted height increase AISC 341 2.5 2 2.5 NL NL 160 160 100

With unlimited height AISC 341 1.5 1 1.5 NL NL NL NL NL

Intermediate reinforced concrete

moment frames

ACI 318, including

Chapter 21

5 3 4.5 NL NL NP NP NP

With permitted height increase ACI 318, including

Chapter 21

3 2 2.5 NL NL 50 50 50

With unlimited height ACI 318, including

Chapter 21

0.8 1 1 NL NL NL NL NL

Steel ordinary moment frames AISC 341 3.5 3 3 NL NL

c,d

With permitted height increase AISC 341 2.5 2 2.5 NL NL 100 100

c,d

With unlimited height AISC 360 1 1 1 NL NL NL NL NL

Ordinary reinforced concrete moment

frames

ACI 318, excluding

Chapter 21

3 3 2.5 NL NP NP NP NP

With permitted height increase ACI 318, excluding

Chapter 21

0.8 1 1 NL NL 50 50 50

NL = no limit and NP = not permitted.

Steel ordinary braced frames are permitted in pipe racks up to 65 ft (20 m).

Steel ordinary moment frames and intermediate moment frames are permitted in pipe racks up to a height of 65 ft (20 m) where the moment

joints of ﬁ eld connections are constructed of bolted end plates.

Steel ordinary moment frames and intermediate moment frames are permitted in pipe racks up to a height of 35 ft (11 m).

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

142

Table 15.4-2 Seismic Coefﬁ cients for Nonbuilding Structures not Similar to Buildings

Nonbuilding Structure Type

Detailing

Requirements

R Ω

Structural Height, h

Limits (ft)

BCD E F

Elevated tanks, vessels, bins or hoppers

On symmetrically braced legs (not similar

to buildings)

15.7.10 3

2.5 NL NL 160 100 100

On unbraced legs or asymmetrically

braced legs (not similar buildings)

15.7.10 2

2.5 NL NL 100 60 60

Horizontal, saddle supported welded steel

vessels

15.7.14 3

2.5 NL NL NL NL NL

Tanks or vessels supported on structural

towers similar to buildings

15.5.5 Use values for the appropriate structure type in the

categories for building frame systems and moment

resisting frame systems listed in Table 12.2-1 or

Table 15.4-1.

Flat-bottom ground-supported tanks: 15.7

Steel or ﬁ ber-reinforced plastic:

Mechanically anchored 3

2.5 NL NL NL NL NL

Self-anchored 2.5

2NLNLNLNLNL

Reinforced or prestressed concrete:

Reinforced nonsliding base 2

2NLNLNLNLNL

Anchored ﬂ exible base 3.25

2NLNLNLNLNL

Unanchored and unconstrained

ﬂ exible base

1.5

1.5 NL NL NL NL NL

All other 1.5

1.5

1.5 NL NL NL NL NL

Cast-in-place concrete silos having walls

continuous to the foundation

15.6.2 3 1.75 3 NL NL NL NL NL

All other reinforced masonry structures not

similar to buildings detailed as intermediate

reinforced masonry shear walls

14.4.1

3 2 2.5 NL NL 50 50 50

All other reinforced masonry structures not

similar to buildings detailed as ordinary

reinforced masonry shear walls

14.4.1 2 2.5 1.75 NL 160 NP NP NP

All other nonreinforced masonry structures

not similar to buildings

14.4.1 1.25 2 1.5 NL NL NP NP NP

Concrete chimneys and stacks 15.6.2 and ACI 307 2 1.5 2.0 NL NL NL NL NL

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MINIMUM DESIGN LOADS

143

Nonbuilding Structure Type

Detailing

Requirements

R Ω

Structural Height, h

Limits (ft)

BCD E F

All steel and reinforced concrete distributed

mass cantilever structures not otherwise

covered herein including stacks, chimneys,

silos, skirt-supported vertical vessels and

single pedestal or skirt supported

Welded steel

Welded steel with special detailing

Prestressed or reinforced concrete

Prestressed or reinforced concrete with

special detailing

15.6.2

15.7.10

15.7.10 & 15.7.10.5

a and b

15.7.10

15.7.10 and ACI 318

Chapter 21, Sections

21.2 and 21.7

Trussed towers (freestanding or guyed),

guyed stacks, and chimneys

15.6.2 3 2 2.5 NL NL NL NL NL

Cooling towers

Concrete or steel 3.5 1.75 3 NL NL NL NL NL

Wood frames 3.5 3 3 NL NL NL 50 50

Telecommunication towers 15.6.6

Truss: Steel 3 1.5 3 NL NL NL NL NL

Pole: Steel 1.5 1.5 1.5 NL NL NL NL NL

Wood 1.5 1.5 1.5 NL NL NL NL NL

Concrete 1.5 1.5 1.5 NL NL NL NL NL

Frame: Steel 3 1.5 1.5 NL NL NL NL NL

Wood 1.5 1.5 1.5 NL NL NL NL NL

Concrete 2 1.5 1.5 NL NL NL NL NL

Amusement structures and monuments 15.6.3 2 2 2 NL NL NL NL NL

Inverted pendulum type structures (except

elevated tanks, vessels, bins, and hoppers)

12.2.5.3 2 2 2 NL NL NL NL NL

Signs and billboards 3.0 1.75 3 NL NL NL NL NL

All other self-supporting structures, tanks,

or vessels not covered above or by reference

standards that are similar to buildings

1.25 2 2.5 NL NL 50 50 50

NL = no limit and NP = not permitted.

See Section 15.7.3a for the application of the overstrength factors, Ω

, for tanks and vessels.

If a section is not indicated in the Detailing Requirements column, no speciﬁ c detailing requirements apply.

For the purpose of height limit determination, the height of the structure shall be taken as the height to the top of the structural frame making up

the primary seismic force-resisting system.

Sections 15.7.10.5a and 15.7.10.5b shall be applied for any Risk Category.

Detailed with an essentially complete vertical load carrying frame.

Table 15.4-2 (Continued)

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

144

650 Appendix E, and API 620 Appendix L as

modiﬁ ed by this standard, and stacks and chimneys

that are designed to ACI 307 as modiﬁ ed by this

standard, shall be subject to the larger of the

minimum base shear value deﬁ ned by the reference

document or the value determined by replacing

Eq. 12.8-5 with the following:

= 0.044S

(15.4-3)

The value of C

shall not be taken as less than 0.01.

and for nonbuilding structures located where S

≥

0.6g, Eq. 12.8-6 shall be replaced by

= 0.5S

/(R/I

) (15.4-4)

Minimum base shear requirements need not apply

to the convective (sloshing) component of liquid in

tanks.

3. The importance factor, I

, shall be as set forth in

Section 15.4.1.1.

4. The vertical distribution of the lateral seismic

forces in nonbuilding structures covered by this

section shall be determined:

a. Using the requirements of Section 12.8.3, or

b. Using the procedures of Section 12.9, or

c. In accordance with the reference document

applicable to the speciﬁ c nonbuilding structure.

5. For nonbuilding structural systems containing

liquids, gases, and granular solids supported at the

base as deﬁ ned in Section 15.7.1, the minimum

seismic design force shall not be less than that

required by the reference document for the speciﬁ c

system.

6. Where a reference document provides a basis for

the earthquake resistant design of a particular type

of nonbuilding structure covered by Chapter 15,

such a standard shall not be used unless the

following limitations are met:

a. The seismic ground accelerations, and seismic

coefﬁ cients, shall be in conformance with the

requirements of Section 11.4.

b. The values for total lateral force and total base

overturning moment used in design shall not be

less than 80 percent of the base shear value and

overturning moment, each adjusted for the

effects of soil–structure interaction that is

obtained using this standard.

7. The base shear is permitted to be reduced in

accordance with Section 19.2.1 to account for the

effects of soil–structure interaction. In no case shall

the reduced base shear be less than 0.7V.

8. Unless otherwise noted in Chapter 15, the effects

on the nonbuilding structure due to gravity loads

and seismic forces shall be combined in accor-

dance with the factored load combinations as

presented in Section 2.3.

9. Where speciﬁ cally required by Chapter 15, the

design seismic force on nonbuilding structures

shall be as deﬁ ned in Section 12.4.3.

15.4.1.1 Importance Factor

The importance factor, I

, and risk category for

nonbuilding structures are based on the relative hazard

of the contents and the function. The value of I

shall

be the largest value determined by the following:

a. Applicable reference document listed in

Chapter 23.

b. The largest value as selected from Table 1.5-2.

c. As speciﬁ ed elsewhere in Chapter 15.

15.4.2 Rigid Nonbuilding Structures

Nonbuilding structures that have a fundamental

period, T, less than 0.06 s, including their anchorages,

shall be designed for the lateral force obtained from

the following:

V = 0.30S

(15.4-5)

where

V = the total design lateral seismic base shear force

applied to a nonbuilding structure

= the site design response acceleration as deter-

mined from Section 11.4.4

W = nonbuilding structure operating weight

= the importance factor determined in accordance

with Section 15.4.1.1

The force shall be distributed with height in

accordance with Section 12.8.3.

15.4.3 Loads

The seismic effective weight W for nonbuilding

structures shall include the dead load and other loads

as deﬁ ned for structures in Section 12.7.2. For

purposes of calculating design seismic forces in

nonbuilding structures, W also shall include all normal

operating contents for items such as tanks, vessels,

bins, hoppers, and the contents of piping. W shall

include snow and ice loads where these loads consti-

tute 25 percent or more of W or where required by the

authority having jurisdiction based on local environ-

mental characteristics.

15.4.4 Fundamental Period

The fundamental period of the nonbuilding

structure shall be determined using the structural

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MINIMUM DESIGN LOADS

145

properties and deformation characteristics of the

resisting elements in a properly substantiated analysis

as indicated in Section 12.8.2. Alternatively, the

fundamental period T is permitted to be computed

from the following equation:

∑

(15.4-6)

The values of f

represent any lateral force distribution

in accordance with the principles of structural

mechanics. The elastic deﬂ ections, δ

, shall be

calculated using the applied lateral forces, f

Equations 12.8-7, 12.8-8, 12.8-9, and 12.8-10 shall

not be used for determining the period of a nonbuild-

ing structure.

15.4.5 Drift Limitations

The drift limitations of Section 12.12.1 need

not apply to nonbuilding structures if a rational

analysis indicates they can be exceeded without

adversely affecting structural stability or attached or

interconnected components and elements such as

walkways and piping. P-delta effects shall be consid-

ered where critical to the function or stability of the

structure.

15.4.6 Materials Requirements

The requirements regarding speciﬁ c materials in

Chapter 14 shall be applicable unless speciﬁ cally

exempted in Chapter 15.

15.4.7 Deﬂ ection Limits and Structure Separation

Deﬂ ection limits and structure separation shall be

determined in accordance with this standard unless

speciﬁ cally amended in Chapter 15.

15.4.8 Site-Speciﬁ c Response Spectra

Where required by a reference document or

the authority having jurisdiction, speciﬁ c types

of nonbuilding structures shall be designed for

site-speciﬁ c criteria that account for local seismicity

and geology, expected recurrence intervals, and

magnitudes of events from known seismic hazards

(see Section 11.4.7 of this standard). If a longer

recurrence interval is deﬁ ned in the reference docu-

ment for the nonbuilding structure, such as liqueﬁ ed

natural gas (LNG) tanks (NFPA 59A), the recurrence

interval required in the reference document shall be

used.

15.4.9 Anchors in Concrete or Masonry

15.4.9.1 Anchors in Concrete

Anchors in concrete used for nonbuilding

structure anchorage shall be designed in accordance

with Appendix D of ACI 318.

15.4.9.2 Anchors in Masonry

Anchors in masonry used for nonbuilding

structure anchorage shall be designed in accordance

with TMS402/ACI 530/ASCE 6. Anchors shall be

designed to be governed by the tensile or shear

strength of a ductile steel element.

EXCEPTION: Anchors shall be permitted to be

designed so that the attachment that the anchor is

connecting to the structure undergoes ductile yielding

at a load level corresponding to anchor forces not

greater than their design strength, or the minimum

design strength of the anchors shall be at least 2.5

times the factored forces transmitted by the

attachment.

15.4.9.3 Post-Installed Anchors in Concrete

and Masonry

Post-installed anchors in concrete shall be

prequaliﬁ ed for seismic applications in accordance

with ACI 355.2 or other approved qualiﬁ cation

procedures. Post-installed anchors in masonry shall be

prequaliﬁ ed for seismic applications in accordance

with approved qualiﬁ cation procedures.

15.5 NONBUILDING STRUCTURES SIMILAR

TO BUILDINGS

15.5.1 General

Nonbuilding structures similar to buildings as

deﬁ ned in Section 11.2 shall be designed in accor-

dance with this standard as modiﬁ ed by this section

and the speciﬁ c reference documents. This general

category of nonbuilding structures shall be designed

in accordance with the seismic requirements of this

standard and the applicable portions of Section 15.4.

The combination of load effects, E, shall be deter-

mined in accordance with Section 12.4.

15.5.2 Pipe Racks

15.5.2.1 Design Basis

In addition to the requirements of Section 15.5.1,

pipe racks supported at the base of the structure shall

be designed to meet the force requirements of Section

12.8 or 12.9. Displacements of the pipe rack and

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146

potential for interaction effects (pounding of the

piping system) shall be considered using the ampliﬁ ed

deﬂ ections obtained from the following equation:

dxe

(15.5-1)

where

= deﬂ ection ampliﬁ cation factor in Table 15.4-1

= deﬂ ections determined using the prescribed

seismic design forces of this standard

= importance factor determined in accordance with

Section 15.4.1.1

See Section 13.6.3 for the design of piping

systems and their attachments. Friction resulting from

gravity loads shall not be considered to provide

resistance to seismic forces.

15.5.3 Steel Storage Racks

Steel storage racks supported at or below grade

shall be designed in accordance with ANSI/RMI MH

16.1 and its force and displacement requirements,

except as follows:

15.5.3.1

Modify Section 2.6.2 of ANSI/RMI MH 16.1 as

follows:

2.6.2 Minimum Seismic Forces

The storage rack shall be designed…

Above-Grade Elevation: Storage rack installed at

elevations above grade shall be designed, fabricated,

and installed in accordance with the following

requirements:

Storage racks shall meet the force and

displacement requirements required of nonbuilding

structures supported by other structures, including the

force and displacement effects caused by

ampliﬁ cations of upper-story motions. In no case shall

the value of V be taken as less than the value of F

determined in accordance with Section 13.3.1 of

ASCE/SEI 7, where R

is taken equal to R, and a

taken equal to 2.5.

15.5.3.2

Modify Section 7.2.2 of ANSI/RMI MH 16.1 as

follows:

7.2.2 Base Plate Design

Once the required bearing area has been

determined from the allowable bearing stress F’

the

minimum thickness of the base plate is determined by

rational analysis or by appropriate test using a test

load 1.5 times the ASD design load or the factored

LRFD load. Design forces that include seismic loads

for anchorage of steel storage racks to concrete or

masonry shall be determined using load combinations

with overstrength provided in Section 12.4.3.2 of

ASCE/SEI 7. The overstrength factor shall be taken

as 2.0.

Anchorage of steel storage racks to concrete

shall be in accordance with the requirements of

Section 15.4.9 of ASCE/SEI 7. Upon request,

information shall be given to the owner or the

owner’s agent on the location, size, and pressures

under the column base plates of each type of upright

frame in the installation. When rational analysis is

used to determine base plate thickness and other

applicable standards do not apply, the base plate

shall be permitted to be designed for the following

loading conditions, where applicable: (balance of

section unchanged)

15.5.3.3

Modify Section 7.2.4 of ANSI/RMI MH 16.1 as

follows:

7.2.4 Shims

Shims may be used under the base plate to

maintain the plumbness of the storage rack. The

shims shall be made of a material that meets or

exceeds the design bearing strength (LRFD) or

allowable bearing strength (ASD) of the ﬂ oor. The

shim size and location under the base plate shall be

equal to or greater than the required base plate size

and location.

In no case shall the total thickness of any set

of shims under a base plate exceed six times the

diameter of the largest anchor bolt used in that

base.

Shims that are a total thickness of less than or

equal to six times the anchor bolt diameter under

bases with less than two anchor bolts shall be

interlocked or welded together in a fashion that is

capable of transferring all the shear forces at the

base.

Shims that are a total thickness of less than or

equal to two times the anchor bolt diameter need not

be interlocked or welded together.

Bending in the anchor associated with shims or

grout under the base plate shall be taken into account

in the design of the anchor bolts.

15.5.3.4 Alternative

As an alternative to ANSI MH 16.1 as modiﬁ ed

above, steel storage racks shall be permitted to be

designed in accordance with the requirements of

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147

Sections 15.1, 15.2, 15.3, 15.5.1, and 15.5.3.5 through

15.5.3.8 of this standard.

15.5.3.5 General Requirements

Steel storage racks shall satisfy the force require-

ments of this section.

EXCEPTION: Steel storage racks supported at

the base are permitted to be designed as structures

with an R of 4, provided that the seismic requirements

of this standard are met. Higher values of R are

permitted to be used where the detailing requirements

of reference documents listed in Section 14.1.1 are

met. The importance factor, I

, for storage racks in

structures open to the public, such as warehouse retail

stores, shall be taken equal to 1.5.

15.5.3.6 Operating Weight

Steel storage racks shall be designed for each

of the following conditions of operating weight,

W or W

a. Weight of the rack plus every storage level loaded

to 67 percent of its rated load capacity.

b. Weight of the rack plus the highest storage level

only loaded to 100 percent of its rated load

capacity.

The design shall consider the actual height of the

center of mass of each storage load component.

15.5.3.7 Vertical Distribution of Seismic Forces

For all steel storage racks, the vertical distribution

of seismic forces shall be as speciﬁ ed in Section

12.8.3 and in accordance with the following:

a. The base shear, V, of the typical structure shall be

the base shear of the steel storage rack where

loaded in accordance with Section 15.5.3.6.

b. The base of the structure shall be the ﬂ oor support-

ing the steel storage rack. Each steel storage level

of the rack shall be treated as a level of the

structure with heights h

and h

measured from the

base of the structure.

c. The factor k is permitted to be taken as 1.0.

15.5.3.8 Seismic Displacements

Steel storage rack installations shall accommodate

the seismic displacement of the storage racks and

their contents relative to all adjacent or attached

components and elements. The assumed total relative

displacement for storage racks shall be not less than 5

percent of the structural height above the base, h

unless a smaller value is justiﬁ ed by test data or

analysis in accordance with Section 11.1.4.

15.5.4 Electrical Power Generating Facilities

15.5.4.1 General

Electrical power generating facilities are power

plants that generate electricity by steam turbines,

combustion turbines, diesel generators, or similar

turbo machinery.

15.5.4.2 Design Basis

In addition to the requirements of Section 15.5.1,

electrical power generating facilities shall be designed

using this standard and the appropriate factors

contained in Section 15.4.

15.5.5 Structural Towers for Tanks and Vessels

15.5.5.1 General

In addition to the requirements of Section 15.5.1,

structural towers that support tanks and vessels shall

be designed to meet the requirements of Section 15.3.

In addition, the following special considerations shall

be included:

a. The distribution of the lateral base shear from the

tank or vessel onto the supporting structure shall

consider the relative stiffness of the tank and

resisting structural elements.

b. The distribution of the vertical reactions from the

tank or vessel onto the supporting structure shall

consider the relative stiffness of the tank and

resisting structural elements. Where the tank or

vessel is supported on grillage beams, the calcu-

lated vertical reaction due to weight and overturn-

ing shall be increased at least 20 percent to account

for nonuniform support. The grillage beam and

vessel attachment shall be designed for this

increased design value.

c. Seismic displacements of the tank and vessel shall

consider the deformation of the support structure

where determining P-delta effects or evaluating

required clearances to prevent pounding of the tank

on the structure.

15.5.6 Piers and Wharves

15.5.6.1 General

Piers and wharves are structures located in

waterfront areas that project into a body of water or

that parallel the shoreline.

15.5.6.2 Design Basis

In addition to the requirements of Section 15.5.1,

piers and wharves that are accessible to the general

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148

public, such as cruise ship terminals and piers with

retail or commercial ofﬁ ces or restaurants, shall be

designed to comply with this standard. Piers and

wharves that are not accessible to the general public

are beyond the scope of this section.

The design shall account for the effects of

liquefaction and soil failure collapse mechanisms, as

well as consider all applicable marine loading combi-

nations, such as mooring, berthing, wave, and current

on piers and wharves as required. Structural detailing

shall consider the effects of the marine environment.

15.6 GENERAL REQUIREMENTS FOR

NONBUILDING STRUCTURES NOT SIMILAR

TO BUILDINGS

Nonbuilding structures that do not have lateral and

vertical seismic force-resisting systems that are

similar to buildings shall be designed in accordance

with this standard as modiﬁ ed by this section and the

speciﬁ c reference documents. Loads and load distribu-

tions shall not be less demanding than those deter-

mined in this standard. The combination of earthquake

load effects, E, shall be determined in accordance

with Section 12.4.2.

EXCEPTION: The redundancy factor, ρ, per

Section 12.3.4 shall be taken as 1.

15.6.1 Earth-Retaining Structures

This section applies to all earth-retaining struc-

tures assigned to Seismic Design Category D, E, or F.

The lateral earth pressures due to earthquake ground

motions shall be determined in accordance with

Section 11.8.3.

The risk category shall be determined by the

proximity of the earth-retaining structure to other

buildings and structures. If failure of the earth-retain-

ing structure would affect the adjacent building or

structure, the risk category shall not be less than that

of the adjacent building or structure. Earth-retaining

walls are permitted to be designed for seismic loads

as either yielding or nonyielding walls. Cantilevered

reinforced concrete or masonry retaining walls shall

be assumed to be yielding walls and shall be designed

as simple ﬂ exural wall elements.

15.6.2 Stacks and Chimneys

Stacks and chimneys are permitted to be either

lined or unlined and shall be constructed from con-

crete, steel, or masonry. Steel stacks, concrete stacks,

steel chimneys, concrete chimneys, and liners shall be

designed to resist seismic lateral forces determined

from a substantiated analysis using reference docu-

ments. Interaction of the stack or chimney with the

liners shall be considered. A minimum separation shall

be provided between the liner and chimney equal to C

times the calculated differential lateral drift.

Concrete chimneys and stacks shall be designed

in accordance with the requirements of ACI 307

except that (1) the design base shear shall be deter-

mined based on Section 15.4.1 of this standard; (2)

the seismic coefﬁ cients shall be based on the values

provided in Table 15.4-2, and (3) openings shall be

detailed as required below. When modal response

spectrum analysis is used for design, the procedures

of Section 12.9 shall be permitted to be used.

For concrete chimneys and stacks assigned to

SDC D, E, and F, splices for vertical rebar shall be

staggered such that no more than 50% of the bars are

spliced at any section and alternate lap splices are

staggered by the development length. In addition,

where the loss of cross-sectional area is greater than

10%, cross sections in the regions of breachings/

openings shall be designed and detailed for vertical

force, shear force, and bending moment demands

along the vertical direction, determined for the

affected cross section using an overstrength factor of

1.5. The region where the overstrength factor applies

shall extend above and below the opening(s) by a

distance equal to half of the width of the largest

opening in the affected region. Appropriate reinforce-

ment development lengths shall be provided beyond

the required region of overstrength. The jamb regions

around each opening shall be detailed using the

column tie requirements in Section 7.10.5 of ACI 318.

Such detailing shall extend for a jamb width of a

minimum of two times the wall thickness and for a

height of the opening height plus twice the wall

thickness above and below the opening, but no less

than the development length of the longitudinal bars.

Where the existence of a footing or base mat precludes

the ability to achieve the extension distance below the

opening and within the stack, the jamb reinforcing

shall be extended and developed into the footing or

base mat. The percentage of longitudinal reinforce-

ment in jamb regions shall meet the requirements of

Section 10.9 of ACI 318 for compression members.

15.6.3 Amusement Structures

Amusement structures are permanently ﬁ xed

structures constructed primarily for the conveyance

and entertainment of people. Amusement structures

shall be designed to resist seismic lateral forces

determined from a substantiated analysis using

reference documents.

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15.6.4 Special Hydraulic Structures

Special hydraulic structures are structures that are

contained inside liquid-containing structures. These

structures are exposed to liquids on both wall surfaces

at the same head elevation under normal operating

conditions. Special hydraulic structures are subjected

to out-of-plane forces only during an earthquake

where the structure is subjected to differential

hydrodynamic ﬂ uid forces. Examples of special

hydraulic structures include separation walls, bafﬂ e

walls, weirs, and other similar structures.

15.6.4.1 Design Basis

Special hydraulic structures shall be designed for

out-of-phase movement of the ﬂ uid. Unbalanced

forces from the motion of the liquid must be applied

simultaneously “in front of” and “behind” these

elements.

Structures subject to hydrodynamic pressures

induced by earthquakes shall be designed for rigid

body and sloshing liquid forces and their own inertia

force. The height of sloshing shall be determined and

compared to the freeboard height of the structure.

Interior elements, such as bafﬂ es or roof supports,

also shall be designed for the effects of unbalanced

forces and sloshing.

15.6.5 Secondary Containment Systems

Secondary containment systems, such as

impoundment dikes and walls, shall meet the require-

ments of the applicable standards for tanks and

vessels and the authority having jurisdiction.

Secondary containment systems shall be designed

to withstand the effects of the maximum considered

earthquake ground motion where empty and two-

thirds of the maximum considered earthquake ground

motion where full including all hydrodynamic forces

as determined in accordance with the procedures of

Section 11.4. Where determined by the risk assess-

ment required by Section 1.5.2 or by the authority

having jurisdiction that the site may be subject to

aftershocks of the same magnitude as the maximum

considered motion, secondary containment systems

shall be designed to withstand the effects of the

maximum considered earthquake ground motion

where full including all hydrodynamic forces as

determined in accordance with the procedures of

Section 11.4.

15.6.5.1 Freeboard

Sloshing of the liquid within the secondary

containment area shall be considered in determining

the height of the impound. Where the primary

containment has not been designed with a reduction in

the structure category (i.e., no reduction in importance

factor I

) as permitted by Section 1.5.3, no freeboard

provision is required. Where the primary containment

has been designed for a reduced structure category

(i.e., importance factor I

reduced) as permitted by

Section 1.5.3, a minimum freeboard, δ

, shall be

provided where

= 0.42DS

(15.6-1)

where S

is the spectral acceleration of the convective

component and is determined according to the

procedures of Section 15.7.6.1 using 0.5 percent

damping. For circular impoundment dikes, D shall be

taken as the diameter of the impoundment dike. For

rectangular impoundment dikes, D shall be taken as

the plan dimension of the impoundment dike, L, for

the direction under consideration.

15.6.6 Telecommunication Towers

Self-supporting and guyed telecommunication

towers shall be designed to resist seismic lateral

forces determined from a substantiated analysis using

reference documents.

15.7 TANKS AND VESSELS

15.7.1 General

This section applies to all tanks, vessels, bins,

and silos, and similar containers storing liquids, gases,

and granular solids supported at the base (hereafter

referred to generically as “tanks and vessels”). Tanks

and vessels covered herein include reinforced con-

crete, prestressed concrete, steel, aluminum, and

ﬁ ber-reinforced plastic materials. Tanks supported on

elevated levels in buildings shall be designed in

accordance with Section 15.3.

15.7.2 Design Basis

Tanks and vessels storing liquids, gases, and

granular solids shall be designed in accordance with

this standard and shall be designed to meet the

requirements of the applicable reference documents

listed in Chapter 23. Resistance to seismic forces shall

be determined from a substantiated analysis based

on the applicable reference documents listed in

Chapter 23.

a. Damping for the convective (sloshing) force

component shall be taken as 0.5 percent.

b. Impulsive and convective components shall be

combined by the direct sum or the square root of

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the sum of the squares (SRSS) method where the

modal periods are separated. If signiﬁ cant modal

coupling may occur, the complete quadratic

combination (CQC) method shall be used.

c. Vertical earthquake forces shall be considered in

accordance with the applicable reference document.

If the reference document permits the user the

option of including or excluding the vertical

earthquake force to comply with this standard,

it shall be included. For tanks and vessels not

covered by a reference document, the forces due to

the vertical acceleration shall be deﬁ ned as

follows:

(1) Hydrodynamic vertical and lateral forces in

tank walls: The increase in hydrostatic pres-

sures due to the vertical excitation of the

contained liquid shall correspond to an

effective increase in unit weight, γ

, of the

stored liquid equal to 0.2S

(2) Hydrodynamic hoop forces in cylindrical tank

walls: In a cylindrical tank wall, the hoop force

per unit height, N

, at height y from the base,

associated with the vertical excitation of the

contained liquid, shall be computed in accor-

dance with Eq. 15.7-1.

NSHy

hDSLL

=−

()

⎛

⎝

⎜

⎞

⎠

⎟

. γ

(15.7-1)

where

= inside tank diameter

= liquid height inside the tank

y = distance from base of the tank to height being

investigated

= unit weight of stored liquid

(3) Vertical inertia forces in cylindrical and

rectangular tank walls: Vertical inertia forces

associated with the vertical acceleration of the

structure itself shall be taken equal to 0.2S

15.7.3 Strength and Ductility

Structural members that are part of the seismic

force-resisting system shall be designed to provide the

following:

a. Connections to seismic force-resisting elements,

excluding anchors (bolts or rods) embedded in

concrete, shall be designed to develop Ω

times the

calculated connection design force. For anchors

(bolts or rods) embedded in concrete, the design of

the anchor embedment shall meet the requirements

of Section 15.7.5. Additionally, the connection of

the anchors to the tank or vessel shall be designed

to develop the lesser of the strength of the anchor

in tension as determined by the reference document

or Ω

times the calculated anchor design force. The

overstrength requirements of Section 12.4.3, and

the Ω

values tabulated in Table 15.4-2, do not

apply to the design of walls, including interior

walls, of tanks or vessels.

b. Penetrations, manholes, and openings in shell

elements shall be designed to maintain the strength

and stability of the shell to carry tensile and

compressive membrane shell forces.

c. Support towers for tanks and vessels with irregular

bracing, unbraced panels, asymmetric bracing, or

concentrated masses shall be designed using the

requirements of Section 12.3.2 for irregular

structures. Support towers using chevron or

eccentric braced framing shall comply with the

seismic requirements of this standard. Support

towers using tension-only bracing shall be

designed such that the full cross-section of

the tension element can yield during overload

conditions.

d. In support towers for tanks and vessels, compres-

sion struts that resist the reaction forces from

tension braces shall be designed to resist the lesser

of the yield load of the brace, A

, or Ω

times the

calculated tension load in the brace.

e. The vessel stiffness relative to the support system

(foundation, support tower, skirt, etc.) shall be

considered in determining forces in the vessel, the

resisting elements, and the connections.

f. For concrete liquid-containing structures, system

ductility, and energy dissipation under unfactored

loads shall not be allowed to be achieved by

inelastic deformations to such a degree as to

jeopardize the serviceability of the structure.

Stiffness degradation and energy dissipation shall

be allowed to be obtained either through limited

microcracking, or by means of lateral force

resistance mechanisms that dissipate energy

without damaging the structure.

15.7.4 Flexibility of Piping Attachments

Design of piping systems connected to tanks and

vessels shall consider the potential movement of the

connection points during earthquakes and provide

sufﬁ cient ﬂ exibility to avoid release of the product by

failure of the piping system. The piping system and

supports shall be designed so as not to impart signiﬁ -

cant mechanical loading on the attachment to the tank

or vessel shell. Mechanical devices that add ﬂ exibil-

ity, such as bellows, expansion joints, and other

ﬂ exible apparatus, are permitted to be used where

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151

they are designed for seismic displacements and

deﬁ ned operating pressure.

Unless otherwise calculated, the minimum

displacements in Table 15.7-1 shall be assumed. For

attachment points located above the support or

foundation elevation, the displacements in Table

15.7-1 shall be increased to account for drift of the

tank or vessel relative to the base of support. The

piping system and tank connection shall also be

designed to tolerate C

times the displacements given

in Table 15.7-1 without rupture, although permanent

deformations and inelastic behavior in the piping

supports and tank shell is permitted. For attachment

points located above the support or foundation

elevation, the displacements in Table 15.7-1 shall be

increased to account for drift of the tank or vessel.

The values given in Table 15.7-1 do not include the

inﬂ uence of relative movements of the foundation and

piping anchorage points due to foundation movements

(e.g., settlement, seismic displacements). The effects

of the foundation movements shall be included in the

piping system design including the determination of

the mechanical loading on the tank or vessel, and the

total displacement capacity of the mechanical devices

intended to add ﬂ exibility.

The anchorage ratio, J, for self-anchored tanks

shall comply with the criteria shown in Table 15.7-2

and is deﬁ ned as

Dw w

()

(15.7-2)

Table 15.7-1 Minimum Design Displacements for Piping Attachments

Condition Displacements (in.)

Mechanically Anchored Tanks and Vessels

Upward vertical displacement relative to support or foundation 1 (25.4 mm)

Downward vertical displacement relative to support or foundation 0.5 (12.7 mm)

Range of horizontal displacement (radial and tangential) relative to support or foundation 0.5 (12.7 mm)

Self-Anchored Tanks or Vessels (at grade)

Upward vertical displacement relative to support or foundation

If designed in accordance with a reference document as modiﬁ ed by this standard

Anchorage ratio less than or equal to 0.785 (indicates no uplift) 1 (25.4 mm)

Anchorage ratio greater than 0.785 (indicates uplift) 4 (101.1 mm)

If designed for seismic loads in accordance with this standard but not covered by a reference document

For tanks and vessels with a diameter less than 40 ft 8 (202.2 mm)

For tanks and vessels with a diameter equal to or greater than 40 ft

12 (0.305 m)

Downward vertical displacement relative to support or foundation

For tanks with a ringwall/mat foundation

0.5 (12.7 mm)

For tanks with a berm foundation 1 (25.4 mm)

Range of horizontal displacement (radial and tangential) relative to support or foundation 2 (50.8mm)

Table 15.7-2 Anchorage Ratio

J Anchorage Ratio Criteria

J < 0.785

No uplift under the design seismic

overturning moment. The tank is

self-anchored.

0.785 < J < 1.54

Tank is uplifting, but the tank is stable

for the design load providing the shell

compression requirements are satisﬁ ed.

The tank is self-anchored.

J > 1.54

Tank is not stable and shall be

mechanically anchored for the design

load.

where

(15.7-3)

= roof load acting on the shell in pounds per foot

(N/m) of shell circumference. Only permanent

roof loads shall be included. Roof live load

shall not be included

= maximum weight of the tank contents that may

be used to resist the shell overturning moment

in pounds per foot (N/m) of shell circumfer-

ence. Usually consists of an annulus of liquid

limited by the bending strength of the tank

bottom or annular plate

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= the overturning moment applied at the bottom

of the shell due to the seismic design loads

in foot-pounds (N-m) (also known as the

“ringwall moment”)

D = tank diameter in feet

= total weight of tank shell in pounds

15.7.5 Anchorage

Tanks and vessels at grade are permitted to be

designed without anchorage where they meet the

requirements for unanchored tanks in reference

documents. Tanks and vessels supported above grade

on structural towers or building structures shall be

anchored to the supporting structure.

The following special detailing requirements shall

apply to steel tank and vessel anchor bolts in SDC C,

D, E, and F. Anchorage shall be in accordance with

Section 15.4.9, whereby the anchor embedment into

the concrete shall be designed to develop the steel

strength of the anchor in tension. The steel strength of

the anchor in tension shall be determined in accor-

dance with ACI 318, Appendix D, Eq. D-3. The

anchor shall have a minimum gauge length of eight

diameters. Post-installed anchors are permitted to be

used in accordance with Section 15.4.9.3 provided the

anchor embedment into the concrete is designed to

develop the steel strength of the anchor in tension. In

either case, the load combinations with overstrength

of Section 12.4.3 are not to be used to size the anchor

bolts for tanks and horizontal and vertical vessels.

15.7.6 Ground-Supported Storage Tanks for Liquids

15.7.6.1 General

Ground-supported, ﬂ at bottom tanks storing

liquids shall be designed to resist the seismic forces

calculated using one of the following procedures:

a. The base shear and overturning moment calculated

as if the tank and the entire contents are a rigid

mass system per Section 15.4.2 of this standard.

b. Tanks or vessels storing liquids in Risk Category

IV, or with a diameter greater than 20 ft (6.1 m),

shall be designed to consider the hydrodynamic

pressures of the liquid in determining the equiva-

lent lateral forces and lateral force distribution

per the applicable reference documents listed in

Chapter 23 and the requirements of Section 15.7

of this standard.

c. The force and displacement requirements of

Section 15.4 of this standard.

The design of tanks storing liquids shall consider the

impulsive and convective (sloshing) effects and their

consequences on the tank, foundation, and attached

elements. The impulsive component corresponds to

the high-frequency ampliﬁ ed response to the lateral

ground motion of the tank roof, the shell, and the

portion of the contents that moves in unison with the

shell. The convective component corresponds to the

low-frequency ampliﬁ ed response of the contents in

the fundamental sloshing mode. Damping for the

convective component shall be 0.5 percent for the

sloshing liquid unless otherwise deﬁ ned by the

reference document. The following deﬁ nitions shall

apply:

= inside diameter of tank or vessel

= design liquid height inside the tank or vessel

L = inside length of a rectangular tank, parallel to

the direction of the earthquake force being

investigated

= hydrodynamic hoop force per unit height in the

wall of a cylindrical tank or vessel

= natural period of the ﬁ rst (convective) mode of

sloshing

= fundamental period of the tank structure and

impulsive component of the content

= base shear due to impulsive component from

weight of tank and contents

= base shear due to the convective component of

the effective sloshing mass

y = distance from base of the tank to level being

investigated

= unit weight of stored liquid

The seismic base shear is the combination of the

impulsive and convective components:

V = V

+ V

(15.7-4)

where

ai i

⎛

⎝

⎜

⎞

⎠

⎟

(15.7-5)

ac e

15.

(15.7-6)

= the spectral acceleration as a multiplier of

gravity including the site impulsive components

at period T

and 5 percent damping

For T

≤ T

= S

(15.7-7)

For T

< T

≤ T

(15.7-8)

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MINIMUM DESIGN LOADS

153

For T

> T

(15.7-9)

NOTES:

a. Where a reference document is used in which the

spectral acceleration for the tank shell, and the

impulsive component of the liquid is independent

of T

, then S

= S

b. Equations 15.7-8 and 15.7-9 shall not be less than

the minimum values required in Section 15.4.1

Item 2 multiplied by R/I

c. For tanks in Risk Category IV, the value of the

importance factor, I

, used for freeboard determina-

tion only shall be taken as 1.0.

d. For tanks in Risk Categories I, II, and III, the value

of T

used for freeboard determination is permitted

to be set equal to 4 s. The value of the importance

factor, I

, used for freeboard determination for

tanks in Risk Categories I, II, and III shall be the

value determined from Table 1.5-1.

e. Impulsive and convective seismic forces for tanks

are permitted to be combined using the square root

of the sum of the squares (SRSS) method in lieu of

the direct sum method shown in Section 15.7.6 and

its related subsections.

= the spectral acceleration of the sloshing liquid

(convective component) based on the sloshing

period T

and 0.5 percent damping

For T

≤ T

=≤

(15.7-10)

For T

> T

(15.7-11)

EXCEPTION: For T

> 4 s, S

is permitted

be determined by a site-speciﬁ c study using one or

more of the following methods: (i) the procedures

found in Chapter 21, provided such procedures,

which rely on ground-motion attenuation equations

for computing response spectra, cover the natural

period band containing T

, (ii) ground-motion

simulation methods employing seismological

models of fault rupture and wave propagation, and

(iii) analysis of representative strong-motion

accelerogram data with reliable long-period content

extending to periods greater than T

. Site-speciﬁ c

values of S

shall be based on one standard

deviation determinations. However, in no case shall

the value of S

be taken as less than the value

determined in accordance with Eq. 15.7-11 using

50% of the mapped value of T

from Chapter 22.

The 80 percent limit on S

required by Sections

21.3 and 21.4 shall not apply to the determination of

site-speciﬁ c values of S

, which satisfy the

requirements of this exception. In determining the

value of S

, the value of T

shall not be less than 4 s

where

⎛

⎝

⎜

⎞

⎠

⎟

368

.tanh

(15.7-12)

and where

D = the tank diameter in ft (m), H = liquid height in

ft (m), and g = acceleration due to gravity in

consistent units

= impulsive weight (impulsive component of

liquid, roof and equipment, shell, bottom, and

internal elements)

= the portion of the liquid weight sloshing

15.7.6.1.1 Distribution of Hydrodynamic and Inertia

Forces Unless otherwise required by the appropriate

reference document listed in Chapter 23, the method

given in ACI 350.3 is permitted to be used to deter-

mine the vertical and horizontal distribution of the

hydrodynamic and inertia forces on the walls of

circular and rectangular tanks.

15.7.6.1.2 Sloshing Sloshing of the stored liquid shall

be taken into account in the seismic design of tanks

and vessels in accordance with the following

requirements:

a. The height of the sloshing wave, δ

, shall be

computed using Eq. 15.7-13 as follows:

= 0.42D

(15.7-13)

For cylindrical tanks, D

shall be the inside

diameter of the tank; for rectangular tanks, the

term D

shall be replaced by the longitudinal plan

dimension of the tank, L, for the direction under

consideration.

b. The effects of sloshing shall be accommodated by

means of one of the following:

1. A minimum freeboard in accordance with Table

15.7-3.

2. A roof and supporting structure designed to

contain the sloshing liquid in accordance with

subsection 3 below.

3. For open-top tanks or vessels only, an overﬂ ow

spillway around the tank or vessel perimeter.

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

154

c. If the sloshing is restricted because the freeboard

is less than the computed sloshing height, then the

roof and supporting structure shall be designed

for an equivalent hydrostatic head equal to the

computed sloshing height less the freeboard. In

addition, the design of the tank shall use the

conﬁ ned portion of the convective (sloshing) mass

as an additional impulsive mass.

15.7.6.1.3 Equipment and Attached Piping Equipment,

piping, and walkways or other appurtenances attached

to the structure shall be designed to accommodate the

displacements imposed by seismic forces. For piping

attachments, see Section 15.7.4.

15.7.6.1.4 Internal Elements The attachments of

internal equipment and accessories that are attached

to the primary liquid or pressure retaining shell or

bottom or that provide structural support for major

elements (e.g., a column supporting the roof rafters)

shall be designed for the lateral loads due to the

sloshing liquid in addition to the inertial forces by a

substantiated analysis method.

15.7.6.1.5 Sliding Resistance The transfer of the total

lateral shear force between the tank or vessel and the

subgrade shall be considered:

a. For unanchored ﬂ at bottom steel tanks, the overall

horizontal seismic shear force is permitted to be

resisted by friction between the tank bottom and

the foundation or subgrade. Unanchored storage

tanks shall be designed such that sliding will not

occur where the tank is full of stored product. The

maximum calculated seismic base shear, V, shall

not exceed

V < W tan 30° (15.7-14)

W shall be determined using the effective seismic

weight of the tank, roof, and contents after reduc-

tion for coincident vertical earthquake. Lower

values of the friction factor shall be used if the

design of the tank bottom to supporting foundation

does not justify the friction value above (e.g., leak

detection membrane beneath the bottom with a

lower friction factor, smooth bottoms, etc.).

Alternatively, the friction factor is permitted to

be determined by testing in accordance with

Section 11.1.4.

b. No additional lateral anchorage is required for

anchored steel tanks designed in accordance with

reference documents.

c. The lateral shear transfer behavior for special

tank conﬁ gurations (e.g., shovel bottoms, highly

crowned tank bottoms, tanks on grillage) can

be unique and are beyond the scope of this

standard.

15.7.6.1.6 Local Shear Transfer Local transfer of the

shear from the roof to the wall and the wall of the

tank into the base shall be considered. For cylindrical

tanks and vessels, the peak local tangential shear per

unit length shall be calculated by

max

(15.7-15)

a. Tangential shear in ﬂ at bottom steel tanks shall

be transferred through the welded connection to

the steel bottom. This transfer mechanism is

deemed acceptable for steel tanks designed in

accordance with the reference documents where

< 1.0g.

b. For concrete tanks with a sliding base where the

lateral shear is resisted by friction between the tank

wall and the base, the friction coefﬁ cient value

used for design shall not exceed tan 30°.

c. Fixed-base or hinged-base concrete tanks transfer

the horizontal seismic base shear shared by

membrane (tangential) shear and radial shear into

the foundation. For anchored ﬂ exible-base concrete

tanks, the majority of the base shear is resisted by

membrane (tangential) shear through the anchoring

system with only insigniﬁ cant vertical bending in

the wall. The connection between the wall and

ﬂ oor shall be designed to resist the maximum

tangential shear.

Table 15.7-3 Minimum Required Freeboard

Value of S

Risk Category

I or II III IV

< 0.167gaaδ

0.167g ≤ S

< 0.33ga aδ

0.33g ≤ S

< 0.50ga0.7δ

≥ 0.50ga0.7δ

NOTE: No minimum freeboard is required.

Freeboard equal to the calculated wave height, δ

, is required

unless one of the following alternatives is provided: (1) Secondary

containment is provided to control the product spill. (2) The roof

and supporting structure are designed to contain the sloshing liquid.

A freeboard equal to 0.7δ

is required unless one of the following

alternatives is provided: (1) Secondary containment is provided to

control the product spill. (2) The roof and supporting structure are

designed to contain the sloshing liquid.

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MINIMUM DESIGN LOADS

155

15.7.6.1.7 Pressure Stability For steel tanks, the

internal pressure from the stored product stiffens thin

cylindrical shell structural elements subjected to

membrane compression forces. This stiffening effect

is permitted to be considered in resisting seismically

induced compressive forces if permitted by the

reference document or the authority having

jurisdiction.

15.7.6.1.8 Shell Support Steel tanks resting on

concrete ring walls or slabs shall have a uniformly

supported annulus under the shell. Uniform support

shall be provided by one of the following methods:

a. Shimming and grouting the annulus.

b. Using ﬁ berboard or other suitable padding.

c. Using butt-welded bottom or annular plates resting

directly on the foundation.

d. Using closely spaced shims (without structural

grout) provided that the localized bearing loads are

considered in the tank wall and foundation to

prevent local crippling and spalling.

Anchored tanks shall be shimmed and grouted.

Local buckling of the steel shell for the peak com-

pressive force due to operating loads and seismic

overturning shall be considered.

15.7.6.1.9 Repair, Alteration, or Reconstruction

Repairs, modiﬁ cations, or reconstruction (i.e., cut

down and re-erect) of a tank or vessel shall conform

to industry standard practice and this standard. For

welded steel tanks storing liquids, see API 653 and

the applicable reference document listed in Chapter

23. Tanks that are relocated shall be re-evaluated

for the seismic loads for the new site and the

requirements of new construction in accordance

with the appropriate reference document and this

standard.

15.7.7 Water Storage and Water Treatment Tanks

and Vessels

15.7.7.1 Welded Steel

Welded steel water storage tanks and vessels

shall be designed in accordance with the seismic

requirements of AWWA D100.

15.7.7.2 Bolted Steel

Bolted steel water storage structures shall be

designed in accordance with the seismic requirements

of AWWA D103 except that the design input forces

of AWWA D100 shall be modiﬁ ed in the same

manner shown in Section 15.7.7.1 of this standard.

15.7.7.3 Reinforced and Prestressed Concrete

Reinforced and prestressed concrete tanks shall

be designed in accordance with the seismic require-

ments of AWWA D110, AWWA D115, or ACI 350.3

except that the importance factor, I

, shall be deter-

mined according to Section 15.4.1.1, the response

modiﬁ cation coefﬁ cient, R, shall be taken from Table

15.4-2, and the design input forces for strength design

procedures shall be determined using the procedures

of ACI 350.3 except

a. S

shall be substituted for C

in ACI 350.3

Section 9.4.2 using Eqs. 15.7-10 for T

≤ T

and

15.7-11. for T

> T

from Section 15.7.6.1; and

b. The value of C

from ACI 350.3 Section 9.4.3

shall be determined using the procedures of

Section 15.7.2(c). The values of I, Ri, and

b as deﬁ ned in ACI 350.3 shall be taken as

1.0 in the determination of vertical seismic

effects.

15.7.8 Petrochemical and Industrial Tanks and

Vessels Storing Liquids

15.7.8.1 Welded Steel

Welded steel petrochemical and industrial tanks

and vessels storing liquids under an internal pressure

of less than or equal to 2.5 psig (17.2 kpa g) shall be

designed in accordance with the seismic requirements

of API 650. Welded steel petrochemical and industrial

tanks and vessels storing liquids under an internal

pressure of greater than 2.5 psig (17.2 kpa g) and less

than or equal to 15 psig (104.4 kpa g) shall be

designed in accordance with the seismic requirements

of API 620.

15.7.8.2 Bolted Steel

Bolted steel tanks used for storage of production

liquids. API 12B covers the material, design, and

erection requirements for vertical, cylindrical, above-

ground bolted tanks in nominal capacities of 100 to

10,000 barrels for production service. Unless required

by the authority having jurisdiction, these temporary

structures need not be designed for seismic loads. If

design for seismic load is required, the loads are

permitted to be adjusted for the temporary nature of

the anticipated service life.

15.7.8.3 Reinforced and Prestressed Concrete

Reinforced concrete tanks for the storage of

petrochemical and industrial liquids shall be designed

in accordance with the force requirements of Section

15.7.7.3.

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

156

15.7.9 Ground-Supported Storage Tanks for

Granular Materials

15.7.9.1 General

The intergranular behavior of the material shall

be considered in determining effective mass and load

paths, including the following behaviors:

a. Increased lateral pressure (and the resulting hoop

stress) due to loss of the intergranular friction of

the material during the seismic shaking.

b. Increased hoop stresses generated from temperature

changes in the shell after the material has been

compacted.

c. Intergranular friction, which can transfer seismic

shear directly to the foundation.

15.7.9.2 Lateral Force Determination

The lateral forces for tanks and vessels storing

granular materials at grade shall be determined by the

requirements and accelerations for short period

structures (i.e., S

15.7.9.3 Force Distribution to Shell and Foundation

15.7.9.3.1 Increased Lateral Pressure The increase in

lateral pressure on the tank wall shall be added to the

static design lateral pressure but shall not be used in

the determination of pressure stability effects on the

axial buckling strength of the tank shell.

15.7.9.3.2 Effective Mass A portion of a stored

granular mass will act with the shell (the effective

mass). The effective mass is related to the physical

characteristics of the product, the height-to-diameter

(H/D) ratio of the tank, and the intensity of the

seismic event. The effective mass shall be used to

determine the shear and overturning loads resisted by

the tank.

15.7.9.3.3 Effective Density The effective density

factor (that part of the total stored mass of product

that is accelerated by the seismic event) shall be

determined in accordance with ACI 313.

15.7.9.3.4 Lateral Sliding For granular storage tanks

that have a steel bottom and are supported such that

friction at the bottom to foundation interface can

resist lateral shear loads, no additional anchorage to

prevent sliding is required. For tanks without steel

bottoms (i.e., the material rests directly on the

foundation), shear anchorage shall be provided to

prevent sliding.

15.7.9.3.5 Combined Anchorage Systems If separate

anchorage systems are used to prevent overturning

and sliding, the relative stiffness of the systems shall

be considered in determining the load distribution.

15.7.9.4 Welded Steel Structures

Welded steel granular storage structures shall be

designed in accordance with the seismic requirements

of this standard. Component allowable stresses and

materials shall be per AWWA D100, except the

allowable circumferential membrane stresses and

material requirements in API 650 shall apply.

15.7.9.5 Bolted Steel Structures

Bolted steel granular storage structures shall be

designed in accordance with the seismic requirements

of this section. Component allowable stresses and

materials shall be per AWWA D103.

15.7.9.6 Reinforced Concrete Structures Reinforced

concrete structures for the storage of granular materi-

als shall be designed in accordance with the seismic

force requirements of this standard and the require-

ments of ACI 313.

15.7.9.7 Prestressed Concrete Structures

Prestressed concrete structures for the storage of

granular materials shall be designed in accordance

with the seismic force requirements of this standard

and the requirements of ACI 313.

15.7.10 Elevated Tanks and Vessels for Liquids

and Granular Materials

15.7.10.1 General

This section applies to tanks, vessels, bins, and

hoppers that are elevated above grade where the

supporting tower is an integral part of the structure, or

where the primary function of the tower is to support

the tank or vessel. Tanks and vessels that are sup-

ported within buildings or are incidental to the

primary function of the tower are considered mechani-

cal equipment and shall be designed in accordance

with Chapter 13.

Elevated tanks shall be designed for the force and

displacement requirements of the applicable reference

document or Section 15.4.

15.7.10.2 Effective Mass

The design of the supporting tower or pedestal,

anchorage, and foundation for seismic overturning

shall assume the material stored is a rigid mass acting

at the volumetric center of gravity. The effects of

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MINIMUM DESIGN LOADS

157

ﬂ uid–structure interaction are permitted to be consid-

ered in determining the forces, effective period, and

mass centroids of the system if the following require-

ments are met:

a. The sloshing period, T

is greater than 3T where T

= natural period of the tank with conﬁ ned liquid

(rigid mass) and supporting structure.

b. The sloshing mechanism (i.e., the percentage of

convective mass and centroid) is determined for

the speciﬁ c conﬁ guration of the container by

detailed ﬂ uid–structure interaction analysis or

testing.

Soil–structure interaction is permitted to be

included in determining T providing the requirements

of Chapter 19 are met.

15.7.10.3 P-Delta Effects

The lateral drift of the elevated tank shall be

considered as follows:

a. The design drift, the elastic lateral displacement of

the stored mass center of gravity, shall be increased

by the factor C

for evaluating the additional load

in the support structure.

b. The base of the tank shall be assumed to be ﬁ xed

rotationally and laterally.

c. Deﬂ ections due to bending, axial tension, or

compression shall be considered. For pedestal

tanks with a height-to-diameter ratio less than 5,

shear deformations of the pedestal shall be

considered.

d. The dead load effects of roof-mounted equipment

or platforms shall be included in the analysis.

e. If constructed within the plumbness tolerances

speciﬁ ed by the reference document, initial tilt

need not be considered in the P-delta analysis.

15.7.10.4 Transfer of Lateral Forces into

Support Tower

For post supported tanks and vessels that are

cross-braced:

a. The bracing shall be installed in such a manner as

to provide uniform resistance to the lateral load

(e.g., pretensioning or tuning to attain equal sag).

b. The additional load in the brace due to the

eccentricity between the post to tank attachment

and the line of action of the bracing shall be

included.

c. Eccentricity of compression strut line of action

(elements that resist the tensile pull from the

bracing rods in the seismic force-resisting systems)

with their attachment points shall be considered.

d. The connection of the post or leg with the founda-

tion shall be designed to resist both the vertical and

lateral resultant from the yield load in the bracing

assuming the direction of the lateral load is

oriented to produce the maximum lateral shear at

the post to foundation interface. Where multiple

rods are connected to the same location, the

anchorage shall be designed to resist the concurrent

tensile loads in the braces.

15.7.10.5 Evaluation of Structures Sensitive to

Buckling Failure

Shell structures that support substantial loads may

exhibit a primary mode of failure from localized or

general buckling of the support pedestal or skirt due

to seismic loads. Such structures may include single

pedestal water towers, skirt-supported process vessels,

and similar single member towers. Where the struc-

tural assessment concludes that buckling of the

support is the governing primary mode of failure,

structures speciﬁ ed in this standard to be designed to

subsections a and b below and those that are assigned

as Risk Category IV shall be designed to resist the

seismic forces as follows:

a. The seismic response coefﬁ cient for this evaluation

shall be in accordance with Section 12.8.1.1 of this

standard with I

/R set equal to 1.0. Soil–structure

and ﬂ uid–structure interaction is permitted to be

utilized in determining the structural response.

Vertical or orthogonal combinations need not be

considered.

b. The resistance of the structure shall be deﬁ ned as

the critical buckling resistance of the element, that

is, a factor of safety set equal to 1.0.

15.7.10.6 Welded Steel Water Storage Structures

Welded steel elevated water storage structures

shall be designed and detailed in accordance with the

seismic requirements of AWWA D100 with the

structural height limits imposed by Table 15.4-2.

15.7.10.7 Concrete Pedestal (Composite) Tanks

Concrete pedestal (composite) elevated water

storage structures shall be designed in accordance

with the requirements of ACI 371R except that the

design input forces shall be modiﬁ ed as follows:

In Eq. 4-8a of ACI 371R,

For T

< T ≤ 2.5 s, replace the term

with

⎛

⎝

⎜

⎞

⎠

⎟

(15.7-24)

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

158

In Eq. 4-8b of ACI 371R, replace the term

25. C

with

⎛

⎝

⎜

⎞

⎠

⎟

(15.7-25)

In Eq. 4-9 of ACI 371R, replace the term 0.5C

with

0.2S

(15.7-26)

15.7.10.7.1 Analysis Procedures The equivalent lateral

force procedure is permitted for all concrete pedestal

tanks and shall be based on a ﬁ xed-base, single

degree-of-freedom model. All mass, including the

liquid, shall be considered rigid unless the sloshing

mechanism (i.e., the percentage of convective mass

and centroid) is determined for the speciﬁ c conﬁ gura-

tion of the container by detailed ﬂ uid–structure

interaction analysis or testing. Soil–structure interac-

tion is permitted to be included. A more rigorous

analysis is permitted.

15.7.10.7.2 Structure Period The fundamental period

of vibration of the structure shall be established using

the uncracked structural properties and deformational

characteristics of the resisting elements in a properly

substantiated analysis. The period used to calculate

the seismic response coefﬁ cient shall not exceed

2.5 s.

15.7.11 Boilers and Pressure Vessels

15.7.11.1 General

Attachments to the pressure boundary, supports,

and seismic force-resisting anchorage systems for

boilers and pressure vessels shall be designed to meet

the force and displacement requirements of Section

15.3 or 15.4 and the additional requirements of this

section. Boilers and pressure vessels categorized as

Risk Categories III or IV shall be designed to meet

the force and displacement requirements of Section

15.3 or 15.4.

15.7.11.2 ASME Boilers and Pressure Vessels

Boilers or pressure vessels designed and con-

structed in accordance with ASME BPVC shall be

deemed to meet the requirements of this section

provided that the force and displacement requirements

of Section 15.3 or 15.4 are used with appropriate

scaling of the force and displacement requirements to

the working stress design basis.

15.7.11.3 Attachments of Internal Equipment

and Refractory

Attachments to the pressure boundary for internal

and external ancillary components (refractory,

cyclones, trays, etc.) shall be designed to resist the

seismic forces speciﬁ ed in this standard to safeguard

against rupture of the pressure boundary. Alternatively,

the element attached is permitted to be designed to fail

prior to damaging the pressure boundary provided that

the consequences of the failure do not place the

pressure boundary in jeopardy. For boilers or vessels

containing liquids, the effect of sloshing on the internal

equipment shall be considered if the equipment can

damage the integrity of the pressure boundary.

15.7.11.4 Coupling of Vessel and Support Structure

Where the mass of the operating vessel or vessels

supported is greater than 25 percent of the total mass

of the combined structure, the structure and vessel

designs shall consider the effects of dynamic coupling

between each other. Coupling with adjacent, connected

structures such as multiple towers shall be considered

if the structures are interconnected with elements that

will transfer loads from one structure to the other.

15.7.11.5 Effective Mass

Fluid–structure interaction (sloshing) shall be

considered in determining the effective mass of the

stored material providing sufﬁ cient liquid surface

exists for sloshing to occur and the T

is greater than

3T. Changes to or variations in material density with

pressure and temperature shall be considered.

15.7.11.6 Other Boilers and Pressure Vessels

Boilers and pressure vessels designated Risk

Category IV, but not designed and constructed in

accordance with the requirements of ASME BPVC,

shall meet the following requirements:

The seismic loads in combination with other

service loads and appropriate environmental effects

shall not exceed the material strength shown in

Table 15.7-4.

Consideration shall be made to mitigate seismic

impact loads for boiler or vessel elements constructed

of nonductile materials or vessels operated in such a

way that material ductility is reduced (e.g., low

temperature applications).

15.7.11.7 Supports and Attachments for Boilers and

Pressure Vessels

Attachments to the pressure boundary and support

for boilers and pressure vessels shall meet the

following requirements:

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MINIMUM DESIGN LOADS

159

a. Attachments and supports transferring seismic

loads shall be constructed of ductile materials

suitable for the intended application and environ-

mental conditions.

b. Anchorage shall be in accordance with Section

15.4.9, whereby the anchor embedment into the

concrete is designed to develop the steel strength

of the anchor in tension. The steel strength of the

anchor in tension shall be determined in accor-

dance with ACI 318 Appendix D Eq. D-3. The

anchor shall have a minimum gauge length of eight

diameters. The load combinations with over-

strength of Section 12.4.3 are not to be used to size

the anchor bolts for tanks and horizontal and

vertical vessels.

c. Seismic supports and attachments to structures

shall be designed and constructed so that the

support or attachment remains ductile throughout

the range of reversing seismic lateral loads and

displacements.

d. Vessel attachments shall consider the potential

effect on the vessel and the support for uneven

vertical reactions based on variations in relative

stiffness of the support members, dissimilar details,

nonuniform shimming, or irregular supports.

Uneven distribution of lateral forces shall consider

the relative distribution of the resisting elements,

the behavior of the connection details, and vessel

shear distribution.

The requirements of Sections 15.4 and 15.7.10.5

shall also be applicable to this section.

15.7.12 Liquid and Gas Spheres

15.7.12.1 General

Attachments to the pressure or liquid boundary,

supports, and seismic force-resisting anchorage

systems for liquid and gas spheres shall be designed

to meet the force and displacement requirements of

Section 15.3 or 15.4 and the additional requirements

of this section. Spheres categorized as Risk Category

III or IV shall themselves be designed to meet the

force and displacement requirements of Section 15.3

or 15.4.

15.7.12.2 ASME Spheres

Spheres designed and constructed in accordance

with Section VIII of ASME BPVC shall be deemed to

meet the requirements of this section providing the

force and displacement requirements of Section 15.3

or 15.4 are used with appropriate scaling of the force

and displacement requirements to the working stress

design basis.

15.7.12.3 Attachments of Internal Equipment

and Refractory

Attachments to the pressure or liquid boundary

for internal and external ancillary components

(refractory, cyclones, trays, etc.) shall be designed to

resist the seismic forces speciﬁ ed in this standard to

safeguard against rupture of the pressure boundary.

Alternatively, the element attached to the sphere

could be designed to fail prior to damaging the

pressure or liquid boundary providing the conse-

quences of the failure does not place the pressure

boundary in jeopardy. For spheres containing liquids,

the effect of sloshing on the internal equipment shall

be considered if the equipment can damage the

pressure boundary.

15.7.12.4 Effective Mass

Fluid–structure interaction (sloshing) shall be

considered in determining the effective mass of the

stored material providing sufﬁ cient liquid surface

exists for sloshing to occur and the T

is greater than

3T. Changes to or variations in ﬂ uid density shall be

considered.

Table 15.7-4 Maximum Material Strength

Material Minimum Ratio F

Max. Material Strength

Vessel Material

Max. Material Strength

Threaded Material

Ductile (e.g., steel, aluminum, copper)

1.33

90%

70%

Semiductile

1.2

70%

50%

Nonductile (e.g., cast iron, ceramics, ﬁ berglass) NA

25%

20%

Threaded connection to vessel or support system.

Minimum 20% elongation per the ASTM material speciﬁ cation.

Based on material minimum speciﬁ ed yield strength.

Minimum 15% elongation per the ASTM material speciﬁ cation.

Based on material minimum speciﬁ ed tensile strength.

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CHAPTER 15 SEISMIC DESIGN REQUIREMENTS FOR NONBUILDING STRUCTURES

160

15.7.12.5 Post and Rod Supported

For post supported spheres that are cross-braced:

a. The requirements of Section 15.7.10.4 shall also be

applicable to this section.

b. The stiffening effect (reduction in lateral drift)

from pretensioning of the bracing shall be consid-

ered in determining the natural period.

c. The slenderness and local buckling of the posts

shall be considered.

d. Local buckling of the sphere shell at the post

attachment shall be considered.

e. For spheres storing liquids, bracing connections

shall be designed and constructed to develop the

minimum published yield strength of the brace. For

spheres storing gas vapors only, bracing connection

shall be designed for Ω

times the maximum

design load in the brace. Lateral bracing connec-

tions directly attached to the pressure or liquid

boundary are prohibited.

15.7.12.6 Skirt Supported

For skirt-supported spheres, the following

requirements shall apply:

a. The requirements of Section 15.7.10.5 shall also

apply.

b. The local buckling of the skirt under compressive

membrane forces due to axial load and bending

moments shall be considered.

c. Penetration of the skirt support (manholes, piping,

etc.) shall be designed and constructed to maintain

the strength of the skirt without penetrations.

15.7.13 Refrigerated Gas Liquid Storage Tanks

and Vessels

15.7.13.1 General

Tanks and facilities for the storage of liqueﬁ ed

hydrocarbons and refrigerated liquids shall meet the

requirements of this standard. Low-pressure welded

steel storage tanks for liqueﬁ ed hydrocarbon gas (e.g.,

LPG, butane, etc.) and refrigerated liquids (e.g.,

ammonia) shall be designed in accordance with the

requirements of Section 15.7.8 and API 620.

15.7.14 Horizontal, Saddle Supported Vessels for

Liquid or Vapor Storage

15.7.14.1 General

Horizontal vessels supported on saddles (some-

times referred to as “blimps”) shall be designed to

meet the force and displacement requirements of

Section 15.3 or 15.4.

15.7.14.2 Effective Mass

Changes to or variations in material density shall

be considered. The design of the supports, saddles,

anchorage, and foundation for seismic overturning

shall assume the material stored is a rigid mass acting

at the volumetric center of gravity.

15.7.14.3 Vessel Design

Unless a more rigorous analysis is performed

a. Horizontal vessels with a length-to-diameter ratio

of 6 or more are permitted to be assumed to be a

simply supported beam spanning between the

saddles for determining the natural period of

vibration and global bending moment.

b. For horizontal vessels with a length-to-diameter

ratio of less than 6, the effects of “deep beam

shear” shall be considered where determining the

fundamental period and stress distribution.

c. Local bending and buckling of the vessel shell at

the saddle supports due to seismic load shall be

considered. The stabilizing effects of internal

pressure shall not be considered to increase the

buckling resistance of the vessel shell.

d. If the vessel is a combination of liquid and gas

storage, the vessel and supports shall be designed

both with and without gas pressure acting (assume

piping has ruptured and pressure does not exist).

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161

Chapter 16

SEISMIC RESPONSE HISTORY PROCEDURES

horizontal ground motion acceleration components

that shall be selected and scaled from individual

recorded events. Appropriate ground motions shall be

selected from events having magnitudes, fault

distance, and source mechanisms that are consistent

with those that control the maximum considered

earthquake. Where the required number of recorded

ground motion pairs is not available, appropriate

simulated ground motion pairs are permitted to be

used to make up the total number required. For each

pair of horizontal ground motion components, a

square root of the sum of the squares (SRSS) spec-

trum shall be constructed by taking the SRSS of the 5

percent-damped response spectra for the scaled

components (where an identical scale factor is applied

to both components of a pair). Each pair of motions

shall be scaled such that in the period range from 0.2T

to 1.5T, the average of the SRSS spectra from all

horizontal component pairs does not fall below the

corresponding ordinate of the response spectrum used

in the design, determined in accordance with Section

11.4.5 or 11.4.7.

At sites within 3 miles (5 km) of the active fault

that controls the hazard, each pair of components shall

be rotated to the fault-normal and fault-parallel

directions of the causative fault and shall be scaled so

that the average of the fault-normal components is not

less than the MCE

response spectrum for the period

range from 0.2T to 1.5T.

16.1.4 Response Parameters

For each ground motion analyzed, the individual

response parameters shall be multiplied by the

following scalar quantities:

a. Force response parameters shall be multiplied by

/R, where I

is the importance factor determined

in accordance with Section 11.5.1 and R is the

Response Modiﬁ cation Coefﬁ cient selected in

accordance with Section 12.2.1.

b. Drift quantities shall be multiplied by C

/R, where

is the deﬂ ection ampliﬁ cation factor speciﬁ ed in

Table 12.2-1.

For each ground motion i, where i is the designa-

tion assigned to each ground motion, the maximum

value of the base shear, V

, member forces, Q

, scaled

as indicated in the preceding text and story drifts, Δ

at each story as deﬁ ned in Section 12.8.6 shall be

16.1 LINEAR RESPONSE

HISTORY PROCEDURE

Where linear response history procedure is performed

the requirements of this chapter shall be satisﬁ ed.

16.1.1 Analysis Requirements

A linear response history analysis shall consist of

an analysis of a linear mathematical model of the

structure to determine its response, through methods

of numerical integration, to suites of ground motion

acceleration histories compatible with the design

response spectrum for the site. The analysis shall be

performed in accordance with the requirements of this

section.

16.1.2 Modeling

Mathematical models shall conform to the

requirements of Section 12.7.

16.1.3 Ground Motion

A suite of not less than three appropriate ground

motions shall be used in the analysis. Ground motion

shall conform to the requirements of this section.

16.1.3.1 Two-Dimensional Analysis

Where two-dimensional analyses are performed,

each ground motion shall consist of a horizontal

acceleration history, selected from an actual recorded

event. Appropriate acceleration histories shall be

obtained from records of events having magnitudes,

fault distance, and source mechanisms that are

consistent with those that control the maximum

considered earthquake. Where the required number of

appropriate recorded ground motion records are not

available, appropriate simulated ground motion

records shall be used to make up the total number

required. The ground motions shall be scaled such

that the average value of the 5 percent damped

response spectra for the suite of motions is not less

than the design response spectrum for the site for

periods ranging from 0.2T to 1.5T where T is the

natural period of the structure in the fundamental

mode for the direction of response being analyzed.

16.1.3.2 Three-Dimensional Analysis

Where three-dimensional analyses are performed,

ground motions shall consist of pairs of appropriate

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CHAPTER 16 SEISMIC RESPONSE HISTORY PROCEDURES

162

determined. Where the maximum scaled base shear

predicted by the analysis, V

, is less than 85 percent of

the value of V determined using the minimum value

of C

set forth in Eq. 12.8-5 or when located where S

is equal to or greater than 0.6g, the minimum value of

set forth in Eq. 12.8-6, the scaled member forces,

, shall be additionally multiplied by

where V is

the minimum base shear that has been determined

using the minimum value of C

set forth in Eq. 12.8-5,

or when located where S

is equal to or greater than

0.6g, the minimum value of C

set forth in Eq. 12.8-6.

Where the maximum scaled base shear predicted by

the analysis, V

, is less than 0.85C

W, where C

from Eq. 12.8-6, drifts shall be multiplied by

0.85

If at least seven ground motions are analyzed, the

design member forces used in the load combinations

of Section 12.4.2.1 and the design story drift used in

the evaluation of drift in accordance with Section

12.12.1 are permitted to be taken respectively as the

average of the scaled Q

and Δ

values determined

from the analyses and scaled as indicated in the

preceding text. If fewer than seven ground motions

are analyzed, the design member forces and the

design story drift shall be taken as the maximum

value of the scaled Q

and Δ

values determined from

the analyses.

Where this standard requires consideration of the

seismic load effects including overstrength factor of

Section 12.4.3, the value of Ω

need not be taken

larger than the maximum of the unscaled value, Q

obtained from the analyses.

16.1.5 Horizontal Shear Distribution

The distribution of horizontal shear shall be in

accordance with Section 12.8.4 except that ampliﬁ ca-

tion of torsion in accordance with Section 12.8.4.3 is

not required where accidental torsion effects are

included in the dynamic analysis model.

16.2 NONLINEAR RESPONSE

HISTORY PROCEDURE

Where nonlinear response history procedure is

performed the requirements of Section 16.2 shall be

satisﬁ ed.

16.2.1 Analysis Requirements

A nonlinear response history analysis shall

consist of an analysis of a mathematical model of the

structure that directly accounts for the nonlinear

hysteretic behavior of the structure’s elements to

determine its response through methods of numerical

integration to suites of ground motion acceleration

histories compatible with the design response spec-

trum for the site. The analysis shall be performed in

accordance with this section. See Section 12.1.1 for

limitations on the use of this procedure.

16.2.2 Modeling

A mathematical model of the structure shall be

constructed that represents the spatial distribution of

mass throughout the structure. The hysteretic behavior

of elements shall be modeled consistent with suitable

laboratory test data and shall account for all signiﬁ -

cant yielding, strength degradation, stiffness degrada-

tion, and hysteretic pinching indicated by such test

data. Strength of elements shall be based on expected

values considering material overstrength, strain

hardening, and hysteretic strength degradation. Linear

properties, consistent with the requirements of Section

12.7.3, are permitted to be used for those elements

demonstrated by the analysis to remain within their

linear range of response. The structure shall be

assumed to have a ﬁ xed-base, or alternatively, it is

permitted to use realistic assumptions with regard to

the stiffness and load-carrying characteristics of the

foundations consistent with site-speciﬁ c soils data and

rational principles of engineering mechanics.

For regular structures with independent orthogo-

nal seismic force-resisting systems, independent 2-D

models are permitted to be constructed to represent

each system. For structures having a horizontal

structural irregularity of Type 1a, 1b, 4, or 5 of Table

12.3-1 or structures without independent orthogonal

systems, a 3-D model incorporating a minimum of

three dynamic degrees of freedom consisting of

translation in two orthogonal plan directions and

torsional rotation about the vertical axis at each level

of the structure shall be used. Where the diaphragms

are not rigid compared to the vertical elements of the

seismic force-resisting system, the model should

include representation of the diaphragm’s ﬂ exibility

and such additional dynamic degrees of freedom as

are required to account for the participation of the

diaphragm in the structure’s dynamic response.

16.2.3 Ground Motion and Other Loading

Ground motion shall conform to the requirements

of Section 16.1.3. The structure shall be analyzed for

the effects of these ground motions simultaneously

with the effects of dead load in combination with not

less than 25 percent of the required live loads.

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MINIMUM DESIGN LOADS

163

16.2.4 Response Parameters

For each ground motion analyzed, individual

response parameters consisting of the maximum value

of the individual member forces, Q

, member

inelastic deformations, ψ

, and story drifts, Δ

, at each

story shall be determined, where i is the designation

assigned to each ground motion.

If at least seven ground motions are analyzed, the

design values of member forces, Q

, member inelastic

deformations, ψ, and story drift, Δ, are permitted to

be taken as the average of the Q

, ψ

, and Δ

values

determined from the analyses. If fewer than seven

ground motions are analyzed, the design member

forces, Q

, design member inelastic deformations, ψ,

and the design story drift, Δ, shall be taken as the

maximum value of the Q

, ψ

, and Δ

values deter-

mined from the analyses.

16.2.4.1 Member Strength

The adequacy of members to resist the combina-

tion of load effects of Section 12.4 need not be

evaluated.

EXCEPTION: Where this standard requires

consideration of the seismic load effects including

overstrength factor of Section 12.4.3, the maximum

value of Q

obtained from the suite of analyses shall

be taken in place of the quantity Ω

E·

16.2.4.2 Member Deformation

The adequacy of individual members and their

connections to withstand the estimated design

deformation values, ψ

, as predicted by the analyses

shall be evaluated based on laboratory test data for

similar elements. The effects of gravity and other

loads on member deformation capacity shall be

considered in these evaluations. Member deformation

shall not exceed two-thirds of a value that results in

loss of ability to carry gravity loads or that results in

deterioration of member strength to less than the 67

percent of the peak value.

16.2.4.3 Story Drift

The design story drift, Δ

, obtained from the

analyses shall not exceed 125 percent of the drift limit

speciﬁ ed in Section 12.12.1.

16.2.5 Design Review

A design review of the seismic force-resisting

system and the structural analysis shall be performed

by an independent team of registered design profes-

sionals in the appropriate disciplines and others

experienced in seismic analysis methods and the

theory and application of nonlinear seismic analysis

and structural behavior under extreme cyclic loads.

The design review shall include, but need not be

limited to, the following:

1. Review of any site-speciﬁ c seismic criteria

employed in the analysis including the develop-

ment of site-speciﬁ c spectra and ground motion

time histories.

2. Review of acceptance criteria used to demonstrate

the adequacy of structural elements and systems to

withstand the calculated force and deformation

demands, together with that laboratory and other

data used to substantiate these criteria.

3. Review of the preliminary design including the

selection of structural system and the conﬁ guration

of structural elements.

4. Review of the ﬁ nal design of the entire structural

system and all supporting analyses.

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c16.indd 164 4/14/2010 11:02:48 AM

165

Chapter 17

SEISMIC DESIGN REQUIREMENTS FOR SEISMICALLY

ISOLATED STRUCTURES

EFFECTIVE STIFFNESS: The value of the

lateral force in the isolation system, or an element

thereof, divided by the corresponding lateral

displacement.

ISOLATION INTERFACE: The boundary

between the upper portion of the structure, which is

isolated, and the lower portion of the structure, which

moves rigidly with the ground.

ISOLATION SYSTEM: The collection of

structural elements that includes all individual isolator

units, all structural elements that transfer force

between elements of the isolation system, and all

connections to other structural elements. The

isolation system also includes the wind-restraint

system, energy-dissipation devices, and/or the

displacement restraint system if such systems and

devices are used to meet the design requirements of

this chapter.

ISOLATOR UNIT: A horizontally ﬂ exible and

vertically stiff structural element of the isolation

system that permits large lateral deformations under

design seismic load. An isolator unit is permitted to

be used either as part of, or in addition to, the

weight-supporting system of the structure.

MAXIMUM DISPLACEMENT: The maximum

considered earthquake lateral displacement, excluding

additional displacement due to actual and accidental

torsion.

SCRAGGING: Cyclic loading or working of

rubber products, including elastomeric isolators, to

effect a reduction in stiffness properties, a portion of

which will be recovered over time.

WIND-RESTRAINT SYSTEM: The collection

of structural elements that provides restraint of the

seismic-isolated structure for wind loads. The wind-

restraint system is permitted to be either an integral

part of isolator units or a separate device.

17.1.3 Notation

= numerical coefﬁ cient as set forth in Table

17.5-1 for effective damping equal to β

= numerical coefﬁ cient as set forth in Table

17.5-1 for effective damping equal to β

b = shortest plan dimension of the structure, in

ft (mm) measured perpendicular to d

17.1 GENERAL

Every seismically isolated structure and every portion

thereof shall be designed and constructed in accor-

dance with the requirements of this section and the

applicable requirements of this standard.

17.1.1 Variations in Material Properties

The analysis of seismically isolated structures,

including the substructure, isolators, and superstruc-

ture, shall consider variations in seismic isolator

material properties over the projected life of the

structure including changes due to aging, contamina-

tion, environmental exposure, loading rate, scragging,

and temperature.

17.1.2 Deﬁ nitions

DISPLACEMENT:

Design Displacement: The design earthquake

lateral displacement, excluding additional

displacement due to actual and accidental

torsion, required for design of the isolation

system.

Total Design Displacement: The design

earthquake lateral displacement, including

additional displacement due to actual and

accidental torsion, required for design of the

isolation system or an element thereof.

Total Maximum Displacement: The maximum

considered earthquake lateral displacement,

including additional displacement due to actual

and accidental torsion, required for veriﬁ cation

of the stability of the isolation system or

elements thereof, design of structure separa-

tions, and vertical load testing of isolator unit

prototypes.

DISPLACEMENT RESTRAINT SYSTEM: A

collection of structural elements that limits lateral

displacement of seismically isolated structures due to

the maximum considered earthquake.

EFFECTIVE DAMPING: The value of equiva-

lent viscous damping corresponding to energy

dissipated during cyclic response of the isolation

system.

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CHAPTER 17 SEISMIC DESIGN REQUIREMENTS FOR SEISMICALLY ISOLATED STRUCTURES

166

= design displacement, in in. (mm), at the

center of rigidity of the isolation system in

the direction under consideration, as

prescribed by Eq. 17.5-1

D′

= design displacement, in in. (mm), at the

center of rigidity of the isolation system in

the direction under consideration, as

prescribed by Eq. 17.6-1

= maximum displacement, in in. (mm), at

the center of rigidity of the isolation

system in the direction under consider-

ation, as prescribed by Eq. 17.5-3

D′

= maximum displacement, in in. (mm), at

the center of rigidity of the isolation

system in the direction under consider-

ation, as prescribed by Eq. 17.6-2

= total design displacement, in in. (mm), of

an element of the isolation system includ-

ing both translational displacement at the

center of rigidity and the component of

torsional displacement in the direction

under consideration, as prescribed by

Eq. 17.5-5

= total maximum displacement, in in. (mm),

of an element of the isolation system

including both translational displacement

at the center of rigidity and the component

of torsional displacement in the direction

under consideration, as prescribed by

Eq. 17.5-6

d = longest plan dimension of the structure, in

ft (mm)

loop

= energy dissipated in kips-in. (kN-mm), in

an isolator unit during a full cycle of

reversible load over a test displacement

range from Δ

to Δ

–

, as measured by the

area enclosed by the loop of the force-

deﬂ ection curve

e = actual eccentricity, in ft (mm), measured

in plan between the center of mass of the

structure above the isolation interface and

the center of rigidity of the isolation

system, plus accidental eccentricity, in ft.

(mm), taken as 5 percent of the maximum

building dimension perpen dicular to the

direction of force under consideration

–

= minimum negative force in an isolator unit

during a single cycle of prototype testing

at a displacement amplitude of Δ

–

= maximum positive force in kips (kN)

in an isolator unit during a single cycle

of proto type testing at a displacement

amplitude of Δ

= total force distributed over the height of

the structure above the isolation interface

as prescribed by Eq. 17.5-9

Dmax

= maximum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the

design displacement in the horizontal

direction under consideration, as

prescribed by Eq. 17.8-3

Dmin

= minimum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the

design displacement in the horizontal

direction under consideration, as

prescribed by Eq. 17.8-4

Mmax

= maximum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the

maximum displacement in the horizontal

direction under consideration, as

prescribed by Eq. 17.8-5

Mmin

= minimum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the

maximum displacement in the horizontal

direction under consideration, as pre-

scribed by Eq. 17.8-6

eff

= effective stiffness of an isolator unit, as

prescribed by Eq. 17.8-1

L = effect of live load in Chapter 17

= effective period, in s, of the seismically

isolated structure at the design displace-

ment in the direction under consideration,

as prescribed by Eq. 17.5-2

= effective period, in s, of the seismically

isolated structure at the maximum

displacement in the direction under

consideration, as prescribed by

Eq. 17.5-4

= total lateral seismic design force or shear

on elements of the isolation system or

elements below isolation system, as

prescribed by Eq. 17.5-7

= total lateral seismic design force or shear

on elements above the isolation system, as

prescribed by Eq. 17.5-8

y = distance, in ft (mm), between the center

of rigidity of the isolation system rigidity

and the element of interest measured

perpendicular to the direction of

seismic loading under consideration

= effective damping of the isolation system

at the design displacement, as prescribed

by Eq. 17.8-7

= effective damping of the isolation system

at the maximum displacement, as pre-

scribed by Eq. 17.8-8

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MINIMUM DESIGN LOADS

167

eff

= effective damping of the isolation system,

as prescribed by Eq. 17.8-2

= maximum positive displacement of an

isolator unit during each cycle of prototype

testing

–

= minimum negative displacement of an

isolator unit during each cycle of prototype

testing

ΣE

= total energy dissipated, in kips-in.

(kN-mm), in the isolation system during a

full cycle of response at the design

displacement, D

ΣE

= total energy dissipated, in kips-in.

(kN-mm), in the isolation system during a

full cycle of response at the maximum

displacement, D

Σ|F

max

= sum, for all isolator units, of the maximum

absolute value of force, in kips (kN), at a

positive displacement equal to D

Σ|F

min

= sum, for all isolator units, of the minimum

absolute value of force, in kips (kN), at a

positive displacement equal to D

Σ|F

–

max

= sum, for all isolator units, of the maximum

absolute value of force, in kips (kN), at a

negative displacement equal to D

Σ|F

–

min

= sum, for all isolator units, of the minimum

absolute value of force, in kips (kN), at a

negative displacement equal to D

Σ|F

max

= sum, for all isolator units, of the maximum

absolute value of force, in kips (kN), at a

positive displacement equal to D

Σ|F

min

= sum, for all isolator units, of the minimum

absolute value of force, in kips (kN), at a

positive displacement equal to D

Σ|F

–

max

= sum, for all isolator units, of the

maximum absolute value of force, in kips

(kN), at a negative displacement equal

to D

Σ|F

–

min

= sum, for all isolator units, of the

minimum absolute value of force, in kips

(kN), at a negative displacement equal

to D

17.2 GENERAL DESIGN REQUIREMENTS

17.2.1 Importance Factor

All portions of the structure, including the

structure above the isolation system, shall be assigned

a risk category in accordance with Table 1.5-1. The

importance factor, I

, shall be taken as 1.0 for a

seismically isolated structure, regardless of its risk

category assignment.

17.2.2 MCE

Spectral Response Acceleration

Parameters, S

and S

The MCE

spectral response acceleration param-

eters S

and S

shall be determined in accordance

with Section 11.4.3.

17.2.3 Conﬁ guration

Each structure shall be designated as having a

structural irregularity based on the structural conﬁ gu-

ration above the isolation system.

17.2.4 Isolation System

17.2.4.1 Environmental Conditions

In addition to the requirements for vertical and

lateral loads induced by wind and earthquake, the

isolation system shall provide for other environmental

conditions including aging effects, creep, fatigue,

operating temperature, and exposure to moisture or

damaging substances.

17.2.4.2 Wind Forces

Isolated structures shall resist design wind loads

at all levels above the isolation interface. At the

isolation interface, a wind-restraint system shall be

provided to limit lateral displacement in the isolation

system to a value equal to that required between

ﬂ oors of the structure above the isolation interface in

accordance with Section 17.5.6.

17.2.4.3 Fire Resistance

Fire resistance for the isolation system shall meet

that required for the columns, walls, or other such

gravity-bearing elements in the same region of the

structure.

17.2.4.4 Lateral Restoring Force

The isolation system shall be conﬁ gured to

produce a restoring force such that the lateral force at

the total design displacement is at least 0.025W

greater than the lateral force at 50 percent of the total

design displacement.

17.2.4.5 Displacement Restraint

The isolation system shall not be conﬁ gured to

include a displacement restraint that limits lateral

displacement due to the maximum considered

earthquake to less than the total maximum displace-

ment unless the seismically isolated structure is

designed in accordance with the following criteria

where more stringent than the requirements of

Section 17.2:

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CHAPTER 17 SEISMIC DESIGN REQUIREMENTS FOR SEISMICALLY ISOLATED STRUCTURES

168

1. Maximum considered earthquake response is

calculated in accordance with the dynamic analysis

requirements of Section 17.6, explicitly considering

the nonlinear characteristics of the isolation system

and the structure above the isolation system.

2. The ultimate capacity of the isolation system and

structural elements below the isolation system shall

exceed the strength and displacement demands of

the maximum considered earthquake.

3. The structure above the isolation system is checked

for stability and ductility demand of the maximum

considered earthquake.

4. The displacement restraint does not become

effective at a displacement less than 0.75 times the

total design displacement unless it is demonstrated

by analysis that earlier engagement does not result

in unsatisfactory performance.

17.2.4.6 Vertical-Load Stability

Each element of the isolation system shall be

designed to be stable under the design vertical load

where subjected to a horizontal displacement equal to

the total maximum displacement. The design vertical

load shall be computed using load combination 5 of

Section 2.3.2 for the maximum vertical load and load

combination 7 of Section 12.4.2.3 for the minimum

vertical load where S

in these equations is replaced

by S

. The vertical loads that result from application

of horizontal seismic forces, Q

, shall be based on

peak response due to the maximum considered

earthquake.

17.2.4.7 Overturning

The factor of safety against global structural

overturning at the isolation interface shall not be less

than 1.0 for required load combinations. All gravity

and seismic loading conditions shall be investigated.

Seismic forces for overturning calculations shall be

based on the maximum considered earthquake, and W

shall be used for the vertical restoring force.

Local uplift of individual elements shall not be

allowed unless the resulting deﬂ ections do not cause

overstress or instability of the isolator units or other

structure elements.

17.2.4.8 Inspection and Replacement

a. Access for inspection and replacement of all

components of the isolation system shall be

provided.

b. A registered design professional shall complete a

ﬁ nal series of inspections or observations of

structure separation areas and components that

cross the isolation interface prior to the issuance of

the certiﬁ cate of occupancy for the seismically

isolated structure. Such inspections and observa-

tions shall indicate that the conditions allow free

and unhindered displacement of the structure to

maximum design levels and that all components

that cross the isolation interface as installed are

able to accommodate the stipulated displacements.

c. Seismically isolated structures shall have a moni-

toring, inspection, and maintenance program for

the isolation system established by the registered

design professional responsible for the design of

the isolation system.

d. Remodeling, repair, or retroﬁ tting at the isolation

system interface, including that of components that

cross the isolation interface, shall be performed

under the direction of a registered design

professional.

17.2.4.9 Quality Control

A quality control testing program for isolator

units shall be established by the registered design

professional responsible for the structural design.

17.2.5 Structural System

17.2.5.1 Horizontal Distribution of Force

A horizontal diaphragm or other structural

elements shall provide continuity above the isolation

interface and shall have adequate strength and

ductility to transmit forces (due to nonuniform ground

motion) from one part of the structure to another.

17.2.5.2 Building Separations

Minimum separations between the isolated

structure and surrounding retaining walls or other

ﬁ xed obstructions shall not be less than the total

maximum displacement.

17.2.5.3 Nonbuilding Structures

Nonbuilding structures shall be designed and

constructed in accordance with the requirements of

Chapter 15 using design displacements and forces

calculated in accordance with Sections 17.5 or 17.6.

17.2.6 Elements of Structures and

Nonstructural Components

Parts or portions of an isolated structure, perma-

nent nonstructural components and the attachments to

them, and the attachments for permanent equipment

supported by a structure shall be designed to resist

seismic forces and displacements as prescribed by this

section and the applicable requirements of Chapter 13.

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17.2.6.1 Components at or above

the Isolation Interface

Elements of seismically isolated structures and

nonstructural components, or portions thereof, that are

at or above the isolation interface shall be designed to

resist a total lateral seismic force equal to the

maximum dynamic response of the element or

component under consideration.

EXCEPTION: Elements of seismically isolated

structures and nonstructural components or portions

designed to resist seismic forces and displacements as

prescribed in Chapter 12 or 13 as appropriate.

17.2.6.2 Components Crossing

the Isolation Interface

Elements of seismically isolated structures and

nonstructural components, or portions thereof, that

cross the isolation interface shall be designed to

withstand the total maximum displacement.

17.2.6.3 Components below the Isolation Interface

Elements of seismically isolated structures and

nonstructural components, or portions thereof, that are

below the isolation interface shall be designed and

constructed in accordance with the requirements of

Section 12.1 and Chapter 13.

17.3 GROUND MOTION FOR

ISOLATED SYSTEMS

17.3.1 Design Spectra

The site-speciﬁ c ground motion procedures set

forth in Chapter 21 are permitted to be used to

determine ground motions for any structure. For

structures on Site Class F sites, site response analysis

shall be performed in accordance with Section 21.1.

For seismically isolated structures on sites with S

greater than or equal to 0.6, a ground motion hazard

analysis shall be performed in accordance with Section

21.2. Structures that do not require or use site-speciﬁ c

ground motion procedures shall be analyzed using the

design spectrum for the design earthquake developed

in accordance with Section 11.4.5.

A spectrum shall be constructed for the MCE

ground motion. The spectrum for MCE

ground

motions shall not be taken as less than 1.5 times

the spectrum for the design earthquake ground

motions.

17.3.2 Ground Motion Histories

Where response-history procedures are used,

ground motions shall consist of pairs of appropriate

horizontal ground motion acceleration components

developed per Section 16.1.3.2 except that 0.2T and

1.5T shall be replaced by 0.5T

and 1.25T

, respec-

tively, where T

and T

are deﬁ ned in Section 17.5.3.

17.4 ANALYSIS PROCEDURE SELECTION

Seismically isolated structures except those deﬁ ned in

Section 17.4.1 shall be designed using the dynamic

procedures of Section 17.6.

17.4.1 Equivalent Lateral Force Procedure

The equivalent lateral force procedure of Section

17.5 is permitted to be used for design of a seismi-

cally isolated structure provided that

1. The structure is located at a site with S

less than

0.60g.

2. The structure is located on a Site Class A, B, C,

or D.

3. The structure above the isolation interface is less

than or equal to four stories or 65 ft (19.8 m) in

structural height, h

, measured from the base as

deﬁ ned in Section 11.2.

4. The effective period of the isolated structure at the

maximum displacement, T

, is less than or equal to

3.0 s.

5. The effective period of the isolated structure at the

design displacement, T

, is greater than three times

the elastic, ﬁ xed-base period of the structure above

the isolation system as determined by Eq. 12.8-7 or

12.8-8.

6. The structure above the isolation system is of

regular conﬁ guration.

7. The isolation system meets all of the following

criteria:

a. The effective stiffness of the isolation system at

the design displacement is greater than one-third

of the effective stiffness at 20 percent of the

design displacement.

b. The isolation system is capable of producing a

restoring force as speciﬁ ed in Section 17.2.4.4.

c. The isolation system does not limit maximum

considered earthquake displacement to less than

the total maximum displacement.

17.4.2 Dynamic Procedures

The dynamic procedures of Section 17.6 are

permitted to be used as speciﬁ ed in this section.

17.4.2.1 Response-Spectrum Procedure

Response-spectrum analysis shall not be used for

design of a seismically isolated structure unless:

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CHAPTER 17 SEISMIC DESIGN REQUIREMENTS FOR SEISMICALLY ISOLATED STRUCTURES

170

1. The structure is located on a Site Class A, B, C, or

2. The isolation system meets the criteria of Item 7 of

Section 17.4.1.

17.4.2.2 Response-History Procedure

The response-history procedure is permitted for

design of any seismically isolated structure and shall

be used for design of all seismically isolated struc-

tures not meeting the criteria of Section 17.4.2.1.

17.5 EQUIVALENT LATERAL

FORCE PROCEDURE

17.5.1 General

Where the equivalent lateral force procedure is

used to design seismically isolated structures, the

requirements of this section shall apply.

17.5.2 Deformation Characteristics of

the Isolation System

Minimum lateral earthquake design displacements

and forces on seismically isolated structures shall

be based on the deformation characteristics of the

isolation system. The deformation characteristics of

the isolation system shall explicitly include the effects

of the wind-restraint system if such a system is used

to meet the design requirements of this standard. The

deformation characteristics of the isolation system

shall be based on properly substantiated tests per-

formed in accordance with Section 17.8.

17.5.3 Minimum Lateral Displacements

17.5.3.1 Design Displacement

The isolation system shall be designed and

constructed to withstand minimum lateral earthquake

displacements, D

, that act in the direction of each of

the main horizontal axes of the structure using

Eq. 17.5-1:

gS T

4π

(17.5-1)

where

g = acceleration due to gravity. The units for g are

in./s

(mm/s

) if the units of the design displace-

ment, D

, are in. (mm)

= design 5 percent damped spectral acceleration

parameter at 1-s period in units of g-s, as

determined in Section 11.4.4

= effective period of the seismically isolated

structure in seconds, at the design displacement

in the direction under consideration, as pre-

scribed by Eq. 17.5-2

= numerical coefﬁ cient related to the effective

damping of the isolation system at the

design displacement, β

, as set forth in

Table 17.5-1

17.5.3.2 Effective Period at Design Displacement

The effective period of the isolated structure at

design displacement, T

, shall be determined using the

deformational characteristics of the isolation system

and Eq. 17.5-2:

= 2π

min

(17.5-2)

where

W = effective seismic weight of the structure

above the isolation interface as deﬁ ned in

Section 12.7.2

Dmin

= minimum effective stiffness in kips/in. (kN/

mm) of the isolation system at the design

displacement in the horizontal direction under

consideration, as prescribed by Eq. 17.8-4

g = acceleration due to gravity

17.5.3.3 Maximum Displacement

The maximum displacement of the isolation

system, D

, in the most critical direction of horizontal

response shall be calculated using Eq. 17.5-3:

gS T

4π

(17.5-3)

Table 17.5-1 Damping Coefﬁ cient, B

or B

Effective Damping, β

or β

(percentage of critical)

a,b

or B

Factor

≤2 0.8

5 1.0

10 1.2

20 1.5

30 1.7

40 1.9

≥50 2.0

The damping coefﬁ cient shall be based on the effective damping

of the isolation system determined in accordance with the

requirements of Section 17.8.5.2.

The damping coefﬁ cient shall be based on linear interpolation for

effective damping values other than those given.

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171

where

g = acceleration of gravity

= maximum considered earthquake 5 percent

damped spectral acceleration parameter at 1-s

period, in units of g-s, as determined in Section

11.4.3

= effective period, in seconds, of the seismically

isolated structure at the maximum displacement

in the direction under consideration, as pre-

scribed by Eq. 17.5-4

= numerical coefﬁ cient related to the effective

damping of the isolation system at the maximum

displacement, β

, as set forth in Table 17.5-1

17.5.3.4 Effective Period at Maximum Displacement

The effective period of the isolated structure at

maximum displacement, T

, shall be determined using

the deformational characteristics of the isolation

system and Eq. 17.5-4:

= 2π

min

(17.5-4)

where

W = effective seismic weight of the structure above

the isolation interface as deﬁ ned in Section

12.7.2 (kip or kN)

Mmin

= minimum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the

maximum displacement in the horizontal

direction under consideration, as prescribed

by Eq. 17.8-6

g = the acceleration of gravity

17.5.3.5 Total Displacement

The total design displacement, D

, and the total

maximum displacement, D

, of elements of the

isolation system shall include additional displacement

due to actual and accidental torsion calculated from

the spatial distribution of the lateral stiffness of the

isolation system and the most disadvantageous

location of eccentric mass.

The total design displacement, D

, and the total

maximum displacement, D

, of elements of an

isolation system with uniform spatial distribution of

lateral stiffness shall not be taken as less than that

prescribed by Eqs. 17.5-5 and 17.5-6:

DD y

TD D

⎡

⎣

⎢

⎤

⎦

⎥

(17.5-5)

DD y

TM M

⎡

⎣

⎢

⎤

⎦

⎥

(17.5-6)

where

= design displacement at the center of rigidity of

the isolation system in the direction under

consideration as prescribed by Eq. 17.5-1

= maximum displacement at the center of

rigidity of the isolation system in the

direction under consideration as prescribed by

Eq. 17.5-3

y = the distance between the centers of rigidity of

the isolation system and the element of interest

measured perpendicular to the direction of

seismic loading under consideration

e = the actual eccentricity measured in plan between

the center of mass of the structure above the

isolation interface and the center of rigidity of

the isolation system, plus accidental eccentricity,

in ft (mm), taken as 5 percent of the longest

plan dimension of the structure perpendicular to

the direction of force under consideration

b = the shortest plan dimension of the structure

measured perpendicular to d

d = the longest plan dimension of the structure

EXCEPTION: The total design displacement,

, and the total maximum displacement, D

, are

permitted to be taken as less than the value prescribed

by Eqs. 17.5-5 and 17.5-6, respectively, but not less

than 1.1 times D

and D

, respectively, provided the

isolation system is shown by calculation to be

conﬁ gured to resist torsion accordingly.

17.5.4 Minimum Lateral Forces

17.5.4.1 Isolation System and Structural Elements

below the Isolation System

The isolation system, the foundation, and all

structural elements below the isolation system shall be

designed and constructed to withstand a minimum

lateral seismic force, V

, using all of the appropriate

requirements for a nonisolated structure and as

prescribed by Eq. 17.5-7:

= k

Dmax

(17.5-7)

where

Dmax

= maximum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the design

displacement in the horizontal direction under

consideration as prescribed by Eq. 17.8-3

= design displacement, in in. (mm), at the center

of rigidity of the isolation system in the

direction under consideration, as prescribed by

Eq. 17.5-1

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172

shall not be taken as less than the maximum

force in the isolation system at any displacement up to

and including the design displacement.

17.5.4.2 Structural Elements above

the Isolation System

The structure above the isolation system shall be

designed and constructed to withstand a minimum

shear force, V

, using all of the appropriate require-

ments for a nonisolated structure and as prescribed by

Eq. 17.5-8:

max

(17.5-8)

where

Dmax

= maximum effective stiffness, in kips/in.

(kN/mm), of the isolation system at the design

displacement in the horizontal direction under

consideration

= design displacement, in in. (mm), at the center

of rigidity of the isolation system in the

direction under consideration, as prescribed by

Eq. 17.5-1

= numerical coefﬁ cient related to the type of

seismic force-resisting system above the

isolation system

The R

factor shall be based on the type of

seismic force-resisting system used for the structure

above the isolation system and shall be three-eighths

of the value of R given in Table 12.2-1, with a

maximum value not greater than 2.0 and a minimum

value not less than 1.0.

17.5.4.3 Limits on V

The value of V

shall not be taken as less than the

following:

1. The lateral seismic force required by Section 12.8

for a ﬁ xed-base structure of the same effective

seismic weight, W, and a period equal to the

isolated period, T

2. The base shear corresponding to the factored

design wind load.

3. The lateral seismic force required to fully activate

the isolation system (e.g., the yield level of a

softening system, the ultimate capacity of a

sacriﬁ cial wind-restraint system, or the break-away

friction level of a sliding system) multiplied by 1.5.

17.5.5 Vertical Distribution of Force

The shear force V

shall be distributed over the

height of the structure above the isolation interface

using Eq. 17.5-9:

Vwh

sxx

∑

(17.5-9)

where

= portion of V

that is assigned to Level x

= total lateral seismic design force or shear on

elements above the isolation system as pre-

scribed by Eq. 17.5-8

= portion of W that is located at or assigned to

Level x

= height above the base of Level x

At each level designated as x, the force, F

, shall

be applied over the area of the structure in accordance

with the mass distribution at the level.

17.5.6 Drift Limits

The maximum story drift of the structure above

the isolation system shall not exceed 0.015h

. The

drift shall be calculated by Eq. 12.8-15 with C

for the

isolated structure equal to R

as deﬁ ned in Section

17.5.4.2.

17.6 DYNAMIC ANALYSIS PROCEDURES

17.6.1 General

Where dynamic analysis is used to design

seismically isolated structures, the requirements of

this section shall apply.

17.6.2 Modeling

The mathematical models of the isolated structure

including the isolation system, the seismic force-

resisting system, and other structural elements shall

conform to Section 12.7.3 and to the requirements of

Sections 17.6.2.1 and 17.6.2.2.

17.6.2.1 Isolation System

The isolation system shall be modeled using

deformational characteristics developed and veriﬁ ed

by test in accordance with the requirements of Section

17.5.2. The isolation system shall be modeled with

sufﬁ cient detail to

a. Account for the spatial distribution of isolator

units.

b. Calculate translation, in both horizontal directions,

and torsion of the structure above the isolation

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MINIMUM DESIGN LOADS

173

interface considering the most disadvantageous

location of eccentric mass.

c. Assess overturning/uplift forces on individual

isolator units.

d. Account for the effects of vertical load, bilateral

load, and/or the rate of loading if the force-

deﬂ ection properties of the isolation system

are dependent on one or more of these

attributes.

The total design displacement and total maximum

displacement across the isolation system shall be

calculated using a model of the isolated structure that

incorporates the force-deﬂ ection characteristics of

nonlinear elements of the isolation system and the

seismic force-resisting system.

17.6.2.2 Isolated Structure

The maximum displacement of each ﬂ oor and

design forces and displacements in elements of the

seismic force-resisting system are permitted to be

calculated using a linear elastic model of the isolated

structure provided that both of the following condi-

tions are met:

1. Stiffness properties assumed for the nonlinear

components of the isolation system are based on

the maximum effective stiffness of the isolation

system; and

2. All elements of the seismic force-resisting

system of the structure above the isolation system

remain elastic for the design earthquake.

Seismic force-resisting systems with elastic

elements include, but are not limited to, irregular

structural systems designed for a lateral force not less

than 100 percent of V

and regular structural systems

designed for a lateral force not less than 80 percent of

, where V

is determined in accordance with Section

17.5.4.2.

17.6.3 Description of Procedures

17.6.3.1 General

Response-spectrum and response-history proce-

dures shall be performed in accordance with Section

12.9 and Chapter 16, and the requirements of this

section.

17.6.3.2 Input Earthquake

The design earthquake ground motions shall be

used to calculate the total design displacement of the

isolation system and the lateral forces and displace-

ments in the isolated structure. The maximum

considered earthquake shall be used to calculate

the total maximum displacement of the isolation

system.

17.6.3.3 Response-Spectrum Procedure

Response-spectrum analysis shall be performed

using a modal damping value for the fundamental

mode in the direction of interest not greater than the

effective damping of the isolation system or 30

percent of critical, whichever is less. Modal damping

values for higher modes shall be selected consistent

with those that would be appropriate for response-

spectrum analysis of the structure above the isolation

system assuming a ﬁ xed base.

Response-spectrum analysis used to determine the

total design displacement and the total maximum

displacement shall include simultaneous excitation of

the model by 100 percent of the ground motion in the

critical direction and 30 percent of the ground motion

in the perpendicular, horizontal direction. The

maximum displacement of the isolation system shall

be calculated as the vectorial sum of the two orthogo-

nal displacements.

The design shear at any story shall not be less

than the story shear resulting from application of

the story forces calculated using Eq. 17.5-9 and a

value of V

equal to the base shear obtained from

the response-spectrum analysis in the direction of

interest.

17.6.3.4 Response-History Procedure

Where a response-history procedure is performed,

a suite of not fewer than three pairs of appropriate

ground motions shall be used in the analysis; the

ground motion pairs shall be selected and scaled in

accordance with Section 17.3.2.

Each pair of ground motion components shall be

applied simultaneously to the model considering the

most disadvantageous location of eccentric mass.

The maximum displacement of the isolation system

shall be calculated from the vectorial sum of the two

orthogonal displacements at each time step.

The parameters of interest shall be calculated for

each ground motion used for the response-history

analysis. If seven or more pairs of ground motions are

used for the response-history analysis, the average

value of the response parameter of interest is permit-

ted to be used for design. If fewer than seven pairs of

ground motions are used for analysis, the maximum

value of the response parameter of interest shall be

used for design.

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17.6.4 Minimum Lateral Displacements and Forces

17.6.4.1 Isolation System and Structural Elements

below the Isolation System

The isolation system, foundation, and all struc-

tural elements below the isolation system shall be

designed using all of the appropriate requirements for

a nonisolated structure and the forces obtained from

the dynamic analysis without reduction, but the design

lateral force shall not be taken as less than 90 percent

of V

determined in accordance as prescribed by Eq.

17.5-7.

The total design displacement of the isolation

system shall not be taken as less than 90 percent of

as speciﬁ ed by Section 17.5.3.5. The total

maximum displacement of the isolation system shall

not be taken as less than 80 percent of D

prescribed by Section 17.5.3.5.

The limits on displacements speciﬁ ed by this

section shall be evaluated using values of D

and

determined in accordance with Section 17.5.5

except that D

′ is permitted to be used in lieu of D

and D

′ is permitted to be used in lieu of D

prescribed in Eqs. 17.6-1 and 17.6-2:

′

()

(17.6-1)

′

()

(17.6-2)

where

= design displacement, in in. (mm), at the center of

rigidity of the isolation system in the direction

under consideration, as prescribed by Eq. 17.5-1

= maximum displacement in in. (mm), at the center

of rigidity of the isolation system in the direction

under consideration, as prescribed by Eq. 17.5-3

T = elastic, ﬁ xed-base period of the structure above

the isolation system as determined by Section

12.8.2

= effective period of seismically isolated structure

in s, at the design displacement in the direction

under consideration, as prescribed by Eq. 17.5-2

= effective period, in s, of the seismically isolated

structure, at the maximum displacement in the

direction under consideration, as prescribed by

Eq. 17.5-4

17.6.4.2 Structural Elements above

the Isolation System

Subject to the procedure-speciﬁ c limits of this

section, structural elements above the isolation system

shall be designed using the appropriate requirements

for a nonisolated structure and the forces obtained

from the dynamic analysis reduced by a factor of R

as determined in accordance with Section 17.5.4.2.

The design lateral shear force on the structure above

the isolation system, if regular in conﬁ guration, shall

not be taken as less than 80 percent of V

, or less than

the limits speciﬁ ed by Section 17.5.4.3.

EXCEPTION: The lateral shear force on the

structure above the isolation system, if regular in

conﬁ guration, is permitted to be taken as less than 80

percent, but shall not be less than 60 percent of V

where the response-history procedure is used for

analysis of the seismically isolated structure.

The design lateral shear force on the structure

above the isolation system, if irregular in conﬁ gura-

tion, shall not be taken as less than V

or less than the

limits speciﬁ ed by Section 17.5.4.3.

EXCEPTION: The design lateral shear force on

the structure above the isolation system, if irregular in

conﬁ guration, is permitted to be taken as less than

100 percent, but shall not be less than 80 percent of

, where the response-history procedure is used for

analysis of the seismically isolated structure.

17.6.4.3 Scaling of Results

Where the factored lateral shear force on struc-

tural elements, determined using either response-

spectrum or response-history procedure, is less than

the minimum values prescribed by Sections 17.6.4.1

and 17.6.4.2, all response parameters, including

member forces and moments, shall be adjusted

upward proportionally.

17.6.4.4 Drift Limits

Maximum story drift corresponding to the design

lateral force including displacement due to vertical

deformation of the isolation system shall not exceed

the following limits:

1. The maximum story drift of the structure above the

isolation system calculated by response-spectrum

analysis shall not exceed 0.015h

2. The maximum story drift of the structure above the

isolation system calculated by response-history

analysis based on the force-deﬂ ection characteris-

tics of nonlinear elements of the seismic force-

resisting system shall not exceed 0.020h

Drift shall be calculated using Eq. 12.8-15 with

the C

of the isolated structure equal to R

as deﬁ ned

in Section 17.5.4.2.

The secondary effects of the maximum consid-

ered earthquake lateral displacement of the structure

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175

above the isolation system combined with gravity

forces shall be investigated if the story drift ratio

exceeds 0.010/R

17.7 DESIGN REVIEW

A design review of the isolation system and related

test programs shall be performed by an independent

engineering team including persons licensed in the

appropriate disciplines and experienced in seismic

analysis methods and the theory and application of

seismic isolation. Isolation system design review shall

include, but not be limited to, the following:

1. Review of site-speciﬁ c seismic criteria including

the development of site-speciﬁ c spectra and ground

motion histories and all other design criteria

developed speciﬁ cally for the project.

2. Review of the preliminary design including the

determination of the total design displacement, the

total maximum displacement, and the lateral force

level.

3. Overview and observation of prototype testing

(Section 17.8).

4. Review of the ﬁ nal design of the entire structural

system and all supporting analyses.

5. Review of the isolation system quality control

testing program (Section 17.2.4.9).

17.8 TESTING

17.8.1 General

The deformation characteristics and damping

values of the isolation system used in the design and

analysis of seismically isolated structures shall be

based on tests of a selected sample of the components

prior to construction as described in this section.

The isolation system components to be tested

shall include the wind-restraint system if such a

system is used in the design.

The tests speciﬁ ed in this section are for estab-

lishing and validating the design properties of the

isolation system and shall not be considered as

satisfying the manufacturing quality control tests of

Section 17.2.4.9.

17.8.2 Prototype Tests

Prototype tests shall be performed separately on

two full-size specimens (or sets of specimens, as

appropriate) of each predominant type and size of

isolator unit of the isolation system. The test speci-

mens shall include the wind-restraint system as

well as individual isolator units if such systems are

used in the design. Specimens tested shall not be used

for construction unless accepted by the registered

design professional responsible for the design of the

structure and approved by the authority having

jurisdiction.

17.8.2.1 Record

For each cycle of each test, the force-deﬂ ection

and hysteretic behavior of the test specimen shall be

recorded.

17.8.2.2 Sequence and Cycles

The following sequence of tests shall be per-

formed for the prescribed number of cycles at a

vertical load equal to the average dead load plus

one-half the effects due to live load on all isolator

units of a common type and size:

1. Twenty fully reversed cycles of loading at a lateral

force corresponding to the wind design force.

2. Three fully reversed cycles of loading at each of

the following increments of the total design

displacement—0.25D

, 0.5D

, 1.0D

, and 1.0D

where D

and D

are as determined in Sections

17.5.3.1 and 17.5.3.3, respectively, or Section 17.6

as appropriate.

3. Three fully reversed cycles of loading at the total

maximum displacement, 1.0D

4. 30S

, but not less than 10, fully reversed

cycles of loading at 1.0 times the total design

displacement, 1.0D

If an isolator unit is also a vertical-load-carrying

element, then item 2 of the sequence of cyclic tests

speciﬁ ed in the preceding text shall be performed for

two additional vertical load cases speciﬁ ed in Section

17.2.4.6. The load increment due to earthquake

overturning, Q

, shall be equal to or greater than the

peak earthquake vertical force response corresponding

to the test displacement being evaluated. In these

tests, the combined vertical load shall be taken as the

typical or average downward force on all isolator

units of a common type and size.

17.8.2.3 Units Dependent on Loading Rates

If the force-deﬂ ection properties of the isolator

units are dependent on the rate of loading, each set of

tests speciﬁ ed in Section 17.8.2.2 shall be performed

dynamically at a frequency equal to the inverse of the

effective period, T

If reduced-scale prototype specimens are used to

quantify rate-dependent properties of isolators, the

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CHAPTER 17 SEISMIC DESIGN REQUIREMENTS FOR SEISMICALLY ISOLATED STRUCTURES

176

reduced-scale prototype specimens shall be of the

same type and material and be manufactured with the

same processes and quality as full-scale prototypes

and shall be tested at a frequency that represents

full-scale prototype loading rates.

The force-deﬂ ection properties of an isolator unit

shall be considered to be dependent on the rate of

loading if the measured property (effective stiffness or

effective damping) at the design displacement when

tested at any frequency in the range of 0.1 to 2.0

times the inverse of T

is different from the property

when tested at a frequency equal to the inverse of T

by more than 15 percent.

17.8.2.4 Units Dependent on Bilateral Load

If the force-deﬂ ection properties of the isolator

units are dependent on bilateral load, the tests

speciﬁ ed in Sections 17.8.2.2 and 17.8.2.3 shall be

augmented to include bilateral load at the following

increments of the total design displacement, D

0.25 and 1.0, 0.5 and 1.0, 0.75 and 1.0, and 1.0

and 1.0

If reduced-scale prototype specimens are used to

quantify bilateral-load-dependent properties, the

reduced-scale specimens shall be of the same type and

material and manufactured with the same processes

and quality as full-scale prototypes.

The force-deﬂ ection properties of an isolator unit

shall be considered to be dependent on bilateral load

if the effective stiffness where subjected to bilateral

loading is different from the effective stiffness where

subjected to unilateral loading, by more than 15

percent.

17.8.2.5 Maximum and Minimum Vertical Load

Isolator units that carry vertical load shall be

statically tested for maximum and minimum down-

ward vertical load at the total maximum displacement.

In these tests, the combined vertical loads shall be

taken as speciﬁ ed in Section 17.2.4.6 on any one

isolator of a common type and size. The dead load, D,

and live load, L, are speciﬁ ed in Section 12.4. The

seismic load E is given by Eqs. 12.4-1 and 12.4-2

where S

in these equations is replaced by S

and

the vertical loads that result from application of

horizontal seismic forces, Q

, shall be based on the

peak response due to the maximum considered

earthquake.

17.8.2.6 Sacriﬁ cial Wind-Restraint Systems

If a sacriﬁ cial wind-restraint system is to be

utilized, its ultimate capacity shall be established

by test.

17.8.2.7 Testing Similar Units

Prototype tests are not required if an isolator unit

is of similar size and of the same type and material as

a prototype isolator unit that has been previously

tested using the speciﬁ ed sequence of tests.

17.8.3 Determination of

Force-Deﬂ ection Characteristics

The force-deﬂ ection characteristics of the

isolation system shall be based on the cyclic load tests

of prototype isolator speciﬁ ed in Section 17.8.2.

As required, the effective stiffness of an isolator

unit, k

eff

, shall be calculated for each cycle of loading

as prescribed by Eq. 17.8-1:

eff

Δ+Δ

+−

(17.8-1)

where F

and F

–

are the positive and negative forces,

at Δ

and Δ

–

, respectively.

As required, the effective damping, β

eff

, of an

isolator unit shall be calculated for each cycle of

loading by Eq. 17.8-2:

eff

loop

eff

Δ+Δ

()

+−

(17.8-2)

where the energy dissipated per cycle of loading, E

loop

and the effective stiffness, k

eff

, shall be based on peak

test displacements of Δ

and Δ

–

17.8.4 Test Specimen Adequacy

The performance of the test specimens shall be

deemed adequate if the following conditions are

satisﬁ ed:

1. The force-deﬂ ection plots for all tests speciﬁ ed in

Section 17.8.2 have a positive incremental force-

resisting capacity.

2. For each increment of test displacement speciﬁ ed

in item 2 of Section 17.8.2.2 and for each vertical

load case speciﬁ ed in Section 17.8.2.2,

a. For each test specimen, the difference between

the effective stiffness at each of the three cycles

of test and the average value of effective

stiffness is no greater than 15 percent.

b. For each cycle of test, the difference between

effective stiffness of the two test specimens of a

common type and size of the isolator unit and

the average effective stiffness is no greater than

15 percent.

3. For each specimen there is no greater than a 20

percent change in the initial effective stiffness over

the cycles of test speciﬁ ed in item 4 of Section

17.8.2.2.

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MINIMUM DESIGN LOADS

177

4. For each specimen there is no greater than a 20

percent decrease in the initial effective damping

over the cycles of test speciﬁ ed in item 4 of

Section 17.8.2.2.

5. All specimens of vertical-load-carrying elements of

the isolation system remain stable where tested in

accordance with Section 17.8.2.5.

17.8.5 Design Properties of the Isolation System

17.8.5.1 Maximum and Minimum Effective Stiffness

At the design displacement, the maximum and

minimum effective stiffness of the isolated system,

Dmax

and k

Dmin

, shall be based on the cyclic tests of

item 2 of Section 17.8.2.2 and calculated using Eqs.

17.8-3 and 17.8-4:

Dmax

max

+−

∑∑

(17.8-3)

min

min min

+−

∑∑

(17.8-4)

At the maximum displacement, the maximum and

minimum effective stiffness of the isolation system,

Mmax

and k

Mmin

, shall be based on the cyclic tests of

item 3 of Section 17.8.2.2 and calculated using Eqs.

17.8-5 and 17.8-6:

max

max max

+−

∑∑

(17.8-5)

min

min min

+−

∑

(17.8-6)

The maximum effective stiffness of the isolation

system, k

Dmax

(or k

Mmax

), shall be based on forces from

the cycle of prototype testing at a test displacement

equal to D

(or D

) that produces the largest value of

effective stiffness. Minimum effective stiffness of the

isolation system, k

Dmin

(or k

Mmin

), shall be based on

forces from the cycle of prototype testing at a test

displacement equal to D

(or D

) that produces the

smallest value of effective stiffness.

For isolator units that are found by the tests of

Sections 17.8.2.2, 17.8.2.3, and 17.8.2.4 to have

force-deﬂ ection characteristics that vary with vertical

load, rate of loading, or bilateral load, respectively,

the values of k

Dmax

and k

Mmax

shall be increased and

the values of k

Dmin

and k

Mmin

shall be decreased, as

necessary, to bound the effects of measured variation

in effective stiffness.

17.8.5.2 Effective Damping

At the design displacement, the effective damping

of the isolation system, β

, shall be based on the

cyclic tests of item 2 of Section 17.8.2.2 and calcu-

lated using Eq. 17.8-7:

∑

max

(17.8-7)

In Eq. 17.8-7, the total energy dissipated per cycle of

design displacement response, ΣE

, shall be taken as

the sum of the energy dissipated per cycle in all

isolator units measured at a test displacement equal to

and shall be based on forces and deﬂ ections from

the cycle of prototype testing at test displacement D

that produces the smallest values of effective

damping.

At the maximum displacement, the effective

damping of the isolation system, β

, shall be based on

the cyclic tests of item 2 of Section 17.8.2.2 and

calculated using Eq. 17.8-8

∑

max

(17.8-8)

In Eq. 17.8-8, the total energy dissipated per cycle of

design displacement response, ΣE

, shall be taken as

the sum of the energy dissipated per cycle in all

isolator units measured at a test displacement equal to

and shall be based on forces and deﬂ ections from

the cycle of prototype testing at test displacement D

that produces the smallest value of effective damping.

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179

Chapter 18

SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES

WITH DAMPING SYSTEMS

18.1.3 Notation

The following notations apply to the provisions

of this chapter:

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

(m = 1) and period of structure equal to T

= numerical coefﬁ cient as set forth in Table

18.6-1 for the effective damping equal to

+ β

and period equal to T

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

(m = 1) and period of structure equal to T

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

and

period of structure equal to T

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

and period of structure equal to T

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

and

period of structure equal to T

V + I

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to the

sum of viscous damping in the fundamental

mode of vibration of the structure in the

direction of interest, β

(m = 1), plus

inherent damping, β

, and period of structure

equal to T

mFD

= force coefﬁ cient as set forth in Table 18.7-1

mFV

= force coefﬁ cient as set forth in Table 18.7-2

= seismic response coefﬁ cient of the funda-

mental mode of vibration of the structure in

the direction of interest, Section 18.4.2.4 or

18.5.2.4 (m = 1)

= seismic response coefﬁ cient of the m

mode

of vibration of the structure in the direction

of interest, Section 18.4.2.4 (m = 1) or

Section 18.4.2.6 (m > 1)

= seismic response coefﬁ cient of the residual

mode of vibration of the structure in the

direction of interest, Section 18.5.2.8

= fundamental mode design displacement

at the center rigidity of the roof level of the

structure in the direction under consideration,

Section 18.5.3.2

18.1 GENERAL

18.1.1 Scope

Every structure with a damping system and every

portion thereof shall be designed and constructed in

accordance with the requirements of this standard as

modiﬁ ed by this section. Where damping devices are

used across the isolation interface of a seismically

isolated structure, displacements, velocities, and

accelerations shall be determined in accordance with

Chapter 17.

18.1.2 Deﬁ nitions

The following deﬁ nitions apply to the provisions

of Chapter 18:

DAMPING DEVICE: A ﬂ exible structural

element of the damping system that dissipates energy

due to relative motion of each end of the device.

Damping devices include all pins, bolts, gusset plates,

brace extensions, and other components required to

connect damping devices to the other elements of the

structure. Damping devices may be classiﬁ ed as either

displacement-dependent or velocity-dependent, or a

combination thereof, and may be conﬁ gured to act in

either a linear or nonlinear manner.

DAMPING SYSTEM: The collection of

structural elements that includes all the individual

damping devices, all structural elements or bracing

required to transfer forces from damping devices to

the base of the structure, and the structural elements

required to transfer forces from damping devices to

the seismic force-resisting system.

DISPLACEMENT-DEPENDENT DAMPING

DEVICE: The force response of a displacement-

dependent damping device is primarily a function of

the relative displacement between each end of the

device. The response is substantially independent of

the relative velocity between each of the devices and/

or the excitation frequency.

VELOCITY-DEPENDENT DAMPING

DEVICE: The force-displacement relation for a

velocity-dependent damping device is primarily a

function of the relative velocity between each

end of the device and could also be a function

of the relative displacement between each end of

the device.

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

180

= fundamental mode maximum displacement at

the center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.5.3.5

= design displacement at the center of rigidity

of the roof level of the structure due to the

mode of vibration in the direction under

consideration, Section 18.4.3.2

= maximum displacement at the center of

rigidity of the roof level of the structure due

to the m

mode of vibration in the direction

under consideration, Section 18.4.3.5

= residual mode design displacement at the

center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.5.3.2

= residual mode maximum displacement at the

center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.5.3.5

= displacement at the center of rigidity of the

roof level of the structure at the effective

yield point of the seismic force-resisting

system, Section 18.6.3

= lateral force at Level i of the structure

distributed approximately in accordance with

Section 12.8.3, Section 18.5.2.3

= inertial force at Level i (or mass point i) in

the fundamental mode of vibration of the

structure in the direction of interest, Section

18.5.2.9

= inertial force at Level i (or mass point i) in

the m

mode of vibration of the structure in

the direction of interest, Section 18.4.2.7

= inertial force at Level i (or mass point i) in

the residual mode of vibration of the struc-

ture in the direction of interest, Section

18.5.2.9

= height of the structure above the base to the

roof level, Section 18.5.2.3

= hysteresis loop adjustment factor as deter-

mined in Section 18.6.2.2.1

DSD

= force in an element of the damping system

required to resist design seismic forces of

displacement-dependent damping devices,

Section 18.7.2.5

mDSV

= forces in an element of the damping system

required to resist design seismic forces of

velocity-dependent damping devices due to

the m

mode of vibration of the structure in

the direction of interest, Section 18.7.2.5

mSFRS

= force in an element of the damping system

equal to the design seismic force of the m

mode of vibration of the structure in the

direction of interest, Section 18.7.2.5

= the fundamental period of the structure in the

direction under consideration

= effective period, in seconds, of the funda-

mental mode of vibration of the structure at

the design displacement in the direction

under consideration, as prescribed by Section

18.4.2.5 or 18.5.2.5

= effective period, in seconds, of the funda-

mental mode of vibration of the structure at

the maximum displacement in the direction

under consideration, as prescribed by Section

18.4.2.5 or 18.5.2.5

= period, in seconds, of the residual mode of

vibration of the structure in the direction

under consideration, Section 18.5.2.7

= design value of the seismic base shear

of the m

mode of vibration of the

structure in the direction of interest,

Section 18.4.2.2

min

= minimum allowable value of base shear

permitted for design of the seismic force-

resisting system of the structure in the

direction of interest, Section 18.2.2.1

= design value of the seismic base shear of the

residual mode of vibration of the structure in

a given direction, as determined in Section

18.5.2.6

= effective fundamental mode seismic weight

determined in accordance with Eq. 18.4-2b

for m = 1

= effective residual mode seismic weight

determined in accordance with Eq. 18.5-13

α = velocity exponent relating damping device

force to damping device velocity

= total effective damping of the m

mode of

vibration of the structure in the direction of

interest at the design displacement, Section

18.6.2

= total effective damping of the m

mode of

vibration of the structure in the direction of

interest at the maximum displacement,

Section 18.6.2

= component of effective damping of the

structure in the direction of interest due to

post-yield hysteretic behavior of the seismic

force-resisting system and elements of the

damping system at effective ductility demand

, Section 18.6.2.2

= component of effective damping of the

structure in the direction of interest due to

post-yield hysteretic behavior of the seismic

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MINIMUM DESIGN LOADS

181

force-resisting system and elements of the

damping system at effective ductility

demand, μ

, Section 18.6.2.2

= component of effective damping of the

structure due to the inherent dissipation of

energy by elements of the structure, at or just

below the effective yield displacement of the

seismic force-resisting system, Section

18.6.2.1

= total effective damping in the residual

mode of vibration of the structure in the

direction of interest, calculated in accordance

with Section 18.6.2 (using μ

= 1.0 and

= 1.0)

= component of effective damping of the m

mode of vibration of the structure in the

direction of interest due to viscous dissipa-

tion of energy by the damping system, at or

just below the effective yield displacement of

the seismic force-resisting system, Section

18.6.2.3

= elastic deﬂ ection of Level i of the structure

due to applied lateral force, f

, Section

18.5.2.3

i1D

= fundamental mode design deﬂ ection of

Level i at the center of rigidity of the

structure in the direction under consideration,

Section 18.5.3.1

= total design deﬂ ection of Level i at

the center of rigidity of the structure

in the direction under consideration,

Section 18.5.3

= total maximum deﬂ ection of Level i

at the center of rigidity of the structure

in the direction under consideration,

Section 18.5.3

iRD

= residual mode design deﬂ ection of Level i

at the center of rigidity of the structure

in the direction under consideration,

Section 18.5.3.1

= deﬂ ection of Level i in the m

mode of

vibration at the center of rigidity of the

structure in the direction under consideration,

Section 18.6.2.3

= design story drift due to the fundamental

mode of vibration of the structure in the

direction of interest, Section 18.5.3.3

= total design story drift of the structure

in the direction of interest, Section

18.5.3.3

= total maximum story drift of the

structure in the direction of interest,

Section 18.5.3

= design story drift due to the m

mode of

vibration of the structure in the direction of

interest, Section 18.4.3.3

= design story drift due to the residual mode of

vibration of the structure in the direction of

interest, Section 18.5.3.3

μ = effective ductility demand on the seismic

force-resisting system in the direction of

interest

= effective ductility demand on the seismic

force-resisting system in the direction of

interest due to the design earthquake ground

motions, Section 18.6.3

= effective ductility demand on the seismic

force-resisting system in the direction

of interest due to the maximum

considered earthquake ground motions,

Section 18.6.3

max

= maximum allowable effective ductility

demand on the seismic force-resisting system

due to the design earthquake ground motions,

Section 18.6.4

= displacement amplitude at Level i of the

fundamental mode of vibration of the

structure in the direction of interest, normal-

ized to unity at the roof level, Section

18.5.2.3

= displacement amplitude at Level i of

the residual mode of vibration of the

structure in the direction of interest

normalized to unity at the roof level,

Section 18.5.2.7

= participation factor of the fundamental mode

of vibration of the structure in the direction

of interest, Section 18.4.2.3 or 18.5.2.3

(m = 1)

= participation factor in the m

mode of

vibration of the structure in the direction of

interest, Section 18.4.2.3

= participation factor of the residual mode of

vibration of the structure in the direction of

interest, Section 18.5.2.7

∇

= design story velocity due to the fundamental

mode of vibration of the structure in the

direction of interest, Section 18.5.3.4

∇

= total design story velocity of the structure in

the direction of interest, Section 18.4.3.4

∇

= total maximum story velocity of the

structure in the direction of interest,

Section 18.5.3

∇

= design story velocity due to the m

mode of

vibration of the structure in the direction of

interest, Section 18.4.3.4

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

182

18.2 GENERAL DESIGN REQUIREMENTS

18.2.1 Seismic Design Category A

Seismic Design Category A structures with a

damping system shall be designed using the design

spectral response acceleration determined in accor-

dance with Section 11.4.4 and the analysis methods

and design requirements for Seismic Design Category

B structures.

18.2.2 System Requirements

Design of the structure shall consider the basic

requirements for the seismic force-resisting system

and the damping system as deﬁ ned in the following

sections. The seismic force-resisting system shall

have the required strength to meet the forces

deﬁ ned in Section 18.2.2.1. The combination of the

seismic force-resisting system and the damping

system is permitted to be used to meet the drift

requirement.

18.2.2.1 Seismic Force-Resisting System

Structures that contain a damping system are

required to have a seismic force-resisting system that,

in each lateral direction, conforms to one of the types

indicated in Table 12.2-1.

The design of the seismic force-resisting system

in each direction shall satisfy the requirements of

Section 18.7 and the following:

1. The seismic base shear used for design of the

seismic force-resisting system shall not be less

than V

min

, where V

min

is determined as the greater

of the values computed using Eqs. 18.2-1 and

18.2-2:

min

(18.2-1)

min

= 0.75V (18.2-2)

where

V = seismic base shear in the direction of

interest, determined in accordance with

Section 12.8

V + I

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to the

sum of viscous damping in the fundamental

mode of vibration of the structure in the

direction of interest, β

(m = 1), plus

inherent damping, β

, and period of

structure equal to T

EXCEPTION: The seismic base shear used for

design of the seismic force-resisting system shall not

be taken as less than 1.0V, if either of the following

conditions apply:

a. In the direction of interest, the damping system

has less than two damping devices on each ﬂ oor

level, conﬁ gured to resist torsion.

b. The seismic force-resisting system has

horizontal irregularity Type 1b (Table 12.3-1) or

vertical irregularity Type 1b (Table 12.3-2).

2. Minimum strength requirements for elements of

the seismic force-resisting system that are also

elements of the damping system or are otherwise

required to resist forces from damping devices

shall meet the additional requirements of

Section 18.7.2.

18.2.2.2 Damping System

Elements of the damping system shall be

designed to remain elastic for design loads including

unreduced seismic forces of damping devices as

required in Section 18.7.2.1, unless it is shown by

analysis or test that inelastic response of elements

would not adversely affect damping system function

and inelastic response is limited in accordance with

the requirements of Section 18.7.2.6.

18.2.3 Ground Motion

18.2.3.1 Design Spectra

Spectra for the design earthquake ground

motions and maximum considered earthquake

ground

motions developed in accordance with Section 17.3.1

shall be used for the design and analysis of a structure

with a damping system. Site-speciﬁ c design spectra

shall be developed and used for design of a structure

with a damping system if either of the following

conditions apply:

1. The structure is located on a Class F site.

2. The structure is located at a site with S

greater

than or equal to 0.6.

18.2.3.2 Ground Motion Histories

Ground motion histories for the design

earthquake and the maximum considered earthquake

developed in accordance with Section 17.3.2 shall be

used for design and analysis of all structures with a

damping system if either of the following conditions

apply:

1. The structure is located at a site with S

greater

than or equal to 0.6.

2. The damping system is explicitly modeled and

analyzed using the response-history analysis

method.

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MINIMUM DESIGN LOADS

183

18.2.4 Procedure Selection

A structure with a damping system shall be

designed using linear procedures, nonlinear proce-

dures, or a combination of linear and nonlinear

procedures, as permitted in this section.

Regardless of the analysis method used, the peak

dynamic response of the structure and elements of the

damping system shall be conﬁ rmed by using the

nonlinear response-history procedure if the structure is

located at a site with S

greater than or equal to 0.6.

18.2.4.1 Nonlinear Procedures

The nonlinear procedures of Section 18.3 are

permitted to be used for design of all structures with

damping systems.

18.2.4.2 Response-Spectrum Procedure

The response-spectrum procedure of Section 18.4

is permitted to be used for design of a structure with a

damping system provided that

1. In the direction of interest, the damping system has

at least two damping devices in each story,

conﬁ gured to resist torsion.

2. The total effective damping of the fundamental

mode, β

(m = 1), of the structure in the direction

of interest is not greater than 35 percent of critical.

18.2.4.3 Equivalent Lateral Force Procedure

The equivalent lateral force procedure of Section

18.5 is permitted to be used for design of a structure

with a damping system provided that

1. In the direction of interest, the damping system has

at least two damping devices in each story,

conﬁ gured to resist torsion.

2. The total effective damping of the fundamental

mode, β

(m = 1), of the structure in the direction

of interest is not greater than 35 percent of critical.

3. The seismic force-resisting system does not have

horizontal irregularity Type 1a or 1b (Table 12.3-1)

or vertical irregularity Type 1a, 1b, 2, or 3 (Table

12.3-2).

4. Floor diaphragms are rigid as deﬁ ned in Section

12.3.1.

5. The height of the structure above the base does not

exceed 100 ft (30 m).

18.2.5 Damping System

18.2.5.1 Device Design

The design, construction, and installation of

damping devices shall be based on response to

maximum considered earthquake ground motions and

consideration of the following:

1. Low-cycle, large-displacement degradation due to

seismic loads.

2. High-cycle, small-displacement degradation due to

wind, thermal, or other cyclic loads.

3. Forces or displacements due to gravity loads.

4. Adhesion of device parts due to corrosion or

abrasion, biodegradation, moisture, or chemical

exposure.

5. Exposure to environmental conditions, including,

but not limited to, temperature, humidity,

moisture, radiation (e.g., ultraviolet light),

and reactive or corrosive substances (e.g., salt

water).

Damping devices subject to failure by low-cycle

fatigue shall resist wind forces without slip, move-

ment, or inelastic cycling.

The design of damping devices shall incorporate

the range of thermal conditions, device wear, manu-

facturing tolerances, and other effects that cause

device properties to vary during the design life of the

device.

18.2.5.2 Multiaxis Movement

Connection points of damping devices shall

provide sufﬁ cient articulation to accommodate

simultaneous longitudinal, lateral, and vertical

displacements of the damping system.

18.2.5.3 Inspection and Periodic Testing

Means of access for inspection and removal of all

damping devices shall be provided.

The registered design professional responsible for

design of the structure shall establish an appropriate

inspection and testing schedule for each type of

damping device to ensure that the devices respond in

a dependable manner throughout their design life. The

degree of inspection and testing shall reﬂ ect the

established in-service history of the damping devices

and the likelihood of change in properties over the

design life of the devices.

18.2.5.4 Quality Control

As part of the quality assurance plan developed in

accordance with Section 11A.1.2, the registered

design professional responsible for the structural

design shall establish a quality control plan for the

manufacture of damping devices. As a minimum, this

plan shall include the testing requirements of Section

18.9.2.

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

184

18.3 NONLINEAR PROCEDURES

The stiffness and damping properties of the damping

devices used in the models shall be based on or

veriﬁ ed by testing of the damping devices as speciﬁ ed

in Section 18.9. The nonlinear force-deﬂ ection

characteristics of damping devices shall be modeled,

as required, to explicitly account for device depen-

dence on frequency, amplitude, and duration of

seismic loading.

18.3.1 Nonlinear Response-History Procedure

A nonlinear response-history analysis shall

utilize a mathematical model of the structure and the

damping system as provided in Section 16.2.2 and

this section. The model shall directly account for the

nonlinear hysteretic behavior of elements of the

structure and the damping devices to determine its

response.

The analysis shall be performed in accordance

with Section 16.2 together with the requirements of

this section. Inherent damping of the structure shall

not be taken as greater than 5 percent of critical

unless test data consistent with levels of deformation

at or just below the effective yield displacement of

the seismic force-resisting system support higher

values.

If the calculated force in an element of the

seismic force-resisting system does not exceed 1.5

times its nominal strength, that element is permitted to

be modeled as linear.

18.3.1.1 Damping Device Modeling

Mathematical models of displacement-dependent

damping devices shall include the hysteretic behavior

of the devices consistent with test data and accounting

for all signiﬁ cant changes in strength, stiffness, and

hysteretic loop shape. Mathematical models of

velocity-dependent damping devices shall include

the velocity coefﬁ cient consistent with test data.

If this coefﬁ cient changes with time and/or tempera-

ture, such behavior shall be modeled explicitly.

The elements of damping devices connecting

damper units to the structure shall be included in

the model.

EXCEPTION: If the properties of the

damping devices are expected to change during

the duration of the time history analysis, the

dynamic response is permitted to be enveloped

by the upper and lower limits of device properties.

All these limit cases for variable device properties

must satisfy the same conditions as if the time-

dependent behavior of the devices were explicitly

modeled.

18.3.1.2 Response Parameters

In addition to the response parameters given in

Section 16.2.4, for each ground motion used for

response-history analysis, individual response param-

eters consisting of the maximum value of the discrete

damping device forces, displacements, and velocities,

in the case of velocity-dependent devices, shall be

determined.

If at least seven pairs of ground motions are used

for response-history analysis, the design values of the

damping device forces, displacements, and velocities

are permitted to be taken as the average of the values

determined by the analyses. If less than seven pairs of

ground motions are used for response-history analysis,

the design damping device forces, displacements,

and velocities shall be taken as the maximum value

determined by the analyses. A minimum of three pairs

of ground motions shall be used.

18.3.2 Nonlinear Static Procedure

The nonlinear modeling described in Section

16.2.2 and the lateral loads described in Section 16.2

shall be applied to the seismic force-resisting system.

The resulting force-displacement curve shall be used

in lieu of the assumed effective yield displacement,

, of Eq. 18.6-10 to calculate the effective ductility

demand due to the design earthquake ground motions,

, and due to the maximum considered earthquake

ground motions, μ

, in Eqs. 18.6-8 and 18.6-9,

respectively. The value of (R/C

) shall be taken as

1.0 in Eqs. 18.4-4, 18.4-5, 18.4-8, and 18.4-9 for the

response-spectrum procedure, and in Eqs. 18.5-6,

18.5-7, and 18.5-15 for the equivalent lateral force

procedure.

18.4 RESPONSE-SPECTRUM PROCEDURE

Where the response-spectrum procedure is used to

analyze a structure with a damping system, the

requirements of this section shall apply.

18.4.1 Modeling

A mathematical model of the seismic force-resist-

ing system and damping system shall be constructed

that represents the spatial distribution of mass,

stiffness, and damping throughout the structure. The

model and analysis shall comply with the require-

ments of Section 12.9 for the seismic force-resisting

system and to the requirements of this section for the

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MINIMUM DESIGN LOADS

185

damping system. The stiffness and damping properties

of the damping devices used in the models shall be

based on or veriﬁ ed by testing of the damping devices

as speciﬁ ed in Section 18.9.

The elastic stiffness of elements of the damping

system other than damping devices shall be explicitly

modeled. Stiffness of damping devices shall be

modeled depending on damping device type as

follows:

1. Displacement-dependent damping devices:

Displacement-dependent damping devices shall be

modeled with an effective stiffness that represents

damping device force at the response displacement

of interest (e.g., design story drift). Alternatively,

the stiffness of hysteretic and friction damping

devices is permitted to be excluded from response

spectrum analysis provided design forces in

displacement-dependent damping devices, Q

DSD

are applied to the model as external loads

(Section 18.7.2.5).

2. Velocity-dependent damping devices: Velocity-

dependent damping devices that have a stiffness

component (e.g., viscoelastic damping devices)

shall be modeled with an effective stiffness

corresponding to the amplitude and frequency of

interest.

18.4.2 Seismic Force-Resisting System

18.4.2.1 Seismic Base Shear

The seismic base shear, V, of the structure in a

given direction shall be determined as the combina-

tion of modal components, V

, subject to the limits of

Eq. 18.4-1:

V ≥ V

min

(18.4-1)

The seismic base shear, V, of the structure shall be

determined by the sum of the square root method

(SRSS) or complete quadratic combination of modal

base shear components, V

18.4.2.2 Modal Base Shear

Modal base shear of the m

mode of vibration,

, of the structure in the direction of interest shall be

determined in accordance with Eqs. 18.4-2:

= C

(18.4-2a)

iim

⎛

⎝

⎜

⎞

⎠

⎟

∑

(18.4-2b)

where

= seismic response coefﬁ cient of the m

mode of

vibration of the structure in the direction of

interest as determined from Section 18.4.2.4

(m = 1) or Section 18.4.2.6 (m > 1)

= effective seismic weight of the m

mode of

vibration of the structure

18.4.2.3 Modal Participation Factor

The modal participation factor of the m

mode of

vibration, Γ

, of the structure in the direction of

interest shall be determined in accordance with Eq.

18.4-3:

iim

∑

(18.4-3)

where

= displacement amplitude at the i

level of the

structure in the m

mode of vibration in the

direction of interest, normalized to unity at the

roof level.

18.4.2.4 Fundamental Mode Seismic

Response Coefﬁ cient

The fundamental mode (m = 1) seismic response

coefﬁ cient, C

, in the direction of interest shall be

determined in accordance with Eqs. 18.4-4 and

18.4-5:

For T

< T

⎛

⎝

⎜

⎞

⎠

⎟

(18.4-4)

For T

≥ T

101

⎛

⎝

⎜

⎞

⎠

⎟

()

(18.4-5)

18.4.2.5 Effective Fundamental Mode

Period Determination

The effective fundamental mode (m = 1) period

at the design earthquake ground motion, T

, and

at the MCE

ground motion, T

, shall be based

on either explicit consideration of the post-yield

force deﬂ ection characteristics of the structure or

determined in accordance with Eqs. 18.4-6 and

18.4-7:

DD11

=μ (18.4-6)

MM11

=μ (18.4-7)

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

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18.4.2.6 Higher Mode Seismic Response Coefﬁ cient

Higher mode (m > 1) seismic response coefﬁ -

cient, C

, of the m

mode of vibration (m > 1) of the

structure in the direction of interest shall be deter-

mined in accordance with Eqs. 18.4-8 and 18.4-9:

For T

< T

⎛

⎝

⎜

⎞

⎠

⎟

(18.4-8)

For T

≥ T

mmD

⎛

⎝

⎜

⎞

⎠

⎟

()

(18.4-9)

where

= period, in seconds, of the m

mode of vibration

of the structure in the direction under

consideration

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

and

period of the structure equal to T

18.4.2.7 Design Lateral Force

Design lateral force at Level i due to the m

mode of vibration, F

, of the structure in the direction

of interest shall be determined in accordance with

Eq. 18.4-10:

im i im

(18.4-10)

Design forces in elements of the seismic force-

resisting system shall be determined by the SRSS or

complete quadratic combination of modal design

forces.

18.4.3 Damping System

Design forces in damping devices and other

elements of the damping system shall be determined

on the basis of the ﬂ oor deﬂ ection, story drift, and

story velocity response parameters described in the

following sections.

Displacements and velocities used to determine

maximum forces in damping devices at each story

shall account for the angle of orientation of each

device from the horizontal and consider the effects of

increased response due to torsion required for design

of the seismic force-resisting system.

Floor deﬂ ections at Level i, δ

and δ

, story

drifts, Δ

and Δ

, and story velocities, ∇

and ∇

shall be calculated for both the design earthquake

ground motions and the maximum considered

earthquake ground motions, respectively, in accor-

dance with this section.

18.4.3.1 Design Earthquake Floor Deﬂ ection

The deﬂ ection of structure due to the design

earthquake ground motions at Level i in the m

mode

of vibration, δ

imD

, of the structure in the direction of

interest shall be determined in accordance with Eq.

18.4-11:

imD

= D

(18.4-11)

The total design deﬂ ection at each ﬂ oor of the

structure shall be calculated by the SRSS or complete

quadratic combination of modal design earthquake

deﬂ ections.

18.4.3.2 Design Earthquake Roof Displacement

Fundamental (m = 1) and higher mode (m > 1)

roof displacements due to the design earthquake

ground motions, D

and D

, of the structure in the

direction of interest shall be determined in accordance

with Eqs. 18.4-12 and to 18.4-13:

For m = 1,

gST

DS D

DS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

(18.4-12a)

gST

DS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

≥

(18.4-12b)

For m > 1,

gST

mD m

DS m

⎛

⎝

⎜

⎞

⎠

⎟

≤

⎛

⎝

⎜

⎞

⎠

⎟

(18.4-13)

18.4.3.3 Design Earthquake Story Drift

Design story drift in the fundamental mode, Δ

and higher modes, Δ

(m > 1), of the structure in the

direction of interest shall be calculated in accordance

with Section 12.8.6 using modal roof displacements of

Section 18.4.3.2.

Total design story drift, Δ

, shall be determined

by the SRSS or complete quadratic combination of

modal design earthquake drifts.

18.4.3.4 Design Earthquake Story Velocity

Design story velocity in the fundamental

mode, ∇

, and higher modes, ∇

(m > 1), of

the structure in the direction of interest shall be

calculated in accordance with Eqs. 18.4-14 and

18.4-15:

For m = 1, ∇

= 2π

(18.4-14)

For m > 1, ∇

= 2π

(18.4-15)

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MINIMUM DESIGN LOADS

187

Total design story velocity, Δ

, shall be determined

by the SRSS or complete quadratic combination of

modal design velocities.

18.4.3.5 Maximum Considered Earthquake Response

Total modal maximum ﬂ oor deﬂ ection at Level i,

design story drift values, and design story velocity

values shall be based on Sections 18.4.3.1, 18.4.3.3,

and 18.4.3.4, respectively, except design roof

displacement shall be replaced by maximum roof

displacement. Maximum roof displacement of

the structure in the direction of interest shall be

calculated in accordance with Eqs. 18.4-16 and

to 18.4-17:

For m = 1,

gST

MS M

MS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ,

(18.4-16a)

gST

MS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

≥

ππ

ΓΓ,

(18.4-16b)

For m >1,

gST

mM m

MS m

⎛

⎝

⎜

⎞

⎠

⎟

≤

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ

(18.4-17)

where

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

and

period of the structure equal to T

18.5 EQUIVALENT LATERAL

FORCE PROCEDURE

Where the equivalent lateral force procedure is used

to design structures with a damping system, the

requirements of this section shall apply.

18.5.1 Modeling

Elements of the seismic force-resisting system

shall be modeled in a manner consistent with the

requirements of Section 12.8. For purposes of

analysis, the structure shall be considered to be ﬁ xed

at the base.

Elements of the damping system shall be modeled

as required to determine design forces transferred

from damping devices to both the ground and the

seismic force-resisting system. The effective stiffness

of velocity-dependent damping devices shall be

modeled.

Damping devices need not be explicitly modeled

provided effective damping is calculated in accor-

dance with the procedures of Section 18.6 and used to

modify response as required in Sections 18.5.2 and

18.5.3.

The stiffness and damping properties of the

damping devices used in the models shall be based on

or veriﬁ ed by testing of the damping devices as

speciﬁ ed in Section 18.9.

18.5.2 Seismic Force-Resisting System

18.5.2.1 Seismic Base Shear

The seismic base shear, V, of the seismic force-resist-

ing system in a given direction shall be determined as

the combination of the two modal components, V

and

, in accordance with Eq. 18.5-1:

VVVV

=+≥

min

(18.5-1)

where

= design value of the seismic base shear of the

fundamental mode in a given direction of

response, as determined in Section 18.5.2.2

= design value of the seismic base shear of the

residual mode in a given direction, as deter-

mined in Section 18.5.2.6

min

= minimum allowable value of base shear

permitted for design of the seismic force-

resisting system of the structure in direction of

the interest, as determined in Section 18.2.2.1

18.5.2.2 Fundamental Mode Base Shear

The fundamental mode base shear, V

, shall be

determined in accordance with Eq. 18.5-2:

= C

(18.5-2)

where

= the fundamental mode seismic response coef-

ﬁ cient, as determined in Section 18.5.2.4

= the effective fundamental mode seismic weight

including portions of the live load as deﬁ ned by

Eq. 18.4-2b for m = 1

18.5.2.3 Fundamental Mode Properties

The fundamental mode shape, φ

, and participa-

tion factor, Γ

, shall be determined by either dynamic

analysis using the elastic structural properties and

deformational characteristics of the resisting elements

or using Eqs. 18.5-3 and 18.5-4:

(18.5-3)

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

188

∑

iil

(18.5-4)

where

= the height above the base to Level i

= the height of the structure above the base to the

roof level

= the portion of the total effective seismic weight,

W, located at or assigned to Level i

The fundamental period, T

, shall be determined

either by dynamic analysis using the elastic structural

properties and deformational characteristics of the

resisting elements, or using Eq. 18.5-5 as follows:

∑

(18.5-5)

where

= lateral force at Level i of the structure distributed

in accordance with Section 12.8.3

= elastic deﬂ ection at Level i of the structure due to

applied lateral forces f

18.5.2.4 Fundamental Mode Seismic

Response Coefﬁ cient

The fundamental mode seismic response coefﬁ cient,

, shall be determined using Eq. 18.5-6 or 18.5-7:

For T

< T

⎛

⎝

⎜

⎞

⎠

⎟

(18.5-6)

For T

≥ T

101

⎛

⎝

⎜

⎞

⎠

⎟

()

(18.5-7)

where

= the design spectral response acceleration

parameter in the short period range

= the design spectral response acceleration

parameter at a period of 1 s

= numerical coefﬁ cient as set forth in Table

18.6-1 for effective damping equal to β

(m = 1) and period of the structure equal to T

18.5.2.5 Effective Fundamental Mode

Period Determination

The effective fundamental mode period at the

design earthquake, T

, and at the maximum consid-

ered earthquake, T

, shall be based on explicit

consideration of the post-yield force deﬂ ection

characteristics of the structure or shall be calculated

using Eqs. 18.5-8 and 18.5-9:

DD11

(18.5-8)

MM11

(18.5-9)

18.5.2.6 Residual Mode Base Shear

Residual mode base shear, V

, shall be deter-

mined in accordance with Eq. 18.5-10:

= C

(18.5-10)

where

= the residual mode seismic response coefﬁ cient

as determined in Section 18.5.2.8

= the effective residual mode effective

weight of the structure determined using

Eq. 18.5-13

18.5.2.7 Residual Mode Properties

Residual mode shape, φ

, participation factor, Γ

effective residual mode seismic weight of the

structure, W

, and effective period, T

, shall be

determined using Eqs. 18.5-11 through 18.5-14:

−

(18.5-11)

= 1 – Γ

(18.5-12)

= W – W

(18.5-13)

= 0.4T

(18.5-14)

18.5.2.8 Residual Mode Seismic

Response Coefﬁ cient

The residual mode seismic response coefﬁ cient,

, shall be determined in accordance with

Eq. 18.5-15:

⎛

⎝

⎜

⎞

⎠

⎟

(18.5-15)

where

= numerical coefﬁ cient as set forth in Table 18.6-1

for effective damping equal to β

, and period of

the structure equal to T

18.5.2.9 Design Lateral Force

The design lateral force in elements of the

seismic force-resisting system at Level i due to

fundamental mode response, F

, and residual mode

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MINIMUM DESIGN LOADS

189

response, F

, of the structure in the direction of

interest shall be determined in accordance with Eqs.

18.5-16 and 18.5-17:

iii1

=φ

(18.5-16)

iR i iR

=φ

(18.5-17)

Design forces in elements of the seismic force-

resisting system shall be determined by taking the

SRSS of the forces due to fundamental and residual

modes.

18.5.3 Damping System

Design forces in damping devices and other

elements of the damping system shall be determined

on the basis of the ﬂ oor deﬂ ection, story drift, and

story velocity response parameters described in the

following sections.

Displacements and velocities used to determine

maximum forces in damping devices at each story

shall account for the angle of orientation of each

device from the horizontal and consider the effects of

increased response due to torsion required for design

of the seismic force-resisting system.

Floor deﬂ ections at Level i, δ

and δ

, story

drifts, Δ

and Δ

, and story velocities, ∇

and ∇

shall be calculated for both the design earthquake

ground motions and the maximum considered

earthquake ground motions, respectively, in

accordance with the following sections.

18.5.3.1 Design Earthquake Floor Deﬂ ection

The total design deﬂ ection at each ﬂ oor of

the structure in the direction of interest shall be

calculated as the SRSS of the fundamental and

residual mode ﬂ oor deﬂ ections. The fundamental

and residual mode deﬂ ections due to the design

earthquake ground motions, δ

i1D

and δ

iRD

, at the center

of rigidity of Level i of the structure in the direction

of interest shall be determined using Eqs. 18.5-18

and 18.5-19:

i1D

= D

(18.5-18)

iRD

= D

(18.5-19)

where

= fundamental mode design displacement at the

center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.5.3.2

= residual mode design displacement at the center

of rigidity of the roof level of the structure in

the direction under consideration, Section

18.5.3.2

18.5.3.2 Design Earthquake Roof Displacement

Fundamental and residual mode displacements

due to the design earthquake ground motions,

and D

, at the center of rigidity of the roof

level of the structure in the direction of interest

shall be determined using Eqs. 18.5-20 and

18.5-21:

gST

DS D

DS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ,

(18.5-20a)

gST

DS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

≥

ππ

ΓΓ,

(18.5-20b)

gST

RD R

DS R

⎛

⎝

⎜

⎞

⎠

⎟

≤

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ

(18.5-21)

18.5.3.3 Design Earthquake Story Drift

Design story drifts, Δ

, in the direction of interest

shall be calculated using Eq. 18.5-22:

Δ=Δ +Δ

DDRD1

(18.5-22)

where

= design story drift due to the fundamental mode

of vibration of the structure in the direction of

interest

= design story drift due to the residual mode of

vibration of the structure in the direction of

interest

Modal design story drifts, Δ

and Δ

shall be determined as the difference of the

deﬂ ections at the top and bottom of the story

under consideration using the ﬂ oor deﬂ ections of

Section 18.5.3.1.

18.5.3.4 Design Earthquake Story Velocity

Design story velocities, ∇

, in the direction of

interest shall be calculated in accordance with Eqs.

18.5-23 through 18.5-25:

∇=∇+∇

DDRD1

(18.5-23)

∇=

2π

(18.5-24)

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190

∇=

2π

(18.5-25)

where

∇

= design story velocity due to the fundamental

mode of vibration of the structure in the

direction of interest

∇

= design story velocity due to the residual mode

of vibration of the structure in the direction of

interest

18.5.3.5 Maximum Considered Earthquake Response

Total and modal maximum ﬂ oor deﬂ ections at

Level i, design story drifts, and design story velocities

shall be based on the equations in Sections 18.5.3.1,

18.5.3.3, and 18.5.3.4, respectively, except that design

roof displacements shall be replaced by maximum

roof displacements. Maximum roof displacements

shall be calculated in accordance with Eqs. 18.5-26

and 18.5-27:

gST

MS M

MS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ,

(18.5-26a)

gST

MS1

⎛

⎝

⎜

⎞

⎠

⎟

≥

⎛

⎝

⎜

⎞

⎠

⎟

≥

ππ

ΓΓ,

(18.5-26b)

gST

RM R

MS R

⎛

⎝

⎜

⎞

⎠

⎟

≤

⎛

⎝

⎜

⎞

⎠

⎟

ππ

ΓΓ

(18.5-27)

where

= the MCE

, 5 percent damped, spectral response

acceleration parameter at a period of 1 s

adjusted for site class effects as deﬁ ned in

Section 11.4.3

= the MCE

, 5 percent damped, spectral response

acceleration parameter at short periods

adjusted for site class effects as deﬁ ned in

Section 11.4.3

= numerical coefﬁ cient as set forth in

Table 18.6-1 for effective damping equal to

(m = 1) and period of structure equal

to T

18.6 DAMPED RESPONSE MODIFICATION

As required in Sections 18.4 and 18.5, response of the

structure shall be modiﬁ ed for the effects of the

damping system.

18.6.1 Damping Coefﬁ cient

Where the period of the structure is greater than

or equal to T

, the damping coefﬁ cient shall be as

prescribed in Table 18.6-1. Where the period of the

structure is less than T

, the damping coefﬁ cient shall

be linearly interpolated between a value of 1.0 at a

0-second period for all values of effective damping

and the value at period T

as indicated in Table 18.6-1.

18.6.2 Effective Damping

The effective damping at the design displace-

ment, β

, and at the maximum displacement, β

, of

the m

mode of vibration of the structure in the

direction under consideration shall be calculated using

Eqs. 18.6-1 and 18.6-2:

βββμβ

mD I Vm D HD

=+ + (18.6-1)

βββμβ

mM I Vm M HM

=+ + (18.6-2)

where

= component of effective damping of the

structure in the direction of interest due to

post-yield hysteretic behavior of the seismic

force-resisting system and elements of

the damping system at effective ductility

demand, μ

= component of effective damping of the struc-

ture in the direction of interest due to post-yield

hysteretic behavior of the seismic force-resist-

ing system and elements of the damping system

at effective ductility demand, μ

= component of effective damping of the struc-

ture due to the inherent dissipation of energy

Table 18.6-1 Damping Coefﬁ cient, B

V+I

, B

(Where Period of the Structure ≥ T

)

Effective Damping, β

(percentage of critical)

v+I

, B

(where period of the structure ≥ T

)

≤2 0.8

5 1.0

10 1.2

20 1.5

30 1.8

40 2.1

50 2.4

60 2.7

70 3.0

80 3.3

90 3.6

≥100 4.0

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MINIMUM DESIGN LOADS

191

by elements of the structure, at or just below

the effective yield displacement of the seismic

force-resisting system

= component of effective damping of the m

mode of vibration of the structure in the

direction of interest due to viscous dissipation

of energy by the damping system, at or just

below the effective yield displacement of the

seismic force-resisting system

= effective ductility demand on the seismic

force-resisting system in the direction of interest

due to the design earthquake ground motions

= effective ductility demand on the seismic

force-resisting system in the direction of

interest due to the maximum considered

earthquake ground motions

Unless analysis or test data supports other values,

the effective ductility demand of higher modes of

vibration in the direction of interest shall be taken

as 1.0.

18.6.2.1 Inherent Damping

Inherent damping, β

, shall be based on the

material type, conﬁ guration, and behavior of the

structure and nonstructural components responding

dynamically at or just below yield of the seismic

force-resisting system. Unless analysis or test data

supports other values, inherent damping shall be taken

as not greater than 5 percent of critical for all modes

of vibration.

18.6.2.2 Hysteretic Damping

Hysteretic damping of the seismic force-resisting

system and elements of the damping system shall be

based either on test or analysis or shall be calculated

using Eqs. 18.6-3 and 18.6-4:

ββ

HD H I

q=−

()

−

⎛

⎝

⎜

⎞

⎠

⎟

064 1

(18.6-3)

ββ

HM H I

q=−

()

−

⎛

⎝

⎜

⎞

⎠

⎟

064 1

(18.6-4)

where

= hysteresis loop adjustment factor, as deﬁ ned in

Section 18.6.2.2.1

= effective ductility demand on the seismic

force-resisting system in the direction of interest

due to the design earthquake ground motions

= effective ductility demand on the seismic

force-resisting system in the direction of interest

due to the maximum considered earthquake

ground motions

Unless analysis or test data supports other

values, the hysteretic damping of higher modes of

vibration in the direction of interest shall be taken

as zero.

18.6.2.2.1 Hysteresis Loop Adjustment Factor The

calculation of hysteretic damping of the seismic

force-resisting system and elements of the damping

system shall consider pinching and other effects that

reduce the area of the hysteresis loop during repeated

cycles of earthquake demand. Unless analysis or test

data support other values, the fraction of full hyster-

etic loop area of the seismic force-resisting system

used for design shall be taken as equal to the factor,

, calculated using Eq. 18.6-5:

= 067

(18.6-5)

where

= period deﬁ ned by the ratio, S

= period of the fundamental mode of vibration of

the structure in the direction of the interest

The value of q

shall not be taken as greater than

1.0 and need not be taken as less than 0.5.

18.6.2.3 Viscous Damping

Viscous damping of the m

mode of vibration of

the structure, β

, shall be calculated using Eqs.

18.6-6 and 18.6-7:

∑

(18.6-6)

mimim

∑

(18.6-7)

where

= work done by j

damping device in one

complete cycle of dynamic response corre-

sponding to the m

mode of vibration of the

structure in the direction of interest at modal

displacements, δ

= maximum strain energy in the m

mode of

vibration of the structure in the direction of

interest at modal displacements, δ

= m

mode inertial force at Level i

= deﬂ ection of Level i in the m

mode of

vibration at the center of rigidity of the struc-

ture in the direction under consideration

Viscous modal damping of displacement-

dependent damping devices shall be based on a

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

192

response amplitude equal to the effective yield

displacement of the structure.

The calculation of the work done by individual

damping devices shall consider orientation and

participation of each device with respect to the mode

of vibration of interest. The work done by individual

damping devices shall be reduced as required to

account for the ﬂ exibility of elements, including pins,

bolts, gusset plates, brace extensions, and other

components that connect damping devices to other

elements of the structure.

18.6.3 Effective Ductility Demand

The effective ductility demand on the seismic

force-resisting system due to the design earthquake

ground motions, μ

, and due to the maximum

considered earthquake ground motions, μ

, shall be

calculated using Eqs. 18.6-8, 18.6-9, and 18.6-10:

=≥

10. (18.6-8)

=≥

10. (18.6-9)

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

111

(18.6-10)

where

= fundamental mode design displacement at the

center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.4.3.2 or 18.5.3.2

= fundamental mode maximum displacement at

the center of rigidity of the roof level of the

structure in the direction under consideration,

Section 18.4.3.5 or 18.5.3.5

= displacement at the center of rigidity of the

roof level of the structure at the effective yield

point of the seismic force-resisting system

R = response modiﬁ cation coefﬁ cient from Table

12.2-1

= deﬂ ection ampliﬁ cation factor from Table

12.2-1

= overstrength factor from Table 12.2-1

= participation factor of the fundamental mode of

vibration of the structure in the direction of

interest, Section 18.4.2.3 or 18.5.2.3 (m = 1)

= seismic response coefﬁ cient of the fundamental

mode of vibration of the structure in the

direction of interest, Section 18.4.2.4 or

18.5.2.4 (m = 1)

= period of the fundamental mode of vibration of

the structure in the direction of interest

The design ductility demand, μ

, shall not exceed

the maximum value of effective ductility demand,

max

, given in Section 18.6.4.

18.6.4 Maximum Effective Ductility Demand

For determination of the hysteresis loop adjust-

ment factor, hysteretic damping, and other parameters,

the maximum value of effective ductility demand, μ

max

shall be calculated using Eqs. 18.6-11 and 18.6-12:

For T

≤ T

max

= 0.5[(R/(Ω

))

+ 1] (18.6-11)

For T

≥ T

max

= R/(Ω

) (18.6-12)

where

= the importance factor determined in accordance

with Section 11.5.1

= effective period of the fundamental mode of

vibration of the structure at the design displace-

ment in the direction under consideration

For T

< T

, μ

max

shall be determined by

linear interpolation between the values of Eqs.

18.6-11 and 18.6-12.

18.7 SEISMIC LOAD CONDITIONS AND

ACCEPTANCE CRITERIA

For the nonlinear procedures of Section 18.3, the

seismic force-resisting system, damping system,

loading conditions, and acceptance criteria for

response parameters of interest shall conform with

Section 18.7.1. Design forces and displacements

determined in accordance with the response-spectrum

procedure of Section 18.4 or the equivalent lateral force

procedure of Section 18.5 shall be checked using the

strength design criteria of this standard and the seismic

loading conditions of Section 18.7.1 and 18.7.2.

18.7.1 Nonlinear Procedures

Where nonlinear procedures are used in analysis,

the seismic force-resisting system, damping system,

seismic loading conditions, and acceptance criteria

shall conform to the following subsections.

18.7.1.1 Seismic Force-Resisting System

The seismic force-resisting system shall satisfy

the strength requirements of Section 12.2.1 using the

seismic base shear, V

min

, as given by Section 18.2.2.1.

The story drift shall be determined using the design

earthquake ground motions.

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MINIMUM DESIGN LOADS

193

18.7.1.2 Damping Systems

The damping devices and their connections shall

be sized to resist the forces, displacements, and

velocities from the maximum considered earthquake

ground motions.

18.7.1.3 Combination of Load Effects

The effects on the damping system due to gravity

loads and seismic forces shall be combined in accor-

dance with Section 12.4 using the effect of horizontal

seismic forces, Q

, determined in accordance with the

analysis. The redundancy factor, ρ, shall be taken

equal to 1.0 in all cases, and the seismic load effect

with overstrength factor of Section 12.4.3 need not

apply to the design of the damping system.

18.7.1.4 Acceptance Criteria for the Response

Parameters of Interest

The damping system components shall be

evaluated using the strength design criteria of this

standard using the seismic forces and seismic loading

conditions determined from the nonlinear procedures

and φ = 1.0. The members of the seismic force-resist-

ing system need not be evaluated where using the

nonlinear procedure forces.

18.7.2 Response-Spectrum and Equivalent Lateral

Force Procedures

Where response-spectrum or equivalent lateral

force procedures are used in analysis, the seismic

force-resisting system, damping system, seismic

loading conditions, and acceptance criteria shall

conform to the following subsections.

18.7.2.1 Seismic Force-Resisting System

The seismic force-resisting system shall satisfy

the requirements of Section 12.2.1 using seismic base

shear and design forces determined in accordance

with Section 18.4.2 or 18.5.2.

The design story drift, Δ

, as determined in either

Section 18.4.3.3 or 18.5.3.3 shall not exceed (R/C

)

times the allowable story drift, as obtained from Table

12.12-1, considering the effects of torsion as required

in Section 12.12.1.

18.7.2.2 Damping System

The damping system shall satisfy the require-

ments of Section 12.2.1 for seismic design forces and

seismic loading conditions determined in accordance

with this section.

18.7.2.3 Combination of Load Effects

The effects on the damping system and its

components due to gravity loads and seismic forces

shall be combined in accordance with Section 12.4

using the effect of horizontal seismic forces, Q

determined in accordance with Section 18.7.2.5. The

redundancy factor, ρ, shall be taken equal to 1.0 in all

cases, and the seismic load effect with overstrength

factor of Section 12.4.3 need not apply to the design

of the damping system.

18.7.2.4 Modal Damping System Design Forces

Modal damping system design forces shall be

calculated on the basis of the type of damping devices

and the modal design story displacements and

velocities determined in accordance with either

Section 18.4.3 or 18.5.3.

Modal design story displacements and velocities

shall be increased as required to envelop the total

design story displacements and velocities determined

in accordance with Section 18.3 where peak response

is required to be conﬁ rmed by response-history

analysis.

1. Displacement-dependent damping devices: Design

seismic force in displacement-dependent damping

devices shall be based on the maximum force in

the device at displacements up to and including the

design story drift, Δ

2. Velocity-dependent damping devices: Design

seismic force in each mode of vibration in veloc-

ity-dependent damping devices shall be based on

the maximum force in the device at velocities up to

and including the design story velocity for the

mode of interest.

Displacements and velocities used to determine

design forces in damping devices at each story

shall account for the angle of orientation of the

damping device from the horizontal and consider the

effects of increased ﬂ oor response due to torsional

motions.

18.7.2.5 Seismic Load Conditions and Combination

of Modal Responses

Seismic design force, Q

, in each element

of the damping system shall be taken as the

maximum force of the following three loading

conditions:

1. Stage of maximum displacement: Seismic

design force at the stage of maximum

displacement shall be calculated in accordance

with Eq. 18.7-1:

QQQ

E mSFRS

DSD

()

∑

(18.7-1)

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

194

where

mSFRS

= force in an element of the damping system

equal to the design seismic force of the m

mode of vibration of the structure in the

direction of interest

DSD

= force in an element of the damping system

required to resist design seismic forces of

displacement-dependent damping devices

Seismic forces in elements of the damping system,

DSD

, shall be calculated by imposing design forces

of displacement-dependent damping devices on the

damping system as pseudostatic forces. Design

seismic forces of displacement-dependent damping

devices shall be applied in both positive and

negative directions at peak displacement of the

structure.

2. Stage of maximum velocity: Seismic design force

at the stage of maximum velocity shall be calcu-

lated in accordance with Eq. 18.7-2:

E mDSV

()

∑

(18.7-2)

where

mDSV

= force in an element of the damping system

required to resist design seismic forces of

velocity-dependent damping devices due to

the m

mode of vibration of the structure

in the direction of interest

Modal seismic design forces in elements of

the damping system, Q

mDSV

, shall be calculated

by imposing modal design forces of velocity-

dependent devices on the nondeformed damping

system as pseudostatic forces. Modal seismic

design forces shall be applied in directions consis-

tent with the deformed shape of the mode of

interest. Horizontal restraint forces shall be

applied at each ﬂ oor Level i of the nondeformed

damping system concurrent with the design forces

in velocity-dependent damping devices such that

the horizontal displacement at each level of the

structure is zero. At each ﬂ oor Level i, restraint

forces shall be proportional to and applied at the

location of each mass point.

3. Stage of maximum acceleration: Seismic design

force at the stage of maximum acceleration shall be

calculated in accordance with Eq. 18.7-3:

QCQCQQ

E mFD 0 mSFRS mFV mDSV

DSD

()

∑

(18.7-3)

The force coefﬁ cients, C

mFD

and C

mFV

, shall be

determined from Tables 18.7-1 and 18.7-2,

respectively, using values of effective damping

determined in accordance with the following

requirements:

For fundamental-mode response (m = 1) in the

direction of interest, the coefﬁ cients, C

1FD

and C

1FV

shall be based on the velocity exponent, α, that

Table 18.7-1 Force Coefﬁ cient, C

mFD

a,b

Effective Damping

μ ≤ 1.0

mFD

= 1.0

α ≤ 0.25 α = 0.5 α = 0.75 α ≥ 1.0

≤0.05 1.00 1.00 1.00 1.00 μ ≥ 1.0

0.1 1.00 1.00 1.00 1.00 μ ≥ 1.0

0.2 1.00 0.95 0.94 0.93 μ ≥ 1.1

0.3 1.00 0.92 0.88 0.86 μ ≥ 1.2

0.4 1.00 0.88 0.81 0.78 μ ≥ 1.3

0.5 1.00 0.84 0.73 0.71 μ ≥ 1.4

0.6 1.00 0.79 0.64 0.64 μ ≥ 1.6

0.7 1.00 0.75 0.55 0.58 μ ≥ 1.7

0.8 1.00 0.70 0.50 0.53 μ ≥ 1.9

0.9 1.00 0.66 0.50 0.50 μ ≥ 2.1

≥1.0 1.00 0.62 0.50 0.50 μ ≥ 2.2

Unless analysis or test data support other values, the force coefﬁ cient C

mFD

for viscoelastic

systems shall be taken as 1.0.

Interpolation shall be used for intermediate values of velocity exponent, α, and ductility

demand, μ.

mFD

shall be taken as equal to 1.0 for values of ductility demand, μ, greater than or equal to

the values shown.

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MINIMUM DESIGN LOADS

195

relates device force to damping device velocity.

The effective fundamental-mode damping shall be

taken as equal to the total effective damping of the

fundamental mode less the hysteretic component of

damping (β

– β

or β

– β

) at the response

level of interest (μ = μ

or μ = μ

For higher-mode (m > 1) or residual-mode

response in the direction of interest, the coefﬁ -

cients, C

mFD

and C

mFV

, shall be based on a value of

α equal to 1.0. The effective modal damping shall

be taken as equal to the total effective damping of

the mode of interest (β

or β

). For determina-

tion of the coefﬁ cient C

mFD

, the ductility demand

shall be taken as equal to that of the fundamental

mode (μ = μ

or μ = μ

18.7.2.6 Inelastic Response Limits

Elements of the damping system are permitted to

exceed strength limits for design loads provided it is

shown by analysis or test that

1. Inelastic response does not adversely affect

damping system function.

2. Element forces calculated in accordance with

Section 18.7.2.5, using a value of Ω

taken as

equal to 1.0, do not exceed the strength required to

satisfy the load combinations of Section 12.4.

18.8 DESIGN REVIEW

A design review of the damping system and related

test programs shall be performed by an independent

team of registered design professionals in the appro-

priate disciplines and others experienced in seismic

analysis methods and the theory and application of

energy dissipation systems.

The design review shall include, but need not be

limited to, the following:

1. Review of site-speciﬁ c seismic criteria including

the development of the site-speciﬁ c spectra and

ground motion histories and all other project-

speciﬁ c design criteria.

2. Review of the preliminary design of the seismic

force-resisting system and the damping system,

including design parameters of damping devices.

3. Review of the ﬁ nal design of the seismic force-

resisting system and the damping system and all

supporting analyses.

4. Review of damping device test requirements,

device manufacturing quality control and assur-

ance, and scheduled maintenance and inspection

requirements.

18.9 TESTING

The force-velocity displacement and damping proper-

ties used for the design of the damping system shall

be based on the prototype tests speciﬁ ed in this

section.

The fabrication and quality control procedures

used for all prototype and production damping devices

shall be identical.

18.9.1 Prototype Tests

The following tests shall be performed separately

on two full-size damping devices of each type

and size used in the design, in the order listed as

follows.

Representative sizes of each type of device are

permitted to be used for prototype testing, provided

both of the following conditions are met:

1. Fabrication and quality control procedures are

identical for each type and size of device used in

the structure.

2. Prototype testing of representative sizes is accepted

by the registered design professional responsible

for design of the structure.

Test specimens shall not be used for construction,

unless they are accepted by the registered design

professional responsible for design of the structure

and meet the requirements for prototype and produc-

tion tests.

Table 18.7-2 Force Coefﬁ cient, C

mFV

a,b

Effective Damping α ≤ 0.25 α = 0.5 α = 0.75 α ≥ 1.0

≤0.05 1.00 0.35 0.20 0.10

0.1 1.00 0.44 0.31 0.20

0.2 1.00 0.56 0.46 0.37

0.3 1.00 0.64 0.58 0.51

0.4 1.00 0.70 0.69 0.62

0.5 1.00 0.75 0.77 0.71

0.6 1.00 0.80 0.84 0.77

0.7 1.00 0.83 0.90 0.81

0.8 1.00 0.90 0.94 0.90

0.9 1.00 1.00 1.00 1.00

≥1.0 1.00 1.00 1.00 1.00

Unless analysis or test data support other values, the force

coefﬁ cient C

mFD

for viscoelastic systems shall be taken as 1.0.

Interpolation shall be used for intermediate values of velocity

exponent, α.

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CHAPTER 18 SEISMIC DESIGN REQUIREMENTS FOR STRUCTURES WITH DAMPING SYSTEMS

196

18.9.1.1 Data Recording

The force-deﬂ ection relationship for each cycle of

each test shall be recorded.

18.9.1.2 Sequence and Cycles of Testing

For the following test sequences, each damping

device shall be subjected to gravity load effects and

thermal environments representative of the installed

condition. For seismic testing, the displacement in the

devices calculated for the maximum considered

earthquake ground motions, termed herein as the

maximum device displacement, shall be used.

1. Each damping device shall be subjected to the

number of cycles expected in the design wind-

storm, but not less than 2,000 continuous fully

reversed cycles of wind load. Wind load shall be

at amplitudes expected in the design windstorm

and shall be applied at a frequency equal to the

inverse of the fundamental period of the structure

= 1/T

EXCEPTION: Damping devices need not be

subjected to these tests if they are not subject to wind-

induced forces or displacements or if the design wind

force is less than the device yield or slip force.

2. Each damping device shall be loaded with ﬁ ve

fully reversed, sinusoidal cycles at the maximum

earthquake device displacement at a frequency

equal to 1/T

as calculated in Section 18.4.2.5.

Where the damping device characteristics vary

with operating temperature, these tests shall be

conducted at a minimum of three temperatures

(minimum, ambient, and maximum) that bracket

the range of operating temperatures.

EXCEPTION: Damping devices are permitted to

be tested by alternative methods provided all of the

following conditions are met:

a. Alternative methods of testing are equivalent to

the cyclic testing requirements of this section.

b. Alternative methods capture the dependence of

the damping device response on ambient

temperature, frequency of loading, and tempera-

ture rise during testing.

c. Alternative methods are accepted by the

registered design professional responsible for

the design of the structure.

3. If the force-deformation properties of the damping

device at any displacement less than or equal to the

maximum device displacement change by more

than 15 percent for changes in testing frequency

from 1/T

to 2.5/T

, then the preceding tests shall

also be performed at frequencies equal to 1/T

and

2.5/T

If reduced-scale prototypes are used to qualify

the rate-dependent properties of damping devices,

the reduced-scale prototypes should be of the same

type and materials, and manufactured with the

same processes and quality control procedures, as

full-scale prototypes, and tested at a similitude-

scaled frequency that represents the full-scale

loading rates.

18.9.1.3 Testing Similar Devices

Damping devices need not be prototype tested

provided that both of the following conditions

are met:

1. All pertinent testing and other damping device data

are made available to and are accepted by the

registered design professional responsible for the

design of the structure.

2. The registered design professional substantiates the

similarity of the damping device to previously

tested devices.

18.9.1.4 Determination of

Force-Velocity-Displacement Characteristics

The force-velocity-displacement characteristics of

a damping device shall be based on the cyclic load

and displacement tests of prototype devices speciﬁ ed

in the preceding text. Effective stiffness of a damping

device shall be calculated for each cycle of deforma-

tion using Eq. 17.8-1.

18.9.1.5 Device Adequacy

The performance of a prototype damping device

shall be deemed adequate if all of the conditions listed

below are satisﬁ ed. The 15 percent limits speciﬁ ed in

the following text are permitted to be increased by the

registered design professional responsible for the

design of the structure provided that the increased

limit has been demonstrated by analysis not to have a

deleterious effect on the response of the structure.

18.9.1.5.1 Displacement-Dependent Damping Devices

The performance of the prototype displacement-

dependent damping devices shall be deemed adequate

if the following conditions, based on tests speciﬁ ed in

Section 18.9.1.2, are satisﬁ ed:

1. For Test 1, no signs of damage including leakage,

yielding, or breakage.

2. For Tests 2 and 3, the maximum force and

minimum force at zero displacement for a damping

device for any one cycle does not differ by more

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MINIMUM DESIGN LOADS

197

than 15 percent from the average maximum and

minimum forces at zero displacement as calculated

from all cycles in that test at a speciﬁ c frequency

and temperature.

3. For Tests 2 and 3, the maximum force and

minimum force at maximum device displacement

for a damping device for any one cycle does

not differ by more than 15 percent from the

average maximum and minimum forces at the

maximum device displacement as calculated from

all cycles in that test at a speciﬁ c frequency and

temperature.

4. For Tests 2 and 3, the area of hysteresis loop (E

loop

)

of a damping device for any one cycle does not

differ by more than 15 percent from the average

area of the hysteresis loop as calculated from all

cycles in that test at a speciﬁ c frequency and

temperature.

5. The average maximum and minimum forces at

zero displacement and maximum displacement,

and the average area of the hysteresis loop (E

loop

calculated for each test in the sequence of Tests 2

and 3, shall not differ by more than 15 percent

from the target values speciﬁ ed by the registered

design professional responsible for the design of

the structure.

18.9.1.5.2 Velocity-Dependent Damping Devices The

performance of the prototype velocity-dependent

damping devices shall be deemed adequate if the

following conditions, based on tests speciﬁ ed in

Section 18.9.1.2, are satisﬁ ed:

1. For Test 1, no signs of damage including leakage,

yielding, or breakage.

2. For velocity-dependent damping devices with

stiffness, the effective stiffness of a damping

device in any one cycle of Tests 2 and 3 does

not differ by more than 15 percent from the

average effective stiffness as calculated from all

cycles in that test at a speciﬁ c frequency and

temperature.

3. For Tests 2 and 3, the maximum force and

minimum force at zero displacement for a damping

device for any one cycle does not differ by more

than 15 percent from the average maximum and

minimum forces at zero displacement as calculated

from all cycles in that test at a speciﬁ c frequency

and temperature.

4. For Tests 2 and 3, the area of hysteresis loop (E

loop

)

of a damping device for any one cycle does not

differ by more than 15 percent from the average

area of the hysteresis loop as calculated from all

cycles in that test at a speciﬁ c frequency and

temperature.

5. The average maximum and minimum forces

at zero displacement, effective stiffness (for

damping devices with stiffness only), and average

area of the hysteresis loop (E

loop

) calculated for

each test in the sequence of Tests 2 and 3, does

not differ by more than 15 percent from the

target values speciﬁ ed by the registered design

professional responsible for the design of the

structure.

18.9.2 Production Testing

Prior to installation in a building, damping

devices shall be tested to ensure that their force-

velocity-displacement characteristics fall within the

limits set by the registered design professional

responsible for the design of the structure. The scope

and frequency of the production-testing program shall

be determined by the registered design professional

responsible for the design of the structure.

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199

Chapter 19

SOIL–STRUCTURE INTERACTION FOR

SEISMIC DESIGN

= the fraction of critical damping for the structure-

foundation system determined in Section 19.2.1.2

= the effective seismic weight of the structure,

which shall be taken as 0.7W, except for struc-

tures where the effective seismic weight is

concentrated at a single level, it shall be taken as

equal to W

19.2.1.1 Effective Building Period

The effective period (T

) shall be determined as

follows:



=+ +

⎛

⎝

⎜

⎞

⎠

⎟

(19.2-3)

where

T = the fundamental period of the structure as

determined in Section 12.8.2

= the stiffness of the structure where ﬁ xed at the

base, deﬁ ned by the following:

⎛

⎝

⎜

⎞

⎠

⎟

π (19.2-4)

where

= the effective height of the structure, which shall

be taken as 0.7 times the structural height (h

except for structures where the gravity load is

effectively concentrated at a single level, the

effective height of the structure shall be taken as

the height to that level

= the lateral stiffness of the foundation deﬁ ned as

the horizontal force at the level of the foundation

necessary to produce a unit deﬂ ection at that

level, the force and the deﬂ ection being mea-

sured in the direction in which the structure is

analyzed

= the rocking stiffness of the foundation deﬁ ned as

the moment necessary to produce a unit average

rotation of the foundation, the moment and

rotation being measured in the direction in which

the structure is analyzed

g = the acceleration of gravity

The foundation stiffnesses (K

and K

) shall be

computed by established principles of foundation

mechanics using soil properties that are compatible

19.1 GENERAL

If the option to incorporate the effects of soil–struc-

ture interaction is exercised, the requirements of this

section are permitted to be used in the determination

of the design earthquake forces and the corresponding

displacements of the structure if the model used for

structural response analysis does not directly incorpo-

rate the effects of foundation ﬂ exibility (i.e., the

model corresponds to a ﬁ xed-based condition with no

foundation springs). The provisions in this section

shall not be used if a ﬂ exible-base foundation is

included in the structural response model.

The provisions for use with the equivalent lateral

force procedure are given in Section 19.2, and those

for use with the modal analysis procedure are given in

Section 19.3.

19.2 EQUIVALENT LATERAL

FORCE PROCEDURE

The following requirements are supplementary to

those presented in Section 12.8.

19.2.1 Base Shear

To account for the effects of soil–structure

interaction, the base shear (V) determined from Eq.

12.8-1 shall be reduced to

= V – ΔV (19.2-1)

The reduction (ΔV) shall be computed as follows and

shall not exceed 0.3V:

Δ= −

⎛

⎝

⎜

⎞

⎠

⎟

⎡

⎣

⎢

⎤

⎦

⎥

≤VCC W V



005

(19.2-2)

where

= the seismic design coefﬁ cient computed from

Eqs. 12.8-2, 12.8-3, and through 12.8-4 using the

fundamental natural period of the ﬁ xed-base

structure (T or T

) as speciﬁ ed in Section 12.8.2

= the value of C

computed from Eqs. 12.8-2,

12.8-3, and through 12.8-4 using the fundamen-

tal natural period of the ﬂ exibly supported

structure (T

) deﬁ ned in Section 19.2.1.1

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CHAPTER 19 SOIL–STRUCTURE INTERACTION FOR SEISMIC DESIGN

200

with the soil strain levels associated with the design

earthquake motion. The average shear modulus (G)

for the soils beneath the foundation at large strain

levels and the associated shear wave velocity (v

)

needed in these computations shall be determined

from Table 19.2-1 where

= the average shear wave velocity for the soils

beneath the foundation at small strain levels

(10

–3

percent or less)

= γv

/g = the average shear modulus for the soils

beneath the foundation at small strain levels

γ = the average unit weight of the soils

Alternatively, for structures supported on mat

foundations that rest at or near the ground surface

or are embedded in such a way that the side wall

contact with the soil is not considered to remain

effective during the design ground motion, the

effective period of the structure is permitted to be

determined from



=+ +

⎛

⎝

⎜

⎞

⎠

⎟

112

(19.2-5)

where

α = the relative weight density of the structure and

the soil deﬁ ned by

(19.2-6)

and r

= characteristic foundation lengths

deﬁ ned by

(19.2-7)

and

= 4

(19.2-8)

where

= the area of the load-carrying foundation

= the static moment of inertia of the load-carrying

foundation about a horizontal centroidal axis

normal to the direction in which the structure is

analyzed

= dynamic foundation stiffness modiﬁ er for

rocking as determined from Table 19.2-2

= shear wave velocity

T = fundamental period as determined in Section

12.8.2

19.2.1.2 Effective Damping

The effective damping factor for the structure-

foundation system (β

) shall be computed as

follows:



ββ=

⎛

⎝

⎜

⎞

⎠

⎟

005

(19.2-9)

where

= the foundation damping factor as speciﬁ ed in

Fig. 19.2-1

For values of

25.

between 0.10 and 0.20 the

values of β

shall be determined by linear interpola-

tion vbetween the solid lines and the dashed lines of

Fig. 19.2-1.

The quantity r in Fig. 19.2-1 is a characteristic

foundation length that shall be determined as

follows:

For

05≤ ., r = r

(19.2-10)

For

1≥ , r = r

(19.2-11)

Table 19.2-1 Values of G/G

and v

Site Class

Value of v

Value of G/G

/2.5 S

/2.5

≤0.1 0.4 ≥0.8 ≤0.1 0.4 ≥0.8

A 1.00 1.00 1.00 1.00 1.00 1.00

B 1.00 0.97 0.95 1.00 0.95 0.90

C 0.97 0.87 0.77 0.95 0.75 0.60

D 0.95 0.71 0.32 0.90 0.50 0.10

E 0.77 0.22

0.60 0.05

aaaaaa

Note: Use straight-line interpolation for intermediate values of

/2.5.

Should be evaluated from site speciﬁ c analysis

Table 19.2-2 Values of α

T α

<0.05 1.0

0.15 0.85

0.35 0.7

0.5 0.6

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MINIMUM DESIGN LOADS

201

where

= the overall length of the side of the

foundation in the direction being analyzed

and r

= characteristic foundation lengths deﬁ ned in

Eqs. 19.2-7 and 19.2-8, respectively

For intermediate values of

, the value of r

shall be determined by linear interpolation.

EXCEPTION: For structures supported on point-

bearing piles and in all other cases where the

foundation soil consists of a soft stratum of

reasonably uniform properties underlain by a much

stiffer, rock-like deposit with an abrupt increase in

stiffness, the factor β

in Eq. 19.2-9 shall be replaced

by β

′ if



where D

is the total depth of the

stratum. β

′ shall be determined as follows:

′

⎛

⎝

⎜

⎞

⎠

⎟

ββ



(19.2-12)

The value of β

computed from Eq. 19.2-9, both

with or without the adjustment represented by Eq.

19.2-12, shall in no case be taken as less than β

0.05 or greater than β

= 0.20.

19.2.2 Vertical Distribution of Seismic Forces

The distribution over the height of the structure

of the reduced total seismic force (V

) shall be

considered to be the same as for the structure without

interaction.

19.2.3 Other Effects

The modiﬁ ed story shears, overturning moments,

and torsional effects about a vertical axis shall be

determined as for structures without interaction using

the reduced lateral forces.

The modiﬁ ed deﬂ ections (δ

) shall be determined

as follows:



δδ

⎡

⎣

⎢

⎤

⎦

⎥

(19.2-13)

where

= the overturning moment at the base using the

unmodiﬁ ed seismic forces and not including the

reduction permitted in the design of the

foundation

= the height above the base to the level under

consideration

= the deﬂ ections of the ﬁ xed-base structure as

determined in Section 12.8.6 using the unmodi-

ﬁ ed seismic forces

The modiﬁ ed story drifts and P-delta effects

shall be evaluated in accordance with the provisions

of Sections 12.8.6 and 12.8.7 using the modiﬁ ed

story shears and deﬂ ections determined in this

section.

19.3 MODAL ANALYSIS PROCEDURE

The following provisions are supplementary to those

presented in Section 12.9.

19.3.1 Modal Base Shears

To account for the effects of soil–structure

interaction, the base shear corresponding to the

fundamental mode of vibration (V

) shall be

reduced to

= V

– ΔV

(19.3-1)

The reduction (ΔV

) shall be computed in accordance

with Eq. 19.2-2 with W

taken as equal to the

effective seismic weight of the fundamental period

of vibration, W

, and C

computed in accordance with

Eq. 12.8-1, except that S

shall be replaced by design

spectral response acceleration of the design response

spectra at the fundamental period of the ﬁ xed-base

structure (T

The period T

shall be determined from Eq. 19.2-3

or from Eq. 19.2-5 where applicable, taking T = T

evaluating k

from Eq. 19.2-4 with W

= W

, and

computing h

as follows:

FIGURE 19.2-1 Foundation Damping Factor

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CHAPTER 19 SOIL–STRUCTURE INTERACTION FOR SEISMIC DESIGN

202

ii i

∑

(19.3-2)

where

= the portion of the total gravity load of the

structure at Level i

= the displacement amplitude at the i

level of the

structure when vibrating in its fundamental

mode

= the height above the base to Level i

The preceding designated values of W

, h

, T, and

also shall be used to evaluate the factor α from Eq.

19.2-6 and the factor β

from Fig. 19.2-1. No reduc-

tion shall be made in the shear components contrib-

uted by the higher modes of vibration. The reduced

base shear (V

) shall in no case be taken less than

0.7V

19.3.2 Other Modal Effects

The modiﬁ ed modal seismic forces, story shears,

and overturning moments shall be determined as for

structures without interaction using the modiﬁ ed base

shear (V

) instead of V

. The modiﬁ ed modal deﬂ ec-

tions (δ

) shall be determined as follows:



δδ

⎡

⎣

⎢

⎤

⎦

⎥

(19.3-3)

and

= δ

for m = 2, 3, . . .

(19.3-4)

where

= the overturning base moment for the fundamen-

tal mode of the ﬁ xed-base structure using the

unmodiﬁ ed modal base shear V

= the modal deﬂ ections at Level x of the ﬁ xed-

base structure using the unmodiﬁ ed modal

shears, V

The modiﬁ ed modal drift in a story (Δ

) shall be

computed as the difference of the deﬂ ections (δ

) at

the top and bottom of the story under consideration.

19.3.3 Design Values

The design values of the modiﬁ ed shears,

moments, deﬂ ections, and story drifts shall be

determined as for structures without interaction by

taking the square root of the sum of the squares

(SRSS) of the respective modal contributions. In the

design of the foundation, it is permitted to reduce the

overturning moment at the foundation–soil interface

determined in this manner by 10 percent as for

structures without interaction.

The effects of torsion about a vertical axis shall be

evaluated in accordance with the provisions of Section

12.8.4, and the P-delta effects shall be evaluated in

accordance with the provisions of Section 12.8.7 using

the story shears and drifts determined in Section 19.3.2.

c19.indd 202 4/14/2010 11:03:48 AM

203

Chapter 20

SITE CLASSIFICATION PROCEDURE FOR

SEISMIC DESIGN

accelerations for liqueﬁ able soils. Rather, a site class

is permitted to be determined in accordance with

Section 20.3 and the corresponding values of F

and

determined from Tables 11.4-1 and 11.4-2.

2. Peats and/or highly organic clays [H > 10 ft (3 m)]

of peat and/or highly organic clay where H =

thickness of soil.

3. Very high plasticity clays [H > 25 ft (7.6 m) with

PI > 75].

4. Very thick soft/medium stiff clays [H > 120 ft

(37 m)] with s

< 1,000 psf (50 kPa).

20.3.2 Soft Clay Site Class E

Where a site does not qualify under the criteria

for Site Class F and there is a total thickness of soft

clay greater than 10 ft (3 m) where a soft clay layer is

deﬁ ned by s

< 500 psf (25 kPa), w ≥ 40 percent, and

PI > 20, it shall be classiﬁ ed as Site Class E.

20.3.3 Site Classes C, D, and E

The existence of Site Class C, D, and E soils

shall be classiﬁ ed by using one of the following three

methods with v

, N

, and s

computed in all cases as

speciﬁ ed in Section 20.4:

1. v

for the top 100 ft (30 m) (v

method).

2. N

for the top 100 ft (30 m) (N

method).

3. N

for cohesionless soil layers (PI < 20) in the

top 100 ft (30 m) and s

for cohesive soil layers

(PI > 20) in the top 100 ft (30 m) (s

method).

Where the N

and s

criteria differ, the site shall

be assigned to the category with the softer soil.

20.3.4 Shear Wave Velocity for Site Class B

The shear wave velocity for rock, Site Class B,

shall be either measured on site or estimated by a

geotechnical engineer, engineering geologist, or

seismologist for competent rock with moderate

fracturing and weathering. Softer and more highly

fractured and weathered rock shall either be measured

on site for shear wave velocity or classiﬁ ed as Site

Class C.

20.3.5 Shear Wave Velocity for Site Class A

The hard rock, Site Class A, category shall be

supported by shear wave velocity measurement either

20.1 SITE CLASSIFICATION

The site soil shall be classiﬁ ed in accordance with

Table 20.3-1 and Section 20.3 based on the upper 100

ft (30 m) of the site proﬁ le. Where site-speciﬁ c data

are not available to a depth of 100 ft (30 m), appropri-

ate soil properties are permitted to be estimated by the

registered design professional preparing the soil

investigation report based on known geologic condi-

tions. Where the soil properties are not known in

sufﬁ cient detail to determine the site class, Site Class

D shall be used unless the authority having jurisdic-

tion or geotechnical data determine Site Class E or F

soils are present at the site. Site Classes A and B shall

not be assigned to a site if there is more than 10 ft

(10.1 m) of soil between the rock surface and the

bottom of the spread footing or mat foundation.

20.2 SITE RESPONSE ANALYSIS FOR SITE

CLASS F SOIL

A site response analysis in accordance with Section

21.1 shall be provided for Site Class F soils, unless

the exception to Section 20.3.1 is applicable.

20.3 SITE CLASS DEFINITIONS

Site class types shall be assigned in accordance with

the deﬁ nitions provided in Table 20.3-1 and this

section.

20.3.1 Site Class F

Where any of the following conditions is satis-

ﬁ ed, the site shall be classiﬁ ed as Site Class F and a

site response analysis in accordance with Section 21.1

shall be performed.

1. Soils vulnerable to potential failure or collapse

under seismic loading, such as liqueﬁ able soils,

quick and highly sensitive clays, and collapsible

weakly cemented soils.

EXCEPTION: For structures having fundamental

periods of vibration equal to or less than 0.5 s, site

response analysis is not required to determine spectral

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CHAPTER 20 SITE CLASSIFICATION PROCEDURE FOR SEISMIC DESIGN

204

on site or on proﬁ les of the same rock type in the

same formation with an equal or greater degree of

weathering and fracturing. Where hard rock condi-

tions are known to be continuous to a depth of 100 ft

(30 m), surﬁ cial shear wave velocity measurements

are permitted to be extrapolated to assess v

20.4 DEFINITIONS OF SITE

CLASS PARAMETERS

The deﬁ nitions presented in this section shall apply to

the upper 100 ft (30 m) of the site proﬁ le. Proﬁ les

containing distinct soil and rock layers shall be

subdivided into those layers designated by a number

that ranges from 1 to n at the bottom where there are

a total of n distinct layers in the upper 100 ft (30 m).

Where some of the n layers are cohesive and others

are not, k is the number of cohesive layers and m is

the number of cohesionless layers. The symbol i

refers to any one of the layers between 1 and n.

20.4.1 v

, Average Shear Wave Velocity

shall be determined in accordance with the

following formula:

∑

(20.4-1)

where

= the thickness of any layer between 0 and

100 ft (30 m)

= the shear wave velocity in ft/s (m/s)

∑

= 100 ft (30 m)

20.4.2 N

, Average Field Standard Penetration

Resistance and N

, Average Standard Penetration

Resistance for Cohesionless Soil Layers

and N

shall be determined in accordance with

the following formulas:

∑

(20.4-2)

where N

and d

in Eq. 20.4-2 are for cohesionless

soil, cohesive soil, and rock layers.

∑

(20.4-3)

where N

and d

in Eq. 20.4-3 are for cohesionless soil

layers only and

∑

where d

is the total

thickness of cohesionless soil layers in the top 100 ft

(30 m). N

is the standard penetration resistance

(ASTM D1586) not to exceed 100 blows/ft (305

blows/m) as directly measured in the ﬁ eld without

corrections. Where refusal is met for a rock layer, N

shall be taken as 100 blows/ft (305 blows/m).

20.4.3 s

, Average Undrained Shear Strength

shall be determined in accordance with the

following formula:

Table 20.3-1 Site Classiﬁ cation

Site Class v

or N

A. Hard rock >5,000 ft/s NA NA

B. Rock 2,500 to 5,000 ft/s NA NA

C. Very dense soil and soft rock 1,200 to 2,500 ft/s >50 >2,000 psf

D. Stiff soil 600 to 1,200 ft/s 15 to 50 1,000 to 2,000 psf

E. Soft clay soil <600 ft/s <15 <1,000 psf

Any proﬁ le with more than 10 ft of soil having the following characteristics:

—Plasticity index PI > 20,

—Moisture content w ≥ 40%,

—Undrained shear strength s

< 500 psf

F. Soils requiring site response analysis

in accordance with Section 21.1

See Section 20.3.1

For SI: 1 ft/s = 0.3048 m/s; 1 lb/ft

= 0.0479 kN/m

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MINIMUM DESIGN LOADS

205

∑

(20.4-4)

where

∑

= d

= the total thickness of cohesive soil layers in

the top 100 ft (30 m)

PI = the plasticity index as determined in accor-

dance with ASTM D4318

w = the moisture content in percent as

determined in accordance with ASTM

D2216

= the undrained shear strength in psf (kPa), not

to exceed 5,000 psf (240 kPa) as determined

in accordance with ASTM D2166 or ASTM

D2850

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207

Chapter 21

SITE-SPECIFIC GROUND MOTION PROCEDURES

FOR SEISMIC DESIGN

site coefﬁ cients in Section 11.4.3 consistent with the

classiﬁ cation of the soils at the proﬁ le base.

21.1.3 Site Response Analysis and

Computed Results

Base ground motion time histories shall be input

to the soil proﬁ le as outcropping motions. Using

appropriate computational techniques that treat

nonlinear soil properties in a nonlinear or equivalent-

linear manner, the response of the soil proﬁ le shall be

determined and surface ground motion time histories

shall be calculated. Ratios of 5 percent damped

response spectra of surface ground motions to input

base ground motions shall be calculated. The recom-

mended surface MCE

ground motion response

spectrum shall not be lower than the MCE

response

spectrum of the base motion multiplied by the average

surface-to-base response spectral ratios (calculated

period by period) obtained from the site response

analyses. The recommended surface ground motions

that result from the analysis shall reﬂ ect consideration

of sensitivity of response to uncertainty in soil

properties, depth of soil model, and input motions.

21.2 RISK-TARGETED MAXIMUM

CONSIDERED EARTHQUAKE (MCE

)

GROUND MOTION HAZARD ANALYSIS

The requirements of Section 21.2 shall be satisﬁ ed

where a ground motion hazard analysis is performed

or required by Section 11.4.7. The ground motion

hazard analysis shall account for the regional tectonic

setting, geology, and seismicity, the expected recur-

rence rates and maximum magnitudes of earthquakes

on known faults and source zones, the characteristics

of ground motion attenuation, near source effects, if

any, on ground motions, and the effects of subsurface

site conditions on ground motions. The characteristics

of subsurface site conditions shall be considered either

using attenuation relations that represent regional and

local geology or in accordance with Section 21.1. The

analysis shall incorporate current seismic interpreta-

tions, including uncertainties for models and param-

eter values for seismic sources and ground motions.

The analysis shall be documented in a report.

21.1 SITE RESPONSE ANALYSIS

The requirements of Section 21.1 shall be satisﬁ ed

where site response analysis is performed or required

by Section 11.4.7. The analysis shall be documented

in a report.

21.1.1 Base Ground Motions

A MCE

response spectrum shall be developed

for bedrock, using the procedure of Sections 11.4.6 or

21.2. Unless a site-speciﬁ c ground motion hazard

analysis described in Section 21.2 is carried out, the

MCE

rock response spectrum shall be developed

using the procedure of Section 11.4.6 assuming Site

Class B. If bedrock consists of Site Class A, the

spectrum shall be adjusted using the site coefﬁ cients

in Section 11.4.3 unless other site coefﬁ cients can be

justiﬁ ed. At least ﬁ ve recorded or simulated horizontal

ground motion acceleration time histories shall be

selected from events having magnitudes and fault

distances that are consistent with those that control

the MCE

ground motion. Each selected time history

shall be scaled so that its response spectrum is, on

average, approximately at the level of the MCE

rock

response spectrum over the period range of signiﬁ -

cance to structural response.

21.1.2 Site Condition Modeling

A site response model based on low-strain shear

wave velocities, nonlinear or equivalent linear shear

stress–strain relationships, and unit weights shall be

developed. Low-strain shear wave velocities shall be

determined from ﬁ eld measurements at the site or

from measurements from similar soils in the site

vicinity. Nonlinear or equivalent linear shear stress–

strain relationships and unit weights shall be selected

on the basis of laboratory tests or published relation-

ships for similar soils. The uncertainties in soil

properties shall be estimated. Where very deep soil

proﬁ les make the development of a soil model to

bedrock impractical, the model is permitted to be

terminated where the soil stiffness is at least as great

as the values used to deﬁ ne Site Class D in Chapter

20. In such cases, the MCE

response spectrum and

acceleration time histories of the base motion devel-

oped in Section 21.1.1 shall be adjusted upward using

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CHAPTER 21 SITE-SPECIFIC GROUND MOTION PROCEDURES FOR SEISMIC DESIGN

208

21.2.1 Probabilistic (MCE

) Ground Motions

The probabilistic spectral response accelerations

shall be taken as the spectral response accelerations in

the direction of maximum horizontal response

represented by a 5 percent damped acceleration

response spectrum that is expected to achieve a 1

percent probability of collapse within a 50-year

period. For the purpose of this standard, ordinates of

the probabilistic ground motion response spectrum

shall be determined by either Method 1 of Section

21.2.1.1 or Method 2 of Section 21.2.1.2.

21.2.1.1 Method 1

At each spectral response period for which the

acceleration is computed, ordinates of the probabilistic

ground motion response spectrum shall be determined

as the product of the risk coefﬁ cient, C

, and the

spectral response acceleration from a 5 percent

damped acceleration response spectrum having a 2

percent probability of exceedance within a 50-year

period. The value of the risk coefﬁ cient, C

, shall be

determined using values of C

and C

from Figs.

22-3 and 22-4, respectively. At spectral response

periods less than or equal to 0.2 s, C

shall be taken

as equal to C

. At spectral response periods greater

than or equal to 1.0 s, C

shall be taken as equal to

. At response spectral periods greater than 0.2 s

and less than 1.0 s, C

shall be based on linear

interpolation of C

and C

21.2.1.2 Method 2

At each spectral response period for which the

acceleration is computed, ordinates of the probabilistic

ground motion response spectrum shall be determined

from iterative integration of a site-speciﬁ c hazard

curve with a lognormal probability density function

representing the collapse fragility (i.e., probability of

collapse as a function of spectral response accelera-

tion). The ordinate of the probabilistic ground motion

response spectrum at each period shall achieve a 1

percent probability of collapse within a 50-year period

for a collapse fragility having (i) a 10 percent prob-

ability of collapse at said ordinate of the probabilistic

ground motion response spectrum and (ii) a logarith-

mic standard deviation value of 0.6.

21.2.2 Deterministic (MCE

) Ground Motions

The deterministic spectral response acceleration

at each period shall be calculated as an 84th-percentile

5 percent damped spectral response acceleration in the

direction of maximum horizontal response computed

at that period. The largest such acceleration calculated

for the characteristic earthquakes on all known active

faults within the region shall be used. For the purposes

of this standard, the ordinates of the deterministic

ground motion response spectrum shall not be taken as

lower than the corresponding ordinates of the response

spectrum determined in accordance with Fig. 21.2-1,

where F

and F

are determined using Tables 11.4-1

and 11.4-2, respectively, with the value of S

taken as

1.5 and the value of S

taken as 0.6.

21.2.3 Site-Speciﬁ c MCE

The site-speciﬁ c MCE

spectral response

acceleration at any period, S

, shall be taken as

the lesser of the spectral response accelerations

from the probabilistic ground motions of Section

21.2.1 and the deterministic ground motions of

Section 21.2.2.

21.3 DESIGN RESPONSE SPECTRUM

The design spectral response acceleration at any

period shall be determined from Eq. 21.3-1:

aaM

(21.3-1)

where S

is the MCE

spectral response acceleration

obtained from Section 21.1 or 21.2. The design

spectral response acceleration at any period shall not

be taken as less than 80 percent of S

determined in

accordance with Section 11.4.5. For sites classiﬁ ed as

Site Class F requiring site response analysis in

accordance with Section 11.4.7, the design spectral

response acceleration at any period shall not be taken

as less than 80 percent of S

determined for Site Class

E in accordance with Section 11.4.5.

21.4 DESIGN ACCELERATION PARAMETERS

Where the site-speciﬁ c procedure is used to determine

the design ground motion in accordance with Section

21.3, the parameter S

shall be taken as the spectral

acceleration, S

, obtained from the site-speciﬁ c spectra

at a period of 0.2 s, except that it shall not be taken as

less than 90 percent of the peak spectral acceleration,

, at any period larger than 0.2 s. The parameter S

shall be taken as the greater of the spectral accelera-

tion, S

, at a period of 1 s or two times the spectral

acceleration, S

, at a period of 2 s. The parameters

and S

shall be taken as 1.5 times S

and S

respectively. The values so obtained shall not be

less than 80 percent of the values determined in

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MINIMUM DESIGN LOADS

209

accordance with Section 11.4.3 for S

and S

and

Section 11.4.4 for S

and S

For use with the Equivalent Lateral Force

Procedure, the site-speciﬁ c spectral acceleration, S

at T shall be permitted to replace S

/T in Eq. 12.8-3

and S

in Eq. 12.8-4. The parameter S

calcu-

lated per this section shall be permitted to be used in

Eqs. 12.8-2, 12.8-5, 15.4-1, and 15.4-3. The mapped

value of S

shall be used in Eqs. 12.8-6, 15.4-2, and

15.4-4.

21.5 MAXIMUM CONSIDERED

EARTHQUAKE GEOMETRIC MEAN (MCE

)

PEAK GROUND ACCELERATION

21.5.1 Probabilistic MCE

Peak

Ground Acceleration

The probabilistic geometric mean peak ground

acceleration shall be taken as the geometric mean

peak ground acceleration with a 2 percent probability

of exceedance within a 50-year period.

21.5.2 Deterministic MCE

Peak

Ground Acceleration

The deterministic geometric mean peak ground

acceleration shall be calculated as the largest 84

percentile geometric mean peak ground acceleration

for characteristic earthquakes on all known active

faults within the site region. The deterministic

geometric mean peak ground acceleration shall not be

taken as lower than 0.5 F

PGA

, where F

PGA

is deter-

mined using Table 11.8-1 with the value of PGA

taken as 0.5 g.

21.5.3 Site-Speciﬁ c MCE

Peak

Ground Acceleration

The site-speciﬁ c MCE

peak ground acceleration,

PGA

, shall be taken as the lesser of the probabilistic

geometric mean peak ground acceleration of Section

21.5.1 and the deterministic geometric mean peak

ground acceleration of Section 21.5.2. The site-

speciﬁ c MCE

peak ground acceleration shall not be

taken as less than 80 percent of PGA

determined

from Eq. 11.8-1.

FIGURE 21.2-1 Deterministic Lower Limit on MCE

Response Spectrum

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