NEHRP Seismic Design Technical Brief No. 11 

Seismic Design of Steel BucklingRestrained Braced Frames

A Guide for Practicing Engineers

NIST GCR 15-917-34

Ryan A. Kersting

Larry A. Fahnestock

Walterio A. López
About The Authors

Ryan A. Kersting, S.E., an Associate Principal at Buehler & Buehler 

Structural Engineers, Inc., has a diverse portfolio of experience spanning 

the full spectrum of structural engineering services, including project 

design, plan review, peer review, and other technical activities. He is 

frequently involved in projects that incorporate innovative structural 

systems, nonlinear analysis techniques, and performance-based 

designs. Ryan has extensive experience with buckling-restrained braced 

frame (BRBF) projects and has contributed to multiple publications, 

presentations, and design examples on the topic. He is very involved 

in the Structural Engineers Association of California (SEAOC), serving 

as 2014-2015 SEAOC President. He has also been an active member 

of the SEAOC Seismology Committee, including a term as Chair, and 

was Chair of the 2007 SEAOC Convention Committee.

About the Review Panel

The contributions of the three review panelists for this publication are 

gratefully acknowledged.

Rafael Sabelli, P.E., S.E., is Director of Seismic Design at Walter P 

Moore, a structural and civil engineering firm with offices nationwide. 

He is a member of the American Institute of Steel Construction Task 

Committee 9 on Seismic Provisions and a member of the Building 

Seismic Safety Council’s 2014 Provisions Update Committee and of 

the American Society of Civil Engineers Seismic Subcommittee for 

ASCE/7-10.

Jerod G. Johnson, Ph.D., S.E., is a Principal and Director of Engineering 

at Reaveley Engineers + Associates in Salt Lake City. He is serving 

as the 2014-2015 president of the Structural Engineers Association of 

Utah and is a member of the board of the Utah Chapter of EERI. He 

contributed to pioneering efforts in BRBF design in the United States 

on projects such as the Bennett Federal Building in Salt Lake City. As 

an adjunct professor at the University of Utah, Jerod has led research 

efforts in the use of buckling-restrained braces for targeted energy 

dissipation in tuned mass damper applications.

Michael D. Engelhardt, Ph.D., P.E., is a Professor in the Department of Civil, 

Architectural and Environmental Engineering at the University of Texas 

at Austin since 1989. He serves as a member of the AISC Committee 

on Specifications, AISC Task Committee 9 on Seismic Design, and the 

AISC Connection Prequalification Review Panel. He has been actively 

involved in research, teaching, and standards development for seismicresistant steel structures for more than 25 years. He has been a recipient 

of the AISC T.R. Higgins Lectureship Award for outstanding contributions 

in structural steel research and the AISC Lifetime Achievement Award.

National Institute of 

Standards and Technology

NIST is a federal technology agency within the U.S. Department of 

Commerce that promotes U.S. innovation and industrial competitiveness 

by advancing measurement science, standards, and technology in 

ways that enhance economic security and improve our quality of life. 

NIST is the lead agency of NEHRP. Dr. John (Jack) R. Hayes, Jr., is the 

Director, and Dr. Steven L. McCabe is the Deputy Director of NEHRP 

within NIST’s Engineering Laboratory.

Applied Technology Council

The Applied Technology Council (ATC) is a nonprofit corporation 

advancing engineering applications for hazard mitigation. This publication 

is a product of Task Order 14-360 under Contract SB134113CQ0009 

between ATC and NIST. Jon A. Heintz serves as the Program Manager 

for work conducted under this contract, and Ayse Hortacsu serves as 

ATC Associate Program Manager on this Task Order.

Consortium of Universities for Research 

in Earthquake Engineering

The Consortium of Universities for Research in Earthquake Engineering 

(CUREE) is a nonprofit organization advancing earthquake engineering 

research, education, and implementation. This publication was 

produced under a cooperative agreement between ATC and CUREE. 

Robert Reitherman served as Associate Program Manager overseeing 

production. Reed Helgens and Darryl Wong served as report production 

and report preparation consultants for this work. 

NEHRP Seismic Design 

Technical Briefs

National Earthquake Hazards Reduction Program (NEHRP) Technical 

Briefs are published by the National Institute of Standards and 

Technology (NIST) as aids to the efficient transfer of NEHRP and other 

research into practice, thereby helping to reduce the nation’s losses 

resulting from earthquakes.

Larry A. Fahnestock, Ph.D., P.E., is an Associate Professor in the 

Department of Civil and Environmental Engineering at the University 

of Illinois at Urbana-Champaign. For his research on the seismic 

behavior and design of braced frames, he has received the 2009 

American Institute of Steel Construction (AISC) Faculty Fellowship, the 

2009 American Society of Civil Engineers (ASCE) Raymond C. Reese 

Research Prize and a 2014 ASCE Walter L. Huber Civil Engineering 

Research Prize. He is a registered professional engineer in California 

and Illinois and a member of AISC, ASCE, the Earthquake Engineering 

Research Institute (EERI), and the Structural Stability Research Council. 

Walterio A. López, S.E., is a Principal at Rutherford + Chekene, a leading 

San Francisco-based structural and geotechnical engineering firm. He 

has extensive knowledge of the seismic design and detailing of costeffective structural steel systems and is an internationally recognized 

authority in the use of BRBF. He was awarded the prestigious AISC 

T.R. Higgins Lectureship Award for his work on BRBF design guidelines 

and has authored technical papers on structural steel braced frames. 

Walterio is a past director of Structural Engineers Association of Northern 

California (SEAONC) and past chair of SEAONC’s Steel Seismology 

Subcommittee and has served on advisory boards for research projects 

dealing with innovative structural steel systems.

Consortium of Universities for Research in 

Earthquake Engineering (CUREE)

1301 South 46th Street, Building 420

Richmond, CA 94804

(510) 665-3529

www.curee.org

Applied Technology Council (ATC)

201 Redwood Shores Parkway, Suite 240

Redwood City, California 94065

(650) 595-1542

www.atcouncil.org

CUREE
By

Applied Technology Council

In association with the

Consortium of Universities for Research in Earthquake Engineering

and

Ryan A. Kersting

Larry A. Fahnestock

Walterio A. López

September 2015

Prepared for

U.S. Department of Commerce

National Institute of Standards and Technology

Engineering Laboratory

Gaithersburg, MD 20899-8600

Seismic Design of Steel BucklingRestrained Braced Frames

A Guide for Practicing Engineers

NIST GCR 15-917-34

U.S. Department of Commerce

Penny Pritzker, Secretary

National Institute of Standards and Technology

Willie E. May, Under Secretary of Commerce for 

Standards and Technology and Director
Disclaimers

This Technical Brief was prepared for the Engineering Laboratory of the National Institute of Standards and Technology (NIST) 

under the National Earthquake Hazards Reduction Program (NEHRP) Earthquake Structural and Engineering Research Contract 

SB134113CQ0009, Task Order 14-360. The contents of this publication do not necessarily reflect the views and policies of NIST or 

the U.S. Government.

This report was produced by the Applied Technology Council (ATC) in association with the Consortium of Universities for Research in 

Earthquake Engineering (CUREE). While endeavoring to provide practical and accurate information, ATC, CUREE, the authors, and the 

reviewers assume no liability for, nor express or imply any warranty with regard to, the information contained herein. Users of information 

in this report assume all liability arising from such use.

Unless otherwise noted, photos, figures, and data presented in this report have been developed or provided by ATC staff, CUREE 

staff, or consultants engaged under contract to provide information as works for hire. Any similarity with other published information is 

coincidental. Photos and figures cited from outside sources have been reproduced in this report with permission. Any other use requires 

additional permission from the copyright owners. 

Certain commercial software, equipment, instruments, or materials may have been used in preparing information contributing to this 

report. Identification in this report is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that such 

software, equipment, instruments, or materials are necessarily the best available for the purpose.

NIST policy is to use the International System of Units (metric units) in all its publications. In this report, however, information is presented 

in U.S. Customary Units (e.g., inch and pound) because this is the preferred system of units in the U.S. earthquake engineering industry.

Cover photo. Buckling-restrained braced frame under construction.

NIST (2015). Seismic design of steel buckling-restrained braced frames: A guide for practicing engineers, GCR 15-917-34, NEHRP 

Seismic Design Technical Brief No. 11, produced by the Applied Technology Council and the Consortium of Universities for Research 

in Earthquake Engineering for the National Institute of Standards and Technology, Gaithersburg, MD.

Introduction ..............................................................................................1

Background of the Buckling-Restrained Braced Frame.....................................5

Principles for Design of BRBFs......................................................................8

Guidance for Analysis of BRBFs..................................................................11

Guidance for Design of BRBFs....................................................................14

BRBF Design and Fabrication Coordination..................................................19

Future Developments...............................................................................23

References.............................................................................................25

Notation and Abbreviations........................................................................29

Credits....................................................................................................30

1. 

2.

3. 

4. 

5. 

6. 

7. 

8.

9.

10.

Contents

How to Cite This Publication
1

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

Buckling-Restrained Braced Frames (BRBFs) are one 

of the newer types of seismic force-resisting systems 

used in modern building designs. As the two example 

configurations shown in Figure 1-1 illustrate, BRBFs 

resist lateral loads as vertical trusses in which the 

axes of the members are aligned concentrically at the 

joints. Although the global geometric configuration of a 

1. Introduction

BRBF is very similar to a conventional Concentrically 

Braced Frame (CBF), the members, connections, and 

behavior of BRBFs are distinctly different from those of 

Ordinary Concentrically Braced Frames (OCBFs) and 

Special Concentrically Braced Frames (SCBFs). The 

key difference is the use and behavior of the BucklingRestrained Brace (BRB) itself. 

Figure 1-1. Typical BRBF configurations.

Buckling-restrained brace

Wide-flange beam

Wide-flange column

Yield length (Ly)

Work-point length (Lwp)

Gusset plate

Yield length (Ly)

Work-point length (Lwp)
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

2

Figure 1-2. Common BRB assembly.

View of overall BRB

View of BRB steel core

Restrained yielding segment

Restrained 

non-yielding 

segment

Unrestrained 

non-yielding 

segment

Yielding region

Concrete fill

Steel tube

Steel core

De-bonding agent

& expansion material

Transition

region

Connection

region

SECTION A-A

A

A

typ. typ.

typ. typ.

Unlike the standard sections used for braces in OCBFs 

and SCBFs, the BRB is a fabricated assembly. As shown 

in Figure 1-2, the most common BRBs consist of a steel 

core-plate (the yielding element, hereafter called the 

“core”) that is surrounded by a steel tube casing filled with 

grout or concrete. Figure 1-2 shows a core consisting of 

a steel plate. Other core cross-sections, such as cruciform 

or multiple plates can also be used. The core is axially 

decoupled from the fill and casing by various means 

that produce a physical isolation or gap. As the name 

states, the BRB assembly restrains core buckling under 

compressive loading and achieves a compressive yield 

strength that is approximately equal to its tensile yield 

strength. Therefore, the core area can be sized for designlevel seismic loads based on the yield stress of the core, 

Fysc, as opposed to braces in conventional CBFs, which 

are sized based on the critical buckling stress, Fcr, of 

the section. Buckling braces in OCBFs and SCBFs have 

significant excess tensile capacity, and the brace buckling 

behavior leads to degrading cyclic response. In contrast, 

as shown in Figure 1-3, a BRB yields axially in tension 

and in compression, exhibiting nominally symmetric cyclic 

response with strain hardening. In BRBFs, the primary 

source of ductility is the axial yielding of the BRB cores. 

Unlike BRBFs, CBFs are subject to buckling of the braces 

and therefore are less ductile. This attribute is reflected in Figure 1-3. Buckling versus buckling-restrained brace behavior.

the larger response modification coefficient, R, assigned to 

BRBFs (R = 8) by ASCE/SEI 7, referred to in this Guide 

as ASCE 7 (ASCE 2010), as compared to OCBFs (R = 

3 1/4) and SCBFs (R = 6). Because the BRBF system is 

more efficient (having a smaller brace area as a result 

of the elimination of brace buckling), BRBFs are more 

flexible than conventional CBFs and may in some cases be 

governed by drift limits rather than strength requirements. 

Like nearly every other ductile seismic force-resisting 

system, the remainder of the frame (beams, columns, 

and connections) is protected from unintended yielding 

through special analysis and proportioning provisions, 

commonly called capacity-based design. 

Tension

Brace axial force

Compression

Brace axial 

deformation

Typical 

buckling 

brace

Bucklingrestrained 

brace
3

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

This Guide addresses the seismic design of steel BRBFs in 

typical building applications within regions of moderate 

to high seismic hazard, corresponding to Seismic Design 

Categories (SDC) C through F as defined in ASCE 7. 

Because current standards address and allow only the 

use of BRBFs in all-steel frames, composite applications 

are not addressed in this Guide, but many of the same 

topics and considerations are applicable. Results from 

experimental testing and numerical simulations will be 

used to illustrate the rationale underlying design and 

detailing provisions. 

This Guide is not a complete treatment of the BRBF 

system or the BRB itself. A number of issues and topics 

related to BRBFs are not addressed in this document, 

including the following:

Specific comparisons of BRBFs to other classes 

of braced frames, such as Eccentrically Braced 

Frames (EBFs), OCBFs, and SCBFs. Information on 

SCBFs is provided in the NEHRP Technical Brief 

on Seismic Design of Steel Special Concentrically 

Braced Frame Systems (NIST 2013). 

BRBFs used with steel Special Moment-Resisting 

Frames (SMRFs) as a dual system. Information 

about steel special moment-resisting frames is 

provided in the NEHRP Technical Brief on 

Seismic Design of Steel Special Moment Frames

(NIST 2009).

BRBFs used with other systems, for example, as 

part of outrigger frames in tall buildings.

BRBs used in non-BRBF conditions or 

configurations, such as

Struts or fuses within a load path, such as along a 

collector line

Buttresses or external bracing

Self-centering frame systems

Damped assemblies

Non-building structures

Non-steel frames (“composite” applications)

This Guide refers to the following building codes and 

standards:

AISC 341, Seismic Provisions for Structural 

Steel Buildings and Commentary, 2010 edition 

(AISC 2010a)

•

•

•

•

-

-

-

-

-

-

•

AISC 360, Specification for Structural Steel 

Buildings and Commentary, 2010 edition 

(AISC 2010b)

ASCE 7, Minimum Design Loads for Buildings and 

Other Structures, 2010 edition (ASCE 2010)

IBC, International Building Code, 2015 edition 

(IBC 2015)

Design engineers are responsible for verifying the 

current building code provisions adopted by the authority 

having jurisdiction of their project. The Technical Briefs 

in this NEHRP Series typically are based on the latest 

available codes and standards, which may not yet have 

been adopted locally. Discussion with and approval by the 

building official should occur to verify that a later version 

of a code or standard not yet adopted locally may be used.

In addition to the code and standards listed above, 

designers should be aware of other valuable resources 

for employing BRBFs:

AISC Seismic Design Manual (AISC 2012)

SEAOC Structural/Seismic Design Manual

(SEAOC 2013)

Seismic Design of Buckling-Restrained Braced Frames

(López and Sabelli 2004)

Ductile Design of Steel Structures (Bruneau et al. 2011)

•

•

•

•

Use of the 2012 versus 2015 Edition of the IBC

Although the 2015 IBC is listed as the basis for 

references to the building code in this Guide, the BRBF 

design requirements under the 2012 IBC match those 

under the 2015 IBC because both editions of the IBC 

use the same editions of the applicable reference 

standards (i.e., ASCE 7-10, AISC 360-10, and AISC 

341-10). At the time of production of this Guide, the 

2016 editions of AISC 341, AISC 360, and ASCE 7 

are nearing completion. Because these documents 

have not been completed and will not be referenced 

(and therefore mandated) until the 2018 edition of the 

IBC, these in-progress standards are not referenced 

in this Guide. 

•

•

•
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

4

This Guide was written to provide guidance to practicing 

structural engineers regarding the use of requirements in 

applicable codes and standards for the design of BRBF 

systems. The Guide is also useful to others seeking to 

understand the basis of, and to correctly implement, the 

appropriate code provisions related to BRBFs, including 

building officials, educators, researchers, and students.

In this Guide, the term “design engineer” is used to 

refer to the person(s) responsible for the design of 

the entire structural system for a given project. The 

BRB manufacturers often have an engineer on staff to 

coordinate with and assist the project’s design engineer 

with different aspects of the BRBF design. When 

necessary to distinguish between these two engineering 

roles, this document refers to the BRB manufacturer’s 

staff engineer as the “manufacturer’s engineer” or 

sometimes simply as the “BRB manufacturer.”

Section 2 of this Guide provides an overview of the 

history of the BRBF system and additional detail on 

BRBs. Section 3 discusses the key principles involved 

in the design of steel BRBFs. Sections 4 and 5 provide 

guidance regarding the analysis and design of BRBFs, 

respectively. Section 6 addresses BRBF coordination 

topics particularly for the design engineer and the 

manufacturer’s engineer, including detailing and 

constructability issues. Section 7 provides a summary 

of forward-looking developments related to the BRBF 

system.

Use of BRBFs in Regions of Lower Seismicity

This Guide discusses BRBFs particularly for use in 

areas of moderate to high seismicity (SDC C through 

F). However, BRBFs are not limited in application 

solely to those regions and have been used in regions 

of low seismicity (SDC A and B) and even in windgoverned designs. In most cases, the benefits of 

using BRBFs are associated with being able to use a 

larger R coefficient to reduce seismic design forces. 

Although the benefit of reduced seismic design 

forces may not be as significant in regions of lower 

seismicity, BRBFs may still be selected as they can 

provide a more economical overall design of braces, 

connections, and foundations and to provide better, 

more reliable performance under lateral loading, for 

example in structures with very long braces and in 

structures of high importance.
5

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

2.1 Historical Context of BRB 

 Development

During the past 15 years, BRBFs have been used 

extensively in the United States as part of the seismic 

force-resisting system for buildings in regions of high 

seismicity. The fundamental concept of confining a steel 

core element so that it can yield in compression as well as 

in tension was investigated experimentally over 40 years 

ago in Japan (Xie 2005), with a concrete panel serving 

as the confining mechanism. Subsequently, a concretefilled steel tube was used as the confining mechanism, 

and excellent energy dissipation and ductility were 

demonstrated experimentally (Watanabe et al. 1988, 

Watanabe 1992). This BRB configuration first gained 

wide acceptance in Japan as a supplemental energy 

dissipation device within a “damage control” design 

philosophy before being adopted in North America as a 

primary seismic force-resisting element. Watanabe et al. 

(1988) and Watanabe (1992) conducted the foundational 

BRB testing program, which demonstrated the 

ductility and energy dissipation capability of the brace 

configuration and illustrated the basic requirement for 

stiffness of the restraining mechanism. In one of the first 

studies in North America, Tremblay et al. (1999) tested 

BRBs in support of a seismic retrofit project in Quebec 

City, Quebec, Canada. In addition, viable all-steel BRBs 

have been developed more recently (Tremblay et al. 2006, 

Wu et al. 2012, and Judd et al. 2015).

BRBs were used extensively in Japan before they gained 

attention in the United States, however, implementation 

of BRBs in the United States required significant effort 

because the U.S. and Japanese design contexts for BRBs 

are appreciably different. In Japan, BRBs are used as 

supplemental energy dissipation devices, which are used 

with moment-resisting frames (Huang et al. 2000, Iwata 

et al. 2003). BRBs function as hysteretic dampers that 

control the response of the moment-resisting frames, 

and the combined system possesses significant stiffness, 

even after the BRBs yield. Broadly speaking, in Japan, a 

damage-control design approach is employed (Kasai et al. 

1998) to protect the primary seismic force-resisting system 

(i.e., the moment-resisting frames) with the dampers (i.e., 

the BRBs). In contrast, the design approach in the United 

States does not require that BRBFs be used as part of a 

dual system, and the BRBF system typically has relatively 

modest overstrength and low post-yield stiffness. 

2. Background of the Buckling-Restrained Braced Frame 

One of the first new construction projects in the 

United States that employed BRBs was the Plant and 

Environmental Sciences Building on the campus of the 

University of California, Davis (Clark et al. 1999, 2000). 

Soon after, one of the first retrofit projects using BRBs 

was the Marin County Civic Center Hall of Justice (Shaw 

and Bouma 2000). Since then, BRBs have been used in 

numerous buildings in the United States and in limited 

applications in bridges (Jones 2014) and other structures 

(Robinson 2012). 

Although BRBs were used in the United States as early 

as 1999, BRBFs were first officially adopted in a model 

building code in 2005 with their inclusion in ASCE 

7-05 (ASCE 2005) and AISC 341-05 (AISC 2005). The 

adoption process was initiated by a joint task group led 

by the American Institute of Steel Construction (AISC) 

and the Structural Engineers Association of California 

(SEAOC), and this task group developed the document 

Recommended Provisions for Buckling-Restrained 

Braced Frames (AISC/SEAOC 2001). System parameters 

from this document were then incorporated in the NEHRP

Recommended Provisions for Seismic Regulations for 

New Buildings and Other Structures (FEMA 2003), 

which led to inclusion in ASCE 7-05 and AISC 341-

05. Currently, design of BRBFs in the United States is 

performed within the framework defined by ASCE 7-10 

(ASCE 2010) and AISC 341-10 (AISC 2010a).

In Canada, BRBF design provisions were developed 

within a similar timeframe as in the United States, with 

BRBFs introduced in the CSA S16 steel design standard in 

2009 (CSA 2009) and the Type D (ductile) BRBF system 

defined in the 2010 edition of the National Building Code 

of Canada (NBCC) (NRC 2010). Although the application 

context in Canada is like that in the United States where 

BRBs are used in place of the conventional steel braces in 

CBFs, differences in U.S. and Canadian code provisions, 

primarily the design seismic hazard level and the BRBF 

system parameters, lead to different BRBF member sizes 

for the same underlying seismicity.

Currently, BRBs are proprietary products in the United 

States. Although this Guide makes no endorsement of 

any commercial product, they are currently fabricated 

by a small number of manufacturers including 

CoreBrace (www.corebrace.com), Nippon Steel (www.

unbondedbrace.com), Star Seismic (www.starseismic.net), 

and Bluescope Buildings (www.bluescopebuildings.com). 
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

6

Figure 2-1. Typical BRBs.

(a) CoreBrace

(b) Nippon Steel

(c) Star Seismic

Representative BRBs from three of the manufacturers are 

shown in Figure 2-1. Extensive testing of BRBs from 

these three manufacturers has been conducted to quantify 

force-deformation characteristics and to qualify the BRBs 

for use in the United States (Black et al. 2002, Merritt et 

al. 2003a and 2003b, Reaveley et al. 2004, Romero et al. 

2006, Benzoni and Innamorato 2007, et al.). Although 

the different BRB manufacturers have unique detailing 

features in their BRBs, which may influence behavior 

particularly with respect to BRB-frame interaction, the 

fundamental BRB force-deformation relationship is 

similar and is the basis for discussion in this Guide.

In addition to the BRB component tests, several largescale BRBF tests have demonstrated cyclic performance 

at the system level for configurations approximately 

representing U.S. practice (Fahnestock et al. 2007a, 

Uriz and Mahin 2008, Tsai et al. 2008, Tsai and Hsiao 

2008, Palmer et al. 2014). Although these tests generally 

demonstrated the ductility and energy dissipation 

capability of BRBFs up to and beyond expected designlevel earthquake demands, they also identified potential 

limitations related to residual drift and localized 

failures in connections, beams, and columns. Beamcolumn connection modifications that are capable of 

mitigating the localized failures have been proposed 

and experimentally validated (Fahnestock et al. 2007a, 

Berman and Bruneau 2009, Prinz et al. 2014). However, 

these modified connections may reduce frame action 

that provides story stiffness after the BRBs have yielded, 

and as a result, peak and residual drifts may increase 

(Fahnestock et al. 2007a, Ariyaratana and Fahnestock 

2011). Numerical simulations of BRBF seismic response 

have established the range of drift and BRB deformation 

demands that can be expected from code-based designs 

using the U.S. provisions, including BRBF-SMRF dual 

systems (Sabelli 2001, Sabelli et al. 2003, Kiggins and 

Uang 2006, Fahnestock et al. 2007b, Uriz and Mahin 

2008, Ariyaratana and Fahnestock 2011, Erochko et 

al. 2011). Evaluation of BRBFs using the FEMA P-695 

methodology (FEMA 2009) demonstrated that the system 

has acceptable margins against seismic collapse and 

that the R and Ω0 values currently used for design are 

appropriate (NIST 2010a, Chen and Mahin 2012).

2.2 Fundamentals of BRB Behavior

CBFs with conventional steel braces are used extensively, 

but their inelastic seismic response is largely dictated 

by brace buckling, which leads to strength and stiffness 

degradation of the frame. Although BRBFs are concentric 
7

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

in their configuration, their behavior is significantly 

distinct from even SCBFs, the most ductile type of 

conventional CBF with buckling braces. 

To address and eliminate the undesirable structural 

response associated with brace buckling, BRBs are 

designed so that they can carry compressive axial force 

without buckling. As discussed above and shown in 

Figure 1-2, this is accomplished by separating the axial 

load-carrying mechanism from the axial bucklingrestraining mechanism (buckling stiffness) of the brace. 

A steel core, which can have a variety of cross-sectional 

shapes, such as flat plate, T-shaped, or cruciform, carries 

the BRB axial force. The BRB core is manufactured with 

several distinct regions along its length that enable stable 

cyclic response. Like a tensile coupon, a BRB core has 

a yielding region with a reduced area in the center of 

the length of the BRB. This approach ensures that the 

inelastic response is restricted to the portion of the BRB 

that is fully contained within the restraining mechanism. 

The yielding region must have a constant cross-section 

so that plastic strain is distributed uniformly along the 

yielding length. In addition, the yielding length must 

be selected so that excessive BRB strains do not lead to 

core fracture. Outside the yielding region, the core crosssectional area increases in the transition regions. These 

regions are partially contained within the restraining 

mechanism but remain elastic even after the yielding 

region has strain hardened. The connection regions at 

each end of the BRB are reinforced to prevent localized 

buckling and to facilitate bolted, welded, or pinned 

connections to the surrounding beams and columns in 

the braced frame. 

Stiffness to prevent member buckling is typically provided 

by a concrete-filled tube. This restraining mechanism 

must be designed with adequate stiffness to prevent both 

local and global buckling modes (Watanabe et al. 1988, 

Black et al. 2002, Takeuchi et al. 2010 and 2012, Wu et al. 

2014, Tsai et al. 2014). The core is decoupled axially from 

the restraining mechanism, and a gap is provided between 

the core and the restraining mechanism to accommodate 

Poisson expansion of the core in compression as well as 

axial deformations in both tension and compression so 

that the restraining mechanism does not carry appreciable 

axial force at large deformation levels.

BRB yielding in compression as well as tension causes 

BRBFs to exhibit ductile cyclic behavior with significant 

energy dissipation. Typical BRB cyclic force-deformation 

Figure 2-2. Typical BRB force-deformation behavior.

BRB axial deformation

BRB axial force

Pysc

Pysc

behavior is illustrated in Figure 2-2, where the evolution 

of cyclic behavior and the significant strain hardening 

response are evident. BRBs exhibit combined isotropic 

and kinematic hardening, and they are typically slightly 

stronger in compression than in tension due to Poisson 

expansion and friction at the interface between the 

core and the restraining mechanism. Within the AISC 

Seismic Provisions, BRB cyclic behavior including strain 

hardening is quantified with the compression strength 

adjustment factor, b, and the strain hardening adjustment 

factor, w. These terms are defined and discussed in more 

detail in the following section.

BRBs as Manufactured Items

A BRB is a fabricated assembly, currently available 

from a small group of manufacturers. BRBs are not 

prefabricated and stockpiled with specific core plate 

sizes, casing sizes, or brace lengths. Instead, each 

BRB is custom-fabricated for each project, although 

use of BRBs on a project does not require additional 

time in the construction schedule. For most designbid-build projects, the design engineer is generally not 

involved in selecting the manufacturer responsible for 

fabrication of the BRBs, but rather, specifies critical 

BRB performance parameters for the fabrication of the 

BRBs to allow competitive bidding by any manufacturer 

(see Section 6). For design-build projects, the owner, 

the general contractor, or even the design team 

might select the BRB manufacturer. In such cases, 

the design engineer will have the benefit of working 

directly with one BRB manufacturer.
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

8

BRBFs are proportioned using the fundamental 

philosophy that is the foundation for all ductile seismic 

design: the BRBs are the yielding elements, which 

are sized for a reduced seismic force level and are 

expected to undergo significant inelastic deformation 

during a design-level earthquake, while all other 

elements in the system are capacity-designed so that 

they remain essentially elastic at the expected strength 

of the BRBs. In the United States, ASCE 7 provides 

the overarching seismic design framework within 

which AISC 341 operates. The ASCE 7 provisions 

specify essential system-independent criteria, seismic 

hazard level, redundancy requirements, limitations 

on analysis methodology, and irregularity conditions. 

The provisions also specify system-specific design 

parameters: R, Ω0, and Cd, and height limits. AISC 341 

contains the provisions relating to the design and detailing 

of the individual members and connections within the 

BRBF, as well as proportioning requirements to ensure 

the desired ductile behavior. 

The BRBF is the primary seismic force-resisting system 

and must resist lateral forces and control deformations 

during a seismic event to maintain the stability of the 

building. In ASCE 7, the BRBF system is assigned 

the largest response modification coefficient (R = 8), 

indicating that the system is expected to withstand 

large inelastic deformation demands yet maintain life 

safety and prevent collapse under the most severe 

seismic ground motion. The anticipated reliability of the 

structure under seismic loading is given in Table C.1.3.1b 

of ASCE 7 and is not system-specific but does depend 

on the Risk Category of the structure.

3. Principles for Design of BRBFs 

The three fundamental steps in BRBF design are 

as follows: (1) the BRBs are sized for ASCE 7 load 

combinations, where the earthquake loads have been 

reduced using R; (2) inelastic design-level drift and 

BRB strain are checked to ensure compliance with 

ASCE 7 and AISC 341 (or more stringent project-specific 

requirements); and (3) the adjusted brace strengths (BRB 

expected capacities accounting for strain hardening 

and compression overstrength at the expected drift) 

are determined and used to design beams, columns, 

and connections so that they remain essentially elastic. 

The first two steps are quite similar in principle to the 

process used for other ductile seismic force-resisting 

systems. However, the coupling among story drift, 

BRB strain, and strain-hardened BRB force is a unique 

and critical aspect of BRBF design. The basic BRBF 

kinematic behavior shown in Figure 3-1 illustrates that, 

under the assumption of small changes of angles, BRB 

axial deformation, Dbx, equals Dxcos(α), where Dx is the 

design story drift and α is the BRB angle of inclination 

with respect to the horizontal. This can be alternately 

expressed in terms of the brace work-point length, Lwp,

and the design story drift angle, qx or Dx/hsx, where hsx

is the story height, as Dbx = qxLwpsin(2α). Then, defining 

the Yield Length Ratio (YLR) as YLR = Ly/Lwp, where Ly

is the length of the yielding region of the BRB steel core 

with area Asc, and assuming that the beam is rigid and 

that elastic deformations in the non-yielding region of the 

BRB steel core are small, the strain in the BRB core, esc, 

can be expressed as:

esc = qxsin2α

2YLR (Equation 1)

Figure 3-1. Basic BRBF kinematic behavior.

L L/2 L/2

Dx Dbx

Dbx

Dx

Lwp

qx

Lwp

α α

hsx

qx
9

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

Figure 3-2. Conceptual BRB cyclic test data and backbone curve.

This relatively simple relationship is a useful tool for 

designers because it allows for rapid estimation of 

core strain demand and consideration of the effect of 

varying key parameters, particularly YLR. To illustrate 

the usefulness of Equation 1, consider, for example, a 

brace with YLR = 0.5 and α = 45 deg. For such a brace, 

the equation shows that the BRB core strain is equal to 

the story drift angle. When evaluated for a 2 percent 

design story drift ratio and a core with Fysc = 40 ksi, the 

design core strain demand is 14.5 times the yield strain, 

ey. The relationship between design strain demand and 

yield strain will vary for each brace based on the factors 

in the equation. This example is not meant to establish 

a typical relationship between esc and ey. Futhermore, 

the inverse relationship between strain and YLR in the 

equation means that for short yield lengths (small YLR), 

large core strains will develop at relatively modest drifts, 

which should be avoided or could otherwise lead to BRB 

fracture. 

Estimation of core strain demand has two important 

implications in the design process: (1) core strain demand 

must be kept below the available strain capacity based 

on BRB qualification testing to ensure acceptable BRBF 

performance, and (2) core strain demand is used to 

calculate the associated strain-hardened core stress that 

is then used for capacity design of the surrounding frame 

elements. Both of these issues require representative 

BRB test data, which are available from the BRB 

manufacturer, typically in the form of a backbone curve. 

Core strain calculations should be performed with the 

racking (global frame “shear” deformation) component of 

story drift, which is directly related to BRB deformation. 

In taller frames and in the upper stories of frames with 

significant overturning effects, column shortening and 

elongation produce global frame “flexural” deformation, 

which leads to story drift that does not cause BRB 

deformation. 

As can be seen from Equation 1, story drift, BRB core 

strain, and YLR are interrelated, and BRB strength 

is also connected to these parameters through strain 

hardening. Per AISC 341, a BRB must be designed 

and detailed (and also validated by prior testing) to 

accommodate expected deformation, which can also be 

expressed as core strain, esc, where expected deformation 

corresponds to a story drift of 2 percent or twice the 

design story drift, whichever is larger. This expected 

deformation (or core strain) is then used to determine 

b and w from a qualification test data backbone curve. 

Figure 3-2 shows representative BRB cyclic test data, 

along with the associated backbone curve. At expected 

Average brace strain (percent)

Brace normalized axial force

Cyclic test data

Backbone curve

-2.5 -2.0 -1.5 -1.0 -0.5 0.5 1.0 1.5 2.0 2.5

0.5

1.0

1.5

-1.5

-1.0

-0.5

w

wb
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

10

strain (deformation), the strain hardening adjustment 

factor, w, is the ratio of the maximum tension force to 

the measured tensile yield force. Similarly, at expected 

strain, the compression strength adjustment factor, 

b, is the ratio of the maximum compression force to 

the maximum tension force. Stated differently, and as 

illustrated in Figure 3-2, the product wb is equal to the 

ratio of the maximum compression force to the measured 

tensile yield force. These adjustment factors are then used 

as part of the capacity design process for proportioning 

the BRBF beams, columns, and connections so that 

they remain essentially elastic and so that the inelastic 

response is limited to the BRBs. The BRB adjustment 

factors vary based on manufacturer, YLR, and other 

detailing features, but ranges of typical values are 1.3 to 

1.5 for w and 1.05 to 1.15 for b. In addition to backbone 

data available directly from a particular manufacturer, 

Saxey and Daniels (2014) have reviewed data from 

numerous tests by CoreBrace, Nippon Steel, and Star 

Seismic and have statistically developed equations for 

design engineers to use to estimate values of w and b.
11

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

ASCE 7 defines the analysis procedures, modeling 

criteria, and other requirements that must be followed 

when analyzing the effects of seismic loading on 

a given structure. For the analysis procedures in 

particular, ASCE 7 provides three different options, 

and ASCE 7 Table 12.6-1 lists the permitted analysis 

procedures for different combinations of parameters, 

such as SDC, risk category, type of construction, 

height, and presence or absence of irregularities. 

The three analysis options are (1) Equivalent Lateral 

Force (ELF) procedure per ASCE 7 §12.8; (2) Modal 

Response Spectrum Analysis (MRSA) procedure per 

ASCE 7 §12.9; and (3) Seismic Response History 

procedure per ASCE 7 Chapter 16, which contains both 

linear and nonlinear procedures. The ELF procedure 

and MRSA procedure are most commonly applied to 

BRBF structures and are the focus of this discussion.

4.1 Elastic Analysis

The ELF and MRSA procedures are both elastic analysis 

procedures that are based on seismic forces reduced by 

the response modification coefficient, R, in accordance 

with ASCE 7. For certain elements beyond the BRBF 

system (such as collectors), ASCE 7 and the IBC require 

design for amplified seismic loads by multiplying the 

elastic results by the overstrength factor, Ω0. Similarly, 

to determine the BRBF design displacements, the elastic 

analysis deflection results are amplified to approximate 

inelastic response in accordance with ASCE 7 by 

multiplying them by the deflection amplification factor, 

Cd. The appropriate values of R, Ω0, and Cd applicable 

to the BRBF system when using either the ELF or the 

MRSA procedures are found in ASCE 7 Table 12.2-1.

Although the ELF procedure is the simplest to 

implement, ASCE 7 Table 12.6-1 does place limitations 

on its use. However, there are no limits on the use of the 

MRSA procedure. Furthermore, with the capabilities 

of today’s commercial structural analysis software 

platforms, the MRSA procedure may often require little 

additional time and effort over the ELF procedure. For 

BRBF systems, especially in taller buildings, the MRSA 

procedure will typically provide more economical frame 

designs than the simpler ELF procedure. When the ELF 

procedure is used, the BRBF system is assigned Ct = 0.03 

in ASCE 7 for calculating the approximate fundamental 

period of the structure, distinct from the value of 0.02 

assigned to conventional CBF systems (considered as 

“All other structural systems” in ASCE 7 Table 12.8-2). 

The difference between the values reflects that fact that 

the BRBF system generally is more flexible and thus 

would have a larger natural period than CBFs.

Like other CBFs, BRBFs are typically modeled with 

columns that are continuous over the frame height and 

with the idealizations that columns have pinned bases 

and that beams and braces have pinned end connections. 

Although beam end connections do have the potential 

for significant moment transfer, particularly when gusset 

plates are present to connect the BRBs to the columnbeam joints, the portion of story shear resisted by these 

mechanisms is generally small in the elastic range. When 

elastic analysis is used to determine the fundamental 

period and the forces and deformations in the BRBF 

members, it is reasonable to neglect frame behavior.

An important analysis consideration for the BRBF system 

is modeling of the BRB elastic stiffness. As shown in 

Figure 1-2, the BRB is a nonprismatic member that has 

three primary regions that each must be considered to 

accurately determine its actual stiffness: yielding core 

region, transition region, and connection region. The 

analysis model needs to account for the actual BRB 

stiffness, which is commonly accomplished with a 

stiffness modification factor, KF, that is multiplied by 

the core area, Asc. When applied, KF will result in the 

elastic stiffness of the modeled prismatic truss element 

matching the elastic stiffness of the actual nonprismatic 

BRB element. The BRB stiffness modification factors 

vary depending on the YLR and several other factors 

related to BRB geometry, end connection detail, and 

even manufacturer. Different types of BRBs will have 

different stiffness modification factors, and multiple 

KF values may be needed for the BRBs in a building. 

A reasonable range of KF is between 1.3 and 1.7. As 

described in Section 6 of this Guide, close coordination 

with the BRB manufacturer is needed to help the design 

engineer understand the actual BRB stiffness and 

determine the appropriate stiffness modification factor(s) 

to use in analysis and design. BRB manufacturers provide 

convenient designs aids for accurately estimating the KF

values for a given project. In addition, directly modeling 

the BRB core as a nonprismatic member is a viable 

alternative for capturing the correct BRB elastic stiffness.

A tolerance on the KF value(s) needs to be specified 

to effectively account for maximum BRB forces that 

are based on expected deformations of the BRBs, 

4. Guidance for Analysis of BRBFs 
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

12

deformations which in turn are based on the KF value(s) 

used. The AISC Seismic Design Manual (AISC 2012) 

provides the following guidance on the issue:

Designers should not perform bounding analyses 

or otherwise place undue emphasis on the effects 

of variability [of elastic stiffness and yield strength] 

beyond accounting for maximum brace forces in 

the design of connections, beams and columns. 

Such variability in stiffness is routinely (and justly) 

neglected in the seismic design of many systems 

and is minimal in the context of the use of elastic 

methods to represent inelastic response.

The main point of the AISC Seismic Design Manual

guidance is that the design engineer need not perform 

endless iterative parametric studies considering numerous 

permutations seeking to determine a precise acceptable 

tolerance for the KF value(s). Instead, the design 

engineer is encouraged to consider and understand the 

general sensitivity of the modeling results to variations 

in BRB stiffness and arrive at a reasonable tolerance. 

Current practice commonly allows for approximately 

+/- 10 percent tolerance in BRB stiffness accounting for 

variation in KF values and Asc. The design engineer needs 

to determine an acceptable tolerance for the KF value(s) 

based on the specific conditions of the given project.

unusual and/or irregular configurations need to be 

justified. Whereas the ELF and MRSA procedures use 

elastic analysis to estimate inelastic response, the NRHA 

procedure directly considers inelasticity and second-order 

effects in the analysis and therefore provides a more 

accurate assessment of story drift, BRB strains, and 

forces and moments in beams, columms, and connections. 

The benefits of using NRHA include the following:

Observing and mitigating undesirable concentrations 

of drift in a single story or a limited number of stories.

Allowing greater flexibility to use system configurations 

that are not permissible when elastic analysis methods 

are employed.

Directly quantifying story drift and BRB strain 

demands, which will typically be smaller than the 

estimates of strain made by amplifying elastic analysis 

results. Smaller BRB strain demands result in less 

strain hardening and reduction of BRB forces that are 

used in designing beams, columns, and connections.

Assessing BRB cumulative ductility demand directly. 

Although BRBs have large cumulative ductility capacity 

and are expected to be capable of sustaining multiple 

large earthquakes without fracture (Fahnestock et 

al. 2003), some special scenarios may require direct 

consideration of cumulative ductility demand.

For accurate inelastic analysis, the following are 

recommended:

Nonlinear truss or frame elements should be used 

to model BRBs. BRBs have relatively simple cyclic 

response: elastic-plastic with strain hardening and 

no strength or stiffness degradation for well-detailed 

configurations. This response can be represented with 

reasonable accuracy using commercial structural 

analysis platforms. BRB cyclic test data should be used 

as the basis for the numerical model, with particular 

attention given to modeling strain hardening in the 

BRB so that the cyclic response matches representative 

BRB experimental data. Calibration of hardening 

parameters to cyclic experimental data is critical 

because calibration to a backbone curve will not provide 

a reasonable model. Commercial structural analysis 

platforms used in design offices contain a variety of 

options for modeling steel hardening behavior, so a 

careful assessment of the BRB modeling approach 

is required to ensure reasonable response over the 

full range of behavior. For example, when kinematic 

hardening is used to model inelastic BRB behavior, 

•

•

•

•

Understanding Tolerance on BRB Stiffness

When determining an acceptable tolerance for 

KF values, the design engineer should consider 

the effect of variations of BRB stiffness on global 

building response rather than on local response. If 

all of the actual BRBs have greater stiffness than 

used in the analysis, the building will have a shorter 

fundamental period and the design engineer needs 

to consider whether this results in an increased 

design base shear and higher BRB design forces. 

If all of the actual BRBs have less stiffness than 

used in the analysis, the building will have a longer 

fundamental period and will be more flexible. In this 

case, the design engineer needs to consider whether 

this results in a decreased design base shear and/or 

results in increased lateral story drifts. 

•

4.2 Inelastic Analysis

Although not commonly used in typical BRBF designs, 

Nonlinear Response History Analysis (NRHA) is a 

valuable inelastic analysis tool for performance-based 

projects, when increased economy is desired, or when 
13

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

the model will harden continuously and may ascribe 

unrealistically large force levels to BRBs at large 

deformations if an inappropriate post-yield stiffness is 

used. This overestimation of BRB hardening can lead 

to unnecessarily large connection design forces but 

can also lead to unrealistic BRB strength and stiffness 

that may cause understated drift demands and overly 

optimistic collapse capacity.

Nonlinear frame elements should be used to model 

beams and columns. In particular, inelastic column 

behavior will be important when significant differences 

in story drifts develop between adjacent stories. 

Although beams and columns in BRBFs are designed 

to remain nominally elastic, actual inelastic seismic 

demands will not match the force distribution(s) used 

in design, and yielding may occur outside the BRBs 

in the surrounding frame.

Connections should accurately represent the actual 

conditions in the BRBF, with consideration for the 

relatively high stiffness provided at beam-column 

connections with gusset plates. In cases where drift 

concentrates in a single story, the frame action 

provided by columns and attached beams will be 

significant and should be captured in the model. The 

high stiffness of the beam-column connections with 

gusset plates means that nonlinear column panel zone 

behavior is unlikely, and panel zone regions may be 

modeled with rigid offsets.

Although not unique to BRBFs, the global destabilizing 

effects of the gravity system must be included in the 

model. These effects can be captured by including 

gravity columns, which carry the tributary seismic 

mass for the modeled BRBF, in parallel with the 

BRBF. Thus, as lateral displacement occurs during 

the analysis, P-Delta effects will amplify demands on 

the BRBF.

Design engineers considering the NRHA procedure 

should consult relevant literature for guidance on 

modeling procedures, including the NEHRP Seismic 

Design Technical Brief Nonlinear Structural Analysis 

for Seismic Design (NIST 2010b). Several references 

that discuss NRHA of BRBFs in more detail include: 

Sabelli et al. (2003), Tremblay and Poncet (2004), 

Fahnestock et al. (2003, 2006, 2007b), Uriz and Mahin 

(2008), and Jones and Zareian (2013). In addition, 

rigorous development of site-specific ground motions 

and external peer review of the design are critical steps 

when using the NRHA procedure.

Nonlinear Static Analysis

In addition to these three analysis procedures defined 

in ASCE 7, nonlinear static analysis can also be a 

valuable tool in the BRBF design process. Nonlinear 

static analysis is discussed extensively in ASCE/SEI 41 

(ASCE 2014), and although ASCE/SEI 41 was written 

as a guide for seismic retrofit projects, it is commonly 

used as a guide when employing nonlinear static 

analysis to assess new building design. The nonlinear 

static analysis procedure should follow the same 

inelastic analysis guidelines provided for the Nonlinear 

Response History Analysis (NRHA) procedure. The 

nonlinear static analysis procedure is simpler than 

the NRHA procedure because it uses monotonic 

static loading and does not require design ground 

motion development and time-stepping integration 

of the governing equations of motion. However, by 

considering only a few lateral load patterns, the 

nonlinear static procedure still provides significant 

insight into the inelastic response of the BRBF system. 

For example, the nonlinear static procedure can identify 

distribution of inelastic demand over the height of the 

frame, expose potential story mechanisms, provide 

demands for use in capacity design of the frame, and 

allow for comparison with nonlinear response of other 

seismic force-resisting systems.

•

•

•

BRBFs in Retrofit Applications

Although the focus of this Guide is on the design 

of new buildings, BRBFs can also be effectively 

implemented in retrofit applications, particularly 

because the stiffness and strength can often be tuned 

to the needs of the given existing building. Depending 

on the governing code or other regulations in the 

jurisdiction of the given retrofit project, BRBFs in a 

retrofit may still need to be designed using the ASCE 7 

and AISC 341 provisions for new construction. In 

other cases, as when nonlinear analysis is used, 

ASCE/SEI 41 provisions might be allowed. ASCE/

SEI 41-13 is the first version to contain modeling 

parameters and acceptance criteria for BRBFs. Prior 

to this version, design engineers developed projectspecific parameters and criteria with the assistance of 

the project peer reviewer, using appropriate projectspecific data from a BRB manufacturer. Even with 

general parameters and criteria now given in ASCE/

SEI 41-13, design engineers should engage with a 

peer reviewer to determine if those parameters and 

criteria are appropriate for the particular project.
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

14

As discussed, proper application of the BRBF provisions 

in AISC 341 should result in a design in which the 

earthquake-induced inelastic deformations are largely 

borne by the BRBs while all other elements of the 

seismic force-resisting system remain nominally elastic 

at the load effects associated with yielded and strainhardened BRBs (the “adjusted brace strength”). Because 

step-by-step design of BRBFs has been covered in other 

publications (López and Sabelli 2004, AISC 2012), this 

Guide only provides additional background and guidance 

regarding the current state of the practice. Section 5 

presents a basic design procedure and other items for 

consideration specifically by the design engineer, whereas 

Section 6 provides discussion of design topics related to 

coordination between the design engineer and the BRB 

manufacturer.

5. Guidance for Design of BRBFs

Figure 5-1. Flowchart for design of BRBFs.

3. Check compliance with ASCE 7

2. Size BRBs

1. Perform Analyses (Compute T, V, etc)

ASCE 7 

No, iterate Requirements met?

Yes, continue

7. Calculate adjustment factors and 

adjusted BRB strengths

6. Show that the BRBs meet 

performance requirements

5. Calculate expected BRB

 deformations

8. Continue design with adjusted BRB

strengths as amplified seismic load

4. Iterate and finalize BRB sizing

Compare T, V

to values from 1

No reasonable differences, end

Significant difference, go to 1
15

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

5.1 Basic Design Procedure

Figure 5-1 presents the basic design procedure for 

BRBFs. BRBF design is analogous to design of other 

high ductility “fuse-based” structural systems in that 

the design process can be simplified into three basic 

concepts: (1) design the ductile yielding elements (the 

fuses) for a reduced seismic force, (2) check the inelastic 

deformation of the ductile elements against acceptable 

limits, and (3) design the remainder of the system 

for the expected capacity of the ductile elements. For 

example, the primary concepts for EBF design are: (1) 

the link beams (the fuses) are proportioned for demands 

from loads reduced by the R coefficient; (2) inelastic 

deformations, concentrated within the link beams, are 

checked to meet acceptable limits; (3) using a capacitybased design approach, the link beam strengths are used 

to proportion the connections, braces, beam outside the 

link, columns, and column bases. Likewise for BRBFs, 

the fundamental design concepts are: (1) the BRBs 

(the fuses) are proportioned for demands from loads 

reduced by the R coefficient; (2) inelastic deformations, 

concentrated within the yielding core of the BRB, are 

checked to meet acceptable limits; (3) using a capacitybased design approach, the connections, frame beams, 

frame columns, and column bases are designed for the 

adjusted BRB strengths. 

The following steps diagrammed in Figure 5-1

summarize the process required by the integrated 

requirements of ASCE 7 and AISC 341:

Perform analyses. Build an analysis model that is 

consistent with the guidelines defined in Section 4 

of this Guide. In order to properly model the BRBs, 

a preliminary value for KF will need to be selected 

with input from the BRB manufacturer or other 

resources as discussed. Likewise, values of w and b

will need to be estimated as discussed in Section 3 in 

order to determine initial sizing of the BRBF beams 

and columns. The values of KF, w, and b will be 

validated later and not need to be overly precise for 

the initial analysis.

Size BRBs. From the required strengths obtained from 

the analysis model, size each BRB such that its design 

strength exceeds the calculated required strength. 

Core plates are generally fabricated from ASTM A36 

steel and BRBs sizes should be based on an Fysc in 

the range of of 38-46 ksi. In general, it is best not to 

1.

2.

unnecessarily oversize BRBs, both for economy and 

performance. This is usually achieved by increasing 

core plate areas in 1/4 square inch to 1/2 square inch 

increments for smaller BRBs and in 1 square inch to 2 

square inch increments for larger BRBs. The number 

of sizes used for a given project is a balance between 

demand capacity ratio efficiency and economy of 

repetition at the judgement of the design engineer. At 

this stage, BRB connections should be preliminarily 

considered in terms of basic type, size, or both, since 

they will affect BRB stiffness and strength adjustment 

factors. 

Check compliance with ASCE 7 requirements. After 

sizing BRBs, perform checks of all ASCE 7 global 

requirements such as story drift ratios, global stability, 

and irregularity. Satisfying these requirements may 

involve several iterations of BRB sizing, frame 

placement, or frame configuration. For the same bay 

geometry and brace configuration, a BRBF will have 

a lower lateral stiffness than an SCBF, and thus BRBF 

designs may be governed by limits on global lateral 

displacements, relative story drift ratios, and torsional 

irregularity. Therefore, drift and displacement should 

be considered earlier in the design process for a BRBF 

than for an OCBF or SCBF design.

Iterate and finalize BRB sizing. Iterate through steps 2 

and 3 as necessary until resizing of BRBs is no longer 

needed. Coordination with the BRB manufacturer 

is important to validate the values selected for KF, 

w, and b to this point in the process. Upon closing 

the iteration, the strength portion of BRB sizing is 

complete.

Calculate expected BRB deformations. Section 3 

of this Guide provides a discussion of one method 

to determine expected BRB deformations given 

that certain parameters of the brace are known 

(particularly YLR). Step-by-step procedures for 

calculating the expected BRB deformations are 

also in AISC (2012) and López and Sabelli (2004). 

The latter reference is based on the requirements 

from AISC 341-05, and the check on expected BRB 

deformations has been modified in AISC 341-10. Per 

AISC 341-10 §F4.2, the expected brace deformations 

are those corresponding to the larger of 2 percent of 

the story height or two times the design story drift 

(where the design story drift is Cd times the elastic 

drift as given in ASCE 7).

3. 

4.

5.
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

16

Design of BRBFs for Out-of-Plane Loading 

The weight of a BRB along its length is comparable to 

that of a heavy W section, and in certain conditions, 

a BRB’s size or length is large enough that its outof-plane inertial seismic force is substantial. In most 

building applications, a structural diaphragm is present 

and can be detailed to provide out-of-plane stability to 

BRBF beams and columns at brace-beam and bracebeam-column intersections. Where such a diaphragm 

is not present, the BRBF beams and columns must 

be designed to have adequate stiffness, strength, and 

stability to resist the out-of-plane seismic forces from 

the BRBs. 

in tension, two different sets of adjusted strengths 

apply for design of BRBF elements, depending 

on the BRB orientation and load direction. Per 

AISC 341, connection designs must account for 

the effects of 1.1 times the adjusted brace strength 

in compression. Additionally, the BRBF beam and 

column members must comply with the prescriptive 

detailing requirements of AISC 341. These detailing 

requirements apply to all systems listed in AISC 341 

and are not specific to BRBFs. Once the required 

strengths are computed for the appropriate load 

combinations, perform calculations and generate 

details to ensure that all other elements of the seismic 

force-resisting system have design strengths, φRn,

greater than the calculated required strengths, Ru. 

Final connection design may also affect the BRB 

stiffness (the final core length and resulting stiffness 

modification factor) and strength adjustment factors. 

Thus, iteration may be required.

Show that the BRBs meet performance requirements. 

The design engineer now has enough information to 

define two of the required BRB parameters: BRB size 

and BRB deformations. A BRB with a specific end 

connection can now be selected from the various types 

offered by the different manufacturers. To demonstrate 

compliance with AISC 341, the selected BRB must 

have been successfully tested to the expected BRB 

deformations for a similar size for each BRB used 

on the project, within the similarity requirements 

specified in AISC 341 §K3. Both strength and 

deformation requirements must be met for the tests 

of a BRB type to have demonstrated conformance. 

This assures that the BRBs selected for the project are 

similar in size and deformation capability to BRBs that 

have successfully demonstrated cyclic deformations 

under appropriate test conditions.

There are at least two potential solutions for 

cases where the selected BRB cannot satisfy the 

requirements of AISC 341 §K3: (1) portions of the 

seismic force-resisting system can be redesigned 

by adding more frames, changing the frame layout 

or adjusting BRB sizes, (2) project-specific BRB 

testing can be done to qualify BRBs for the expected 

deformations. When calculating BRB deformations, 

consideration of beam, column, and gusset plate 

sizes are critical because they affect the BRB yield 

length, which should be maximized. 

Calculate adjustment factors and adjusted BRB 

strengths. After a BRB with a specific end connection 

is chosen, the strain hardening adjustment factor 

and compression strength adjustment factor are 

determined using the BRB backbone curve provided 

by the BRB manufacturer, as illustrated in Figure 

3-2. These adjustment factors are used to calculate the 

adjusted BRB strengths. The design engineer should 

examine the backbone curve received, ensuring that it 

corresponds to qualifying tests and that it is applicable 

to project conditions. 

Continue design with adjusted brace strengths as 

amplified seismic load. The adjusted brace strengths 

in tension and in compression computed in Step 7 are 

used as the amplified seismic load in the applicable 

load combinations for the design of the remaining 

components of the frame, such as the frame beams, 

frame columns, brace connections, and column bases. 

Because the adjusted brace strength in compression 

is β times greater than the adjusted brace strength 

6.

7.

8.

5.2 Frame Layout and Configuration 

 Considerations 

When designing BRBFs, the design engineer is called 

upon to coordinate with the architect and others regarding 

the location and configuration of BRBFs. This type of 

coordination is routine for any structural system. Because 

BRBs can be easily economized by design engineers to 

efficiently provide strength to match demand, the sizing 

of BRBs during the earliest stages of design can often 

indicate that fewer BRBs are required compared to 

conventional CBFs. However, the economic benefits of 

fewer braces need to be considered alongside the negative 

effects of less redundancy, higher design forces for 

collectors and foundation elements, and possibly higher 

story drifts and therefore higher strength adjustment 
17

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

factors. Furthermore, care should be taken in distributing 

frames in plan to minimize the negative effects of 

torsional response. 

In terms of frame configuration and BRB orientations, 

greater latitude is given to BRBFs compared to other 

CBFs because BRBFs mitigate the consequences of 

brace buckling. Figure 5-2 shows examples of BRBF 

configurations. In multistory buildings, stacked 

inverted-V (chevron) and V configurations of BRBFs 

are common. The beam in a stacked inverted-V and in 

a V configuration needs to be sized for the unbalanced 

loading. However, the difference in axial forces 

between BRB tension and compression, when yielded 

and strain-hardened, does not generate unbalanced 

vertical loads as large as if the system were an SCBF. 

The adjusted compressive brace strength of a BRB 

is larger than (or at least equal to) its tensile adjusted 

brace strength. Therefore, the beam in an inverted-V 

frame configuration has an unbalanced vertical load 

counteracting gravity loads. Generally, multistory X 

configurations, Figure 5-2(e), are preferred because 

they offer advantages by minimizing both unbalanced 

vertical loading and axial loads to the frame beams and 

by providing opportunity to better distribute yielding 

across multiple stories. Single diagonals in the same 

direction along the same line are permitted by the code 

for BRBFs. In multistory applications, arranging single 

diagonals in a zig-zag configuration minimizes axial 

loads in frame beams.

5.3 Preventing Story Mechanisms 

Compared to conventional CBF designs, BRBFs have 

lower initial stiffness and reduced post-yield stiffness 

and therefore may be more susceptible to the formation of 

story mechanisms. Although the possible formation of a 

story mechanism is not unique to BRBFs, story strengths 

are more easily “tuned” in BRBFs than in other seismic 

force-resisting systems because the design engineer has 

the ability to carefully choose the steel core area that 

is needed and to minimize system overstrength. When 

sizing BRBs along the height of a frame, it is desirable 

to increase the size of the BRBs from smallest at the 

roof to largest at the base, at least maintaining similar 

demand-to-capacity ratios, to achieve distribution of 

the yielding in multiple stories. Although not a specific 

code requirement, good seismic design philosophy 

would lead a design engineer to continually increase the 

story strength from the roof to the base. Consider, for 

example, the case where two adjacent stories have the 

same story strength. As expected, the lower story has a 

larger shear demand than the upper story. Because both 

stories have the same story strength, the lower story will 

undergo more ductility demand than the upper story. 

More importantly, not paying attention to the vertical 

distribution of BRB sizing may result in the creation of 

a weak story where an upper story is adjacent to a taller 

lower story or where an upper story with inverted-V or 

V configurations is adjacent to a lower story with single 

diagonals. Furthermore, the use of a back-up frame 

(beam-column moment connections) and a dual system, 

or both, will enhance the resistance to the formation of 

a story mechanism.

5.4 Connection Considerations 

For BRBFs, there are three types of connections within 

the frame to consider: (1) connection of the BRB to 

the gusset plate, (2) connection of the beam to column 

(including gusset plates), and (3) connection of the column 

to base plate.

AISC 341 requires BRBF gusset plates to be designed 

for 1.1 times the adjusted brace strength in compression. 

BRBF gusset plates are not intended to develop a hinge 

zone the way SCBF gusset plates are detailed to develop. 

In SCBFs, gusset plate hinging is part of the brace buckling 

mechanism, but in BRBFs, the design objective is to limit 

the inelastic deformation to the BRB cores. General 

(a) Inverted V-bracing

(Chevron)

(b) V-bracing (c) Diagonal bracing

(same direction)

(d) Diagonal bracing

(Zig-zag)

(a) Multistory X-bracing

Figure 5-2. Examples of BRBF configurations.

(a) Inverted V-bracing

(chevron)

(b) V-bracing (c) Diagonal bracing 

(same direction)

(d) Diagonal bracing 

(zig-zag)

(e) Multistory X- bracing 
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

18

principles for design of gusset plates are discussed in 

AISC Design Guide 29 (Muir and Thornton 2015). As 

noted by Muir and Thornton, additional nonnegligible 

frame action demands develop in braced frames when 

the story drifts become large. As a result, the design and 

detailing of the BRBF beam-column connection needs to 

be adequate for the expected demands (Lin et al. 2015).

Column bases need to be designed for the maximum 

axial compressive and axial tensile loads to which the 

column will be subjected, including the effect of BRBs 

attached directly to column bases. Per AISC 341 §F4.3, 

these loads are determined assuming that the forces in 

all BRBs correspond to their adjusted brace strengths in 

tension and compression to ensure a complete load path 

from the top of the BRBF to the foundation. Included in 

the definition of column bases are the column-to-base 

welds, the base plate, and the anchor rods. Although not 

explicitly required by codes, the concrete foundation 

receiving the anchor rods and providing bearing support 

to the base plate should also have a design strength greater 

than the required axial strength of the column base. If 

the foundation were to be designed to a lower strength, 

although allowed by code, it would imply that the 

foundation would have to undergo inelastic deformations, 

which would not align with the AISC 341 intent that 

inelastic deformations occur primarily in the BRBs. If the 

best practice approach of designing the foundations for 

the strength of the column bases is adopted, reinforcing 

bars in those foundations need not comply with ductile 

detailing requirements, because inelastic deformations 

are not anticipated.
19

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

The required area of the steel core, Asc, and any 

allowable tolerances in meeting such value.

The required yield stress of the steel core, Fysc, to be 

validated by coupon testing of the actual material to 

be used by the BRB manufacturer, and any allowable 

tolerances in meeting such value. 

The BRB required axial strength; further specify 

whether it represents a Load and Resistance Factor 

Design (LRFD) or an Allowable Stress Design (ASD) 

value.

The stiffness modification factor(s), KF, used in the 

analyses and any allowable tolerances in meeting 

such value(s).

The expected BRB deformations to which BRBs are 

to be designed and for which the BRB supplier is to 

demonstrate compliance with the testing requirements 

of AISC 341 §K3.

The maximum permissible strain-hardening adjustment 

factor, w, and the BRB deformation at which the factor 

is to be calculated (see item 5).

The maximum permissible compression strength 

adjustment factor, b, and the BRB deformation at 

which the factor is to be calculated (see item 5).

The type of BRB end connection(s) allowed. If a 

specific end-connection or configuration is not allowed 

because of aesthetic or performance issues, such 

restriction should be noted.

The maximum permissible casing size and the casing 

shape agreed upon between the design engineer and 

project design team. If there are no requirements on 

casing size and shape, documents should so state, 

because there is a potential for more economical 

designs if the BRB manufacturer is allowed to execute 

its casing design unencumbered by constraints.

Items 1 through 3 of the preceding list are interrelated 

when sizing BRBs, for which there are two methods 

commonly used by design engineers. The first method 

is characterized by keeping Asc fixed while allowing Fysc

to vary within permissible tolerances. Since Asc does not 

vary, Asc must be sized for the lowest Fysc allowed within 

the specified tolerances. This first method allows for more 

As a performance-specified item, BRBFs are 

characterized by special considerations that are unique 

to its design compared to other seismic force-resisting 

systems. During the design phase, there are certain 

performance decisions made by the design engineer 

regarding material strength, ductility demand, casing 

size, and other items that need to be communicated 

to and coordinated with the BRB manufacturer to 

ensure that the fabricated product will meet the design 

intent for the BRBF. In addition, it is becoming more 

common in the United States for BRB manufacturers 

to provide design assistance that extends beyond 

the out-to-out dimensions of the BRBs. Therefore, 

construction documents need to communicate not 

only BRB performance requirements but also the 

design scope, if any, delegated by the design engineer 

to the BRB manufacturer’s engineer. Only the project 

Engineer of Record (EOR) can delegate scope as the 

licensed professional responsible for sealing the contract 

documents. For some projects, the EOR and the design 

engineer may be the same person, although in most cases 

the design engineer is under the responsible charge of 

the EOR. The discussion that follows emulates Section 

3 of the Code of Standard Practice for Steel Buildings 

and Bridges (AISC 2010c) and is supplementary to the 

requirements of AISC 341 §A4.1 and §A4.2.

BRB manufacturers and practicing engineers have 

collaborated to give design engineers guidance 

regarding how to effectively specify and coordinate 

BRB design and detailing parameters (Robinson and 

Black 2011; Robinson et. al. 2012). A BRB cannot be 

fabricated with zero tolerances from specified values, 

and the design engineer should also want to allow for 

differences between manufacturers or BRB types. 

Therefore the design engineer is strongly encouraged to 

contact at least one BRB manufacturer to understand the 

level of tolerance needed for BRB stiffness and strength 

parameters for the design of a given project. To quantify 

the performance of a BRB, it is reasonable to expect that 

design documents would define the nine items described 

below for each BRB, including acknowledgment of the 

tolerances acceptable to maintain the design intent. (See 

also Figure 6-1). 

6. BRBF Design and Fabrication Coordination 

1.

2.

3.

4. 

5.

6.

7.

8.

9.
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

20

Figure 6-1. Flowchart for design and fabrication coordination (with arrows indicating the direction of the flow of 

information from the design engineer to and from the BRB manufacturer.)

φPysc (tolerances)

2. Fysc (tolerances)

1. Asc (tolerances)

KF within tolerances?

No, adjust KF required.

Re-analyze only if 

needed; see Section 4.1

Yes, no further action

From qualifying tests. Manufacturer 

provides backbone curve, w and b

Qualifying tests should include 

data up to expected deformations

Manufacturer confirms 

requirements can be met

For use in the generation of 

BRB fabrication drawings

Manufacturer confirms

Asc, Fysc,φPysc, 

requirements can be met

KF corresponding to 

projects conditions

4. KF assumed in analyses

(tolerances)

5. Expected BRB deformations

6. & 7. Maximum permissible w, b

at expected deformations

No, adjust permissible w, b. Re-analysis required 

w, b less than 

permissible?

DESIGN DOCUMENTS BRB MANUFACTURER

Yes, no further action

8. Type of BRB end connection, 

9. Permissible casing size

3. BRB required axial strength, 

LRFD or ASD value
21

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

control of the calculated interstory drifts but may result in 

larger forces for all other members of the seismic forceresisting system, because the maximum Fysc allowed is 

applied to a fixed Asc as part of the BRB expected strength 

calculation. The second method is characterized by 

minimizing overdesign in the brace design axial strength, 

φPysc. The BRB manufacturer is allowed to adjust Asc as 

Fysc varies within tolerances, based on coupon testing of 

the actual core plate material, such that φPysc is as close 

to Pu as possible. The axial forces in all other members of 

the seismic force-resisting system are potentially smaller 

than those corresponding to the first method. However, 

the design engineer needs to establish reasonable limits 

on the variability of Asc to avoid having to recheck base 

shear and drift calculations after receipt of BRB shop 

drawings with the final Asc values. A hybrid of these 

two methods has been successfully implemented by 

design engineers with prior BRBF experience working 

in close collaboration with the BRB manufacturer to 

maintain minimum stiffness and strength, minimize 

BRB overstrength, and still allow for efficient detailing 

and fabrication practices.

While conducting analyses, the design engineer needs to 

use appropriate values of the BRB stiffness modification 

factors, KF, in the analysis model. These factors are 

manufacturer-specific and depend on BRB sizes, lengths, 

configuration (single diagonal vs. chevron), YLR, endconnection type, and other parameters. The stiffness 

factors used in the analyses need to be representative 

of what can be furnished by any BRB manufacturer, 

and the design engineer should coordinate with the 

BRB manufacturer on the appropriate values to use. 

Acceptable tolerances must be considered and specified. 

Refer to Section 4.1 above for guidance regarding 

acceptable tolerance on BRB elastic stiffness.

The expected BRB deformation is one of the most 

important performance parameters to define. Such 

deformation is the minimum deformation to which 

BRBs must have been subjected in qualifying tests. At 

such deformation, the values of w and b are determined 

and are to be used for design of all other elements of the 

seismic force-resisting system. The design engineer needs 

to clearly define this deformation value in the design 

documents such that there is no ambiguity as to what kind 

of performance is expected of the BRBs on the project. 

At this deformation, qualifying tests should show stable 

hysteretic loops, and the observed behavior of the BRB 

should show no sign of buckling, binding, instability, or 

other detrimental characteristics.

BRB Connection Design and Coordination

In parts of the western United States, it is common 

practice for the Engineer of Record (EOR) to fully 

develop the design and details for the connections 

associated with the seismic force-resisting system. In 

the case of BRBFs, that would imply that connection 

components such as gusset plates, welds, and bolts 

would be shown on the EOR’s design drawings. On 

some projects, BRB manufacturers have helped the 

EOR by providing the design for the gusset connections. 

Authorities having jurisdiction over the issuance of 

building permits for BRBF projects generally have not 

had any objection to engineers other than the EOR 

designing the gusset connections. As long as the gusset 

design is performed under the responsible charge of 

the EOR, who also complies with all ethical, code of 

conduct, and licensing regulations of the jurisdiction 

in which he/she practices, the codes do not mandate 

that the gusset designer needs to be an employee of 

the EOR.

Although there is general agreement that the gusset 

connections can be designed by the BRB manufacturer 

as long as the EOR maintains overall responsibility, 

there is no agreement as to when such designs should 

appear in the contract documents. Jurisdictions seem to 

be split in allowing the design of the gusset connections 

to be a deferred approval item. This Guide recommends 

that gusset connection detailing appear in the drawings 

prior to securing a building permit and not be a deferred 

approval item. Arguments for the gusset connection 

design to be a deferred approval item appear to be about 

competitiveness in the marketplace. One argument 

against a deferred approval of the gusset connection 

design is that KF, BRB strains, and BRB adjustment 

factors are affected by the length of the gussets. A 

second argument against a deferred approval of the 

gusset connection design is that BRBF behavior is 

affected by the length of the gussets. The seismic 

response of a frame beam or frame column may change 

from a flexure-governed response to a shear-governed 

response depending on the interaction between story 

heights, bay lengths, and gusset lengths. A third 

argument against a deferred approval of the gusset 

connection is that frame beams and columns could be 

subject to revision once the design of the connection is 

finalized and the design engineer reviews the applicable 

requirements of AISC 360 §J10. If the gusset design 

is not known until after the building permit is granted, 

assurances need to be in place that adequate values of 

KF were used, BRB strains are within qualified ranges, 

beams and columns have been designed to adequate 

force levels, and the response of beams and columns 

is aligned with the response assumed in the analysis. 

For these reasons, it is considered preferred practice 

to include the detailing of the gusset connections in the 

contract documents prior to obtaining a building permit. 
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

22

The remaining important parameters in the coordination 

between design engineer and BRB manufacturer are the 

BRB end connection type, casing shape, and maximum 

allowed casing size. The BRB end connection type is 

sometimes specified or limited based on aesthetic reasons 

when the BRBs are exposed. Sometimes the connection 

type is dictated by performance requirements. A pinended BRB is preferred by some design engineers at 

steep-angle conditions to avoid large flexural demands 

at expected interstory drift ratios. The casing shape and 

maximum casing size are often chosen to satisfy the 

building’s space planning and functional needs. The 

design engineer must coordinate casing shape and size 

to validate that the basis of design can be furnished by 

the BRB manufacturer.
23

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

7. Future Developments 

7.1 Enhanced Seismic Stability and 

 Residual Drift Control

As currently used, BRBFs exhibit good ductility and 

energy dissipation capability. Additional enhancements 

are possible through modifications in BRB and system 

configuration. BRBFs may concentrate drift in one 

story because BRB yielding in a given story can cause 

the stiffness of that story to drop, perhaps significantly. 

This drift concentration is undesirable because it could 

lead to global instability caused by P-Delta effects, or it 

could cause potentially problematic residual drift. There 

are currently no specific U.S. provisions to address 

this concern. However, Canadian design provisions for 

BRBFs, which are otherwise similar to U.S. provisions, 

have an additional column design requirement. CSA S16 

(CSA 2014) requires BRBF columns to be designed to 

resist axial forces from analysis using expected BRB 

capacity plus minimum additional bending moments 

induced by nonuniform drifts developing in adjacent 

stories. These moments are approximated as 20 percent 

of the column plastic moment strength.

Beyond the basic BRBF design provisions, several options 

have been proposed for preventing concentration of drift 

in a single story. A hybrid BRB has been studied, which 

uses different grades of steel in the BRB core (Atlayan 

2013, Atlayan and Charney 2014). This modification 

is intended to provide a wider region of controlled 

yielding in the BRBs so that positive global stiffness is 

maintained up to higher drift levels. Similarly, positive 

global stiffness can be maintained by using a dual system 

that provides secondary stiffness–after the BRBs have 

yielded–with parallel special moment-resisting frames 

(Kiggins and Uang 2006, Ariyaratana and Fahnestock 

2011). This BRBF-SMRF configuration, which is shown 

schematically in Figure 7-1(a), is included as an option 

in ASCE 7 and places the two components of the dual 

system in parallel. As shown in Figure 7-1(b), another 

type of BRBF dual system has also been proposed. This 

dual system configuration uses an elastic truss spine 

with BRBs (Tremblay 2003, Tremblay and Merzouq 

2004a and 2004b). The elastic truss that spans over the 

height of the building causes BRB yielding to occur 

over multiple stories and prevents concentration of drift 

in one story.

Figure 7-1. Schematic BRBF dual system configurations.

(a) BRBF-SMRF (b) BRBF with elastic truss 

(adapted from Tremblay and Poncet 2004) 

SMRF

Gravity frame

BRB BRB

Elastic truss
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

24

7.2 Novel BRB Configurations

In addition to the dual system configurations presented 

above, BRBs may be used in other novel configurations 

that have not been incorporated into current design 

provisions. One class of application strategically positions 

BRBs in locations and orientations that leverage global 

flexural building deformations to produce axial BRB 

deformations. Figure 7-2a illustrates a configuration 

where BRBs are used in place of columns at the base of 

a taller braced frame. In this case, the braced frame uses 

conventional steel braces in the remainder of the frame 

and focuses the inelastic response and energy dissipation 

at the base of the frame in the BRBs. Similarly, Figure 

7-2b illustrates a configuration where BRBs are used as 

energy dissipating outriggers in a tall building system. 

In this case, the primary seismic force-resisting system 

is a steel special plate shear wall, and the BRBs are used 

for supplementary energy dissipation. There is a wide 

range of related opportunities for incorporating BRBs as 

supplementary energy dissipation devices, including the 

approach employed in Japan where BRBs are metallic 

yielding dampers used within moment-resisting frames, 

BRB fuses are used as horizontal diaphragm collectors, 

and diagonal BRB struts are placed outside a building as 

a retrofit solution for a deficient seismic force-resisting 

system.

7.3 Performance-based Seismic Design

Although performance-based seismic design is a broader 

topic than BRBFs, it is of particular relevance to BRBFs 

Buckling-restrained 

brace

because they are one of the more straightforward seismic 

force-resisting systems to model for nonlinear analysis 

procedures commonly used for performance-based 

design and because they can be tailored for different 

performance objectives at different seismic hazard 

levels. As performance-based seismic design becomes 

more common, the application for BRBFs is expected to 

grow, particularly for taller structures and buildings of 

high importance or in need of high performance. The 

enhancements and novel applications discussed in the 

previous sections provide additional system configurations 

that expand the range of options for consideration in the 

performance-based design process. In addition, these 

enhancements relate to system parameters and response 

quantities, such as post-yield stiffness and residual drift, 

which are not directly considered in the current codebased design framework. Performance-based seismic 

design provides more flexibility to the design engineer in 

proportioning a seismic force-resisting system. BRBFs 

employed in a hybrid or dual configuration or BRBs 

employed in more novel arrangements as fuses with other 

systems can be adapted through choice of a variety of 

parameters to achieve desired performance objectives.

Figure 7-2. Novel BRB configurations.

(a) Interior vertically-oriented BRBs at base of frame 

(Bruneau et al. 2011)

(b) Exterior outrigger BRBs 

“Outrigger” 

column

Buckling-restrained 

brace

“Outrigger” 

frame

Gravity-resisting 

structural system

BRBs in 

“outrigger” frame

Primary lateral forceresisting system

Regular gravityresisting structural 

system

Special steel plate 

shear wall
25

Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

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Steel Construction, Chicago, IL.

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Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

9. Notations and Abbreviations

Asc

Cd

Fcr

Fysc

hsx

KF

Lwp

Ly

Pu 

Pysc

R

T

V

YLR

α

b

φ

Dx

Dbx

esc

e y

qx

Ω0

w

cross-sectional area of the yielding segment of 

steel core

deflection amplification factor as given in ASCE 7

critical stress

specified minimum yield stress of the steel core 

or actual yield stress of the steel core as determined from a coupon test

story height

stiffness modification factor

brace work-point length

length of the yielding segment of steel core

required axial strength

axial yield strength of steel core

response modification coefficient as given in 

ASCE 7

fundamental period of the structure

design base shear

yield length ratio

brace angle of inclination with respect to the 

horizontal

compression strength adjustment factor

strength reduction factor

design story drift

BRB deformation

core strain

yield strain

design story drift angle

overstrength factor as given in ASCE 7

strain hardening adjustment factor

American Institute of Steel Construction

American Society of Civil Engineers

Allowable Strength Design

Applied Technology Council

Buckling-Restrained Brace

Buckling-Restrained Braced Frame

Concentrically Braced Frame

Consortium of Universities for Research in 

Earthquake Engineering

Eccentric Braced Frame

Equivalent Lateral Force

Engineer of Record

International Building Code

Load and Resistance Factor Design

Modal Response Spectrum Analysis

Nonlinear Response History Analysis

National Institute of Standards and Technology

National Earthquake Hazards Reduction 

Program

Ordinary Concentrically Braced Frame

Special Concentrically Braced Frame

Special Moment-Resisting Frame

Seismic Design Category

Structural Engineers Association of California

AISC

ASCE

ASD

ATC

BRB

BRBF

CBF

CUREE

EBF

ELF

EOR

IBC

LRFD

MRSA

NRHA

NIST

NEHRP

OCBF

SCBF

SMRF

SDC

SEAOC
Seismic Design of Steel Buckling-Restrained Braced Frames: A Guide for Practicing Engineers

30

10. Credits

Cover photo Image courtesy of Walterio A. López

Figure 2-1(a) Image courtesy of Brandt Saxey, CoreBrace

Figure 2-1(b) Image courtesy of Cameron Black, SIE Inc.

Figure 2-1(c) Image courtesy of Kimberley Robinson, Star Seismic LLC

Figure 7-2(a) Image courtesy of Rafael Sabelli, Walter P Moore

The authors provided images not individually credited.