1

Chapter 1: Composition and history of Buckling‐restrained Braces

Buckling‐restrained Braces and Applications1

Buckling-Restrained Braces and Applications

Toru Takeuchi, Akira Wada, Ryota Matsui, Ben Sitler, Pao-Chun Lin,

Fatih Sutcu, Hiroyasu Sakata, Zhe Qu

Japan Society of Seismic Isolation, 2017

30-years from the first application, BRBs are still actively researched andexpanding in applications. This book is the first devoted specifically to BRBs.

introduction

2

Chapter 1: Composition and history of Buckling‐restrained Braces

Buckling‐restrained Braces and Applications2

Contents Chapter 1: Composition and history of buckling-restrained braces Chapter 2: Restrainer design and clearancesChapter 3: Local bulging failureChapter 4: Connection design and global stabilityChapter 5: Cumulative deformation capacityChapter 6: Performance test specification for BRB Chapter 7: BRBF Applications

7.1 Damage tolerant concept7.2 Response evaluation of BRBF 7.3 Seismic retrofit with BRBs7.4 Response Evaluation of BRBs Retrofit for RC Frames7.5 Direct Connections to RC Frames 7.6 Applications for truss and spatial structures7.7 Spine frame concepts

AppendixA1 Typical BRB detailsA2 Rotational spring at connections A3 BRB buckling capacity

introduction

3

Chapter 1: Composition and history of Buckling‐restrained Braces

Buckling‐restrained Braces and Applications3

Concept of Buckling-restrained Brace

Types of restrainerAppearance of typical BRB

1.1 Composition of buckling-restrained Braces (BRB)

Mortar

4

Chapter 1: Composition and history of Buckling‐restrained Braces

Buckling‐restrained Braces and Applications4

-600-400-200

0200400600

-40 -20 0 20 40Axial deformation (mm)

Axi

al fo

rce

(kN

)

Hysteresis of well‐designed BRB

Clearance and eccentricity

Development of higher buckling mode

RestrainerCore plate

5

Chapter 1: Composition and history of Buckling‐restrained Braces

Buckling‐restrained Braces and Applications5

The first application of Buckling‐restrained Brace (Unbonded Brace, 1987)

Nippon Steel Headquarter No.2 (Tokyo) BRB installation

BRB experiment 1987

M Fujimoto, A Wada, E Saeki, T Takeuchi, A Watanabe: Development of Unbonded Braces, Quarterly Column, No.115, pp.91‐96, 1990.1

1.2 History of Development

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Chapter 2: Restrainer Design and Clearances

Buckling‐restrained Braces and Applications6

Quality Requirement for Hysteresis models

Inappropriate clearance

Plastic strainconcentration

Local buckling Local bulging

Uneven stiffness

Degradationin compression side

Unevenstrength

Unevenstrength Local bulging Degradation

in compression side

Bulging-induced failure

Tearing

FractureSlack 

(pin connection)

Buckling

Buckling-induced failure

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Chapter 2: Restrainer Design and Clearances

Buckling‐restrained Braces and Applications7

2. Restrainer Design and Clearance

Global Stability, including:

Restrainer End

Higher Mode Buckling

Connection Strength

Fatigue Fracture

ConnectionsRestrainer

Failure pattern and stability conditions

1.Restrainer successfully suppresses core first‐mode buckling (Chapter 2)2.Debonding mechanism decouples axial demands and allows for Poisson effects (Chapter 2)3.Restrainer wall bulging due to higher mode buckling is suppressed (Chapter 3)4.Global out‐of‐plane stability is ensured, including connection (Chapter 4)5.Low‐cycle fatigue capacity is sufficient for expected demands (Chapter 5)

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Chapter 3: Local Bulging Failure

Buckling‐restrained Braces and Applications8

in‐plane local bulging failure

out‐of‐plane local bulging failure

(Tokyo Institute of Technology)

(National Center for Research on Earthquake Engineering)

3. Local Bulging Failure

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Chapter 4: Connection Design and Global Stability

Buckling‐restrained Braces and Applications9

The AIJ Recommendations provide rigorous evaluation methods for BRB connection out‐of‐plane buckling.  Two concepts below are presented:

AIJ (2009) Recommendations for stability design of steel structures. Architectural Institute of Japan.

4. Connection design and global stability

Moment transfercapacity is lost at the

end of restrainer

EIB

JEIB

JEIB

L0

L0

lB L0

Connectionzone

Connectionzone

Restrainedzone

=Plasticzone

EIB

>

Bendingmomenttransfer

Gusset plate

JEIB EIB

>JEIB EIB

KRg

KRg

Restrainer-endzone

Connectionzone

Connectionzone

Restrainer-endzone

Plasticzone

Restrainedzone

1: Cantilevered gusset 2: Restrainer end continuity

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Chapter 5: Cumulative Deformation Capacity until Fracture

Buckling‐restrained Braces and Applications10

Expected Plastic Zone

Plastic Zone

(a) Ordinary Tube Brace

(b) Incomplete Buckling-restrained Brace

(c) Complete Buckling-restrained Brace

Local Buckling Mechanism

Plastic stress concentration

Mild local buckling and averaged strain distribution along plastic zone

Friction

Local buckling distribution until fracture

5. Cumulative deformation capacity

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Chapter 6: Performance Test Specification for BRB

Buckling‐restrained Braces and Applications11

(a) ANSI/AISC 341-05 and US practiceCycle Inelastic Deformation Cumulative strain Cumulative

(Story drift angle) ( bm = 4 by ) ( by=0.25%) Inelastic strain

by ×2 =2×4× by - by ) =0 by =2×4×0.25=2% =2×4×0=0%0.5 bm ×2 =2×4× by - by ) =8 by =2×4×0.5=4% =2×4×0.25=2%1.0 bm ×2 =2×4× by - by ) =24 by =2×4×1.0=8% =2×4×0.75=6%1.5 bm ×2 =2×4× by - by ) =40 by =2×4×1.5=12% =2×4×1.25=10%

.0 bm ×2 =2×4× by - by ) =56 by =2×4×2.0=16% =2×4×1.75=14%1.5 bm ×4 =4×4× by - by ) =80 by =4×4×1.5=24% =4×4×1.25=20%

Total =208 by =56% =52%

(b) BCJ and Japanese practiceCycle Inelastic Deformation Cumulative strain Cumulative

(Plastic length strain) ( by=0.25%) ( by=0.25%) Inelastic strain

by ×3 =3×4× by - by ) =0 by =3×4×0.25=3% =3×4×0=0%0.5%×3 =3×4× by - by ) =8 by =3×4×0.5=6% =3×4×0.25=3%1.0%×3 =3×4× by - by ) =36 by =3×4×1.0=12% =3×4×0.75=9%

.0% ×3 =3×4× by - by ) =84 by =3×4×2.0=24% =3×4×1.75=21%

×3 =3×4× by - by ) =132 by =3×4×3.0=36% =3×4×2.75=33%

Total =264 by =81% =66%

(1.5 bm until fracture)

(3.0% until fracture)

6. Performance test specification for BRB

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Chapter 7.1: Damage Tolerant Concept

Buckling‐restrained Braces and Applications12

Triton Square Project

7.1 Damage tolerant concept

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Chapter 7.1: Damage Tolerant Concept

Buckling‐restrained Braces and Applications13

Grand Tokyo North Tower Election of Large BRBF

Following Damage Tolerant Projects

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Solar-panel Envelope StructureFlexible and Lightweight structure over the main frame

Main FrameSpiral Layout of Energy-dissipation Fuses around Perimeter zones

Open Space

Energy Dissipation Brace

Energy-dissipation Skins with Solar Cells2. Disaster Prevention and Environmental Sustainability Grid skin structures

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Chapter 7.3: Seismic retrofit with BRBs

Buckling‐restrained Braces and Applications15Midorigaoka-1st Building Retrofit concept

7.3 Seismic retrofit with BRBs

Before Retrofit

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Chapter 7.3: Seismic retrofit with BRBs

Buckling‐restrained Braces and Applications16

After Retrofit

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Chapter 7.5: Direct connections to RC frames

Buckling‐restrained Braces and Applications17

7.5 Direct connections to RC frames

2000 2000

2000

2800

2000

225

2000 kN Actuator

1000 kN Actuator

+

Bea

m

Column

For strut

Out-of-plane restrained

Out-of-plane restrained

Out-of-plane restrained

40.4º

+

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Chapter 7.6: Applications for truss and spatial structures

Buckling‐restrained Braces and Applications18

7.6 Applications for truss and spatial structures a) Truss structures

△ △ △ △ △ △

Buckling BRB -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

y

軸歪み [%]

ForceLimitingFunction

Devices

Response Control for Truss Structures

Device Layout Types for Response-controlled Truss Structures

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Chapter 7.6: Applications for truss and spatial structures

Buckling‐restrained Braces and Applications19

Horizontal Acceleration

Vertical Acceleration

Horizontal Input

(R‐1) Roof with Dampers (R‐2) Base IsolatedRoof

(R‐3) Substructure with Dampers (R‐4) Entire Base Isolation

Seismic Response of Raised Roof

Device Layout for Response-controlled Roof Structures

b) Roof structures

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Chapter 7.7: Spine frame concepts

Buckling‐restrained Braces and Applications20

7.7 Spine frame concepts