Buckling Restrained Braces andStructural FusesStructural Fuses
Michel Bruneau, Ph.D., P.Eng. ProfessorProfessor
Department of Civil, Structural, and Environmental EngineeringUniversity at Buffalo
Outline• Description of Structural Fuse Concept
(SFC)• Description of Buckling Restrained Braces p g
(BRB)• Applications of BRB and SFC to BridgesApplications of BRB and SFC to Bridges
Energy DissipationEnergy DissipationEnergy DissipationEnergy DissipationEarthquake-resistant design has long relied on hysteretic energy dissipation to provide life-safety hysteretic energy dissipation to provide life safety level of protectionAdvantages of yielding steel
S bl i l i ll k i i Stable material properties well known to practicing engineersNot a mechanical device (no special maintenance)Reliable long term performance (resistance to aging)
For traditional structural systems, ductile behavior achieved by stable plastic deformation of structural achieved by stable plastic deformation of structural members = damage to those membersIn conventional structural configurations, serves life-safety purposes but translates into property loss safety purposes, but translates into property loss, and need substantial repairs
Energy DissipationEnergy Dissipation
DuctilityDuctility
(↓) (S ) (↓)Brittle (↓) (Somewhat) Ductile (↓)
Structural FusesStructural Fuses
From Energy Dissipation to Structural FuseResearchers have proposed that hysteretic energy Researchers have proposed that hysteretic energy dissipation should instead occur in “disposable” structural elements (i.e., structural fuses)
AnalogyAnalogy
S ifi i l l t t t t th t f th Sacrificial element to protect the rest of the system.
Weak LinkWeak Link
Brittle (↓) (Somewhat) Ductile (↓)
Capacity DesignCapacity Design
Roeder and Popov (1977)Roeder and Popov (1977)
Ductile seismic behaviorConcentrating energy “Ductile Fuse”“Ductile Fuse” Concentrating energy dissipation in special elements + capacity designLinks not literally disposableLinks not literally disposable
Other studies:
Eccentrically Braced FrameEccentrically Braced Frame
Fintel and Ghosh (1981)Aristizabal-Ochoa (1986)Basha and Goel (1996)Basha and Goel (1996)Carter and Iwankiw (1998)Sugiyama (1998)Rezai et al. (2000)
Eccentrically Braced FrameEccentrically Braced FrameEccentrically Braced FrameEccentrically Braced Frame
(Opening a parenthesis)
Tubular Eccentrically Braced FrameTubular Eccentrically Braced FrameTubular Eccentrically Braced FrameTubular Eccentrically Braced Frame
EBFs with wide flange (WF) links require EBFs with wide-flange (WF) links require lateral bracing of the link to prevent lateral torsional buckling
bbb
torsional bucklingLateral bracing is difficult to provide in bridge piers
tw Fyftw Fyftw Fyf
bridge piersDevelopment of a laterallystable EBF link is warranted d
tf
w
Fyw
yd
tf
w
Fyw
yd
tf
w
Fyw
ystable EBF link is warrantedConsider rectangular cross-section – No LTBsection No LTB
ProofProof--ofof--Concept TestingConcept TestingProofProof ofof Concept TestingConcept Testing
ProofProof--ofof--Concept TestingConcept TestingProofProof ofof Concept TestingConcept Testing
Finite Element Modeling of Finite Element Modeling of ProofProof ofof Concept TestingConcept TestingProofProof--ofof--Concept TestingConcept Testing
Hysteretic Results for Refined ABAQUS Model and Proof-of-Concept Experiment
(Closing a parenthesis)
Structural Fuse AnalogyStructural Fuse Analogy
EBF (Incomplete Fuse Analogy)Ductile linkMaybe not easily replaceable
Need to configurations that decouple the Need to configurations that decouple the energy dissipating system from the gravity carrying load systemcarrying load systemBRB is one of many devices that could serve as a structural fuseserve as a structural fuse
What is a Buckling Restrained What is a Buckling Restrained B ?B ?Brace?Brace?
Explained by comparison with regular concentric brace not restrained
against buckling
δ+
OAP E F
ΔPΔ
δδ-
ΔDO
AB
BC
Δ
C
O
δCD
DEΔ= Plastic Hinge (Mpr)
= Real Hinge
C ’
BG
A EFΔ
Small residual deformationCrCr’
Ductile Design of Steel Structures
CBFsCBFs
KL/r – compression and tension strengths are unequalare unequal
Less energy dissipation in compressionUnbalanced force issuesUnbalanced force issuesLocal buckling and fracture
Ductile Design of Steel Structures
MPMPVV
XMP PVV
XVV
XXDuctile Design of Steel Structures
Buckling Restrained BracesBuckling Restrained Braces
The disadvantages of the CBF system can be overcome if the brace can yield during b th t i d i ith t both tension and compression without buckling. A b d f th t i t thi t A braced frame that incorporates this type of brace is the buckling restrained brace (BRB) Frame (BRBF)(BRB) Frame (BRBF)BRBF is a special class of CBF that precludes brace buckling
Ductile Design of Steel Structures
precludes brace buckling
BRB ConceptsBRB ConceptsBRB ConceptsBRB Concepts
Most of the BRBs developed to date are proprietary, p p p y,but the concepts are similar
Ductile steel core, designed to yield during both tension and compressionand compressionSteel core placed inside a steel casing (usually a hollow structure shape) Unbonding material wraps steel coreCasing is filled with mortar or concrete. Unbonding material minimizes / eliminates transfer of axial Unbonding material minimizes / eliminates transfer of axial force from steel core to mortarNote: Poisson effect causes steel core to expand under
i
Ductile Design of Steel Structures
compression
BucklingBuckling--Restrained Brace Restrained Brace MechanicsMechanicsMechanicsMechanics
Encasing Encasing mortarmortar
Yielding steel Yielding steel
DecouplingDecouplingBucklingBuckling
corecore
DecouplingDecouplingRestraintRestraintUnbonding material Unbonding material
between steel core and between steel core and mortarmortar
U b d d B TU b d d B T
Steel tubeSteel tube
Ductile Design of Steel Structures
Unbonded Brace TypeUnbonded Brace Type
WHAT IS A BUCKLING-RESTRAINED BRACE? Two Definitions
De-Coupled Stress and Buckling Balanced Hysteresis(Mechanics Definition) (Performance Definition)
Ductile Design of Steel Structures
Ductile Design of Steel Structures
TEST OBSERVATIONSTEST OBSERVATIONS
Ductile Design of Steel Structures
Ductile Design of Steel Structures
Ductile Design of Steel Structures
Ductile Design of Steel Structures
Ductile Design of Steel Structures
Buckling Restrained Braces in Buckling Restrained Braces in Buckling Restrained Braces in Buckling Restrained Braces in Structural Fuse ApplicationStructural Fuse Application
Vargas, R., Bruneau, M., (2009). “Analytical Response of Buildings Designed with Metallic Structural Fuses”, ASCE Journal of Structural Engineering, Vol.135, No.4, pp.386-393.g g, , , ppVargas, R., Bruneau, M., (2009). “Experimental Response of Buildings Designed with Metallic Structural Fuses”, ASCE Journal of Structural Engineering, Vol.135, No.4, pp.394-403.g g ppVargas, R., Bruneau, M., “Experimental Investigation of the Structural Fuse Concept”, Technical Report MCEER-06-0005, Multidisciplinary Center for Earthquake Engineering Research, State University of New q g g yYork at Buffalo, Buffalo, NY, 2006.Vargas, R., Bruneau, M., “Analytical Investigation of the Structural Fuse Concept”, Technical Report MCEER-06-0004, Multidisciplinary p p p yCenter for Earthquake Engineering Research, State University of New York at Buffalo, Buffalo, NY, 2006.
Wada et al. (1992)Wada et al. (1992)DamageDamage--controlled or controlled or ggDamageDamage--tolerant Structurestolerant Structures
Ductile elements were used to reduce inelastic used to reduce inelastic deformations of the main structurestructureConcept applied to high rise buildings (T > 4 s)Other studies:
Connor et al. (1997)
g ( )
Shimizu et al. (1998)Wada and Huang (1999)Wada et al (2000)Wada et al. (2000)Huang et al. (2002)
t t l f dmass, m
structural fuse, d
frame, fbraces bbraces, b
Ground Motion, ü (t)Ground Motion, üg(t)
Benefits of Structural Fuse Concept:Benefits of Structural Fuse Concept:Benefits of Structural Fuse Concept:Benefits of Structural Fuse Concept:
Seismicall ind ced damage is Seismically induced damage is concentrated on the fusesFollowing a damaging
Vp
VTotal
Following a damaging earthquake only the fuses would need to be replaced
K1
αK1 = Kf
VVyd
VyStructural Fuses
would need to be replacedOnce the structural fuses are removed, the elastic structure
KfKa
Vyf
Frame
,returns to its original position (self-recentering capability)
Δya Δyf u
αμmax 10 5 2.5 1.67
0.05.4
.6
.8
1.0
2
.4
.6
.8
1.0
.4
.6
.8
1.0
2
.4
.6
.8
1.0
.0
.2
.0 .2 .4 .6 .8 1.0.0
.2
.0 .2 .4 .6 .8 1.0.0
.2
.0 .2 .4 .6 .8 1.0
1.0
8
1.0 1.0
.0
.2
.0 .2 .4 .6 .8 1.0
8
1.0
0.25
0
.2
.4
.6
.8
0.2
.4
.6
.8
0
.2
.4
.6
.8
0.2
.4
.6
.8
V/Vp
0 50
.0.0 .2 .4 .6 .8 1.0
.0.0 .2 .4 .6 .8 1.0
.0.0 .2 .4 .6 .8 1.0
.6
.8
1.0
.6
.8
1.0
.6
.8
1.0
.0.0 .2 .4 .6 .8 1.0
.6
.8
1.0
0.50
.0
.2
.4
.0 .2 .4 .6 .8 1.0.0
.2
.4
.0 .2 .4 .6 .8 1.0.0
.2
.4
.0 .2 .4 .6 .8 1.0.0
.2
.4
.0 .2 .4 .6 .8 1.0
Frame Damping System Total
u/Δyf
Structural Fuses
αα= 0.05= 0.05 Drift Limit (NL THA)Drift Limit (NL THA)Drift Limit (Suggested)Drift Limit (Suggested)
ΔΔ yfyf
μμmaxmax = 10= 10 Drift Limit (Suggested)Drift Limit (Suggested)
max
max
//ΔΔμμ ff
=u=umm
ηη=0.2=0.2
μμT=T=
ηη=1.0=1.0
T=T=
System PropertiesSystem Properties
IB, ZB
IC IC H
IB, ZB
IC HICAb Ab
L
θ θ
bwL
Bare FrameBare FrameL
BRBsBRBsIB, ZB IB, ZB
bw
t
IC IC HAb Ab
N platesIC IC HAb Ab
Shear Panelhh
L
θ θ
L
θ θtbftfL
TT--ADASADASL
Shear PanelShear Panel
Model withModel withNippon Steel BRBsNippon Steel BRBs
Eccentric GussetEccentric Gusset--PlatePlateEccentric GussetEccentric Gusset--PlatePlate
Test 1 Test 1 Test 1 Test 1 (PGA = 1g)(PGA = 1g)
Test 1Test 1First Story BRBFirst Story BRBFirst Story BRBFirst Story BRB
30
40
10
20
30
rce
(kip
s)
-10
0
10
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5y A
xial
For
-30
-20
10
1st S
tory
-40
30
Axial Deformation (in)
Test 1 (Nippon Steel BRB Frame)Test 1 (Nippon Steel BRB Frame)First Story Columns ShearFirst Story Columns ShearFirst Story Columns ShearFirst Story Columns Shear
100
50
75
ear
(kN
)
0
25
5 4 3 2 1 0 1 2 3 4 5olum
ns S
h
-50
-25-5 -4 -3 -2 -1 0 1 2 3 4 5
st S
tory
Co
-100
-75
Inter-Story Drift (mm)
1s
Inter Story Drift (mm)
Static Test Static Test -- Nippon Steel BRBsNippon Steel BRBsNote: Replacement is to reNote: Replacement is to re--center the building center the building
(not due to BRB fracture life)(not due to BRB fracture life)
BRB and SFC in BridgesBRB and SFC in Bridges
Ductile DiaphragmsBRB SFC in end diaphragmsBRB SFC in end-diaphragms
Rocking Trusses (Rocking Braced Frames)SFC with BFB at base
ABC Piers BRB SFC between dual columns
Ductile DiaphragmsDuctile DiaphragmsDuctile DiaphragmsDuctile Diaphragmswith Structural Fuseswith Structural Fuses
Zahrai, S.M., Bruneau, M. (1999). “Cyclic Testing of Ductile End-Diaphragms for Slab-on-Girder Steel Bridges”, ASCE Journal of Structural Engineering, Vol.125, No.9, pp.987-996.Zahrai, S.M., Bruneau, M. (1999). “Ductile End-Diaphragms for the Seismic Retrofit of Slab-on-Girder Steel Bridges”, ASCE Journal of Structural Engineering, Vol.125, No.1, 1999, pp.71-80.Sarraf M Bruneau M (1998) “Ductile Seismic Retrofit of Steel Deck Truss Sarraf, M., Bruneau, M. (1998). “Ductile Seismic Retrofit of Steel Deck-Truss Bridges. I: Strategy and Modeling”, ASCE Journal of Structural Engineering, Vol.124, No.11, 1998, pp.1253-1262.Sarraf, M., Bruneau, M. (1998). “Ductile Seismic Retrofit of Steel Deck-Truss Sarraf, M., Bruneau, M. (1998). Ductile Seismic Retrofit of Steel Deck Truss Bridges. II: Design Applications", ASCE Journal of Structural Engineering, Vol.124, No.11, 1998, pp. 1263-1271.Zahrai, S.M., Bruneau, M. (1998). “Impact of Diaphragms on Seismic Response of Straight Slab-on-girder Steel Bridges”, ASCE Journal of Structural Engineering, Vol.124, No.8, pp.938-947.
Vulnerable Vulnerable Vulnerable Vulnerable Bridge Bridge SubstructureSubstructureSubstructureSubstructure
Inelastic Behavior of Proposed andInelastic Behavior of Proposed andExisting EndExisting End-- DiaphragmDiaphragm
Implementation of ConceptImplementation of ConceptMinato Bridge (Hanshin Expressway Corporation)Minato Bridge (Hanshin Expressway Corporation)g ( p y p )g ( p y p )
Ductile Cross-Frames implemented as part of a comprehensive seismic rehabilitation processKANAJI, H., KITAZAWA, M., SUZUKI, N., “Seismic Retrofit Strategy using Damage Control Design Concept and the Response Reduction Effect for a Long-span Truss Bridge”, US-Japan Bridge Workshop, 2005
BRB and SFC BRB and SFC i R ki T Pi i R ki T Pi in Rocking Truss Piers in Rocking Truss Piers
Pollino, M., Bruneau, M., (2010). “Bi-Directional Behavior and Design of Controlled Pollino, M., Bruneau, M., (2010). Bi Directional Behavior and Design of Controlled Rocking 4-Legged Bridge Steel Truss Piers,” ASCE J. of Struct. Eng. (in press).Pollino, M., Bruneau, M., (2010). “Seismic Testing of a Bridge Truss Pier Designed for Controlled Rocking,” ASCE J. of Struct. Eng. (in press).Pollino, M., Bruneau, M., (2007). “Seismic Retrofit of Bridge Steel Truss Piers Using a Controlled Rocking Approach”, ASCE J. of Struct. Eng. , Vol.12, No.5, pp.600-610.P lli M B M (2008) “A l ti l d E i t l I ti ti f Pollino, M., Bruneau, M., (2008). “Analytical and Experimental Investigation of a Controlled Rocking Approach for Seismic Protection of Bridge Steel Truss Piers”, Technical Report MCEER-08-0003, Multidisciplinary Center for Earthquake Engineering Research, State University of New York at Buffalo, Buffalo, NY, 2008.g g , y , , ,Pollino, M., Bruneau, M., “Seismic Retrofit of Bridge Steel Truss Piers using a Controlled Rocking Approach”, Technical Report MCEER-04-0011, Multidisciplinary Center for Earthquake Engineering Research, State University of N Y k B ff l B ff l NY 2004 New York at Buffalo, Buffalo, NY, 2004.
Controlled Rocking/Energy Controlled Rocking/Energy SSDissipation SystemDissipation System
Absence of base of leg Absence of base of leg connection creates a rocking bridge pier system
ti ll i l ti th partially isolating the structure
I t ll ti f t l Installation of steel yielding devices (buckling-restrained braces) at the steel/concrete interface controls the rocking response while providing
Retrofitted Towerresponse while providing energy dissipation
Existing Rocking BridgesExisting Rocking BridgesSouth Rangitikei Rail Bridge Lions Gate Bridge North Approach
Static, Hysteretic Behavior of Controlled Static, Hysteretic Behavior of Controlled Rocking PierRocking PierRocking PierRocking Pier
FPED=0F =w/2FPED=w/2
Device Response
General Design Constraints for General Design Constraints for C t ll d R ki S tC t ll d R ki S tControlled Rocking SystemControlled Rocking System
(1) Deck-level displacement limits need to be established on a case by case basisestablished on a case-by-case basis
Maintain pier stabilityBridge serviceability requirementsBridge serviceability requirements
(2) Strains on buckling-restrained brace (uplifting displacements) need to be limited such that it behaves p )in a stable, reliable manner(3) Capacity Protection of existing, vulnerable resisting ( ) p y g, gelements considering 3-components of excitation and dynamic forces developed during impact and uplift(4) Allow for self-centering of pier
Design ProcedureDesign Procedure
A l ti
Design ConstraintsDesign Chart:
10h/d=4
Limit forces through vulnerable members
i t t l “f ”
Acceleration⇒
8
VelocityControl impact energy to foundation and impulsive
⇒
using structural “fuses”
4
6
Aub
(in2
)A ub
foundation and impulsive loading on tower legs by limiting velocity
Displacement Ductility⇒
2p yLimit μL of specially detailed, ductile “fuses”
0 100 200 300 4000
constraint1Lub (in.)Lub
β<1⇒ Inherent re-centering (Optional)constraint2constraint3constraint4constraint5
Experimental TestingExperimental TestingArtificial Mass Simulation Scaling Procedure
λL>5 (Crane Clearance)λA=1.0 (1-g Field) Δh/d=4.1Wm=70kN (We=76kN)Tom=0.34sec (Toe=0.40sec)
L di S t
λL=5
λ =2 26.1m
Loading SystemPhase I
5DOF Shake Table
λt=2.2
5DOF Shake TablePhase II
6DOF Shake Table
1.5m
Synthetic EQ 150% of Design Synthetic EQ 150% of DesignSynthetic EQ 150% of DesignFree Rocking
Synthetic EQ 150% of DesignTADAS Case ηL=1.0
Synthetic EQ 150% of Design – Free Rocking
Synthetic EQ 175% of Design - Viscous Dampers
ABC Bridge Pier with ABC Bridge Pier with ABC Bridge Pier with ABC Bridge Pier with Structural FusesStructural Fuses
El-Bahey, S., Bruneau, M., (2010). “Structural Fuse Concept For Bridges”, Transportation Research Record (a J l f th T t ti R h B d) (i )Journal of the Transportation Research Board), (in press).El-Bahey, S., Bruneau, M., (2010). “Structural Fuse Concept For Bridges”, MCEER Report (in press).Concept For Bridges , MCEER Report (in press).
Simulate ABC ConstructionSimulate ABC ConstructionSimulate ABC ConstructionSimulate ABC Construction
Simulate ABC ConstructionSimulate ABC ConstructionSimulate ABC ConstructionSimulate ABC Construction
New “Short Length” BRB New “Short Length” BRB New “Short Length” BRB New “Short Length” BRB Developed by Star Seismic Developed by Star Seismic
Specimen S2Specimen S2--11
Experimental versus Analytical Experimental versus Analytical Experimental versus Analytical Experimental versus Analytical Results for Specimen S2Results for Specimen S2--11
Onset of BRB i ldiyielding
Onset of ColumnOnset of Column yielding
Specimen with BRB FusesSpecimen with BRB Fuses
Specimen with BRB FusesSpecimen with BRB Fuses
Pushover Comparison of Frame Pushover Comparison of Frame Pushover Comparison of Frame Pushover Comparison of Frame with Different Structural Fuseswith Different Structural Fuses
1200
1300
1400
BRB SPSL (with Restraints)
800
900
1000
1100
ce (k
N) 30% SPSL (no Restraints)
60%
400
500
600
700
Tot
al F
orc
Bare Frame
0
100
200
300
0 20 40 60 80 100 120 140 160 180 200 220
μmax=3.3
0 20 40 60 80 100 120 140 160 180 200 220Top Displacement (mm)
ConclusionsConclusionsR tl d l d ti f i i d i d t fit Recently developed options for seismic design and retrofit illustrated (BRB with Fuse, TEBF, Rocking)Instances for which replacement of sacrificial structural members (considered to be structural fuses dissipating hysteric energy) was accomplished, in some cases repeatedly. Article/Clauses for the design of some of these systems are Article/Clauses for the design of some of these systems are being considered by:
CSA-S16 committee for 2009 Edition of S16AISC TC9 Subcommittee for the 2010 AISC Seismic ProvisionsAISC TC9 Subcommittee for the 2010 AISC Seismic Provisions
Emerging field: opportunities to develop structural fuse concepts still exist
AcknowledgmentsAcknowledgmentsFormer Ph.D. Students:
Michael Pollino (Case Western University) – Rocking Steel F d S tFramed SystemsJeffrey Berman (University of Washington) – Seismic Retrofit of Large Bridges Braced BentRamiro Vargas (University of Panama) – Enhancing Resilience using Passive Energy Dissipation SystemsSamer El-Bahey (Stevenson and Associates, Phoenix) –St t l F f B idStructural Fuses for BridgesMajid Sarraf (Parsons) – Ductile Cross-Frames in TrussesMehdi Zahrai (University of Tehran) – Ductile Diaphragms( y ) p g
Funding from:National Science Foundation (to MCEER)Federal Highway Administration (to MCEER)Federal Highway Administration (to MCEER)NSERC (Canada)
Thank o !Thank o !Thank you!Thank you!
Questions?Questions?Questions?Questions?
