cie-580 2010 seminar...
TRANSCRIPT
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Buckling Restrained Braces andBuckling Restrained Braces andStructural Fuses
Michel Bruneau, Ph.D., P.Eng. Professor
Department of Civil, Structural, and Environmental EngineeringUniversity at Buffalo
Outline• Description of Structural Fuse Concept
(SFC)• Description of Buckling Restrained Braces
(BRB)• Applications of BRB and SFC to Bridges
Energy DissipationEnergy DissipationEarthquake-resistant design has long relied on hysteretic energy dissipation to provide life-safety level of protectionAdvantages of yielding steel
Stable material properties well known to practicing engineersengineersNot 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 members = damage to those membersIn conventional structural configurations, serves life-safety purposes, but translates into property loss, and need substantial repairs
Energy DissipationEnergy Dissipation
DuctilityDuctility
Brittle (↓) (Somewhat) Ductile (↓)Structural FusesStructural Fuses
From Energy Dissipation to Structural FuseResearchers have proposed that hysteretic energy dissipation should instead occur in “disposable” structural elements (i e structural fuses)structural elements (i.e., structural fuses)
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AnalogyAnalogy
Sacrificial element to protect the rest of the system.
Weak LinkWeak Link
Brittle (↓) (Somewhat) Ductile (↓)
Capacity DesignCapacity DesignRoeder and Popov (1977)Roeder and Popov (1977)
Ductile seismic behaviorConcentrating energy dissipation in special elements + capacity designLinks not literally disposable
“Ductile Fuse”“Ductile Fuse”
Eccentrically Braced FrameEccentrically Braced Frame
Other studies:Fintel and Ghosh (1981)Aristizabal-Ochoa (1986)Basha and Goel (1996)Carter and Iwankiw (1998)Sugiyama (1998)Rezai et al. (2000)
Eccentrically Braced FrameEccentrically Braced Frame
(((((Opening a parenthesis)
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Tubular Eccentrically Braced FrameTubular Eccentrically Braced Frame
EBFs with wide-flange (WF) links require lateral bracing of the link to prevent lateral torsional bucklingLateral bracing is difficult to provide in
b
dtf
tw
Fyw
Fyf
b
dtf
tw
Fyw
Fyf
b
dtf
tw
Fyw
Fyf
Lateral bracing is difficult to provide in bridge piersDevelopment of a laterallystable EBF link is warrantedConsider rectangular cross-section – No LTB
ProofProof--ofof--Concept TestingConcept Testing
ProofProof--ofof--Concept TestingConcept TestingFinite Element Modeling of Finite Element Modeling of ProofProof--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 replaceabley y p
Need to configurations that decouple the energy dissipating system from the gravity carrying load systemBRB is one of many devices that could serve as a structural fuse
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What is a Buckling Restrained What is a Buckling Restrained Brace?Brace?
Explained by comparison with regular concentric brace not restrained
against buckling
PΔ
δ+
δ-
OAP
ΔD
E F
O
δ
AB
BC
CD
Δ
Δ= Real Hinge
Ductile Design of Steel Structures
B
CG
δ
A
DE
EFΔ
Δ= Plastic Hinge (Mpr)
Small residual deformationCrCr’
CBFsCBFs
KL/r – compression and tension strengths are unequal
Less energy dissipation in compression
Ductile Design of Steel Structures
Less energy dissipation in compressionUnbalanced force issuesLocal buckling and fracture
XMP
MPVV
VV
Ductile Design of Steel Structures
X
Buckling Restrained BracesBuckling Restrained Braces
The disadvantages of the CBF system can be overcome if the brace can yield during both tension and compression without buckling
Ductile Design of Steel Structures
buckling. A braced frame that incorporates this type of brace is the buckling restrained brace (BRB) Frame (BRBF)BRBF is a special class of CBF that precludes brace buckling
BRB ConceptsBRB Concepts
Most of the BRBs developed to date are proprietary, but the concepts are similar
Ductile steel core, designed to yield during both tension and compressionSteel core placed inside a steel casing (usually a hollow
Ductile Design of Steel Structures
Steel 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 force from steel core to mortarNote: Poisson effect causes steel core to expand under compression
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BucklingBuckling--Restrained Brace Restrained Brace MechanicsMechanics
Encasing Encasing mortarmortar
Yielding steel Yielding steel corecore
Ductile Design of Steel Structures
Unbonded Brace TypeUnbonded Brace Type
DecouplingDecouplingBucklingBucklingRestraintRestraint
Steel tubeSteel tube
Unbonding material Unbonding material between steel core and between steel core and mortarmortar
WHAT IS A BUCKLING-RESTRAINED BRACE? Two Definitions
De-Coupled Stress and Buckling(Mechanics Definition)
Balanced Hysteresis(Performance Definition)
Ductile Design of Steel Structures Ductile Design of Steel Structures
TEST OBSERVATIONSTEST OBSERVATIONS
Ductile Design of Steel Structures
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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 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.Vargas, R., Bruneau, M., (2009). “Experimental Response of Buildings D i d ith M t lli St t l F ” ASCE J l f St t l Designed with Metallic Structural Fuses”, ASCE Journal of Structural Engineering, Vol.135, No.4, pp.394-403.Vargas, 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 York at Buffalo, Buffalo, NY, 2006.Vargas, R., Bruneau, M., “Analytical Investigation of the Structural Fuse Concept”, Technical Report MCEER-06-0004, Multidisciplinary Center 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 DamageDamage--tolerant Structurestolerant Structures
Ductile elements were used to reduce inelastic deformations of the main structureConcept applied to high
Other studies:Connor et al. (1997)Shimizu et al. (1998)Wada and Huang (1999)Wada et al. (2000)Huang et al. (2002)
Concept applied to high rise buildings (T > 4 s)
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mass, m
frame f
structural fuse, d
Ground Motion, üg(t)
frame, fbraces, b
Benefits of Structural Fuse Concept:Benefits of Structural Fuse Concept:
Seismically induced damage is concentrated on the fusesFollowing a damaging earthquake only the fuses
αK1 = Kf
V
Vp
VTotal
earthquake only the fuses would need to be replacedOnce the structural fuses are removed, the elastic structure returns to its original position (self-recentering capability)
Δya Δyf u
KfKa
K1
Vyf
Vyd
Vy
Frame
Structural Fuses
αμmax
0.05
0.25
.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0
4
.6
.8
1.0
4
.6
.8
1.0
4
.6
.8
1.0
.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0
4
.6
.8
1.0
10 5 2.5 1.67
V/Vp
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
.6
.8
1.0
.0 .2 .4 .6 .8 1.0.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0
.0
.2
.4
.0 .2 .4 .6 .8 1.0
.0
.2
.4
.6
.8
1.0
.0 .2 .4 .6 .8 1.0
Frame Damping System Total
p
u/Δyf
Structural Fuses
uu max
max
//ΔΔyfyf
ηη=0.2=0.2
αα= 0.05= 0.05
μμmaxmax = 10= 10Drift Limit (NL THA)Drift Limit (NL THA)Drift Limit (Suggested)Drift Limit (Suggested)
μμ ff==
T=T=
ηη
ηη=1.0=1.0
System PropertiesSystem Properties
IB, ZB
IC IC
L
H
Bare FrameBare Frame
IB, ZB
IC
L
HIC
θ θ
Ab Ab
BRBsBRBsbw
BRBsBRBsIB, ZB
IC IC
L
H
θ θ
Ab Ab
N plates
TT--ADASADAS
IB, ZB
IC IC
L
H
θ θ
Ab Ab
Shear Panel
Shear PanelShear Panel
h
t
ht
bftf
Model withModel withNippon Steel BRBsNippon Steel BRBs
Eccentric GussetEccentric Gusset--PlatePlate
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Test 1 Test 1 (PGA = 1g)(PGA = 1g)
Test 1Test 1First Story BRBFirst Story BRB
0
10
20
30
40
al F
orce
(kip
s)
-40
-30
-20
-10
0-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
Axial Deformation (in)
1st S
tory
Axi
a
Test 1 (Nippon Steel BRB Frame)Test 1 (Nippon Steel BRB Frame)First Story Columns ShearFirst Story Columns Shear
25
50
75
100
ns S
hear
(kN
)
-100
-75
-50
-25
0-5 -4 -3 -2 -1 0 1 2 3 4 5
Inter-Story Drift (mm)
1st S
tory
Col
umn
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-diaphragms
R ki T (R ki B d F )Rocking Trusses (Rocking Braced Frames)SFC with BFB at base
ABC Piers BRB SFC between dual columns
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Ductile 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 g ,Engineering, Vol.125, No.1, 1999, pp.71-80.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 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 Bridge Bridge Bridge Bridge SubstructureSubstructure
Inelastic Behavior of Proposed andInelastic Behavior of Proposed andExisting EndExisting End-- DiaphragmDiaphragm
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Implementation of ConceptImplementation of ConceptMinato Bridge (Hanshin Expressway Corporation)Minato Bridge (Hanshin Expressway Corporation)
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
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BRB and SFC BRB and SFC in Rocking Truss Piers in Rocking Truss Piers
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 Using a Controlled Rocking Approach , ASCE J. of Struct. Eng. , Vol.12, No.5, pp.600-610.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.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 New York at Buffalo, Buffalo, NY, 2004.
Controlled Rocking/Energy Controlled Rocking/Energy Dissipation SystemDissipation SystemAbsence of base of leg connection creates a rocking bridge pier system partially isolating the structure
Retrofitted Tower
structure
Installation of steel yielding devices (buckling-restrained braces) at the steel/concrete interface controls the rocking response 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 Pier
Device Response
FPED=0FPED=w/2
General Design Constraints for General Design Constraints for Controlled Rocking SystemControlled Rocking System
(1) Deck-level displacement limits need to be established on a case-by-case basis
Maintain pier stabilityBridge serviceability requirements
(2) Strains on buckling-restrained brace (uplifting (2) Strains on buckling restrained brace (uplifting displacements) need to be limited such that it behaves in a stable, reliable manner(3) Capacity Protection of existing, vulnerable resisting elements considering 3-components of excitation and dynamic forces developed during impact and uplift(4) Allow for self-centering of pier
Velocity
Limit forces through vulnerable members using structural “fuses”
Acceleration⇒
Design ProcedureDesign Procedure
Design ConstraintsDesign Chart:
6
8
10h/d=4
(in2) ubVelocity
Control impact energy to foundation and impulsive loading on tower legs by limiting velocity
⇒
Displacement DuctilityLimit μL of specially detailed, ductile “fuses”
⇒
β<1⇒ Inherent re-centering (Optional)
0 100 200 300 4000
2
4
constraint1constraint2constraint3constraint4constraint5
Lub (in.)
Aub
(
Lub
A u
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Experimental TestingExperimental TestingArtificial Mass Simulation Scaling Procedure
λL>5 (Crane Clearance)λA=1.0 (1-g Field)Wm=70kN (We=76kN)T 0 34 (T 0 40 )
Δ
λL=5h/d=4.1
6.1mTom=0.34sec (Toe=0.40sec)Loading System
Phase I5DOF Shake Table
Phase II6DOF Shake Table
λt=2.2
1.5mSynthetic 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 Structural FusesStructural Fuses
El-Bahey, S., Bruneau, M., (2010). “Structural Fuse y ( )Concept For Bridges”, Transportation Research Record (a Journal of the Transportation Research Board), (in press).El-Bahey, S., Bruneau, M., (2010). “Structural Fuse Concept For Bridges”, MCEER Report (in press).
Simulate ABC ConstructionSimulate ABC ConstructionSimulate ABC ConstructionSimulate ABC Construction
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Simulate ABC ConstructionSimulate ABC ConstructionSimulate ABC ConstructionSimulate ABC ConstructionNew “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 Results for Specimen S2Results for Specimen S2--11
Onset of BRB yielding
Onset of Column yielding
Specimen with BRB FusesSpecimen with BRB Fuses Specimen with BRB FusesSpecimen with BRB Fuses
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Pushover Comparison of Frame Pushover Comparison of Frame with Different Structural Fuseswith Different Structural Fuses
1000
1100
1200
1300
1400
BRB60%
SPSL (with Restraints)
0
100
200
300
400
500
600
700
800
900
0 20 40 60 80 100 120 140 160 180 200 220Top Displacement (mm)
Tot
al F
orce
(kN
)
μmax=3.3
30%
Bare Frame
SPSL (no Restraints)
ConclusionsConclusionsRecently 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 hysteric energy) was accomplished, in some cases repeatedly. 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 Provisions
Emerging field: opportunities to develop structural fuse concepts still exist
AcknowledgmentsAcknowledgmentsFormer Ph.D. Students:
Michael Pollino (Case Western University) – Rocking Steel Framed SystemsJeffrey Berman (University of Washington) – Seismic Retrofit of Large Bridges Braced BentRamiro Vargas (University of Panama) – Enhancing Resilience using Passive Energy Dissipation SystemsResilience using Passive Energy Dissipation SystemsSamer El-Bahey (Stevenson and Associates, Phoenix) –Structural Fuses for BridgesMajid Sarraf (Parsons) – Ductile Cross-Frames in TrussesMehdi Zahrai (University of Tehran) – Ductile Diaphragms
Funding from:National Science Foundation (to MCEER)Federal Highway Administration (to MCEER)NSERC (Canada)
Thank you!Thank you!yy
Questions?Questions?