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Structural FusesStructural Fuses

Michel Bruneauf CSProfessor, CSEE

University at Buffalo

Energy DissipationEnergy DissipationEarthquake-resistant design has long relied on hysteretic energy dissipation to provide life-safety level of protectionlevel of protectionAdvantages of yielding steel

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 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

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Energy DissipationEnergy Dissipation

DuctilityDuctility

Brittle (↓) (Somewhat) Ductile (↓)( ) ( ) ( )

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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)

AnalogyAnalogy

Sacrificial element to protect the rest of the psystem.

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Weak LinkWeak Link

B i l (↓) (S h ) D il (↓)Brittle (↓) (Somewhat) Ductile (↓)

Capacity DesignCapacity Design

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Eccentrically Braced Frames Eccentrically Braced Frames with Tubular Linkswith Tubular Links

Roeder and Popov (1977)Roeder and Popov (1977)

Ductile seismic behaviorConcentrating energy dissipation in special elements

“Ductile Fuse”“Ductile Fuse”dissipation in special elements + capacity designLinks not literally disposable

Other studies:Fintel and Ghosh (1981)Aristizabal-Ochoa (1986)

Eccentrically Braced FrameEccentrically Braced Frame( )

Basha and Goel (1996)Carter and Iwankiw (1998)Sugiyama (1998)Rezai et al. (2000)

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Eccentrically Braced FrameEccentrically Braced Frame

Tubular Eccentrically Braced FrameTubular Eccentrically Braced Frame

EBFs with wide-flange (WF) links require

bbb

lateral bracing of the link to prevent lateral torsional bucklingLateral bracing is difficult to provide in bridge piersDevelopment of a laterally

dtf

tw

Fyw

Fyfd

tf

tw

Fyw

Fyfd

tf

tw

Fyw

Fyf

p ystable EBF link is warrantedConsider rectangular cross-section – No LTB

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ProofProof--ofof--Concept TestingConcept Testing

ProofProof--ofof--Concept TestingConcept Testing

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Finite Element Modeling of Finite Element Modeling of ProofProof--ofof--Concept TestingConcept Testing

Hysteretic Results for Refined ABAQUS Model and Proof-of-Concept Experiment

Link Testing Link Testing –– ResultsResultsLarge Deformation Cycles of Specimen X1L1.6

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Design SpaceDesign SpaceStiffened LinksUnstiffened Links ft

b

ρ

ρ = 1.6yfFE0.64

ywFE1.67

ywFE0.64

yw

wtd

Buckling Restrained Braces in Buckling Restrained Braces in Structural Fuse ApplicationStructural Fuse Application

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Wada et al. (1992)Wada et al. (1992)DamageDamage--controlled or controlled or DamageDamage--tolerant Structurestolerant Structures

Ductile elements were used to reduce inelastic

f f

Other studies:C t l (1997)

deformations of the main structureConcept applied to high rise buildings (T > 4 s)

Connor et al. (1997)Shimizu et al. (1998)Wada and Huang (1999)Wada et al. (2000)Huang et al. (2002)

mass, mstructural fuse, d

frame, fbraces, b

Ground Motion, üg(t)

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Benefits of Structural Fuse Concept:Benefits of Structural Fuse Concept:

Seismically induced damage is concentrated on the fusesFollowing a damaging earthquake only the fuses would need to be replacedOnce the structural fuses are Kf

Ka

K1

αK1 = Kf

Vyf

Vyd

Vy

Vp

V

Frame

Structural Fuses

Total

removed, the elastic structure returns to its original position (self-recentering capability)

Δya Δyf u

αμmax

0.05

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

10 5 2.5 1.67

0.25

.0.0 .2 .4 .6 .8 1.0

0.0 .2 .4 .6 .8 1.0

.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 .6 .8 1.0

8

1.0

8

1.0

8

1.0

0.0 .2 .4 .6 .8 1.0

.0

.2

.4

.6

.8

1.0

.0 .2 .4 .6 .8 1.0

8

1.0

V/Vp

0.50

.0

.2

.4

.6

.8

.0 .2 .4 .6 .8 1.0.0

.2

.4

.6

.8

.0 .2 .4 .6 .8 1.0.0

.2

.4

.6

.8

.0 .2 .4 .6 .8 1.0.0

.2

.4

.6

.8

.0 .2 .4 .6 .8 1.0

Frame Damping System Total

u/Δyf

Structural Fuses

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ΔΔyfyf

αα= 0.05= 0.05

μμmaxmax = 10= 10Drift Limit (NL THA)Drift Limit (NL THA)Drift Limit (Suggested)Drift Limit (Suggested)

μμ ff=u=u

max

max

//ΔΔ

ηη=0.2=0.2

ηη=1.0=1.0

T=T=

System PropertiesSystem Properties

IB, ZB

IC IC H

IB, ZB

IC HIC

θ θ

Ab Ab

L

Bare FrameBare FrameL

θ θ

BRBsBRBsIB, ZB

I I HA AN plates

IB, ZB

I I HShear Panel

h

b

h

w

t

IC IC

L

H

θ θ

Ab Ab

TT--ADASADAS

IC IC

L

H

θ θ

Ab Ab

Shear PanelShear Panel

tbftf

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Model withModel withNippon Steel BRBsNippon Steel BRBs

Eccentric GussetEccentric Gusset--PlatePlate

Test 1 Test 1 (PGA = 1g)(PGA = 1g)

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Test 1Test 1First Story BRBFirst Story BRB

30

40s)

-20

-10

0

10

20

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

1st S

tory

Axi

al F

orce

(kip

-40

-30

Axial Deformation (in)

1

Test 1 (Nippon Steel BRB Frame)Test 1 (Nippon Steel BRB Frame)First Story Columns ShearFirst Story Columns Shear

75

100

N)

50

-25

0

25

50

-5 -4 -3 -2 -1 0 1 2 3 4 5

tory

Col

umns

She

ar (k

N

-100

-75

-50

Inter-Story Drift (mm)

1st S

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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)

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Rocking Trusses Rocking Trusses (Rocking Braced Frames)(Rocking Braced Frames)

Controlled Rocking/Energy Controlled Rocking/Energy Dissipation SystemDissipation SystemAbsence of base of leg connection creates a connection creates a rocking bridge pier system partially isolating the structure

Installation of steel yielding devices (buckling-

Retrofitted Tower

restrained braces) at the steel/concrete interface controls the rocking response while providing energy dissipation

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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

F =0

Device Response

FPED=0FPED=w/2

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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 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

(3) Capacity Protection (cont.)(3) Capacity Protection (cont.)

An increase from the t ti h

-0.5

0

0.5

1

1.5

-5 -3 -1 1 3 5

P/P y

Static Horizontal Response

Dynamic Response

static response has been observed due to dynamic excitation of vertical modes of vibration even when

-1.5

-1

Δ/Δy

Static Horizontal Response

subjected solely to horizontal base accelerations

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1

mm

2

mm

3

mm

4

mm

4 6

mm

5 7

ΣM=0

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Acceleration⇒

Design ProcedureDesign Procedure

Design ConstraintsDesign Chart:

10h/d=4

VelocityControl impact energy to foundation and impulsive loading on tower legs by limiting velocity

⇒

Limit forces through vulnerable members using structural “fuses”

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6

8

Aub

(in2

)A u

b

by limiting velocityDisplacement Ductility

Limit μL of specially detailed, ductile “fuses”

⇒

β<1⇒ Inherent re-centering (Optional)

0 100 200 300 4000

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constraint1constraint2constraint3constraint4constraint5

Lub (in.)Lub

Experimental TestingExperimental TestingArtificial Mass Simulation Scaling Procedure

λL>5 (Crane Clearance)λL 5 (Crane Clearance)λA=1.0 (1-g Field)Wm=70kN (We=76kN)Tom=0.34sec (Toe=0.40sec)

Loading SystemPhase I

Δ

λL=5h/d=4.1

λt=2.26.1m

5DOF Shake TablePhase II

6DOF Shake Table

1.5m

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Synthetic EQ 150% of DesignFree Rocking

Synthetic EQ 150% of DesignTADAS Case ηL=1.0

Synthetic EQ 150% of Design – Free Rocking

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Synthetic EQ 175% of Design - Viscous Dampers

ABC Bridge Pier with ABC Bridge Pier with Structural FusesStructural Fuses

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Specimen S2Specimen S2--11

Experimental Hysteretic Curve Experimental Hysteretic Curve versus Analytical Pushover Curveversus Analytical Pushover Curve

Onset of Column yielding

Onset of BRB yielding

Onset of Column yielding

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Specimen with BRB FusesSpecimen with BRB Fuses

Specimen with BRB FusesSpecimen with BRB Fuses

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ConclusionsConclusionsRecently developed options for seismic design and retrofit ill t t d (BRB ith F TEBF R ki )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 being considered by:

CSA-S16 committee for 2009 Edition of S16CSA 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

AcknowledgmentsAcknowledgments

Ph.D. Students: Michael Pollino Rocking Steel Framed Michael Pollino – Rocking Steel Framed SystemsJeffrey Berman – Seismic Retrofit of Large Bridges Braced BentRamiro Vargas – Enhancing Resilience using Passive Energy Dissipation SystemsSamer El Bahey Structural Fuses for BridgesSamer El-Bahey – Structural Fuses for Bridges

Funding to MCEER from:National Science Foundation Federal Highway Administration

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Thank you!Thank you!

Questions?Questions?