seismic response of typical highway bridges in...

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SeismicResponseofTypicalHighwayBridgesinCaliforniato

ComponentModelingandCharacteristics

Bahareh Mobasher1, Roshanak Omrani2,Ertugrul Taciroglu2,FarzinZareian1

1UniversityofCalifornia,Irvine2UniversityofCalifornia,LosAngeles

The42ndRisk,Hazard&UncertaintyWorkshop; Hydra,2016

Outline

ü Introductionü Problemstatement&Objectivesü BridgeModeling

• Shearkeys• Backfillpassive resistance

ü Analysis/Discussion• EDP:ColumnDriftRatio,Deckrotation,longitudinalandtransverse

deckmovement

ü ConcludingRemarks

Historyofbridgeseismicdesign

ü Caltrans(CaliforniaDepartment ofTransportation)formulatedthefirstcoderequirements intheUnitedStatesforseismic designofbridges in1940.

TheNewhallPassinterchange

Ø Insufficient seatwidth

FoothillFreewayInterchange

ü Hingerestrainersü Increasetheamountofsteelspiralsandties incolumnsü Increaseearthquake designforce

Historyofbridgeseismicdesign

ü LomaPrieta earthquake,1989

Ø Collapse ofupperdeckandsupportcolumns.Ø Localsoileffect(Amplified groundmotion)Ø Insufficient hoopreinforcement

ü Northridgeearthquake, 1994.

Lessons fromprevious earthquakes:

ü Understand seismicbehaviorofbridges.

ü Specifyimportantcomponents inbridges.

ü Updatecodesandguidelinebasedonthecurrent state-of-the-art.

PreviousWork

q Outcomes:§ Recommendations foradoption ofappropriatemodeldimension (2Dor3D)§ Assessment ofvariousplastichingemodeling optionsforcapturingnonlinear

response ofbentcolumns§ Criteriaforselection ofanalysismethods

q Shortcomings:§ Linearanalysisofsoil-structure interaction§ Simplified (orlackof)modelsforabutments, foundation,columns,expansion joints,

andshearkeys§ Groundmotionselection andscaling

PEER2008/03- Guidelines forNonlinear AnalysisofBridgeStructures inCaliforniaAdy Aviram,KevinR.Mackie,Bozidar Stojadinovic

ProblemStatement

θ

ü Current-state-of-research inperformanceassessment ofbridgestructures ismostlyconfined intothetwoStructural andGeotechnicaldomains.

GeotechnicalStructural

ProblemStatementü Current-state-of-research inperformanceassessment ofbridgestructures ismostly

confined intothetwoStructural andGeotechnicaldomains.

GeotechnicalStructural

θ

Beam with hinges

Rigid link

Elastic beam column element

Exterior Shear Key

CIDH and H Pile

ProblemStatementü There isagapbetween therecommendedmodeling approachesbyseismic design

guidelines andthecurrentstate-of-the-art inbridgecomponentmodeling

Quantifytheadvantages(anddisadvantages)ofutilizingadvancedcomponentmodels, comparedwithsimpleones

ProblemStatementü Currentperformancebaseassessment

• Neglects time-dependent effects(i.e.,combination ofcorrosion,andpreviousseismic damages)conditioned onhazardlevels.

Developenhanceddemandmodel(EDP|IM)

HazardCurve

IM

λ EDP

DemandCurve

ExteriorShearkeyü What is a shear key?

• Shear keys are used at bridge abutments to provide transverse support to bridge superstructure.

ü There are two types of shear keys• Exterior shear key. • Interior shear key (Interior shear keys are not recommended by Caltrans

because of maintenance problems).

Exterior shear key

Stem wall

Back wall

Footing

Wing wall

interior shear keyBearings

Schematic of typical seat-type abutment

ExteriorShearkey

ü The are two kinds of failure mechanism for exterior shear key joints (Bozorgzadeh et al. 2004, Megally et al. 2001).

• A single horizontal crack that develops at the Interface (sliding shear failure).

• Multiple diagonal cracks along the direction of predominant principal compressive stresses (Strut-and-Tie failure)

(Bozorgzadeh et al. 2004)

DesigncriteriaüIsolatedShearKey(Brittle)

üNon-isolated ShearKey(Ductile)

Shearkey Model

Concrete02

ENT

EPPG

Bilinear

ENT

Hysteretic

Back Wall

Stem Wall

Shear Key

(a) (b)

db

Area=a x d

h Force

Deformation

A

B

Ck1

k2

k3

K1=(h/AG+h3/3EI)-1

K2=f.k1f=(0.5%- %2.5)

h :Heightofshearkeyd :DepthofshearkeyG:ShearmodulusE:ModulusofelasticityI:Momentofinertia

k3 =%2.5.K1

Shear key Failure

Force

Deformation

A’B’

C’ D’Vn

Vs

Shear key Failure

Forc

e

Deformation

Forc

e

Deformation

EPPG material Concrete 02 materialFo

rce

Deformation

Bilinear hysteretic material

Forc

e

Deformation

Forc

e

ENT material

Vs

Vc

Validatedmacroelement modelsforabutmentshearkeysandseismic responsesensitivityofordinarybridgestoshearkeybehavior.(EngineeringStructures)Bahareh Mobasher ,Roshanak Omrani ,Ertugrul Taciroglu ,FarzinZareian

Based on Test Results:ü Bozorgzadeh et al. 2004 ü Megally et al. 2001.

BackfillPassivePressure

ExternalShearKeyWingWall

Deck

Force&

Deflec)on&

Pbw&

Gap&between&deck&and&back&wall&

Kabut&

!! !≈ !50!!"#/!"

!" !

!!!"#$ != !! .!.ℎ!"5.5!" !!!!!!!!!!. !.!"#$!

!!" != !! . 5.0!!"#. !!"!.! !!!!!!!!!!. !.!"#$ !!! != ℎ!" .!!" !!!!!!!!!!!!

UCDavis(1995);UCLA(2007)

BackfillPassivePressureü Abutment backfill soil type classification in California Highway Bridges (Earth

Mechanics, Inc. , 2005):I. DensetoverydensesandwithgravelII.Mediumdense silty sands,somewithgravelIII.MediumClayeysands,somewithgravelIV.Stiff-hardclayswithfinetocoarse-grained sands,somewithsilts

v Singleforce-deformationcannotcapturedifferent

typesofsoil

Variability inthePredictedSeismicPerformanceofaTypicalSeat-typeBridgeDuetoEpistemicUncertainties initsAbutmentBackfillandShear-keyModels.(Engineering Structures)Roshanak Omrani ,Bahareh Mobasher ,FarzinZareian,Ertugrul Taciroglu


LSHmodel(Shamsabadietal.,2007)Log-Spiralfailuresurface+

Hyperbolicstress-strainmodel

GHFDmodel(Khalili-Tehranietal.,2011)GeneralizedHyperbolicForce-Displacementmodel

( )r

n

r

rHHHH

ybHyafyF ≡

+= ˆ,ˆˆδ

CalibratedforgranularandcohesivebackfillsutilizingextensivesimulationsgeneratedbytheLSHmodel.

δfba rr ,, γφ,,c


!

SkewedAbutment??

üUnseatingüShearkey failure

üDeckRotationüHighseismicdemandsoncolumns

SkewedAbutment1. Linearpassivereduction,

α

SkewedModel

ACUT

OBTfromGHFDmodel

Skewedabutmentmodel(Kavianietal.,2012).

3. Non-uniformpassive reduction

(Kaviani etal.,2012)

!60tantan3.0 αβ ×=

Stiffness/StrengthVariationFactor

SkewedAbutment1. Linearpassivereduction,

α

SkewedModel

ACUT

OBTfromGHFDmodel

Skewedabutmentmodel(Kavianietal.,2012).

3. Non-uniformpassive reduction

2. Uniformpassivereduction(RollinsandJesse(2012),andMarshetal.(2013))

(Kaviani etal.,2012)

!60tantan3.0 αβ ×=



5 28 10 0.0181 1R α α−= × − +

SelectedBridgeü Jack Tone Road Overcrossing (Type A), a bridge with two spans supported on a

single-column bent

ü La Veta Avenue Overcrossing (Type B), a bridge with two spans and a two-column bent

Bridge Type Bridge No. Structure Name

Bridge Length

(m)

Width (m)

Year Built

2 Span Single Column 29 0315K JACKTONE-SB 99 ON-RAMP SEPARAT 67.2 8.3 20012 Span Multiple Column 55 0938 LA VETA AVENUE OC 91.4 23 20013 Span Single Column 29 0318 JACK TONE ROAD OH 127.5 23.5 2001

SelectedBridge

SelectedBridge

θ

θ

Beam with hinges

Rigid link




γ

Χ

Ζ

Bearings + abutment stiffnessSpring element

(Hyperbolic Gap Material)

BridgeB

Exterior Shear Key

BridgeA

CIDH and H Pile CIDH and H Pile

GroundMotion

10-110-1

100

100

Sa(g)

Periods(s)

Medianresponsespectrum

ü Selected bridgeissubjectedtoasetof40pulse-like groundmotions withtwohorizontalcomponents,and21differentincident angles (Baker2007)

Geometricmeanresponsespectra(FN/FPcomponents)forselected pulse-likerecords(ShahiandBaker,2011)

Collapsecriteria

ü Collapse is defined as either the column drift ratio larger than 8% (Hutchinson et al., 2004)

ü The deck displacement relative to the abutment and in longitudinal direction is larger than the seat width (i.e., 30").

d

H≥ 8%100)./( Hδ

ü Deck rotation, column drift ratio, and deck movement considered as three engineering demand parameters (EDP) in this research

α

Wing%wall%

Back%wall%

Deck%C.L%

C.L%C.L%

Columndriftratio% Abutment unseating

ShearKeys&DeckRotation

1.5$ 1.5$ 1.5$ 1.5$

Uniform(backfill(Bridge(B)(

Linear(backfill(Bridge(B)(

Deck$Rota-on$(Rad)$

IM$(g)$

IM$(g)$

Brittle Shearkey

DuctileShearkey

CompoundEffectofShearkeyandBackfill

b)

uniform backfill resistance

Column

Resultant Force

Non-uniform backfill resistance

Column

Resultant Force

a)

BackfillModel&ColumnDriftRatio

Ø Non-uniformpassive reduction,BrittleShearkey


(a)

(b)

ColumnCollapse

AbutmentCollapse

ü 0-15o:ColumnCollapse

ü 30-60o:Unseating

Ø Non-uniformpassivereduction,Brittle Shearkey


ColumnCollapse

AbutmentCollapse

(a)

(b)

(a)

(b)


ColumnCollapse

AbutmentCollapse

ColumnCollapse

AbutmentCollapse

UniformBF

Non-uniformBF

ConcludingRemarks1. NewGuidelines forNonlinearAnalysisofBridgeStructures inCalifornia.2. Inastraightabutmentconfiguration,

a. Columnfailureisfoundtobethemajorcollapsemechanism (atmost10%).

b. Columndriftratioissignificantlyaffected bythelevelofpassiveresistance.

2. Atlargerskewangles (30o andabove)a. Abutmentunseatingbecomesnoticeable.b. Thebackfillandshear-key responses areshowntobecoupled.c. Thedynamicequilibriumamongthereaction forcesdefine the

directionandextentofbridgerotation,anddominanceofeitherofthetwofailuremechanisms (columnfailureorabutmentunseating).

ConcludingRemarks3. Theactualforce-deformation capacityofshear-keys predominantly

controlsthecouplingbetween longitudinalandtransverse seismicresponse ofthebridge.

4. Themethodologyemployedforreducing thepassive resistance ofbackfillinskewedconfiguration isshowntosignificantlyaffect thecollapsemechanism

ConcludingRemarksBridgeDesignFrameworkforTargetSeismicLoss(Zakeri &Zareian,2016)

IM EDP DM DV

GroundMotionBridgeResponse Component

DamagesPERFORMANCE


1000yearReturnperiod

AcknowledgmentsThis study is based on work supported by the CaliforniaDepartment of Transportation (Caltrans) under Award No.65A0454. This financial support is gratefully acknowledged. Anyopinions, findings, and conclusions or recommendationsexpressed in this paper are those of the authors and do notnecessarily reflect the viewsof sponsors.

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