Reliability-based design of prestressed concrete g

StructuralEngineeringandMechanics,Vol.50,No.3(2014)305-322DOI:©2014Techno-Press,Ltd.=sem&subpage=8ISSN:1225-4568(Print),1598-6217(Online)Reliability-baseddesignofprestressedconcretegirdersinintegralAbutmentBridgesforthermaleffectsWooSeokKim1a,JeffreyA.Laman2bandJongYilPark31CivilEngineering,ChungnamNationalUniversity,Deajeon,305-764,Korea2CivilandEnvironmentalEngineering,PennsylvaniaStateUniversity,UniversityPark,PA,16802,USA3SafetyEngineering,SeoulNationalUniversityofScienceandTechnology,139-743,Seoul,Korea(ReceivedApril17,2013,RevisedMarch11,2014,AcceptedMarch20,2014)Abstract.Reliability-baseddesignlimitstatesandassociatedpartialloadfactorsprovideaconsistentlevelofdesignsafetyacrossbridgetypesandmembers.However,limitstatesinthecurrentAASHTOLRFDhavenotbeendevelopedexplicitlyforthesituationencounteredbyintegralabutmentbridges(IABs)thathaveuniqueboundaryconditionsandloadswithinherentuncertainties.Therefore,newreliability-basedlimitstatesforIABsconsideringthevariabilityoftheabutmentsupportconditionsandthermalloadingmustbedevelopedtoachieveIABdesignsthatachievethesamesafetylevelasotherbridgedesigns.Prestressedconcretegirderbridgesareconsideredinthisstudyandaresubjectedtoconcretetime-dependenteffects(creepandshrinkage),backfillpressure,temperaturefluctuationandtemperaturegradient.Basedonthepreviouslyestablisheddatabaseforbridgeloadsandresistances,reliabilityanalysesareperformed.TheIABlimitstatesproposedhereinareintendedtosupplementcurrentAASHTOLRFDlimitstatesasspecifiedinAASHTOLRFDTable3.4.1-1.Keywords:structuralreliability;bridgedesign;integralabutment;AASHTO,LRFD1.IntroductionIntegralabutmentbridges(IABs)havebecomeapreferrednewbridgeconstructionoverthelasttwodecadesduetomanyadvantagesoriginatingfromremovingexpansionjoints(Arockiasamyetal.2004).However,IABbehaviorisgenerallydifficulttopredict,prohibitingtheuseofconventionalbridgeanalysismethodsduetocomplexboundaryconditions,uncertaintiesandnonlinearitiesrelatedtoambienttemperaturechanges,soil-structureinteraction,andconcretecreepandshrinkage–amuchmorecomplexconditionthanforjointedbridgesbecausethesethermalloadsaresecondaryloadsinjointedbridgebutmainloadsinintegralabutmentbridges.Nevertheless,currentIABdesignpracticeutilizeslimitstatesbyAASHTOLoadandResistanceFactorDesignBridgeDesignSpecifications(ASSHTOLRFD2010)establishedforconventionaljointedbridgedesign.Although,significantloadeffectsexperiencedinIABsasaresultofCorrespondingauthor,AssistantProfessor,E-mail:[e-mail],E-mail:[e-mail],E-mail:[e-mail],JeffreyA.LamanandJongYilParkLengthSpansGirderMomentofinertia(in4)X-Secarea(in2)18.3m(60')61.0m(200')121.9m(400')124AASHTOIIIBT72BT72125,390545,894545,894560767767Fig.1Typicalcrosssectionandbridgedimensionsforparametricstudyhorizontalearthpressure(EH),temperaturegradient(TG),creep(CR),shrinkage(SH)anduniformtemperature(TU),definedinAASHTOLRFD(2010),cannotbedirectlyadoptedforIABdesignprocessbecauseofdifferentboundaryconditions.Thepresentstudy,therefore,intendstoproposeadditionallimitstatesforIABssupplementaltothecurrentAASHTOLRFDlimitstates.ThisstudydevelopednewlimitstatesforthreelimitstatesequivalenttoAASHTOLRFDlimitstate:StrengthI,ServiceIandServiceIII.TheproposedlimitstatesusedthesameformatasthoseofthecurrentAASHTOLRFDspecificationscoveringfourprestressedconcretegirderhighwayIABswithshorttomediumlengths.ThetypicalsectionconsideredinthepresentstudyispresentedinFig.1(KimandLaman2010a).Windloadsonstructures(WS)wereignorabletodeterminegirdermomentcapacityinthislengthrangeofgirderbridges.Basedonapreviouslong-termfieldmonitoringstudy(KimandLaman2012),axialforcesthatmightexistinagirderwerenotconsideredforgirderbendingcapacity.ThetypicalcontrollingAASHTOLRFDlimitstatesforprestressedconcretegirderjointedbridgedesignareasfollowsStrengthI:1.25DC+1.5DW+1.75(LL+IM)ServiceI:1.0DC+1.0DW+1.0(LL+IM)ServiceIII:1.0DC+1.0DW+0.8(LL+IM)(1a)(1b)(1c)Theabovelimitstatesconsiderbridgecomponentdeadload(DC),wearingsurfacedeadload(DW),trafficliveload(LL),andvehiculardynamicloadallowance(IM).AASHTOLRFD(2010)alsospecifiesEH,TU,TG,CRandSH.FortheStrengthIlimitstate,theloadfactorforTGistakenas0.0forTU,CRandSHas0.5or1.0,andforEHas1.50or0.9fortheactivecondition,1.35or0.9fortheat-restconditionandnotgivenforthepassivecondition.FortheServiceIcombination,allloadfactorsare1.0exceptTUiseither1.00or1.20,andTGistakenas0.5whentheliveloadisconsideredor1.0whenliveloadisnotconsidered.TheloadfactorsfortheServiceIIIcombinationisthesameasServiceIexceptthattheLLfactoris0.8.CurrentpracticeusesthesamelimitstatesaboveforIABs,i.e.,EH,TU,TG,CRandSHareconsideredassecondary,(45'-212)(11'-112)(11'-112)(11'-112)(812)13.8m216mm3.4m3.4m3.4m306Reliability-baseddesignofprestressedconcretegirdersinintegralAbutmentBridgesTable1IABresponsepredictionmodels(KimandLaman2010b)BridgeBendingMomentatMidspan(kN-m)(+)93α–850H+940P–19≥0180α+160H+330P–4700≥045α+1000P–3500≥0forL≤39.7