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SeismicCollapseSafetyofReinforcedConcreteBuildings.II:ComparativeAssessmentofNonductileandDuctileMomentFramesAbbieB.Liel,M.ASCE1;CurtB.Haselton,M.ASCE2;andGregoryG.Deierlein,F.ASCE3Abstract:Thisstudyisthesecondoftwocompanionpaperstoexaminetheseismiccollapsesafetyofreinforcedconcreteframebuildings,andexaminesnonductilemomentframesthatarerepresentativeofthosebuiltbeforethemid-1970sinCalifornia.Theprobabilisticassessmentreliesonnonlineardynamicsimulationofstructuralresponsetocalculatethecollapserisk,accountingforuncertaintiesinground-motioncharacteristicsandstructuralmodeling.TheevaluationconsidersasetofarchetypicalnonductileRCframestructuresofvaryingheightthataredesignedaccordingtotheseismicprovisionsofthe1967UniformBuildingCode.TheresultsindicatethatnonductileRCframestructureshaveameanannualfrequencyofcollapserangingfrom5to14×103atatypicalhigh-seismicCaliforniasite,whichisapproximately40timeshigherthancorrespondingresultsformoderncode-conformingspecialRCmomentframes.Thesemetricsdemonstratetheeffectivenessofductiledetailingandcapacitydesignrequirements,whichhavebeenintroducedoverthepast30yearstoimprovethesafetyofRCbuildings.DataoncomparativesafetybetweennonductileandductileframesmayalsoinformthedevelopmentofpoliciesforappraisingandmitigatingseismiccollapseriskofexistingRCframebuildings.DOI:10.1061/(ASCE)ST.1943-541X.0000275.©2011AmericanSocietyofCivilEngineers.CEDatabasesubjectheadings:Structuralfailures;Earthquakeengineering;Structuralreliability;Reinforcedconcrete;Concretestructures;Seismiceffects;Frames.Authorkeywords:Collapse;Earthquakeengineering;Structuralreliability;Reinforcedconcretestructures;Buildings;Commercial;Seismiceffects.IntroductionReinforcedconcrete(RC)framestructuresconstructedinCalifor-niabeforethemid-1970slackimportantfeaturesofgoodseismicdesign,suchasstrongcolumnsandductiledetailingofreinforce-ment,makingthempotentiallyvulnerabletoearthquake-inducedcollapse.ThesenonductileRCframestructureshaveincurredsignificantearthquakedamageinthe1971SanFernando,1979ImperialValley,1987WhittierNarrows,and1994NorthridgeearthquakesinCalifornia,andmanyotherearthquakesworldwide.ThesefactorsraiseconcernsthatsomeofCalifornia’sapproxi-mately40,000nonductileRCstructuresmaypresentasignificanthazardtolifeandsafetyinfutureearthquakes.However,dataarelackingtogaugethesignificanceofthisrisk,inrelationtoeitherthebuildingpopulationatlargeortospecificbuildings.Thecollapseriskofanindividualbuildingdependsnotonlyonthebuildingcodeprovisionsemployedinitsoriginaldesign,butalsostructuralconfiguration,constructionquality,buildinglocation,andsite-spe-cificseismichazardinformation.Apartfromthechallengesofac-curatelyevaluatingthecollapseriskisthequestionofrisktoleranceandtheminimumlevelofsafetythatisappropriateforbuildings.Inthisregard,comparativeassessmentofbuildingsdesignedaccord-ingtooldversusmodernbuildingcodesprovidesameansofevalu-atingthelevelofacceptableriskimpliedbycurrentdesignpractice.Buildingcoderequirementsforseismicdesignanddetailingofreinforcedconcretehavechangedsignificantlysincethemid-1970s,inresponsetoobservedearthquakedamageandanin-creasedunderstandingoftheimportanceofductiledetailingofreinforcement.IncontrasttooldernonductileRCframes,moderncode-conformingspecialmomentframesforhigh-seismicregionsemployavarietyofcapacitydesignprovisionsthatpreventordelayunfavorablefailuremodessuchascolumnshearfailure,beam-columnjointfailure,andsoft-storymechanisms.Althoughthereisgeneralagreementthatthesechangestobuildingcoderequire-mentsareappropriate,thereislittledatatoquantifytheassociatedimprovementsinseismicsafety.Performance-basedearthquakeengineeringmethodsareappliedinthisstudytoassessthelikelihoodofearthquake-inducedcollapseinarchetypicalnonductileRCframestructures.Performance-basedearthquakeengineeringprovidesaprobabilisticframeworkforre-latingground-motionintensitytostructuralresponseandbuildingperformancethroughnonlineartime-historysimulation(Deierlein2004).TheevaluationofnonductileRCframestructuresisbasedonasetofarchetypicalstructuresdesignedaccordingtothepro-visionsofthe1967UniformBuildingCode(UBC)(ICBO1967).Thesearchetypestructuresarerepresentativeofregularwell-designedRCframestructuresconstructedinCaliforniabetweenapproximately1950and1975.Collapseispredictedthrough1AssistantProfessor,Dept.ofCivil,EnvironmentalandArchitecturalEngineering,Univ.ofColorado,Boulder,CO80309.E-mail:abbie.liel@colorado.edu2AssistantProfessor,Dept.ofCivilEngineering,CaliforniaStateUniv.,Chico,CA95929(correspondingauthor).E-mail:chaselton@csuchico.edu3Professor,Dept.ofCivilandEnvironmentalEngineering,StanfordUniv.,Stanford,CA94305.Note.ThismanuscriptwassubmittedonJuly14,2009;approvedonJune30,2010;publishedonlineonJuly15,2010.DiscussionperiodopenuntilSeptember1,2011;separatediscussionsmustbesubmittedforindividualpapers.ThispaperispartoftheJournalofStructuralEngineer-ing,Vol.137,No.4,April1,2011.©ASCE,ISSN0733-9445/2011/4-492–502/$25.00.492/JOURNALOFSTRUCTURALENGINEERING©ASCE/APRIL2011J.Struct.Eng.2011.137:492-502.Downloadedfromascelibrary.org
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