中英文對(duì)照外文翻譯文獻(xiàn)(文檔含英文原文和中文翻譯)Influenceofisolatorcharacteristicsontheresponseofbase-isolatedstructureVasantA.Matsaar1Z.S.JanidsAbstractTheinfluenceofisolatorcharacteristicsontheseismicresponseofmulti-storybase-isolatedstructureisinvestigated.Theisolatedbuildingismodeledasasheartypestructurewithlateraldegree-of-freedomateachfloor.Theisolatorsaremodeledbyusingtwodifferentmathematicalmodelsdepictedbybi-linearhystereticandequivalentlinearelastic-viscousbehaviors.ThecoupleddifferentialequationsofmotionfortheisolatedsystemarederivedandsolvedintheincrementalformusingNewmark'sstep-by-stepmethodofintegration.Thevariationoftopfloorabsoluteaccelerationandhearingdisplacementforvariousbi-linearsystemsunderdifferentearthquakesiscomputedtostudytheeffectsoftheshapeoftheisolatorhysteresisloop.Theinfluenceoftheshapeofisolatorforce-deformationloopontheresponseofisolatedstructureisstudiedunderthevariationofimportantsystemparameterssuchasisolatoryielddisplacement,superstructureflexibility,isolationtimeperiodandnumberofstoryofthebase-isolatedstructure.Itisobservedthatthecodespecifiedequivalentlinearelasticviscousdampingmodelofabi-linearhystereticsystemoverestimatesthedesignbearingdisplacementandunderestimatesthesuperstructureacceleration.Theresponseofbase-isolatedstructureissignificantlyinfluencedbytheshapeofhysteresisloopofisolator.Thelowvalueofyielddisplace-mentofisolator(i.e.slidingtypeisolationsystems)tendstoincreasethesuperstructureaccelerationsassociatedwithhighfrequencies.Further,thesuperstructureaccelerationalsoincreaseswiththeincreaseofthesuperstructureflexibility.keywords:Baseisolation;Earthquake;ElastomtricbearingSlidingsystem;Bearingdisplacement;Superstructureacceleration;Bi-linearhysteresis;Equivalentlinear.1IntroductionSeismicisolation,whichisnowrecognizedasamatureandefficienttechnology,canbeadoptedtoimprovetheseismicperformanceofstrategicallyimportantbuildingssuchasschools,hospitals,industrialstructuresetc.,inadditiontotheplaceswheresensitiveequipmentsareintendedtoprotectfromhazardouseffectsduringearthquake[1-3].Basedontheextentofcontroltobeachievedovertheseismicresponse,thechoiceoftheisolationsystemvariesandthereuponitsdesignisdonetosuittherequirementsofuseofthestructure.Inseismicallybase-isolatedsystems,thesuperstructureisdecoupledfromtheearthquakegroundmotionbyintroducingaflexibleinterfacebetweenthefoundationandthebaseofstructure.Thereby,theisolationsystemshiftsthefundamentaltimeperiodofthestructuretoalargevalueand/ordissipatestheenergyindamping,limitingtheamountofforcethatcanbetransferredtothesuperstructuresuchthatinter-storydriftandflooraccelerationsarereduceddrastically.Thematchingoffundamentalfrequenciesofbase-isolatedstructuresandthepredominantfrequencycontentsofearthquakesisalsoconsequentlyavoided,leadingtoaflexiblestructuralsystemmoresuitablefromearthquakeresistanceviewpoint.Thetwomostcommontypesofbaseisolationsystemsadoptedinpracticeutilizeeitherrubberbearingsorslidingsystemsbetweenthefoundationandsuperstructureforthepurposeofisolationfromgroundmotionsinthebuildingsaswellasbridges.Itisveryessentialtounderstandthedifferentparametersaffectingtheresponseofbase-isolatedstructurewhenusedforseismicprotectionofthestructures.Especiallyincaseofthebase-isolatedstructures,thathousessensitiveequipments,determinationofaccelerationimpartedandassociatedpeakdisplacementarethekeyissuesforthedesignengineer[4].Moreover,thepoundingandstructuralimpactsincaseofbaseisolatedstructuresmadeupontheadjacentstructures,whenseparationgapdistancesareinadequate,becomeamajorconcernbecausethesephenomenamayleadtocatastrophicfailuresleadingtoimmenseisolatordamage.Suchfailuresanddamagescanbeavoidedbyproperlyestimatingthepeakisolatordisplacementandrecommendationofappropriateisolationgapdistances.Inordertopredictpeakdisplacementanddetermineaccurateseparationgapdistancerequirementforabase-isolatedstructure,itismandatorytoknow,inprior,thedifferentparametersthataffectthebearingdisplacementanditsconsequenteffectonthesuperstructureacceleration.Thefailuresduetosuchimpactscanbeavoidedbyreducingthepeakbearingdisplacementbycompromisingwithincreaseinsuperstructureaccelerationtoanacceptableleveli.e.tolerablereductionineffectivenessofisolation.Selectionofdifferentparameterscharacterizinganisolationsystemisimportantinviewofkeepingacontroloverresponsequantitiesespeciallytheexcessivebearingdisplacementatisolatorlevel.Thebehaviorofisolationsystemsandthebaseisolatedstructuresisnowwellestablishedandcodesaredevelopedfordesigningthebase-isolatedstructures[5–9].Fornon-linearisolationsystems,thecodesallowtousetheequivalentlinearmodeltopermittheuseofresponsespectrummethodfordesigningtheisolatedstructures.Theequivalentlinearmodelsarebasedontheeffectivestiffnessatthedesigndisplacementandtheequivalentviscousdampingisevaluatedfromtheareaofthehysteresisloop.Thecomparisonofequivalentlinearandactualnon-linearmodelfortheresponseofisolatedbridgestructureshadbeendemonstratedinthepast[10–13]andshownthattheequivalentlinearmodelcanbeusedforpredictingtheactualnon-linearresponseofthesystem.However,theabovestudieswererestrictedtothebridgeidealizedasarigidbodyandthenon-linearbehavioroftheisolatorwaslimitedtothelead–rubberbearingsidealizedbybi-linearcharacteristics.Theequivalentlinearmodelmaygivedifferentresponseofisolatedstructuresincomparisontotheactualnon-linearmodelforflexiblesuperstructuresandthetypeofnon-linearhysteresisloopoftheisolatorassociatedwithslidingtypeisolationsystems.Therefore,itwillbeinterestingtostudythecomparisonofthetwomodelsfordifferenthystereticbehavioroftheisolatorandthesystemparameters.Here-in,theseismicresponseofmulti-storystructuresupportedonnon-linearbaseisolationsystemsisinvestigated.Thespecificobjectivesofthestudyare:(i)tocomparetheseismicresponseofbase-isolatedflexiblebuildingobtainedfromvariousbi-linearhystereticmodelanditsequivalentlinearmodel;(ii)tostudytheinfluenceofshapeoftheisolatorhysteresisloopanditsparameters(i.e.yielddisplacementandforce)ontheeffectivenessoftheisolationsystemand(iii)toinvestigatetheeffectsofsuperstructureflexibilityontheresponseofbase-isolatedstructures.2.Structuralmodelofbase-isolatedbuildingFig.1(a)showstheidealizedmathematicalmodeloftheN-storybase-isolatedbuildingconsideredforthepresentstudy.Thebase-isolatedbuildingismodeledasasheartypestructuremountedonisolationsystemswithonelateraldegree-of-freedomateachfloor.Followingassumptionsaremadeforthestructuralsystemunderconsideration:1.Thesuperstructureisconsideredtoremainwithintheelasticlimitduringtheearthquakeexcitation.Thisisareasonableassumptionastheisolationattemptstoreducetheearthquakeresponseinsuchawaythatthestructureremainswithintheelasticrange.2.Thefloorsareassumedrigidinitsownplaneandthemassissupposedtobelumpedateachfloorlevel.3.Thecolumnsareinextensibleandweightlessprovidingthelateralstiffness.4.Thesystemissubjectedtosinglehorizontalcomponentoftheearthquakegroundmotion.5.Theeffectsofsoil–structureinteractionarenottakenintoconsideration.Forthesystemunderconsideration,thegoverningequationsofmotionareobtainedbyconsideringtheequilibriumofforcesatthelocationofeachdegreesof-freedom.Theequationsofmotionforthesuperstructureunderearthquakegroundaccelerationareexpressedinthematrixformaswhere[Ms],[Cs]and[Ks]arethemass,dampingandstiffnessmatricesofthesuperstructure,respectively;aretheunknownrelativefloordisplacement,velocityandaccelerationvectors,respectively;andaretherelativeaccelerationofbasemassandearthquakegroundacceleration,respectively;and{r}isthevectorofinfluencecoefficients.ThecorrespondingequationofmotionforthebasemassunderearthquakegroundaccelerationisexpressedbywherembandFbarethebasemassandrestoringforcedevelopedintheisolationsystem,respectively;k1isthestorystiffnessoffirstfloor;andc1isthefirststorydamping.Therestoringforcedevelopedintheisolationsystem,Fbdependsuponthetypeofisolationsystemconsideredandapproximatenumericalmodelsshallbeused.3.MathematicalmodelingofisolatorsForthepresentstudy,theforce-deformationbehavioroftheisolatorismodeledas(i)non-linearhystereticrepresentedbythebi-linearmodeland(ii)thecodespecifiedequivalentlinearelastic–viscousdampingmodelforthenon-linearsystems.Acomparisonoftheresponseoftheisolatedstructurebyusingtheabovetwomodelswillbeusefulinestablishingthevalidityofthecodespecifiedequivalentlinearmodel.3.1.Bi-linearhystereticmodelofisolatorsThenon-linearforce-deformationbehavioroftheisolationsystemismodeledthroughthebi-linearhysteresisloopcharacterizedbythreeparametersnamely:(i)characteristicstrength,Q(ii)post-yieldstiffness,kband(iii)yielddisplacement,q(referFig.1(b)).Thebi-linearbehaviorisselectedbecausethismodelcanbeusedforallisolationsystemsusedinpractice.Thecharacteristicstrength,Qisrelatedtotheyieldstrengthoftheleadcoreintheelastomericbearingsandfrictioncoefficientoftheslidingtypeisolationsystems.Thepost-yieldstiffnessoftheisolationsystem,kbisgenerallydesignedinsuchawaytoprovidethespecificvalueoftheisolationperiod,Tbexpressedas:whereM＝（＋）isthetotalmassofthebase-isolatedstructure;andmjisthemassofjthfloorofthesuperstructure.Thus,thebi-linearhystereticmodelofthebaseisolationsystemcanbecharacterizedbyspecifyingthethreeparametersnamelyTb,Qandq.Thecharacteristicstrength,Qisnormalizedbytheweightofthebuilding,W=Mg(wheregisthegravitationalacceleration3.2.Equivalentlinearelastic–viscousdampingmodelofisolatorsAsperUniformBuildingCode[8]andInternationalBuildingCode[9],thenon-linearforce-deformationcharacteristicoftheisolatorcanbereplacedbyanequivalentlinearmodelthrougheffectiveelasticstiffnessandeffectiveviscousdamping.Thelinearforcedevelopedintheisolationsystemcanbeexpressedas:whereistheeffectivestiffness;c＝2istheeffectiveviscousdampingconstant;istheeffectiveviscousdampingratio;＝2=Teffistheeffectiveisolationfrequency;andT＝2istheeffectiveisolationperiod.Theequivalentlinearelasticstiffnessforeachcycleofloadingiscalculatedfromexperimentallyobtainedforce-deformationcurveoftheisolatorandexpressedmathematicallyas:whereF+andF_arethepositiveandnegativeforcesattestdisplacementsD+andD–,respectively.Thus,thekeffistheslopeofthepeak-to-peakvaluesofthehysteresisloopasshowninFig.1(c).TheeffectiveviscousdampingoftheisolatorunitcalculatedforeachcycleofloadingisspecifiedaswhereEistheenergydissipationpercycleofloading.Ataspecifieddesignisolationdisplacement,D,theeffectivestiffnessanddampingratioforabi-linearsystemareexpressedas:4.SolutionofequationsofmotionClassicalmodalsuperpositiontechniquecannotbeemployedinthesolutionofequationsofmotionherebecause(i)thesystemisnon-classicallydampedbecauseofthedifferenceinthedampinginisolationsystemcomparedtothedampinginthesuperstructureand(ii)theforce-deformationbehaviorfortheisolationsystemsconsideredisnon-linear.Therefore,theequationsofmotionaresolvednumericallyusingNewmark’smethodofstep-by-stepintegration;adoptinglinearvariationofaccelerationoverasmalltimeintervalofDt.Thetimeintervalforsolvingthequationsofmotionistakenas0.02/200s(i.e.=0:0001s).5.NumericalstudySeismicresponseofamulti-storybase-isolatedbuildingisinvestigatedundervariousrealearthquakegroundmotionsforbi-linearandequivalentlinearisolatorcharacteristics.TheearthquakemotionsselectedforthestudyareN00Ecomponentof1989LomaPrietaearthquakerecordedatLosGatosPresentationCenter,N90Scomponentof1994NorthridgeearthquakerecordedatSylmarStationandN00Scomponentof1995KobeearthquakerecordedatJMA.Thepeakgroundacceleration(PGA)ofLomaPrieta,NorthridgeandKobeearthquakemotionsare0.57,0.60and0.86g,respectively.Thedisplacementandaccelerationspectraoftheabovegroundmotionsfor2%ofthecriticaldampingareshowninFig.2.Themaximumordinatesofthepseudo-accelerationare3.559,1.969and3.606goccurringatperiodof0.64,0.52and0.36sforLomaPrieta,NorthridgeandKobeearthquakes,respectively.Thisimpliesthattheselectedgroundmotionsarerecordedonstationshavingfirmsoilorrockyterrain.Theresponsequantitiesofinterestarethetopfloorabsoluteaccelerationandrelativebearingdisplacement.Theaboveresponsequantitiesareofimportancebecauseflooraccelerationsdevelopedinthesuperstructureareproportionaltotheforcesexertedbecauseofearthquakegroundmotion.Ontheotherhand,thebearingdisplacementsarecrucialinthedesignofisolationsystems.Forthepresentstudy,themassmatrixofthesuperstructure[Ms]isadiagonalmatrixandcharacterizedbythemassofeachfloor,whichiskeptconstant.Further,thebaseraftoftheisolatedstructureisconsideredsuchthatthemassratio,mb/m=1.Thedampingmatrixofthesuperstructure,[Cs],isnotknownexplicitly.Itisconstructedbyassumingthemodaldampingratioineachmodeofvibrationforsuperstructure,whichiskeptconstant.Thedampingratioofthesuperstructure,ns,istakenas0.02andkeptconstantforallmodesofvibration.Theinter-storystiffnessofthesuperstructureisadjustedsuchthataspecifiedfundamentaltimeperiodofthesuperstructure,Tsisachieved.Thenumberofstoryinthesuperstructureisconsideredas1and5.Forthefive-storybuilding,theinter-storystiffnessk1,k2,k3,k4andk5aretakeninproportionof1,1.5,2,2.5and3,respectively.5.1.Comparisonofresponseforbi-linearandequivalentlinearmodelInthissection,acomparisonofearthquakeresponseofbase-isolatedstructureismadeforbi-linearandequivalentlinearmodelofisolationsystems.Thebilinearbehaviorisselectedinawaytorepresenttheforce-deformationbehaviorofthecommonlyusedisolationsystemssuchaselastomeric(i.e.lead–rubberbearings)andslidingsystems(i.e.frictionpendulumsystem).Theequivalentlinearbehaviorisconsideredbyselectingtheappropriatevaluesoftheeffectiveisolationtimeperiod,Teffandtheeffectiveviscousdamping,beff.Thedesigndisplacement,D,isconsideredasthemaximumisolatordisplacementofarigidsuperstructureisolatedbythelinearisolationsystemhavingtheparametersTeffandbeff.Fortheassumedvalueoftheyielddisplacement,q,dependinguponthetypeofisolationsystem,theparametersofthebi-linearhysteresislooparederivedsuchthatithasaneffectivetimeperiodasTeffanddampingratiobefffromEqs.(7)and(8),respectively,atthedesigndisplacementD.Thevaluesofdesigndisplacement,D,usedforsuchtransformationare53.61,34.06and32.58cmunderLomaPrieta,NorthridgeandKobeearthquakegroundmotions,respectively,obtainedfromequivalentlinearmodelwithT＝2sand=0.1.InFig.3,timevariationoftopfloorabsoluteaccelerationandbearingdisplacementofafive-storybuildingisplottedforlinearandbi-linearisolatormodelsunderLomaPrieta,1989earthquakemotion.Theparametersoftheequivalentlinearsystemconsideredare:T＝2sand=0.1.Forthebi-linearsystem,twovaluesofyielddisplacementi.e.0.0001cmand2.5cmareconsideredwhichcorrespondstofrictionpendulumsystemandlead–rubberbearingisolators,respectively.Thepeaksuperstructureaccelerationobtainedbybi-linearhystereticmodelare0.665and0.701gfortheyielddisplacementof2.5and10_4cm,respectively.Thecorrespondingpeaksuperstructureaccelerationobtainedfromtheequivalentlinearmodelis0.582g.Thisimpliesthatthetopflooraccelerationinabase-isolatedstructureisunderestimatedbytheequivalentlinearmodelascomparedtothatobtainedfromtheactualbi-linearhystereticmodel.Ontheotherhand,thepeakbearingdisplacementobtainedbythebi-linearhystereticmodelforthesamesystemis42.52and40.17cm,fortheyielddisplacementsof2.5and10_4cm,respectively,whereas,thatobtainedfromitsequivalentlinearmodelis53.06cm.Thisindicatesthatthebearingdisplacementinabaseisolatedstructureisoverestimatedbytheequivalentlinearmodelascomparedtothatobtainedfromthebi-linearhystereticmodel.Similartrendofcomparisonbetweenlinearandbi-linearmodelsisalsoobservedforNorthridge,1994andKobe,1995earthquakesmotionsasshowninFigs.4and5,respectively.Thus,itcanbeconcludedthattheequivalentlinearmodelunder-predictsthepeaksuperstructureaccelerationandover-predictsthebearingdisplacementascomparedtotheactualbi-linearhystereticmodel.Thecorrespondingforce-deformationdiagramsareshowninFig.6forequivalentlinearandbi-linearmodelsoftheisolationsystem.Fig.7showsthecomparisonofcorrespondingFFTamplitudespectra(forbothequivalentlinearandbilinearhystereticmodels)ofthetopflooraccelerationforfive-storynon-isolatedandisolatedstructuresunderdifferentearthquakemotions(referFigs.3–5forthetimehistoryoftopflooracceleration).ThereisasignificantdifferencebetweentheFFTspectraofthetopflooraccelerationobtainedfromtheequivalentlinearandbi-linearmodels.TheequivalentlinearmodelshowsthepeakofFourieramplitudeinthevicinityof0.5Hz(i.e.thiscorrespondstotheisolationfrequency)andinsignificantcontributionfromtheotherfrequencies.Ontheotherhand,forthebi-linearsystems,thereiscontributioninthesuperstructureaccelerationforwiderangingfrequenciesespeciallyfromthehigherfrequencies.Theseeffectsarefoundtobemorepronouncedforthebi-linearsystemwithlowisolatoryielddisplacement(i.e.q=0.001cmrepresentingslidingtypeisolationsystem).Thesehigherfrequencycontributionsinthesuperstructureaccelerationcanbedetrimentaltothesensitiveequipmentswithhighfrequencyplacedwithinthebase-isolatedstructures.Thus,thebaseisolationsystemswithverylowyielddisplacementtransmitmoreaccelerationinthesuperstructureassociatedwithhighfrequenciesandthisphenomenonisnotpredictedbytheequivalentlinearmodels.Thecomparisonofthepeakresponseoftheisolatedstructureforequivalentlinearandbi-linearmodelsisshowninTables1and2forsingleandfive-storystructure,respectively.Theresponseiscomparedfordifferentvaluesofeffectiveisolationtimeperiod(i.e.T＝2,2.5,3s),effectiveisolationdamping(i.e.=0.1.0:05,0.1)andisolatoryielddisplacement(i.e.q=0.001,2.5,5cm)underthreeearthquakemotions.Asobservedearlier,thepeaktopflooraccelerationforallearthquakegroundmotionsishigherforbi-linearmodelsincomparisontotheequivalentlinearforallcombinationsofsystemparameters.Thisconfirmsthatthesuperstructureaccelerationwillbeunderestimatedifthebi-linearforce-deformationcharacteristicoftheisolatorismodeledbyanequivalentlinearmodel.Ontheotherhand,thepeakbearingdisplacementspredictedbytheequivalentlinearmodelishigherthanthecorrespondingbi-linearhystereticmodel.InsomecasesunderKobe,1995earthquakemotion,thepeakbearingdisplacementsestimatedbytheequivalentlinearmodelarelessthanthebi-linearmodelforq=2:5and5cm.Thisisattributedduetothetypicalvariationofthespectraldisplacementofthisearthquakemotion,inwhichthepeakdisplacementdecreaseswiththeincreaseoftimeperiodintherangefrom1.5to3s(referFig.2).Thus,theequivalentlinearmodelofhystereticisolatorsystemover-predictsthepeakbearingdisplacements.5.2.EffectsofisolatoryielddisplacementInordertounderstandtheinfluenceoftheshapeofthebi-linearhysteresisloopoftheisolator,thevariationofpeaktopflooraccelerationandbearingdisplacementofafive-storystructureisplottedagainstyielddisplacement,qinFigs.8–10underLomaPrieta,1989,Northridge,1994andKobe,1995earthquakes,respectively.Theresponsesareshownforthreeisolatorcharacteristicstrengths(i.e.Q/W=0:05,0.075and0.1)andthreevaluesofisolationtimeperiodsbasedonthepost-yieldstiffness(i.e.Tb2,2.5and3s).Itisobservedthatwiththeincreaseintheisolatoryielddisplacementthetopflooraccelerationdecreasessubstantially.Ontheotherhand,thebearingdisplacementshowsmarginalincreasingtrendwiththeincreaseintheisolatoryielddisplacement.Thisimpliesthattheyielddisplacement(ortheshapeofthehysteresisloop)hassignificanteffectsontheresponseofthebaseisolatedstructure.Thissignificantinfluenceofyielddisplacementontheresponseofthebase-isolatedstructureisnotcapturedbyanequivalentlinearviscousmodelastheqhadnoeffectontheeffectivestiffnessandaverylittleeffectontheeffectivedampingforlargedesigndisplacement(referEqs.(7)and(8)).Further,itisalsoobservedfromFigs.8–10thatwiththeincreaseincharacteristicstrength,Q,thetopflooraccelerationincreasesandthebearingdisplacementdecreases.Thisisexpectedbecauseforhigherisolatorcharacteristicstrengths,theisolationsystemremainsmuchmoretimeintheelasticstatewhichproduceslessflexibilityinthestructuralsystemandtherebylessenergydissipation.Asaresult,thesuperstructureaccelerationincreasesandbearingdisplacementdecreaseswiththeincreaseoftheisolatorcharacteristicstrength.Thus,itcanbeconcludedthattheresponseofbase-isolatedstructureissignificantlyinfluencedbytheshapeandparametersofthebi-linearhysteresisloopoftheisolator.5.3.EffectsofsuperstructureflexibilityTheflexibilityinthebase-isolatedstructureismainlyconcentratedattheisolationlevel,asaresult,theresponseofbase-isolatedstructurecanbeinvestigatedbymodelingthesuperstructureasrigid[14–16].However,itwillbeinterestingtocomparetheseismicresponseofabase-isolatedstructurewithsuperstructure\odeledasrigidandflexibletostudytheinfluenceofthesuperstructureflexibility.Fig.11showsthevariationoftopflooraccelerationandbearingdisplacementofafive-storybase-isolatedstructureagainstthesuperstructurefundamentaltimeperiod,Ts.Theisolationsystemparametersconsideredareisolationperiod,T=2s,normalizedcharacteristicsstrength,Q/W=0:05anddifferentisolatoryielddisplacementvaluessuchasq10_4,2.4and5cm.Itisobservedthatthereissignificantdifferenceinthetopflooraccelerationobtainedwhensuperstructureisrigid(i.e.Ts=0s)andflexible(i.e.Ts>0).Thereissubstantialincreaseinthetopflooraccelerationasthefundamentaltimeperiodofsuperstructureincreases.Thisimpliesthatthesuperstructureaccelerationswillbeunder-estimatedifthesuperstructureflexibilityisignoredanditismodeledasarigidbody.Theincreaseinthesuperstructureaccelerationsisfoundtobemorepronouncedfortheisolationsystemwithlowvalueofyielddisplacement(i.e.slidingtypesystems).Ontheotherhand,thebearingdisplacementisnotmuchinfluencedwiththeincreaseinsuperstructureflexibility.SimilareffectsofthesuperstructureflexibilityaredepictedinFig.12wherethecorrespondingresponsesareshownforTb=3sunderdifferentearthquakemotions.Thus,theflexibilityofsuperstructureincreasesthesuperstructureaccelerationbutitdoesnothavesignificantinfluenceonthebearingdisplacements.6.ConclusionsInfluenceofisolatorcharacteristicparametersontheseismicresponseofmulti-storybase-isolatedstructuresisinvestigated.Acomparisonoftheresponseoftheisolatedstructureforequivalentlinearandbi-linearforce-deformationbehavioroftheisolatorismade.Inaddition,theeffectsoftheshapeofisolatorloopandsuperstructureflexibilityontheseismicresponseofthebase-isolatedstructurearealsoinvestigated.Fromthetrendsoftheresultsofthepresentstudy,followingconclusionsaredrawn1.Thecodespecifiedequivalentlinearelastic–viscousdampingmodelforabi-linearhystereticmodeloftheisolatorunder-predictsthesuperstructureaccelerationandover-predictsthebearingdisplacement.2.Thereisasignificantdifferenceinthefrequencycontentofsuperstructureaccelerationofbase-isolatedstructurepredictedbytheequivalentlinearandbi-linearisolatormodels.3.Theresponseofbase-isolatedstructureissignificantlyinfluencedbytheshapeandparametersofthebi-linearhysteresisloopoftheisolator.4.Thebaseisolationsystemwithverylowyielddisplacement(i.e.slidingtypeisolationsystems)transmitsmoreearthquakeaccelerationsintothesuperstructureassociatedwithhighfrequencies.Thisphenomenonisnotpredictedbytheequivalentlinearmodelsofanalysis.5.Theflexibilityofsuperstructureincreasesthesuperstructureacceleration.However,thebearingdisplacementsarenotmuchinfluencedbythesuperstructureflexibility.References[1]KellyJM.Aseismicbaseisolation:reviewandbibliography.SoilDynamicsandEarthquakeEngineering1986;13:202–16.[2]BuckleIG,MayesRL.Seismicisolationhistory,applicationandperformance—aworldreview.EarthquakeSpectra1990;6:161–202.[3]JangidRS,DattaTK.Seismicbehaviorofbaseisolatedbuilding:astate-of-the-art-review.StructuresandBuildings1995;110(2):186–203.[4]StantonJ,RoederC.Advantagesandlimitationsofseismicisolation.EarthquakeSpectra1991;2:301–22.[5]KellyJM.Baseisolation:li