北京交通大學畢業(yè)設(shè)計（論文）外文翻譯第1頁Influenceofisolatorcharacteristicsontheresponseofbase-isolatedstructureVasantA.Matsaar1Z.S.JanidsAbstractTheinfluenceofisolatorcharacteristicsontheseismicresponseofmulti-storybase-isolatedstructureisinvestigated.Theisolatedbuildingismodeledasasheartypestructurewithlateraldegree-of-freedomateachfloor.Theisolatorsaremodeledbyusingtwodifferentmathematicalmodelsdepictedbybi-linearhystereticandequivalentlinearelastic-viscousbehaviors.ThecoupleddifferentialequationsofmotionfortheisolatedsystemarederivedandsolvedintheincrementalformusingNewmarksstep-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,whichisnowrecognizedasamatureandefficient北京交通大學畢業(yè)設(shè)計（論文）外文翻譯第2頁technology,canbeadoptedtoimprovetheseismicperformanceofstrategicallyimportantbuildingssuchasschools,hospitals,industrialstructuresetc.,inadditiontotheplaceswheresensitiveequipmentsareintendedtoprotectfromhazardouseffectsduringearthquake1-3.Basedontheextentofcontroltobeachievedovertheseismicresponse,thechoiceoftheisolationsystemvariesandthereuponitsdesignisdonetosuittherequirementsofuseofthestructure.Inseismicallybase-isolatedsystems,thesuperstructureisdecoupledfromtheearthquakegroundmotionbyintroducingaflexibleinterfacebetweenthefoundationandthebaseofstructure.Thereby,theisolationsystemshiftsthefundamentaltimeperiodofthestructuretoalargevalueand/ordissipatestheenergyindamping,limitingtheamountofforcethatcanbetransferredtothesuperstructuresuchthatinter-storydriftandflooraccelerationsarereduceddrastically.Thematchingoffundamentalfrequenciesofbase-isolatedstructuresandthepredominantfrequencycontentsofearthquakesisalsoconsequentlyavoided,leadingtoaflexiblestructuralsystemmoresuitablefromearthquakeresistanceviewpoint.Thetwomostcommontypesofbaseisolationsystemsadoptedinpracticeutilizeeitherrubberbearingsorslidingsystemsbetweenthefoundationandsuperstructureforthepurposeofisolationfromgroundmotionsinthebuildingsaswellasbridges.Itisveryessentialtounderstandthedifferentparametersaffectingtheresponseofbase-isolatedstructurewhenusedforseismicprotectionofthestructures.Especiallyincaseofthebase-isolatedstructures,thathousessensitiveequipments,determinationofaccelerationimpartedandassociatedpeakdisplacementarethekeyissuesforthedesignengineer4.Moreover,thepoundingandstructuralimpactsincaseofbaseisolatedstructuresmadeupontheadjacentstructures,whenseparationgapdistancesareinadequate,becomeamajorconcernbecausethesephenomenamayleadtocatastrophicfailuresleadingtoimmenseisolatordamage.Suchfailuresanddamagescanbeavoidedbyproperlyestimatingthepeakisolatordisplacementandrecommendationofappropriateisolationgapdistances.Inordertopredictpeakdisplacementanddetermineaccurateseparationgapdistancerequirementforabase-isolatedstructure,itismandatorytoknow,inprior,thedifferentparametersthataffectthebearingdisplacementanditsconsequenteffectonthesuperstructureacceleration.Thefailuresduetosuchimpactscanbeavoidedbyreducingthepeakbearingdisplacementbycompromisingwithincreasein北京交通大學畢業(yè)設(shè)計（論文）外文翻譯第3頁superstructureaccelerationtoanacceptableleveli.e.tolerablereductionineffectivenessofisolation.Selectionofdifferentparameterscharacterizinganisolationsystemisimportantinviewofkeepingacontroloverresponsequantitiesespeciallytheexcessivebearingdisplacementatisolatorlevel.Thebehaviorofisolationsystemsandthebaseisolatedstructuresisnowwellestablishedandcodesaredevelopedfordesigningthebase-isolatedstructures59.Fornon-linearisolationsystems,thecodesallowtousetheequivalentlinearmodeltopermittheuseofresponsespectrummethodfordesigningtheisolatedstructures.Theequivalentlinearmodelsarebasedontheeffectivestiffnessatthedesigndisplacementandtheequivalentviscousdampingisevaluatedfromtheareaofthehysteresisloop.Thecomparisonofequivalentlinearandactualnon-linearmodelfortheresponseofisolatedbridgestructureshadbeendemonstratedinthepast1013andshownthattheequivalentlinearmodelcanbeusedforpredictingtheactualnon-linearresponseofthesystem.However,theabovestudieswererestrictedtothebridgeidealizedasarigidbodyandthenon-linearbehavioroftheisolatorwaslimitedtotheleadrubberbearingsidealizedbybi-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-isolated北京交通大學畢業(yè)設(shè)計（論文）外文翻譯第4頁buildingconsideredforthepresentstudy.Thebase-isolatedbuildingismodeledasasheartypestructuremountedonisolationsystemswithonelateraldegree-of-freedomateachfloor.Followingassumptionsaremadeforthestructuralsystemunderconsideration:1.Thesuperstructureisconsideredtoremainwithintheelasticlimitduringtheearthquakeexcitation.Thisisareasonableassumptionastheisolationattemptstoreducetheearthquakeresponseinsuchawaythatthestructureremainswithintheelasticrange.2.Thefloorsareassumedrigidinitsownplaneandthemassissupposedtobelumpedateachfloorlevel.3.Thecolumnsareinextensibleandweightlessprovidingthelateralstiffness.4.Thesystemissubjectedtosinglehorizontalcomponentoftheearthquakegroundmotion.5.Theeffectsofsoilstructureinteractionarenottakenintoconsideration.Forthesystemunderconsideration,thegoverningequationsofmotionareobtainedb