A base isolation system for bridges subjected to s

EARTHQUAKEENGINEERINGANDSTRUCTURALDYNAMICSEarthquakeEngngStruct.Dyn.2002;31:1093–1112(DOI:10.1002/eqe.140)AbaseisolationsystemforbridgessubjectedtoseismicdisturbancesH.Kaplan1andA.Seireg1;2;∗;†1DepartmentofMechanicalEngineering;UniversityofWisconsin-Madison;1513UniversityAvenue;Madison;WI53706-1572;U.S.A.2UniversityofFlorida-Gainesville;Gainesville;FL32611-6300;U.S.A.SUMMARYThestudyreportedinthispaperinvestigatesthefeasibilityofdevelopinganactivebaseisolationsystemfortheprotectionofbridgessubjectedtoearthquakes.Theproposedsystemincorporatessphericalsup-ports,camsandspringswhichcanbeoptimallydesignedtominimizethetransmissibilityoftheseismicdisturbancestothebridge.Theconsideredexampleshowsthattheproposeddesignisimplementableandcanprovideanorderofmagnitudereductioninthemaximumstressresultingfromseismicwavesactingonthebridgeinthetransverseorlongitudinaldirection.Sincethesystemperformanceishighlydependentontherapidunlockingofthecamsintheeventofaseismicdisturbance,carefulconsiderationshouldbegiventothedesignofareliablecamreleasecontrol.Thiscanbeachievedbyspringloadingeachcamsuchthatitwouldbenormallyunlocked.Ahydraulicactuatorwouldbeusedtoforceittorotatetothelockingpositionunder
uidpressurewhichwouldbeconstantlymaintainedatthedesignlevelduringnormalconditions.Theactuatorwouldbeequippedwithaquickresponsereleasevalveforrapidlyreleasingthepressureandconsequentlyunlockingthecamassoonasanearthquakeisdetected.Copyright?2002JohnWiley&Sons,Ltd.KEYWORDS:baseisolationsystem;bridgeprotectionINTRODUCTIONBridgesareessentialforrailroadandhighwaytransportation.Whentheyarebuiltinseismicsensitiveregions,theirstructuraldesignrequiresspecialconsideration.Theseismicresponseanalysisandbaseisolationofbridgesarestudiedbymanyresearchers.Adisplacement-basedconventionalearthquakeresistantdesignofmulti-degree-of-freedombridgesystemswasin-vestigatedbyCalviandKingsley[1].Anexperimentalstudyutilizingafrictionalpendulumsystem(FPS)inbridgeseismicisolationwasinvestigatedbyTsopelasandConstantinou[2].Theisolationmechanismisinstalledbetweenthedeckandthepierandatgroundcon-∗Correspondenceto:A.Seireg,DepartmentofMechanicalEngineering,UniversityofWisconsin-Madison,1513UniversityAvenue,Madison,WI53706-1572,U.S.A.†E-mail:aaseireg@facsta.wisc.eduReceived30July2000Revised10April2001Copyright?2002JohnWiley&Sons,Ltd.Accepted21August20011094H.KAPLANANDA.SEIREGnections.Theirexperimentalresultsshowedthatthetransmittedinertiaforcesanddisplace-mentscanbesubstantiallyreducedbyincorporationoftheFPS.AnotherstudyusingtheFPSwasundertakenbyWangetal.[3].Athreespanbridgewasconsideredfortheanal-ysisoftheslidingsupportingstructuresunderharmonicandearthquakedisturbances.Theuseofthesteelrubbercomposite(highdampingrubber)bearingsinbridgesystemswasinvestigatedbyJankowskietal.[4].Anon-linearve-degree-of-freedombridgemodelwasconsideredinthetransverseandlongitudinaldirectionsunderdierentgroundexcitations.Theyfoundthatcollisionisacriticalfactorinthestructuralresponseespeciallyinthelongi-tudinaldirectionandthattheresponsedependsonthegapsizebetweenthesegments.ActivecontrolofbridgeswithahybridcontrolsystemunderseismicexcitationswasstudiedbyYangandYu[5].Theyshowedthattheuseofacombinationofactivecontrol(actuators)andpassiveisolationsystems(rubberbearingsorfrictionalslidingsystems)canbebenecialforbridgesunderstrongearthquakes.Twodierentcombinations(rubberandactuatorsandrubberandslidingmechanism)wereconsideredandacontinuousactiveslidingmodecontrolstrategywaspresentedfortheseismicresponseanalysis.SymansandKelly[6]investigatedthefuzzylogiccontrolofbridgestructuresusingintelligentsemi-activeseismicisolationsys-tems.Theirresultsshowthatbothpassiveandactiveisolationmechanismswithsupplementalenergydissipationdevicescanbeeectiveinreducingtheseismicresponseandthatintel-ligentsemi-activesystemscancontrolthemaximumdisplacementofthedecks.FadaliandEl-Zayyat[7]studiedthedisturbancerejectioncontrolofbridgesunderearthquakeexcita-tions.Thelongitudinalmotionwasanalysedforseismicresponse.Theirsimulationresultsshowthatthebridgedeckdisplacementscanbereducedtolessthan0:015mwiththeuseoflargecontrolforcesandthenaldesigncanbeselectedbasedonacompromisebetweenthemagnitudeofrequiredforcesanddisplacements.OthersignicantcontributionstothissubjectcanbefoundinReferences[8–17].SYSTEMMODELAgenerallumpedmassmodelofthebridgeconsideredinthisstudyisshowninFigure1.Thepiersareassumedtoberigidlyattachedtothegroundandthedecksareassumedtoberigidlypinnedtothepiers.Thedeckisalsoassumedtobefreetomoveinthelongitudinal(x)directionwithindenedlimitsatthebothends.Intheconsideredmodel,thesystemisrepresentedbylumpedmassesandthestinessmatrixisdeterminedbyusinganiteelementanalysis.Fortheinputdisturbancesthefollowingconsiderationsaremade:1.Theinputforcingfunctionisaspatialvariableatthegroundsupportlocationsdependingupongeologicalandgeometricalheterogeneities(soilfactor),nitevelocityofwavepropagationandwavesourcetype[8]aswellasconsideringthephasedierenceatthedierentpierlocations.Thelatterisevaluatedbyusingtherelationship:t=lcwhe