《土木工程專業(yè)英語 第2版》 課件 Unit9 Passive Base Isolation with Merits and Demerits Analysis

Unit9PassiveBaseIsolationwithMeritsandDemeritsAnalysisEnglishforCivilEngineering——Teacher:Prof.ZhengLuE-mail:luzheng111@（SchoolofCivilEngineering,TONGJIUNIVERSITY）Unit9PassiveBaseIsolationwithMeritsandDemeritsAnalysis9.1Introduction引言9.2ConceptofBaseIsolation基礎(chǔ)隔震概念9.3BaseIsolationSystems基礎(chǔ)隔震體系9.3.1Elastomeric-basedSystems彈性體系9.3.2IsolationSystemsBasedonSliding滑移隔震體系9.3.3IsolationSystemsBasedonSlidingSpring-typeSystems滑移彈簧隔震體系9.3.4RockingSystems搖擺體系9.4MeritsandDemeritsAnalysis優(yōu)缺點(diǎn)9.4.1Merits優(yōu)點(diǎn)9.4.2Demerits缺點(diǎn)9.1Introduction

Theconventionalapproachtoseismic-resistantdesignistoincorporateadequatestrength,stiffnessandinelasticdeformationcapacityintothebuildingstructuresothatitcanwithstandinducedinertiaforces.Thiswaswiththepresumptionthatduringstronggroundmotion,wheneverinertiaforcesexceedtheirdesignearthquakelevels,thestructurewilldissipatethisexcessenergythroughdeformationsatpredefinedlocationsscatteredoverthestructuralframework.Itwasobservedthat,evenwithmembersdesignedforductility,thestructuresdidnotalwaysperformasdesired,whichcouldbebecauseofreasonssuchas:Strong-columnweak-beammechanismfailedtodevelopasaresultofstiffeningeffectofwallsbeingpresentCreationofshortcolumnsbecauseofchangesinwalllayout,introducedlaterPoorconcretingatjointsduetoreinforcementcongestion傳統(tǒng)抗震設(shè)計(jì)方法簡介seismic-resistant抗震；inertiaforces

慣性力；predefined預(yù)定9.1Introduction

Thefrequencyofvibrationoflow-to-medium-risebuildingsfallsintherangewhereearthquakeenergyishigh.Thishasoftenresultedinconsiderabledamagetosuchbuildingsduetotheenormousdestructivestrengthofanearthquake.Theprevailingearthquake-resistantdesignmethodstacitlyacceptthatduringamajorearthquake,structuraldamage,sometimessubstantialinmagnitude,isunavoidable.However,theextremelyhighcostofrepairingandrebuildingdamagedstructuresmotivateddesignerstore-lookattheconceptofincorporatingaflexiblemediumbetweengroundandthebuilding,whichwasfirstattemptedinitsrudimentaryform,overacenturyearlier.傳統(tǒng)抗震方法問題prevailing盛行的；tacitly

默許的；rudimentary初步的9.1Introduction

Theconceptofbaseisolationisquitesimple.Thesystemdecouplesthebuildingorstructurefromthehorizontalcomponentsofthegroundmotionbyinterposingstructuralelementswithlowhorizontalstiffnessbetweenthestructureandthefoundation.Thisgivesthestructureafundamentalfrequencythatismuchlowerthanbothitsfixed-basefrequencyandthepredominantfrequenciesofthegroundmotion.Thefirstdynamicmodeoftheisolatedstructureinvolvesdeformationonlyintheisolationsystem,thestructureabovebeingtoallintentsandpurposesrigid.Thehighermodesthatproducedeformationinthestructureareorthogonaltothefirstmodeand,consequently,tothegroundmotion.Thesehighermodesdonotparticipateinthemotion,sothatthehighenergyinthegroundmotionatthesehigherfrequenciescannotbetransmittedintothestructure.隔震概念簡述component分量；predominant主要的；orthogonal正交9.1Introduction

Theconceptofbaseisolationhasalsoprovidedarichsourceoftheoreticalwork,bothinthedynamicsoftheisolatedstructuralsystemandinthemechanicsoftheisolatorsthemselves.Thistheoreticalwork,widelypublishedinstructuralengineeringandearthquakeengineeringjournals,hasledtodesignguidelinesforisolatedstructuresanddesignrulesforisolators.Inparallelinthe1980s,effortsgotunderwaytodevelopcodesspecificallyapplicabletoseismicallyisolatedbuildingsandinduecourse,code

provisionswereintroducedcommencingwiththepublicationin1986of“TentativeSeismicIsolationDesignRequirements”bySeismologyCommitteeofStructuralEngineersAssociationofCalifornia(SEAOC).TheseguidelinesandtheirsubsequentrevisionsprovedtobetheprecursortotheintroductionofdesignguidelinesbyFederalEmergencyManagementAgency(FEMA)followedbythe“UniformBuildingCode”and“InternationalBuildingCode”.隔震規(guī)范歷史簡介provisions條款；commencing開始；precursor先驅(qū)9.2ConceptofBaseIsolation

Todiminishvulnerabilityofabuildingtodamageduringanearthquake,baseisolationhasemergedasaviablestructuraloption.Itisasophisticatedpracticalsolutiontoimproveseismicresponseofabuildingbyminimizingthestructuraldamage,whichwasearliertakentobeunavoidableduringstronggroundmotion.Becauseofthelowhorizontalstiffnessofthisdeformablemedium,italtersthefundamentalperiodofastiffstructuresuchthatitissignificantlyhigherthanthatofthehighenergyimpartinggroundmotions.Asaresult,foritsfundamentalmodeofvibration,thesuperstructureissubjectedtomuchlowerinertiaforceswithconsequentreduction(Fig.9-1)inbaseshear.基礎(chǔ)隔震原理簡介diminish減小；alters代替

；superstructure上部結(jié)構(gòu)9.2ConceptofBaseIsolation

Ontheflipside,ifthefoundingstratumissoft,thenthereisadistinctpossibilityoftheenhancedperiodduetobaseisolationbeingclosetotheperiodwhereanearthquakeislikelytohaveconsiderableenergy.Suchasituationcanleadtoanincreaseintheresponse.Thus,itcanbesaidthatbaseisolationisbestsuitedforbuildingswithahighnaturalfundamentalfrequency(Tlessthanabout1s)andpreferablythosesupportedonrockorstiffsoils.Reinforcedconcretemomentframedbuildingsuptoabout8–9storeysandthosewithshearwallsupto12–15storeysaresaidtobeidealcandidatesforbaseisolation.隔震適用范圍stratum層；candidates候選

；9.2ConceptofBaseIsolation

Ifaframedstructureweresupportedonhardstrata,itwoulddeformasinFig.9-2a.However,whensupportedonisolators,thelateraldisplacementinthefirstmodeisconcentratedatisolatorlevelwhilethesuperstructurebehavesalmostlikearigidbody.Asaresult,forbuildingssupportedonbaseisolators,thereislessneedtoprovideductileenergydissipatingregions(e.g.nearbeam-columnjoints)asinconventionalfixedbasedstructures.However,inviewoflimitedexperienceofsuchsystemsandasamatterofabundantprecaution,codesrecommendretentionofthepresentformofductiledetailing.Thisisalsotoobviatepossiblebrittlefailureunderamaximumcredibleearthquake(MCE)intheregionorearthquakeswithlongperiodenergyinputs.Inaddition,codesalsocallforrigoroustestingoftheproposedisolatorsandpeerreviewofthedesign,sinceitisanemergingtechnologyandfailureofanisolatorsystemcouldprovecatastrophic.隔震框架的變形precaution預(yù)防措施；retention保留；rigorous嚴(yán)格的9.2ConceptofBaseIsolation

Fig.9-2DisplacedMDOFsystem:(a)fixedbasedand(b)onisolators9.2ConceptofBaseIsolation

Isolatorsshouldbelocatedsuchthatthereisampleaccesstothemformaintenance,repairandreplacement,ifnecessary.Afulldiaphragmshouldbeemployedtodistributelateralloadsasuniformlyaspossibletotheisolators.Generally,isolatorscanbeplacedatthebottomofcolumnsatbasementslablevel.Thislocationhastheadvantagethatnospecialtreatmentisrequiredforelevatororservicelinesastheytraversethebearinglevel.Ontheotherhand,iftheyareplacedattopofbasement,thenelevatorshaftandinternalstaircaseandcladdingdetailsmayrequirespecialtreatmentbelowfirstfloorlevel.隔震支座布置位置ample充足；diaphragm隔板；traverse穿越；shaft井；cladding包層9.2ConceptofBaseIsolation

Isolatorsdosubstantiallyenhancethefundamentalperiodofastiffstructurebutattheexpenseofincreasedbuildingdisplacements.Thefirstmodedeformationoccursattheisolationlevelonly.Therealchallengewhiledesigningabaseisolatedstructureistheneedtocontroldisplacementsduringamajorearthquakewhilemaintaininggoodperformanceformoderatelevelearthquakes.Sincethesuperstructurewillfunctionessentiallyaslinearlyelastic,thestructuralframeworkisexpectedtoremainundamagedevenduringamoderate-levelearthquake.隔震支座布置位置essentially理想中的；moderate-level中級的；9.3BaseIsolationSystems

Baseisolationisnowamaturetechnologyandisusedinmanycountries,andthereareanumberofacceptableisolationsystems,theconstructionofwhichiswellunderstood.Nevertheless,theconceptappearstohaveanirresistibleattractiontoinventors,andmanynewanddifferentsystemsofisolatorsareproposedandpatentedeachyear.Manyofthesenewsystemswillprovetobeimpracticalandsomemightactuallybelethal,butthenumbercontinuestoincreaseyearbyyear.Mostsystemsusedtodayincorporateeitherelastomericbearings,withtheelastomerbeingeithernaturalrubberorneoprene,orslidingbearings,withtheslidingsurfacebeingTeflonandstainlesssteel(althoughotherslidingsurfaceshavebeenused).Systemsthatcombineelastomericbearingsandslidingbearingshavealsobeenproposedandimplemented.隔震支座類型irresistible不可抗拒的；neoprene氯丁橡膠Teflon特氟龍；

9.3BaseIsolationSystems

Naturalrubberbearingswerefirstusedfortheearthquakeprotectionofbuildingsin1969forthePestalozziSchoolinSkopje,Macedonia.Thebearingsarelargerubberblockswithoutthesteelreinforcingplatesusedtodayandcompressbyabout25%undertheweightofthebuilding.Thebearingshaveaverticalstiffnessthatisonlyafewtimesthehorizontalstiffnessandtherubberisrelativelyundamped.ThissystemwastestedontheshaketableattheEERCin1982.Characteristicofisolationsystemsofthiskind,thehorizontalmotionisstronglycoupledtoarockingmotion,sothatpurelyhorizontalgroundmotioninducesverticalaccelerationsintherockingmode.Thesystemalsohasfoam-glassblocksoneithersideofarubberbearingthatareintendedtoactasfusestopreventmovementinthebuildingunderwind,internalfoottraffic,orlowseismicinput.Thesystemisstillinplaceandismonitoredfromtimetotime.彈性體系簡述EERC地震工程研究所；foam-glass泡沫玻璃；

9.3BaseIsolationSystems

Low-dampingnaturalrubberbearingsandsyntheticrubberbearingshavebeenwidelyusedinJapaninconjunctionwithsupplementarydampingdevices,suchasviscousdampers,steelbars,leadbars,frictionaldevices,andsoon.TheelastomerusedinJapancomprisesnaturalrubber,whileinFranceneoprenehasbeenusedinseveralprojects.Theisolatorshavetwothicksteelendplatesandmanythinsteelshims,asshowninFig.9-3.Therubberisvulcanizedandbondedtothesteelinasingleoperationunderheatandpressureinamold.Thesteelshimspreventbulgingoftherubberandprovideahighverticalstiffnessbuthavenoeffectonthehorizontalstiffness,whichiscontrolledbythelowshearmodulusoftheelastomer.Thematerialbehaviorinshearisquitelinearuptoshearstrainsabove100%,withthedampingintherangeof2-3%ofcritical.Thematerialisnotsubjecttocreep,andthelong-termstabilityofthemodulusisgood.低阻尼天然橡膠支座簡介conjunction連合；endplates端板；creep蠕變

9.3BaseIsolationSystems

Thelead-plugbearingwasinventedinNewZealandin1975andhasbeenusedextensivelyinNewZealand,Japan,andtheUnitedStates.Lead-plugbearingsarelaminatedrubberbearingssimilartolow-dampingrubberbearingsbutcontainoneormoreleadplugsthatareinsertedintoholes,asshowninFig.9-4.Thesteelplatesinthebearingforcetheleadplugtodeforminshear.Theleadinthebearingdeformsphysicallyataflowstressofaround10MPa(1500psi),providingthebearingwithabilinearresponse.Theleadmustfittightlyintheelastomericbearing,andthisisachievedbymakingtheleadplugslightlylargerthantheholeandforcingitin.Becausetheeffectivestiffnessandeffectivedampingofthelead-plugbearingisdependentonthedisplacement,itisimportanttostatethedisplacementatwhichaspecificdampingvalueisrequired.Lead-plugbearingshavebeenextensivelytestedinNewZealand,andthereareverycompleteguidelinesontheirdesignandmodeling.鉛芯橡膠支座簡介insert插入；bilinear雙線性；

9.3BaseIsolationSystems

Fig.9-4Lead-plugisolator.9.3BaseIsolationSystems

Thedevelopmentofanaturalrubbercompoundwithenoughinherentdampingtoeliminatetheneedforsupplementarydampingelementswasachievedin1982bytheMalaysianRubberProducers’ResearchAssociation(MRPRA)oftheUnitedKingdom.Thedampingisincreasedbyaddingextrafinecarbonblock,oilsorresins,andotherproprietaryfillers.Thedampingisincreasedtolevelsbetween10and20%at100%shearstrains,withthelowerlevelscorrespondingtolowhardness(50-55durometer)andashearmodulusaround0.34MPa(50psi)andthehighlevelstohighhardness(70-75durometer)andahighshearmodulus11.40MPa(200psi).Themethodsofvulcanization,bonding,andconstructionoftheisolatorsareunchanged.高阻尼橡膠支座簡介extrafine超等；resins樹脂；durometer

硬度9.3BaseIsolationSystems

Thematerialisnonlinearatshearstrainslessthan20%(Fig.9-5)andischaracterizedbyhigherstiffnessanddamping,whichtendstominimizeresponseunderwindloadandlow-levelseismicload.Overtherangeof20-120%shearstrain,themodulusislowandconstant.Atlargestrainsthemodulusincreasesduetoastraincrystallizationprocessintherubberthatisaccompaniedbyanincreaseintheenergydissipation.Thisincreaseinstiffnessanddampingatlargestrainscanbeexploitedtoproduceasystemthatisstiffforsmallinput,isfairlylinearandflexibleatdesignlevelinput,andcanlimitdisplacementsunderunanticipatedinputlevelsthatexceeddesignlevels.摩擦滑移支座簡介crystallization晶化；exploit利用；9.3BaseIsolationSystems

Thedampingintheisolatorsisneitherviscousnorhysteretic,butsomewhatinbetween.Inapurelylinearviscouselementtheenergydissipationisquadraticinthedisplacement;inahystereticsystemittendstobelinearindisplacement.TestsonalargenumberofdifferentrubberisolatorsattheEERC(Fig.9-6)demonstratethattheenergydissipatedpercycleisproportionaltothedisplacementaroundthevalueofpower1.5.Thischaracteristiccanbeexploitedsothatitispossibletomodelthebearingresponse,whichcombineslinearviscousandelastic-plasticelements.高阻尼橡膠支座簡介hysteretic滯變；proportional成比例的；power冪，乘方；9.3BaseIsolationSystems

Apurelyslidingsystemistheearliestandsimplestisolationsystemtobeproposed.Asystemusingpureslidingwasproposedin1909byJohannesAveticanCalantarients,amedicaldoctorinEngland.Hesuggestedseparatingthestructurefromthefoundationbyalayeroftalc(shadedportioninFig.9-7).Asisevidentinhisdiagrams,Calantarientsclearlyunderstoodthattheisolationsystemreducedaccelerationsintheisolatedbuildingattheexpenseoflargerelativedisplacementsbetweenthebuildingandthefoundation,forhedesignedasetofingeniousconnectionsforutilities—inthosedaysrestrictedtogaslinesandsewagepipes—toaccommodatethesedisplacements.Infact,Calantarients’ssystemincorporatedalltheelementsnowconsiderednecessaryinabaseisolationsystem:amethodofdecouplingthebuildingandthefoundation,amethodwherebyutilitylinescanwithstandlargerelativedisplacements,andawindrestraintsystem.摩擦滑移支座歷史簡介separating

分開；talc滑石；ingenious巧妙的；9.3BaseIsolationSystems

Fig.9-7Calantarients’sbaseisolationsystemusingalayeroftalcastheisolatingmedium.9.3BaseIsolationSystems

Whenslidingisolatorsareprovided,thebuildingissupportedonsurfacesofstainlesssteelslidingagainstaverylowfrictionmaterialliketeflon.Thispermitstransmissionofshearforcesacrossisolatorinterfaceonlytotheextentoffrictionalresistancebetweenslidinglayers.Suchasystemisrelativelylessexpensiveandisidealforretrofitting.Itiseffectiveoverawiderangeoffrequenciesnormallyprevalentininputgroundmotions.Anotheradvantageisthatthemaximumtransmissibilityofaccelerationtothesuperstructureislimitedtothemaximumforcethatcangenerateatthefrictionalinterface.摩擦滑移支座優(yōu)點(diǎn)簡述retrofit翻新；prevalent廣泛的；transmissibility可傳遞性Inaslidingisolator,sincethefrictionalforcegeneratedisproportionaltotheweightitsupports,thecenterofmassandcenterofresistancenaturallycoincide.Asaresult,thesesystemsarelesssensitivetotorsionalcoupling.Manyvariationsofhisfundamentalsystemhavebeendeveloped,whichincludeaslidingsurfacewithvaryingcurvature,twocylindricalslidingsurfaceswithdifferentcurvatureswhichareplacedperpendiculartoeachother,etc.However,thesystemmostfrequentlyadoptedanddescribedhereinisanisolatorwithasinglesphericalslidingsurface.AschematicofsuchanisolatorisshowninFig.9-8.摩擦滑移支座簡介coincide一致；curvature曲率；perpendicular垂直的；schematic簡圖9.3BaseIsolationSystems

Fig.9-8Typicalslidingoscillator.9.3BaseIsolationSystems

Aconsiderableamountoftheoreticalanalysishasbeendoneonthedynamicsofstructuresonslidingsystemssubjectedtoharmonicinputortoearthquakeinput.Forexample,asarepresentationofabase-isolatedbuilding,WestermoandUdwadiastudiedtheperiodicresponseofalinearoscillatoronacoulombfrictionslidinginterface.Contrarytothegeneralperceptionthatfrictionwillalwaysreducetheresponse,theyfoundthattheresponsemaybelargerthanthatforthesamefixed-basemodelandthatthesingledegreeoffreedommodelhadsubharmonicresonancefrequenciesgeneratedbytheslidinginterface.TheresponseofasimilarmodeltoearthquakeinputwasstudiedbyMostagheletal.摩擦滑移支座理論發(fā)現(xiàn)harmonic諧波；

linearoscillator

線性振子；subharmonic垂直的；9.3BaseIsolationSystems

Theassumptionofcoulombfrictionisgenerallyusedinthesetheoreticalanalysesbutisunlikelytobeanaccuraterepresentationofrealbehavior.Themostcommonlyusedmaterialsforslidingbearingsareunfilledorfilledpolytetrafluoroethylene(PTFE,orTeflon)onstainlesssteel,andthefrictionalcharacteristicsofthissystemaredependentontemperature,velocityofinterfacemotion,degreeofwear,andcleanlinessofthesurface.MuchtestingworkhasbeendoneontheseaspectsofthemechanicalbehaviorofsuchslidingcomponentsandanextensivereviewwasdonebyCampbellandKong.摩擦滑移支座摩擦特新因素簡介polytetrafluoroethylene聚四氟乙烯9.3BaseIsolationSystems

Thissystemwasdevelopedintheearly1970sforapplicationtonuclearpowerplantfacilities.Theutilitydevelopedastandardnuclearpowerplantwiththesafetygradeequipmentqualifiedfor0.2gacceleration.Whenthestandardplantwastobelocatedatsitesofhigherseismicity,itwasisolatedtokeeptheequipmentaccelerationlevelsbelowthequalificationvalue.Thesystemcombineslaminatedneoprenebearings(essentiallystandardbridgebearingsmanufacturedtohigherqualitycontrolstandards)withlead-bronze

alloyincontactwithstainlesssteel,theslidingsurfacebeingmountedontopoftheelastomericbearing.Thecoefficientoffrictionoftheslidingsurfaceissupposedtobe0.2overtheservicelifeoftheisolator.Theneoprenepadhasaverylowdisplacementcapacity,probablynotmorethan±5.0cm(2in.).Whenthedisplacementsexceedthis,theslidingelementprovidestheneededmovement.Electricité-de-France系統(tǒng)簡介facilities設(shè)施；

lead-bronzealloy鉛銅合金；9.3BaseIsolationSystems

AcombinationelastomericandslidingsystemwasdevelopedandtestedontheshaketableattheEERC.Inthissystem,theinteriorcolumnsofthestructurewerecarriedonTeflononstainlesssteelslidingelementsandtheexteriorcolumnsonthelow-dampingnaturalrubberbearings.Theelastomericbearingsprovidedrecenteringcapabilityandcontrolledthetorsionofthestructurewhiletheslidingelementsprovideddamping.EERC組合系統(tǒng)簡介interior內(nèi)部的；

recenter回到中心位置；9.3BaseIsolationSystems

TheTASSsystemwasdevelopedbytheTAISEICorp.inJapan.Inthissystem,theentireverticalloadiscarriedonTeflon-stainlesssteelelements.Inaddition,laminatedneoprenebearingsthatcarrynoloadareusedtoproviderecenteringforces.TheTeflonslidingsurfacehasapressureofaround10MPa(1450psi),andthecoefficientfrictionrangesfrom0.05atslowslidingspeedstoaround0.15athigherspeeds.Thedisadvantagesofthissystemarethatbecausetheelastomericbearingscarrynoverticalload,theyexperiencetension,andthevelocitysensitivityoftheslidingsurfacemakesmodelingofthesystemquitedifficult.TASS系統(tǒng)簡介TAISEI大成；

tension拉力；9.3BaseIsolationSystems

Theresilient-frictionbaseisolation(R-FBI)bearingattemptstoovercometheproblemofthehighfrictioncoefficientofTeflononstainlesssteelathighvelocitiesbyusingmanyslidinginterfacesinasinglebearing.Thusthevelocitybetweenthetopandbottomofthebearingisdividedbythenumberoflayerssothatthevelocityateachfaceissmall,maintainingalowfrictioncoefficient(Fig.9-9).Inadditiontotheslidingelements,thereisacentralcoreofrubberthatcarriesnoverticalloadbutprovidesarestoringforce.Testsofthissystemfoundthattherubbercoredidnotpreventthedisplacementfrombeingconcentratedatasingleinterface;therefore,acentralsteelrodwasinsertedintherubbercorethatimprovedthedistributionofdisplacementamongtheslidinglayers.AshaketableexperimentaltestprogramusingR-FBIbearingsandafive-story,40-tonsteelframemodelwascarriedoutattheEERCin1988.自復(fù)位摩擦隔震系統(tǒng)簡介resilient自復(fù)位；

rod棍棒；9.3BaseIsolationSystems

Fig.9-9Resilient-frictionbaseisolationsystem.9.3BaseIsolationSystems

Thefrictionpendulumsystem(FPS)isafrictionalisolationsystemthatcombinesaslidingactionandarestoringforcebygeometry.TheFPSisolator,shownschematicallyinFig.9-10,hasanarticulatedsliderthatmovesonastainlesssteelsphericalsurface.Thesideofthearticulatedsliderincontactwiththesphericalsurfaceiscoatedwithalow-frictioncompositematerial.Theothersideofthesliderisalsospherical,coatedwithstainlesssteel,andsitsinasphericalcavity,alsocoatedwiththelow-frictioncompositematerial.Astheslidermovesoverthesphericalsurface,itcausesthesupportedmasstoriseandprovidestherestoringforceforthesystem.Frictionbetweenthearticulatedsliderandthesphericalsurfacegeneratesdampingintheisolators.Theeffectivestiffnessoftheisolatorandtheisolationperiodofthestructureiscontrolledbytheradiusofcurvatureoftheconcavesurface.摩擦擺系統(tǒng)簡介pendulum

自復(fù)位；

schematically要領(lǐng)的；articulate鉸接的9.3BaseIsolationSystems

Fig.9-10Schematicoffrictionpendulumsystem.9.3BaseIsolationSystems

TheGERBsystemforseismicisolationwasdevelopedoriginallyforthevibrationisolationofpowerplantturbinegeneratingequipment.Ituseslargehelicalsteelspringsthatareflexiblebothhorizontallyandvertically.Theverticalfrequencyisaround3-5timesthehorizontalfrequency.ThesteelspringsarecompletelywithoutdampingandthesystemisalwaysusedinconjunctionwiththeGERBviscodamper.Asinallthree-dimensionalsystems,thereisverystrongcouplingbetweenhorizontalmotionandrockingmotionbecausethecenterofgravityoftheisolatedstructureisabovethecenterofstiffnessoftheisolationsystem.Thistypeofsystembecomespracticalinsituationswherethecenterofgravityandthecenterofstiffnessareatthesamelevel—inareactorvesselinanuclearpowerplant,forexample.滑移彈簧隔震體系簡介pendulum

自復(fù)位；

schematically要領(lǐng)的；articulate鉸接的9.3BaseIsolationSystems

Tallslenderstructuresoftop-heavyconstructionwillinevitablydevelopoverturningmomentsthatwillproducetensionatthefoundationlevel.Itisextremelyexpensivetoprovidetensioncapacityinbuildingfoundationsusinganchorsindeepcaissons.Asanalternative,itispossibletoallowthecolumns—orpiersinthecaseofbridges—tostepoffthefoundation.Thisformofpartialisolationreducestheseismicloadsthroughoutthestructure,particularlythetensionforcesgeneratedincolumnsorpiers.ThedynamicsofthesteppingstructurearequitedifferentfromconventionalstructuresbuthavebeenextensivelystudiedboththeoreticallyandexperimentallyinshaketabletestsattheEERC.搖擺體系簡介inevitably

不可避免的；

caissons沉箱；9.4MeritsandDemeritsAnalysis

Becauseofitslowstiffness,useofanisolatorsystemleadstoanincreaseinthenaturalperiodofastructureascomparedtothatforafixedbasestructure.Thismovesthesystemawayfromtheperiodatwhichgroundmotioncontainssubstantialenergy.Thisresultsinlow