桥梁隧道英汉文翻译.docx

桥梁隧道英汉文翻译.docx

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桥梁隧道英汉文翻译

LONG-TERMDETERIORATIONOFHIGH

DAMPINGRUBBERBRIDGEBEARING

Inrecentyears,highdampingrubber（HDR）bridgebearingshavebecomewidelyusedbecauseoftheexcellentabilitytoprovidehighdampingaswellasflexibility.However,therearefewsystematicstudiesonthedeteriorationproblemsofHDRsduringtheirservicelife,andusuallythelong-termperformancewasnotconsideredinthedesignstage.Inthisresearch,throughacceleratedthermaloxidationtestsonHDRblocks,thepropertyvariationsinsidetheHDRbridgebearingareexamined.Adeteriorationpredictionmodelisdevelopedtoestimatethepropertyprofiles.ThenusingaconstitutivemodelandcarryingoutFEManalysis,thebehaviorofaHDRbridgebearingduringitslifespanisclarified.Adesignprocedureisproposedthattakesthelong-termperformanceinthesiteenvironmentintoconsideration.

KeyWords:

highdampingrubberbearing,thermaloxidation,deterioration,long-termperformance

1.INTRODUCTION

SinceHyogoken-NanbuearthquakethatoccurredonJanuary17th,1995,bridgebearingshavebeenwidelyadoptedinJapanasaneffectivemeanstoweakentheseveredamageofsteelandconcretepiersduetoanearthquake1）,2）.Rubberisfrequentlyappliedinbridgebearingsbecauseofitsspecialpropertiessuchashighelasticityandlargeelongationatfailure.However,naturalrubbercannotaffordsufficientdampingwhichisindispensabletoaseismicisolationsystem.Usuallyrubberbearingisusedtogetherwithsteelbars,leadplugs,orothertypesofdampingdevices.Inordertoaddenergydissipationtotheflexibilityexistinginlaminatedrubberbearings,intheearly1980’s,thedevelopmentinrubbertechnologyledtonewrubbercompounds,whichweretermedhighdampingrubber（HDR）.HDRmaterialpossessesbothflexibilityandhighdampingproperties.ThebridgebearingsmadeofHDRcannotonlyextendthenaturalperiodofthebridge,butalsoreducethedisplacementresponseofstructures3）.Moreover,becauseoftheinherenthighdampingcharacteristicsofHDR,thereisnoneedofadditionaldevicestoachievetherequiredlevelsofprotectionfromearthquakesformostapplications,sothattheseismicisolationsystembecomesmorecompact.

InthemanufactureprocessofHDR,naturalrubberisvulcanizedtogetherwithcarbonblack,plasticizer,oilandsoon.ConsequentlyHDRpossessesspecificcharacteristicssuchasmaximumstrain-dependencyofstressevolution,energyabsorbingpropertiesandhardeningproperties.Yuanetal.4）experimentallystudiedthedynamicbehaviorsofHDRbearing.Yoshidaetal.5）,6）developedamathematicalmodelofHDRmaterialsandproposedathree-dimensionalfiniteelementmodelingmethodologytosimulatethebehaviorsofaHDRbearingnumerically.Besides,aseriesofacceleratedexposuretestswereperformedbyItohetal.7）,8）onvariousrubbermaterialsincludingHDRtoinvestigatethedegradationeffectsofdifferentenvironmentalfactors.Itwasfoundthatthethermaloxidationisthemostpredominantdegradationfactoraffectingthe

HDRmaterial.Sinceoxygenisabletopermeateintotheinteriorofathickrubber,inthisresearchthedeteriorationofHDRbridgebearingsisassumedtobemainlycausedbythethermaloxidation.Forthepurposeofclarifyingthedeteriorationcharacteristicsofbridgerubberbearingsduringtheirlifespan,somebearingspracticallyinusewererecalledandtheirmechanicalpropertiesweretested9）～11）.However,becauseoftheirscatternatureandthelackofdata,thelong-termperformanceofHDRisnotveryclear.Duringthedesignprocess,usuallythebehaviorsofdeterioratedbridgerubberbearingsduringtheirlifespanarenotconsidered.

Inthepreviousresearch,Itohetal.12）,13）studiedthelong-termperformanceofnaturalrubber（NR）bridgebearings.ThroughacceleratedthermaloxidationtestscarriedoutonNRblocks,thedeteriorationcharacteristicsofboththeouterandtheinteriorregionswereexamined.Basedonthetestresults,apredictionmodelwasestablishedtoestimatethepropertyprofilesofthedeterioratedNRbridgebearing.ThenusingtheconstitutivelawproposedbyYoshida5）,finiteelementmodelwasbuiltandtheanalysiswasperformed,whichenabledthelong-termperformanceofNRbridgebearingtobepredicted.Therelationsamongpropertyvariation,temperature,agingtimeandbearingsizewerealsoinvestigated.

Inthisresearch,throughthesimilaracceleratedthermaloxidationtestsonHDRblocks,thedeteriorationcharacteristicsofHDRbridgebearingsarestudied,andtheirlong-termmechanicalperformanceisinvestigatedbytakingthesiteenvironmenttakenintoconsideration.TheHDRspecimensareprovidedbyTokaiRubberIndustries,Ltd.Itispossiblethatwhensufferedbyaging,theHDRfromothercompaniesmaybehavedifferentlyduetothedifferenceofchemicalcompound.ThedeteriorationcharacteristicsoftheHDRmaterialwithothercompoundingingredientsandadditiveswillbediscussedinthefuturestudy.

2.ACCELERATEDTHERMALOXIDATIONTESTS

Amongdifferentdegradationfactorssuchasoxidation,ultravioletradiation,ozone,temperature,acidandhumidity,itisfoundthatthermaloxidationchangestheHDRpropertiesmoregreatlythanotherfactors5）,resultinginanincreaseofHDR’sstiffnessandadecreasesofelongationatbreakaswellastensilestrength.Besides,forthickrubbers,itisobviousthatthesurfaceismoreeasilyaffectedbydeteriorationfactorsthantheinteriorbecauseofthediffusion-limitedoxidationeffect14）,15）.InordertounderstandthevariationofthematerialpropertiesinsideHDRbearings,acceleratedtestswereperformedusingrubberblocksfocusingonthemostsignificantdegradationfactor,thermaloxidation.Thetestmethodandresultsaredescribedasfollows.

2.1Acceleratedthermaloxidationtestmethod

FifteenHDRblocksweretested.Thedimensionis220×150×50mm（length×width×thickness）.ThespecimenswerekeptinaThermalAgingGeerOven.TheaccelerationtestconditionsarelistedinTable1.Thetemperatureswerekeptatthreeelevatedtemperatures,60℃,70℃,and80℃intheoven.Forthetestateachtemperature,theexperimentdurationweresetas5stages,withthemaximumof300days.ThesimilartestshavealreadybeenperformedonNR10）.Whentheagingtestwasfinished,HDRblockswereslicedintopieceswithathicknessof2mm.Fromeachslice,fourspecimenswithNo.3dumbbellshapewerecutout16）,asshowninFig.1.Thenumberofthespecimenswas1,500intotal.Thenthroughthetensiletestsonthesedumbbellspecimens,thestress-straincurveswereobtained,whichrepresentedtherubberpropertiesatthecorrespondingposition.

Inthisresearch,strainenergywaschosenforexaminationbecauseitcanexhibittheeffectofthermaloxidationmoreremarkablythanstressesatcertainstrains.Inthefollowingdescription,U100standsforthestrainenergycorrespondingtothestrainof100%,UBstandsforthestrainenergyuptothebreak,andM100standsforthestresscorrespondingtothestrainof100%.Similarly,U100profilestandsforthedistributionofU100insideHDRblocks,andpropertyprofilemeansthedistributionofthemechanicalpropertiessuchasstressescorrespondingtocertainstrains,elongationatbreak（EB）andtensilestrength（TS）.Asfortherubberbreakage,EBisfocusedon.Inaddition,U0andEB0standforU100andEBintheinitialstate,respectively.

2.2Testresultsandexaminations

TheprofilesofU100/U0andEB/EB0ateverytesttemperatureareillustratedinFig.2andFig.3,respectively.ThehorizontalaxisshowstherelativepositionwithregardtothethicknessofHDRblock.Thevalues0and1onthisaxiscorrespondtothesurfaceoftheblock.TheverticalaxisshowsthenormalizedchangeofU100withtheoriginalvalueregardedas1.0inFig.2,andshowsthenormalizedchangeofEBinFig.3.Inthesefigures,everypointrepresentsthemeanvalueoffourspecimensfromthesameslice.Becauseofthescatternatureofrubbermaterials,atanypositionfourspecimensaretestedinordertoimprovetheaccuracy.Sincetheoxidizedrubberinhibitstheingressofoxygen,andconsideringtheshapeoftherubberblock,thefourspecimensarecutoutintheareaofatleast25mm,ahalfoftheblockthickness,awayfromthearoundsurface.Thusthesespecimensonlyreflectthepropertyvariationsinthethicknessdirection.Thestandarddeviationofeveryfour-specimengroupisquitesmallandusuallylessthan5%ofthemeanvalue.

FromFig.2andFig.3,itcanbefoundthatattheearlieststageofthetest,thematerialpropertiesattheoutsidesurfacechangetogetherwiththeinteriorregions.Thepropertyvariationoftheinteriorregionsoonreachestheequilibriumstateandmaintainsstable.However,thepropertiesnearthesurfacekeepchangingoverthetime,andchangemostgreatlyatthesurface.

Fromthesurfacetotheinterior,thepropertiesvarylessandless,untiltoacertaindepth,whichiscalled“criticaldepth”.Thecriticaldepthisabout11.5mmfromtheblocksurfaceat60℃,8.5mmat70℃,and6mmunder80℃.FromtheresultsofthesametestsonNRblocks12）,itisfoundthatgenerallyHDRandNRhaveasimilartendencyofpropertyvariation.BothU100andEBprofilesdisplaythefeaturesofadiffusion-limitedoxidation.Initiallytheprofilesarerelativelyhomogeneous,butstrongheterogeneitydevelopswithaging.Thepropertiesintheouterregionchangemorethantheinteriorandkeepchangingoverthetime.However,unlikethecaseofNR,theinteriorregionofHDRblockexperiencesarapidincreaseandsoonreachestheequilibriumstate.Incontrast,theinteriorregionofNRblockdoesnotchangeatall.Inaddition,afterthesameagingtime,