桥梁设计外文翻译文献Word格式.docx

桥梁设计外文翻译文献Word格式.docx

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原文：

ABridgeForAllCenturies

Anextremelylong-andrecordsetting-mainspanwasdesignedforthesecondbridgetoacrossthePanamaCanalinordertomeettheowner’srequirementthatnopiersbeplacedinthewater.Becausenodisruptionofcanaltrafficwaspermittedatanytime,thecable-stayedbridgeofcast-in-placecancretewascarefullyconstructedusingthebalanced-cantilevermethod.

In1962,theBridgeofAmericas（PuentedelasAmerica）openedtotraffic,servingastheonlyfixedlinkacrossthePanamaCanal.Thebridgewasdesignedtocarry60,000vehiclesperdayonfourlanes,butithasbeenoperatingaboveitscapacityformanyyears.Toalleviatebottlenecksontheroutethatthebridgecarriesoverthecanal-thePan-AmericanHighway（Inter-AmericanHighway）-andpromotegrowthonthewesternsideofPanama,thecountry’sMinistryofPublicWorks（MinisteriodeObrasPublicas,orMOP）decidedtobuildanewhighwaysystermlinkingthenorthernpartofPanamaCity,ontheeasternsideofthecanal,tothetownofArraijan,locatedonthewesternsideofthecanal.TheCentennialBridge–namedtocommemorate100yearsofPanamanianindependence-hasnoebeenconstructedand,whenopend,willcarrysixlanesoftraffic.Thiscable-stayedbridgeofcast-in-placecancretefeaturesamainspanof420m,thelongestsuchspanforthistypeofbridgeintheWesternHemisphere.

In200theMOPinvitedinternationalbridgedesignfirmstocompeteforthedesignofthecrossing,requestingatwo-packageproposal:

onetechinical,theotherfinancial.AtotalofeightproposalswerereceivedbyDecember2000fromestablishedbridgedesignfirmsallovertheworld.Aftershort-listingthreefirmsonthebasisofthetechnicalmeritsoftheirproposals,theMOPselectedT.Y.LinInternational,ofSanFrancisco,topreparethebridgedesignandprovidefieldconstructionsupportbasedonthefirm’sfinancialpackage.

TheCentennialBridgedesigeprocesswasuniqueandaggressive,incorporatingconceptsfromthetraditionaldesign/build/bidmethod,thedesign/buildmethod,andthesa-calledfast-trackdesignprocess.Tocompletetheconstructionontime-thatis,withinjust27months-thedesignofthebridgewascarriedouttoalevelof30percentbeforeconstructionbiddingbegan,inDecember2001.Theselectedcontractor-theWiesbaden,Germany,officeofBilfingerBerger,AG-wasbroughtonboardimmediatelyafterbeingselectedbytheMOP,justaswouldbethecaseinafast-trackapproach.Thedesigeofthebridgewasthencompletedinconjunctionwithconstruction,aprocessthatidsimilantodesige/build.

Thedesignselectedbytheclientfeaturestwosingle-masttowers,eachsupportingtwosetsofstaycablesthataligninoneverticalplane.Concretewasusedtoconstructboththetowersandtheboxgirderdeck,aswellastheapproachstructures.

TheMOP,inconjunctionwiththePanamaCanalAuthority,establishedthefollowingrequirementsforthebridgedesign:

A420m,theminimumlengthforthemainspantoaccommodatetherecentlywidenedGaillardCut,anarrowportionofthecanalcrossingtheContinentalDividethatwasstraightenedandwidenedto275min2002;

Anavigationalenvelopeconsistingof80mofverticalclearanceand70mofhorizontalclearancetoaccommodatethesafepassageofacraneofWorldWar11vintage-agiftfromtheU.S.governmentthatisusedbythePanamaCanalAuthoritytomaintainthecanalgatesandfacilities;

Aroadwaywideenoughtocarrysixlanesoftraffic,threeineachdirection;

Adeckabletoaccommodatea1.5mwidepedestrianwalkway;

AdesignthatwouldadheretotheAmericanAssociationofStateHighwayandTransportationOfficialstandardfora100-yearservicelifeandofferHS-25truckloading;

Astructurethatcouldcarrytwo0.6mdianeterwaterlines;

Aconstructionmethodthatwouldnotcrossthecanalatanytimeorinterruptcanaloperationainanyway.

Becauseofthebridge’slongmainspanandthepotentialforstrongseismicactivityinthearea,nosinglebuildingcodecoveredallaspectsoftheproject.ThereforetheteamfromT.Y.LinInternationaldetermindedwhichportionsofseveralstandardbridgespecificationswereapplicableandwhichwerenot.Thefollowingdesigncodeswereusedindevelopingthedesigncriteriaforthebridge，itisstandardspecificationsforhighwaybridge,16thed,1996

Itwasparamountthatthetowersofthecable-stayedstructucturebeerectedonlandtoavoidpotentialshipcollisionandtheneedtoconstructexpensivedeepfoundationinwater.However,geologicalmapsandboringlogsproducedduringthepreliminarydesignphraserevealedthattheeastandwestbanksofthecanal,wherethetowersweretobelocated,featuredvastlydifferentgeologicalandsoilconditions.Ontheeastsideofthecanal,beneathshallowlayersofoverburdenthatrangsinconsistencyfromsofttohard,liesablockofbasaltrangingfrommediumhardtohardwithverycloselyspacedjoint.Theengineersdeterminedthatthebasaltwouldprovideacompetentplatformfortheconstructionofshallowfoundationfortower,piers,andapproachstructuresonthissideofbridge.Thewestside,however,featuredtheinfamousCucarachaFormation,whichisaheterogeneousconglomerateofclayshalewithinclusionsofsandstone,basalt,andashthatispronetolandslide.AsasudsurfacestratumtheCucarachaFormationisquitestable,butitquicklyerodeswhenexposedtotheelements.Theengineersdeterminedthatdeepfoundationswouldthereforebeneededforthewesternapproachstructure,thewesttower,andthewesternpiers.

Beforeadetaileddesignofthefoundationacouldbedeveloped,athoroughanalysisoftheseismichazardsatthesitewasrequired,Thedesignseismicloadfortheprojectwasdevelopedonthebasisofaprobabilisticseismichazardassessmentthatconsideredtheconditionsatthesite.Suchanassessmentestablishesthereturnperiodforagivenearthquakeandthecorrespondingintensityofgroundshakinginthehorizontaldirecttionintermsofanaccelerationresponsespectrum.ThePSHAdeterminedtwodominantseismicsources:

asubductionsourcezoneassociatedwiththeNorthPanamaDeformedBeltcapableofproducingaseimiceventasstrongas7.7MW,andtheRioGatunFault,capableofproducinganeventasstrongas6.5MW.

The7.7MWNPDBeventwasusedasthesafetyevluationearthquake,thatis,themaximumearthquakethatcouldstrikewithoutputtingthebridgeoutofservice.Thedamagetothebridgewouldbeminorbutwouldrequiresomeclosuresofthebridge.The6.5MWRioGatunFaulteventwasusedasthefoundationalevaluationearthquake,alower-leveltemblorthatwouldcauseminimaldamagetothebridgeandwouldnotrequireclosures.FortheFEEloadcase,theSEEloadingwasscaledbackbytwo-thirds.TheFEEisassumedtohaveapeakaccelerationof0.21gandareturnperiodof500years;

theprobabilitythatitwillbeexceededwithin50yearsis10pencentandwithin100years,18persent.TheSEEisassumedtohaveapeakaccelerationof1.33gandareturnperiodof2,500years;

theprobabilitythatitwillbeexceededwithin50yearsis2pencentandwithin100years,4persent.

Becauseofuncertaintyaboutthedirectionfromwhichtheseismicwaveswouldapproachthesite,asingleresponsespectrum-acurveshowingthemathematicallycomputedmaximumresponseofasetofsimpledampedharmonicoscillatorsofdifferentnaturalfrequenciestoaparticularearthquakegroundacceleration-wasusedtocharacterizemitionsintwomutuallyorthogonaldirectionsinthehorizontalplane.Toconductatime-historyanalysisofthebridge’smultiplesupports,asetofsyntheticmotionswiththreecomponents-longitudinal,transverse,andvertical-wasdevelopdusinganiterativetechnique.RecordedgroundmotionsfromanearthquakeinChilein1985wereusedas“seed”motionsforthesythesisprocess.

Atimedelayestimate-thatis,anestimateofthetimeitwouldtakeforthemotionsgeneratedbytheSEEandFEEearthquakestotravelfromonepointtothenext-wascreateusingtheassumedseismicwavevelocityandthedistancebetweenthepiersofthebridge.Usinganassumedwasvelocityofapproximately2.5km/s,adelayontheorderofhalfasecondtoasecondisappropriateforabridge1to2kmlong.

Soil-foundationinteractionstudieswereperformedtodeterminethestiffnessofthesoilandfoundationaswellastheseismicexcitationmeasurementthatwouldbeusedinthedynamicanalyses.Thestudieswereconductedbymeansofsoil-pilemodelsusinglinearandnonlinearsoillayeraofvaryingdepths.Theequivalentpilelengthsinthestudies-thatis,thelengthsrepresentingtheportionsofagivenpilethatwouldactuallybeaffectedbyagivenearthquake-inducedgroundmotion-rangedfrom2to10m.Insuchathree-dimensionalmodel,therearesixwaysinwhichthesoilcanresistthemovementofthelpilebecauseofitsstiffness:

thronghaxialforceinthethreedirectionsandthroughbendingmomentsinthreedirections.Becausethebridgesitecontainssomanylayersofvaryingsoiltypes,eachlayerhadtoberepresentedbyadifferentstiffnessmatrixandthenanalyzed.

Oncetheaboveanalyseswerecompleted,theT.Y.LinInternationalengineers-takingintoconsiderationtheprojectrequirementsdevelopedbytheowener-evaluatedseveraldifferentconcretecable-stayeddesigns.Anumberofstructuralsystemswereinvestigated,themainvariables,superstructurecrosssections,andthevaryingsupportconditionsdescribedabove.

Therequirementthattheevevationofthedeckbequitehighstronglyinfluencedthetowerconfiguration.Fortheproposeddeckelevationofmorethan80m,themosteconomicaltowershapesincludedsingle-anddual-masttowersaswellas“goalpost”towers-thatis,ad