桥梁论文中英译文.docx

桥梁论文中英译文.docx

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桥梁论文中英译文

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附录A英文文献

Bridges

Bridgesaregreatsymbolsofmankind’sconquestofspace.ThesightofthecrimsontraceryoftheGoldenGateBridgeagainstasettingsuninthePacificOcean,ortheatchoftheGarabitBiaductsoaringtriumphantlyabovethedeepgorge.Fillsone’sheartwithwonderandadmirationfortheartoftheirbuilders[11].Theyaretheenduringexpressionsofmankind’sdeterminationtoremoveallbarriersinitspursuitofabetterandfreerworld.Theirdesignandbuildingschemesareconceivedindream-likebisions.Butvisionanddeterminationarenotenough.Allthephysicalforcesofnatureandgravitymustbeunderstoodwithmathematicalprecisionandsuchforceshavetoberesistedbymanipulatingtherightmaterialsintherightpattern.Thisrequiresboththeinspirationofanartistandtheskillofanartisan.

Scientificknowledgeaboutmaterialsandstructuralbehaviorhasexpandedtremendously,andcomputingtechniquesarenowwidelyavailabletomanipulatecomplextheoriesininnumerablewaysveryquickly.Engineershavevirtuallyrevolutionizedbridgedesignandconstructionmethodsinthepastdecade.Theadvancesapplytoshort-mediumandlong-spanbridges.

Forpermanentbridge，themostcommonlyusedmaterialsaresteelandconcrete.Bridgeofmanydifferenttypearebuiltwiththesematerials,usedsinglyorincombination.Timbermaybeusedfortemporaryabove-waterconstruction,fortheelementsofastructurethatliebelowthewaterline（particularlytimberpiles）,orforshort-spanbridgeslocatedonsecondaryroads.Afewshort-spanaluminumbridgeshavebeenbuiltintheUnitedStatesonanexperimentalbasis.

Theprincipalportionsofabridgemaybesaidtobethe“substructure”andthe“superstructure.”Thisdivisionisusedheresimplyforconvenience,sinceinmanybridgesthereisnocleardividinglintbetweenthetwo.

Commonelementsofthesubstructureareabutments（usuallyatthebridgeends）andpiers（betweentheabutments）.Piersandabutmentsoftenrestonseparatelyconstructedfoundationssuchasconcretespreadfootingsorgroupsofbearingpiles;thesefoundationsarepartofthesubstructure.Occasionallyabridgesubstructurecomprisesaseriesofpilebentsinwhichthepilesextendabovethewaterlineandaretoppedbyapilecapthat,inturn,supportsthemajorstructuralelementsofthesuperstructure.Suchbentsoftenareusedinarepetitivefashionaspartofalong,low,over-watercrossing.

Inrecentyears,thedividinglinesbetweenshort-mediumandlong-spanbridgehaveblurredsomewhat.Currently,spansof20to100ft（6.1to30.5m）areregardedasshortbymanydesigners,whohavedevelopedmanystandardizeddesignstohandlethesespanseconomically.Mediumspansrangeupto,per-haps,400ft（121.9m）inmodernbridgepractice,dependingontheorganizationinvolvedandthematerialsused.Longspansrangeupto4000ft（1219.2m）ormore,butaclearspanabove1000ft（304.8m）iscomparativelyrare.

IntheUnitedStates,highwaybridgesgenerallymustmeetloading,design,andconstructionrequirementsoftheAASHTOSpecification.ThedesignandconstructionofrailwaybridgesaregovernedbyprovisionsoftheAREAManualforRailwayEngineering.Designrequirementsforpedestriancrossingsandbridgesservingotherpurposesmaybeestablishedbylocalorregionalcodesandspecifications.ACICodeprovisionsareoftenincorporatedbyreference,andinmostcasesserveasmodelprovisionsforothergoverningdocuments.

Bridgespanstoabout100ftoftenconsistofpre-castintegral-deckunits.Theseunitsofferlowinitialcost,minimummaintenance,andfasteasyconstrction,withtrafficinterruption.Suchgirdersaregenerallypretensioned,theunitsareplacedsidebyside,andareoftenpost-tensionedlaterallyatintermediatediaphragmlacations,Afterwhichshearkeysbetweenadjacentunitsarefilledwithnon-shrinkingmortar.Forhighwayspans,anasphaltwearingsurfacemaybeapplieddirectlytothetopofthepre-castconcrete.Insomecases,acast-in-placeslabisplacedtoprovidecompositeaction.

Formedium-spanhighwaybridges,toabout120ft,AASHTOstandardIbeamsaregenerallyused.heareintendedforusewithacompositecast-in-placeroadwayslab.Suchgirdersoftencombinepre-tensioningofthepre-castmemberwithpost-tensioningofthecompositebeamafterthedeckisplaced.

Pre-castgirdersmaynotbeusedforspansmuchinexcessof120ftbecauseoftheproblemsoftransportinganderectinglarge,heavyunits.Ontheotherhand,thereisacleartrendtowardtheuseoflongerspansforbridges.Highwaysafetyisimprovedbyeliminatingcentralpiersandmovingouterpiersawayfromtheedgeofdividedhighways.Forelevatedurbanexpressways,longspansfacilitatea