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关于桥梁的英语简介

发布时间：2023-12-01 13:22:16 来源：文档文库

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BridgesBridgesareamongthemostimportant,andoftenthemostspectacular,ofallcivilengineeringworks.Theimposingbridgesthathavesurvivedfromancienttimesarearchedstructuresofheavymasonry,usuallystonedrbrick..Herodotus,thegreekhistorianofthefifthcenuryB.C.,howevermentionsawoodenbridgesacrosstheEuphratesRiveratBabylon.Inrome,thebridgeofFabricis,builtin62B.C.andnamedforitsengineer,stillcarriestrafficacrosstheataiberRiver,asdoestheSant′AngeloBridge,builtinabout136A.D.Bothofthesebridges,andmanyotherRomanbridges,haveaseriesofarchessupportedbyheavypiersthatextenddowntobedrock.Ancientsourcesalsomentionpontoonbridegs,usuallyinconnectionwithmilitaryoperation.Apontoonisahollowdrumthatcanfloat;aseriesofpontoonsanchoredtoariverbedcansupportaoadway.TheIncasofper-ColumbianPerubuiltremarkablesuspensionbridges,supportedbycablesofnaturalfibers,thatcrossedmanyofthedeepgorgesintheirmonutainouscountry.Thesuddenexpansionintransportationsystemsthatbeganinthaeighteenthcentury,andstillcontinuesinourownday,hasenormouslyincreaedtheneedforbridgesasapartofhighwaysandrailroad,Betterunderstandingoftheforcesthatareexertedonstructuresandtheimprovedmaterialsthatbecameavailableinthenineteenthcenturyhavemadeitpossibletobuildincreasinglylongerangstrongerbridges.Withtheabilitytospangreaterdistances,thedamlikeeffectofmasonryarchbridgeswithseveralheavypiersthat;blockheflowofastreamcanbelargelyeliminaed.Thesimplesttypeofspanisabeambridge,consistingofarigidbeambetweentwosupports.Todaymostsimplebeambridgesarestrengthenedbyatruss,whichisbasedonthetriangle.Diagonal
bamsthatextendbetweenthehorizontalandverticalbeamsgivesupportagainstbothcomperssionandtension.Manyearlytrussbridgeswerebuiltofwood;onethatwaseectedacrosstheSusquehannaRiverinPennslvaniain1815hadaspanof110meters.Ironandthensteelwerelaterusedintheconsructionoftrussbridges,stillfurtherincreasingtheirstength.Trussesarenotonlystrongbutalsolight,becauseallunnecessarymaterialhasbeeneliminatedintheirdesign.Anothertypeofbeambridgeisthecantilever,inwhichahorizontalbeamextendsbeyonditssupport.Cantileverbridges,liketusses,hadalsobeenbuiltbeforeironandsteelbecameavailable.Mostcantileverbridgeshavewoarmsoftrussstructurethatmeetorsupportasectionbetweenthem.Cantileversenabledbridges.Duringtheninteenthcentury,cantileverswerefrequentlyusedtobuildrailroadbridges.TheQuebecBridge,whichcrossestheSt.lawrenceRiverinCanada,isthelongestcantileverbridgeintheworld,withaspanof540meters.Itwascompletedin1917,anduntil1919itwasthelongestbridgeofanytypeintheworld.Athirdtypeofmoderbridgeishesteelarchbridge,whichcancarryaroadwayeitheraboveorbelowitsarchofsteelbeams.Anarchexertsstrongdownwardanddiagonalthrusts,sothepiersthatsupportitmustbeespeciallystrong.ProbablythemostfamoussteelarchbridgeistheSydenyHarborBridgeinAustralia,wihaspanof495meters.TheBayonneBidgebetweenNewJerseyandStatenIslandinNewYorkhasaspanonemeterlonger.Suspensionbridgesspanevenlongerdistancethanothertypesofbridge.ThelongestbridgeofanytypeistheVerrazano-NarrowsBridgeinNewYork,withaspanof1,280meters.Thedeckorroadwayofasuspensionbridgeissuspendedfromsteelcablesaresupportedbymassivetowers.Thefirstmodernsuspensionbridgesusedlinkedchainsmadeofwrougheiron.Someofthemsurvivedformanyyears,likeoneacrosstheDanubeRiverin

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