Unit 9BridgesText Bridgestouchallourlives—everydaywearelikelytocrossorgounderabridge.Buthowmanyofusstoptoconsiderhowthebridgeworksandwhatsortofpeopledesignedandbuiltit. Therearethreepracticalrequirementsforasuccessfulbridge—firmfoundations,strongstructure,andeffectiveworking.Firmfoundationsareespeciallycriticalfortraditionalstructuressuchasarches.Indeedonceerected,archeswillstayinplaceforaverylongtimeaslongasthefoundationsdon’tmove.Allbridgesrequirestrongrobustandstablestructure.However,therealtestforasuccessfulbridgeiswhetheritworkseffectively.Bridgesstandupbecausethebasicstructuralcomponentsinteractandworkeffectivelywitheachother.Thefoundations,strength,andeffectivenessoftheaesthetic,social,andculturalaspectsofbridgesaremuchmoredifficulttocapturebutarenonethelessveryimportant. Bridgesareiconsforwholecities—thinkofNewYork’sBrooklynBridge,Sydney’sHarbourBridge,andBrunel’sCliftonBridgeinBristol.Witharecordedhistoryofabout5000years,Chinahasavastterritory,topographicallyhigherinthenorthwestandlowerinthesoutheast.Networkedwithrivers,Chinahasthewell-knownvalleysoftheYangtzeRiver,theYellowRiver,andthePearlRiver,whicharethecradleoftheChinesenationandculture.TextThroughouthistory,theChinesenationerectedthousandsofbridges,whichformanimportantpartofChineseculture. Allbridgesandotherstructures,includingthehumanbody,havewhatscientistscallanaturalfrequency—whenobjectsvibratefreely.BridgeswithspanssimilartotheLondonMillenniumBridgetypicallyvibratewithnaturalfrequenciesbetween0.5and1.0cyclespersecond.Ifwindorpedestriansapplyforcestothebridgeatthesamefrequencyasthenaturalfrequencythenresonanceoccursandthevibrationscanbecomeverylargeindeed.Whenwewalkacrossabridgewepushdownwitheachstepbutwealsopushoutwardsslightlyaswell.Thestructuralengineersdidextensivecalculationsandthoughtthattheyhadallthesepossiblesourcesofwobblecovered. Thelistofmaterialsfromwhichbridgesaremadeisactuallyquiteshort.Itincludestimber,masonry,concrete,iron,steel,andmorerecentlyaluminiumandplastics,butlittleelse.Bridgematerialsmustbestrongenoughforthejobtheywillbeaskedtodo,readilyavailable,andnottooexpensive.Ofcoursecombinationsofmaterialareused.Forexample,becauseconcreteisstrongwhensquashedbutweakwhenpulled,steelbarsareusedtoreinforceit.TextThe‘grammar’ofhowbridgesputtogetheraregenerallybasedoncombinationsoffoursub-structuraltypes—BATS—beams,arches,trusses,andsuspensions[1].Forexample,theGoldenGateBridgeisasuspensionbridgewitharoadwaydeckonastifftrussbeam.BeamBridges Simpleinstructure,convenienttofabricateanderect,easytomaintain,andwithlessconstructiontimeandlowcost,beamstructureshavefoundwideapplicationinshort-tomedium-spanbridges.In1937,overtheQiantangRiver,inthecityofHangzhou,arailway-highwaybipurposebridgewaserected,withatotallengthof1453m,thelongestspanbeing67m.Whencompleted,itwasaremarkablemilestoneofthebeambridgedesignedandbuiltbyChineseengineersthemselves.Reinforcedconcretebeamstructuresaremostcommonlyusedforshort-tomedium-spanbridges.ArepresentativemasterpieceistheRongRiverBridgecompletedin1964inthecityofNanning,thecapitalofGuangxiZhuangzuAutonomousRegion.Thebridge,withamainspanof55mandacrosssectionofathin-walledboxwithcontinuouscells,designedinaccordancewithclosedthinwalledmembertheory,isthefirstofitskindinChina.Prestressedconcretebeambridgesareanewtypeofstructure.Chinabegantoresearchanddeveloptheirconstructioninthe1950s.TextTheextensiveconstructionofcontinuousbeambridgeshasledtotheapplicationoftheincrementallaunchingmethodespeciallytostraightandplanecurvedbridges[2].Inaddition,largecapacity(500t)floatingcraneinstallationandmovableslipformsaswellasspanerectionschemeshavealsoattainedremarkableadvancement.ArchBridges OfalltypesofbridgesinChina,thearchbridgetakestheleadingroleinvarietyandmagnitude.Statisticsfromallthesourcesavailableshowthatcloseto60%ofhighwaybridgesarearchbridges.Chinaisrenownedforitsmountainswithanabundantsupplyofstone.Stonehasbeenusedasthemainconstructionmaterialforarchbridges.MostofthearchesusedinChinafallintothefollowingcategories:boxarch,two-waycurvedarch,ribbedarch,trussedarch,andrigidframedarch.Themajorityofthesestructuresaredeckbridgeswithwideclearance,anditcostslesstobuildsuchbridges.Theboxarchisespeciallysuitableforlong-spanbridges.ThelongeststonearcheverbuiltinChinaistheWuRiverBridgeinBeiling,SichuanProvince,whosespanisaslongas120m.TheWanxianYangtzeRiverBridgeinWanxian,SichuanProvincewithaspectacularspanof420msetaworldrecordintheconcretearchliterature.TextAuniqueandsuccessfulimprovementofthereinforcedconcretearch,thetwo-waycurvedarchstructure,whichoriginatedinWuxi,JiangsuProvince,hasfoundwideapplicationalloverthecountry,becauseofitsadvantagesofsavinglaborandfalsework.T-TypeandContinuousRigidFrameBridges TheprestressedconcreterigidT-framebridgewasprimarilydevelopedandbuiltinChinainthe1960s.Thiskindofstructureismostsuitabletobeerectedbybalancedcantileverconstructionprocess,eitherbycantileversegmentalconcretingwithsuspendedformworkorbycantilevererectionwithsegmentsofprecastconcrete[3].ThefirstexampleofcantilevererectionistheWeiRiverBridge(completedin1964)inWuling,HenanProvince,whiletheLiuRiverBridge(completedin1967)inLiuzhouinGuangxiZhuangzuAutonomousRegionisthefirstbycantilevercasting.TheYangtzeRiverHighwayBridgeatChongqing(completedin1980),havingamainspanof174m,isregardedasthelargestofthiskindatpresent.FromprestressedconcreterigidT-framebridgesweredevelopedmultipleprestressedconcretecontinuousbeamandcontinuousrigidframebridges,whichcanhavelongerspansandofferbettertrafficconditions.Amongothers,theLuoxiBridgeinGuangzhou,GuangdongProvince(completedin1988)featuresa180-mmainspan.TheHuangshiYangtzeRiverBridgeinHubeiProvincehasamainspanof245m.TextAndtheHumenContinuousRigidFrameBridgeinGuangdongProvince(completedin1997),whichhasa270-mmainspan,isregardedasthelargestofthiskindintheworld.Luoxibridge,thelongestprestressedconcretecontinuousrigidframebridgeinChina,spansPearlRiverinGuangzhou,GuangdongProvince.Itis1916.04mlongand15.5mwide.Themainbridgehasspansof65+125+180+110m,providinganavigationclearanceof34×120m.SteelBridges Steelstructuresareemployedprimarilyforrailwayandrailway–highwaybi-purposebridges.In1957,inthecityofWuhan,arailway–highwaybi-purposebridgewaserectedovertheYangtzeRiver,anothermilestoneinChina’sbridgeconstructionhistory.NanjingYangtzeRiverBridgeisahighwayandrailwaydouble-deckcontinuoussteeltrussbridgeinNanjing,JiangsuProvince.Ontheupperdecktherearefourlanesofhighwaytraffic,whichare15mwide,plustwosidewalksof2.25mwideeach,andonthelowerdecktwotracksforrailway.Themainbridgeis1576mlong.Ifapproachesaretakenintoaccount,thelengthoftherailwaybridgereaches6772mandthehighwaybridgeis4588mlong[4].TextCable-StayedBridges Cable-stayedbridges,likesuspensionbridges,areheldupbycables.However,inacable-stayedbridge,lesscableisrequiredandthetowersholdingthecablesareproportionatelyshorter.Thefirstknowncable-stayedbridgewasdesignedin1784byC.T.Loescher.Thelongestcable-stayedbridgeistheSutongBridgeovertheYangtzeRiverinChina.Fixedormovablebridges Mostbridgesarefixedbridges,meaningtheyhavenomovingpartsandstayinoneplaceuntiltheyfailoraredemolished.Temporarybridges,suchasBaileybridges,aredesignedtobeassembled,andtakenapart,transportedtoadifferentsite,andre-used.Theyareimportantinmilitaryengineering,andarealsousedtocarrytrafficwhileanoldbridgeisbeingrebuilt.Movablebridges

aredesignedtomoveoutofthewayofboatsorotherkindsoftraffic,whichwouldotherwisebetootalltofit.Thesearegenerallyelectricallypowered.SuspensionBridges Suspensionbridgesaresuspendedfromcables.Theearliestsuspensionbridgesweremadeofropesorvinescoveredwithpiecesofbamboo[5].Inmodernbridges,thecableshangfromtowersthatareattachedtocaissonsorcofferdams.Thecaissonsorcofferdamsareimplanteddeepintothefloorofalakeorriver.TextThelongestsuspensionbridgeintheworldisthe12,826feet(3,909m)AkashiKaikyoBridgeinJapan.Seesimplesuspensionbridge,stressedribbonbridge,underspannedsuspensionbridge,suspended-decksuspensionbridge,andself-anchoredsuspensionbridge. Allpreventivemaintenanceprojectsshouldconsiderappropriatewaystomaintainorenhancethecurrentlevelofsafetyandaccessibility.Isolatedorobviousdeficienciesshouldalwaysbeaddressed.Safetyenhancementssuchastheinstallationorupgradingofguardrailandendtreatments,installationorreplacementoftrafficsignsandpavementmarkings,removalorshieldingofroadsideobstacles,mitigationofedgedropoffs,theadditionofpavedorstabilizationofunpavedshoulders,orinstallationofmilledrumblestripsshouldbeencouragedandincludedinprojectswheretheyaredeterminedtobeacosteffectivewaytoimprovesafety.Timelypreventivemaintenanceandpreservationactivitiesarenecessarytoensureproperperformanceofthetransportationinfrastructure.Experiencehasshownthatwhenproperlyapplied,preventivemaintenanceisacost-effectivewayofextendingtheservicelifeofhighwayfacilitiesandthereforeiseligibleforFederal-aidfunding.Byusinglower-costsystempreservationmethods,thecountycanimprovesystemconditions,minimizeroadconstructionimpactsonthetravelingpublic,andbettermanagetheirresourcesneededforlong-termimprovementssuchasreconstructionorexpansion.NewWordsandPhrasesrobusta.強(qiáng)健的；粗野的；粗魯?shù)腸radlen.搖籃；發(fā)源地，發(fā)祥地pedestriann.行人；a.步行的，徒步的wobblev.搖晃；搖擺squashv.受擠壓；擠入fabricatev.制作，建筑；裝配，組合erectv.使豎立；建造；安裝incrementala.增加的；遞增的falseworkn.腳手架；臨時(shí)支架precasta.預(yù)制的；預(yù)澆鑄的milestonen.里程碑，劃時(shí)代的事件militarya.軍事的；軍人的；適于戰(zhàn)爭(zhēng)的navigationn.航行，航海，航運(yùn)proportionatelyadv.相稱地，成比例地vinen.藤本植物；攀緣植物implantv.嵌入；埋置，埋藏deficiencyn.缺陷，缺點(diǎn)；缺乏guardrailn.護(hù)欄；欄桿；[鐵路]護(hù)軌mitigationv.減輕；緩和；平靜eligiblea.合格的，合適的NewWordsandPhrasesnaturalfrequencyn.固有頻率LondonMillenniumBridgen.倫敦千禧橋GoldenGateBridgen.金門(mén)大橋beambridgen.梁橋archbridgen.拱橋continuousrigidframebridgen.連續(xù)剛構(gòu)橋cable-stayedbridgen.斜拉橋suspensionbridgen.懸索橋，吊橋Notes1.The‘grammar’ofhowbridgesputtogetheraregenerallybasedoncombinationsoffoursub-structuraltypes—BATS—beams,arches,trusses,andsuspensions. 橋梁成為一個(gè)整體的基本原理在于四種亞結(jié)構(gòu)類(lèi)型(BATS)的組合：梁、拱、桁架和懸架。2.Theextensiveconstructionofcontinuousbeambridgeshasledtotheapplicationoftheincrementallaunchingmethodespeciallytostraightandplanecurvedbridges. 連續(xù)梁橋的大型構(gòu)造導(dǎo)致了頂推法的應(yīng)用，該方法尤其適用于直線和平面彎橋。3.Thiskindofstructureismostsuitabletobeerectedbybalancedcantileverconstructionprocess,eitherbycantileversegmentalconcretingwithsuspendedformworkorbycantilevererectionwithsegmentsofprecastconcrete. 此類(lèi)結(jié)構(gòu)最適合采用平衡懸臂施工工藝豎起，或采用帶有懸吊式模板的懸臂分段式澆筑工藝或預(yù)制混凝土段懸臂梁架設(shè)工藝。4.Ifapproachesaretakenintoaccount,thelengthoftherailwaybridgereaches6772mandthehighwaybridgeis4588mlong. 如果考慮路徑，則鐵路橋的長(zhǎng)度達(dá)到6772m，公路橋長(zhǎng)度為4588m。5.Theearliestsuspensionbridgesweremadeofropesorvinescoveredwithpiecesofbamboo. 最早的懸索橋是由繩索或樹(shù)藤覆蓋以竹板構(gòu)成。Exercise（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）1.因?yàn)楣敖Y(jié)構(gòu)不一定要求材料具有抗拉強(qiáng)度，所以拱橋可以用磚或石塊建造。2.橫跨河流以很小的間距布置石堆作為橋墩，然后用平坦的石頭橫過(guò)相鄰的橋墩就建成連接兩岸的通道。3.Tobuildbridgepiers,workersneedawater-freeenvironmenttoexcavateordigthefoundations.Thisisachievedbyusingacaisson,ahollow,water--tightstructuremadeofconcrete,steel,orothermaterialthatcanbesunkintotheground.Whenbuildingabridgeoverariver,workerssinkacaissonfilledwithcompressedairintotheriveruntilitreachestheriverbottom.Theworkersthengointothecaissonanddigoutsoilfromtheriverbeduntiltheycometobedrock.Thecaisson,whic