1、Unit9BridgesTextBridgestouchallourliveseverydaywearelikelytocrossorgounderabridge.Buthowmanyofusstoptoconsiderhowthebridgeworksandwhatsortofpeopledesignedandbuiltit.There are three practical requirements for a successful bridgefirm foundations,strongstructure,andeffectiveworking.Firmfoundationsarees
2、peciallycriticalfortraditionalstructuressuchas arches.Indeed once erected,arches will stay in place for a very long time as long as thefoundationsdontmove.Allbridgesrequirestrongrobustandstablestructure.However,therealtestforasuccessfulbridgeiswhetheritworkseffectively.Bridgesstandupbecausethebasics
3、tructuralcomponents interact and work effectively with each other.The foundations,strength,andeffectiveness of the aesthetic,social,and cultural aspects of bridges are much more difficult tocapturebutarenonethelessveryimportant.BridgesareiconsforwholecitiesthinkofNewYorksBrooklynBridge,SydneysHarbou
4、rBridge,andBrunelsCliftonBridgeinBristol.Witharecordedhistoryofabout5000years,Chinahasavastterritory,topographicallyhigherinthenorthwestandlowerinthesoutheast.Networkedwithrivers,Chinahasthewell-knownvalleysoftheYangtzeRiver,theYellowRiver,andthePearlRiver,whicharethecradleoftheChinesenationandcultu
5、re.TextThroughouthistory,theChinesenationerectedthousandsofbridges,whichformanimportantpartofChineseculture.Allbridgesandotherstructures,includingthehumanbody,havewhatscientistscallanaturalfrequencywhenobjectsvibratefreely.BridgeswithspanssimilartotheLondonMillenniumBridgetypically vibrate with natu
6、ral frequencies between 0.5 and 1.0 cycles per second.If wind orpedestrians apply forces to the bridge at the same frequency as the natural frequency thenresonanceoccursandthevibrationscanbecomeverylargeindeed.Whenwewalkacrossabridgewepushdownwitheachstepbutwealsopushoutwardsslightlyaswell.Thestruct
7、uralengineersdidextensivecalculationsandthoughtthattheyhadallthesepossiblesourcesofwobblecovered.Thelistofmaterialsfromwhichbridgesaremadeisactuallyquiteshort.Itincludestimber,masonry,concrete,iron,steel,and more recently aluminium and plastics,but little else.Bridgematerialsmustbestrongenoughforthe
8、jobtheywillbeaskedtodo,readilyavailable,andnottooexpensive.Ofcoursecombinationsofmaterialareused.Forexample,becauseconcreteisstrongwhensquashedbutweakwhenpulled,steelbarsareusedtoreinforceit.TextThegrammarofhowbridgesputtogetheraregenerallybasedoncombinationsoffoursub-structuraltypesBATSbeams,arches
9、,trusses,andsuspensions1.Forexample,theGoldenGateBridgeisasuspensionbridgewitharoadwaydeckonastifftrussbeam.Beam BridgesSimpleinstructure,convenienttofabricateanderect,easytomaintain,andwithlessconstructiontimeandlowcost,beamstructureshavefoundwideapplication inshort-tomedium-span bridges.In1937,ove
10、rtheQiantangRiver,inthecityofHangzhou,arailway-highwaybipurposebridgewaserected,with a total length of 1453 m,the longest span being 67 m.When completed,it was a remarkablemilestoneofthebeambridgedesignedandbuiltbyChineseengineersthemselves.Reinforcedconcretebeam structures are most commonly used fo
11、r short-to medium-span bridges.A representativemasterpieceistheRongRiverBridgecompletedin1964inthecityofNanning,thecapitalofGuangxiZhuangzuAutonomousRegion.Thebridge,withamainspanof55mandacrosssectionofathin-walledboxwithcontinuouscells,designedinaccordancewithclosedthinwalledmembertheory,isthefirst
12、ofitskindinChina.Prestressedconcretebeambridgesareanewtypeofstructure.Chinabegantoresearchanddeveloptheirconstructioninthe1950s.TextThe extensive construction of continuous beam bridges has led to the application of the incrementallaunchingmethodespeciallytostraightandplanecurvedbridges2.Inaddition,
13、largecapacity(500t)floatingcraneinstallationandmovableslipformsaswellasspanerectionschemeshavealsoattainedremarkableadvancement.Arch BridgesOfalltypesofbridgesinChina,thearchbridgetakestheleadingroleinvarietyandmagnitude.Statisticsfromallthesourcesavailableshowthatcloseto60%ofhighwaybridgesarearchbr
14、idges.Chinais renowned for its mountains with an abundant supply of stone.Stone has been used as the mainconstructionmaterialforarchbridges.MostofthearchesusedinChinafallintothefollowingcategories:boxarch,two-waycurvedarch,ribbedarch,trussedarch,andrigidframedarch.Themajorityofthesestructuresaredeck
15、bridgeswithwideclearance,anditcostslesstobuildsuchbridges.Theboxarchisespeciallysuitableforlong-spanbridges.ThelongeststonearcheverbuiltinChinaistheWuRiverBridgeinBeiling,SichuanProvince,whosespanisaslongas120m.TheWanxianYangtzeRiverBridgeinWanxian,SichuanProvincewithaspectacularspanof420msetaworldr
16、ecordintheconcretearchliterature.TextAuniqueandsuccessfulimprovementofthereinforcedconcretearch,thetwo-waycurvedarchstructure,whichoriginatedinWuxi,JiangsuProvince,hasfoundwideapplicationalloverthecountry,becauseofitsadvantagesofsavinglaborandfalsework.T-Type and Continuous Rigid Frame BridgesThepre
17、stressedconcreterigidT-framebridgewasprimarilydevelopedandbuiltinChinainthe1960s.This kind of structure is most suitable to be erected by balanced cantilever construction process,either bycantileversegmentalconcretingwithsuspendedformworkorbycantilevererectionwithsegmentsofprecastconcrete3.Thefirste
18、xampleofcantilevererectionistheWeiRiverBridge(completedin1964)inWuling,HenanProvince,whiletheLiuRiverBridge(completedin1967)inLiuzhouinGuangxiZhuangzuAutonomousRegionisthefirstbycantilevercasting.TheYangtzeRiverHighwayBridgeatChongqing(completedin1980),havingamainspanof174m,isregardedasthelargestoft
19、hiskindatpresent.FromprestressedconcreterigidT-framebridgesweredevelopedmultipleprestressedconcretecontinuousbeamandcontinuousrigidframebridges,whichcanhavelongerspansandofferbettertrafficconditions.Amongothers,theLuoxiBridgeinGuangzhou,GuangdongProvince(completedin1988)featuresa180-mmainspan.TheHua
20、ngshiYangtzeRiverBridgeinHubeiProvincehasamainspanof245m.TextAndtheHumenContinuousRigidFrameBridgeinGuangdongProvince(completedin1997),whichhasa270-mmainspan,isregardedasthelargestofthiskindintheworld.Luoxibridge,thelongestprestressed concrete continuous rigid frame bridge in China,spans Pearl River
21、 in Guangzhou,GuangdongProvince.Itis1916.04mlongand15.5mwide.Themainbridgehasspansof65+125+180+110m,providinganavigationclearanceof34120m.Steel BridgesSteelstructuresareemployedprimarilyforrailwayandrailwayhighwaybi-purposebridges.In1957,inthecityofWuhan,arailwayhighwaybi-purposebridgewaserectedover
22、theYangtzeRiver,anothermilestoneinChinasbridgeconstructionhistory.NanjingYangtzeRiverBridgeisahighwayandrailwaydouble-deckcontinuoussteeltrussbridgeinNanjing,JiangsuProvince.Ontheupperdecktherearefourlanesofhighwaytraffic,whichare15mwide,plustwosidewalksof2.25mwide each,and on the lower deck two tra
23、cks for railway.The main bridge is 1576 m long.Ifapproachesaretakenintoaccount,thelengthoftherailwaybridgereaches6772mandthehighwaybridgeis4588mlong4.TextCable-Stayed BridgesCable-stayed bridges,like suspension bridges,are held up by cables.However,in a cable-stayedbridge,lesscableisrequiredandtheto
24、wersholdingthecablesareproportionatelyshorter.Thefirstknowncable-stayedbridgewasdesignedin1784byC.T.Loescher.Thelongestcable-stayedbridgeistheSutongBridgeovertheYangtzeRiverinChina.Fixed or movable bridgesMostbridgesarefixedbridges,meaningtheyhavenomovingpartsandstayinoneplaceuntiltheyfailoraredemol
25、ished.Temporarybridges,suchasBaileybridges,aredesignedtobeassembled,andtakenapart,transportedtoadifferentsite,andre-used.Theyareimportantinmilitaryengineering,andarealsousedtocarrytrafficwhileanoldbridgeisbeingrebuilt.Movablebridgesaredesignedtomoveoutofthewayofboatsorotherkindsoftraffic,whichwouldo
26、therwisebetootalltofit.Thesearegenerallyelectricallypowered.Suspension BridgesSuspensionbridgesaresuspendedfromcables.Theearliestsuspensionbridgesweremadeofropesorvinescoveredwithpiecesofbamboo5.Inmodernbridges,thecableshangfromtowersthatareattachedtocaissonsorcofferdams.Thecaissonsorcofferdamsareim
27、planteddeepintothefloorofalakeorriver.TextThelongestsuspensionbridgeintheworldisthe12,826feet(3,909m)AkashiKaikyoBridgeinJapan.Seesimplesuspensionbridge,stressedribbonbridge,underspannedsuspensionbridge,suspended-decksuspensionbridge,andself-anchoredsuspensionbridge.Allpreventivemaintenanceprojectss
28、houldconsiderappropriatewaystomaintainorenhancethecurrent level ofsafetyand accessibility.Isolated orobvious deficiencies should always beaddressed.Safetyenhancementssuchastheinstallationorupgradingofguardrailandendtreatments,installationorreplacementoftrafficsignsandpavementmarkings,removalorshield
29、ingofroadsideobstacles,mitigationofedgedropoffs,theadditionofpavedorstabilizationofunpavedshoulders,orinstallationofmilledrumblestripsshouldbeencouraged andincludedinprojectswheretheyaredeterminedtobeacosteffectivewaytoimprovesafety.Timelypreventivemaintenanceandpreservationactivitiesarenecessaryto
30、ensure proper performance of the transportation infrastructure.Experience has shown that whenproperlyapplied,preventivemaintenanceisacost-effectivewayofextendingtheservicelifeofhighwayfacilities and therefore is eligible for Federal-aid funding.By using lower-cost system preservationmethods,thecount
31、ycanimprovesystemconditions,minimizeroadconstructionimpactsonthetravelingpublic,andbettermanagetheirresourcesneededforlong-termimprovementssuchasreconstructionorexpansion.New Words and Phrasesrobust a.强健的；粗野的；粗鲁的cradle n.摇篮；发源地，发祥地pedestrian n.行人；a.步行的，徒步的wobble v.摇晃；摇摆squash v.受挤压；挤入fabricate v.制作，
32、建筑；装配，组合erect v.使竖立；建造；安装incremental a.增加的；递增的falsework n.脚手架；临时支架precast a.预制的；预浇铸的milestone n.里程碑，划时代的事件military a.军事的；军人的；适于战争的navigation n.航行，航海，航运proportionately adv.相称地，成比例地vine n.藤本植物；攀缘植物implant v.嵌入；埋置，埋藏deficiency n.缺陷，缺点；缺乏guardrail n.护栏；栏杆；铁路护轨mitigation v.减轻；缓和；平静eligible a.合格的，合适的New W
33、ords and Phrasesnatural frequency n.固有频率London Millennium Bridge n.伦敦千禧桥Golden Gate Bridge n.金门大桥beam bridge n.梁桥arch bridge n.拱桥continuous rigid frame bridge n.连续刚构桥cable-stayed bridge n.斜拉桥suspension bridge n.悬索桥，吊桥Notes1.Thegrammarofhowbridgesputtogetheraregenerallybasedoncombinationsoffoursub-st
34、ructuraltypesBATSbeams,arches,trusses,andsuspensions.桥梁成为一个整体的基本原理在于四种亚结构类型(BATS)的组合：梁、拱、桁架和悬架。2.Theextensiveconstructionofcontinuousbeambridgeshasledtotheapplicationoftheincrementallaunchingmethodespeciallytostraightandplanecurvedbridges.连续梁桥的大型构造导致了顶推法的应用，该方法尤其适用于直线和平面弯桥。3.Thiskindofstructureismos
35、tsuitabletobeerectedbybalancedcantileverconstructionprocess,eitherbycantileversegmentalconcretingwithsuspendedformworkorbycantilevererectionwithsegmentsofprecastconcrete.此类结构最适合采用平衡悬臂施工工艺竖起，或采用带有悬吊式模板的悬臂分段式浇筑工艺或预制混凝土段悬臂梁架设工艺。4.Ifapproachesaretakenintoaccount,thelengthoftherailwaybridgereaches6772man
36、dthehighwaybridgeis4588mlong.如果考虑路径，则铁路桥的长度达到6772m，公路桥长度为4588m。5.Theearliestsuspensionbridgesweremadeofropesorvinescoveredwithpiecesofbamboo.最早的悬索桥是由绳索或树藤覆盖以竹板构成。Exercise（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）1.因为拱结构不一定要求材料具有抗拉强度，所以拱桥可以用砖或石块建造。2.横跨河流以很小的间距布置石堆作为桥墩，然后用平坦的石头横过相邻
37、的桥墩就建成连接两岸的通道。3.Tobuildbridgepiers,workersneedawater-freeenvironmenttoexcavateordigthefoundations.Thisisachievedbyusingacaisson,ahollow,water-tightstructuremadeofconcrete,steel,orothermaterialthatcanbesunkintotheground.Whenbuildingabridgeoverariver,workerssinkacaissonfilledwithcompressedairintotheri
38、veruntilitreachestheriverbottom.Theworkersthengointothecaissonanddigoutsoilfromtheriverbeduntiltheycometobedrock.Thecaisson,whichhassharpbottomedges,continuallymovesdownwardduringthedigginguntilitcomestorestonbedrock.Concreteisthenpouredintothecaissontoformthelowestsectionofthenewbridgepier.Exercise
39、（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）4.Threekindsofforcesoperateonanybridge:thedeadload,theliveload,andthedynamicload.Deadloadreferstotheweightofthebridgeitself.Likeanyotherstructure,abridgehasatendencytocollapsesimplybecauseofthegravitationalforcesactingonthematerialsofwhic
40、hthebridgeismade.Liveloadreferstotrafficthatmovesacrossthebridgeaswellasnormalenvironmentalfactorssuch as changes in temperature,precipitation,and winds.Dynamic load refers to environmentalfactors that go beyond normal weather conditions,factors such as sudden gusts of wind andearthquakes.Allthreefa
41、ctorsmustbetakenintoconsiderationinthedesignofabridge.5.Consideringthecomplexgeologicconditionsatthebridgesite,differenttypesoffoundationswereused:heavyconcretecaissonswithadepthofpenetrationreaching54.87mforareaswithshallowwateranddeepcoverings;afloating-typesteelcaissoncombinedwithpipecolumnfoundationswasusedforthefirsttimeatsitesofdeepwater.ThebridgewasdesignedandconstructedbytheMajorBridgeEngineeringBureau,MinistryofRailways.ItwascompletedinDecember1968.
