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1、英國倫敦塔橋（附圖） TOWERBRIDGELONDON Originally,LondonBridgewastheonlycrossingovertheThames.AsLondongrew,somorebridgeswereadded,butthesewerealltothewestofLondonBridge,sincetheareaeastofLondonBridgehadbecomeabusyport.Inthe19thcentury,theeastendofLondonbecam
2、esodenselypopulatedthatpublicpressuremountedforabridgetotheeastofLondonBridge,asjourneysforpedestriansandvehicleswerebeingdelayedliterallybyhours. Finallyin1876,theCorporationofLondon,whowereresponsibleforthatpartoftheThames,decidedthattheproblemcou
3、ldbeputoffnolonger.?TowerBridgewascompletedin1894,after8yearsofconstruction.However,manypeopledon'trealisewhyitissodifferentfromLondon'sotherbridges. HowaDesignwasChosen ThebigproblemfortheCorporationofLondonwashowtobuildabridgedownstreamfromLondon
4、Bridgewithoutdisruptingrivertrafficactivities.Togetasmanyideasaspossible,the"SpecialBridgeorSubwayCommittee"wasformedin1876,andopenedthedesignofthenewcrossingtopubliccompetition. Over50designswereputforwardforconsideration,someofwhichyoucanseeifyouv
5、isitTheTowerBridgeExhibition.However,itwasn'tuntilOctober1884thatHoraceJones,theCityArchitect,incollaborationwithJohnWolfeBarry,offeredthechosendesignforTowerBridgeasasolution. TheBuildingoftheBridge Ittook8years,5majorcontractorsandtherelentlessla
6、bourof432constructionworkerstobuildTowerBridge. Twomassivepiershadtobesunkintotheriverbedtosupporttheconstruction,over11,000tonsofsteelprovidedtheframeworkforthetowersandwalkways.ThiswasthencladinCornishgraniteandPortlandstone,bothtoprotecttheunderl
7、yingsteelworkandtogivethebridgeamorepleasingappearance. HowitWorks-Then?Now Whenitwasbuilt,TowerBridgewasthelargestandmostsophisticatedbasculebridgeeverbuilt（"bascule"comesfromtheFrenchfor"see-saw"）.Itwasahydraulicallyoperatedbridge,usingsteamtopow
8、ertheenormouspumpingengines.Theenergycreatedwasthenstoredinsixmassiveaccumulatorssothat,assoonaspowerwasrequiredtoliftthebridge,itwasreadilyavailable.Theaccumulatorsfedthedrivingengines,whichdrovethebasculesupanddown.Despitethecomplexityofthesystem,t
