london bridge is falling down

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1、22.LONDONBRIDGEISFALLINGDOWNIn1996,theLondonBoroughofSouthwarkandtheRoyalInstituteofBritishArchitects,togetherwiththeFinancialTimesnewspaper,heldacompetitiontodesignanewfootbridgeacrosstheThames,fromtheproposedTateModernartgallerytoSt.Paul’sCathedral.Ateamthatinclude

2、dthearchitectSirNormanFoster,thesculptorSirAnthonyCaro,andtheengineeringfirmofOveArupsubmittedthewinningentry:aspectacular“lateralsuspension”bridgewithsteelbalustradesprojectingoutatobtuseanglesfromanarrowaluminumroadway.Thedesignlookedlikesomethingoutofascienceficti

3、onmovie;itsoriginatorsinsisteditwouldsupportfivethousandpedestrians.TheBritishgovernment,whichwaslookingtocommemoratetheupcomingmillennium,agreedtohelpfinancetheproject,whichbecameknownastheMillenniumBridge.OnJune10,2000,QueenElizabethopenedthebridge,andthousandsofpe

4、oplesetoffacrossit.Withinminutes,thefootwaystartedtotiltandswayalarmingly,forcingsomepedestrianstoclingtothesiderails.Severalofthemreportedfeeling“seasick.”Theauthoritiespromptlyshutthebridge,claimingthattoomanypeoplewereusingit;whentheyreopenedit,theshakingbeganagai

5、n.OnMonday,June12,2000,amidgreatembarrassment,thebridgewascloseddownforanindefiniteperiod.Initially,thesourceoftheswayingwasamystery:somepeoplesuspectedthebridge’sfoundations,othersanunusualairpattern.TheengineersfromOveArupconcludedthattherealproblemwasthepedestrian

6、sonthefootway.Thebridgehadbeendesignedtoswinggentlytoandfrointhebreeze,butitsdesignershadn’ttakenadequateaccountofhowthepeoplewalkingacrossthebridgewouldexaggerateitsmovements.Whenanyofuswalks,liftinganddroppingeachfootinturn,weproduceaslightsidewaysforce.Ifhundredso

7、fpeoplearewalkinginaconfinedspace,andsomehappentowalkinstep,theycangenerateenoughlateralmomentumtomoveafootbridge.Oncethefootwaystartsswaying,morepedestriansadjusttheirgaittogetcomfortable,steppingtoandfroinsyncwiththebridge.Ifeverybodydoesthisatthesametime,thesidewa

8、ysforcescanincreasedramatically,andthebridgecanstarttolurchviolently.Inotherwords,thewobblecanfeedonitself.Theengineersconcludedtha