suspension bridge | Definition, Mechanics, History ...

A suspension bridge carries vertical loads through curved cables in tension. These loads are transferred both to the towers, which carry them by vertical ... suspensionbridge TableofContents IntroductionFormandmechanicsConstructionHistoryanduses FastFacts RelatedContent Media Images More MoreArticlesOnThisTopic Contributors ArticleHistory Home Technology Engineering CivilEngineering suspensionbridge engineering Print print Print Pleaseselectwhichsectionsyouwouldliketoprint: TableOfContents Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/technology/suspension-bridge More GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites HistoryofBridges-SuspensionBridgeHistoryandFacts By TheEditorsofEncyclopaediaBritannica • EditHistory GeorgeWashingtonBridge Seeallmedia KeyPeople: JohnAugustusRoebling IsambardKingdomBrunel EmilyWarrenRoebling SirMarcIsambardBrunel OthmarHermanAmmann ...(Showmore) RelatedTopics: bridge deflectiontheory ...(Showmore) Seeallrelatedcontent→ suspensionbridge,bridgewithoverheadcablessupportingitsroadway.Modernsuspensionbridgesarelightandaestheticallypleasingandcanspanlongerdistancesthananyotherbridgeform.Theyarealsoamongthemostexpensivebridgestoconstruct.Thoughsuspensionbridgescanbemadestrongenoughtosupportfreighttrains,theyhavenearlyallbeendesignedforautomobiletraffic.Budapest:SzéchenyiChainBridgeSzéchenyiChainBridgeovertheDanubeRiver,Budapest.©WilfredoRodríguez(ABritannicaPublishingPartner)FormandmechanicsAsuspensionbridgecarriesverticalloadsthroughcurvedcablesintension.Theseloadsaretransferredbothtothetowers,whichcarrythembyverticalcompressiontotheground,andtotheanchorages,whichmustresisttheinwardandsometimesverticalpullofthecables.Thesuspensionbridgecanbeviewedasanupside-downarchintensionwithonlythetowersincompression.Becausethedeckishungintheair,caremustbetakentoensurethatitdoesnotmoveexcessivelyunderloading.Thedeckthereforemustbeeitherheavyorstifforboth.suspensionbridgeAsuspensionbridge,withforcesoftensionrepresentedbyredlinesandforcesofcompressionbygreenlines.EncyclopædiaBritannica,Inc. ReadMoreonThisTopic bridge:Suspension Asuspensionbridgecarriesverticalloadsthroughcurvedcablesintension.Theseloadsaretransferredbothtothetowers,... Sincetheearly20thcentury,deflectiontheoryhasbeenusedinthedesignofsuspensionbridgestocalculatehowthehorizontaldeckandcurvedcablesworktogethertocarryloads.Firstpublishedin1888bytheAustrianacademicJosefMelan,deflectiontheoryexplainshowdeckandcablesdeflecttogetherundergravityloads,sothat,asspansbecomelongerandthesuspendedstructureheavier,therequiredstiffnessofthedeckactuallydecreases.Deflectiontheoryespeciallyinfluenceddesigninthe1930s,asengineersattemptedtoreducetheratioofgirderdepthtospanlengthinordertoachievealighter,moregracefulappearancewithoutcompromisingsafety.ConstructionWhenbridgesrequiringpiersarebuiltoverabodyofwater,foundationsaremadebysinkingcaissonsintotheriverbedandfillingthemwithconcrete.Caissonsarelargeboxesorcylindersthathavebeenmadefromwood,metal,orconcrete.Inthecaseofsuspensionbridges,towersarebuiltatopthecaissons.Theearlysuspension-bridgetowerswerestone,butnowtheyareeithersteelorconcrete.Next,theanchoragesarebuiltonbothends,usuallyofreinforcedconcretewithembeddedsteeleyebarstowhichthecableswillbefastened.Aneyebarisalengthofmetalwithahole(or“eye”)attheends.Cablesforsomeofthefirstsuspensionbridgesweremadeoflinkedwrought-ironeyebars;now,however,cablesaregenerallymadeofthousandsofsteelwiresspuntogetherattheconstructionsite.Spinningisdonebyropepulleysthatcarryeachwireacrossthetopofthetowerstotheoppositeanchorageandback.Thewiresarethenbundledandcoveredtopreventcorrosion.Whenthecablesarecomplete,suspendersarehung,andfinallythedeckiserected—usuallybyfloatingdecksectionsoutonships,hoistingthemwithcranes,andsecuringthemtothesuspenders.suspensionbridgecablesCross-sectionaldesignsforparallelwires,wireropestrands,andeyebarsusedinsuspensionbridgeconstruction.EncyclopædiaBritannica,Inc.HistoryandusesOneoftheoldestofengineeringforms,suspensionbridgeswereconstructedbyprimitivepeoplesusingvinesforcablesandmountingtheroad-orwalkwaydirectlyonthecables.AmuchstrongertypewasintroducedinIndiaaboutthe4thcenturycethatusedcablesofplaitedbambooandlaterofironchain,withtheroadwaysuspended.Inmoderntimes,thesuspensionbridgeprovidedaneconomicalsolutiontotheproblemoflongspansovernavigablestreamsoratothersiteswhereitisdifficulttofoundpiersinthestream.British,French,American,andotherengineersofthelate18thandearly19thcenturiesencounteredseriousproblemsofstabilityandstrengthagainstwindforcesandheavyloads;failuresresultedfromstorms,heavysnows,anddrovesofcattle.CreditforsolvingtheproblembelongsprincipallytoJohnAugustusRoebling,aGerman-bornAmericanengineerwhoaddedawebtrusstoeithersideofhisroadwaysandproducedastructuresorigidthathesuccessfullybridgedtheNiagaraGorgeatNiagaraFalls,NewYork,theOhioRiveratCincinnati,and,finally,inhismasterpiece,theBrooklynBridgespanningtheEastRiverbetweenBrooklynandManhattanatNewYorkCity.BrooklynBridge,NewYorkCityBrooklynBridge,spanningtheEastRiver,NewYorkCity.©JoshuaHaviv/Shutterstock.comThetechniqueofcablespinningforsuspensionbridgeswasinventedbytheFrenchengineerLouisVicat,acontemporaryofRoebling.Vicat’smethodemployedatravelingwheeltocarrythecontinuouscablestrandfromtheanchorageononesideupoverthetower,downonapredeterminedsag(catenary)tothemidpointofthebridge,upandoverthetoweronthefarthersidetothefartheranchorage,whereacrewreceivedthewheel,anchoredthestrand,andreturnedthewheel,layingafreshstrand.Fromthesesuccessiveparallelstrandsacablewasbuiltup.Anothermajordevelopmentinthemodernsuspensionbridgewasthepneumaticcaisson,whichpermittedpierfoundationatgreatdepths.ItwasusedinitiallybyFrench,British,andAmericanengineers,includingWashingtonRoebling,whocompletedhisfather’sBrooklynBridge.Foratimeinthe1930s,Americanengineersexperimentedwithanarrowsolidgirderinplaceofthewebtrusstostiffentheroadway,butthefailureoftheTacomaNarrowsBridgein1940underaerodynamicforcesinstigatedareturntothewebtruss.Lateraerodynamicallystableboxgirdersreplacedthewebtruss.TacomaNarrowsBridgeCollapseoftheTacomaNarrowsBridge,Washingtonstate,1940.LibraryofCongress,Washington,DC(LC-USZ62-46682)Acable-bracedbridgewasdevelopedbyGermanengineersatCologne,Düsseldorf,andelsewhereinthe1950sand’60s;inthisformasingletoweratthemidpointsupportstheroadwaybymeansofanumberofcables.Anotherdevelopmentofthe1960s,aimedatreducingtimeofconstruction,wascablefabricatedintheshop.Bythelate1980s,threesuspensionbridges(theGoldenGate,inSanFrancisco,theVerrazano-Narrows,inNewYorkCity,andtheHumberBridge,nearHull,England)hadmain-spanlengthsofmorethan1,200metres(4,000feet).SanFrancisco:GoldenGateBridgeGoldenGateBridge,SanFrancisco.©HDFanatic/FotoliaModernsteelalloysarecapableofmuchgreaterspans,and,sincethelate20thcentury,anumberofrecord-breakingsuspensionbridgeshavebeenbuiltinAsia.ThelongestistheAkashiStraitBridge(1998),whichspans1,991metres(6,530feet)betweentheislandsHonshuandShikokuinJapan.In2019Chinacompletedthesecondandthirdlongestsuspensionbridgesintheworld:theYangsigangYangtzeRiverBridge,spanning1,700metres(5,577feet)inWuhan(Hubei),andtheNanshaBridge,spanning1,688metres(5,538feet)inDongguan(Guangdong).AkashiKaikyoBridgeAkashiKaikyoBridge,spanningtheAkashiStrait,west-centralJapan.KimRötzelTheEditorsofEncyclopaediaBritannicaThisarticlewasmostrecentlyrevisedandupdatedbyMelissaPetruzzello.