桥梁设计外文翻译曼哈顿大桥的研究与分析Word文档下载推荐.docx

桥梁设计外文翻译曼哈顿大桥的研究与分析Word文档下载推荐.docx

《桥梁设计外文翻译曼哈顿大桥的研究与分析Word文档下载推荐.docx》由会员分享，可在线阅读，更多相关《桥梁设计外文翻译曼哈顿大桥的研究与分析Word文档下载推荐.docx（17页珍藏版）》请在冰豆网上搜索。

JulianStaden

DepartementofCivilandArchitecturalEngineering,UniversityofBath

Abstract:

ThispaperprovidesdetailedinformationaboutthedifferentaspectsofthedesignoftheManhattanSuspensionBridge.Analyticalreasoningisgiventowhyeachdesignfeaturewasdesignedinthemanoritwasinordertofulfiltheengineers’designcriteria.Anattemptisalsomadetoillustrateanyshortcominginthedesignofthestructureandanywaysinwhichtheengineerscouldhavepotentiallyimprovedthedesignofthebridge.Attentionwillalsobepaidtothewaysinwhichthebridgewouldbedesignedandconstructedifitweretobebuiltinthe21stcentury.Thereasonswhydesignprincipalsandconstructionmethodshavechangedwillalsobeoutlined.

Keywords:

truss,stiffness,tension,deck,torsion

Figure1:

ManhattanBridge.ViewfromManhattanside.

1OverviewofTheManhattanBridge

TheManhattanBridge,althoughunfinished,wasopenedin1909andwasthethirdbridgetospantheEastRiverrunningbetweenBrooklynandManhattan.Itwasbuilttoprovideanothertransportlinkbetweenthetwoboroughs.Beforeconstructionbegantherewasagreatdealofcontroversyovertheproposeddesignsforthebridge.EventuallyafairlytypicallookingsuspensionbridgedesignwasapprovedthatwasdesignedbyengineerLeonMoisieff.Thebridgewastospan448metresbetweenpiers,whichwasasomewhatshorterdistancethanthemainspansofeithertheBrooklynorWilliamsburgbridgesthatneighboreit..EventhoughtheManhattanBridgemadenoadvancementinthespannedlengthachievablebyasuspensionbridge,itdidrepresentasignificantstepforwardintheprogressionofbridgebuilding.Thebridgewasthefirsttobedesignedusingdeflectiontheory,whichquicklyreplacedallpreviousmethodsofbridgedesign.Thedesignalsoincorporatedsteeltowersthatwereonlybracedintwodimensionsratherthanthree.ThiswasanotheraspectofbridgedesignthathadnotbeenseenpriortothebuildingoftheManhattanBridge.

朗读

显示对应的拉丁字符的拼音

TheentirestructureoftheManhattansuspensionbridgewastobedesignedinsteel.Thedeckstructureiscomprisedoffoursteelstiffeningtrussesthatwereeachsupportedbyregularlyspacedsuspendersthathangfromoneofthefourmaincables.Thefourcablesaresupportedbythetwotowersandarehelddownbyanchorages224metresfromeachsideofthemainspan.

2DesigningTheStructure

TheStructureTheManhattanBridgewasthefirstsuspensionbridgetobedesignedusingdeflectiontheoryincalculatinghowthehorizontaldeckandcurvedcablesworkedtogethertocarryloads.Untilthispoint,suspensionbridgescouldonlybedesignedusingelastictheorywhichmeantassumingsmalldeflections.However,whilstthiswasanincorrectapproximation,assuspendedstructuresweresometimesobservedtoundergosignificantdeflections,thiswastheonlymathematicalmodellingthathadbeenapplieduptothattime.AtthetimetheManhattanBridgewasdesigned,thiswasthefirstoccasiontherehadbeenanappropriateopportunitytouseMelan’sdeflectiontheory.Thisnewmethodofanalysisallowedtheengineerstodesignthebridgewithamoreaccurateunderstandingofhowitwouldactuallyperform,allowingagreatereconomyofmaterialusage.

Deflectiontheorymeantthatallsuspensionbridgeswereprovedtobestrongerthanpreviouslyconsideredduetothecurveinthemaincablesbeingmoreefficientacarryingloadsthanstifferformsofbridge.ThenewtheoryallowedtheManhattanBridgetobedesignedtobelighter,withsmallerstiffeningtrusses,thanitotherwisewouldhavebeenusingelastictheory.Thesesmallerlightertrusseswouldhavebeenacceptableinnormalcircumstances.forexample,ifthebridgewastocarryonlyvehiculartraffic,butinthecaseoftheManhattanBridge,itwastoalsocarrysubwaytrains.

Despitetheapplicationofthenewtheory,aftertheinitialiseofthebridge,itbecameclearthattherewasasignificantflawinitsdesign.

2.1InadequacyofDesign

Eachtimeaheavysubwaytrainpassedoverthebridge,itcausedlocaldeflectionofthestiffeningtrussesonthesideofthedeckofthetrain’spassage.Thedeflectionononesideinducedtorsioninthedeck.Thisproblemwasfurtheraccentuatedwhentrainsbegantopassovereachsideofthebridgeinopposingdirectionsatthesametime.Itwasreportedthatatthispoint,eachsideofthedeckdeflectedbyupto1.2meters,meaningatotalrelativedeflectionofover2meters.Thisputsignificantstressesintothebridgedeckandsubsequentlyleadtoextensiverepairsandstiffeningworkneedingtobecarriedoutinordertoallowthebridgetoremainserviceable.

Inmymind,themostobviousfailinginthedesignoftheManhattanBridgeisthelocationofthetrackssubway.Theyhavebeenlocatedateachedge,ratherthanplacingtheminthecentralsectionofthedeck,withroadlanesseparatingthem.Keepingthetracksclosetogetherwouldhavereducedthelengthoftheeffectiveleverarmthatthetrains’sliveloadingwouldhavehad,reducingthetorsionmomentinduced.

AlthoughIamuncertainastothedesignengineer’sreasoningbehindlocatingthesubwaytracksinthesepositions,apossiblereasonbecomesapparentwhenlookingatacrosssectionofthedeck.

Figure2:

Crosssectionshowinglocationoflanesacrossdeck

Figure3:

Thefourmaincablesarenotevenlyseparated.

Thefiguresillustratethatthemaincablesandcorrespondingstiffeningtrussesare“paired”oneachsidetoenclosearegionofdeckresultinginalargerspanofdeckbetweenthem.

Asshowninfigures4and5,theseenclosedregionsarewherethedesignengineerslocatedthesubwaytracksandiswherethedistancebetweenthestiffeningtrussesissmaller.Theengineerswouldhaverealisedthattheheavyliveloadingfromthesubwaytrainswouldhavecausedasignificantlygreaterdegreeofbendingacrossthedeckbetweenstiffeningtrussesincomparisontothebendingduetovehicularloadingoverthesamespan.Thereforeitwouldhavemadesensetolocatethelightervehicularliveloadingoverthelargerspanofdeckintheregionbetweenthetwopairsoftrusses.Bythenlocatingthesubwaytracksinthesmallerspanningregionsofdeck,theresultingbendingmomentfromtheirloadisfarsmallerthaniftheywerelocatedinthecentralsection.Thiswouldhavemeantthatthedesignbendingmomentacrossthewholedeckcouldhavebeenofasimilarmagnitude,allowingthesupportingdeckstructuretobedesignedmoreeconomicallythanotherwiseusingasectionwithaconstantmomentcapacityacrossthewholedeck.I.e.exactlythesamethebeamsectioncouldbeusedoverthedecksfullwidth,resultinginsimplerconstructionandlesswastedmaterial.Thesepairedcablesconsequentlycouldhavebeendesignedinthiswayintentionallyforthepurposeofaccommodatingthesubwaytracks.Itispossiblethereforethatthedistributionoftheloadtypesacrossthedeckinthisconfigurationwasafundamentalpartofthedesignofthewholesuperstructure.

Asagreatdealofplanningwasmostlikelygiventothemostefficientlocationofthesubwaytracksasdiscussedabove,itisunfortunatethatthechosenconfigurationwouldgoontocausetorsioninthedeck..

Analternativesolutiontochangingthelocationofthesubwaytrackswouldhavebeentousedeeperstiffeningtrusses.Thesewouldhavehelpedpreventthedeflectionoftheoutermaincablesandhencereducedtorsioninthedeck.Howeverthiswouldhaveresultedinasignificantdetrimentaleffectonthebridgesaestheticqualities.

Overallthebridgewasdesignedadequatelyinatwodimensionalsense,butproperanalysisappearsnottobeencarriedoutinthreedimensions,otherwisethetorsionaldeflectionscouldhavebeenprevented.

Thewholeprocesswouldbeeasilyavoidedinthedesignofamodernsuspensionbridge.Threedimensionalfiniteelementanalysissoftwarewouldbeusedinordertocheckthestructuralcapacityofthedeckinlongitudinalandtransversedirections.

2.2TowerDesign

TheManhattanBridgewasthefirstsuspensionbridgetobedesignedwithtowersbracedonlyinaplanetransversetothedeck..

Figure4:

Thetowersarebracedforstiffnessintwodimensions,ratherthanthree

Makingthetowersflexibleinthesameplaneasthemaincablesallowsforanymovementatthetopofthetowerstobetakenasbendinginthetowers.Theflexingofthetowerspreventslargebendingmomentsbeingtransferredstraighttothefoundations.Thereforesmallerfoundationsunderthepiersareneededcomparedtoundermoretypicaltowerdesignforthetimethebridgewasdesignedandbuilt.Thisispossiblebecausethefoundationswouldmostlybetheretotaketheverticalload,ratherthanacombinationofaverticalloadandalargebendingmoment.

Thefourmainsteelsectionsthatcompriseeachtowerhavehoweverbeenbracedwithcrossmembersinthetransverseplanetothedeck.Elasticityinthisplanewouldbeundesirableandofabsolutelynobenefit.

Theengineerswouldhavebeenfullyawarethatwithoutthebracinginthisplane,thestructurewouldbemuchmoreunstable,andthatthecolumnscouldpotentiallybuckleundertheloadofthemaincablessupportingthedeck.

ThedesignofthetowersoftheManhattanBridgewasthefirstexampleoftheapplicationofmanyoftheprincipalsadoptedinthedesignofmodernsuspensionbridgetowers.

Towardsthebaseofeachpier,thesteelsectionincreasesinsizeuntilitmeetsthemasonryfooting.Thesewouldhavebeendesignedinthismanner