大型桥梁及施工外文翻译-大跨度桥梁

大型桥梁及施工外文翻译--大跨度桥梁1LargeSpanBridgeSuspensionBridgeThesuspensionbridgeiscurrentlytheonlysolutioninexcessof600m,andisregardedascompetitivefordownto300.Theworld’slongestbridgeatpresentistheVerrazanoNarrowsbridgeinNewYork.AnothermodernexampleistheSevernBridgeinEngland.Thecomponentsofasuspensionbridgeare:(a)flexiblecables,(b)towers,(c)anchorages,(d)suspenders,(e)deckand，(f)stiffeningtrusses.Thecablenormallyconsistsofparallelwiresofhightensilesteelindividuallyspunatsiteandboundintooneunit.Eachwireisgalvanizedandthecableiscoverwithaprotectivecoating.Thewireforthecableshouldbecold-drawnandnotoftheheat-treatedvariety.Specialattentionshouldbepaidtoaestheticsinthedesignoftherowers.Thetowerishighandisflexibleenoughtopermittheiranalysisashingedatbothends.Thecableisanchoredsecurelyanchoredtoverysolidanchorageblocksatbothends.Thesuspenderstransfertheloadformthedecktothecable.Theyaremadeupofhightensilewiresandarenormallyvertical.Thedeckisusuallyorthotropicwithstiffenedsteelplate,ribsortroughs，floorbeam,etc.Stiffeningtrusses,pinnedatthetowers,areproviding.Thestiffeningsystemservestocontrolaerodynamicmovementsandtolimitthelocalanglechangesinthedeck.Ifthestiffeningsystemisinadequate,torsionaloscillationsduetowindmightresultinthecollapseofthestructure,asillustratedinthetragicfailurein1940ofthefirstTacomaNarrowsThesidespantomainspanratiovariesfrom0.17to0.50.Thespantodepthratioforthestiffeningtrussinexistingbridgeliesbetween85and100forspansupto1,000mandrisesrathersteeplyto177.Theratioofspantowidthofdeckforexistingbridgesrangesfrom20to56.Theaerodynamicstabilitywillhavebetobeinvestigatedthoroughlybydetailedanalysisaswellaswindtunneltestsonmodels.Thecable-stayedbridgeDuringthepastdecadecable-stayedbridgeshavefoundwideapplication,s\especiallyinWesternEurope,andtoalesserextentinotherpartsoftheworld.Therenewalofthecable-stayedsysteminmodernbridgeengineeringwasduetothetendencyofbridgeengineeringinEurope,primarilyGermany,toobtainoptimumstructuralperformancefrommaterialwhichwasinshortsupply-duringthepost-waryears.大型桥梁及施工外文翻译--大跨度桥梁全文共1页，当前为第1页。Cable-stayedbridgesareconstructedalongastructuralsystemwhichcomprisesanorthotropicdeckandcontinuousgirderswhicharesupportedbystays,i.e.inclinedcablespassingoverorattachedtotowerslocatedatthemainpiers.大型桥梁及施工外文翻译--大跨度桥梁全文共1页，当前为第1页。Theideaofusingcablestosupportbridgespanbridgespanisbynomeansnew,andanumberofexamplesofthistypeofconstructionwererecordedalongtimeago.Unfortunatelythesystemingeneralmetwithlittlesuccess,duetothefactthatthestaticswerenotfullyunderstoodandthatunsuitablematerialssuchasbarsandchainswereusedtoformtheinclinedsupportsorstays.Staysmadeinthismannercouldnotbefullytensionedandinaslackconditionallowedlargedeformationsofthedeckbeforetheycouldparticipateintakingthetensileloadsforwhichtheywereintended.Wideandsuccessfulapplicationofcable-stayedsystemswasrealizedonlyrecently,withtheintroductionofhigh-strengthsteels,orthotropicdecks,developmentofweldingtechniquesandprogressinstructuralanalysis.Thedevelopmentandapplicationofelectroniccomputersopenedupnewandpracticallyunlimitedpossibilitiesforexactsolutionofthesehighlystaticallyindeterminatesystemsandforprecisestoicalanalysisoftheirthree-dimensionalperformance.Existingcable-stayedbridgesprovideusefuldataregardingdesign,fabrication,erectionandmaintenanceofthemewsystem.Withtheconstructionofthesebridgesmanybasicproblemsencounteredintheirengineeringareshowntohavebeensuccessfullysolved.However,theseimportantdatahaveapparentlyneverbeforebeensystematicallypresented.Theapplicationofinclinedcablegaveanewstimulustoconstructionoflargebridges.Theimportanceofcable-stayedbridgesincreasedrapidlyandwithinonlyonedecadetheyhavebecomesosuccessfulthattheyhavetakentheirrightfulplaceamongclassicalbridgesystem.Itisinterestingtonotenowhowthisdevelopmentwhichhassorevolutionizedbridgeconstruction,butwhichinfactisnonewdiscovery,cameabout.Thebeginningofthissystem,probably,maybetracedbacktothetimewhenitwasrealizedthatrigidstructurescouldbeformedbyjoiningtrianglestogether.Althoughmostoftheseearlierdesignswerebasedonsoundprinciplesandassumptions,thegirderstiffenedbyinclinedcablessufferedvariousmisfortuneswhichregrettablyresultedinabandonmentofthesystem.Nevertheless,thesysteminitselfwasnotatallunsuitable.Thesolutionoftheproblemhadunfortunatelybeenattemptedinthewrongway.大型桥梁及施工外文翻译--大跨度桥梁全文共2页，当前为第2页。Therenaissanceofthecable-stayed,however,wasfinallysuccessfullyachievedonlyduringthelastdecade.大型桥梁及施工外文翻译--大跨度桥梁全文共2页，当前为第2页。Moderncable-stayedpresentathree-dimensionalsystemconsistingofstiffeninggirders,transverseandlongitudinalbracings,orthotropic-typedeckandsupportingpartssuchastowersincompressionandinclinedcablesintension.Theimportantcharacteristicsofsuchathree-dimensionalstructureisthefullparticipationofthetransverseconstructionintheworkofthemainlongitudinalstructure.Thismeansaconsiderableincreaseinthemomentofinertiaoftheconstructionwhichpermitsareductioninthedepthofthegirdersandeconomyinsteel.Longspanconcretebridgesareusuallyofpost-tensionedconcreteandconstructedeitherasconditionsbeamstypesorasfreeversatilestructures.Manymethodshavebeendevelopedforcontinuousdeckconstruction.Iftheclearancebetweenthegroundandbottomofthedeckissmallandthesoilisfirm,thesuperstructurecanbebuiltonstaging.Thismethodisbecomingobsolete.Currently,free-cantileverandmovablescaffoldsystemsareincreasinglyusedtosavetimeandimprovesafety.Themovablescaffoldsystememploysmovableformsstiffenedbysteelframes.Theseformsextendonespanlengthandaresupportedbysteelgirderswhichrestonapieratoneendandcanbemovedfromspantospanonasecondsetofauxiliarysteelgirders.Aneconomicalconstructiontechniqueknownasincrementalpush-launchingmethodisdevelopedbyBaur-Leonhardteam.Thetotalcontinuousdeckissubdividedlongitudinallyintosegmentsof10to30mlengthdependingonthelengthofspansandthetimeavailableforconstruction.Eachofthesesegmentsisconstructedimmediatelybehindtheabutmentofthebridgeinsteelframedforms,whichremaininthesameplaceforconcretingallsegments.Theformsaresodesignedastobecapableofbeingmovedtransverselyorrotatedonhingestofacilitateeasystrippingaftersufficienthardeningofconcrete.Attheheadofthefirstsegment,asteelnoseconsistingofalighttrussisattachedtofacilitatereachingofthefirstandsubsequentpierswithoutincludingatoolargecanyieldermomentduringconstruction.Thesecondandthefollowingsegmentsareconcreteddirectlyonthefaceofthehardenedportionandthelongitudinalreinforcementcancontinueacrosstheconstructionjoint.Thepushingisachievedbyhydraulicjackswhichactagainsttheabutment.SincethecoefficientoffrictionofTeflonslidingbearingsisonlyabout2percent,lowcapacityhydraulicjackswouldsufficetomovethebridgeevenoverlonglengthsofseveralhundredmetres.Thismethodcanbeusedforstraightandcontinuouslycurvedbridgesuptoaspanofabout120m.大型桥梁及施工外文翻译--大跨度桥梁全文共3页，当前为第3页。Thefree-cantileversystemwaspioneeredbyDyckerhoffandWillmanninGermany.Inthissystem,thesuperstructureiserectedbymeansofcantilevertruckinsectionsgenerallyof3.5m.Thecantilevertruck,whosecostisrelativelysmallandwhichisattachedfirmlytopermanentconstruction,emitsbyrepeatedusetheconstructionoflargebridges.Theavoidanceofscaffoldfrombelow,thespeedofworkandthesavinginlaborcostresultintheconstructionbeingveryeconomical.Thefree-cantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileversystemisideallysuitedforlaunchedgirderswithalargedepthabovethepiercantileveringtothemiddleofthespan.大型桥梁及施工外文翻译--大跨度桥梁全文共3页，当前为第3页。Anothertechniqueistheuseofthepneumaticcaisson.Thecaissonisahugecylinderwithabottomedgethatcancutintothewaterbed.Whencompressedispumpedintoit,thewaterisforcedout.Caissonsmustbeusedwithextremecare.foronething,workerscanonlystayinthecompressionchamberforshortperiodsoftime.Foranother,iftheycomeuptonormalatmosphericpressuretoorapidly,theyaresubjecttothebends,orcaissondiseaseasitisalsocalled,whichisacripplingorevenfatalconditioncausedbyexcessnitrogenintheblood.WhentheEadsBridgeacrosstheMississippiRiveratSt.Louiswasunderconstructionbetween1867and1874,atatimewhenthedangerofworkingincompressedairwasnotfullyunderstood,fourteendeathswascausedbythebends.Whenextrastrengthisnecessaryinthepiers,theysometimeskeyedintothebedrock-thatis,theyareextendeddownintothebedrock.ThismethodwasusedtobuildthepiersfortheGoldenGateBridgeinSanFrancisco,whichissubjecttostrongtidiesandhighwinds,andislocatedinanearthquakezone.Thedrillingwascarriedoutunderwaterbydeep-seadivers.Wherebedrockcannotbereached,pilesaredrivenintothewaterbed.Today,thepilesinconstructionareusuallymadeofprestressedconcretebeams.Oneingenioustechnique,usedfortheTappanZeeBridgeacrosstheHudsonRiverinNewYork,istorestahollowconcreteboxontopofalayerofpiles.Whentheboxispumpeddry,itbecomesbuoyantenoughtosupportalargeproportionoftheweightofthebridge.Eachtypeofbridgeindeedeachindividualbridgepresentsspecialconstructionproblems.Withsometrussbridges,thespanisfloatedintopositionafterthepiershavebeenerectedandthenraisedintoplacebymeansofjacksorcranes.Archbridgescanbeconstructedoverafalsework,ortemporaryscaffolding.Thismethodisusuallyemployedwithreinforcedconcretearchbridges.Withsteelarches,however,atechniquehasbeendevelopedwherebythefinishedsectionsareheldinplacebywiresthatsupplyacantileversupport.Cranesmovealongthetopofthearchtoplacenewsectionsofsteelwhilethetensioninthecablesincreases.大型桥梁及施工外文翻译--大跨度桥梁全文共4页，当前为第4页。Withsuspensionbridges,thefoundationsandthetowersarebuiltfirst.Thenacableisrunfromtheanchorage-concreteblockinwhichthecableisfastened-uptothetowerandacrosstotheoppositetowerandanchorage.Awheelthatunwindswirefromareelpunsalongthiscable.Whenthereelreachestheotherside,anotherwireisplacedonit,andthewheelreturnstoitsoriginalposition.Whenallthewireshavebeenputinplace,anothermachinemovesalongthecabletocompactandtobindthem.Constructionbeginsonthedeckwhenthecablesareinplace,withworkprogressingtowardthemiddlefromeachendofthestructure.大型桥梁及施工外文翻译--大跨度桥梁全文共4页，当前为第4页。Theloadstobeconsideredinthedesignofsubstructuresandbridgefoundationsincludeloadsandforcestransmittedfromthesuperstructure,andthoseactingdirectlyonthesubstructureandfoundation.AASHTOloads.Section3ofAASHTOspecificationssummarizestheloadsandforcestobeconsideredinthedesignofbridges(superstructureandsubstructure).Briefly,thesearedeadload,liveload,impactordynamiceffectofliveload,windload,andotherforcessuchaslongitudinalforces,centrifugalforce,thermalforces,earthpressure,buoyancy,shrinkageandlongtermcreep,ribshortening,erectionstresses,iceandcurrentpressure,collisionforce,andearthquakestresses.Besidestheseconventionalloadsthataregenerallyquantified,AASHTOalsorecognizesindirectloadeffectssuchasfrictionatexpansionbearingsandstressesassociatedwithdifferentialsettlementofbridgecomponents.TheLRFDspecificationsdivideloadsintotwodistinctcategories:permanentandtransient.大型桥梁及施工外文翻译--大跨度桥梁全文共5页，当前为第5页。大型桥梁及施工外文翻译--大跨度桥梁全文共5页，当前为第5页。大跨度桥梁悬索桥悬索桥是现行的跨径超过600m大桥的唯一解决方案，而且对跨径在300m以上的桥梁它也是被认为是一种很有竞争力的方案。现在世界上最大跨径的桥梁是纽约的威拉查诺（Verrazano）海峡大桥，另一个是英国的塞温（Savern）大桥。悬索桥的组成部分有：柔性，主塔，锚碇，吊索（挂索），桥面板和加劲桁架。主缆是有一组平行的单根高强钢丝在现场扭在一起并绑扎成型的钢丝束组成的。每根钢丝都是经过渡锌处理的，并且整个用保护层覆盖着。所用的钢丝应该是冷拔钢丝而不是经过热处理的各种钢丝。在进行主塔设计时应该特别注意其在美学上的要求。主塔很高而且具有足够的柔性，使其每一座塔顶都可认为是与主缆铰接。主缆的两端很安全的锚固在非常坚实的锚碇上。吊索把桥面板上的荷载传递到主主缆上。吊索也是有高强钢丝制成的而且通常是竖直的。桥面板通常是有加劲钢板，肋或槽型板，横梁制成的异性结构。提供一些加劲梁连接在其主塔之间，能够起到控制空气动力运动并限制桥面板局部倾角变化。如果加劲系统不适当，由于风引起的竖向振动也许会导致结构倾斜，就像塔科玛（Tacoma）海峡大桥的悲剧性的破坏所表明的那样。边跨与主跨的跨径比的变化范围是0.17~0.50。在现有的采用加劲梁的桥梁上，当跨径高大1000米时跨径与桥梁的建筑高度之比为85与100之间。现有的桥梁的跨径与桥面板宽度之比约为20~56。桥梁结构的空气动力稳定性必须得通过对其模型的风洞试验及细部分析进行全面的研究。斜拉桥体系在过去的十年间，斜拉桥得以广泛的应用，尤其实在欧洲，而在世界其它地区，应用相对少一些。在现代桥梁工程中，斜拉桥体系的重新兴旺起来是由于欧洲（主要是德国）的桥梁工程师有一种趋势，即从因为战争而短缺的材料上获得最佳的结构性能。斜拉桥是有按各向异性桥面板和由吊索支撑的连续梁构成的体系建造起来的，这些吊索是一些穿过或固定的位于主桥墩的索塔顶上的倾斜主缆。大型桥梁及施工外文翻译--大跨度桥梁全文共6页，当前为第6页。用主缆来支撑桥跨并不是一种新思想，在很早以前就有大量此类结构的的记载。不幸的是这一体系只有很少成功的例子，这是由于人们对静力学的原理没有完全弄明白，并且还没有构成倾斜支撑或吊索的适当的材料，例如主缆和钢链等。这种吊索在它们能够按计划承担拉力之前不能完全被拉紧，而应处于允许桥面板产生较大变形的松弛状态。大型桥梁及施工外文翻译--大跨度桥梁全文共6页，当前为第6页。斜拉体系的广泛的成功的应用只在近年来，随着高强钢，各种异性桥面板的引入、焊接技术的发展和结构分析方法的进步才得以实现。电子计算机的发展和应用，导致了解决高次超静定体系的精确值及它们的三维空间性能的精确静力分析的新的无实际限制的可能性。现有的斜拉桥提供了许多关于设计、制造、安装和维修的有用的数据。随着这些桥梁的建造，许多工程中遇到的基本问题已表明的到了成功的解决。然而这些重要的数据很显然在这以前决没有被系统的揭示出来。斜吊索的应用对大型桥梁建造带来了一个新刺激。斜拉桥的重要性迅速增加起来，并且在仅三十年间这种桥梁类型就变的这样成功，已使其在古典桥梁体系中取得了它应有的地位。如果我们注意到这种桥梁建造带来如此彻底的变革的发展是怎样发生的话，我们都会感兴趣的，因为这一发展事实上并没有什么任何新发现。这一体系的开始也许可以追溯到人们开始认识到通过三角形连接在一起能够构成刚性结构的时代。尽管大多数这种设计是基于结构坚固的原理和假定的，但斜拉加劲梁还是遭受各种各样的不幸事故，而最终令人遗憾的导致了这一体系被放弃。尽管这样，这一体系并不是完全不适应，只是问题的解决被不幸的应用错误的方式去尝试。然而，斜拉体系的复兴只是在近十年来才最终获得成功。现代的斜拉桥提出了加劲梁、横向及纵向联系梁、各项异性桥面板和支撑部分（例如处于受压状态的索塔及受拉状态的斜吊索）组成的三维空间体系。象这种空间三维结构的重要特征是横向结构全部参与主要纵向结构的工作状态。这就意味着结构的惯性矩大大增加，这使的桥的建筑高度可以减少，并且使用钢材是最经济的。大跨度桥梁经常是连续梁形式或悬臂梁形式的预应力混凝土桥梁。以前许多的施工方法已发展为连续梁桥的施工方法。如果模板和地面之间的距离较小并且土质坚硬，桥梁的上部结构可以使用支架施工方法。不过这种施工方法已经越来越过时了。目前，自由悬臂法和移动模架法的应用渐广并能节省时间和提高安全性。移动模架法是利用固定在钢制台架上的移动系统而形成，这种系统能够达到一跨长并支承在一端支承在桥墩上并借助于第二根钢导梁逐跨移动的钢梁上。大型桥梁及施工外文翻译--大跨度桥梁全文共7页，当前为第7页。一种经济的施工方法是被广泛知晓的由Baur-leonhard团队所发展的使用广泛的顶推法。整个的连续梁被划分成10-30米长度的节段，这种划分主要依据跨径和能够利用的施工时间。每个节段在桥台后面的钢模上能够快速浇注，钢模可以周转使用而浇注所有的节段。这样设计模板是为了能够横向移动或在铰上转动，以便在混凝土充分硬化后脱模。在第一节段的顶端安装上一个由轻型桁架组成的钢导梁，以实现第一节段