桥梁工程毕业设计外文翻译(箱梁)

西南交通大学本科毕业设计〔论文〕外文资料翻译年级:学号:姓名:专业:指导老师:2013年6月外文资料原文：13Bxgiders13.1GeneralThebxgirderisthemostflexiblebridgedeckform.Itcancoverarangeofspansfrom25muptothelargestnon-suspendedconcretedecksbuilt,oftheorderof300m.Singlebxgirdersmayalsocarrydecksupto30mwide.orthelongerspanbeams,beyondabout50m,theyarepracticallytheonlyfeasibledecksection.ortheshorterspanstheyareincompetitionwithmostoftheotherdecktypesdiscussedinthisbook.Theadvantagesofthebxformareprincipallyitshighstructuralefficiency(5.4),whichminimisestheprestressforcerequiredtoresistagivenbendingmoment,anditsgreattorsionalstrengthwiththecapacitythisgivestore-centreeccentricliveloads,minimisingtheprestressrequiredtocarrythem.Thebxformlendsitselftomanyofthehighlyproductivemethodsofbridgeconstructionthathavebeenprogressivelyrefinedoverthelast50years,suchasprecastsegmentalconstructionwithorwithoutepxyresininthejoints,balancedcantilevererectioneithercastin-situorcoupledwithprecastsegmentalconstruction,andincrementallaunching(Chapter15).13.2Cast-in-situconstructionofboxes13.2.1GeneralOneofthemaindisadvantagesofbxdecksisthattheyaredifficulttocastin-situduetotheinaccessibilityofthebottomslabandtheneedtoextracttheinternalshutte.Eitherthebxhastobedesignedsothattheentirecrosssectionmaybecastinonecontinuouspou,orthecrosssectionhastobecastinstages.13.2.2CastingthedeckcrosssectioninstagesThemostcommonmethodofbuildingbxdecksinsituistocastthecrosssectioninstages.Eithe,thebottomslabiscastfirstwiththewebsandtopslabcastinasecondphase,orthewebsandbottomslabconstitutethefirstphase,completedbythetopslab.Whenthebottomslabiscastfirst,theconstructionjointisusuallylocatedjustabovetheslab,givingakickerforthewebformwork,position1inigure13.1.Ajointinthislocationhasseveraldisadvantageswhicharedescribedinigue13.1AlternativepositionsofconstructionjointAlternativel,thejointmaybeinthebottomslabclosetothewebs,oratthebeginningofthehaunches,position2.Theadvantagesoflocatingthejointinthebottomslabarethatitdoesnotcrossprestressingtendonsorheavyreinforcement;itisprotectedfromtheweatherandisalsolessprominentvisuall.Themaindisadvantageisthattheslabonlyconstitutesasmallproportionofthetotalconcretetobecast,leavingamuchlargersecondpou.Thejointmaybelocatedatthetopoftheweb,justbelowthetopslab,position3.Thisretainsmanyofthedisadvantagesofposition1,namelythattheconstructionjointiscrossedbyprestressingductsatashallowangle,anditisdifficulttoprepareforthenextpourduetothepresenceofthewebreinforcement.Inaddition,mostofthedifficultyofcastingthebottomslabhasbeenre-introduced.Theadvantagesarethatthejointislessprominentvisuallyandisprotectedfromtheweatherbythesidecantileve,thequantityofconcreteineachpourissimilarandlessoftheshutteristrappedinsidethebx.Castingacrosssectioninphasescausesthesecondphasetocrackduetorestraintbythehardenedconcreteofthefirstphase.Althoughthesectionmaybereinforcedtolimitthewidthofthecracks,itisnotdesirableforaprestressedconcretedecktobecrackedunderpermanentloads.Eliminatingcracksaltogetherwouldrequireveryexpensivemeasuressuchascoolingthesecondphaseconcretetolimittheriseintemperatureduringsettingoradoptingcracksealingadmixtures13.2.3CastingthecrosssectioninonepourTherearetwoapproachestocastingabxsectioninonepou.Thebottomslabmaybecastfirstwiththehelpoftrunkingpassingthroughtemporaryholesleftinthesoffitformofthetopslab.Thisrequiresaccessforlabourerstospreadandvibratetheconcrete,andisonlygenerallypossiblefordecksthatareatleast2mdeep.Thecastingofthewebsmustfollowonclosel,sothatcoldjointsareavoided.Thefluidityoftheconcreteneedstobedesignedsuchthattheconcretewillnotslumpoutofthewebs.Thisisassistedifthereisastripoftopshuttertothebottomslababout500mmwidealongeachweb.Thismethodputsnorestrictiononthewidthofthebottomslab,igure13.2(a).Alternativelythedeckcrosssectionmaybeshapedsothatconcretewillflowfromthewebsintothebottomslab,whichnormallyhasacompletetopshutte,igure13.2(b).Thismethodofconstructionismostsuitableforbeswithrelativelynarrowbottomflanges.Thecompactionofthebottomslabconcreteneedstobeeffectedbyexternalvibrators,whichimpliestheuseofsteelshutters.Theconcretemaybecastdownbothwebs,withinspectionholesintheshutterthatallowairtobeexpelledandthecompletefillingofthebottomslabtobeconfirmed.Alternativel,concretemaybecastdownonewebfirstwiththesecondwebbeingcastonlywhenconcreteappearsatitsbase,demonstratingthatthebottomslabisfull.Theconcretemixdesigniscriticalandfull-scaletrialsrepresentingboththegeometryofthecrosssectionanddensityofreinforcementandprestresscablesareessential.Figure13.2CastingdeckinonepourHoweverthesectioniscast,thecoreshuttermustbedismantledandremovedthroughaholeinthetopslab,ormadecollapsiblesoitmaybewithdrawnlongitudinallythroughthepierdiaphragm.Despitethesedifficulties,castingthesectioninonepourisunde-used.Therecentdevelopmentofsel-compactingconcretecouldrevolutionisetheconstructionofdecksinthismanne.Thiscouldbeparticularlyimportantformediumlengthbridgeswithspansbetween40mand55m.Suchspansaretoolongfortwinribtypedecks,andtooshortforcast-in-situbalancedcantileverconstructionofbxgirders,whileatotallengthofbxsectiondeckoflessthanabout1,000mdoesnotjustifysettingupaprecastsegmentalfacilit.Currentl,itisthistypeofbridgethatisleastfavourableforconcreteandwheresteelcompositeconstructionisfoundtobecompetitive.13.3EvolutiontowardstheboxformChapters11and12describedhowsolidslabsevolveintoribbedslabsinordertoallowincreasedspanswithgreatereconom.Theprincipaladvantageofribbedslabsistheirsimplicityandspeedofconstruction.Howeverthistypeofdecksuffersfromseveraldisadvantages,notabl:thespanislimitedtoabout45m;liveloadsarenotefficientlycentred,resultinginaconcentratedload(suchasanHBvehicle)beingcarriedapprximately1.7timesforadeckwithtworibs,requiringadditionalprestressforce;thesectionhaspoorefficienc,leadingtotherequirementforarelativelylargerprestressforce;thedeckcannotbemadeveryshallo;thepiersneedeithermultiplecolumnstocarryeachrib,oracrossheadthatisexpensiveandvisuallyverysignificant.Bxsectiondecksovercomeallthesedisadvantages.13.4Shapeandappearanceofboxes13.4.1GeneralAbxsectiondeckconsistsofsidecantilevers,topandbottomslabsofthebxitselfandthewebs.oragooddesign,theremustbearationalbalancebetweentheoverallwidthofthedeck,andthewidthofthebx.Bxsectionssufferfromacertainblandnessofappearance;theobserverdoesnotknowwhetherthebxismadeofanassemblageofthinplates,orissolidconcrete.Also,thelargeflatsurfacesofconcretetendtoshowupanydefectsinthefinishandanychangesincolou.Thedesignershouldbeawareoftheseproblemsanddowhathecanwithintheconstraintsoftheprojectbudgettoalleviatethem.13.4.2SidecantileversSidecantilevershaveanimportanteffectontheappearanceofthebx.Thethicknessofthecantileverrootandtheshadowcastonthewebmaskthetruedepthofthedeck.Ifthedeckisofvariabledepth,theperceivedvariationwillbeaccentuatedbythesetwoeffects,igure13.3(15.4.2).Ingeneral,thecantilevershouldbemadeaswideaspossible,thatissomeseventoeighttimesthedepthoftheroot(9.2).13.4.3TheboxcrosssectionBesmayberectangularortrapezoidal,withthebottomflangenarrowerthanthetop.ectangularbxsectionsareeasiertobuild,andarevirtuallyessentialforthelongestspansduetothegreatdepthofthegirders.Howeve,theyhavethedisadvantagesthattheirappearanceissomewhatsevere,andthattheirbottomslabsmaybewiderthannecessar.Thevisualimpactofthedepthofthebxisreducedifithasatrapezoidalcrosssection.Thisinclinationofthewebmakesitappeardarkerthanaverticalsurface,animpressionthatisheightenediftheedgeparapetofthedeckisvertical.Thetrapezoidalcrosssectionisfrequentlyeconomicalaswellasgoodlooking.Ingeneral,thewidthofthetopofthebxisdeterminedbytheneedtoprovidepointsofsupporttothetopslabatsuitableintervals.Thecrosssectionareaofthebottomslabislogicallydeterminedatmid-spanbytheneedtoprovideabottommodulussufficienttocontroltherangeofbendingstressesunderthevariationofliveloadbendingmoments.orabxofrectangularcrosssectionofspan/depthratiodeeperthanabout1/20,theareaofbottomslabisgenerallygreaterthannecessar,resultinginredundantweight.Choosingatrapezoidalcrosssectionallowstheweightofthebottomslabtobereduced.Closetothepiers,theareaofbottomslabisdeterminedbytheneedtolimitthemaximumbendingstressonthebottomfibreandtoprovideanadequateultimatemomentofresistance.Ifthenarrowbottomslabdefinedbymid-spancriteriaisinadequate,itissimpletothickenitlocall.oraverywidedeckthathasadeepspan/depthratio,thislogicmaygiverisetowebsthatareinclinedataveryflatangle.Thedesignershouldbeawareofthedifficultiesincastingsuchwebs,andmakesuitableallowancesinspecifyingtheconcreteandindetailingthereinforcement.Also,animportantconsiderationinthedesignofbxsectiondecksisthedistortionofthecrosssectionundertheeffectofeccentricliveloads(6.13.4).Theeffectofthisdistortionisreducedinatrapezoidalcrosssection.Besmayhaveasinglecellormultiplecells.InChapter8itwasexplainedhowimportantitisforeconomytominimisethenumberofwebs.urthermore,itismoredifficulttobuildmulti-cellbes,anditisworthwhileextendingthesingle-cellbxasfaraspossiblebeforeaddinginternalwebs.Figure13.3RiverDeeBridge:effectofsidecantileverontheappearanceofavariabledepthdeck(Photo:EdmundNuttall)13.4.4VariationofdepthOncethespanofabxsectiondeckeceedsabout45m,itbecomesrelevanttoconsidervaryingthedepthofthebeam.Thisisnotanautomaticdecisionasitdependsonthemethodofconstruction.orinstance,whenthedeckistobeprecastbythecounte-castmethod(Chapter14),ifthenumberofsegmentsisrelativelylowitislikelytobemoreeconomicaltokeepthedepthconstantinordertosimplifythemould.Ontheotherhand,ifthedeckistobebuiltbycast-in-situbalancedcantilevering,itisrelativelysimpletodesignthemouldtoincorporateavariabledepth,evenforasmallnumberofquiteshortspans.Clearl,thisdecisionalsohasanaestheticcomponent.Thedepthmaybevariedcontinuouslyalongthelengthofthebeam,adoptingacircula,parabolic,ellipticalorIslamicprofile,igure13.4.Alternativel,thedeckmaybehaunched.Thedecisiononthesoffitprofilecloselylinksaestheticandtechnicalcriteria.Figure13.4Variabledepthdecksorinstance,whenthedepthvariescontinuouslyitisoftenjudgedthatanellipticalprofileisthemostbeautiful.Howeve,thiswilltendtocreateadesignproblemtowardsthequarterpoints,asattheselocationsthebeamisshallowerthanoptimal,bothforshearresistanceandforbendingstrength.Asaresult,thewebsandbottomslabmayneedtobethickenedlocall,andtheprestressincreased.Howeve,theeconomicpenaltymaybesmallenoughtoaccept.TheIslamicformislikelytoprovidethemostflexiblemethodofoptimisingthedepthatallpointsalongthegirde,butthecuspatmid-spanmaygiveaproblemfortheprofileofthecontinuitytendonswhileforlongspansthegreaterweightofthedeeperwebseithersideofmid-spanimpliesasignificantcostpenalt.Also,theappearancemaynotbesuitablefortheparticularcircumstance.Whenthechangeinthedepthofthebxisnottoogreat,hauncheddecksareoftenchosenfortheprecastsegmentalformofconstruction,astheyreducethenumberoftimestheformworkmustbeadjusted,assistinginkeepingtotheall-importantdailycycleofproduction.Howeve,hereagainthereisaconflictbetweenthetechnicaloptimisationoftheshapeofthebeamandaestheticconsiderations.Thebeginningofthehaunchispotentiallyacriticaldesignsection,bothforshearandbending.Thiscriticalityisrelievedifthehaunchextendstosome25–30percentofthespanlength.Howeve,theappearanceofthebeamisconsiderablyimprovedifthehaunchlengthislimitedto20percentofthespanorless.Whenvariationofthedepthiscombinedwithatrapezoidalcrosssection,thebottomslabwillbecomenarrowerasthedeckbecomesdeepe,igure13.5.Thishasanimportantaestheticimpact,aswellasgivingrisetocomplicationsintheconstruction.Whenadeckisbuiltbythecast-in-situbalancedcantilevermethod,suchasthe929mlongBhairabBridge[1]inBangladeshdesignedbyBenaim,igure13.6,theformworkmaybedesignedtoacceptthisarrangementwithoutecessiveadditionalcost.Howeverforaprecastdeckitisbettertoavoidthiscombination,asthemodificationstotheformworkincreasethecostandcomplexityofthemouldandinterferewiththecastingprogramme.Itiseasiertocopewithahauncheddeckthanacontinuouslyvaryingdepth,asintheformercasethenarrowingofthebottomslabislimitedtoarelativelysmallproportionofthesegments,andtherateatwhichitnarrowsisconstant.Figure13.5VariabledepthwithtrapezoidalcrosssectionFigure13.6BhairabBridge,Bangladesh(Photo:RoadsandHighwaysDepartment,GovernmentofBangladeshandEdmundNuttall)Ifthebottomslabismaintainedataconstantwidth,thewebsurfaceswillbewarped.oradeckthathasacontinuouslyvaryingdepth,thetimbershuttersofacast-in-situcantileveringfalseworkcanacceptthiswarp,whereasthismaynotbethecaseforthesteelshutterofaprecastsegmentalcastingcell.Howeve,forahauncheddeckthewarpwouldbeintroducedsuddenlyatthebeginningofthehaunch,whichwouldprobablybeimpossibletobuild,andwouldlookterrible.外文资料译文：第13章箱梁13.1概述箱梁桥是最具柔性的一种桥面形式。它的跨度范围可以从25m到最大的跨度约为300m的非悬索结构混凝土桥。单箱室也可以做到承载30m宽的桥面。对于超过50m的较大跨度的主梁，箱梁几乎是唯一可行的桥面形式。对于较小跨径，它与大多数其他桥面形式的竞争也将在本书中进行讨论。箱形梁的优势主要是其高效的结构性能，这最大限度地减少了所需的抵抗弯矩的预应力，其巨大的抗扭强度能力也减少了需要承载偏心活载所需的预应力。在过去的50年中，箱形梁已经通过许多高效的桥梁生产建设方法得到日益完善，例如预制梁在接缝处需不需要加环氧树脂，悬臂施工时要么在现场浇筑要么将预制构件连接起来，或者用顶推法〔第15章〕。13.2现浇箱梁13.2.1概述箱梁的主要缺点之一是由于施工时难以接近混凝土梁底面以及需要取出内部浇筑模板造成的现场浇筑的难度。施工时要么模板已经设计好因此整个节段可以一次连续浇筑，要么节段必须分阶段施工。分阶段浇筑最常用的现场浇筑箱梁的方法是将横截面划分成几个阶段。首先浇筑底板，然后腹板和浇筑顶板一起浇筑，或者首先浇筑腹板和底板再以浇筑顶板结束。当首先浇筑底板时，施工接缝通常刚好位于底板面的上方，给腹板流出支模空间，如图13.1所示。在这个位置的接缝有众多的不利影响，具体在在有详细阐述。或者，接缝可以在底板靠近腹板的位置，或者在梗腋开始的位置，图中13.1的2的位置。接缝位于底板优点在于它不会穿过预应力筋或大量配筋；也能防止受天气的影响，视觉上也不突出。主要的缺点是底板只占了所有浇筑混凝土的一小局部，因此第二次浇筑时的浇筑量很大。接缝的位置也可以位于腹板的顶部，刚好在底板的底部，如图13.1的3的位置。该位置具有位置1的很多缺点，即接缝被浅层的预应力管道穿过，由于腹板钢筋的存在，在准备下一次次浇筑时也比拟困难。此外，又引入了许多浇筑底板时的困难。其优点在于该处的接缝更不显眼，以及由于悬臂的保护不收天气的影响，此外每次浇筑的混凝土量更小，更少的模具留在箱梁内部。分阶段浇筑会导致第二个阶段的混凝土由于第一阶段的混凝土硬化产生裂缝。虽然可以通过配筋来限制裂缝的宽度，但预应力混凝土在恒荷载下产生裂缝是不符合要求的。完全消除裂缝需要非常高本钱的措施，例如冷却第二阶段的混凝土以限制在采用裂缝密封剂时的气温的上升。13.2.3一次浇筑有两种方法一次浇筑箱梁截面。底板可以在穿过顶板下部模板留的临时孔洞的管道的帮助下首先浇筑。这就需要入口来使工人散布和振捣混凝土，并且一般只可能适用于至少2m高的梁。腹板的浇筑必须紧接着进行，以防止接缝冷却。流态的混凝土必须设计好以防止混凝土溢出腹板的模板。如果有一条沿每个腹板从顶部模板到底板的宽约500mm的长条，这种情况将得到改善。这种方法对于底板的宽度没有限制，如图13.2〔a〕.或者整个界面的形状可由混凝土从腹板流进底板从而成型，这种施工方法需要一个完整的模板，如图13.2〔b〕。这种浇筑方法特别适用底地板相对较窄的箱梁。底板混凝土的密实度需要外部的震荡器来实现，这意味着需要使用钢模板。混凝土可以从两个腹板向下浇筑，同时模板上需要有检视孔以确认空气被排出以及底板混凝土填充完整。或者，混凝土先从一个腹板往下浇筑待另一个腹板底部出现混凝土时再从此腹板往下浇筑，以此证明整个底板被填充完整。混凝土的配合比设计是具有决定性的，全面的实验表示截面的几何形状和配筋率以及预应力钢束同样重要。然而，当整个截面浇筑完成之后，模板必须经分解后再从顶板的洞中取出来，或是折叠后从墩顶横隔板纵向取出。尽管有这些困难，但一次浇筑法仍然在使用。近期的自密实混凝土技术的开展将给这种浇筑方式带来革命性的变化。这对于跨度介于40m至55m的中等跨度桥梁尤其重要。这种跨度对于双肋梁式桥来说太长，而对于现浇平衡悬臂施工的箱梁桥来说太短了。对于总长度小于1000m的箱型梁桥，采用预制构件被证明是不合理的。目前，这种桥型使用钢混结构最有利且具有竞争力。13.3箱型梁的开展第11章和第12章阐述了为了在经济的前提下增加跨度，实心板式梁是如何向带肋梁转变的。肋梁主要的优点在于它能简单快速施工。然而它也有一些缺点，特别是：跨度被限制在约45m；活载不能有效地集中，导致两根肋要承受大约1.7倍的集中荷载〔如HB车辆荷载〕，这就需要额外的预应力。截面承载力差，导致需要相对很大的预应力；梁体高度不能做的太小；桥墩上需要的承载肋梁的多种支座或是十字头支承比拟昂贵而且视觉上也很突出。箱梁能克服以上所有的缺点。13.4箱梁的外形13.4.1概述一个箱梁截面由端悬臂，顶板底板以及腹板组成。对于一个好的设计，桥面的总宽度与箱体的宽度必须有以合理的平衡关系。箱梁的的外形有一定的柔度；旁观者不知道箱梁是由几片薄板组合而成，还是就是实心混凝土。此外，混凝土大面积的平坦外表在浇筑完成时容易表现出缺陷，同样颜色的改变也容易表现出缺陷。设计者应该意识到这些问题并能在方案的要求下尽自己所能来防止这些问题。13.4.2端悬臂端悬臂对整个箱梁外形有重要的影响。端悬臂根部的厚度以及靠近腹板处的渐变段使得板的厚度变得模糊。如果板厚是变化的，那么感知上的变化会被这两种影响加重，如图13.3〔〕。一般来说，端悬臂的宽度应该做的尽量长，大约是根部长度的7到8倍〔9.2〕。13.4.3箱梁横截面箱梁可以是矩形或是梯形的，梯形的底部比顶