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月毕业设计外文资料翻译第1页外文资料原文：13Boxgirders13.1GeneralTheboxgirderisthemostflexiblebridgedeckform.Itcancoverarangeofspansfrom25muptothelargestnon-suspendedconcretedecksbuilt,oftheorderof300m.Singleboxgirdersmayalsocarrydecksupto30mwide.Forthelongerspanbeams,beyondabout50m,theyarepracticallytheonlyfeasibledecksection.Fortheshorterspanstheyareincompetitionwithmostoftheotherdecktypesdiscussedinthisbook.Theadvantagesoftheboxformareprincipallyitshighstructuralefficiency(5.4),whichminimisestheprestressforcerequiredtoresistagivenbendingmoment,anditsgreattorsionalstrengthwiththecapacitythisgivestore-centreeccentricliveloads,minimisingtheprestressrequiredtocarrythem.Theboxformlendsitselftomanyofthehighlyproductivemethodsofbridgeconstructionthathavebeenprogressivelyrefinedoverthelast50years,suchasprecastsegmentalconstructionwithorwithoutepoxyresininthejoints,balancedcantilevererectioneithercastin-situorcoupledwithprecastsegmentalconstruction,andincrementallaunching(Chapter15).13.2Cast-in-situconstructionofboxes13.2.1GeneralOneofthemaindisadvantagesofboxdecksisthattheyaredifficulttocastin-situduetotheinaccessibilityofthebottomslabandtheneedtoextracttheinternalshutter.Eithertheboxhastobedesignedsothattheentirecrosssectionmaybecastinonecontinuouspour,orthecrosssectionhastobecastinstages.毕业设计外文资料翻译第2页13.2.2CastingthedeckcrosssectioninstagesThemostcommonmethodofbuildingboxdecksinsituistocastthecrosssectioninstages.Either,thebottomslabiscastfirstwiththewebsandtopslabcastinasecondphase,orthewebsandbottomslabconstitutethefirstphase,completedbythetopslab.Whenthebottomslabiscastfirst,theconstructionjointisusuallylocatedjustabovetheslab,givingakickerforthewebformwork,position1inFigure13.1.Ajointinthislocationhasseveraldisadvantageswhicharedescribedin11.7.1Figure13.1AlternativepositionsofconstructionjointAlternatively,thejointmaybeinthebottomslabclosetothewebs,oratthebeginningofthehaunches,position2.Theadvantagesoflocatingthejointinthebottomslabarethatitdoesnotcrossprestressingtendonsorheavyreinforcement;itisprotectedfromtheweatherandisalsolessprominentvisually.Themaindisadvantageisthattheslabonlyconstitutesasmallproportionofthetotalconcretetobecast,leavingamuchlargersecondpour.Thejointmaybelocatedatthetopoftheweb,justbelowthetopslab,position3.Thisretainsmanyofthedisadvantagesofposition1,namelythattheconstructionjointiscrossedbyprestressingductsatashallowangle,anditisdifficulttoprepareforthenextpourduetothepresenceofthewebreinforcement.Inaddition,mostofthedifficultyofcastingthebottomslabhasbeenre-introduced.Theadvantagesarethatthejointislessprominentvisuallyandisprotectedfromtheweatherbythesidecantilever,thequantityofconcreteineachpourissimilarandlessoftheshutteristrappedinsidethebox.Castingacrosssectioninphasescausesthesecondphasetocrackduetorestraintbythehardenedconcreteofthefirstphase.Althoughthesectionmaybereinforcedtolimitthewidthofthecracks,itisnotdesirableforaprestressedconcretedecktobecrackedunderpermanentloads.Eliminatingcracksaltogether毕业设计外文资料翻译第3页wouldrequireveryexpensivemeasuressuchascoolingthesecondphaseconcretetolimittheriseintemperatureduringsettingoradoptingcracksealingadmixtures13.2.3CastingthecrosssectioninonepourTherearetwoapproachestocastingaboxsectioninonepour.Thebottomslabmaybecastfirstwiththehelpoftrunkingpassingthroughtemporaryholesleftinthesoffitformofthetopslab.Thisrequiresaccessforlabourerstospreadandvibratetheconcrete,andisonlygenerallypossiblefordecksthatareatleast2mdeep.Thecastingofthewebsmustfollowonclosely,sothatcoldjointsareavoided.Thefluidityoftheconcreteneedstobedesignedsuchthattheconcretewillnotslumpoutofthewebs.Thisisassistedifthereisastripoftopshuttertothebottomslababout500mmwidealongeachweb.Thismethodputsnorestrictiononthewidthofthebottomslab,Figure13.2(a).Alternativelythedeckcrosssectionmaybeshapedsothatconcretewillflowfromthewebsintothebottomslab,whichnormallyhasacompletetopshutter,Figure13.2(b).Thismethodofconstructionismostsuitableforboxeswithrelativelynarrowbottomflanges.Thecompactionofthebottomslabconcreteneedstobeeffectedbyexternalvibrators,whichimpliestheuseofsteelshutters.Theconcretemaybecastdownbothwebs,withinspectionholesintheshutterthatallowairtobeexpelledandthecompletefillingofthebottomslabtobeconfirmed.Alternatively,concretemaybecastdownonewebfirstwiththesecondwebbeingcastonlywhenconcreteappearsatitsbase,demonstratingthatthebottomslabisfull.Theconcretemixdesigniscriticalandfull-scaletrialsrepresentingboththegeometryofthecrosssectionanddensityofreinforcementandprestresscablesareessential.毕业设计外文资料翻译第4页Figure13.2CastingdeckinonepourHoweverthesectioniscast,thecoreshuttermustbedismantledandremovedthroughaholeinthetopslab,ormadecollapsiblesoitmaybewithdrawnlongitudinallythroughthepierdiaphragm.Despitethesedifficulties,castingthesectioninonepourisunder-used.Therecentdevelopmentofself-compactingconcretecouldrevolutionisetheconstructionofdecksinthismanner.Thiscouldbeparticularlyimportantformediumlengthbridgeswithspansbetween40mand55m.Suchspansaretoolongfortwinribtypede