桥梁工程毕业设计外文翻译箱梁.docx
- 文档编号:5737560
- 上传时间:2022-12-31
- 格式:DOCX
- 页数:12
- 大小:490.58KB
桥梁工程毕业设计外文翻译箱梁.docx
《桥梁工程毕业设计外文翻译箱梁.docx》由会员分享,可在线阅读,更多相关《桥梁工程毕业设计外文翻译箱梁.docx(12页珍藏版)》请在冰豆网上搜索。
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:
13
Boxgirders
13。
1General
Theboxgirderisthemostflexiblebridgedeckform.Itcancoverarangeofspansfrom25muptothelargestnon-suspendedconcretedecksbuilt,oftheorderof300m.Singleboxgirdersmayalsocarrydecksupto30mwide。
Forthelongerspanbeams,beyondabout50m,theyarepracticallytheonlyfeasibledecksection。
Fortheshorterspanstheyareincompetitionwithmostoftheotherdecktypesdiscussedinthisbook.
Theadvantagesoftheboxformareprincipallyitshighstructuralefficiency(5。
4),whichminimisestheprestressforcerequiredtoresistagivenbendingmoment,anditsgreattorsionalstrengthwiththecapacitythisgivestore-centreeccentricliveloads,minimisingtheprestressrequiredtocarrythem。
Theboxformlendsitselftomanyofthehighlyproductivemethodsofbridgeconstructionthathavebeenprogressivelyrefinedoverthelast50years,suchasprecastsegmentalconstructionwithorwithoutepoxyresininthejoints,balancedcantilevererectioneithercastin-situorcoupledwithprecastsegmentalconstruction,andincrementallaunching(Chapter15)。
13.2Cast—in—situconstructionofboxes
13.2.1General
Oneofthemaindisadvantagesofboxdecksisthattheyaredifficulttocastin-situduetotheinaccessibilityofthebottomslabandtheneedtoextracttheinternalshutter.Eithertheboxhastobedesignedsothattheentirecrosssectionmaybecastinonecontinuouspour,orthecrosssectionhastobecastinstages。
13.2。
2Castingthedeckcrosssectioninstages
Themostcommonmethodofbuildingboxdecksinsituistocastthecrosssectioninstages。
Either,thebottomslabiscastfirstwiththewebsandtopslabcastinasecondphase,orthewebsandbottomslabconstitutethefirstphase,completedbythetopslab.
Whenthebottomslabiscastfirst,theconstructionjointisusuallylocatedjustabovetheslab,givingakickerforthewebformwork,position1inFigure13。
1。
Ajointinthislocationhasseveraldisadvantageswhicharedescribedin11。
7.1
Figure13。
1Alternativepositionsofconstructionjoint
Alternatively,thejointmaybeinthebottomslabclosetothewebs,oratthebeginningofthehaunches,position2.Theadvantagesoflocatingthejointinthebottomslabarethatitdoesnotcrossprestressingtendonsorheavyreinforcement;itisprotectedfromtheweatherandisalsolessprominentvisually。
Themaindisadvantageisthattheslabonlyconstitutesasmallproportionofthetotalconcretetobecast,leavingamuchlargersecondpour.
Thejointmaybelocatedatthetopoftheweb,justbelowthetopslab,position3.Thisretainsmanyofthedisadvantagesofposition1,namelythattheconstructionjointiscrossedbyprestressingductsatashallowangle,anditisdifficulttoprepareforthenextpourduetothepresenceofthewebreinforcement。
Inaddition,mostofthedifficultyofcastingthebottomslabhasbeenre-introduced。
Theadvantagesarethatthejointislessprominentvisuallyandisprotectedfromtheweatherbythesidecantilever,thequantityofconcreteineachpourissimilarandlessoftheshutteristrappedinsidethebox.
Castingacrosssectioninphasescausesthesecondphasetocrackduetorestraintbythehardenedconcreteofthefirstphase.Althoughthesectionmaybereinforcedtolimitthewidthofthecracks,itisnotdesirableforaprestressedconcretedecktobecrackedunderpermanentloads.Eliminatingcracksaltogetherwouldrequireveryexpensivemeasuressuchascoolingthesecondphaseconcretetolimittheriseintemperatureduringsettingoradoptingcracksealingadmixtures
13。
2。
3Castingthecrosssectioninonepour
Therearetwoapproachestocastingaboxsectioninonepour。
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。
Figure13.2Castingdeckinonepour
Howeverthesectioniscast,thecoreshuttermustbedismantledandremovedthroughaholeinthetopslab,ormadecollapsiblesoitmaybewithdrawnlongitudinallythroughthepierdiaphragm。
Despitethesedifficulties,castingthesectioninonepourisunder-used.Therecentdevelopmentofself-compactingconcretecouldrevolutionisetheconstructionofdecksinthismanner.Thiscouldbeparticularlyimportantformediumlengthbridgeswithspansbetween40mand55m.Suchspansaretoolongfortwinribtypedecks,andtooshortforcast-in—situbalancedcantileverconstructionofboxgirders,whileatotallengthofboxsectiondeckoflessthanabout1,000mdoesnotjustifysettingupaprecastsegmentalfacility。
Currently,itisthistypeofbridgethatisleastfavourableforconcreteandwheresteelcompositeconstructionisfoundtobecompetitive。
13。
3Evolutiontowardstheboxform
Chapters11and12describedhowsolidslabsevolveintoribbedslabsinordertoallowincreasedspanswithgreatereconomy.Theprincipaladvantageofribbedslabsistheirsimplicityandspeedofconstruction.Howeverthistypeofdecksuffersfromseveraldisadvantages,notably:
•thespanislimitedtoabout45m;
•liveloadsarenotefficientlycentred,resultinginaconcentratedload(suchasanHBvehicle)beingcarriedapproximately1.7timesforadeckwithtworibs,requiringadditionalprestressforce;
•thesectionhaspoorefficiency,leadingtotherequirementforarelativelylargerprestressforce;
•thedeckcannotbemadeveryshallow;
•thepiersneedeithermultiplecolumnstocarryeachrib,oracrossheadthatisexpensiveandvisuallyverysignificant。
Boxsectiondecksovercomeallthesedisadvantages。
13。
4Shapeandappearanceofboxes
13。
4.1General
Aboxsectiondeckconsistsofsidecantilevers,topandbottomslabsoftheboxitselfandthewebs.Foragooddesign,theremustbearationalbalancebetweentheoverallwidthofthedeck,andthewidthofthebox。
Boxsectionssufferfromacertainblandnessofappearance;theobserverdoesnotknowwhethertheboxismadeofanassemblageofthinplates,orissolidconcrete。
Also,thelargeflatsurfacesofconcretetendtoshowupanydefectsinthefinishandanychangesincolour.Thedesignershouldbeawareoftheseproblemsanddowhathecanwithintheconstraintsoftheprojectbudgettoalleviatethem。
13.4。
2Sidecantilevers
Sidecantilevershaveanimportanteffectontheappearanceofthebox。
Thethicknessofthecantileverrootandtheshadowcastonthewebmaskthetruedepthofthedeck。
Ifthedeckisofvariabledepth,theperceivedvariationwillbeaccentuatedbythesetwoeffects,Figure13。
3(15.4.2)。
Ingeneral,thecantilevershouldbemadeaswideaspossible,thatissomeseventoeighttimesthedepthoftheroot(9.2).
13.4。
3Theboxcrosssection
Boxesmayberectangularortrapezoidal,withthebottomflangenarrowerthanthetop.Rectangularboxsectionsareeasiertobuild,andarevirtuallyessentialforthelongestspansduetothegreatdepthofthegirders。
However,theyhavethedisadvantagesthattheirappearanceissomewhatsevere,andthattheirbottomslabsmaybewiderthannecessary.
Thevisualimpactofthedepthoftheboxisreducedifithasatrapezoidalcrosssection.Thisinclinationofthewebmakesitappeardarkerthanaverticalsurface,animpressionthatisheightenediftheedgeparapetofthedeckisvertical。
Thetrapezoidalcrosssectionisfrequentlyeconomicalaswellasgoodlooking。
Ingeneral,thewidthofthetopoftheboxisdeterminedbytheneedtoprovidepointsofsupporttothetopslabatsuitableintervals.Thecrosssectionareaofthebottomslabislogicallydeterminedatmid-spanbytheneedtoprovideabottommodulussufficienttocontroltherangeofbendingstressesunderthevariationofliveloadbendingmoments。
Foraboxofrectangularcrosssectionofspan/depthratiodeeperthanabout1/20,theareaofbottomslabisgenerallygreaterthannecessary,resultinginredundantweight。
Choosingatrapezoidalcrosssectionallowstheweightofthebottomslabtobereduced.Clo
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 桥梁工程 毕业设计 外文 翻译