桥梁外文翻译Word下载.docx
- 文档编号:21108222
- 上传时间:2023-01-27
- 格式:DOCX
- 页数:10
- 大小:28.13KB
桥梁外文翻译Word下载.docx
《桥梁外文翻译Word下载.docx》由会员分享,可在线阅读,更多相关《桥梁外文翻译Word下载.docx(10页珍藏版)》请在冰豆网上搜索。
PrestressedconcretehasbeenusedextensivelyinU.S.bridgeconstructionsinceitsfirstintroductionfromEuropeinthelate1940s.Literallythousandsofhighwaybridgesofbothprecast,prestressedconcreteandcast-in-placepost-tensionedconcretehavebeenconstructedintheUnitedStates.Railroadbridgesutilizingprestressedconcretehavebecomecommonaswell.Theuseandevolutionofprestressedconcretebridgesisexpectedtocontinueintheyearsahead.
Short-spanBridge
Short-spanBridge,asshowninFig.18forthepurposesofthisdiscussion,willbeassumedtohaveamaximumspanof45ft(13.7m).Itshouldbeunderstoodthatthisisanarbitraryfigure,andthereisnodefinitelineofdemarcationbetweenshort,moderate,andlongspansinhighlybridges.Short-spanbridgesaremostefficientlymadeofprecastprestressed-concretehollowslabs,I-beams,solidslabsorcast-placesolidslabs,andtheT-beamsofrelativilygenerousproportions.
Precastsolidslabsaremosteconomicalwhenusedonveryshortspans.Theslabscanbemadeinanyconvenientwidth,butwidthsof3or4ft(0.9to1.2m)havebeencommon.Keysfrequentlyarecastinthelongitudinalsidesoftheprecastunits.Aftertheslabshavebeenerectedandjointsbetweentheslabshavebeenfilledwithconcrete,thekeystransferliveloadshearforcesbetweentheadjacentslabs.
Precasthollowslabsusedinshort-spanbridgemayhaveroundorsquarevoid.Theytooaregenerallymadeinunits3to4ft(0.9to1.2m)widewiththicknessesfrom18to27inch9(45.7to68.8cm).Precasthollowslabscanbemadeinanyconvenientwidthanddepth,andfrequentlyareusedinbridgeshavingspansfrom20to50ft(6.1to15.2cm).Longitudinalshearkeysareusedinthejointsbetweenadjacenthollowslabsinthesamewayaswithsolidslabs,buttheuseofalevelingcourseofsometypenormallyisrequiredasameansofobtaininganacceptableappearanceandlevelness.
Transversereinforcementnormallyisprovidedinprecastconcretebridgesuperstructuresforthepurposeoftyingthestructuretogetherinthetransversedirection.Well-designedtiesensurethattheindividuallongitudinalmembersformingthesuperstructurewillactasaunitundertheeffectsoftheliveload.Inslabbridgeconstruction,transversetiesmostfrequentlyconsistofthreadedsteelbarsplacedthroughsmallholesformedtransverselythroughthememberduringfabrication.Nutsfrequentlyareusedasfastenersateachendofthebars.Insomeinstances,thetransversetiesconsistofposttensionedtendonsplaced,stressed,andgroutedaftertheslabshavebeenerected.Thetransversetieusuallyextendsfromonesideofthebridgetotheother.
Theshearforcesimposedonthestringersinshort-spanbridgesfrequentlyaretoolargetoberesistedbytheconcretealone.Hence,shearreinforcementnormallyisrequired.Theamountofshearreinforcementrequiredmayberelativelylargeifthewebsofthestringersarerelativelythin.
Concretediaphragms,reinforcedwithpost-tensionedreinforcementornonprestressedreinforcement,normallyareprovidedtransverselyatendsandatintermediatelocationsalongthespaninstringer-typebridges.Thediaphragmsensurethelateral-distributionoftheliveloadstothevariousstringersfromdisplacingorrotatingsignificantlywithrespecttotheadjacentstringers.
Nogeneralitieswillbemadehereabouttherelativecostofeachoftheabovetypesofconstruction;
constructioncostsareafunctionofmanyvariableswhichprohibitmeaningfulgeneralizations.However,itshouldbenotedthatthestringertypeofconstructionrequiresaconsiderablygreaterconstructiondepththatisrequiresaconsiderablygreaterconstructiondepththatisrequiredforsolid,hollow,orchannelslabbridgesuperstructure.Stringerconstructiondoesnotrequireaseparatewearingsurface,asdotheprecastslabtypesofconstruction,unlessprecastslabsareusedtospanbetweenthestringersinlieuofthemorecommonlyusedcast-in-placereinforcedconcretedeck.Stringsconstructionfrequentlyrequiressmallerquantitiesofsuperstructurematerialsthandoslabbridges(unlessthespansareveryshort).Theconstructiontimeneededtocompleteabridgeaftertheprecastmembershavebeenerectedisgreaterwithstringerframingthanwiththeslabtypeofframing.
Bridgeofmoderatespan
Againforthepurposesofthisdiscussiononly,moderatespansforbridgesofprestressedconcretearedefinedasbeingfrom45to80ft(13.7to24.4m).Prestressedconcretebridgesinthisspansrangegenerallycanbedividedintotwotypes;
stringer-typebridgesandslab-typebridgesandslab-typebridges.ThemajorityoftheprecastprestressedconcretebridgesconstructedintheUnitedStateshavebeenstringerbridgesusingI-shapedstringers,butalargenumberofprecastprestressedconcretebridgeshavebeenconstructedwithprecasthollow-boxgirders(sometimesalsocalledstringer).Cast-in-placepost-tensionedconcretehasbeenusedextensivelyintheconstructionofhollow-boxgirderbridges-aformofconstructionthatcanbeconsideredtobeaslabbridge.
Stringerbridges,whichemployacomposite,cast-in-placedeckslab,havebeenusedinvirtuallyallpartsoftheUnitedStates.Thesestringersnormallyareusedatspacingofabout5to6ft(1.5to1.8m).Thecast-in-placedeckisgenerallyform6.0to8.0inch(15.2to20.3cm)inthickness.Thistypeofframingisverymuchthesameasthatusedoncompositestringerconstructionforshort-spanbridges.
Diaphragmdetailsinmoderate-spanbridgesaregenerallysimilartothoseoftheshortspans,withtheexceptionthattwoorthreeinteriordiaphragmssometimeareused,ratherthanjustoneatmidspanasintheshort-spanbridge.
Asinthecaseofshort-spanbridges,theminimumdepthofconstructioninbridgesofmoderatespanisobtainedbyusingslabconstruction,whichmaybeeithersolid-orhollow-boxincrosssection.Averageconstructiondepthsarerequiredwhenstringerswithlargeflangesareusedincompositeconstruction,andlargeconstructiondepthsarerequiredwhenstringerswithsmallbottomflangesareused.Compositeconstructionmaybedevelopedthroughtheuseofcast-in-placeconcretedecksorwithprecastconstructionmaybedevelopedthroughtheuseofcast-in-placeconcretedecksorwithprecastconcretedecks.Lowerquantitiesofmaterialsnormallyarerequiredwithcompositeconstruction,anddeadweightofthematerialsnormallyislessforstringerconstructionthanforslabconstruction.
Long-SpanBridges
Prestressedconcretebridgeshavingspansoftheorderof100ftareofthesamegeneraltypesofconstructionasstructureshavingmoderatespanlengths,withthesingleexceptionthatsolidslabsarenotusedforlongspans.Thestringerspacingsarefrequentlygreater(withstringersat7to9ft)asthespanlengthsofbridgesincrease.Becauseofdeadweightconsideration,precasthollow-boxconstructiongenerallyisemployedforspansofthislengthonlywhenthedepthofconstructionmustbeminimized.Cast-in-placepost-tensionedhollow-boxbridgeswithsimpleandcontinuesspansfrequentlyareusedforspansontheorderof100ftandlonger.
Simple,precast,prestressedstringerconstructionwouldbeeconomicalintheUnitedStatesinspansupto300ftundersomecondition.However,onlylimitedusehasbeenmadeofthistypeofconstructiononspansgreaterthan100ft.Forverylongsimplespans,theadvantageofprecastingfrequentlyisnullifiedbythedifficultiesinvolvedinhanding,transporting,anderectingthegirders,whichmayhavedepthsasgreatas10ftandweightover200tons.Theexceptionstothisoccuronlargeprojectswhereallofthespansareoverwaterofsufficientdepthandcharacterthatprecastbeamscanbehandledwithfloatingequipment,whencustomgirderlauncherscanbeused,andwhensegmentalconstructiontechniquescanbeused.
Theuseofcast-in-place,post-tensioned,box-girderbridgeshasbeenextensive.Althoughstructuresofthesetypesoccasionallyareusedforspanslessthan100ft,theymoreoftenareusedforspansinexcessof100ftandhavebeenusedinstructureshavingspansinexcessof300ft.Structureefficientinflexure,especiallyforcontinuesbridges,theboxgirderistorsionallystiffandhenceanexcellenttypeofstructureforuseonbridgesthathavehorizontalcurvature.Somegovernmentalagenciesusethisformofconstructionalmostexclusivelyinurbanareaswhereappearancefromtheside,isconsideredimportant.
SegmentalBridges
Bridgesthatareconstructedinpiecesofonevariousconnectedtogetherinsomeway,frequentlyarereferredtoassegmentalbridges.Thesegmentsmaybecast-in-placeorprecast,elongatedunits,suchasportionsofstringersorgirders,orrelativelyshortunitsthatareaswideasthecompletedbridgesuperstructure.
TheEsblyBridgeinFranceisanexampleofoneoftheearliestprecastconcretesegmentalbridges.Thisbridgeisoneoffivebridgesthatweremadewiththesamedimensionsandutilizedthesamesteelmoldsforcastingtheconcreteunits.AllofthebridgesspantheRiverMarne,andbecauseoftherequirednavigationalclearancesandthelowgradesontheroadsapproachingthebridge,thedepthofconstructionatthecenterofeachspanwasrestricted.Thebridgeswereformedofprecastelements,6ftlong,andweremadeinelaboratemoldsbyfirstcastingandsteam-curingthetopandbottomflangesinwhichtheendsofthewebreinforcementwereembedded.Theflangeswerethenjackedapart,andheldapartbythewebformsresultedintheprestressingofthewebs.The6-ft-longelementsweretemporarilypost-tensionedinthefactoryintounitsapproximately
- 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 外文 翻译