土木工程 桥梁 毕业设计 外文文献翻译 中英文文档格式.docx
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土木工程 桥梁 毕业设计 外文文献翻译 中英文文档格式.docx
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文献翻译@#@BridgeMaintenanceTechniques@#@Essentialmaintenancegenerallyinvolvesstrengtheningorreplacementofbridgeelements.Strengtheningtechniquesincludewelding,platebondingandexternalpost-tensioningwhichincreasethestiffnessofbridgedecks.Replacementofelementshasbeenusedfordeckslabsandbeams,piersandcolumns.Theprimarypurposeofessentialmaintenanceistoincreasetheloadcarryingcapacityandthereasonfortheinadequatecapacityissecondary.Ifthereasonissimplyincreasedloadingthemaintenancecanbelimitedtoincreasingthecapacity,butifthereasonisdeteriorationthenmaintenancemustalsoincluderepairsandpreventativemaintenance.@#@Theselectionofthemaintenancemethodforrepairspreventiondependsprimarilyonthecauseofdeterioration.Forsteelconstructionthemaincauseofdeteriorationiscorrosionandregularmaintenancepaintingshouldbecarriedouttopreventthesteelfromcorroding.Ifcorrosiondoesoccurthentheonlyrepairoptionistogritblastbacktoshinymetalbeforerepainting.Anassessmentofloadcarryingcapacityshouldbecarriedoutifcorrosionhasresultedinasignificantreductionofsteelsection.@#@Theselectionofrepairandpreventionmethodsforconcreteconstructionismorecomplexbecausetherearenumerouscausesofconcretedeterioration.Thedeteriorationofreinforcedconcretecanbeconvenientlysub-dividedintodeteriorationoftheconcreteanddeteriorationofthesteelreinforcement.Themaincausesofconcretedeteriorationaresulphates,free-thawcyclesandalkali-silicareaction(ASR).Deteriorationcanalsoberelatedtopoormixdesignandconstructionprocesssuchascompactionandcuring.Thesetypesofdeteriorationcanonlybepreventedbyactionstakenatthetimeofconstruction;@#@therearenoeffectivepreventativeactionsthatcanbetakenafterconstruction.ForexamplewheretheenvironmentisknowntocontainsignificantquantitiesofsulphideitissensibletoconsidertheuseofsulphateresistingPortlandcement.Inregionsexperiencinglargenumbersoffreeze-thawcyclesfrostdamagetoconcretecanbepreventedbyaddingairentrainingagenttotheconcretemix.Frostdamageisworseinconcretethatissaturatedwithsaltywatersotechniquessuchaswaterproofingmembranesandsilanetreatmentsmaybehelpful.Alkali-silicareactionbetweenaggregatesandthealkaliincementcanbepreventedbyavoidingthemostreactivetypesofaggregateandbykeepingthealkalicontentofthecementbelowthedesignatedlimit.TosetupdamagingstressesinconcretetheASRrequireswatersoprocedurestoreducethewatercontentsuchaswaterproofingmembranesandsilanetreatmentsmayhelp.IftheseformsofconcretedeteriorationtakeplacetheonlyviablerepairmethodisconcretereplacementwhichmaybeextensiveespeciallyforASRwhereentiresectionscanbeaffected.Sulphateandfreeze-thawdamagenormallyoccuronlyinthecover@#@zoneoftheconcrete.Itisimportanttonotethatdeteriorationoftheconcretewillincreasetheriskofcorrosiontothereinforcementbecausesteeldepassivators,likechloridesandcarbondioxide,willbeabletomovemoreeasilythroughtheconcretetothereinforcement.@#@Deteriorationofthereinforcingsteeliscausedbycorrosionandcanbepreventedbyactionstakenatthetimeofconstructionandforaperiodafterconstruction.Preventativetechniquesthatcanbeappliedatconstructionincludetheuseofepoxycoatedmildsteel,stainlesssteelofcarbonorglassfibrereinforcement,inhibitors,cathodicprotection,anti-carbonationcoatings,silanetreatmentsandwaterproofingmembranes.Allofthesetechniques,exceptthelastthree,directlyprotectthereinforcementagainstcorrosionandtodate,havebeenusedonlyoccasionallylargelyongroundsofcost.Waterproofingmembranes,silanetreatments,andanti-carbonationcoatingsareappliedtotheconcreteandaredesignedtoslowdowntheingressofcarbondioxideandchloridesintotheconcretetherebyincreasingtheageofthestructurewhenthereinforcementbeginstocorrode.Thesetechniquescanbeusedafterconstructionbecausetheyareappliedtotheconcretesurfaceandtheyshouldbeeffective,providingcorrosionofthereinforcementhasnotalreadybegun.Itisimportantnottooverlooktheimportanceofwellcompactedandcured,lowwater:
@#@cementratioconcreteinpreventingreinforcementcorrosion.@#@Whencorrosionofthereinforcementoccursitresultinalossofsteelsectionand/orcracking,spallinganddelaminationofconcreteduetothestressesproducedasaresultofthelowdensityofrustcomparedwithdensityofthesteel.Reinforcementcorrosionrepairmethodshavetwomainfunctions,tocretereplacement;@#@cathodicprotection;@#@desalination;@#@realkalization.@#@Concretereplacementhastobeusedtorepairthedam
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