6外文翻译双面打印Word文档下载推荐.docx
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6外文翻译双面打印Word文档下载推荐.docx
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Baseduponanalysisofthereasonscausedthecracksofconcretethetemperaturestressofconcreteisstudied.Thecontrolmeasuresoftemperaturestressaswellaspreventivemeasuresofcracksareelaboratedindetailinordertoavoidproductionofcracksinconstructionprocesstoensureconstructionquality.
Keywords:
concrete,temperaturestress,crack,construction
Inthemassconcrete,temperaturestressandtemperaturecontrolsystemhasgreatsignificance.Therearetworeasons:
1)Intheconstructionofconcreteitoftenappeartemperaturecracks,whichaffectstheintegrityanddurabilityofthestructure;
2)Intheoperationprocess,thetemperaturechangeshaveinfluenceonstressstateofstructurewhichcannotbeignored.Sincetemperaturecrackcausedintheconstructionismainlymet,thecausesofcracksandProcessingmeasuresintheconstructionisexploredinthispaper.
1.thecausesofthecracks
Cracksinconcreteareavarietyofreasons,mainlytemperatureandhumiditychanges,brittleandunevenconcrete,aswellasthestructureisirrational,failureofrawmaterials(suchasalkali-aggregatereaction),templatedeformation,andsoonthebasisofdifferentialsettlement.
Theconcretetohardenoffalargenumberofcementduringthehydrationheat,theinternaltemperaturerisingonthesurfacecausedbytensilestress.Lateinthecoolingprocess,duetocoagulationonthebasisoforbeboundbytheold,willemergeintheconcretetensilestress.Lowertemperaturesintheconcretesurfacewillbealotoftensilestress.Whenthetensilestressbeyondthecapacityofconcretecrack,thecrackswillappear.Anumberofconcretechangesintheinternalhumidityorchangesverylittleslow,butpossiblechangesinsurfacehumidityormoredramaticchanges.Suchasconservation,failedtokeepdrywhenwet,surfaceshrinkagedeformationofconcretesubjecttointernalconstraints,butalsooftenleadstocracks.Short-termloadingatthetimeofultimatetensiledeformationonly(0.6~1.0)×
104,thelimitoflong-termloadingspaceswhentheonlystretchdeformation(1.2~2.0)×
104.Unevenlyasaresultofrawmaterials,water-cementratioofinstability,andtransportationandpouringintheprocessofsegregationphenomena,inthesamepieceofconcreteinthetensilestrengthisuneven,therearemanylowtensilecapacity,easytofractureinaweakposition.Inreinforcedconcrete,thetensilestressismainlybornebythesteel,concreteissubjecttocompressivestress.Inplainconcreteorreinforcedcoagulationontheedgeofthesiteifthestructureofthetensilestressappearstoberelyingonitsownconcretecommitment.
2.thermalstressanalysis
Accordingtotheformationofthermalstresscanbedividedintothefollowingthreestages:
(1)early:
Sincethebeginningofpouringconcretetocementtheendofexothermicbasicgeneralabout30days.Twocharacteristicsofthisstage,first,toreleasealargenumberofcementhydrationheat,andtheotheristheelasticmodulusofcoagulationdramaticchanges.Modulusofelasticityasaresultofchangeswithinthisperiodintheformationofresidualstressintheconcrete.
(2)medium-term:
fromthebasicroleofcementheatuntiltheendofthestabletemperatureoftheconcretecoolingtime,duringthisperiod,thetemperaturestresswasmainlyduetocoolingandtheoutsideconcretecausedbytemperaturechanges,stressandearlyformationoftheseresidualstresssuperpositionphase,duringwhichthecoagulationoftheelasticmoduluschangedlittle.
(3)late:
concretecompletelycoolingperiodaftertheoperation.Thermalstressismainlycausedbyexternaltemperaturechanges,thestressandthefirsttwo-phasesuperpositionofresidualstress.
Underthethermalstresscausedbythereasonscanbedividedintotwocategories:
(1)self-stress:
thereisnoconstraintontheborderorcompletelystaticstructure,iftheinternaltemperaturedistributionisnonlinear,duetostructuralconstraintsarisingfromtheirco-temperaturestress.Forexample,theconversionlayerofitsrelativelylargersize,concretecoolingsurfacetemperaturelow,theinternaltemperaturesarehigh,thesurfacetensilestress,compressivestressappearsinthemiddle.
(2)boundbystress:
thestructureofallorpartoftheboundaryboundbytheoutsideworldcannotbefree-formdeformationcausedbystress.Roofbox,suchasconcreteandconcretebarrier.
Boththetemperatureandtheconcretestressisoftencausedbyshrinkageofthecombinedeffectofstress.
Knowntobeinaccordancewithanaccurateanalysisofthetemperatureofthethermalstressdistribution,sizeisamorecomplextask.Inmostcases,theneedtorelyonmodeltestornumericalcalculation.Creepofconcretesothatthetemperaturethereisconsiderablestressrelaxation,thermalstresscalculation,wemustconsidertheeffectsofcreep,isnolongercalculatedindetailhere.
3.temperaturecontrolandmeasurestopreventthecracks
Inordertopreventcracking,reducethethermalstresscancontroltheconditionsoftemperatureandtoimprovethebindingoftwoaspects.
Temperaturecontrolmeasuresareasfollows:
(1)usedtoimprovetheaggregategradation,dryhardconcrete,mixedmixture,addair-entrainingagentorplasticizer,etc.measurestoreducetheamountofcementconcrete;
(2)mixingconcretebyaddingwaterorcoolingwaterwillbegravelandpouringconcretetoreducethetemperature;
(3)pouringhotdaystoreducethepouringofconcretethickness,theuseofpouringheatlevels;
(4)laidinconcretewaterpipes,accesstocoldwatertocool;
(5)theprovisionsofreasonabletime,thetemperaturedropwhenthesurfaceinsulation,concretesurfaceinordertoavoidasharptemperaturegradient;
(6)Constructionoflong-termexposuretoblockthesurfaceoftheconcretepouring,orthin-walledstructures,thermalinsulationinthecoldseasontotakemeasures;
Measurestoimprovetheconstraintsare:
(1)areasonablesub-blockjoints;
(2)basistoavoidtoomuchupsanddowns;
(3)reasonablearrangementsfortheconstructionprocess,toavoidexcessivesideelevationandlong-termexposure;
Inaddition,toimprovetheperformanceofconcretetoimprovetheanti-crackingability,tostrengthentheconservation,topreventsurfacedrying,inparticular,istoensurethequalityofconcreteisveryimportanttopreventcracks,shouldpayspecialattentiontoavoidcross-cracksappearstorestoretheintegrityofitsstructureitisverydifficult,sotheconstructionshouldbetopreventtheoccurrenceofcross-cuttingthemaincrack.
Inconcreteconstruction,inordertoincreasetheturnoverrateofthetemplate,oftenrequirenewpouringconcreteassoonaspossible.Whentheconcretetemperatureishigherthanthetemperatureshouldbeappropriatetoconsidertime,soastoavoidtheearlycracksintheconcretesurface.Newpouringearly,alotofthesurfacetensilestress,a"
temperatureshock"
phenomenon.Concretepouringintheearlyheatofhydrationasaresultofthedisseminationofthesurfacecausedbyalargetensilestress,whenthesurfacetemperatureishigherthanthetemperatureatthistimetoremovethetemplate,asharpfallinsurfacetemperatureisboundtoleadtotemperaturegradient,soanadditionaloneonthesurfacetensilestress,thermalstresssuperpositionandhydration,coupledwiththeshrinkageofconcrete,
Tensilestresstoreachthesurfaceofgreatvalue,thereisthedangerofleadtocracks,butifinatimelymanneraftertheremovalofthetemplateonthesurfacecoverageofalightinsulatingmaterial,suchasfoamspongeandsoon,haveaconcretesurfacetopreventexcessivetensilestress,withsignificantresults.
Reinforcedconcreteonthelargevolumeofthermalstresshaslittleeffectbecausethelargevolumeofconcretereinforcedwithaverylowrate.Onlyonthegeneralimpactofreinforcedconcrete.Nottoohighintemperatureandstressbelowtheyieldlimitundertheconditionofthepropertiesofsteelisstable,andwiththestress,timeandtemperaturehasnothingtodo.Linearexpansioncoefficientofsteelandconcretelinearexpansioncoefficientdifferencebetweenthesmallchangesintemperaturebetweenthetwowithonlyaverysmallstress.Sincethemodulusofelasticityofsteeltoconcreteelasticmodulusof7~15-fold,whenthestressreachedthetensilestrengthofconcreteandcracking,thesteelstresswillnotexceed100~200kg/cm2..So
Wanttouseinreinforcedconcretetopreventtheemergenceofsmallcracksisdifficult.However,afterthereinforcedstructureofthenumberofcracksingeneralhasbecomemorethanasmalldistance,asmallerwidthanddepth.Andifthediameterofsteelthinandclosespacing,thecrackresistanceofconcretetoenhancetheeffectofbetter.Concreteandreinforcedconcretestructureofthesurfaceoftenoccurcracksinthinandshallow,mostofthembelongingtoshrinkagecracks.Whilethisisgenerallyshallowcracks,butitsstrengthanddurabilityofthestructureisstillacertainimpact.
Inordertoensurethequalityofconcretetopreventcrackingandimprovethedurabilityofconcrete,theproperuseofadmixturesisalsooneofthemeasurestoreducecracking.Suchastheuseofanti-crackingagentandwater,inpractice,itsmajorroleinconcludingasfollows:
(1)theexistenceofalargenumberofporesintheconcretethat,afterevaporationofwatergeneratedbycapillarycapillarytension,deformationoftheconcreteshrinkage.Poresincreasedcapillarydiametercanreducethesurfacetension,butwouldreducethestrengthofconcrete.
(2)theimpactofwater-cementrat
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