土木工程畢業(yè)設(shè)計外文翻譯原文+翻譯橋梁

西西南交通大學(xué)本科畢業(yè)設(shè)計外文翻譯ThebridgecrackproducedthereasontosimplyanalyseInrecentyears,thetrafficcapitalconstructionofourprovincegetsswiftdevelopment,allpartshavebuiltalargenumberofconcretebridges.Inthecourseofbuildingandusinginthebridge,relevanttoinfluenceprojectqualityleadofcommonoccurrencereportthatbridgecollapseevenbecausethecrackappearsTheconcretesaidto"oftenhaveillnesscomingon"whilefracturingand"frequently-occurrin",oftenperplexbridgeengineersandtechnicians.Infact,iftakecertaindesignandconstructionmeasure,alotofcrackscanbeovercomeandcontrolled.Forstrengthenunderstandingofconcretebridgecrackfurther,isitpreventprojectfromendangcracktotryone'sbest,thistextmakeanmoreoverallanalysis,summarytoconcandreasonofproduction,bridgeofcrackasmuchaspossible,inordertodesign,constructandfindoutthefeasiblemethodwhichcontrolthecrack,gettheresultprecautionsagainstYuWeiRan.Concretebridgecrackkind,origincauseofformationInfact,theorigincauseofformationoftheconcretestructurecrackiscomplicatedandvarious,evenmanykfactorsinfluenceeachother,buteverycrackhasitsoneorseveralkindsofmaproduced.Thekindoftheconcretebridgecrack,onitsreasontoproduce,canroughlydivideseveralkindsasfollows:(1)loadthecrackcausedConcreteinroutinequiet.Isitloadtomoveandcrackthatproduceclaimtoloadthecrackunderthetstressbridge,summinguphasdirectstresscracks,twokindsstresscrackoncesDirectstresscrackrefertooutsideloaddirectcrackthatstressproducethatcause.Thereasonwhythecrackproducesisasfollows,1,Designthestageofcalculating,calculateorleaksandcalculatespartlywhilecalculatinginstructure;Calculateisunreasonable;Thestructureissupposedandaccordedwithbystrengthactuallybystrength;Loadandcalculateorleakandcalculatefew;Internalforceandmatchingthemistakeincomputationofmuscle;Safetycoefficientofstructureisnotenough.Donotconsiderthepossibilitythatconstructatthetimeofthestructuraldesign;Ititodesignthesection;Itissimplylittleandassigningthemistakeforreinforciup;Structurerigidityisinsufficient;Constructanddealwithimproperly;Thedesigndrawingcannotbeexplainedclearlyetc..2,Constructionstage,doesnotpileupandconstructthemachines,materiallimiting;Isitprefabricatestructurestructurereceivestrengthcharacteristic,standup,isithang,transport,installtogetupatwilltounderstand;Constructnotaccordingtothedesigndrawing,altertheconstructionthestructurewithoutauthorization,changethestructureandreceivethestrengtnotdothetiredintensitycheckingcomputationsundermachinevibrationandwaitstructure.3,Usingstage,theheavy-dutyvehiclewhichgoesbeyondthedesignloadpassesthebridgReceivethecontact;,strikingofthevehicle,shipping;Strongwind,heavysnow,earthquakehappen,explodeetc..Stresscrackoncemeansthestressofsecondarycausedbyloadingoutsideproducesthecrack.Thereasonwhythecrackproducesisasfollows,1,Indesignoutsideloadfunction,becauseactualworkingstandroutine,structureofthingcalculatehavediscrepancyorisitconsidertocausestressoncetocausethestructuretofractureinsomeposition.Twoisitarchfootisitisitassign"X"shapereinforcingbar,cutdownthisplacewaysizedesignandcutwithscissorsatthesametimetoadoptoftentodesigntocutwithscissors,theorycalculateplacethiscanstorecurvedsquarein,butrealityshoresistcurvedstilltocutwithscissors,sothatpresentthecrackandcausethebarcorrosion.2,Bridgestructureisitdigtrough,turnonhole,setupoxlegoften,difficulttouseaaccurateonediagrammatictoisitisitcalculatetoimincalculatinginroutine,setupandreceivethestrengthreinforcingbaringeneralfoundationexperience.Studieshaveshown,afterbeingdugtheholebythestrengthcomponent,itwillproducethediffractionphenomenonthatstrengthflows,intenstheholeinautensil,producedtheenormousstresstoconcentrate.Inlongtostepprestressingforceofthecontinuousroofbeam,oftenblockthesteelbunchaccotheneedsofsectioninternalforceinstepping,setuptheanchorhead,butcanofcrackintheanchorfirmsectionadjacentplace.Soifdealwithimproper,incornerorcomponentformsuddenchangeoffice,blockplacetobeeasytoappearcrackstrengthreinforcingbarofstructurethe.Intheactualproject,stresscrackonceproducecommonreasonwhichloadsthecrack.Stresscrackoncebelongtoonemorepieceofnatureofdrawing,splittingoff,shearing.Stresscrackonceisloadedandcaused,onlyseldomcalculateaccordingtotheroutinetoo,butwithmoderntocalculateconstantperfectionofmeans,timesofstresscracktocanaccomplishreasonablecheckingcomputationstoo.Forexampletosuchstresses2timesofproducingasprestressingcreeping,etc.,department'sfiniteelementprocedurecalculateslevelspolecorrebutmoredifficult40yearsago.Inthedesign,shouldpayattentiontoavoidingsuddenchange(orsectionsuddenchange),whenitisunabletoavoid,shoulddopwith,cornerforinstance,makeroundhorn,suddenchangeofficemakeintothegrzonetransition,isitisitmixmuscletoconstructtostrengthenatthesametimeagainobliquetoreinforcingbar,astolargeholeinautensilcansetupproteperimeteratthetermsofhavinganglesteel.Loadthecrackcharacteristiaccordanceinwithloadingdifferentlyandpresentingdifferentcharacteristicsdifferently.Thecrackappearpersonwhodrawmore,thecuttingareaortheseriouspositionofvibratiopointout,isitgetupcoverorhavealongkeepintoshortcrackofdirectiontoappearpersonwhopress,oftenthestructurereachesthesignofbearingtheweightofstrengthlimit,itisanomenthatthestructureisdestroyed,itsreasonisoftenthatsepartialandsmall.Receivethestrengthwaydifferentlyaccordingtothestructure,characteristicproducedisasfollows:1,Thecentreisdrawn.Thecrackrunsthrcomponentcrosssection,theintervalisequalonthewhole,andisperpendiculartoreceivingthestrengthdirection.Whileadoptingthewhorlreinforcingbar,lieinthesecond-classcracknearthereinforcingbarbetweenthecracks.2,Thecentreispisparallelontheshortanddenseparallelcrackwhichreceivethestrengthdirectiontoappearalongthecomponent.3,Receivecurved.Mostnearthelargesectionfromboritappearanddrawintodirectionverticalcracktobeginpersonwhodrawcurvedanddeveloptowardneutralizationaxlegradually.Whileadoptingthewhorlreinforcingbar,canseeshortersecond-classcrackamongthecracks.Whenthestructurematchesmusclesless,therearefewbutwidecracks,fragilitydestructionmaytakeplaceinthestructure4,Pressedbigandpartial.Heavytopressandmixpersonwhodrawmuscleonelighttopigeonholeintothecomponentwhilebeingpartialwhilebeingpartialtoreceivingthecurvedcomponent.5,Pressedsmallandpartial.Smalltopressandmixpersonwhodrawmuscleamoreoneheavytopigeonholeintothecomponentwhilebeipartialwhilebeingpartial,similartothecentreandpressedthecomponent.6,obliqulywhenthehoopmuscleistoodenseanddestroy,theobliquecrackwhichisthan45??directionappearsalongthebellyofroofbeamend;Isitisitisitdestocuttohappenwhenthehoopmuscleisproper,underpartisitinvite45??directionparallelobliquecrackeachothertoappearalongroofbeamend.7,Sprained.Componesidebellyappearmanydirectionobliquecrack,45??oftreaty,first,andtolspiraldirectionbeingadjoint.8,Washedandcut.4sideisitinvite45??directplanedrawandsplittotakeplacealongcolumncapboard,formthetangentplaneofwashing.9,Someandispressed.Sometoappearpersonwhopressdirectionroughlyparallellargeshortcrackswithpressure.(2)crackcausedintemperaturechangeTheconcretehasnatureofexpandingwithheatandcontractwithcold,lookonexternalenvironmentconditionorthestructuretemperaturechanges,concretetakoutofshape,ifoutofshapetorestrainfrom,producethestressinthestructuthetemperaturecrackpromptlywhenexceedingconcretetensilestrengthinstress.beingheavytostepfoot-pathamongthebridge,temperaturestresscanisitgobeyondlivingyearstresseventoreach.Thetemperaturecrackdistinguishesthemaincharaofothercrackswillbevariedwithtemperatureandexpandedorclosedup.Themainisasfollows,tocausetemperatureandchange1,Annualdifferenceintemperature.Temperatureischangingconstantlyinfourseasonsinoneyear,butchangerelativelyslowly,theimpactonstructureofthebridgeismainlytheverticaldisplacementwhichcausesthebridge,canpropupseatmoveorsetupflexiblemound,etc.nottocmeasurecoordinate,throughbridgefloorexpansionjointgenerally,cancausetempcrackonlywhenthedisplacementofthestructureislimited,forexamplearchedjustbridgeetc.TheannualdifferenceintemperatureofourcountrygenerallycharangewiththeconductoftheaveragetemperatureinthemoonofJanuaryandJuly.Consideringthecreepcharacteristicoftheconcrete,theelasticmouldamountofshouldbeconsideredrollingoverandreducingwhentheinternalforceoftheannualdifferenceintemperatureiscalculated.2,Rizhao.Afterbeingtannedbythesunbtothesideofbridgepanel,thegirderorthepier,temperatureisobviouslyhigherthanotherposition,thetemperaturegradientispresentedanddistributedbythelineshape.Becauseofrestrainoneselffunction,causepartdrawstresstoberelativelyheavyappears.Rizhaoandfollowingtoisitcausestructurecommonreasonmost,temperacracktolowerthetemperaturesuddenly3,Lowerthetemperaturesuddenly.Fallheavyrain,coldairattack,sunset,etc.cancausestructuresurfacetemperaturesuddesuddenly,butbecauseinsidetemperaturechangerelativelyslowproducingtemperaturegradient.Rizhaoandlowerthetemperatureinternalforcecanadoptdesignspecificconsultrealbridgematerialsgoonwhencalculatingsuddenly,concreteelasticmouldamountdoesnotconsiderconvertingintoandreducing4,Heatofhydration.Appearcourseofconstructing,thelargevolumeconcrete(thicknessexceeds2.0),afterbecausecementwatersendoutheat,causeinsideverymuchhightemperature,theinandexternaldifferenceintemperatureistoolarge,causethesurfacetoappearinShouldaccordingtoactualconditionsinconstructing,isitchooseheatofhydracementvarietytotryone'sbest,limitcementunit'sconsumption,reducetheaggrenterthetemperatureofthemould,reducetheinternalandexternaldifferenceintemperature,andlowerthetemperatureslowly,canadoptthecirculationcoolingsycarryontheinsidetodispeltheheatincaseofnecessity,oradoptthethinlayerinsuccessioninordertoacceleratedispellingtheheat.5,Theconstructionmeasureisimproperatthetimeofsteammaintenanceorthewinterconstruction,theconcreteissuddenandcoldandsuddenandhot,internalandexternaltemperatureisuneven,appearinthecrack.6,PrefabricateTroofbeamhorizontalbafflewhentheinstallation,propupseatburystencilplatewithtransferflatstencilplatewhenweldinginweldmeasuretobeimproper,ironpiecesofnearbyconcreteeasytoisitfractureAdoptelectricheatpiecedrawlawpiecedrawprestressingforceatthecomponent,prestressingforcesteeltemperaturecanriseto350degreesCentigrade,theconcretecomponentisapttofracture.Experimentalstudyindicates,arecausedtheintensityofconcretethatthehightemperatureburnstoobviouslyreducewithrisingoftempersuchreasonsasthefire,etc.,glueingformingthedeclinethereuponofstrengthofreinforcingbarandconcrete,tensilestrengthdropby50%afterconcretetemperaturereaches300degreesCentigrade,compressionstrengthdropsby60%,glueingthestrofformingtodropby80%ofonlyroundreinforcingbarandconcrete;Becauseheat,concretebodydissociateinkevaporateandcanproduceandshrinksharplyinalargeamount(3)shrinkthecrackcausedIntheactualproject,itisthemostcommonbecauseconcreteshrinksthecrackShrinkkindinconcrete,plasticityshrinkisititshrinks(isitcontracttodo)reasonthatthevolumeofconcreteoutofshapehappenstoshrink,shrinkspontaneoadditionandthecharshrink.Plasticityshrink.About4hoursafteritisbuiltthatinthecourseofconstructing,concretehappens,thecementwaterresponseisfierceatthismoment,thestrandtakesshapegradually,secretewaterandmoisturetoevaporatestheconcretedesiccatesandshrinks,itisatthesametimeconductoneselfwithdsinkingbecauseaggregate,sowhenhardenconcreteyet,itcallplasticityshrink.Theplasticityshrinkproducingamountgradeisverybig,canbeuptoabout1%.Ifstthereinforcingbarwhiletheaggregatesinks,formthecrackalongthereinforcingbardirection.Ifweb,roofbeamofTandroofbeamofcaseandcarrybaseplatehanofficeincomponentverticaltobecomesectionalplace,becausesinktooreallytosuperficialobeyingthewebdirectioncrackwillhappenevenlybeforehardenning.Forreducingconcreteplasticityshrink,itshouldcontrolbywaterdustwhenbeingconstructthan,lastlong-timemixing,unloadingshouldnottooquick,isitisittakeclossmashtoshake,verticaltobecomesectionalplaceshoulddividelayerbuild.Shrshrink(doandcontract).Aftertheconcreteisformedhard,asthetoplayermevaporatedprogressively,thehumidityisreducedprogressively,thevolumeofcisreduced,iscalledandshrunktoshrink(doandcontract).Becauseconcretetoplayermoisturelosssoon,itisslowforinsidetolose,producesurfaceshrinkheavy,insideshrinkalightoneeventoshrink,itisoutofshapetorestrainfrombytheinsforsurfacetoshrink,causethesurfaceconcretetobearpullingforce,whenthesurfaceconcretebearspullingforcetoexceeditstensilestrength,produceandshrinkthecrack.Theconcretehardensafter-contractiontojustshrinkandshrinkmainly.Suchasmixmusclerateheavycomponent(exceed3%),betweenreinforcingbarandmoreobviousrestraintsrelativelythatconcreteshrink,theconcretesurfaceisapttoappearcrackscrackle.Shrinkspontaneously.Spontaneoustoitshrinkstobeconcreteinofhardenning,cementandwatertakeplaceinkreact,theshrinkwithhavenothibyexternalhumidity,andcanpositive(whethershrink,suchasordinaryportlandconcrete),cannegativetoo(whetherexpand,suchasconcrete,concreteofslagcemcementofflyash).Thecharshrinks.Betweencarbondioxideandhyrateofcementofatmospheretakeplaceoutofshapeshrinkthatchemicalreactioncause.Thecharandcouldhappenonlyabout50%ofhumidity,andacceleratewithincreaseofthedofthecarbondioxide.Thecharshrinksandseldomcalculates.Thecharacteristicconcreteshrinksthecrackisthatthemajoritybelongstothesurfacecrack,thecrackisrelativelydetailedinwidth,andcriss-cross,becomethefullofcracksform,thnothaveanylaw.Studieshaveshown,influenceconcreteshrinkmainfactorofcfollows,1,Varietyofcement,gradeandconsumption.Slagcement,quick-hardeningcement,low-heatcementconcretecontractivityarerelativelyhigh,ordinarycement,volcanicashcement,aluminacementconcretecontractivityarerelativelylow.Cementgradelowinaddition,unitvolumeconsumptionheavyrubingdetaileddegreeheavy,theconcreteshrinksthemoregreatly,andshrinktimeisthelonger.Forexample,toimprovetheintensityoftheconcrete,oftenadoptandincreasethecementconsmethodbyforcewhileconstructing,theresultshrinksthestresstoobviouslystreVarietyofaggregate.Suchabsorbingwaterratesasthequartz,limestone,clorock,granite,feldspar,etc.aresmaller,contractivityisrelativelylowintheaggabsorbingwaterratesasthesandstone,slate,angleamphibolite,etc.aregreater,contractivityisrelativelyhigh.Aggregategrainsoffoot-pathheavytoshrinklightinaddition,watercontentbigtoshrinkthelarger.3,Watergraythan.Theheavierwaterconsumptionis,thehigherwateranddustare,theconcreteshrinksthemoregreatlthepharmaceuticaloutside.Itisthebettertomixpharmaceuticalwater-retainingoutside,thentheconcreteshrinksthesmaller.5,MaintainWaterthathemethod.goodmaintenancecanacceleratetheconcretereacts,obtaintheintensityofhigherconcrete.Keephumidityhigh,lowmaintainingtimetobethelongertemperaturewhenmaintaithentheconcreteshrinksthesmaller.Steammaintainwaythanmaintainwayconcrettakelighttoshrinknaturall.6,Externalenvironment.Thehumidityislittle,thetemperaturearehigh,thewindspeedislargeintheatmosphere,thentheconcreteisevaporatedfast,theconcreteshrinksthefaster.7,ShakeandsmashthewayaMachineryshakewayofsmashingthanmakefirmbyrammingortampingwayconcretecontractivitytakelittlebyhand.Shakingshoulddetermineaccordingtomechanicalperformancetosmashtime,aregenerallysuitablefor55s/time.Itistooshortcannotsmashcloselyknit,itisinsufficientornoteveninintensitytoformthistoolong,causeanddividestorey,thickaggregatesinkstothegroundfloor,stratathatthedetailedaggregatestays,theintensityisnoteven,theuppersshrinkthecrack.Andshrinkthecrackcausedtotemperature,worthyofconstructreinforcingbaragainingcanobviouslyimprovetheresistingthesplittingofconcrete,structureofespeciallythinwall(thick200cmofwall).Mixmuscleshouldisitadiameterreinforcingbar(8|?construct14|?)tohavepriority,littleintervalassign(whether@10construct@15cm)onconstructing,thewholesectionisitmixmuscberateunsuitabletobelowerthan0toconstruct.3%,cangenerallyadopt0.3%(4),crackthatcausesoutofshapeofplinthofthegroundBecausefoundationverticaltoeventosubsideorhorizontaldirectiondisplamakethestructureproducetheadditionalstress,gobeyondresistingtheabilityoofconcretestructure,causethestructuretofracture.Theevenmainreasonthatthefoundationisasfollows,1,Reconnoitrestheprecisionandisnotenoughformaterialsinaccuratlyingeology.Designing,constructingwithoutfullygraspingthegeologicalsituation,thisisthemainreasonthatcausethegroundnottosubsidSuchashillsareaorbridge,districtofmountainridge,,holeintervaltobetoofarwhenreconnoitring,andgroundriseandfallbigtherock,reconnoitringthereportcan'tfullyreflecttherealgeologicalsituation.2,ThegeologicaldifferenceofthegroundBuildingitinthebridgeofthevalleyoftheditchofmountainarea,geologyofplaceandplaceonthehillsidechangelarger,eventhereareweakgroundsinthebecausethesoilofthegrounddoesnotcausesanddoesnotsubsideevenlywiththecompressing.3,Thestructureloadsthedifferencetoobig.Undertheunanimousterms,wheneveryfoundationtooheavytoloaddifferenceingeologicalsituation,maycauseevenlytosubside,forexamplehightofilloutsoilcaseshapeinthemiddlepartoftheculvertthantoisittakeheavytoloadbothsides,tosubsidesoonheavythanmiddlepart,caseisitmightfracturetocontain4,Thedifferenceofbasictypeisgreat.Uniteitinthebridgethesamly,mixanduseanddoesnotexpandthefandafoundationwiththefoundation,oradoptafoundationwhenafoot-pathoralongdifferenceisgreatatthesametime,oradoptthefoundationofexpandingwhenbasiselevationiswidelydifferentatthesametime,maycausethegroundnottosubsidtoo5,Foundationbuiltbystages.Inthenewly-builtbridgenearthefoundationobridge,ifthehalfabridgeaboutexpresswaybuiltbystages,thenewly-builtbrorthefoundationcausesthesoilofthegroundtoconsolidateagainwhiledealingwith,maycauseandsubsidethefoundationoforiginalbridgegreatly6,Thegroundisbloatedly.Thegroundsoilofhighermoisturecontentontermsthatlowerthanzeroexpandsbecauseofbeingicy;Oncetemperaturegoesup,thefrozensoilismelted,thesettingofground.SothegroundisicyormeltscausesanddoesnotsubsideevenlyBridgefoundationputonbody,cavewithstalactitesandstalagmites,activityfaucomingdownatthebadgeology,maycauseanddoesnotsubsideevenly.8,Afterthebridgeisbuiltup,theconditionchangeoforiginalground.Aftermostnaturalgartificialgroundsaresoakedwithwater,especiallyusuallyfilloutsuchsoilofspecialgroundasthesoil,loess,expandingintheland,etc.,soilbodyintensitymeetcompressoutofshapetostrengthen.Inthesoftsoilground,seasoncausesthewtodroptodrawwateroraridartificially,thegroundsoillayerconsolidatesandreducethebuoyancyonthefoundationatthesametime,shoulderingtheobstrucrubingtoincrease,thefoundationiscarriedonone'sshoulderorbackandstrengthened.Somebridgefoundationisitputtooshallowtobury,erode,isitdflood,thefoundationmightbemoved.Groundloadchangeofterms,bridgenearbyiitabolishsquare,grit,etc.inalargeamounttoputtopilewithcavein,lreasonforinstance,itisoutofshapethatthebridgelocationrangesoillayermaybecompressedagain.So,theconditionoforiginalgroundchangewhileusingmaycausdoesnotsubsideevenlyProducethestructurethingofhorizontalthrusttoarchedbridge,etc.,itisthemainreasonthathorizontaldisplacementcrackemergestodoriginalgeologicalconditionwhentothatitisunreasonabletograspincompletelyandconstructinthegeologicalsituation.

橋梁裂縫產(chǎn)生原因淺析近年來，我省交通基礎(chǔ)建設(shè)得到迅猛發(fā)展，各地興建了大量的混凝土橋梁。在橋梁建造和使用過程中，有關(guān)因出現(xiàn)裂縫而影響工程質(zhì)量甚至導(dǎo)橋梁垮塌的報道屢見不鮮。混凝土開裂可以說是“常發(fā)病”和“多發(fā)病”，經(jīng)常困擾著橋梁工程技術(shù)人員。其實，如果采取一定的設(shè)計和施工措施，很多裂縫是可以克服和控制的。為了進一步加強對混凝土橋梁裂縫的認識，盡量避免工程中出現(xiàn)危害較大的裂縫，本文盡可能對混凝土橋梁裂縫的種類和產(chǎn)生的原因作較全面的分析、總結(jié)，以方便設(shè)計、施工找出控制裂縫的可行辦法，達到防范于未然的作用?；炷翗蛄毫芽p種類、成因?qū)嶋H上，混凝土結(jié)構(gòu)裂縫的成因復(fù)雜而繁多，甚至多種因素相互影響，但每一條裂縫均有其產(chǎn)生的一種或幾種主要原因?；炷翗蛄毫芽p的種類，就其產(chǎn)生的原因，大致可劃分如下幾種：一、荷載引起的裂縫混凝土橋梁在常規(guī)靜、動荷載及次應(yīng)力下產(chǎn)生的裂縫稱荷載裂縫，歸納起來主要有直接應(yīng)力裂縫、次應(yīng)力裂縫兩種。直接應(yīng)力裂縫是指外荷載引起的直接應(yīng)力產(chǎn)生的裂縫。裂縫產(chǎn)生的原因有：1、設(shè)計計算階段，結(jié)構(gòu)計算時不計算或部分漏算；計算模型不合理；結(jié)構(gòu)受力假設(shè)與實際受力不符；荷載少算或漏算；內(nèi)力與配筋計算錯誤；結(jié)構(gòu)安全系數(shù)不夠。結(jié)構(gòu)設(shè)計時不考慮施工的可能性；設(shè)計斷面不足；鋼筋設(shè)置偏少或布置錯誤；結(jié)構(gòu)剛度不足；構(gòu)造處理不當；設(shè)計圖紙交代不清等。2、施工階段，不加限制地堆放施工機具、材料；不了解預(yù)制結(jié)構(gòu)結(jié)構(gòu)受力特點，隨意翻身、起吊、運輸、安裝；不按設(shè)計圖紙施工，擅自更改結(jié)構(gòu)施工順序，改變結(jié)構(gòu)受力模式；不對結(jié)構(gòu)做機器振動下的疲勞強度驗算等。3、使用階段，超出設(shè)計載荷的重型車輛過橋；受車輛、船舶的接觸、撞擊；發(fā)生大風、大雪、地震、爆炸等。次應(yīng)力裂縫是指由外荷載引起的次生應(yīng)力產(chǎn)生裂縫。裂縫產(chǎn)生的原因有：1、在設(shè)計外荷載作用下，由于結(jié)構(gòu)物的實際工作狀態(tài)同常規(guī)計算有出入或計算不考慮，從而在某些部位引起次應(yīng)力導(dǎo)致結(jié)構(gòu)開裂。例如兩鉸拱橋拱腳設(shè)計時常采用布置“X”形鋼筋、同時削減該處斷面尺寸的辦法設(shè)計鉸，理論計算該處不會存在彎矩，但實際該鉸仍然能夠抗彎，以至出現(xiàn)裂縫而導(dǎo)致鋼筋銹蝕。2、橋梁結(jié)構(gòu)中經(jīng)常需要鑿槽、開洞、設(shè)置牛腿等，在常規(guī)計算中難以用準確的圖式進行模擬計算，一般根據(jù)經(jīng)驗設(shè)置受力鋼筋。研究表明，受力構(gòu)件挖孔后，力流將產(chǎn)生繞射現(xiàn)象，在孔洞附近密集，產(chǎn)生巨大的應(yīng)力集中。在長跨預(yù)應(yīng)力連續(xù)梁中，經(jīng)常在跨內(nèi)根據(jù)截面內(nèi)力需要截斷鋼束，設(shè)置錨頭，而在錨固斷面附近經(jīng)?？梢钥吹搅芽p。因此，若處理不當，在這些結(jié)構(gòu)的轉(zhuǎn)角處或構(gòu)件形狀突變處、受力鋼筋截斷處容易出現(xiàn)裂縫。實際工程中，次應(yīng)力裂縫是產(chǎn)生荷載裂縫的最常見原因。次應(yīng)力裂縫多屬張拉、劈裂、剪切性質(zhì)。次應(yīng)力裂縫也是由荷載引起，僅是按常規(guī)一般不計算，但隨著現(xiàn)代計算手段的不斷完善，次應(yīng)力裂縫也是可以做到合理驗算的。例如現(xiàn)在對預(yù)應(yīng)力、徐變等產(chǎn)生的二次應(yīng)力，不少平面桿系有限元程序均可正確計算，但在40年前卻比較困難。在設(shè)計上，應(yīng)注意避免結(jié)構(gòu)突變（或斷面突變），當不能回避時，應(yīng)做局部處理，如轉(zhuǎn)角處做圓角，突變處做成漸變過渡，同時加強構(gòu)造配筋，轉(zhuǎn)角處增配斜向鋼筋，對于較大孔洞有條件時可在周邊設(shè)置護邊角鋼。荷載裂縫特征依荷載不同而異呈現(xiàn)不同的特點。這類裂縫多出現(xiàn)在受拉區(qū)、受剪區(qū)或振動嚴重部位。但必須指出，如果受壓區(qū)出現(xiàn)起皮或有沿受壓方向的短裂縫，往往是結(jié)構(gòu)達到承載力極限的標志，是結(jié)構(gòu)破壞的前兆，其原因往往是截面尺寸偏小。根據(jù)結(jié)構(gòu)不同受力方式，產(chǎn)生的裂縫特征如下：1、中心受拉。裂縫貫穿構(gòu)件橫截面，間距大體相等，且垂直于受力方向。采用螺紋鋼筋時，裂縫之間出現(xiàn)位于鋼筋附近的次裂縫。2、中心受壓。沿構(gòu)件出現(xiàn)平行于受力方向的短而密的平行裂縫。3、受彎。彎矩最大截面附近從受拉區(qū)邊沿開始出現(xiàn)與受拉方向垂直的裂縫，并逐漸向中和軸方向發(fā)展。采用螺紋鋼筋時，裂縫間可見較短的次裂縫。當結(jié)構(gòu)配筋較少時，裂縫少而寬，結(jié)構(gòu)可能發(fā)生脆性破壞。4、大偏心受壓。大偏心受壓和受拉區(qū)配筋較少的小偏心受壓構(gòu)件，類似于受彎構(gòu)件。5、小偏心受壓。小偏心受壓和受拉區(qū)配筋較多的大偏心受壓構(gòu)件，類似于中心受壓構(gòu)件。6、受剪。當箍筋太密時發(fā)生斜壓破壞，沿梁端腹部出現(xiàn)大于45°方向的斜裂縫；當箍筋適當時發(fā)生剪壓破壞，沿梁端中下部出現(xiàn)約45°方向相互平行的斜裂縫。7、受扭。構(gòu)件一側(cè)腹部先出現(xiàn)多條約45°方向斜裂縫，并向相鄰面以螺旋方向展開。8、受沖切。沿柱頭板內(nèi)四側(cè)發(fā)生約45°方向斜面拉裂，形成沖切面。9、局部受壓。在局部受壓區(qū)出現(xiàn)與壓力方向大致平行的多條短裂縫。二、溫度變化引起的裂縫混凝土具有熱脹冷縮性質(zhì)，當外部環(huán)境或結(jié)構(gòu)內(nèi)部溫度發(fā)生變化，混凝土將發(fā)生變形，若變形遭到約束，則在結(jié)構(gòu)內(nèi)將產(chǎn)生應(yīng)力，當應(yīng)力超過混凝土抗拉強度時即產(chǎn)生溫度裂縫。在某些大跨徑橋梁中，溫度應(yīng)力可以達到甚至超出活載應(yīng)力。溫度裂縫區(qū)別其它裂縫最主要特征是將隨溫度變化而擴張或合攏。引起溫度變化主要因素有：1、年溫差。一年中四季溫度不斷變化，但變化相對緩慢，對橋梁結(jié)構(gòu)的影響主要是導(dǎo)致橋梁的縱向位移，一般可通過橋面伸縮縫、支座位移或設(shè)置柔性墩等構(gòu)造措施相協(xié)調(diào)，只有結(jié)構(gòu)的位移受到限制時才會引起溫度裂縫，例如拱橋、剛架橋等。我國年溫差一般以一月和七月月平均溫度的作為變化幅度?？紤]到混凝土的蠕變特性，年溫差內(nèi)力計算時混凝土彈性模量應(yīng)考慮折減。2、日照。橋面板、主梁或橋墩側(cè)面受太陽曝曬后，溫度明顯高于其它部位，溫度梯度呈非線形分布。由于受到自身約束作用，導(dǎo)致局部拉應(yīng)力較大，出現(xiàn)裂縫。日照和下述驟然降溫是導(dǎo)致結(jié)構(gòu)溫度裂縫的最常見原因。3、驟然降溫。突降大雨、冷空氣侵襲、日落等可導(dǎo)致結(jié)構(gòu)外表面溫度突然下降，但因內(nèi)部溫度變化相對較慢而產(chǎn)生溫度梯度。日照和驟然降溫內(nèi)力計算時可采用設(shè)計規(guī)范或參考實橋資料進行，混凝土彈性模量不考慮折減。4、水化熱。出現(xiàn)在施工過程中，大體積混凝土（厚度超過2.0米）澆筑之后由于水泥水化