土木建筑工程工程管理中英文資料外文翻譯文獻Abstract:Tostudytheapplicationofcontinuumstructuraltopologyoptimizationmethodstorealengineeringstructures,anoptimizationmethodforanoptimaltopologydesignofmultistorysteelframebracingsystemsispresented.Onasensitivityanalysis,anelementremovalcriterionforcontinuumstructureswithstressandmulti-displacementconstraintsundermultiplelateralloadingconditionsisproposed.Aconceptofmeanthicknessofadesigndomainisprovidedtoensurethereasonablenessofoptimalresults.Intheproposedoptimizationmethod,theoptimaldesignofanunbracedsteelframewithoutdisplacementconstraintsisperformedfirstly,andthentheoptimaltopologyofabracingsystemforthemultistorysteelframeconsideringdisplacementconstraintsisobtainedbyusingevolutionarystructuraloptimizationandthegivenremovalcriterion,andfinallytheoptimalayoutofthebracingsystemisinterpretedasbracingmembers.Anexampleof3-bay12-storyplanesteelframeshowsthatitiseffectiveforthegivenoptimizationmethodintheoptimaldesignofbracingsystemsformultistorysteelframes.Keywords:steelframe;bracingsystem;continuum;topologyoptimization;evolutionarystructuraloptimization2.1ReinforcedConcretePlainconcreteisformedfromahardenedmixtureofcement,water,fineaggregate,coarseaggregate(crushedstoneorgravel),air,andoftenotheradmixtures.Theplasticmixisplacedandconsolidatedintheformwork,thencuredtofacilitatetheaccelerationofthechemicalhydrationreactionlfthecement/watermix,resultinginhardenedword文檔可自由復制編輯concrete.Thefinishedproducthashighcompressivestrength,andlowresistancetotension,suchthatitstensilestrengthisapproximatelyonetenthlfitscompressivestrength.Consequently,tensileandshearreinforcementinthetensileregionsofsectionshastobeprovidedtocompensatefortheweaktensionregionsinthereinforcedconcreteelement.Itisthisdeviationinthecompositionofareinforcesconcretesectionfromthehomogeneityofstandardwoodorsteelsectionsthatrequiresamodifiedapproachtothebasicprinciplesofstructuraldesign.Thetwocomponentsoftheheterogeneousreinforcedconcretesectionaretobesoarrangedandproportionedthatoptimaluseismadeofthematerialsinvolved.Thisispossiblebecauseconcretecaneasilybegivenanydesiredshapebyplacingandcompactingthewetmixtureoftheconstituentingredientsareproperlyproportioned,thefinishedproductbecomesstrong,durable,and,incombinationwiththereinforcingbars,adaptableforuseasmainmembersofanystructuralsystem.Thetechniquesnecessaryforplacingconcretedependonthetypeofmembertobecast:thatis,whetheritisacolumn,abean,awall,aslab,afoundation.amasscolumns,oranextensionofpreviouslyplacedandhardenedconcrete.Forbeams,columns,andwalls,theformsshouldbewelloiledaftercleaningthem,andthereinforcementshouldbeclearedofrustandotherharmfulmaterials.Infoundations,theearthshouldbecompactedandthoroughlymoistenedtoabout6in.indepthtoavoidabsorptionofthemoisturepresentinthewetconcrete.Concreteshouldalwaysbeplacedinhorizontallayerswhicharecompactedbymeansofhighfrequencypower-drivenvibratorsofeithertheimmersionorexternaltype,asthecaserequires,unlessitisplacedbypumping.Itmustbekeptinmind,however,thatovervibrationcanbeharmfulsinceitcouldcausesegregationoftheaggregateandbleedingoftheconcrete.Hydrationofthecementtakesplaceinthepresenceofmoistureattemperaturesabove50°F.Itisnecessarytomaintainsuchaconditioninorderthatthechemicalhydrationreactioncantakeplace.Ifdryingistoorapid,surfacecrackingtakesplace.Thiswouldresultinreductionofconcretestrengthduetocrackingaswellasthefailuretoattainfullchemicalhydration.Itisclearthatalargenumberofparametershavetobedealtwithinproportioningareinforcedconcreteelement,suchasgeometricalwidth,depth,areaofreinforcement,steelstrain,concretestrain,steelstress,andsoon.Consequently,trialandadjustmentisnecessaryinthechoiceofconcretesections,withassumptionsbasedonconditionsatsite,word文檔可自由復制編輯availabilityoftheconstituentmaterials,particulardemandsoftheowners,architecturalandheadroomrequirements,theapplicablecodes,andenvironmentalreinforcedconcreteisoftenasite-constructedcomposite,incontrasttothestandardmill-fabricatedbeamandcolumnsectionsinsteelstructures.Atrialsectionhastobechosenforeachcriticallocationinastructuralsystem.Thetrialsectionhastobeanalyzedtodetermineifitsnominalresistingstrengthisadequatetocarrytheappliedfactoredload.Sincemorethanonetrialisoftennecessarytoarriveattherequiredsection,thefirstdesigninputstepgeneratesintoaseriesoftrial-and-adjustmentanalyses.Thetrial-and–adjustmentproceduresforthechoiceofaconcretesectionleadtotheconvergenceofanalysisanddesign.Henceeverydesignisananalysisonceatrialsectionischosen.Theavailabilityofhandbooks,charts,andpersonalcomputersandprogramssupportsthisapproachasamoreefficient,compact,andspeedyinstructionalmethodcomparedwiththetraditionalapproachoftreatingtheanalysisofreinforcedconcreteseparatelyfrompuredesign.2.2EarthworkBecauseearthmovingmethodsandcostschangemorequicklythanthoseinanyotherbranchofcivilengineering,thisisafieldwheretherearerealopportunitiesfortheenthusiast.In1935mostofthemethodsnowinuseforcarryingandexcavatingearthwithrubber-tyredequipmentdidnotexist.Mostearthwasmovedbynarrowrailtrack,nowrelativelyrare,andthemainmethodsofexcavation,withfaceshovel,backacter,ordraglineorgrab,thoughtheyarestillwidelyusedareonlyafewofthemanycurrentmethods.Tokeephisknowledgeofearthmovingequipmentuptodateanengineermustthereforespendtinestudyingmodernmachines.Generallytheonlyreliableup-to-dateinformationonexcavators,loadersandtransportisobtainablefromthemakers.Earthworksorearthmovingmeanscuttingintogroundwhereitssurfaceistoohigh(cuts),anddumpingtheearthinotherplaceswherethesurfaceistoolow(fills).Toreduceearthworkcosts,thevolumeofthefillsshouldbeequaltothevolumeofthecutsandwhereverpossiblethecutsshouldbeplacedneartofillsofequalvolumesoastoreducetransportanddoublehandlingofthefill.Thisworkofearthworkdesignfallsontheengineerwholaysouttheroadsinceitisthelayoutoftheearthworkmorethananythingelsewhichdecidesitscheapness.Fromtheavailablemapsahdlevels,theengineeringmusttrytoreachasmanydecisionsaspossibleinthedrawingofficebyword文檔可自由復制編輯drawingcrosssectionsoftheearthwork.Onthesitewhenfurtherinformationbecomesavailablehecanmakechangesinjissectionsandlayout,butthedrawinglfficeworkwillnothavebeenlost.Itwillhavehelpedhimtoreachthebestsolutionintheshortesttime.Thecheapestwayofmovingearthistotakeitdirectlyoutofthecutanddropitasfillwiththesamemachine.Thisisnotalwayspossible,butwhenitcanbedoneitisideal,beingbothquickandcheap.Draglines,bulldozersandfaceshovelsandothis.Thelargestradiusisobtainedwiththedragline,andthelargesttonnageofearthismovedbythebulldozer,thoughonlyovershortdistances.Thedisadvantagesofthedraglinearethatitmustdigbelowitself,itcannotdigwithforceintocompactedmaterial,itcannotdigonsteepslopws,anditsdumpinganddiggingarenotaccurate.Faceshovelsarebetweenbulldozersanddraglines,havingalargerradiusofactionthanbulldozersbutlessthandraglines.Theyareanletodigintoaverticalclifffaceinawaywhichwouldbedangeroustorabulldozeroperatorandimpossibleforadragline.Eachpieceofequipmentshouldbeleveloftheirtracksandfordeepdigsincompactmaterialabackacterismostuseful,butitsdumpingradiusisconsiderablylessthanthatofthesameescavatorfittedwithafaceshovel.Rubber-tyredbowlscrapersareindispensableforfairlyleveldiggingwherethedistanceoftransportistoomuchtoradraglineorfaceshovel.Theycandigthematerialdeeply(butonlybelowthemselves)toafairlyflatsurface,carryithundredsofmetersifneedbe,thendropitandlevelitroughlyduringthedumping.Forharddiggingitisoftenfoundeconomicaltokeepapushertractor(wheeledortracked)onthediggingsite,topusheachscraperasitreturnstodig.Assoonasthescraperisfull,thepushertractorreturnstothebeginningofthedigtoheoptohelpthenestscraper.Bowlscrapersareoftenextremelypowerfulmachines;manymakersbuildscrapersof8cubicmetersstruckcapacity,whichcarry10m3heaped.Thelargestself-propelledscrapersareof19m3struckcapacity(25m3heaped)andtheyaredrivenbyatractorengineof430horse-powers.Dumpersareprobablythecommonestrubber-tyredtransportsincetheycanalsoconvenientlybeusedforcarryingconcreteorotherbuildingmaterials.Dumpershavetheearthcontaineroverthefrontaxleonlargerubber-tyredwheels,andthecontainertipsforwardsonmosttypes,thoughinarticulateddumpersthedirectionoftipcanbewidelyvaried.Thesmallestdumpershaveacapacityofabout0.5m3,andthelargeststandardtypesareofabout4.5m3.Specialtypesincludetheself-loadingdumperofupto4m3word文檔可自由復制編輯andthearticulatedtypeofabout0.5m3.Thedistinctionbetweendumpersanddumptrucksmustberemembered.dumperstipforwardsandthedriversitsbehindtheload.Dumptrucksareheavy,strengthenedtippinglorries,thedrivertravelsinfrontlftheloadandtheloadisdumpedbehindhim,sotheyaresometimescalledrear-dumptrucks.2.3SafetyofStructuresTheprincipal scopeof specificationsis to provide generalprinciples andcomputationalmethodsinordertoverifysafetyofstructures.The“safetyfactor ”,whichaccordingtomoderntrendsisindependentofthenatureandcombinationofthematerialsused,canusuallybedefinedastheratiobetweentheconditions.Thisratioisalsoproportionaltotheinverseoftheprobability(risk)offailureofthestructure.Failurehastobeconsiderednotonlyasoverallcollapseofthestructurebutalsoasunserviceabilityor,accordingtoamoreprecise.Commondefinition.Asthereachingofa“l(fā)imitstate ”whichcausestheconstructionottoaccomplishthetaskitwasdesignedfor.Therearetwocategoriesoflimitstate:(1)Ultimatelimit sate,whichcorrespondstothehighestvalueoftheload-bearingcapacity.Examplesincludelocalbucklingorglobalinstabilityofthestructure;failureofsomesectionsandsubsequenttransformationofthestructureintoamechanism;failurebyfatigue;elasticorplasticdeformationorcreepthatcauseasubstantialchangeofthegeometryofthestructure;andsensitivityofthestructuretoalternatingloads,tofireandtoexplosions.(2)Servicelimitstates,whicharefunctionsoftheuseanddurabilityofthestructure.Examplesincludeexcessivedeformationsanddisplacementswithoutinstability;earlyorexcessivecracks;largevibrations;andcorrosion.Computationalmethodsusedtoverifystructureswithrespecttothedifferentsafetyconditionscanbeseparatedinto:(1)Deterministicmethods,inwhichthemainparametersareconsideredasnonrandomparameters.(2)Probabilisticmethods,inwhichthemainparametersareconsideredasrandomparameters.Alternatively,withrespecttothedifferentuseoffactorsofsafety,computationalmethodscanbeseparatedinto:(1)Allowablestressmethod,inwhichthestressescomputedundermaximumloadsarecomparedwiththestrengthofthematerialreducedbygivensafetyfactors.word文檔可自由復制編輯(2)Limitstatesmethod,inwhichthestructuremaybeproportionedonthebasisofitsmaximumstrength.Thisstrength,asdeterminedbyrationalanalysis,shallnotbelessthanthatrequiredtosupportafactoredloadequaltothesumofthefactoredliveloadanddeadload(ultimatestate).Thestressescorrespondingtoworking(service)conditionswithunfactoredliveanddeadloadsarecomparedwithprescribedvalues(servicelimitstate).Fromthefourpossiblecombinationsofthefirsttwoandsecondtwomethods,wecanobtainsomeusefulcomputationalmethods.Generally,twocombinationsprevail:(1)deterministicmethods,whichmakeuseofallowablestresses.(2)Probabilisticmethods,whichmakeuseoflimitstates.Themainadvantageofprobabilisticapproachesisthat,atleastintheory,itispossibletoscientificallytakeintoaccountallrandomfactorsofsafety,babilisticapproachesdependupon:Randomdistributionofstrengthofmaterialswithrespecttotheconditionsoffabricationanderection(scatterofthevaluesofmechanicalpropertiesthroughoutthestructure);Uncertaintyofthegeometryofthecross-sectionsandofthestructure(faultsandimperfectionsduetofabricationanderectionofthestructure);Uncertaintyofthepredictedliveloadsanddeadloadsactingonthestructure;(4)Uncertaintyrelatedtotheapproximationofthecomputationalmethodused(deviationoftheactualstressesfromcomputedstresses).Furthermore,probabilistictheoriesmeanthattheallowableriskcanbebasedonseveralfactors,suchas:(1)Importanceoftheconstructionandgravityofthedamagebyitsfailure;(2)Numberofhumanliveswhichcanbethreatenedbythisfailure;(3)Possibilityand/orlikelihoodofrepairingthestructure;(4)Predictedlifeofthestructure.Allthesefactorsarerelatedtoeconomicandsocialconsiderationssuch：asInitialcostoftheconstruction;Amortizationfundsforthedurationoftheconstruction;Costofphysicalandmaterialdamageduetothefailureoftheconstruction;Adverseimpactonsociety;Moralandpsychologicalviews.Thedefinitionofalltheseparameters,foragivensafetyfactor,allowsconstructionword文檔可自由復制編輯attheoptimumcost.However,thedifficultyofcarryingoutacompleteprobabilisticanalysishastobetakenintoaccount.Forsuchananalysisthelawsofthedistributionoftheliveloadanditsinducedstresses,ofthescatterofmechanicalpropertiesofmaterials,andofthegeometryofthecross-sectionsandthestructurehavetobeknown.Furthermore,itisdifficulttointerprettheinteractionbetweenthelawofdistributionofstrengthandthatofstressesbecausebothdependuponthenatureofthematerial,onthecross-sectionsandupontheloadactingonthestructure.Thesepracticaldifficultiescanbeovercomeintwoways.Thefirstistoapplydifferentsafetyfactorstothematerialandtotheloads,withoutnecessarilyadoptingtheprobabilisticcriterion.Thesecondisanapproximateprobabilisticmethodwhichintroducessomesimplifyingassumptions(semi-probabilisticmethods).中文翻譯摘要：為了研究連續(xù)型拓撲優(yōu)化理論在實際工程中的應(yīng)用，該文給出了一種多層鋼框架支撐體系連續(xù)型拓撲優(yōu)化設(shè)計方法?；陟`敏度分析，探討了連續(xù)體結(jié)構(gòu)在多工況荷載作用下、同時受應(yīng)力和多位移約束的拓撲優(yōu)化刪除準則。為保證拓撲優(yōu)化結(jié)果的合理性，提出了設(shè)計區(qū)域平均厚度的概念。在該文給出的優(yōu)化設(shè)計方法中，首先在不考慮位移約束的情況下對無支撐鋼框架進行優(yōu)化設(shè)計，然后在有位移約束的條件下采用漸進結(jié)構(gòu)優(yōu)化算法和刪除準則對支撐體系進行連續(xù)型拓撲優(yōu)化設(shè)計，并將獲得的支撐最優(yōu)拓撲構(gòu)形轉(zhuǎn)化成相應(yīng)的桿件。通過一個 3跨12層鋼框架支撐體系的拓撲優(yōu)化設(shè)計實例驗證了該文給出的鋼框架支撐體系連續(xù)型拓撲優(yōu)化設(shè)計方法的有效性。關(guān)鍵詞：鋼框架；支撐體系；連續(xù)型；拓撲優(yōu)化；漸進結(jié)構(gòu)優(yōu)化1.1鋼筋混凝土素混凝土是由水泥、水、細骨料、粗骨料（碎石或；卵石） 、空氣，通常還有其他外加劑等經(jīng)過凝固硬化而成。將可塑的混凝土拌合物注入到模板內(nèi)，并將其搗實，然后進行養(yǎng)護，以加速水泥與水的水化反應(yīng)，最后獲得硬化的混凝土。其最終制成品具有較高的抗壓強度和較低的抗拉強度。其抗拉強度約為抗壓強度的十分之一。因此，截面的受拉區(qū)必須配置抗拉鋼筋和抗剪鋼筋以增加鋼筋混凝土構(gòu)件中較弱的受拉區(qū)的強度。由于鋼筋混凝土截面在均質(zhì)性上與標準的木材或鋼的截面存在著差異，因此，需要對結(jié)構(gòu)設(shè)計的基本原理進行修改。將鋼筋混凝土這種非均質(zhì)截面的兩種組成部分按一定比例適當布置，可以最好的利用這兩種材料。這一要求是可以達到的。因混凝土由配料攪拌成濕拌合物，經(jīng)過振搗并凝固硬化，可以做成任何一種需要的形狀。如果拌制混凝土的各種材料配合比恰當，則混凝土制成品的強度較高，經(jīng)久耐用，配置鋼筋后，可以作為任何結(jié)構(gòu)體系的主要構(gòu)件。澆筑混凝土所需要的技術(shù)取決于即將澆筑的構(gòu)件類型，諸如：柱、梁、墻、板、基礎(chǔ)，大體積混凝土水壩或者繼續(xù)延長已澆筑完畢并且已經(jīng)凝固的混凝土等。對于梁、柱、墻等構(gòu)件，當模板清理干凈后應(yīng)該在其上涂油，鋼筋表面的銹及其他有害物質(zhì)也應(yīng)該被清除干凈。澆筑基礎(chǔ)前，應(yīng)將坑底土夯實并用水浸濕6英寸，以免土壤從新澆的混凝土中吸收水分。一般情況下，除使用混凝土泵澆筑外，混凝土都應(yīng)在水平方向分層澆筑，并使用插入式或表面式高頻電動振搗器搗實。必須記住，過分的振搗將導致骨料離析和混凝土泌漿等現(xiàn)象，因而是有害的。水泥的水化作用發(fā)生在有水分存在，而且氣溫在50°F以上的條件下。為了保證水泥的水化作用得以進行，必須具備上述條件。如果干燥過快則會出現(xiàn)表面裂縫，這將有損與混凝土的強度，同時也會影響到水泥水化作用的充分進行。設(shè)計鋼筋混凝土構(gòu)件時顯然需要處理大量的參數(shù)，諸如寬度、高度等幾何尺寸，配筋的面積，鋼筋的應(yīng)變和混凝土的應(yīng)變，鋼筋的應(yīng)力等等。因此，在選擇混凝土截面時需要進行試算并作調(diào)整，根據(jù)施工現(xiàn)場條件、混凝土原材料的供應(yīng)情況、業(yè)主提出的特殊要求、對建筑和凈空高度的要求、所用的設(shè)計規(guī)范以及建筑物周圍環(huán)境條件等最后確定截面。鋼筋混凝土通常是現(xiàn)場澆注的合成材料，它與在工廠中制造的標準的鋼結(jié)構(gòu)梁、柱等不同，因此對于上面所提到的一系列因素必須予以考慮。對結(jié)構(gòu)體系的各個部位均需選定試算截面并進行驗算，以確定該截面的名義強度是否足以承受所作用的計算荷載。由于經(jīng)常需要進行多次試算，才能求出所需的截面，因此設(shè)計時第一次采用的數(shù)值將導致一系列的試算與調(diào)整工作。選擇混凝土截面時，采用試算與調(diào)整過程可以使復核與設(shè)計結(jié)合在一起。因此，當試算截面選定后，每次設(shè)計都是對截面進行復核。手冊、圖表和微型計算機以及專用程序的使用，使這種設(shè)計方法更為簡捷有效，而傳統(tǒng)的方法則是把鋼筋混凝土的復核與單純的設(shè)計分別進行處理。1.2土方工程由于和土木工程中任何其他工種的施工方法與費用相比較，土方挖運的施工方法與費用的變化都要快得多，因此對于有事業(yè)心的人來說，土方工程是一個可以大有作為的領(lǐng)域。在 1935年，目前采用的利用輪胎式機械設(shè)備進行土方挖運的方法大多數(shù)還沒有出現(xiàn)。那是大部分土方是采用窄軌鐵路運輸，在這目前來說是很少采用的。當時主要的開挖方式是使用正鏟、反鏟、拉鏟或抓斗等挖土機，盡管這些機械目前仍然在廣泛應(yīng)用，但是它們只不過是目前所采用的許多方法中的一小部分。因此，一個工程師為了使自己在土方挖運設(shè)備方面的知識跟得上時代的發(fā)展，他應(yīng)當花費一些時間去研究現(xiàn)代的機械。一般說來，有關(guān)挖土機、裝載機和運輸機械的唯一可靠而又最新的資料可以從制造廠商處獲得。土方工程或土方挖運工程指的是把地表面過高處的土壤挖去（挖方） ，并把它傾卸到地表面過低的其他地方（填方）。為了降低土方工程費用，填方量應(yīng)該等于挖方量，而且挖方地點應(yīng)該盡可能靠近土方量相等的填方地點，以減少運輸量和填方的二次搬運。土方設(shè)計這項工作落到了從事道路設(shè)計的工程師的身上，因為土方工程的設(shè)計比其他任何工作更能決定工程造價是否低廉。根據(jù)現(xiàn)有的地圖和標高，道路工程師應(yīng)在設(shè)計繪圖室中的工作也并不是徒勞的。它將幫助他在最短的時間內(nèi)獲得最好的方案。費用最低的運土方法是用同一臺機械直接挖方取土并且卸土作為填方。 這并不是經(jīng)?？梢宰龅降?，但是如果能夠做到則是很理想的，因為這樣做既快捷又省錢。拉鏟挖土機。推土機和正鏟挖土機都能做到這點。拉鏟挖土機的工作半徑最大。推土機所推運的圖的數(shù)量最多，只是運輸距離很短。拉鏟挖土機的缺點是只能挖比它本身低的土，不能施加壓力挖入壓實的土壤內(nèi)，不能在陡坡上挖土，而且挖。卸都不準確。正鏟挖土機介于推土機和拉鏟挖土機的之間，其作用半徑大于推土機，但小于拉鏟挖土機。正鏟挖土機能挖取豎直陡峭的工作面，這種方式對推土機司機來說是危險的，而對拉鏟挖土機則是不可能的。每種機械設(shè)備應(yīng)該進行最適合它的性能的作業(yè)。正鏟挖土機不能挖比其停機平面低很多的土，而深挖堅實的土壤時，反鏟挖土機最適用，但其卸料半徑比起裝有正鏟的同一挖土機的卸料半徑則要小很多。在比較平坦的場地開挖，如果用拉鏟或正鏟挖土機運輸距離太遠時，則裝有輪胎式的斗式鏟運機就是比不可少的。它能在比較平的地面上挖較深的土（但只能挖機械本身下面的土），需要時可以將土運至幾百米遠，然后卸土并在卸土的過程中把土大致鏟平。在挖掘硬土時，人們發(fā)現(xiàn)在開挖場地經(jīng)常用一輛助推拖拉機（輪式或履帶式），對返回挖土的鏟運機進行助推這種施工方法是經(jīng)濟的。一旦鏟運機裝滿，助推拖拉機就回到開挖的地點去幫助下一臺鏟運機。斗式鏟運機通常是功率非常大的機械，許多廠家制造的鏟運機鏟斗容量為8m3，滿載時可達10m3。最大的自行式鏟運機鏟斗容量為19立方米（滿載時為25m3），由430馬力的牽引發(fā)動機驅(qū)動。翻斗機可能是使用最為普遍的輪胎式運輸設(shè)備， 因為它們還可以被用來送混凝土或者其他建筑材料。翻斗車的車斗位于大橡膠輪胎車輪前軸的上方，盡管鉸接式翻斗車的卸料方向有很多種，但大多數(shù)車斗是向前翻轉(zhuǎn)的。最小的翻斗車的容量大約為0.5立方米，而最大的標準型翻斗車的容量大約為 4.5m3。特殊型式的翻斗車包括容量為 4m3的自裝式翻斗車，和容量約為 0.5m3的鉸接式翻斗車。必須記住翻斗車與自卸卡車之間的區(qū)別。翻斗車車斗向前傾翻而司機坐在后方卸載，因此有時被稱為后卸卡車。1.3結(jié)構(gòu)的安全度規(guī)范的主要目的是提供一般性的設(shè)計原理和計算方法，以便驗算結(jié)構(gòu)的安全度。就目前的趨勢而言，安全系數(shù)與所使用的材料性質(zhì)及其組織情況無關(guān)，通常把它定義為發(fā)生破壞的條件與結(jié)構(gòu)可預(yù)料的最不利的工作條件之比值。這個比值還與結(jié)構(gòu)的破壞概率（危險率）成反比。破壞不僅僅指結(jié)構(gòu)的整體破壞，而且還指結(jié)構(gòu)不能正常的使用，或者，用更為確切的話來說，把破壞看成是結(jié)構(gòu)已經(jīng)達到不能繼續(xù)承擔其設(shè)計荷載的“極限狀態(tài)”。通常有兩種類型的極限狀態(tài)，即：1）強度極限狀態(tài)，它相當于結(jié)構(gòu)能夠達到的最大承載能力。其例子包括結(jié)構(gòu)的局部屈曲和整體不穩(wěn)定性；某此界面失效，隨后結(jié)構(gòu)轉(zhuǎn)變?yōu)闄C構(gòu)；疲勞破壞；引起結(jié)構(gòu)幾何形狀顯著變化的彈性變形或塑性變形或徐變；結(jié)構(gòu)對交變荷載、火災(zāi)和爆炸的敏感性。2）使用極限狀態(tài)，它對應(yīng)著結(jié)構(gòu)的使用功能和耐久性。器例子包括結(jié)構(gòu)失穩(wěn)之前的過大變形和位移；早期開裂或過大的裂縫；較大的振動和腐蝕。根據(jù)不同的安全度條件，可以把結(jié)構(gòu)驗算所采用的計算方法分成：1）確定性的方法，在這種方法中，把主要參數(shù)看作非隨機參數(shù)。2）概率方法，在這種方法中，主要參數(shù)被認為是隨機參數(shù)。此外，根據(jù)安全系數(shù)的不同用途，可以把結(jié)構(gòu)的計算方法分為：1）容許應(yīng)力法，在這種方法中，把結(jié)構(gòu)承受最大荷載時計算得到的應(yīng)力與經(jīng)過按規(guī)定的安全系數(shù)進行折減后的材料強度作比較。2）極限狀態(tài)法，在這種方法中，結(jié)構(gòu)的工作狀態(tài)是以其最大強度為依據(jù)來衡量的。由理論分析確定的這一最大強