土木工程类外文文献翻译.d

..1摘要：为了研究连续型拓扑优化理论在实际工程中的应用，该文给出了一种多层钢框架支撑体系连续型拓扑优化设计方式。基于灵敏度分析，探讨了连续体结构在多工况荷载作用下、同时受应力和多位移约束的拓扑优化删除准那么。为保证拓扑优化结果的合理性，提出了设计区域平均厚度的概念。在该文给出的优化设计方式中，首先在不考虑位移约束的情况下对无支撑钢框架进行优化设计，然后在有位移约束的条件下采纳渐进结构优化算法和删除准那么对支撑体系进行连续型拓扑优化设计，并将获得的支撑最优拓扑构形转化成相应的杆件。经过一个3跨12层钢框架支撑体系的拓扑优化设计实例验证了该文给出的钢框架支撑体系连续型拓扑优化设计方式的有效性。关键词：钢框架；支撑体系；连续型；拓扑优化；渐进结构优化弱的受拉区的强度。耐用，配置钢筋后，能够作为任何结构体系的主要构件。根底，大体积混凝土水坝或者继续延长已浇筑完毕并且已经凝固的混凝土等。对待梁、柱、墙等构件，当模板清理洁净后应该在其上涂油，钢筋外表的锈及其他有害物质也应该被去除洁净。浇筑根底前，应将坑底土夯实并用水浸湿6英寸，以免土壤从新浇的混凝土中汲取水分。一般情况下，除使用混凝土泵浇筑外，混凝土都应在水平方向分层浇筑，并使用插入式或外表式高频电动振捣器捣实。必需记住，过分的振捣将导致骨料离析和混凝土泌浆等现象，因而是有害的。50°F缝，这将有损与混凝土的强度，同时也会影响到水泥水化作用的充分进行。配筋的面积，钢筋的应变和混凝土的应变，钢筋的应力等等。因此，在选择混凝土截面时需要进行试算并作调整，依据施工现场条件、混凝土原材料的供应情况、业主提出的格外要求、对建筑和净空高度的要求、所用的设计标准以及建筑物周围环境条件等最后确定截面。钢筋混凝土通常是现场浇注的合成材料，它与在工厂中制截面，因此设计时第一次采纳的数值将导致一系列的试算与调整工作。当试算截面选定后，每次设计都是对截面进行复核。手册、图表和微型计算机以及专用程序的使用，使这种设计方式更为简捷有效，而传统的方式那么是把钢筋混凝土的复核与单纯的设计分别进行处理。1935唯一可靠而又最新的资料能够从制造厂商处获得。获得最好的方案。拉铲挖土机。推土机和正铲挖土机都能做到这点。拉铲挖土机的工作半径最大。推土机所推运的图的数量最多，只是运输距离很短。拉铲挖土机的缺点是只能挖比它本身低的土，不能施加压力挖入压实的土壤内，不能在陡坡上挖土，而且挖。卸都不准确。挖土机最适用，但其卸料半径比起装有正铲的同一挖土机的卸料半径那么要小很多。装满，助推拖拉机就回到开挖的地点去协助下一台铲运机。8mm³430机坐在前方卸载，因此有时被称为后卸卡车。标准的主要目的是提供一般性的设计原理和计算方式，以便验算结构的平安结构的破坏概率〔危急率〕成反比。确切的话来说，把破坏看成是结构已经到达不能继续承当其设计荷载的“极限状态〞。通常有两种类型的极限状态，即：〔1〕强度极限状态，它相当于结构能够到达的最大承载能力。其例子包括结和爆炸的敏感性。〔2〕使用极限状态，它对应着结构的使用功能和耐久性。器例子包括结构失稳之前的过大变形和位移；早期开裂或过大的裂缝；较大的振动和腐蚀。依据不同的平安度条件，能够把结构验算所采纳的计算方式分成：〔1〕确定性的方式，在这种方式中，把主要参数看作非随机参数。〔2〕概率方式，在这种方式中，主要参数被认为是随机参数。〔1〕容许应力法，在这种方式中，把结构承受最大荷载时计算得到的应力与经过按规定的平安系数进行折减后的材料强度作比拟。〔2〕极限状态法，在这种方式中，结构的工作状态是以其最大强度为依据来到一些有用的计算方式。通常采纳下列两种计算方式：概率方式，这种方式采纳极限状态。将这些随机平安系数组合成确定的平安系数。概率法取决于：〔1〕制作和安装经过中材料强度的随机分布〔整个结构的力学性能数值的分〔2〕截面和结构几何尺寸的不确定性〔由结构制作和安装造成的误差和缺陷对作用在结构上的活载和恒载的猜测的不确定性；建筑物的重要性和建筑物破坏造成的危害性；〔2〕由于建筑物破坏使生活受到威胁的人数；〔3〕修复建筑的可能性；〔4〕建筑物的预期寿命。所有这些因素均与经济和社会条件有关，例如：〔1〕建筑物的初始建设费；〔2〕建筑物使用期限内的折旧费；〔3〕由于建筑物破坏而造成的物质和材料损失费；〔4〕在社会上造成的不良影响；〔5〕精神和心理上的考虑。就给定的平安系数而论，所有这些参数确实定都是以建筑物的最准确本钱为依据的。但是，应该考虑到进行全概率分析的困难。对待这种分析来说，应该认识活载及其所引起的盈利的分布规律、材料的力学性能的分散性和截面的结构几何尺寸这些实际困难能够采纳两种方式来克服。第一种方式对材料和荷载采纳不同的平安系数，而不需要采纳概率准那么；第二种方式是引入一些而简化假设的近似概率方式2Abstract:Tostudytheapplicationofcontinuumstructuraltopologyoptimizationmethodstorealengineeringstructures,anoptimizationmethodforanoptimaltopologydesignofmultistorysteelframebracingsystemsispresented.Onasensitivityanalysis,anelementremovalcriterionforcontinuumstructureswithstressandmulti-displacementconstraintsundermultiplelateralloadingconditionsisproposed.Aconceptofmeanthicknessofadesigndomainisprovidedtoensurethereasonablenessofoptimalresults.Intheproposedoptimizationmethod,theoptimaldesignofanunbracedsteelframewithoutdisplacementconstraintsisperformedfirstly,andthentheoptimaltopologyofabracingsystemforthe multistorysteelframeconsideringdisplacementconstraintsisobtainedbyusingevolutionarystructuraloptimizationandthegivenremovalcriterion,andfinallytheoptimalayoutofthebracingsystemisinterpretedasbracingmembers.Anexampleof3-bay12-storyplanesteelframeshowsthatitiseffectiveforthegivenoptimizationmethodintheoptimaldesignofbracingsystemsformultistorysteelframes.Key words:steel frame;bracing system;continuum;topology optimization;evolutionary structuraloptimizationReinforcedConcretePlainconcreteisformedfromahardenedmixtureofcement,water,fineaggregate,coarseaggregate(crushedstoneorgravel),air,andoftenotheradmixtures.Theplasticmixisplacedandconsolidatedintheformwork,thencuredtofacilitatetheaccelerationofthechemicalhydrationreactionlfthecement/watermix,resultinginhardenedconcrete.Thefinishedproducthashighcompressivestrength,andlowresistancetotension,suchthatitstensilestrengthisapproximatelyonetenthlfitscompressivestrength.Consequently,tensileandshearreinforcementinthetensileregionsofsectionshastobeprovidedtocompensatefortheweaktensionregionsinthereinforcedconcreteelement.Itisthisdeviationinthecompositionofareinforcesconcretesectionfromthehomogeneityofstandardwoodorsteelsectionsthatrequiresamodifiedapproachtothebasic principles of structural design. The two components of the reinforcedconcretesectionaretobesoarrangedandproportionedthatoptimaluseismadeofthematerialsinvolved.Thisispossiblebecauseconcretecaneasilybegivenanydesiredshapebyplacingandcompactingthewetmixtureoftheconstituentingredientsare properly proportioned, the finished product becomes strong, durable, and, combinationwiththereinforcingbars,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,availabilityoftheconstituentmaterials,particulardemandsoftheowners,architecturalandheadroomrequirements,theapplicablecodes,andenvironmentalreinforcedconcreteisoftenasite-constructedcomposite,incontrasttothestandardmill-fabricatedbeamandcolumnsectionsinsteelstructures.Atrialsectionhastobechosenforeachcriticallocationinastructuralsystem.Thetrialsectionhastobeanalyzedtodetermineifitsnominalresistingstrengthisadequatetocarrytheappliedfactoredload.Sincemorethanonetrialisoftennecessarytoarriveatthe required section, the first design input step generates into a series trial-and-adjustmentanalyses.Thetrial-andadjustmentproceduresforthechoiceofaconcretesectionleadtotheconvergenceofanalysisanddesign.Henceeverydesignisananalysisonceatrialsectionischosen.Theavailabilityofhandbooks,charts,andpersonalcomputersandprogramssupportsthisapproachasamoreefficient,compact,andspeedyinstructionalmethodcomparedwiththetraditionalapproachoftreatingtheanalysisofreinforcedconcreteseparatelyfrompuredesign.EarthworkBecauseearthmovingmethodsandcostschangemorequicklythanthoseinanyotherbranchofcivilengineering,thisisafieldwheretherearerealopportunitiesfortheenthusiast.In1935mostofthemethodsnowinuseforcarryingandexcavatingearthwithrubber-tyredequipmentdidnotexist.Mostearthwasmovedbynarrowrailtrack,nowrelativelyrare,andthemainmethodsofexcavation,withfaceshovel,backacter,ordraglineorgrab,thoughtheyarestillwidelyusedareonly afewofthemany methods.Tokeephisknowledgeofearthmovingequipmentuptodateanengineermustthereforespendtinestudyingmodernmachines.Generallytheonlyreliableup-to-dateinformationonexcavators,loadersandtransportisobtainablefromthemakers.Earthworksorearthmovingmeanscuttingintogroundwhereitssurfaceistoohigh(cuts),anddumpingtheearthinotherplaceswherethesurfaceistoolow(fills).Toreduceearthworkcosts,thevolumeofthefillsshouldbeequaltothevolumeof cutsandwhereverpossiblethecutsshouldbeplacedneartofillsofequalvolumesoastoreducetransportanddoublehandlingofthefill.Thisworkofearthworkdesignfallsontheengineerwholaysouttheroadsinceitisthelayoutoftheearthworkmorethananythingelsewhichdecidesitscheapness.Fromtheavailablemapsahdlevels,theengineeringmusttrytoreachasmanydecisionsaspossibleinthedrawingofficebydrawingcrosssectionsoftheearthwork.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,whichcarry10m³ heaped.Thelargestself-propelledscrapersareof19m³struckcapacity(25m³ heaped)andtheyaredrivenbyatractorengineof430horse-powers.m³m³.Specialtypesincludetheself-loadingdumperofupto4m³andthearticulatedtypeofabout0.5m³.Thedistinctionbetweendumpersanddumptrucksmustberemembered.dumperstipforwardsandthedriversitsbehindtheload.Dumptrucksareheavy,strengthenedtippinglorries,thedrivertravelsinfrontlftheloadandtheloadisdumpedbehindhim,sotheyaresometimescalledrear-dumptrucks.SafetyofStructuresThe principal scope of specifications is to provide general principles computationalmethodsinordertoverifysafetyofstructures.The“safetyfactor〞,whichaccordingtomoderntrendsisindependentofthenatureandcombinationofthematerialsused,canusuallybedefinedastheratiobetweentheconditions.Thisratioisalsoproportionaltotheinverseoftheprobability(risk)offailureofthestructure.Failurehastobeconsiderednotonlyasoverallcollapseofthestructurebutalsoasunserviceabilityor,accordingtoamoreprecise.Commondefinition.Asthereachingofalimitstatewhichcausestheconstructionnottoaccomplishthetaskitwasdesignedfor.Therearetwocategoriesoflimitstate:Ultimatelimitsate,whichcorrespondstothehighestvalueoftheload-bearingcapacity.Examplesincludelocalbucklingorglobalinstabilityofthestructure;failureofsomesectionsandsubsequenttransformationofthestructureintoamechanism;failurebyfatigue;elasticorplasticdeformationorcreepthatcauseasubstantialchangeofthegeometryofthestructure;andsensitivityofthestructuretoalternatingloads,tofireandtoexplosions.Servicelimitstates,whicharefunctionsoftheuseanddurabilityofthestructure.Examplesincludeexcessivedeformationsanddisplacementswithoutinstability;earlyorexcessivecracks;largevibrations;andcorrosion.Computationalmethodsusedtoverifystructureswithrespecttothedifferentsafetyconditionscanbeseparatedinto:Deterministicmethods,inwhichthemainparametersareconsideredasnonrandomparameters.Probabilisticmethods,inwhichthemainparametersareconsideredasrandomparameters.Alternatively,withrespecttothedifferentuseoffactorsofsafety,computationalmethodscanbeseparatedinto:Allowablestressmethod,inwhichthestressescomputedundermaximumloadsarecomparedwiththestrengthofthematerialreducedbygivensafetyfactors.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;Uncertaintyrelatedtotheapproximationofthecomputationalmethodused(deviationoftheactualstressesfrom