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外文原文Text StructureofBuildingsReadingMaterialA StructuralPlanninganddesignReadingMaterialB TypesofLoadsandTypesofStressContentsUNITONEText IntroductiontoMechanicsofMaterialsReadingMaterialAShearCenter BAllowableStressDesignandStrengthDesignUNITTWOText TheTensileTestReadingMaterialAComparativeStudyoftheMechanicalPropertiesofDuctileandBrittleMaterialsBStrengthTheoriesUNITTHREEText ApplicationofMechanicsofMaterialsandItsStudyMethodReadingMaterialAStress BMethodofSectionsUNITFOURText DescriptionoftheForceandDisplacementMethodReadingMaterialATypesofBeams BMethodsofJointsandSectionsforAnalyzingaTrussUNITFIVEText StructureofBuildingsReadingMaterialAStructuralPlanningandDesign BTypesofLoadsandTypesofStressUNITSIXText PurposeofStructuralAnalysisModelingofStructuresandRelationofAnalysisandDesignReadingMaterialAMatrixAnalysisofStructuresbytheStiffnessMethod BEquilibriumofSingleMembersUNITSEVENText PropertiesofConcreteandReinforcedConcreteReadingMaterialAPropertyofStructuralSteel BNatureofWoodandMasonryUNITEIGHTText BuildingCodeⅠReadingMaterialABuildingCodeⅡ BBuildingCodeⅢUNITNINEText EarlyHistoryofCementandConcreteReadingMaterialATheHydrationReaction BDistressandFailureofConcreteUNITTENText AdvantagesandDisadvantagesofConcreteandItsWater-CementRatioReadingMaterialASlumpTestandConcreteProportioning BCuringConcreteUNITELEVENText MortarReadingMaterialAWaterRetentively BCementMortarandLimeMortarUNITTWELVEText GeneralPlanningConsiderationsReadingMaterialAHousing BHouseUNITTHIRTEENText FactoryDesignReadingMaterialAModernBuildingConstruction BBuildingUNITFOURTEENText FundamentalObjectiveofStructuralDynamicsAnalysisReadingMaterialAOrganizationoftheText BMethodsofDiscretizationUNITFIFTEENText ContentsofTheoryofElasticityReadingMaterialABasicAssumptionsinClassicalElasticity BMembersinaStateofTwo-DimensionalStressUNITSIXTEENText HistoricalDevelopmentofFiniteElementMethodReadingMaterialAGeneralDescriptionoftheFiniteElementMethod BIntroductionofDisplacementApproachAppendixⅠ VocabularyAppendixⅡ TranslationforReferenceAppendixⅢ KeytoExercises目录
一、ForeignoriginalUNITFIVE
1.TextStructureofBuildings··········································1-
32.ReadingMaterialA StructuralPlanninganddesign·················································································4-
53.ReadingMaterialB TypesofLoadsandTypesofStress·················································································6-8⑴TypesofLoads································································6-7⑵Typesofstress····························································7-8
二、外文译文 第五单元
1.课文建筑物的结构···························································9-
102.阅读材料A结构的规划和设计···········································
113.阅读材料B荷载类型及应力类型··································12-13⑴负载类型············································································12⑵应力类型··········································································13UNITFIVETextStructureofBuildings
[1]Consideringonlytheengineeringessentialsthestructureofabuildingcanbedefinedastheassemblageofthosepartswhichexistforthepurposeofmaintainingshapeandstability.Itsprimarypurposeistoresistanyloadsappliedtothebuildingandtotransmitthosetotheground.
[2]Intermsofarchitecturethestructureofabuildingisanddoesmuchmorethanthat.Itisaninseparablepartofthebuildingformandtovaryingdegreesisageneratorofthatform.Usedskillfullythebuildingstructurecanestablishorreinforceordersandrhythmsamongthearchitecturalvolumesandplanes.Itcanbevisuallydominantorrecessive.Itcandevelopharmoniesorconflicts.Itcanbebothconfiningandemancipating.Andunfortunatelyinsomecasesitcannotbeignored.Itisphysical.
[3]Thestructuremustalsobeengineeredtomaintainthearchitecturalform.Theprinciplesandtoolsofphysicsandmathematicsprovidethebasisfordifferentiatingbetweenrationalandirrationalformsintermsofconstruction.Artistscansometimesgenerateshapesthatobviateanyconsiderationofsciencebutarchitectscannot.
[4]Thereareatleastthreeitemsthatmustbepresentinthestructureofabuilding:stabilitystrengthandstiffnesseconomy
[5]Takingthefirstofthethreerequirementsitisobviousthatstabilityisneededtomaintainshape.Anunstablebuildingstructureimpliesunbalancedforcesoralackofequilibriumandaconsequentaccelerationofthestructureoritspieces.
[6]Therequirementofstrengthmeansthatthematerialsselectedtoresistthestressesgeneratedbytheloadsandshapesofthestructuresmustbeadequate.Indeedafactorofsafetyisusuallyprovidedsothatundertheanticipatedloadsagivenmaterialisnotstressedtoalevelevenclosetoitsrupturepoint.Thematerialpropertycalledstiffnessisconsideredwiththerequirementofstrength.Stiffnessisdifferentfromstrengthinthatitdirectlyinvolveshowmuchastructurestrainsordeflectsunderload.Amaterialthatisverystrongbutlackinginstiffnesswilldeformtoomuchtobeofvalueinresistingtheforcesapplied.
[7]Economyofabuildingstructurereferstomorethanjustthecostofthematerialsused.Constructioneconomyisacomplicatedsubjectinvolvingrawmaterialsfabricationerectionandmaintenance.Designandconstructionlaborcostsandthecostsofenergyconsumptionmustbeconsidered.Speedofconstructionandthecostofmoneyinterestarealsofactors.Inmostdesignsituationsmorethanonestructuralmaterialrequiresconsideration.Competitivealternativesalmostalwaysexistandthechoiceisseldomobvious.
[8]Apartfromthesethreeprimaryrequirementsseveralotherfactorsareworthyofemphasis.Firstthestructureorstructuralsystemmustrelatetothebuildingsfunction.Itshouldnotbeinconflictintermsofform.Forexamplealinearfunctiondemandsalinearstructureandthereforeitwouldbeimpropertoroofabowlingalleywithadome.Similarlyatheatermusthavelargeunobstructedspansbutafinerestaurantprobablyshouldnot.Statedsimplythestructuremustbeappropriatetothefunctionitistoshelter.
[9]Secondthestructuremustbefire-resistant.Itisobviousthatthestructuralsystemmustbeabletomaintainitsintegrityatleastuntiltheoccupantsaresafelyout.Buildingcodesspecifythenumberofhoursforwhichcertainpartsofabuildingmustresisttheheatwithoutcollapse.Thestructuralmaterialsusedforthoseelementsmustbeinherentlyfire-resistantorbeadequatelyprotectedbyfireproofingmaterials.Thedegreeoffireresistancetobeprovidedwilldependuponanumberofitemsincludingtheuseandoccupancyloadofthespaceitsdimensionsandthelocationofthebuilding.
[10]Thirdthestructureshouldintegratewellwiththebuildingscirculationsystems.Itshouldnotbeinconflictwiththepipingsystemsforwaterandwastetheductingsystemsforairormostimportantthemovementofpeople.Itisobviousthatthevariousbuildingsystemsmustbecoordinatedasthedesignprogresses.Onecandesigninasequentialstep-by-stepmannerwithinanyonesystembutthedesignofallofthemshouldmoveinaparallelmannertowardcompletion.Spatiallyallthevariouspartsofabuildingareinterdependent.
[11]Fourththestructuremustbepsychologicallysafeaswellasphysicallysafe.Ahigh-riseframethatswaysconsiderablyinthewindmightnotactuallybedangerousbutmaymakethebuildinguninhabitablejustthesame.Lightweightfloorsystemsthataretoo“bouncycanmaketheusersveryuncomfortable.Largeglasswindowsuninterruptedbydividingmullionscanbequitesafebutwillappearveryinsecuretotheoccupantstandingnexttoone40floorsabovethestreet.
[12]Sometimesthearchitectmustmakedeliberateattemptstoincreasetheapparentstrengthorsolidnessofthestructure.Thisapparentsafetymaybemoreimportantthanhonestlyexpressingthebuildingsstructurebecausetheuntrainedviewercannotdistinguishbetweenrealandperceivedsafety.ReadingMaterialAStructuralPlanninganddesignThebuildingdesignerneedstounderstandthebehaviorofphysicalstructuresunderload.Anabilitytointuitorfeelstructuralbehaviorispossessedbythosehavingmuchexperienceinvolvingstructuralanalysisbothqualitativeandquantitative.Theconsequentknowledgeofhowforcesstressesanddeformationsbuildupindifferentmaterialsandshapesisvitaltothedevelopmentofthis”sense”Beginningthisstudyofforcesandstressesanddeformationsismosteasilydonethroughquantitativemethods.Thesetwosubjectsformthebasisforallstructuralplanninganddesignandareverydifficulttolearnintheabstract.Inmostbuildingdesigneffortstheinitialstructuralplanningisdonebythearchitect.Ideallythestructuralandmechanicalconsultantsshouldworksidebysidewiththearchitectfromtheconceptionofaprojecttothefinaldaysofconstruction.Inmostcaseshoweverthearchitectmustmakesomeinitialassumptionsabouttherelationshipstobedevelopedbetweenthebuildingformandthestructuralsystem.Asolidbackgroundinstructuralprinciplesandbehaviorisneededtomaketheseassumptionswithanyreasonabledegreeofconfidence.Theshapeofthestructuralenvelopethelocationofallmajorsupportingelementsthedirectionalityifanyofthesystemtheselectionofthemajorstructuralmaterialsandthepreliminarydeterminationofspanlengthsareallpartofthestructuralplanningprocess.Structuraldesignontheotherhandisdonebyboththearchitectandtheengineer.Thepreliminarydeterminationofthesizeofmajorstructuralelementsprovidingacheckontherationalityofpreviousassumptionsisdonebythearchitectand/ortheengineer.Finalstructuraldesigninvolvingacompleteanalysisofallthepartsandcomponentstheworkingoutofstructuraldetailsandthespecifyingofstructuralmaterialsandmethodsofconstructionisal-mostalwaysdonebythestructuralengineer.Ofthetwoareasstructuralplanningisfarmorecomplexthanstructuraldesign.Itinvolvesthepreviouslymentioned“feelingforstructure”orintuitionthatcomesthroughexperience.Structuraldesigncanbelearnedfromlecturesandbooksbutitislikelythatstructuralplanningcannot.Neverthelesssomeinsightandjudgmentcanbedevelopedfromaminimalbackgroundinstructuralanalysisanddesign.Ifpossiblethisshouldbegainedfromanarchitecturalstandpointemphasizingtherelationshipbetweenthequantitiesandtheresultingqualitieswhereverpossibleratherthanfromanengineeringapproach.Thisstudyofquantitativestructurescanbethoroughenoughtopermitthearchitecttodocompletelytheanalysisforsmallerprojectsalthoughsuchdepthisnotabsolutelynecessary.Attheveryleastitshouldprovidetheknowledgeandvocabularynecessarytoworkwiththeconsultingengineer.Itmustberememberedthatthearchitectreceivesmuchmoreeducationthatisorientedtowardcreativitythandoestheengineerandthereforeneedstomaintaincontroloverthedesign.Itisuptothearchitecttoaskintelligentquestionsandsuggestviablealternatives.Ifhandicappedbystructuralignorancesomeofthedesigndecisionswillineffectbemadebyothers.ReadingMaterialBTypesofLoadsandTypesofStressTypesofLoadsIngeneralloadsthatactonbuildingstructurescanbedividedintotwogroups;thoseduetogravitationalattractionandthoseresultingfromothernaturalcausesandelements.Gravityloadscanbefurtherclassifiedintotwogroups:liveloadanddeadload.Buildingliveloadsincludepeopleandmostmovableobjectswithinthestructureorontopofit.Snowisaliveload.Soisagrandpianoasafeorawaterbed.AppendixOprovidessometypicallyrecommendedliveloadsforvarioustypesofoccupancywithinbuildingstructures.Researchbearsoutthatthesefiguresrepresentprobablemaximumvaluesforliveloadsduringthelifetimeofastructure.Suchloadsareseldomrealized.Whatismorelikelyisanunexpectedchangeintheuseofthespace.Onecansensetheproblemsthatmightresultifanabandonedschoolispurchasedforuseasawarehousetostorebowlingballs.Deadloadsontheotherhandgenerallyincludetheimmovableobjectsinabuilding.Thewallsbothinteriorandexteriorfloorsmechanicalandelectricalequipmentandthestructuralelementsthemselvesareexamplesofdeadloads.ThesnowmapofAppendixNgivesthemaximumsnowloadthatcanreasonablybeexpectedinvariouspartsoftheUnitedStates.Likethelive-loadvaluessuchlargesnowfallsseldomoccur.Neverthelesswemustdesignforsomelevelofprobabilityandshouldnotforgetsuchoccurrencesasthemorethan-500-millimetersnowfallthathitthesoutheasternUnitedStatesin1974resultinginmanysmallbuildingfailures.Naturalforcesnotduetogravitythatactonbuildingsareprovidedbywindandearth-quakes.Windloadisalateralloadthatvariesinintensitywithheight.Hurricanesandtornadoespresentspecialdesignproblemsandlocalbuildingcodesoftenrequirecertaintypesofresistiveconstruction.AprobablewindpressuremapisgiveninAppendixN.Earthquakesarealsotreatedaslateralloadsatleastforpreliminarydesignpurposesbutitiswellknownthatbuildingsinearthquakesaresubjectedtoverticalforcesaswell.De-signmethodsarenotfullydevelopedfordisasterloadingssuchastornadoesandearthquakesandresearchcontinuesintheseareas.Onefinaltypeofloadisanimpactloadusuallyduetomovingequipmentwhichoccurswithinoronthestructure.Moststructuralmaterialscanwithstandasuddenandtemporaryloadofhighermagnitudethanaloadthatisappliedslowly.Forthisreasonthespecifiedpermissiblestressmagnitudesaresubstantiallyincreasedwhensuchloadsgovernthedesign.Nopermanentdamageisdonebymoderateimpactloadprovidedthatitdoesnotoccurrepeatedly.Anearthquakeisagoodexampleofasevereandrepeatingimpactload.Allthetablesandmapsreferredtointhistextaspartoftheappendicesprovideroughdataonly.Thedesignershouldconsultlocalbuildingcodeswhichalwaystakeprecedence.ThedesigneralsobearstheProfessionalresponsibilityforincreasinganyrecommendeddesignloadswhenthesituationwarrantsit.TypesofstressAfundamentalconceptinthestructuralanalysisofbuildingsisthatobjectsareinastateofequilibrium.Thismeanstherearenounbalancedforcesactingonthestructureoritspartsatanypoint.Allforcescounteractoneanotherandthisresultsinequilibrium.Thestructuralelementorobjectdoesnotacceleratebecausethenetforceactingonitiszerobutitdoesrespondtotheseforcesinternally.Itispushedorpulledandotherwisedeformedgivingoffenergyasheatasitresiststheforces.Internalstressesofvaryingtypesandmagnitudesaccompanythedeformationstoprovidethisresistance.Thesestressesarenamedbytheiractionorbehaviori.e.tensioncompressionshearandbending.Tensileandcompressivestresseswhichactthroughtheaxisorcenterofmassofanobjectareevenlydistributedovertheresistingareaandresultinallthematerialfibersbeingstressedtolikeamounts.Shearingstressesandmoreimportantbendingstressesarenotuniformandusuallyresultinafewfibersofmaterialbeingdeformedtotheirlimitwhileothersre-mainunstressedornearlyso.Bendingisbyfarthestructurallyleastefficientwaytocarryloads.Assumingforthemomentthatwehaveamaterialequallystrongintensioncompressionshearandbendingitwouldbebesttoloaditintensiontoachieveitsmaximumstructuralcapacity.Compressiveforcesifappliedtoalongslenderstructurecancausebuckling.Bucklingalwaysoccursunderlessloadthanwouldberequiredtofailthematerialsintruecompressioni.e.crushing.Ofcoursematerialsarenotequalinstrengthwhenloadedindifferentways.Somematerialshavealmostnotensilestrengthandgeneralizationsareverydifficulttomake.Asexplainedinsucceedingchaptersshearingstresseswillcausetensionandcompression;andbendingisactually-acombinationofsheartensionandcompression.Becauseofthepreviouslymentionedunevendistributionofstressintensityhoweverbendingisalwaysthemostdamagingloadthatcanbeappliedtoanyresistingstructuralmaterial.中文译文第五单元课文建筑物的结构
[1]如果只考虑工程要点建筑物结构可以定义为保持形状与稳定而存在的那些部分的集合其主要目的是抵制任何作用于建筑物上的负载,并将其传输到地上
[2]根据建筑,建筑的结构不止那些它是建筑形式的不可分割的一部分并在不同程度上是那种形式的产物熟练使用上,建筑结构可以建立或加强建筑体量和平面之间的顺序和节奏它可以直观地主导或隐性它可以发展和谐或冲突它可以同时受限和解放不幸的是在某些的情况下,它不能被忽略它是物质性的
[3]结构也必须保持建筑形式的工程化原则与物理、数学工具依据建造提供了区分理性与非理性形式的基本原理艺术家有时可以产生消除任何科学考虑的形状,但建筑师却不能
[4]存在至少三个必须出现在建筑结构上的项目稳定强度和刚度经济
[5]采取这三种的需求的第一个显然稳定需要保持形状一个不稳定的建筑结构意味着不平衡的力或缺乏平衡和随之加速的结构或其构件
[6]强度的要求意味着被选择抵制通过结构负载和形状产生的应力必须是足够的的确一个“安全系数”是经常被提供的以致于在预期的荷载作用下一个给定的材料是不强调一个甚至接近其破裂点的水平被称为刚度的材料属性是和强度要求是一起被考虑的刚度不同于强度因为它直接涉及结构在荷载作用下的拉伤和偏斜多少强度高但刚度弱的材料在抵抗应用力价值方面将变形太多
[7]建筑结构经济涉及到的不仅是材料使用费工程经济是一个复杂的主题,涉及原料、制造、安装及保养必须考虑设计和建设劳动成本和能源消耗成本建设速度和钱利息的成本也是因素在大多数的设计情况下,多个结构材料需要考虑竞争的选择几乎总是存在的,选择是不明显的
[8]除了这三个主要要求,其他几个因素是值得强调的首先,结构或结构系统必须与建筑的功能相关它不应从形式上冲突例如线性函数要求一个线性的结构,因此不适合给有圆顶的保龄球馆盖以屋顶同样,剧院必须有大、无障碍物阻挡视线的范围,但高级餐厅可能不一定简单地说,结构必须适合它作为住房的功能
[9]第二结构必须是防火的显然,结构系统必须能够保持其完整性,至少直到居民是安全的建筑规范规定建筑必须抗火不塌的小时数这些结构材料用于那些固有抗火或通过防水材料被充分保护的元素被提供的抗火程度将取决于一大批项目包括空间的使用和占有荷载、它的尺寸和建筑物位置
[10]第三结构应也与这座大楼的流通系统很好地集成它不应与水和垃圾管道系统,空气调节系统或(最重要的)人的运动有冲突很明显的是各种建筑系统必须与设计过程相协调人们可以设计在任何一个的系统内顺序的分步方式,但他们所有的设计应以并行方式移动完成空间上,建筑物的所有各部分是相互依存的
[11]第四结构必须心理和物理安全一样在风中剧烈摇摆的高层建筑框架也许实际上是不危险的但也许使建筑还是一样不适宜居住太”弹性”的轻质楼板系统会使用户感到不舒适不被分割的竖框打断的大玻璃窗可能相当安全但将对临近一个街道上的一40层楼非常不安全
[12]有时建筑师必须故意试图增加结构表面强度或硬度这种明显的安全也许比真诚地表现建筑结构更重要,因为未经训练的观察者无法区分真正的和可预见的安全阅读材料A结构的规划和设计建筑设计者需要了解负载下的物理结构的行为本能或“感觉”结构行为的能力是通过那些已有很多涉及结构定性和定量的分析的经验获得的随之而来的怎样建立不同材料和、形状的力、应力和变形知识对这种“感觉”的发展至关重要开始力、应力和变形的研究是最容易通过定量方法实现的形成所有结构规划和设计基础的这两个主题是非常难以抽象学习的在大多数建筑设计的努力下最初的结构计划是由建筑师完成的理想的情况下结构和机械咨询师应从项目构想到施工竣工伴随建筑师左右工作但是,在大多数的情况下,建筑师必须做出一些有关结构形式和结构体系之间被发展的关系的初始假设在结构的原则和行为方面的扎实背景需要做这些与任何信心合理程度有关的假设结构层的形状、所有主要支持元素的位置、系统的方向性(如果有的话)主要结构材料和跨度长度的初步确定都是结构规划进程的组成部分另外一方面,结构设计是由建筑师和工程师共同完成的提供对以前的假设的合理性进行检查的主要结构元素大小的初步测定是通过建筑师和工程师完成的最后渉及所有的零部件全面的分析、结构详细的论述和结构材料、施工方法细则的最终结构设计几乎总是由结构工程师完成的在这两个的领域中,结构规划是比结构设计的复杂得多它涉及到前面提到的“对结构的感受”或来自经验的直觉结构设计可以从讲座和书上学到,但很可能的是结构规划却不能不过,一些见解和判断可以从结构分析与设计中的最小背景中发展而来如果可能的话这应该来自一个建筑观点不论可能在哪,都强调数量和最终质量之间的关系而不是来自一个工程的方法虽然这种深度不是绝对必要的,但是这项定量结构研究可能足够彻底地允许建筑师完全做较小项目的分析至少,它应提供知识和可能与咨询工程师一起工作的必要词汇必须记住的是,建筑师接收更多的教育是面向创造力的而不是工程师所做的,因此需要保持对设计的控制它可以向建筑师提问智能问题并建议可行的选择如果结构忽略残缺的话,一些设计决策实际上将被他人完成阅读材料B荷载类型及应力类型负载类型一般情况下,作用在建筑结构上的荷载可分为两组由于地球引力产生的荷载和由于其他自然因素和元素引起的荷载重力负荷可以进一步分为两个组别活荷载和恒荷载建设活荷载包括在结构内或它的顶部上的人和大多数可移动的物体雪是活荷载大钢琴、冷藏室或水床也是附录O代表性地提供了一些在建筑结构内占据的各种类型的活荷载研究证实了这些数字表示一个结构生命期内活荷载的可能最大值这种负荷很少会被意识到在空间使用上的意外变化更有可能人们可以感觉如果一个废弃的学校用作存储保龄球的仓库可能导致的问题另外一方面,恒载一般包括建筑物内的不动的物体(内部和外部)的墙壁、地板、机械电气设备和结构元素本身都是恒载的例子附录N中的雪地图提供最大的雪荷载,它可以在美国各地被合理预测像活荷载的值,这样大的降雪很少发生然而,我们必须为一些可能性水平设计而不应该忘记正如发生于1974年美国东南部的超过500毫米降雪的情况,它导致许多小建筑毁坏自然力不是由于作用在建筑上的重力,而是由风和地球地震提供的风荷载是横向的负荷,它随高度而产生不同强度飓风和龙卷风呈现了特别设计的问题,并且当地建筑法规通常需要某些抵制施工的类型一个可能的风压地图被载于附录N地震(至少因为初步设计意图)也被视为横向荷载,但众所周知,在地震中的建筑物也受到垂直力的作用设计方法因如龙卷风和地震的灾难荷载而不完善,并且研究在这些领域继续前进最终类型的负载是一种冲击荷载,通常,由于发生在结构内或结构上的移动设备引起的大多数结构材料能承受一种比慢慢地应用的负载较高规模的突然和临时的负载由于这个原因,当这些荷载控制设计时,指定的许用应力幅度是基本增长的无永久性损伤是通过提供不反复出现的适度冲击荷载实现的(地震是一个严重和重复冲击荷载的好例子所有涉及在此文中的图表作为这些附录的一部分,它只提供粗略的数据设计者应咨询当地始终优先的建筑法规当情况需要时,设计人员也承担着增加任何推荐设计荷载的职业责任应力类型建筑结构分析中的一个基本概念是对象处于平衡的状态这意味着作用在结构或其部件上的任何一点没有不平衡力所有力都一个一个抵消,这将导致力的平衡因为它没有净力作用在结构元素或对象上,故它不加速,但是它对这些内力产生响应它是受推或受拉的,否则它会变形,释放出和它抗拒力一样的能量不同类型和规模的内部应力伴随着提供这种阻力的变形这些应力是通过它们的行动或行为(即,拉伸、压缩、剪切,和弯曲)命名的通过作用在轴或对象质心的拉伸和压缩应力是均匀地分布在抗区上的并将产生所有像数额一样被强调的材料光纤更重要的是,剪应力、弯曲应力并不一致,并通常产生一些物质纤维,但其他材料保持无应力或接近这样时这种材料将变形到极至到目前为止弯曲是结构上承受荷载的最有效方式假设目前我们在拉伸、压缩、剪切,和弯曲上有同样强烈的的材料,最好在张力上加载它以实现其最大的结构容量应用到一个细长结构上的压力会导致屈曲屈曲总是将要在真正压缩(即粉碎)使材料失效的较小荷载发生当然,当以不同方式加载时,材料将在强度上不平等一些材料几乎没有拉伸强度,并且难以概括正如后续章节解释的那样,剪力将引起拉伸和压缩;且弯曲实际上是剪拉压的组合由于前面涉及应力强度是不均匀分布的,因而,弯曲总是可以用于任何抵抗结构材料的最具破坏性的荷载。