Unit1第一單Fundamentally,engineeringisanend-product-orienteddisciplinethatisinnovative,cost-consciousandmindfulofhumanfactors.Itisconcernedwiththecreationofnewentities,devicesormethodsofsolution:anewprocess,anewmaterial,animprovedpowersource,amoreefficientarrangementoftaskstoplishadesiredgoaloranewstructure.Engineeringisalsomoreoftenthannotconcernedwithobtainingeconomicalsolutions.And,finally,humansafetyisalwaysakey從根本上，工程是一個以最終產品為導向的行業，它具有創新、成本意識，同時也注意到人為因素。它與創建新的實體、設備或解決方案有關：新工藝、新材料、一個改進的動力來源、任務的一項更有效地安排，用以完成所需的目標或創建一個新的結構。工程Engineeringisconcernedwiththeuseof scientificwaysofthinkingandofdefiningrealworldproblems.Theuseofidealizationsanddevelopmentofproceduresforestablishingboundswithinwhichbehaviorcanbeascertainedarepartoftheprocess.Manyproblems,bytheirverynature,can’tbefullydescribed—evenafterthefact,muchlessattheoutset.Yetacceptableengineeringsolutionstotheseproblemsmustbefoundwhichsatisfythedefinedneeds.Engineering,then,frequentlyconcernsthedeterminationofpossiblesolutionswithinacontextoflimiteddata.Intuitionorjudgmentisakeyfactorinestablishingpossiblealternativestrategies,processes,orsolutions.Andthis,too,isallapartofengineering.問題可接受的工程解決方案，來滿足預定的需求。或判斷是建立可能的替代策略、流程或解決方案的關鍵因素。。而這也是工程的一部分。Civilengineeringisoneofthemostdiversebranchesofengineering.Thecivilengineerplans,designs,constructs,andmaintainsalargevarietyofstructuresandfacilitiesforpublic,commercialandindustrialuse.Thesestructuresincluderesidential,office,andfactorybuildings;highways,,airports,tunnels,bridges,harbors,channels,andpipelines.Theyalsoincludemanyotherfacilitiesthatareapartofthetransportationsystemsofmostcountries,aswellassewageandwastedisposalsystemsthataddtoourconvenienceandsafeguardourhealth.土木工程是工程的最多樣化的分支機構之Theterm“civilengineer”didnotcomeintouseuntilabout1750,whenJohnSmeaton,thebuilderoffamousEddystonelighthousenearPlymouth,England,issaidtohavebeguncallinghimselfa“civilengineer”todistinguishhimselffromthemilitaryengineersofhistime.However,theprofessionisasoldascivilization.InancientEgyptthesimplestmechanicalprinciplesanddeviceswereusedtoconstructmanytemplesandpyramidsthatarestillstanding,includingthegreatpyramidatGizaandthetempleofAmon-RaatKarnak.Thegreatpyramid,481feet(146.6meters)high,ismadeof2.25millionstoneblockshavinganaverageweightofmorethan1.5tons(1.4metrictons).Greatnumbersofmenwereusedintheconstructionofsuchmonuments.TheEgyptiansalsomadeobelisksbycuttinghugeblocksofstone,someweighingasmuchas1000tons(900metrictons).Cuttingtoolsofhardbronzewereused.古埃及人用最簡單的機械原理和裝置建造了許多至今仍矗立的廟宇和金字塔，包括吉薩大金字塔和在卡Amon-Ra個大金字塔，481（146.6）高，由個石塊組成，石塊的平均重量超1.5（1.4噸。建造如此的紀念性建筑使用了大量的人力。埃及人也作了一些重達1000900)的石頭的大塊切割的方尖塔。硬青銅的切削刀具在其中使用到了。TheEgyptiansbuiltcausewaysandroadsfortransportingstonefromthequarriestotheNile.ThelargeblocksofstonethatwereerectedbytheEgyptiansweremovedbyusinglevers,inclinedplanes,rollers,and TheEgyptianswereprimarilyinterestedintheknow-howofconstruction;Theyhadverylittleinterestinwhy-forofuse.Incontrast,theGreeksmadegreatstridesinintroducingtheoryintoengineeringproblemsduringthe6thto3rdcenturiesB.C.Theydevelopedan knowledgeoflines,angles,surfaces,andsolidsratherthanreferringtospecificobjects.ThegeometricbaseforGreekbuildingconstructionincludedfiguressuchasthesquare,rectangle,andtriangle.埃及人主要對如何建造感；他們對為什么這么使用沒有什么太多的。相反，在公元前六世紀到公元前三世紀希臘人取得了巨大的進步于工程理論的推廣。他們發展了線、角度、面，和實體的抽象的知識，而不是與特定的對象產生聯系。希臘建筑施工的幾TheGreekarchitektonwasusuallythedesigner,aswellasthebuilder,ofarchitecturalandengineeringmasterpieces.Hewasanarchitectandengineer.Craftsmen,masons,andsculptorsworkedunderhissupervision.IntheclassicalperiodofGreeceallimportantbuildingswerebuiltoflimestoneormarble;theParthenon,forexample,wasbuiltofmarble.希臘建筑師通常是建筑工程杰作的設計師同時也是。他既是一個建筑師也是工程師。工匠、石匠和雕塑家在他的監督下工作。Unit2二單土木工程是涉及自然資源的開發、區域性和局部地區的供水、排洪設施、廢物處理設施、以及人們所需要的其他結構物的規劃、設計和施工的一個工程領域。具備學歷、經驗又有國家關于土木工程專業實踐要求認證的人員被稱為土木工程師土木工程師職業標準作為專業人員，土木工程師在履行他們職責的同時，應當遵循以下的的。（即在為子孫后代保護自然資源基礎的同時滿足當前的需要和工程目標稱為每一位雇主貨委托人的忠實貨委托人，并且要避免利益保持學習，總是自愿地參與理念于技術信息方面的專業交流只能在能力范圍內履行職責；其他范圍內，工程師可以與有資格的同事、顧問，或者雇員一起合作來執行任務。因此，土木工程的工程項目應當被規劃、設計和施工以滿足下列標準進行評定的時機。工程費用不應當超過業主的施工預算，并且當完全投入使用后，其運營、和工程的設計和施工要滿足相關法律要求，符合公認的工程標準，同時，要避免建筑工人、工程操作者以及公眾的健康和安全。應當將工程設計成滿足可持續發展的要求，即在為子孫后代保藏和保護周圍環境質量及自然資源的基礎上滿足當前工程項目的需要。 這程常常。咨詢工程師一個咨詢工程師被定義為一個熟練運用科原理來解決工程難題的專業。作為專業人，咨詢工程應該他們的顧一樣對公負責。了提專業服務，詢程師也經商業易。詢工程一些資企，合伙司，有建議和咨詢計劃規用發。設計主人。Unit3TheGreeksandRomanssometimesusedironrodsorclampstostrengthentheirbuildingThecolumnsoftheParthenoninAthens（雅典的帕臺農神廟）,forexample,haveholesdrilled（鉆孔）inthemforironbarsthathavenowrustedaway（銹蝕殆盡）TheRomansalsousedanaturalcementcalledpozzolanamadefromvolcanicash,thatbecameashardasstoneunderwater.其他一些粘合劑粘合在一起。希臘人和羅馬人有時用鐵條或來加固他們的房屋。例如，雅典的帕臺農神廟柱子中曾鉆孔以便加入Bothsteelandcement,thetwomostimportantconstructionmaterialsofmoderntimes,wereintroduced（推廣）inthenineteenthcenturySteel,basicallyanalloyofiron（鐵合金）andasmallamountofcarbon,hadbeenmadeuptothattime（到那個時候）byalaborious（繁復的）processthatrestrictedittosuchspecialusesasswordblades（刀刃）.AftertheinventionoftheBessemerprocess（貝塞麥煉鋼法）in1856,steelwasavailableinlargetiesatlowprices.Theenormousadvantageofsteelisitstensilestrengththatisitdoesnotloseitsstrengthwhenitisunderacalculateddegree適當的oftension,aforcewhich,aswehaveseentendsto（往往）pullapartmanymaterialsNewalloyshavefurtherincreasedthestrengthofsteelandeliminatedsomeofitsproblemssuchasfatigue,whichisatendencyforittoweakenasaresultofcontinualchangesinstress（連續的應力變化）.1856Moderncement,calledPortlandcement,wasinventedin1824.Itisamixtureoflimestone（石灰石）andclaywhichheatedandthengroundintoapowder（磨成粉末）.Itismixedatorneartheconstructionsite（施工現場）withsand,aggregatesmallstonescrushedrock,orgravelandwatertomakeconcreteDifferentproportionsoftheingredients（配料）produceconcretewithdifferentstrengthandweightConcreteisveryversatileitcanbepoured,pumpedorevensprayedinto（噴射成）allkindsofshapes.Andwhereassteelhasgreattensilestrength,concretehasgreatstrengthundercompression.Thus,thetwosubstancescomplementeachother（互補）.Theyalsocomplementeachotherinanotherway:theyhavealmostthesamerateofcontractionandexpansionTheythereforecanworktogetherinsituationswhere（在…情況下）bothcompressionandtensionarefactors（主要因素）.Steel（鋼筋）areembeddedin（埋入）concretetomakereinforcedconcreteinconcretebeamsorstructureswheretensionwilldevelop（出現）.Concreteandsteelalsoformsuchastrongbondtheforcethatunites（粘合）themthatthesteelcannotslip（滑移）withtheconcrete.Still（還有）anotheradvantageisthatsteeldoesnotrustinconcrete.Acid（酸）corrodessteelwhereasconcretehasanalkalinechemicalreactiontheoppositeof它也另外互：們乎相的縮和率因，們拉壓主因時共工。出拉Theadoptionofstructuralsteelandreinforcedconcretecausedmajorchangesintraditionalconstructionpractices（施工作業）Itwasnolongernecessarytousethickwallsofstoneorbrickformultistorybuildings,anditbecamemuchsimplertobuildfire-resistantfloors（防火地面）Boththesechangesservedto（有利于）reducethecostofconstruction.Italsobecamepossibletoerect（建造）buildingswithgreaterheightsandlongerspans.Sincetheweightofmodernstructuresiscarried（承受）bythesteelorconcreteframethewallsdonotsupportthebuildingTheyhaveecurtainwallswhichkeepouttheweatherandletinlightIntheearliersteelorconcreteframebuilding,thecurtainwallsweregenerallymadeofmasonry;theyhadthesolidlookofbearingwalls（承重墻）.Today,however,curtainwallsareoftenmadeoflightweightmaterialssuchasglassaluminum,orplastic,invariousAnotheradvanceinsteelconstruction（結構）isthemethodoffasteningtogether（連在一起）thebeamsFormanyyearsthestandardmethodwasriveting.Arivetisaboltwithaheadthatlookslikeabluntscrew（圓頭螺絲釘）withoutthreads（螺紋）Itisheatedplacedinholesthroughthepiecesofsteel（鋼構件）andasecondheadisformedattheothertogetherofpiecesofsteelbymelting（熔化）asteelmaterialbetweenthemunderhighheat.Prestressedconcreteisanimprovedformofreinforcement（加強方法）.Steelrodsarebentintotheshapestogivethemthenecessarydegreeoftensilestrength.Theyarethenusedtoprestress（對..預加應力）concreteusuallybyoneoftwodifferentmethodsThefirstistoleavechannelsinaconcretebeamthatcorrespondto（相應于）theshapesofthesteelrodsWhentherodsarerunthroughthechannels,theyarethenbondedtotheconcretebyfillingthechannelswithgroutathinmortarorbindingagentIntheother(andmorecommonmethodtheprestressedsteelrodsareplacedinthelowerpartofaform（模板）thatcorrespondstotheshapeofthefinishedstructure（成品結構）,andtheconcretedesirable（非常理想）material.預應力混凝土是加強法的改進形式。將鋼筋彎成一定的形狀以使它們具有必要的抗拉強度，然后用該鋼筋對混凝土施加預應力，通可采用兩種不同方法中的任何一種。第法是在混凝土梁中按鋼筋的形狀留下孔道，當鋼筋穿過孔道后，通過在孔道內灌注薄砂arenas,withlargespaceunbrokenbyanyobstructingsupports（阻礙的支撐物）.Theusesforthisrelativelynewstructuralmethodareconstantlybeingdeveloped（不斷地擴大）.Thecurrenttendencyistodevelop（采用）lightermaterialsaluminum,forexample,weighsmuchlessthansteelbuthasmanyofthesameproperties.Aluminumbeamshavealreadybeenusedforbridgeconstructionandfortheframeworkofafewbuildings.Lightweightconcretes,anotherexample,arenowrapidlydevelo（發展）throughouttheworld.Theyareusedfortheirthermalinsulation(絕熱性Thethreetypesareillustratedbelow（舉例說明如下）:a)Concretesmadewithlightweightcasting;(c)No-finesconcretes.ab（S；(cAllthreetypesareusedfortheirinsulatingproperties（絕熱性）,mainlyinhousing,wheretheygivehigh（非常）comfortincoldclimatesandalowcostofcooling（降溫成本）inhotclimates.Inhousing,therelativeweaknessoflightweightconcretewallsisunimportant,butitmatters（有重大關系）inroofslabs,floorslabsandbeams.Insomelocations,somelightweightaggregatescostlittlemorethan（幾乎等于）thebestdense（致密）aggregatesandalargenumberof（大量）floorslabshavethereforebeenbuiltoflightweightaggregateconcretepurelyforitsweightsaving,withnothoughtof（沒考慮）itsinsulationvalue.Thelightweightaggregatereducesthefloordeadload（恒載）byabout20percentresultingin（導致）considerablesavingsinthefloor（樓蓋結構）steelineveryfloorandtheroofaswellasinthecolumnsteelandlessinthefoundations.OneLondoncontractor（承包商）preferstouselightweightaggregatebecauseitgiveshimthesameweightreductioninvalueofthelightweightaggregateisonlyimportantintheroofinsulation,whichisgreatlyimproved（改進）.2（的Unit4四單（施加力）.InMechanicsofEngineeringMaterialsthemembershaveshapesthateitherexistinactualstructuresorarebeingconsideredfortheirsuitability（根據其需要）aspartsofproposed（擬建的）engineeringstructuresThematerialsinthemembershavepropertiesthatarecharacteristicofcommonlyused（常用的）engineeringmaterialssuchassteel,aluminum,concrete,andwood.Asyoucanseealreadyfromthevarietyofmaterials,forcesandshapesmentioned,MechanicsofEngineeringMaterialsisofinterestto（對..有價值）allfieldsofengineering.TheengineerusestheprinciplesofMechanicsofMaterialstodetermineifthematerialpropertiesandthedimensionsofamemberareadequateto（足以）ensurethatitcancarryitsloadssafelyandwithoutexcessivedistortion.Ingeneral（通常）,thenweareinterestedinboththesafeloadthatamembercancarryandtheassociated（相關的）deformation.Engineeringdesignwouldbeasimpleprocessifthedesignercouldtakeintoconsideration（考慮）theloadsandthemechanicalpropertiesofthematerials,manipulate（利用）anequation,andarriveat（得到）suitabledimensions.Designisseldomthatsimple.Usually（通常）onthebasisof（根據）experience,thedesignerselectsatrial（試算）memberandthendoesanysistoseeifthatmembermeetsthespecifiedrequirements.Frequently（常常）,itdoesnotsolutionisobtainedThenumberofcycles（循環次數）requiredtofindanacceptabledesigndiminishesasthedesignergainsexperience.DesignofAxiallyLoadedMembers向力構件的設Togiveyousomeinsightinto（使..有一些了解）thedesigncycleanextremelysimplememberwillbedealtwithfirst.ThatmemberisaprismaticbarwithaforceP,actingalongitslongitudinalaxisinthedirection（縱軸向）suchthatittendstoelongatethebarSuchaforceisreferredtoas（稱為）anaxialtensileload（軸向拉力）andwecanreadilyimagineittryingto（努力..）pullthefibersapartandtocausefailureonatransverseplane（橫向平arebeingpulledapartwiththesameloadintensity（荷載強度）WiththisassumptiontheloadintensityorstressisuniformonatransverseplaneandisgivenbywhenPisin（以..為單位）bydefinition（根據定義）Pascals(Pa).的Foragivenaxialloadandgivendimensions,thestresscanbecalculatedfrom4-1)andcomparedwith（與..相比）theAsafetyfactor（安全系數）,frequentlyimposedbyalegallyestablishedcode（）,isappliedtothestrength,asdeterminedbytests,togivetheallowablestress.Th（-是通對材料試驗確定的該（驗）材照與所考（驗）的桿相同規范制。根據規通常對驗所確定的強度考慮安全系數后得到許用應力。許用應力為這里，為材料失效（失效在下文有定義）時的應力nBeforeapproving（核準）trialdimensionsthedesignermakescertain（確信）thatthedesignissafebydeterminingthattheinequality（不等式）issatisfied.TheinequalityisusuallymoreconvenientintheItmightatfirst（起先）seemthatthedesignerwouldalwaysdimension（選定..的尺寸）thecrosssection（橫截面）sothatsizessoitisusuallymoreeconomicaltowastesomematerialbyselectingthenext（接近的）largerstandardsizeabovethatrequiredbytheallowablestress.Departurefrom（背離）standardsizesisjustified（合理的）incaseswherethepenalty（不利）forexcessweightisverysevere,asinaircraft（航天器）orspace-ship（宇宙飛船）design.諸航器宇飛的計證是理，為重產的利很重。DesignofBeams的設Uptothispoint（至此）wehavelookedat（考慮）thebeamproblemasaprobleminysisthatis（即）,foragivensetofloads,spanandcrosssectionwehavebeencalculatingthestressThemorecommonlyencounteredproblemistoselectastandardsection,ordesignamemberforagivenspanandloadswithoutexceedingacertainallowablestress.Undersomeconditionstheallowablestressmaybedependentuponthedimensionsandshapeofthecrosssectioninwhichcasetheselectionofthememberesmoredifficult.Forthepresent（暫時）wewilltaketheallowablestressas（似乎）itdependsonlyonthestrengthofthematerialandthesafety（）（）能依賴橫截面尺寸形狀這種情下的件選會變比較。暫時用許應力法似乎只取于材的強度Atrialmemberwillbeacceptable（合格）whenthestressisequalto,orlessthantheallowablestress,thatis,ifFordesignpurposesthisinequalityismoreusefulintheformIntheusualdesignprocesstheumbendingmomentistakenfrom（取自于）thebendingmomentdiagram（彎矩圖）theallowablestressisdetermined(quitefrequentlyinaccordancewith（根據）therulesofsomelegallyconstitutedcode)fromstandardstrengthtestsincombinationwith（與..結合）asafetyfactorTheright-handsideof4-6isthenknown,anditremains（仍然是）toselectordesignamemberthatwillsatisfytheinequality.WhenastandardsectionistoThistakesmoretimethanisreallynecessarysincethetablesalsoprovidethevalueofI/cforeachmemberundertheheading（標題）S,thesectionmodulus（截面模量）.在通常的計過中，大的彎從彎圖上得，而用力通過標強度驗并慮安全數后定（往是根一些的規則（46）I和c（-SIc的值。Thatis,thesectionmodulusisdefinedas（定義為withveryhighvaluesofSwillobviouslybeunderstressed（應力不足的）andwastefulofmaterial.Thebestdesigniftherearenootherconstraints,willbethatwhichsatisfies(4-8)withtheminimumamountofmaterial.WithtabulatedvaluesofSavailableitismuchmoreconvenienttouse(4-6)intheThesmallestacceptableSdoesnotnecessarilycoincidewith（符合）themosteconomicalmember.ToselectthelightestandmosteconomicalstandardsectionthelistedvaluesofmassshouldbeexaminedtofindthelightestmemberwithanacceptableS.Theproblemesmuchmorecomplexifbuilt-up（組合）memberisbeingdesignedbecauseitscostwilldependuponthecombinedcostsofwebplateanglesandcoverplatesaswellasfabrication（裝配）costssothatthelightestmemberisnotnecessarilythemosteconomical.果沒有其他的限制，最好的設計將是以最少的材料滿足式（4-8）。能接受的最小S是最經濟的構件。為了選擇最輕和最經濟的標準截面，應檢查列出的質量值，以找到能接受的S值下的最輕構件。如果在設計一個組合構件時，則問題變得復雜得多，因為它DeflectionsDuetoBending彎曲撓度Themainpurposeofthischapter（本節）wastodevelop（提出）theflexure（屈曲）formulas,andtoprovidesomeexperienceinapplyingthem.Staticallyindeterminate（超靜定）caseswereencounteredandsomeinsight（認識）gainedasto（就..）thedifficultyandimportanceofthiscategoryofproblem.,familiarwith（熟悉）superpositionwasmoreimportantthanfindingsolutionstotheproblems（問題的答案）becausesuperpositionhasapplicationinmanyareasofstressysisandwillbeusedfrequentlyinourfuturestudies.Moment-area（彎距圖面積法）wasfoundtobeaconvenientmethodforsolvingvariousproblemsItisamethodthatesquitecomplicatedandrequiresfurtherdevelopment（展開）whenmoreadvancedstructuresareencounteredAtthepresent（長半徑）curvedbeamswasintroduced（引入）toillustratethepoweroftheprinciplesunderlying（構成..的基礎）themoment-areamethodandsothatyouwouldappreciate（知道）thedifferencesbetweenstraightandcurvedbeams.為決同問，現距面法一很利方但遇更進結時此得常雜需進Thischapteraffordedanopportunitytoefamiliarwithsingularityfunctions（奇異函數）,andyouhaveseenthatcertainproblemscanbegreatlysimplifiedbytheiruse.Itmustbeappreciated（）thatmerelyanintroductiontothetopichasbeengiven;thereismuchmoretolearnedbythosewhohaveaspecialinterestToillustrateaseriouslimitation（缺陷）atourpresentstage,wecanexpressdistributedloads（分布荷載）thatarevariableandareintermittent,butwecannotwritealoadfunctionforconcentratedloadsIfwehadtakenthenextstepanddealtwiththeconcentratedload,wewouldhaveencounteredthesourceoftheexpression（表達式）“singularityfunction”buthavingregardfor（考慮）thescopeofthisbookwehavestoppedshortof（達不到）thatFailureTheories失效理論intestspecimens（試件）thathadalsobeensubjectedtouniaxialloadThisisthesimplestofalldesignproblemsthemethodisquiteadequate（合適的）sincethenature（性能）oftheloadsandthestressesinthetestandinthepartbeingdesignedareidenticalHowever,wesoonencountercaseswherethememberbeingdesignedisnotsosimpleandthestressesarenotuniaxial;considerforexamplethestressesinthewebofabeamorinapressurevessel（壓力容器）.ortriaxial.Foratrctrehvngbxialortrixalsrsse,hwshuldehektheaetyfhedsgn?hemostoviosaywouldbetocnucttes（進行）inhchseciensresrssd（受力tofiluenhesaemlixl多軸的）mannrasinthesrctu;teallwblemltixalsressthneetemnedbytheapliaionofnaqutesaftyfactr.Howvr,hiswuldreurearopoftetsfrevrynwetofmutaialsresesthtccredindeig.Suchetsaedfiulttoprorm,andteostofpeforingthminthereqiedubeswuldberhibiv.Consqunly,wenedatoryyhihhersltsoftestadrduixalestcanbesedopedcttefalreofaprtmadeofhesmeatrilwenhestesesaremulixal.noterors）,wenedaaluether.（試件）將要組驗這的驗難行而以要數行驗費也是的因，們要個論根可通過Toillustratetheneedforafailuretheory,letusconsideracylindricalpressurevessel.Toavoidunnecessarycomplications,wewillconsiderthatallwelds（焊縫）are100%efficientandthatthewalls（容器壁）arethinUnderinternalpressurethemainstresses（主應力）arecircumferentialandlongitudinal,anditwasimplied（認為）inanearliercasetheadequacyofthedesign.Inthisapproachwetacitly（默認）assumedthattheumstresscouldbetreatedas（看作為）auniaxialstressandthatitalonedeterminedthesafetyofthedesignThelongitudinalstresswasnotconsideredalthoughitmay,withoutourknowledge（在我們的知識之外）havehadaninfluenceonstrength.Ithappensthatourapproachinthiscaseisacceptable,but,inabiaxialstateofstress,thesecondstressisnotalwaysinconsequential（不重要）andanunderstandingoffailuretheoryisnecessaryinordertoavoidmakingsomeseriouserrors.（）Unfortunay,aswewilldiscover,nosingletheory（單一理論）willbefoundtoapplyinallcases;forexample,theoriesthataresatisfactoryforductilematerialsarenotacceptableforbrittlematerialsWewillalsofindthatoneofthebesttheoriesistoocomplexforeverydayuseandthatmostdesignersprefer（更喜歡）asimplertheorythatintroduces（產生）asmallbutsafeside（安全的Indevelo（提出）thevariousfailuretheories,wecannotavoidthree-dimensionaleffects,butwewilltreat（討論）onlythosecasesinwhichoneofthestressesiszerothusavoidingcomplicationsthatwouldtendtoobscure（使..模糊不清）theimportantpartofthetheories.Thisisnotaseriouslimitationsinceinengineeringpractice（工程實踐）mostproblemsarereducedto（簡化為）thebiaxialstressstatefordesignWhenshearstresses（剪應力）occuralong（與..一起）normalstresses（正應力）,theprincipalstresses（主應力）aredetermined.Thus,forpractical（實用的）stressiszeroForeasein（為了便于..）designating（稱呼）thoseprincipalstresseswewillusenumericalsubscripts在提出同的失理論，我不能免三的影響但只討其中某個應為零情況因而免了復性，它往往使便于稱呼那些主應力，我們采用數字下標：和作為非零應力，而為零。WecannotdiscussfailuretheoryuntilwehavedefinedfailureWemighttaketheobviousdefinitionthatamaterialhasfailedwhenithasbrokeninto（分為）twoormoreparts.However,ithasalreadybeenpointedoutthatinmostapplicationsamemberwouldbeunserviceable（不再適用）duetoexcessivedistortionlongbefore（早在）itactuallyruptured（斷裂）.Consequently,wewillrelatefailuretoyieldingandconsiderthatamaterialhasfailedwhenitwillnolongerreturnsaythataductilematerialhasfailedwhenthematerialbeginstoyieldThenforuniaxialstressfailureoccurswhenithertensionor在我們義了失后才對其行討。我可能會一個顯的定，即當料分兩部或時失。但是在多應用中經被，一個件早它實斷裂前由過分的形而再適用因此，效與服聯起來并認為旦荷解除而材BrittlematerialsfailbyadifferentmechanismandwillbediscussedafterthetheoriesforductilematerialshavebeenUnit5第五單buildings,bridges,towers,,anddams.Theprocess（過程）ofcreatinganyofthesestructuresrequiresplanning（規劃）,ysis,design,andconstruction（施工）.Structuralysisconsistsof（包括）avarietyofmathematicalprocedures（數學程序）fordeterminingsuchtiesasthememberforcesandvariousstructuraldisplacements（位移）isoftenapartofstructuralysis.結由系相的以撐載構組。著例括筑橋、、大等建這結中任Onlytwoassumptionsaremaderegarding（關于）thematerialsusedinthestructuresofthischapter.Firstthematerialhasalinearstress-strainrelationship（線性的應力-應變關系）Secondthereisnodifferenceinthematerialbehaviorwhenstressedintensionvis-a-vis（與..相比）compression.Theframesandtrussesstudiedareplanestructuralsystemswillfailduetoanelasticinstability（彈性失穩）.Theveryimportantconsiderationregardingsuchinstabilitywillbeleftforthespecific（具體的）designcourse.Allsrucuresreasumdtoundrgoolysmlldefratiosasteyarelade.saconequnc（）essumenochaneinhepostinordiecionofaoresareutof）trutualeflctin（.Fialy,sicelnearelasicmaerilsandmalldiplaemetreasume,hepricipeofsperosiionillaplynllcaes.Thustedispaceentsorintrnalorcsthtriseromtwoiffeentfocessytemsppledoneatati）aybeaddedlgeraiall（）todterinethestrcuresresonsewhenbothsysem()areaplidsiulaneosly.Intherealsense（真正意義上）anexactysisofastructurecanneverbecarriedoutsinceestimatesalwayshaveto（作用點）fortheloadingsmustalsobeestimated.Itisimportant,therefore,thatthestructuralengineers（形成）theabilitytomodel（模擬）oridealize（使..理想化）astructuresothatheorshecanperformapracticalforceysisofthemembers.真正意義上對一個結構準確的分析是也不可能進行的，因為總是不得不估計荷載和構成結構的材料的強度。而且，Structuralmembersarejoinedtogetherinvariouswaysdependingontheintent（意圖）ofthedesignerThetwotypesofjointsmostoftenspecified（規定的）arethepinconnectionandthefixedjoint（節點）Apin-connectedjointallowssomefreedomforslight（輕微）rotation,whereasthefixedjointallowsnorelativerotationbetweentheconnectedmembers.Inreality,however,allconnectionsexhibit（顯現）somestiffnesstowardjointrotations,owingtofriction（摩擦）andmaterialbehaviorWhenselectingaparticularmodelforeachsupport（支座）orjointtheengineermustbeawareforthestructuraldesign.Inreality,allstructuralsupportsactuallyexert（產生）distributedsurfaceloads（面荷載）ontheircontactingmembers.Theresultants（合力）oftheseloaddistributionsareoftenidealizedastheconcentratedforces（集中力）andmoments,byexperience.Inengineeringpractice,ifit esdoubtful（不明確）astohowtomodelastructureortransferthesothatitcanresist（抵抗）theloadingsinalltheidealizedItmayberecalled（回想）fromstaticsthatastructureoroneofitsmembersisinequilibrium（處于平衡）whenitmaintainsabalanceofforceandmomentWhenalltheforcesinastructurecanbedeterminedstrictlyfromtheseequationsthestructureisreferredtoasstaticallydeterminate（靜定的）.Structureshavingmoreunknownforcesthanavailableequilibriumequations（平衡方程）arecalledstaticallyindeterminateAsageneralruleastructurecanbeidentifiedas（確定）beingeitherstaticallydeterminateorstaticallyindeterminatebydrawingfree-bodydiagrams（體圖）ofallitsmembers,orselectivepartsofitsmembers,andthencomparingthetotalnumberofunknownreactiveforceandmomentcomponents（分量）withthetotalnumberofavailableequilibriumequations.過畫出所構件經選擇部分件的體圖然后比知的反力彎矩分量總目與用的平方程數目是等來確Inparticularifastructureisstaticallyindeterminate,theadditionalequations（附加方程）neededtosolvefor（求解）theunknownreactions（反力）areobtainedbyrelatingtheappliedloadsandreactionstothedisplacementorslope（轉角）atdifferentpointsonthestructureTheseequationswhicharereferredtoascompatibilityequations（相容性方程或協調方程）,mustbeequalinnumbertothedegreeofindeterminacy（不確定次數）ofthestructureCompatibilityequationsinvolve（涉及）thegeometricandphysicalpropertiesofthestructure.Therearetwofundamentalmethodsofysisfortrusses:themethodofjointsandthemethodofsections.Bothstartwith（從..著手）afree-bodydiagramofthetrussasawhole（基本上）,fromwhichtheequilibriumequationsarewrittenandsolvedforthesupportreactions（支座反力）.ThemethodofjointsAfterthesupportreactionshavebeenfoundajointisselectedthathasnomorethan（不超過）twomembersconnectingforwhichtheaxialforcesareunknownThefree-bodydiagramofthatjointisdrawn,theforcesaresummed（合計）intwodirectionsandeachsumisequatedto（等于）zeroWhendrawingthefree-bodydiagramitisagoodideatoassumethattheunknownforcesaretensionsandtoshow（表示）themsoonthefree-bodydiagrambytheirexertingapullon（對..施加拉力）thejointWhenthisisassumedtheresultingsign（符號）oftheunknownswhenitsmemberseknowns,andadjacentjoints（相鄰節點）,whichmighthavehadthreeormoreunknowns,canthenbesolvedsincesomeoftheseunknownshaveeknownsThisprocess（過程）continuesfromjointtojointeachtimeselectingajointwhosenumberofunknownmembersdoesnotexceed2.節點法：出支反力后選擇個節點上連著軸向知的構件超過根。畫節點的體，將在兩個上進行合計，每個向（）的合等于。當畫出圖時，好主意是定未力是拉，并在體上通對該節加一個拉構件，相的節可能曾有三或未知，但因中的一些經成已知，此也求出。個過從一個到另一個（繼續）jointbyjointtowardtheotherendIfitisnecessarytoevaluatetheforcescarriedbyamemberlocated（于）somedistancefromtheendsthemethodofjointsrequiresthecalculationoftheforcesinmanymembersbeforethedesiredoneisreachedThemethodofsectionsprovidesameans（方法）foradirectcalculationinthesecasesAfterthesupportreactionshavebeencalculatedthetrussiscutthrough（切開）(ytically分析上)sothatonepartofthetrussiscompleyseveredfromtherest.Whenthisisdone,nomorethanthreeunknownmembersshouldbecut.Ifpossible（如果可能）thecut（切口）shouldpassthroughthememberormemberswhoseinternalforcesaretobefound.Afree-bodydiagramofthepartofthetrussononesideof（在..一邊）thissectionisdrawn,andtheinternalforcesarefoundthroughtheequilibriumequations.Sincethesystemofforces（力系）onthefree-bodydiagramisaplanenon-concurrent（非共點）forcesystem,threeequilibriumequationsmaybewrittenandsolvedforthethreeunknowns.計算（，該出超三構的是知。果能口穿將求內的件畫在面邊桁部的體Influencelines（影響線）haveimportantapplicationfor（應用）thedesignofstructuresthatresistlargelive（活荷載）.Aninfluencelinerepresents（代表）thevariationofeitherthereaction,shear,momentordeflectionataspecific（特定的）pointinamemberasconcentratedforcemovesoverthemember.Oncethislineisconstructed（作圖）,onecanlataglance（一眼便知）wherealiveloadshouldbeplacedonthestructuresothatitcreates（引起）thegreatestinfluenceatthespecifiedpoint.Furthermorethemagnitude（大小）oftheassociated（相關的）reaction,shearmoment,ordeflectionatthepointcanthenbecalculatedfromtheordinates（縱坐標）oftheinfluence-linediagram.Forthesereasons（因此）influencelinesplayanimportantpartinthedesignofbridgesindustrialcranerails（吊車軌道）,conveyors,andotherstructureswhereloadsmoveacrosstheirspan（全長）.Althoughtheprocedure（步驟）forconstructinganinfluencelineisratherbasic（基本的）,oneshouldclearlybeawareofthedifferencebetweenconstructin