河北建筑工程學(xué)院畢業(yè)設(shè)計（論文）外文資料翻譯系別：土木工程系專業(yè)：土木工程專業(yè)班級：工043班姓名：臧海月學(xué)號：19EnglishCivilEngineering（用外文寫）指導(dǎo)教師評語：簽字：年月日注：請將該封面與附件裝訂成冊。外文原文Loads,Strength,andStructuralSafetyA.LoadsLoadsthatactonstructuresareusuallyclassifiedasdeadloadsorliveloads.Deadloadsarefixedinlocationandconstantinmagnitudethroughoutthelifeofthestructure.Usuallytheself-weightofastructureisthemostimportantpartofthedeadload.Thiscanbecalculatedclosely,basedonthedimensionsofthestructureandtheunitweightofthematerial.Concretedensityvariesfromabout90to120pcf(14to19kN/m3)forlightweightconcrete,andisabout145pcf(23kN/m3)fornormalconcrete.Incalculatingthedeadloadofstructuralconcrete,usuallya5pcf(1kN/m3)incrementisincludedwiththeweightoftheconcretetoaccountforthepresenceofthereinforcement.Liveloadsareloadssuchasoccupancy,snow,wind,ortrafficloads,orseismicforces.Theymaybeeitherfullyorpartiallyinplace,ornotpresentatall.Theymayalsochangeinlocation.Althoughitistheresponsibilityoftheengineertocalculatedeadloads,liveloadsareusuallyspecifiedbylocal,regional,ornationalcodesandspecifications.TypicalsourcesarethepublicationsoftheAmericanNationalStandardsInstitute,theAmericanAssociationoftheStateHighwayandTransportationOfficialsand,forwendloads,therecommendationsoftheASCETaskCommitteeonWindForce.Specifiedliveloadsusuallyincludesomeallowanceforoverload,andmayincludedynamiceffects,explicitlyorimplicitly.Liveloadscanbecontrolledtosomeextentbymeasuressuchaspostingofmaximumloadsforfloorsorbridges,buttherecanbenocertaintythatsuchloadswillnotbeexceeded.Itisoftenimportanttodistinguishbetweenthespecifiedload,andwhatistermedthecharacteristicload,thatis,theloadthatactuallyisineffectundernormalconditionsofservice,whichmaybesignificantlyless.Inestimatingthelong-termdeflectionofastructure,forexample,itisthecharacteristicloadthatisimportant,notthespecifiedload.Thesumofthecalculateddeadloadandthespecifiedliveloadiscalledtheserviceload,becausethisisthemaximumloadwhichmayreasonablybeexpectedtoactduringtheservicelifeofthestructure.Thefactoredload,orfailureloadwhichastructuremustjustbecapableofresistingisamultipleoftheserviceload.Loadsarerandomprocesses;moreprecisely,theyarestochasticprocesses.However,inordertomatchtherequirementsofthemethodsofcalculationactuallyusedinmoststructuralspecification(allowablestressesandsemi-probabilisticmethods),eachloadisalsocharacterizedbytheparametersrepresentativeofthedifferentcomputationalmethods.Theloadscanbeclassifiedwithrespecttotheireffectonthestructure(staticordynamic)orwithrespecttotheirvariationofintensity.Loadscanalsobeclassifiedwithrespecttosomeparticularaspect,suchaslimitedornotlimited,havinglongorshortduration,dependentornotonhumanactivitiesetc.Loadsconsistof:(1)concentratedanddistributedforces(directactions),(2)imposeddeformations(indirectactions).Aloadisassumedasasingleloadifitisnotrelatedtoanyotherloadorimposeddeformationactingonthestructure.Inpracticemorethanonesingleloadactsonthestructure,althoughitisconvenienttoconsidereachloadseparately.Loadsarerandomprocesses;moreprecisely,theyarestochasticprocesses.However,inordertomatchtherequirementsofthe:methodsofcalculationactuallyusedinmoststructuralspecifications('allowablestressesandsemi-probabilisticmethods),eachloadisalsocharacterizedbytheparametersrepresentativeofthedifferentcomputationalmethods',Theloadscanbeclassifiedwithrespecttotheireffectonthestructure(staticordynamic)orwithrespecttotheirvariationofintensity.Loadscanalsobeclassifiedwithrespecttosomeparticularaspect,suchaslimitedornotlimited,havinglongorshortduration,dependentornotonhumanactivitiesetc.B.StrengthThestrengthofastructuredependsonthestrengthofthematerialsfromwhichitismade.Thepropertiesofsteelthathavebeendescribedsofarareapplicableonlyiftheambienttemperaturestayswithinreasonableproximityof70。F,say,from30toll0。F.Thepropertiesofsteeldonotchangeappreciablyfortemperaturesuptoapproximately300。Fto400。F,althoughthestress-straincurveshowsincreasingnonlinearitywhenthetemperatureexceeds250。F.Itisthereforefortunatethatmoststructureswillneverexperienceheatlevelsthatgopastthesepoints,andeveninthosethatdo,thehightemperaturesarenormallyofveryshortdurationandappearonlyoverasmallportionofthestructure.Atypicalexampleiswhatmaytakeplaceinastructureduringafire:Thetemperaturesmayreachhighlevels,butonlyforaveryshorttime,andnormallyonlyinhighlylocalizedspots.Exceptionsdoappear,ashasbeenevidencedbysomeofthemorespectacularfire-relatedcollapses(McCormickPlace,inChicago,Illinois,forexample),butthesearefortunatelyfewandfarbetween.Realisticconditionsarebetterrepresentedbywhattookplaceduringthefull-scalefiretestthatwasconductedinaparkinggarageinScranton,Pennsylvania,in1972:Damagewaslocalized,andmostofitwaseasilyrepaired,forexample,bycleaningblackenedareasandreplacingdamagedtiles.Nevertheless,itisimportanttoknowhowheataffectsthematerial,and,ifnecessary,totakeheatintoaccountinthedesignprocess.TherelationshipsbetweenthetemperatureandtheprimarystrengthandstiffnesscharacteristicsofsteelareshowninFig.5.6.Forallpracticalpurposes,Fy,Fu,andEshowdecreasingvaluesasthetemperatureincreases,althoughtherateofdecreasebecomessignificantonlyafterthetemperaturehasreachedapproximately1,000*F.Fuactuallyexhibitsaslightincreasebetween250*and600*F,whichisduetothephenomenonofstrainaging.Theyieldandultimatestresseshavedroppedtoaboutone-halfoftheirroomtemperaturevalueat1,100--1,200'F;atthislevelEhasreachedabout60percentofitsoriginalvalue.ThelevelofEisactuallymoreimportantforthestructure,sincedeflectionsaredirectlyproportionaltothemodulusofelasticity.Thephenomenonofcreepwillalsocomeintoplayiftheloadedstructureissubjectedtoincreasedtemperaturesforanextendedperiod.Temperingofsteelisnormallydoneinconjunctionwithquenching,suchaswhenthehigh-strengthquenchedandtemperedsteelsareproduced.Therapidcoolingofthesteelduetoquenchingwillproducethehard,fine-grainedstructurecalledmartensite.Althoughverystrong,martensiteisalsoverybrittle,andthetemperingisdonetoreshapethecrystallingstructureonlytotheextentthatductilityandtoughnessareincreased,butstrengthismaintained.Anyamountofheatinputandsubsequentcoolingwillproduceacertainlevelofbuilt-inorYii'~stresses,duetotherestraintsofthematerialandthestructuretothecontractionsthat3musttakeplace.Thisoccursveryprominentlyinweldedjoints;itwillalsooccurthroughoutanystructureorpartofitthathasbeenheated.Iftheheathasbeenappliedunevenly,andthecontractionsarenotrestrained,acertainamountofdistortionisboundtoappear.Thismaymakestructuralfitupdifficult,butappropriateapplicationofheatandcontrolledcoolingmayrelievesuchproblems.Thedesignerthatisconcernedaboutweldingandotherresidualstressesinjointswithhighdegreesofrestraintmaychoosetoredesigntheconnectiongeometrytoavoidproblems.Referencedetailsthesolutiontosuchproblemsastheypertaintolamellartearing,buttherecommendationsareexcellentadviceforthedesignandfabricationofweldedconnectionsingeneral.Itisalsopossibletousestressrelievinginsomeform,aswasdoneforanumberofthebeam-column-diagonalconnectionsintheexteriorframesoftheJohnHancockCenterinChicago,IllinoisLocalquenchingeffectsmayappearasafireisextinguishedinastructure,andwaterfromthefirehoseshitsheatedsteel.However,itisrareforlocalquenchingeffectstooccuroveranythingbutaminorarea.Thestructuraleffectisthereforeminimal,butheattreatmentcanbeappliedtoremoveanyproblemspots,iftheownerofthestructureisleeryofdoingnothing.Naturally,ifthemembershavebeendeformedbadlytheymayrequirereplacementanyway.However,thematerialinitselfdoesnotusuallysufferirreparabledamageduetoafire.C.StructuralSafetyandReliabilitySafetyrequiresthatthestrengthofastructurebeadequateforallloadsthatmayconceivablyactonit.Ifstrengthcouldbepredictedaccuratelyandifloadswereknownwithequalcertainty,thensafetycouldbeassuredbyprovidingstrengthjustbarelyinexcessoftherequirementsoftheloads.Buttherearemanysourcesofuncertaintyintheestimationofloadsaswellasinanalysis,design,andconstruction.Theseuncertaintiesrequireasafetymargin.Inrecentyearsengineershavecometorealizethatthematterofstructuralsafetyisprobabilisticinnature,andthesafetyprovisionsofmanycurrentspecificationsreflectthisview.Separateconsiderationisgiventoloadsandstrength.Loadfactors,largerthanunity,ateappliedtothecalculateddeadloadsandestimatedorspecifiedserviceliveloads,toobtainfactoredloadsthatthemembermustjustbecapableofsustainingatincipientfailure.Loadfactorspertainingtodifferenttypesofloadsvary,dependingonthedegreeofuncertaintyassociatedwithloadsofvarioustypes,andwiththelikelihoodofsimultaneousoccurrenceofdifferentloads.Morestructuralreliabilitytheoryisconcernedwiththerationaltreatmentofuncertaintiesinstructuralengineeringandwiththemethodsforassessingthesafetyandserviceabilityofcivilengineeringandotherstructures.Itisasubjectwhichhasgrownrapidlyduringthelastdecadeandhasevolvedfrombeingatopicforacademicresearchtoasetofwell-developedordevelopingmethodologieswithawiderangeofpracticalapplications.Uncertaintiesexistinmostareasofcivilandstructuralengineeringandrationaldesigndecisionscannotbemadewithoutmodellingthemandtakingthemintoaccount.Manystructuralengineersareshieldedfromhavingtothinkaboutsuchproblems,atleastwhendesigningsimplestructures,becauseoftheprescriptiveandessentially-deterministicnatureofmostcodesofpractice.Thisisanundesirablesituation.Mostloadsandotherstructuraldesignparametersarerarelyknownwithcertaintyandshouldberegardedasrandomvariablesorstochasticprocesses,evenifindesigncalculationstheyareeventuallytreatedasdeterministic.Someproblemssuchastheanalysisofloadcombinationscannotevenbeformulatedwithoutrecoursetoprobabilisticreasoning.Untilfairlyrecentlytherehasbeenatendencyforstructuralengineeringtobedominatedbydeterministicthinking,characterizedindesigncalculationsbytheuseofspecifiedminimummaterialproperties,specifiedloadintensitiesandbyprescribedproceduresforcomputingStressesanddeflections.Thisdeterministicapproachhasalmostcertainlybeenreinforcedbytheverylargeextenttowhichstructuralengineeringdesigniscodifiedandthelackoffeedbackabouttheactualperformanceofstructures.Forexample,actualstressesarerarelyknown,deflectionsarerarelyobservedormonitored,andsincemoststructuresdonotcollapsetherealreservesofstrengthsaregenerallynotknown.Incontrast,inthefieldofhydraulicsystems,muchmoreisknownabouttheactualperformanceof,say,pipenetworks,weirs,spillwaysetc.,astheirperformanceinservicecanberelativelyeasilyobservedordetermined.Moststructuraldesignisundertakeninaccordancewithcodesofpractice,whichinmanycountrieshavelegalstatus,meaningthatcompliancewiththecodeautomaticallyensurescompliancewiththerelevantclausesofthebuildinglaws.Structuralcodestypicallyandproperlyhaveadeterministicformatanddescribewhatareconsideredtobetheminimumstandardsfordesign,constructionandworkmanshipforeachtypeofstructure.Mostcodescanbeseentobeevolutionaryinnature,withchangesbeingintroducedormajorrevisionsmadeatintervalsof3-10yearstoallowfor:newtypesofstructuralform,theeffectsofimprovedunderstandingofstructuralbehaviour,theeffectsofchangesinmanufacturingtolerancesorqualitycontrolprocedures,abetterknowledgeofloads,etc.Thelackofinformationabouttheactualbehaviourofstructurescombinedwiththeuseofcedesembodyingrelativelyhighsafetyfactorscanleadtotheview,stillheldbysomeengineersaswellasbysomemembersofthegeneralpublic,thatabsolutesafetycanbeachieved.Absolutesafetyisofcourseunobtainable;andsuchagoalisalsoundesirable,sinceabsolutesafetycouldbeachievedonlybydeployinginfiniteresources.Itisnowwidelyrecognized,however,thatsomeriskofunacceptablestructuralperformancemustbetolerated.Themainobjectofstructuraldesignisthereforetoensure,atanacceptablelevelofprobability,thateachstructurewillnotbecomeunfitforitsintendedpurposeatanytimeduringitsspecifieddesignlife.Moststructures,however,havemultipleperformancerequirements,commonlyexpressedintermsofasetofserviceabilityandultimatelimitstates,mostofwhicharenotindependent;andthustheproblemismuchmorecomplexthanthespecificationofjustasingleprobability.Thereisaneedforallstructuralengineerstodevelopanunderstandingofstructuralreliabilitytheoryandforthistobeappliedindesignandconstruction,eitherindirectlythroughcodesorbydirectapplicationinthecaseofspecialstructureshavinglargefailureconsequences,theaiminbothcasesbeingtoachieveeconomytogetherwithallappropriatedegreeofsafety.Thesubjectisnowsufficientlywelldevelopedforittobeincludedasaformalpartofthetrainingofallcivilandstructuralengineers,bothatundergraduateandpost-graduatelevels.Coursesonstructuralsafetyhavebeengivenatsomeuniversitiesforanumberofyears.2、外文資料翻譯譯文荷載、強度和結(jié)構(gòu)安全一、荷載作用在結(jié)構(gòu)上的荷載通常分為恒載或活載。恒載在結(jié)構(gòu)整個使用壽命期間的位置是固定的，其大小是不變的。通常，結(jié)構(gòu)的自重是恒載是最重要部分。它可以根據(jù)結(jié)構(gòu)的尺寸和材料的單位重量進行精確計算。混凝土的密度是變化的，對于輕質(zhì)混凝土大約從90至120pcf(14至19KN/M=3\*Arabic3)的增加量?；钶d就是如人群、雪、風(fēng)和車輛荷載或地震力等荷載。他們可能全部或部分地出現(xiàn)，或者根本不出現(xiàn)。這些荷載的位置是變化的。計算恒荷載是工程師的職責(zé)，然而活何載通常由當(dāng)?shù)氐牡貐^(qū)的或國家的規(guī)范和準(zhǔn)則所規(guī)定。標(biāo)準(zhǔn)的來源是美國國家標(biāo)準(zhǔn)學(xué)會，美國州際公路與運輸工作者協(xié)會主辦的刊物，對于風(fēng)荷載采用美國土木工程學(xué)會風(fēng)力專題委員會的建議。規(guī)定活荷載一般包含某些容許的超載，并可以明顯地或隱含地計入沖擊作用?；钶d可以采用在樓板或橋梁標(biāo)明最大荷載那牙膏的措施在某種程度上加以控制，但是也不能肯定這些荷載不會被超過。將規(guī)定荷載所謂特征荷載區(qū)別開來往往是很重要的，也就是說，后者是正常使用情況下實際起作用的荷載，它是很小的。例如在計算結(jié)構(gòu)的長期撓度時，重要的是特征荷載，而不是規(guī)定荷載。計算得到的恒載和規(guī)定的活載的總和稱為使用荷載，因為這是在結(jié)構(gòu)使用壽命期間可預(yù)料到要作用的最大荷載。使用荷載乘以一個系數(shù)就是計算荷載，即使破壞荷載，它就是結(jié)構(gòu)必須恰好能抵抗的荷載。二、強度結(jié)構(gòu)的強度取決于建造它的材料的強度。到目前為止所知道的鋼材的強度只適用于環(huán)境溫度保持在70度上下的情況，大約從30度到110度。當(dāng)溫度超250度時，雖然應(yīng)力應(yīng)變曲線呈現(xiàn)出非線形增長，但溫度達到300度到400度時鋼材的性質(zhì)仍沒有明顯改變。幸虧大多數(shù)結(jié)構(gòu)從不處于超出這些數(shù)字的熱度，即使處于那種溫度下，高溫持續(xù)時間都很短，并且只是結(jié)構(gòu)的一小部分處于此溫度下，一個典型的例子就是當(dāng)火災(zāi)發(fā)生時所發(fā)生的一切：溫度可能達到很高值，但持續(xù)時間很短，并且高溫只出現(xiàn)在結(jié)構(gòu)的局部。就象被一些比較令人震驚的與火災(zāi)有關(guān)的倒塌事件（如美國芝加哥市的MCCORMICK廣場）所證明的那樣，確實有例外，幸虧此類事件極少發(fā)生。1972年，在賓夕法尼亞洲市斯科蘭頓市一個停車場的汽車修理廠內(nèi)所進行的原型火災(zāi)實驗中所發(fā)生的一切較好的描述了火災(zāi)發(fā)生時的真實情況，損壞只發(fā)生在局部，并且大部分都容易修補，如清理掉發(fā)黑的區(qū)域并替換下?lián)p壞的面磚。盡管如此了解溫度對鋼材料性質(zhì)影響仍然很重要，并且如果有必要的話在結(jié)構(gòu)設(shè)計過程中考慮溫度的影響。鋼材的初始強度和韌性于溫度的關(guān)系如圖所示。實際上，屈服強度、極限強度和彈性模量隨著溫度的升高而降低。只有當(dāng)溫度達到約1000度時降低的速度才加劇。由于應(yīng)變硬化現(xiàn)象的影響在250度到600度之間，極限強度隨溫度的升高略呈上升的趨勢。在1100到1200度時，屈服應(yīng)力和極限應(yīng)力值已經(jīng)降低到室溫下的一半，此時彈性模量E已達到初始值的60%。對結(jié)構(gòu)來說E的水平更為重要，因為結(jié)構(gòu)的變形與彈性模量成正比。如果承載結(jié)構(gòu)長期處于升溫狀態(tài)下蠕變現(xiàn)象也會發(fā)生。如同在生產(chǎn)高強度淬火和回火鋼材過程中一樣，鋼材的回火和淬火同時發(fā)生。因淬火而使鋼材冷卻將產(chǎn)生堅硬的被稱作馬氏體的細粒狀結(jié)構(gòu)物。馬氏體強度雖然很高但非常脆，而且回火使晶狀體結(jié)構(gòu)的形狀僅在某種程度上發(fā)生改變，即延性和韌性增加了，但強度仍保持不變。適當(dāng)升溫僅接著再降溫會產(chǎn)生一定的內(nèi)在或殘余應(yīng)力，產(chǎn)生的原因是降溫時產(chǎn)生的收縮變形受到了材料和結(jié)構(gòu)的限制。這種情況在焊接節(jié)點中經(jīng)常出現(xiàn)，結(jié)構(gòu)或結(jié)構(gòu)的一部分在加熱的整個過程中也會出現(xiàn)殘余應(yīng)力。如果結(jié)構(gòu)受熱不均勻而且收縮變形也不受限制，則在結(jié)構(gòu)中將會產(chǎn)生一定的扭曲變形，此變形使結(jié)構(gòu)組裝困難，適當(dāng)?shù)纳郎夭⒖刂平禍乜梢允勾藛栴}得到緩解。關(guān)心高度約束節(jié)點中，殘余應(yīng)力和其它類型殘余應(yīng)力的設(shè)計人員可能采用重新設(shè)計連接的幾何形狀來避免殘余應(yīng)力的問題。文獻詳細論述了關(guān)于層狀