《土木工程專(zhuān)業(yè)英語(yǔ) 第2版》 翻譯版 課件 Unit 3 Introduction to Steel Structures；Unit 4 Seismic Design；Unit 5 Composite Construction

Unit3IntroductiontoSteelStructuresEnglishforCivilEngineering——Unit3IntroductiontoSteelStructures3.1StructuralDesign（結(jié)構(gòu)設(shè)計(jì)）3.2PrinciplesofDesign（設(shè)計(jì)準(zhǔn)則）3.3HistoricalBackgroundofSteelStructures（鋼結(jié)構(gòu)背景）3.4Loads（荷載）3.4.1DeadLoad（靜荷載）3.4.2LiveLoad（活荷載）3.4.3HighwayLiveLoads（高速公路活荷載）3.4.4Impact（沖擊荷載）3.4.5SnowLoad（雪荷載）3.4.6WindLoad（風(fēng)荷載）3.4.7EarthquakeLoad（地震作用）3.5TypesofStructuralSteelMembers（鋼結(jié)構(gòu)構(gòu)件）3.5.1TensionMembers（受拉構(gòu)件）3.5.2CompressionMembers（受壓構(gòu)件）3.5.3Beams（梁）3.5.4BendingandAxialLoad（壓（拉）彎構(gòu)件）Structuraldesignmaybedefinedasamixtureofartandscience,combiningtheexperiencedengineer’sintuitivefeelingforthebehaviorofastructurewithasoundknowledgeoftheprinciplesofstatics,dynamics,mechanicsofmaterials,andstructuralanalysis,toproduceasafeeconomicalstructurethatwillserveitsintendedpurpose.結(jié)構(gòu)設(shè)計(jì)的定義intuitive直觀的；sound合理的；intended預(yù)期的3.1StructuralDesignStructuraldesignmaybedefinedasamixtureofartandscience,(combiningtheexperiencedengineer’sintuitivefeelingforthebehaviorofastructurewithasoundknowledgeoftheprinciplesofstatics,dynamics,mechanicsofmaterials,andstructuralanalysis),toproduceasafeeconomicalstructure(thatwillserveitsintendedpurpose.)結(jié)構(gòu)設(shè)計(jì)可以定義為藝術(shù)和科學(xué)的結(jié)合，再加上有經(jīng)驗(yàn)的工程師基于靜力學(xué)，動(dòng)力學(xué)，材料力學(xué)和結(jié)構(gòu)分析方面合理的知識(shí)而對(duì)于一個(gè)結(jié)構(gòu)行為的直觀感受，來(lái)設(shè)計(jì)一個(gè)能夠達(dá)成它的預(yù)期目的的安全經(jīng)濟(jì)的結(jié)構(gòu)。3.1StructuralDesignUntilabout1850,structuraldesignwaslargelyanartrelyingonintuitiontodeterminethesizeandarrangementofthestructuralelements.Earlyman-madestructuresessentially

conformedtothosewhichcouldalsobeobservedinnature,suchasbeamsandarches.Astheprinciplesgoverningthebehaviorofstructuresandstructuralmaterialshavebecomebetterunderstood,designprocedureshavebecomemorescientific.早期的結(jié)構(gòu)設(shè)計(jì)intuition直覺(jué)；

conformedto符合；

essentially基本上；governing控制3.1StructuralDesignUntilabout1850,structuraldesignwaslargelyanart(relyingonintuitiontodeterminethesizeandarrangementofthestructuralelements).Earlyman-madestructuresessentiallyconformedtothosewhichcouldalsobeobservedinnature,suchasbeamsandarches.(Astheprinciplesgoverningthebehaviorofstructuresandstructuralmaterialshavebecomebetterunderstood),designprocedureshavebecomemorescientific.直到1850，結(jié)構(gòu)設(shè)計(jì)很大程度上是一種依賴直覺(jué)決定結(jié)構(gòu)構(gòu)件尺寸和分布位置的藝術(shù)。早期的人造結(jié)構(gòu)基本上和那些可以在自然界中觀察到的結(jié)構(gòu)構(gòu)件一致，比如梁和拱。隨著控制結(jié)構(gòu)行為和結(jié)構(gòu)材料的原則變得越來(lái)越清楚，設(shè)計(jì)過(guò)程變得越來(lái)越科學(xué)。3.1StructuralDesignComputationsinvolvingscientificprinciplesshouldserveasaguidetodecisionmakingandnotbefollowedblindly.Theartorintuitiveabilityoftheexperiencedengineerisutilizedtomakethedecisions,guidedbythecomputationalresults.結(jié)構(gòu)設(shè)計(jì)的原則isutilizedto利用3.1StructuralDesignComputationsinvolvingscientificprinciplesshouldserveasaguidetodecisionmakingandnotbefollowedblindly.Theartorintuitiveabilityoftheexperiencedengineerisutilizedtomakethedecisions,(guidedbythecomputationalresults).具有科學(xué)依據(jù)的計(jì)算應(yīng)該起到對(duì)決策起指導(dǎo)作用而且應(yīng)不被盲目遵從。一個(gè)有經(jīng)驗(yàn)工程師應(yīng)在計(jì)算結(jié)果的指導(dǎo)之下，利用設(shè)計(jì)藝術(shù)或者直覺(jué)來(lái)做決策。3.1StructuralDesignDesignisaprocessbywhichanoptimumsolutionisobtained.Inthistexttheconcerniswiththedesignofstructures—inparticular,steelstructures.Inanydesign,certaincriteriamustbeestablishedtoevaluatewhetherornotanoptimumhasbeenachieved.Forastructure,typicalcriteriamaybe(a)minimumcost;(b)minimumweight;(c)minimumconstructiontime;(d)minimumlabor;(e)minimumcostofmanufactureofowner’sproducts;and(f)maximumefficiencyofoperationtoowner.Usuallyseveralcriteriaareinvolved,eachofwhichmayrequireweighting.Observingtheabovepossiblecriteria,itmaybeapparentthatsettingclearlymeasurablecriteria(suchasweightandcost)forestablishinganoptimumfrequentlywillbedifficult,andperhapsimpossible.Inmostpracticalsituations,theevaluationmustbequalitative.設(shè)計(jì)準(zhǔn)則的要求optimum最佳的，最佳效果；criteria原則；manufacture建造；weighting加權(quán)重；qualitative定性的3.2PrinciplesofDesignDesignisaprocess

(bywhichanoptimumsolutionisobtained).Inthistexttheconcerniswiththedesignofstructures—inparticular,steelstructures.Inanydesign,certain

criteriamustbeestablished(toevaluatewhetherornotanoptimumhasbeenachieved).Forastructure,typical

criteriamaybe(a)minimumcost;(b)minimumweight;(c)minimumconstructiontime;(d)minimumlabor;(e)minimumcostofmanufactureofowner’sproducts;and(f)maximumefficiencyofoperationtoowner.Usuallyseveralcriteriaareinvolved,(eachofwhichmayrequireweighting).Observingtheabovepossiblecriteria,itmaybeapparentthatsettingclearlymeasurablecriteria(suchasweightandcost)forestablishinganoptimumfrequentlywillbedifficult,andperhapsimpossible.Inmostpracticalsituations,theevaluationmustbequalitative.設(shè)計(jì)是一個(gè)尋找最佳解決方案的過(guò)程。在這篇文章中，尤其關(guān)心的是鋼結(jié)構(gòu)的設(shè)計(jì)。在任何設(shè)計(jì)中，有些標(biāo)準(zhǔn)必須被建立來(lái)評(píng)價(jià)是否實(shí)現(xiàn)了最佳方案。對(duì)一個(gè)結(jié)構(gòu)來(lái)說(shuō)，典型的標(biāo)準(zhǔn)比如（a）最低花費(fèi)；（b）最低重量；（c）最低建造時(shí)間；（d）最低勞動(dòng)力；（e）最低制造花費(fèi)；和（f）最大工作效率。通常的設(shè)計(jì)會(huì)考慮幾個(gè)標(biāo)準(zhǔn)，每個(gè)標(biāo)準(zhǔn)也許都會(huì)有一定的權(quán)重。觀察上述所有可能的標(biāo)準(zhǔn)，顯然為了實(shí)現(xiàn)最佳目標(biāo)（比如重量和花費(fèi)）而頻繁建立明確的可以量化的標(biāo)準(zhǔn)是很困難的，甚至是不可能的。在多數(shù)實(shí)際情況中，評(píng)價(jià)必須是定性的。3.2PrinciplesofDesignIfaspecificobjectivecriterioncanbeexpressedmathematically,thenoptimization

techniquesmaybeemployedtoobtainamaximumorminimumfortheobjectivefunction.Optimizationproceduresandtechniquescompriseanentiresubjectthatisoutsidethescopeofthistext.Thecriterionofminimumweightisemphasizedthroughout,underthegeneralassumptionthatminimummaterialrepresentsminimumcost.Othersubjectivecriteriamustbekeptinmind,eventhoughtheintegrationofbehavioralprincipleswithdesignofstructuralsteelelementsinthistextutilizesonlysimpleobjectivecriteria,suchasweightorcost.結(jié)構(gòu)設(shè)計(jì)的優(yōu)化方法criterion標(biāo)準(zhǔn)；optimization

techniques優(yōu)化方法；scope范圍；comprise

包含assumption假定；integration整合；utilize利用3.2PrinciplesofDesignIfaspecificobjectivecriterioncanbeexpressedmathematically,thenoptimizationtechniquesmaybeemployedtoobtainamaximumorminimum(fortheobjectivefunction).Optimizationproceduresandtechniquescompriseanentiresubjectthatisoutsidethescopeofthistext.Thecriterionofminimumweightisemphasizedthroughout,(underthegeneralassumptionthatminimummaterialrepresentsminimumcost).Othersubjectivecriteriamustbekeptinmind,eventhoughtheintegrationofbehavioralprincipleswithdesignofstructuralsteelelementsinthistextutilizesonlysimpleobjectivecriteria,suchasweightorcost.如果一個(gè)明確客觀的標(biāo)準(zhǔn)可以用數(shù)學(xué)公式表達(dá)，那么可以采用優(yōu)化技術(shù)來(lái)獲取目標(biāo)函數(shù)的最大或最小值。優(yōu)化過(guò)程和技術(shù)包含一個(gè)主體，它已經(jīng)超出了本文討論的范圍。最小重量的標(biāo)準(zhǔn)從頭到尾都在強(qiáng)調(diào)，在通常的假設(shè)下最少的材料代表最小花費(fèi)。盡管這篇文章中提到的設(shè)計(jì)原理和鋼結(jié)構(gòu)單元的綜合只用到了簡(jiǎn)單客觀的標(biāo)準(zhǔn)，其它主觀的標(biāo)準(zhǔn)必須被記住，比如重量或者花費(fèi)。3.2PrinciplesofDesignThedesignproceduremaybeconsideredtobecomposedoftwoparts—functionaldesignandstructuralframeworkdesign.Functionaldesignensuresthatintendedresultsareachieved,suchas(a)adequateworkingareasandclearances;(b)properventilationand/orairconditioning;(c)adequatetransportationfacilities,suchaselevators,stairways,andcranesormaterialshandlingequipment;(d)adequatelighting;and(e)aesthetics.設(shè)計(jì)過(guò)程包含兩部分——功能設(shè)計(jì)和結(jié)構(gòu)框架設(shè)計(jì)adequate充足的；clearance空隙；ventilation通風(fēng)系統(tǒng)；crane吊車(chē)；aesthetics美觀3.2PrinciplesofDesignThedesignproceduremaybeconsideredtobecomposedoftwoparts—functionaldesignandstructuralframeworkdesign.Functionaldesignensuresthatintendedresultsareachieved,suchas(a)adequateworkingareasandclearances;(b)properventilationand/orairconditioning;(c)adequatetransportationfacilities,suchaselevators,stairways,andcranesormaterialshandlingequipment;(d)adequatelighting;and(e)aesthetics.設(shè)計(jì)過(guò)程一般認(rèn)為包含兩部分——功能設(shè)計(jì)和結(jié)構(gòu)框架設(shè)計(jì)。功能設(shè)計(jì)確保預(yù)期結(jié)果可以達(dá)成，例如（a）充足的工作區(qū)域和空隙；（b）合適的通風(fēng)設(shè)備和空調(diào)；（c）足夠的運(yùn)輸設(shè)備，例如電梯，樓梯，吊車(chē)和材料處理設(shè)備；（d）充足的照明；和（e）美觀。3.2PrinciplesofDesignThestructuralframeworkdesignistheselectionofarrangementandsizesofstructuralelementssothatserviceloadsmaybesafelycarried,anddisplacementsarewithinacceptablelimits.結(jié)構(gòu)框架設(shè)計(jì)3.2PrinciplesofDesignThestructuralframeworkdesignistheselectionofarrangementandsizesofstructuralelements(sothatserviceloadsmaybesafelycarried,anddisplacementsarewithinacceptablelimits).結(jié)構(gòu)框架設(shè)計(jì)是選擇結(jié)構(gòu)單元的尺寸和順序的過(guò)程，由此工作荷載可以安全的加載并且位移也在可接受的限制內(nèi)。3.2PrinciplesofDesignTheiterativedesignproceduremaybeoutlinedasfollows:1.Planning.Establishmentofthefunctionsforwhichthestructuremustserve.Setcriteriaagainstwhichtomeasuretheresultingdesignforbeinganoptimum.2.Preliminarystructuralconfiguration.Arrangementoftheelementstoservethefunctionsinstep1.3.Establishmentoftheloadstobecarried.4.Preliminarymemberselection.Basedonthedecisionsofsteps1,2,and3selectionofthemembersizestosatisfyanobjectivecriterion,suchasleastweightorcost.設(shè)計(jì)過(guò)程的具體步驟1—4iterative重復(fù)的；preliminary初步的；configuration配置；satisfy達(dá)到3.2PrinciplesofDesignTheiterativedesignproceduremaybeoutlinedasfollows:1.Planning.Establishmentofthefunctionsforwhichthestructuremustserve.Setcriteriaagainstwhichtomeasuretheresultingdesignforbeinganoptimum.2.Preliminary

structural

configuration.Arrangementoftheelementstoservethefunctionsinstep1.3.Establishmentoftheloadstobecarried.4.Preliminary

member

selection.Basedonthedecisionsofsteps1,2,and3selectionofthemembersizestosatisfyanobjectivecriterion,suchasleastweightorcost.重復(fù)的設(shè)計(jì)過(guò)程可以被概括如下：1.計(jì)劃。建立結(jié)構(gòu)必須具有的功能。為實(shí)現(xiàn)最佳效果的設(shè)計(jì)制定標(biāo)準(zhǔn)。2.初始的結(jié)構(gòu)配置。排列結(jié)構(gòu)單元來(lái)實(shí)現(xiàn)第一步中的功能。3.建立要加載的荷載。4.初步的單元選定。根據(jù)第一，第二，第三步中的決定選擇單元的尺寸大小來(lái)滿足客觀的標(biāo)準(zhǔn)，例如最小的重量或最少的花費(fèi)。3.2PrinciplesofDesign5.Analysis.Structuralanalysisinvolvingmodelingtheloadsandthestructuralframeworktoobtaininternalforcesandanydesireddeflections.6.Evaluation.Areallstrengthandserviceabilityrequirementssatisfiedandistheresultoptimum?Comparetheresultwithpredeterminedcriteria.7.Redesign.Repetitionofanypartofthesequence1through6foundnecessaryordesirableasaresultofevaluation.Steps1through6representaniterativeprocess.Usuallyinthistextonlysteps3through6willbesubjecttothisiterationsincethestructuralconfigurationandexternalloadingwillbeprescribed.8.Finaldecision.Thedeterminationofwhetherornotanoptimumdesignhasbeenachieved.設(shè)計(jì)過(guò)程的具體步驟5—8internalforces內(nèi)力；serviceabilityrequirements使用要求；prescribed規(guī)定3.2PrinciplesofDesign5.Analysis.Structuralanalysisinvolvingmodelingtheloadsandthestructuralframeworktoobtaininternalforcesandanydesireddeflections.6.Evaluation.Areallstrengthandserviceabilityrequirementssatisfiedandistheresultoptimum?Comparetheresultwithpredeterminedcriteria.7.Redesign.Repetitionofanypartofthesequence1through6foundnecessaryordesirableasaresultofevaluation.Steps1through6representaniterativeprocess.Usuallyinthistextonlysteps3through6willbesubjecttothisiterationsincethestructuralconfigurationandexternalloadingwillbeprescribed.8.Final

decision.Thedeterminationofwhetherornotanoptimumdesignhasbeenachieved.5.分析。結(jié)構(gòu)分析包括為荷載和結(jié)構(gòu)框架建模來(lái)獲取內(nèi)力和任何需要的變形。6.評(píng)估。是否所有的強(qiáng)度和使用性要求都被滿足了？是否是最優(yōu)解決方案？比較結(jié)果和之前決定的標(biāo)準(zhǔn)。7.重新設(shè)計(jì)。重復(fù)步驟一到六的任何一部分，找到必要的或需要的作為評(píng)估的結(jié)果。步驟一到步驟六代表一個(gè)重復(fù)的過(guò)程。通常在這篇文章中，只有步驟三到步驟六受這個(gè)循環(huán)過(guò)程支配因?yàn)榻Y(jié)構(gòu)配置和外部荷載會(huì)被規(guī)定。8.最終決定。決定是否為最佳設(shè)計(jì)方案。3.2PrinciplesofDesignMetalasastructuralmaterialbeganwithcastiron,usedona100-ft(30-m)archspanwhichwasbuiltinEnglandin1777-1779.Anumberofcast-ironbridgeswerebuiltduringtheperiod1780-1820,mostlyarch-shapedwithmaingirdersconsistingofindividualcast-ironpiecesformingbarsortrusses.Castironwasalsousedforchainlinksonsuspensionbridgesuntilabout1840.鑄鐵的應(yīng)用castiron鑄鐵；girder梁；bar條形；truss桁架；chainlinks鎖鏈；suspensionbridges懸索橋3.3HistoricalBackgroundofSteelStructuresMetalasastructuralmaterialbeganwithcastiron,(usedona100-ft(30-m)archspanwhichwasbuiltinEnglandin1777-1779).Anumberofcast-ironbridgeswerebuiltduringtheperiod1780-1820,(mostlyarch-shapedwithmaingirdersconsistingofindividualcast-ironpiecesformingbarsortrusses).Castironwasalsousedforchainlinksonsuspensionbridgesuntilabout1840.金屬作為一種結(jié)構(gòu)材料始于鑄鐵，在1777—1779年英格蘭建造的30m的拱橋中得到應(yīng)用。很多鑄鐵橋在1780—1820這段時(shí)間修建起來(lái)，大多數(shù)是拱形的帶有由單個(gè)鑄鐵塊組成條狀或桁架的主梁。鑄鐵也被應(yīng)用于懸索橋上的鎖鏈連接直到大約1840年。3.3HistoricalBackgroundofSteelStructuresThedevelopmentoftheBessemerprocess(1855),theintroductionofabasiclinerintheBessemerconverter(1870),andtheopen-hearthfurnacebroughtwidespreaduseofironoreproductsinbuildingmaterials.Since1890,steelhasreplacedwroughtironastheprincipalmetallicbuildingmaterial.Currently(1989),steelshavingyieldstressesvaryingfrom24,000to100,000poundspersquareinch,psi(165to690megapascals,MPa),andavailableforstructuraluses.金屬材料從鍛鐵向鋼鐵轉(zhuǎn)變Bessemerprocess貝塞麥（轉(zhuǎn)爐）煉鋼法；Bessemerconverter貝氏轉(zhuǎn)爐；open-hearthfurnace平爐；ironore鐵礦石；wroughtiron鍛鐵（熟鐵）3.3HistoricalBackgroundofSteelStructuresThedevelopmentoftheBessemerprocess(1855),theintroductionofabasiclinerintheBessemerconverter(1870),andtheopen-hearthfurnacebroughtwidespreaduseofironoreproductsinbuildingmaterials.Since1890,steelhasreplacedwroughtironastheprincipalmetallicbuildingmaterial.Currently(1989),steelshavingyieldstressesvaryingfrom24,000to100,000poundspersquareinch,psi(165to690megapascals,MPa),andavailableforstructuraluses.貝塞麥（轉(zhuǎn)爐）煉鋼法的發(fā)展，貝氏轉(zhuǎn)爐基本班輪的介紹，還有平爐在建筑材料方面給鐵礦石產(chǎn)品帶來(lái)了廣泛應(yīng)用。自從1890年，鋼材代替熟鐵成為主要金屬建筑材料。目前（1989），剛才的屈服應(yīng)力可達(dá)到165—690MPa，可以勝任結(jié)構(gòu)使用。3.3HistoricalBackgroundofSteelStructuresTheaccuratedeterminationoftheloadstowhichastructureorstructuralelementwillbesubjectedisnotalwayspredictable.Eveniftheloadsarewellknownatonelocationinastructure,thedistributionofloadfromelementtoelementthroughoutthestructureusuallyrequiresassumptionsandapproximations.Someofthemostcommonkindsofloadsarediscussedinthefollowingsections.荷載概述distribution分布；approximations近似3.4LoadsTheaccuratedeterminationoftheloads(towhichastructureorstructuralelementwillbesubjected)isnotalwayspredictable.Eveniftheloadsarewellknownatonelocationinastructure,thedistributionofload(fromelementtoelementthroughoutthestructure)usuallyrequiresassumptionsandapproximations.Someofthemostcommonkindsofloadsarediscussedinthefollowingsections.一個(gè)結(jié)構(gòu)或結(jié)構(gòu)單元所承受的精確的荷載并不總是可預(yù)測(cè)的。即便結(jié)構(gòu)中一個(gè)位置的荷載可以很清楚的知道，在結(jié)構(gòu)中的從單元到單元的荷載分布通常需要假設(shè)和近似。下面部分討論一些常見(jiàn)荷載。3.4LoadsDeadloadisafixed-positiongravityserviceload,socalledbecauseitactscontinuouslytowardtheearthwhenthestructureisinservice.Theweightofthestructureisconsidereddeadload,aswellasattachmentstothestructuresuchaspipes,electricalconduit,air-conditioningandheatingducts,lightingfixtures,floorcovering,roofcovering,andsuspendedceilings;thatis,allitemsthatremainthroughoutthelifeofthestructure.靜荷載定義attachments附屬物3.4.1DeadLoadDeadloadisafixed-positiongravityserviceload,(socalledbecauseitactscontinuouslytowardtheearthwhenthestructureisinservice).Theweightofthestructureisconsidereddeadload,aswellasattachments

(tothestructuresuchaspipes,electricalconduit,air-conditioningandheatingducts,lightingfixtures,floorcovering,roofcovering,andsuspendedceilings);thatis,allitemsthatremainthroughoutthelifeofthestructure.靜荷載是一種固定位置的重力荷載，這么叫是因?yàn)樗诋?dāng)結(jié)構(gòu)服役的時(shí)候方向總是指向地球。結(jié)構(gòu)的重量被認(rèn)為是靜荷載，還有結(jié)構(gòu)的附屬物，例如管子，電子導(dǎo)管，空調(diào)和暖氣管，照明設(shè)備，樓板，屋蓋和吊頂，也就是說(shuō)所有在結(jié)構(gòu)生命周期內(nèi)一直存在的東西。3.4.1DeadLoadDeadloadsareusuallyknownaccuratelybutnotuntilthedesignhasbeencompleted.Understeps3through6ofthedesignprocedure,theweightofthestructureorstructuralelementmustbeestimated,preliminarysectionselected,weightrecomputed,andmemberselectionrevisedifnecessary.Thedeadloadofattachmentsisusuallyknownwithreasonableaccuracypriortothedesign.靜荷載的確定過(guò)程revise修改；priorto在……之前3.4.1DeadLoadDeadloadsareusuallyknownaccurately(butnotuntilthedesignhasbeencompleted).(Understeps3through6ofthedesignprocedure),theweightofthestructureorstructuralelementmustbeestimated,preliminary

sectionselected,weightrecomputed,andmemberselectionrevisedifnecessary.Thedeadloadofattachmentsisusuallyknown(withreasonableaccuracypriortothedesign).靜荷載通常能夠精確計(jì)算，但是要等到設(shè)計(jì)全部完成。在設(shè)計(jì)過(guò)程第三步到第六步，結(jié)構(gòu)和結(jié)構(gòu)單元的重量必須進(jìn)行估算，初步的截面選擇，重量重新計(jì)算，如果需要的話還要重新選擇構(gòu)件。附屬部分的靜荷載通常是可以在設(shè)計(jì)之前足夠精確的計(jì)算出來(lái)。3.4.1DeadLoadGravityloadsactingwhenthestructureisinservice,butvaryinginmagnitudeandlocation,aretermedliveloads.Examplesofliveloadsarehumanoccupants,furniture,movable

equipment,vehicles,andstoredgoods.Someliveloadsmaybepracticallypermanent,othersmaybehighlytransient.Becauseoftheunknownnatureofthemagnitude,location,anddensityofliveloaditems,realisticmagnitudesandthepositionsofsuchloadsareverydifficulttodetermine.活荷載的定義magnitude大??；termed被稱(chēng)為；occupants居住者；movableequipment移動(dòng)設(shè)備；permanent永久的；transient短暫的3.4.2LiveLoad(Gravityloadsactingwhenthestructureisinservice),butvarying

(inmagnitudeandlocation,)aretermedliveloads.Examplesofliveloadsarehumanoccupants,furniture,movableequipment,vehicles,andstoredgoods.Someliveloadsmaybepracticallypermanent,othersmaybehighlytransient.Becauseoftheunknownnatureofthemagnitude,location,anddensityofliveloaditems,realisticmagnitudesandthepositionsofsuchloadsareverydifficulttodetermine.重力荷載當(dāng)結(jié)構(gòu)服役時(shí)起作用，但是荷載的大小和作用位置會(huì)發(fā)生變化的荷載稱(chēng)為活荷載?；詈奢d的例子包括居住者，家具，可移動(dòng)的設(shè)備，車(chē)輛和儲(chǔ)存貨物。有些活荷載也許是幾乎永久的，其它的也許是很短暫的。由于對(duì)荷載大小，作用位置和活荷載物品密度的未知性，真實(shí)的大小和作用位置是很難確定的。3.4.2LiveLoadBecauseofthepublicconcernforadequatesafety,liveloadstobetakenasserviceloadsindesignareusuallyprescribedbystateandlocalbuildingcodes.Theseloadsaregenerallyempiricalandconservative,basedonexperienceandacceptedpracticeratherthanaccuratelycomputedvalues.Whereverlocalcodesdonotapply,ordonotexist,theprovisionsfromoneofseveralregionalandnationalbuildingcodesmaybeused.OnesuchwidelyrecognizedcodeistheAmericannationalStandardMinimumDesignLoadsforBuildingsandOtherStructuresANSIA58.1oftheAmericanNationalStandardsInstitute(ANSI),fromwhichsometypicalliveloadsarepresented.ThecodewillhenceforthbereferredtoastheANSIStandard.Thisstandardisupdatedfromtimetotime,mostrecentlyin1982.活荷載的確定方法adequate足夠的；serviceloads使用荷載；empirical憑經(jīng)驗(yàn)的；conservative保守的；provision規(guī)范；regional區(qū)域的；henceforth今后3.4.2LiveLoad(Becauseofthepublicconcernforadequatesafety),liveloads(tobetakenasserviceloadsindesign)areusuallyprescribedbystateandlocalbuildingcodes.Theseloadsaregenerallyempiricalandconservative,(basedonexperienceandacceptedpracticeratherthanaccuratelycomputedvalues).(Whereverlocalcodesdonotapply,ordonotexist),theprovisionsfromoneofseveralregionalandnationalbuildingcodesmaybeused.OnesuchwidelyrecognizedcodeistheAmericannationalStandardMinimumDesignLoadsforBuildingsandOtherStructuresANSIA58.1(oftheAmericanNationalStandardsInstitute(ANSI),fromwhichsometypicalliveloadsarepresented).ThecodewillhenceforthbereferredtoastheANSIStandard.Thisstandardisupdatedfromtimetotime,mostrecentlyin1982.由于公眾對(duì)于足夠安全性的關(guān)心，活荷載作為使用荷載在設(shè)計(jì)中通常由州或者地方規(guī)范來(lái)規(guī)定。這些荷載通常是經(jīng)驗(yàn)的，保守的，以經(jīng)驗(yàn)和可接受的實(shí)例為依據(jù)而不是用精確計(jì)算的值。在地方規(guī)范不適用的情況下，或者不存在的情況下，那些地區(qū)性的或者全國(guó)規(guī)范中的規(guī)定可能被采納。一個(gè)被如此廣泛應(yīng)用的規(guī)范就是《美國(guó)建筑和其它結(jié)構(gòu)最低設(shè)計(jì)荷載標(biāo)準(zhǔn)》，全美標(biāo)準(zhǔn)協(xié)會(huì)A58.1條，其中一些典型的活荷載在表5.4.1中體現(xiàn)。這個(gè)規(guī)范從此之后被稱(chēng)為“ANSI標(biāo)準(zhǔn)“。這個(gè)標(biāo)準(zhǔn)經(jīng)常被更新，最近一次在1982年。3.4.2LiveLoadLiveloadwhenappliedtoastructureshouldbepositionedtogivethemaximumeffect,includingpartialloading,alternatespanloading,orfullspanloadingasmaybenecessary.Thesimplifiedassumptionoffulluniformloadingeverywhereshouldbeusedonlywhenitagreeswithrealityorisanappropriateapproximation.Theprobabilityofhavingtheprescribedloadingapplieduniformlyoveranentirefloor,oroverallfloorsofabuildingsimultaneously,isalmostnonexistent.Mostcodesrecognizethisbyallowingforsomepercentagereductionfromfullloading.Forinstance,forliveloadsof100psformoreANSIStandardallowsmembershavinganinfluenceareaof400ft2ormoretobedesignedforareducedliveloadaccordingtoEq.3-1，asfollows:確定取得最大效應(yīng)的活荷載分布partialloading局部荷載；alternatespanloading交替跨荷載；fullspanloading全跨荷載；fulluniformloading均布荷載；appropriate適當(dāng)?shù)模籹imultaneously同時(shí)3.4.2LiveLoadLiveload(whenappliedtoastructure)shouldbepositionedtogivethemaximumeffect,(includingpartialloading,alternatespanloading,orfullspanloadingasmaybenecessary).Thesimplifiedassumptionoffulluniformloadingeverywhereshouldbeusedonly(whenitagreeswithrealityorisanappropriateapproximation).Theprobability(ofhavingtheprescribedloadingapplieduniformlyoveranentirefloor,oroverallfloorsofabuildingsimultaneously,)isalmostnonexistent.Most

codesrecognizethisbyallowingforsomepercentagereductionfromfullloading.Forinstance,forliveloadsof100psformoreANSIStandardallowsmembershavinganinfluenceareaof400ft2ormoretobedesignedforareducedliveloadaccordingtoEq.3-1，asfollows:當(dāng)活荷載作用在結(jié)構(gòu)上的時(shí)候應(yīng)該指明達(dá)到最大荷載效應(yīng)的活荷載位置，包括局部荷載，交替跨荷載或者需要的話全跨荷載。關(guān)于全部均勻分布荷載的簡(jiǎn)化假設(shè)只有當(dāng)符合實(shí)際情況或者合理近似的時(shí)候才能應(yīng)用。讓規(guī)定的荷載均勻的分布在整個(gè)樓板上或者同時(shí)分布在所有樓板上幾乎是不可能的。大多數(shù)的規(guī)范通過(guò)容許對(duì)全部均布荷載進(jìn)行一定程度的折減。例如，對(duì)于不小于100psf的活荷載，ANSI標(biāo)準(zhǔn)允許結(jié)構(gòu)單元在影響區(qū)域不小于400ft2時(shí)，對(duì)于活荷載按照等式3-1進(jìn)行折減，方程如下：3.4.2LiveLoadHighwayvehicleloadingintheUnitedStateshasbeenstandardizedbytheAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)intostandardtruckloadsandlaneloadsthatapproximateaseriesoftrucks.Therearetwosystems,designatedHandHS,thatareidentifiedbythenumberofaxlespertruck.TheHsystemhastwoaxles,whereastheHSsystemhasthreeaxlespertruck.Thereareseveralclassesofloading;however,theusualonesareknownasH20andHS20,showninFig.3-1.高速公路活荷載的分類(lèi)laneloads車(chē)道荷載；designated指定的；axle車(chē)軸3.4.3HighwayLiveLoadsHighwayvehicleloadingintheUnitedStateshasbeenstandardizedbytheAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)intostandardtruckloadsandlaneloadsthatapproximateaseriesoftrucks.Therearetwosystems,designatedHandHS,thatareidentifiedbythenumberofaxlespertruck.TheHsystemhastwoaxles,whereastheHSsystemhasthreeaxlespertruck.Thereareseveralclassesofloading;however,theusualonesareknownasH20andHS20,showninFig.3-1.在美國(guó)的高速公路車(chē)輛荷載由全美國(guó)家高速公路和交通運(yùn)輸協(xié)會(huì)進(jìn)行規(guī)定，歸類(lèi)為卡車(chē)荷載和車(chē)道荷載，其中車(chē)道荷載近似為一列卡車(chē)。有兩個(gè)系統(tǒng)，H和HS，他們是由每輛卡車(chē)的車(chē)軸數(shù)量確定的。H系統(tǒng)每輛車(chē)有兩個(gè)車(chē)軸，HS系統(tǒng)每輛車(chē)有三個(gè)車(chē)軸。有幾種不同等級(jí)的荷載。然而，通常熟知的是H20和HS20，如圖3-1所示。3.4.3HighwayLiveLoadsIndesigningagivenbridge,eitheronetruckloadingisappliedtotheentirestructure,orthelaneloadingisapplied.Whenthelaneloadingisused,theuniformportionisdistributedoverasmuchofthespanorspansaswillcausethemaximumeffect.Inaddition,theoneconcentratedload(formaximumnegativemomentoncontinuousspans,asecondconcentratedloadisalsoused)ispositionedforthemostsevereloadingeffect.Theloaddistributionacrossthewidthofabridgetoitsvarioussupportingmembersistakeninaccordancewithsemiempiricalrulesthatdependonthetypeofbridgedeckandsupportingstructure.作用于橋梁上的車(chē)輛荷載如何考慮load

distribution荷載分布；inaccordancewith符合；semiempirical半經(jīng)驗(yàn)的；bridgedeck橋面板3.4.3HighwayLiveLoadsIndesigningagivenbridge,eitheronetruckloadingisappliedtotheentirestructure,orthelaneloadingisapplied.Whenthelaneloadingisused,theuniformportionisdistributed(overasmuchofthespanorspansaswillcausethemaximumeffect).Inaddition,theoneconcentratedload(formaximumnegativemomentoncontinuousspans,asecondconcentratedloadisalsoused)ispositionedforthemostsevereloadingeffect.Theloaddistributionacrossthewidthofabridgetoitsvarioussupportingmembersistaken(inaccordancewithsemiempiricalrulesthatdependonthetypeofbridgedeckandsupportingstructure).設(shè)計(jì)一個(gè)給定的橋梁中，要么是將一個(gè)卡車(chē)的荷載加到整個(gè)結(jié)構(gòu)上，要么是將車(chē)道荷載施加到結(jié)構(gòu)上。當(dāng)使用車(chē)道荷載時(shí)，均布的部分要盡可能覆蓋多跨度，以到達(dá)最大的響應(yīng)。除此之外，將一個(gè)集中荷載（對(duì)于在連續(xù)跨度上的最大負(fù)彎矩，第二個(gè)集中荷載也被用到）施加到使得結(jié)構(gòu)產(chǎn)生最大荷載響應(yīng)的位置。荷載在橋面上的分布和在橋的各種支撐部件的分布符合半經(jīng)驗(yàn)的規(guī)則，而這是由橋面板的類(lèi)型和支承結(jié)構(gòu)決定的。3.4.3HighwayLiveLoadsThesingletruckloadingprovidestheeffectofaheavyconcentratedloadandusuallygovernsonrelativelyshortspans.Theuniformlaneloadistosimulatealineoftraffic,andtheaddedconcentratedloadistoaccountforthepossibilityofoneextraheavyvehicleinthelineoftraffic.Theseloadshavebeenusedwithnoapparentdifficultysince1944,beforewhichtimealineoftruckswasactuallyusedfortheloading.Ontheinterstatesystemofhighways,amilitaryloadingisalsousedthatconsistsoftwo24kip(107kN)axleloadsspaced4ft(1.2m)apart.均布車(chē)道荷載模擬一列車(chē)輛荷載governs控制；simulate模擬；interstatesystemofhighways州際高速公路系統(tǒng)3.4.3HighwayLiveLoadsThesingletruckloadingprovidestheeffectofaheavyconcentratedloadandusuallygovernsonrelativelyshortspans.Theuniformlaneloadistosimulatealineoftraffic,andthe

addedconcentratedloadistoaccountforthepossibilityofoneextraheavyvehicleinthelineoftraffic.Theseloadshavebeenusedwithnoapparentdifficultysince1944,beforewhichtimealineoftruckswasactuallyusedfortheloading.Ontheinterstatesystemofhighways,amilitaryloadingisalsousedthatconsistsoftwo24kip(107kN)axleloadsspaced4ft(1.2m)apart.單個(gè)的卡車(chē)荷載產(chǎn)生一個(gè)大的集中荷載的效應(yīng)并且在相對(duì)短的跨度情況下起控制作用。均布的車(chē)道荷載用來(lái)模擬一列交通工具，附加的集中荷載用來(lái)考慮在一列車(chē)輛中可能出現(xiàn)的額外較重的車(chē)輛。這些荷載自從1944年來(lái)一直沿用，并且沒(méi)遇到什么困難。而在此之前，事實(shí)上用一列卡車(chē)來(lái)計(jì)算荷載。在州際的高速公路系統(tǒng)中，也會(huì)用到軍事（車(chē)輛）荷載，這是由兩個(gè)間距1.2m的107kN車(chē)軸荷載組成的。3.4.3HighwayLiveLoadsThetermimpactasordinarilyusedinstructural