《土木工程专业英语 第2版》 课件 Unit3 Introduction to Steel Structures

Unit3IntroductiontoSteelStructuresEnglishforCivilEngineering——Teacher:Prof.ZhengLuE-mail:luzheng111@（SchoolofCivilEngineering,TONGJIUNIVERSITY）Unit3IntroductiontoSteelStructures3.1StructuralDesign（结构设计）3.2PrinciplesofDesign（设计准则）3.3HistoricalBackgroundofSteelStructures（钢结构背景）3.4Loads（荷载）3.4.1DeadLoad（静荷载）3.4.2LiveLoad（活荷载）3.4.3HighwayLiveLoads（高速公路活荷载）3.4.4Impact（冲击荷载）3.4.5SnowLoad（雪荷载）3.4.6WindLoad（风荷载）3.4.7EarthquakeLoad（地震作用）3.5TypesofStructuralSteelMembers（钢结构构件）3.5.1TensionMembers（受拉构件）3.5.2CompressionMembers（受压构件）3.5.3Beams（梁）3.5.4BendingandAxialLoad（压（拉）弯构件）Structuraldesignmaybedefinedasamixtureofartandscience,combiningtheexperiencedengineer’sintuitivefeelingforthebehaviorofastructurewithasoundknowledgeoftheprinciplesofstatics,dynamics,mechanicsofmaterials,andstructuralanalysis,toproduceasafeeconomicalstructurethatwillserveitsintendedpurpose.结构设计的定义intuitive直观的；sound合理的；intended预期的3.1StructuralDesignUntilabout1850,structuraldesignwaslargelyanartrelyingonintuitiontodeterminethesizeandarrangementofthestructuralelements.Earlyman-madestructuresessentially

conformedtothosewhichcouldalsobeobservedinnature,suchasbeamsandarches.Astheprinciplesgoverningthebehaviorofstructuresandstructuralmaterialshavebecomebetterunderstood,designprocedureshavebecomemorescientific.早期的结构设计intuition直觉；

conformedto符合；

essentially基本上；governing控制3.1StructuralDesignComputationsinvolvingscientificprinciplesshouldserveasaguidetodecisionmakingandnotbefollowedblindly.Theartorintuitiveabilityoftheexperiencedengineerisutilizedtomakethedecisions,guidedbythecomputationalresults.结构设计的原则isutilizedto利用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.设计准则的要求optimum最佳的，最佳效果；criteria原则；manufacture建造；weighting加权重；qualitative定性的3.2PrinciplesofDesignIfaspecificobjectivecriterioncanbeexpressedmathematically,thenoptimization

techniquesmaybeemployedtoobtainamaximumorminimumfortheobjectivefunction.Optimizationproceduresandtechniquescompriseanentiresubjectthatisoutsidethescopeofthistext.Thecriterionofminimumweightisemphasizedthroughout,underthegeneralassumptionthatminimummaterialrepresentsminimumcost.Othersubjectivecriteriamustbekeptinmind,eventhoughtheintegrationofbehavioralprincipleswithdesignofstructuralsteelelementsinthistextutilizesonlysimpleobjectivecriteria,suchasweightorcost.结构设计的优化方法criterion标准；optimization

techniques优化方法；scope范围；comprise

包含assumption假定；integration整合；utilize利用3.2PrinciplesofDesignThedesignproceduremaybeconsideredtobecomposedoftwoparts—functionaldesignandstructuralframeworkdesign.Functionaldesignensuresthatintendedresultsareachieved,suchas(a)adequateworkingareasandclearances;(b)properventilationand/orairconditioning;(c)adequatetransportationfacilities,suchaselevators,stairways,andcranesormaterialshandlingequipment;(d)adequatelighting;and(e)aesthetics.设计过程包含两部分——功能设计和结构框架设计adequate充足的；clearance空隙；ventilation通风系统；crane吊车；aesthetics美观3.2PrinciplesofDesignThestructuralframeworkdesignistheselectionofarrangementandsizesofstructuralelementssothatserviceloadsmaybesafelycarried,anddisplacementsarewithinacceptablelimits.结构框架设计3.2PrinciplesofDesignTheiterativedesignproceduremaybeoutlinedasfollows:1.Planning.Establishmentofthefunctionsforwhichthestructuremustserve.Setcriteriaagainstwhichtomeasuretheresultingdesignforbeinganoptimum.2.Preliminarystructuralconfiguration.Arrangementoftheelementstoservethefunctionsinstep1.3.Establishmentoftheloadstobecarried.4.Preliminarymemberselection.Basedonthedecisionsofsteps1,2,and3selectionofthemembersizestosatisfyanobjectivecriterion,suchasleastweightorcost.设计过程的具体步骤1—4iterative重复的；preliminary初步的；configuration配置；satisfy达到3.2PrinciplesofDesign5.Analysis.Structuralanalysisinvolvingmodelingtheloadsandthestructuralframeworktoobtaininternalforcesandanydesireddeflections.6.Evaluation.Areallstrengthandserviceabilityrequirementssatisfiedandistheresultoptimum?Comparetheresultwithpredeterminedcriteria.7.Redesign.Repetitionofanypartofthesequence1through6foundnecessaryordesirableasaresultofevaluation.Steps1through6representaniterativeprocess.Usuallyinthistextonlysteps3through6willbesubjecttothisiterationsincethestructuralconfigurationandexternalloadingwillbeprescribed.8.Finaldecision.Thedeterminationofwhetherornotanoptimumdesignhasbeenachieved.设计过程的具体步骤5—8internalforces内力；serviceabilityrequirements使用要求；prescribed规定3.2PrinciplesofDesignMetalasastructuralmaterialbeganwithcastiron,usedona100-ft(30-m)archspanwhichwasbuiltinEnglandin1777-1779.Anumberofcast-ironbridgeswerebuiltduringtheperiod1780-1820,mostlyarch-shapedwithmaingirdersconsistingofindividualcast-ironpiecesformingbarsortrusses.Castironwasalsousedforchainlinksonsuspensionbridgesuntilabout1840.铸铁的应用castiron铸铁；girder梁；bar条形；truss桁架；chainlinks锁链；suspensionbridges悬索桥3.3HistoricalBackgroundofSteelStructuresThedevelopmentoftheBessemerprocess(1855),theintroductionofabasiclinerintheBessemerconverter(1870),andtheopen-hearthfurnacebroughtwidespreaduseofironoreproductsinbuildingmaterials.Since1890,steelhasreplacedwroughtironastheprincipalmetallicbuildingmaterial.Currently(1989),steelshavingyieldstressesvaryingfrom24,000to100,000poundspersquareinch,psi(165to690megapascals,MPa),andavailableforstructuraluses.金属材料从锻铁向钢铁转变Bessemerprocess贝塞麦（转炉）炼钢法；Bessemerconverter贝氏转炉；open-hearthfurnace平炉；ironore铁矿石；wroughtiron锻铁（熟铁）3.3HistoricalBackgroundofSteelStructuresTheaccuratedeterminationoftheloadstowhichastructureorstructuralelementwillbesubjectedisnotalwayspredictable.Eveniftheloadsarewellknownatonelocationinastructure,thedistributionofloadfromelementtoelementthroughoutthestructureusuallyrequiresassumptionsandapproximations.Someofthemostcommonkindsofloadsarediscussedinthefollowingsections.荷载概述distribution分布；approximations近似3.4LoadsDeadloadisafixed-positiongravityserviceload,socalledbecauseitactscontinuouslytowardtheearthwhenthestructureisinservice.Theweightofthestructureisconsidereddeadload,aswellasattachmentstothestructuresuchaspipes,electricalconduit,air-conditioningandheatingducts,lightingfixtures,floorcovering,roofcovering,andsuspendedceilings;thatis,allitemsthatremainthroughoutthelifeofthestructure.静荷载定义attachments附属物3.4.1DeadLoadDeadloadsareusuallyknownaccuratelybutnotuntilthedesignhasbeencompleted.Understeps3through6ofthedesignprocedure,theweightofthestructureorstructuralelementmustbeestimated,preliminarysectionselected,weightrecomputed,andmemberselectionrevisedifnecessary.Thedeadloadofattachmentsisusuallyknownwithreasonableaccuracypriortothedesign.静荷载的确定过程revise修改；priorto在……之前3.4.1DeadLoadGravityloadsactingwhenthestructureisinservice,butvaryinginmagnitudeandlocation,aretermedliveloads.Examplesofliveloadsarehumanoccupants,furniture,movable

equipment,vehicles,andstoredgoods.Someliveloadsmaybepracticallypermanent,othersmaybehighlytransient.Becauseoftheunknownnatureofthemagnitude,location,anddensityofliveloaditems,realisticmagnitudesandthepositionsofsuchloadsareverydifficulttodetermine.活荷载的定义magnitude大小；termed被称为；occupants居住者；movableequipment移动设备；permanent永久的；transient短暂的3.4.2LiveLoadBecauseofthepublicconcernforadequatesafety,liveloadstobetakenasserviceloadsindesignareusuallyprescribedbystateandlocalbuildingcodes.Theseloadsaregenerallyempiricalandconservative,basedonexperienceandacceptedpracticeratherthanaccuratelycomputedvalues.Whereverlocalcodesdonotapply,ordonotexist,theprovisionsfromoneofseveralregionalandnationalbuildingcodesmaybeused.OnesuchwidelyrecognizedcodeistheAmericannationalStandardMinimumDesignLoadsforBuildingsandOtherStructuresANSIA58.1oftheAmericanNationalStandardsInstitute(ANSI),fromwhichsometypicalliveloadsarepresented.ThecodewillhenceforthbereferredtoastheANSIStandard.Thisstandardisupdatedfromtimetotime,mostrecentlyin1982.活荷载的确定方法adequate足够的；serviceloads使用荷载；empirical凭经验的；conservative保守的；provision规范；regional区域的；henceforth今后3.4.2LiveLoadLiveloadwhenappliedtoastructureshouldbepositionedtogivethemaximumeffect,includingpartialloading,alternatespanloading,orfullspanloadingasmaybenecessary.Thesimplifiedassumptionoffulluniformloadingeverywhereshouldbeusedonlywhenitagreeswithrealityorisanappropriateapproximation.Theprobabilityofhavingtheprescribedloadingapplieduniformlyoveranentirefloor,oroverallfloorsofabuildingsimultaneously,isalmostnonexistent.Mostcodesrecognizethisbyallowingforsomepercentagereductionfromfullloading.Forinstance,forliveloadsof100psformoreANSIStandardallowsmembershavinganinfluenceareaof400ft2ormoretobedesignedforareducedliveloadaccordingtoEq.3-1，asfollows:确定取得最大效应的活荷载分布partialloading局部荷载；alternatespanloading交替跨荷载；fullspanloading全跨荷载；fulluniformloading均布荷载；appropriate适当的；simultaneously同时3.4.2LiveLoadHighwayvehicleloadingintheUnitedStateshasbeenstandardizedbytheAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)intostandardtruckloadsandlaneloadsthatapproximateaseriesoftrucks.Therearetwosystems,designatedHandHS,thatareidentifiedbythenumberofaxlespertruck.TheHsystemhastwoaxles,whereastheHSsystemhasthreeaxlespertruck.Thereareseveralclassesofloading;however,theusualonesareknownasH20andHS20,showninFig.3-1.高速公路活荷载的分类laneloads车道荷载；designated指定的；axle车轴3.4.3HighwayLiveLoadsIndesigningagivenbridge,eitheronetruckloadingisappliedtotheentirestructure,orthelaneloadingisapplied.Whenthelaneloadingisused,theuniformportionisdistributedoverasmuchofthespanorspansaswillcausethemaximumeffect.Inaddition,theoneconcentratedload(formaximumnegativemomentoncontinuousspans,asecondconcentratedloadisalsoused)ispositionedforthemostsevereloadingeffect.Theloaddistributionacrossthewidthofabridgetoitsvarioussupportingmembersistakeninaccordancewithsemiempiricalrulesthatdependonthetypeofbridgedeckandsupportingstructure.作用于桥梁上的车辆荷载如何考虑load

distribution荷载分布；inaccordancewith符合；semiempirical半经验的；bridgedeck桥面板3.4.3HighwayLiveLoadsThesingletruckloadingprovidestheeffectofaheavyconcentratedloadandusuallygovernsonrelativelyshortspans.Theuniformlaneloadistosimulatealineoftraffic,andtheaddedconcentratedloadistoaccountforthepossibilityofoneextraheavyvehicleinthelineoftraffic.Theseloadshavebeenusedwithnoapparentdifficultysince1944,beforewhichtimealineoftruckswasactuallyusedfortheloading.Ontheinterstatesystemofhighways,amilitaryloadingisalsousedthatconsistsoftwo24kip(107kN)axleloadsspaced4ft(1.2m)apart.均布车道荷载模拟一列车辆荷载governs控制；simulate模拟；interstatesystemofhighways州际高速公路系统3.4.3HighwayLiveLoadsThetermimpactasordinarilyusedinstructuraldesignreferstothedynamiceffectofasuddenlyappliedload.Inthebuildingofastructure,thematerialsareaddedslowly;peopleenteringabuildingarealsoconsideredagradualloading.Deadloadsarestaticloads;i.e.,theyhavenoeffectotherthanweight.Liveloadsmaybeeitherstaticortheymayhaveadynamiceffect.Personsandfurniturewouldbetreatedasstaticliveload,butcranesandvarioustypesofmachineryalsohavedynamiceffects.冲击荷载的定义term术语；crane起重机3.4.4ImpactConsiderthespring-masssystemofFig.3-2a,wherethespringmaybethoughtofasanalogoustoanelasticbeam.Whenloadisgraduallyapplied(i.e.,staticloading)themass(weight)deflectsanamountxandtheloadonthespring(beam)isequaltotheweightW.InFig.3-2btheloadissuddenlyapplied(dynamicloading),andthemaximumdeflectionis2x;i.e.,themaximumloadonthespring(beam)is2W.Inthiscasethemassvibratesinsimpleharmonicmotionwithitsneutralpositionequaltoitsstaticdeflectedposition.Inrealstructures,theharmonic(vibratory)motionisdampedout(reducedtozero)veryrapidly.Oncethemotionhasstopped,theforceremaininginthespringistheweightW.Toaccountfortheincreasedforceduringthetimethememberisinmotion,aloadequaltotwicethestaticloadWshouldbeused—add100%ofthestaticloadtorepresentthedynamiceffect.Thisiscalleda100%impactfactor.考虑冲击效应的影响——冲击因子analogous相似的；deflect偏离；vibrate振动；simpleharmonicmotion简谐运动；neutralposition中性位置；dampedout衰减的；neutralposition平衡位置3.4.4ImpactAnyliveloadthatcanhaveadynamiceffectshouldbeincreasedbyanimpactfactor.Whileadynamicanalysisofastructurecouldbemade,suchaprocedureisunnecessaryinordinarydesign.Thusempirical

formulasandimpactfactorsareusuallyused.Incaseswherethedynamiceffectissmall(saywhereimpactwouldbelessthanabout20%),itisordinarilyaccountedforbyusingaconservative(higher)valueforthespecifiedliveload.Thedynamiceffectsofpersonsinbuildingsandofslow-movingvehiclesinparkinggaragesareexampleswhereordinarydesignliveloadisconservative,andusuallynoexplicitimpactfactorisadded.冲击系数取值empiricalformulas经验公式；conservative保守的；explicit明确的3.4.4ImpactInEq.3-2,L(expressedinfeet)isthelengthoftheportionofthespanthatisloadedtogivethemaximumeffectonthemember.Sincevehiclestraveldirectlyonthesuperstructure,allpartsofitaresubjectedtovibrationandmustbedesignedtoincludeimpact.Thesubstructure,includingallportionsnotrigidlyattachedtothesuperstructuresuchasabutments,retainingwalls,andpiers,areassumedtohaveadequatedampingorbesufficientlyremotefromtheapplicationpointofthedynamicloadsothatimpactmightnotbeconsidered.Again,conservativestaticloadsmayaccountforthesmallerdynamiceffects.需要考虑冲击效应的结构部件portion部分；superstructure上部结构；vibration振动；substructure附属结构；abutments桥台；retainingwalls挡土墙；pier桥墩；damping阻尼3.4.4ImpactTheliveloadingforwhichroofsaredesignediseithertotallyorprimarilyasnowload.Sincesnowhasavariablespecificgravity,evenifoneknowsthedepthofsnowforwhichdesignistobemade,theloadperunitareaofroofisatbestonlyaguess.由于雪的比重不确定，雪荷载难以直接确定3.4.5SnowLoadThebestprocedureforestablishingsnowloadfordesignistofollowtheANSIStandard.ThisCodeusesamapoftheUnitedStatesgivingisolinesofgroundsnowcorrespondingtoa50-yearmeanrecurrence

intervalforuseindesigningmostpermanentstructures.Thegroundsnowisthenmultipliedbyacoefficientthatincludestheeffectofroofslope,windexposure,nonuniformaccumulationonpitchedorcurvedroofs,multipleseriesroofs,andmultilevelroofsandroofareasadjacenttoprojectionsonarooflevel.考虑雪荷载的方式isolines等值线；correspondingto相当于；recurrence重现；interval间隔；multiply乘以；coefficient系数；exposure暴露；pitched有坡度的；curved曲面的；nonuniformaccumulation不均匀堆积3.4.5SnowLoadItisapparentthatthesteepertheroofisthelesssnowcanaccumulate.Also,partialsnowloadingmustbeconsideredinadditiontofullloading,ifitisbelievedsuchloadingcanoccurandwouldcausemaximumeffects.Windmayalsoactonastructurethatiscarryingsnowload.Itisunlikely,however,thatmaximumsnowandwindloadswouldactsimultaneously.考虑雪荷载需要考虑的因素——部分堆积雪荷载、屋面坡度、风荷载steeper倾斜的；accumulate堆积；simultaneously同时3.4.5SnowLoadIngeneral,thebasicsnowloadusedindesignvariesfrom30to40psf(1400to1900MPa)inthenorthernandeasternstatesto20psf(960MPa)orlessinthesouthernstates.Flatroofsinnormallywarmclimatesshouldbedesignedfor20psf(960MPa)evenwhensuchaccumulationofsnowmayseemdoubtful.Thisloadingmaybethoughtofasduetopeoplegatheredonsucharoof.Furthermore,thoughwindisfrequentlyignoredasaverticalforceonaroof,neverthelessitmaycausesuchaneffect.Forthesereasons,a20psf(960MPa)minimumloading,eventhoughitmaynotalwaysbesnow,isreasonable.Localcodes,actualweatherconditions,ANSI,ortheCanadianStructuralDesignManual,shouldbeusedwhendesigningforsnow.规范中规定的雪荷载值flatroof平屋面；nevertheless然而3.4.5SnowLoadAllstructuresaresubjecttowindload,butitisusuallyonlythosemorethanthreeorfourstorieshigh,otherthanlongbridges,forwhichspecialconsiderationofwindisrequired.需要考虑风荷载的结构otherthan除了3.4.6WindLoadOnanytypicalbuildingofrectangularplanandelevation,windexertspressureonthewindwardsideandsuctionontheleewardside,aswellaseitherupliftordownwardpressureontheroof.Formostordinarysituations,verticalroofloadingfromwindisneglectedontheassumptionthatsnowloadingwillrequireagreaterstrengththanwindloading.Thisassumptionisnottrueforsouthernclimateswheretheverticalloadingduetowindmustbeincluded.Furthermore,thetotallateralwindload,windwardandleewardeffect,iscommonlyassumedtobeappliedtothewindwardfaceofthebuilding.如何考虑风荷载plan平面；elevation高度；windwardside迎风面；suction吸力；leewardside背风面；uplift向上的；lateral侧面的3.4.6WindLoadThecommonlyusedwindpressureof20psf,asspecifiedbymanybuildingcodes,correspondstoavelocityof88milesperhour(mph)fromEq.3-4.AnexposurefactorCeof1.0,agustfactorCgof2.0,andashapefactor

Cpof1.3foranairtightbuilding,alongwitha20psfequivalentstaticpressurep,willgivefromEq.3-5adynamicpressureqof7.7psf,whichcorrespondsusingEq.3-4,toawindvelocityof55mph.Forallbuildingshavingnonplanarsurfaces,planesurfacesinclinedtothewinddirection,orsurfaceshavingsignificantopenings,specialdeterminationofthewindforcesshouldbemadeusingsuchsourcesastheANSIStandard,ortheNationalBuildingCodeofCanada.Formoreextensivetreatmentofwindloads,thereaderisreferredtotheTaskCommitteeonWindForces.规范中风荷载取值specify规定；velocity速度；exposurefactor风压高度变化系数；gustfactor风振系数；shapefactor风荷载体型系数；airtight封闭的；nonplanar非平面的；inclined倾斜的；extensivetreatment众多的处理方法；3.4.6WindLoadAnearthquakeconsistsofhorizontalandverticalgroundmotions,withtheverticalmotionusuallyhavingmuchthesmallermagnitude.Becausethehorizontalmotionofthegroundcausesthemostsignificanteffect,itisthateffectwhichisusuallythoughtofasearthquakeload.Whenthegroundunderanobject(structure)havingacertainmasssuddenlymoves,theinertiaofthemasstendstoresistthemovement,asshowninFig.3-4.Ashearforceisdevelopedbetweenthegroundandthemass.MostbuildingcodeshavingearthquakeprovisionsrequirethedesignertoconsideralateralforceCWthatisusuallyempiricallyprescribed.Thedynamicsofearthquakeactiononstructuresisoutsidethescopeofthistext,andthereaderisreferredtoChopra,CloughandPenzien.地震作用概述inertia惯性；provision规定；lateralforce横向力；empirically以经验为主的3.4.7EarthquakeLoadInordertosimplifythedesignprocess,mostbuildingcodescontainanequivalentlateralforceprocedurefordesigningtoresistearthquakes.OneofthemostwidelyuseddesignrecommendationsisthatofStructuralEngineersAssociationofCalifornia(SEAOC),thelatestversionofwhichis1974.Sincethattime,theAppliedTechnologyCouncil(ATC)preparedasetofdesignprovisions.SomerecentrulesfortheequivalentlateralforceprocedurearethosegivenbytheANSIStandard.InANSIthelateralseismicforceV,expressedasfollows,areassumedtoactnonconcurrentlyinthedirectionofeachofthemainaxesofthestructure.等效侧向力方法recommendation建议；nonconcurrently不作用于同一点的3.4.7EarthquakeLoadThefunctionofastructureistheprincipalfactordeterminingthestructuralconfiguration.Usingthestructuralconfigurationalongwiththedesignloads,individualcomponentsareselectedtoproperlysupportandtransmitloadsthroughoutthestructure.SteelmembersareselectedfromamongthestandardrolledshapesadoptedbytheAmericanInstituteofSteelConstruction(AISC)(alsogivenbyAmericanSocietyforTestingandMaterials[ASTM]A6Specification).Ofcourse,weldingpermitscombiningplatesand/orotherrolledshapestoobtainanyshapethedesignermayrequire.钢构件的种类——轧制型钢和焊接钢构件principal主要的；configuration布置；rolledshapes轧制型钢；adoptedby采用；Specification规格3.5TypesofStructuralSteelMembersTypicalrolledshapes,thedimensionsforwhicharefoundintheAISCManual,areshowninFig.3-5.Themostcommonlyusedsectionisthewide-flangeshape(Fig.3-5a)whichisformedbyhotrollinginthesteelmill.Thewide-flangeshapeisdesignatedbythenominaldepthandtheweightperfoot,suchasaW18×97whichisnominally18in.deep(actualdepth=18.59in.accordingtoAISCManual)andweighs97poundsperfoot.(InSIunitstheW18×97sectioncouldbedesignatedW460×142,meaningnominally460mmdeepandhavingamassof142kg/m.)TwosetsofdimensionsarefoundintheAISCManual,onesetstatedindecimalsforthedesignertouseincomputations,andanothersetexpressedinfractions(1/16in.asthesmallestincrement)forthedetailertouseonplansandshopdrawings.RolledWshapesarealsodesignatedbyANSI/ASTMA6inaccordancewithwebthicknessasGroupsIthroughV,withthethinnestwebsectionsinGroup1.规范中轧制型钢命名方式wide-flangeshape宽翼缘型钢（H型钢）；steelmill钢铁厂；designated命名为；decimal小数；fraction分数；detailer放样员；inaccordancewith按照3.5TypesofStructuralSteelMembersTheAmericanStandardbeam(Fig.3-5b),commonlycalledtheI-beam,hasrelativelynarrowandslopingflangesandathickwebcomparedtothewide-flangeshape.UseofmostI-beamshasbecomerelativelyuncommonbecauseofexcessivematerialinthewebandrelativelackoflateralstiffnessduetothenarrowflanges.I型钢sloping倾斜的；excessiv