土木工程專業(yè)英語 課件 3.1.Load Conditions and Load Paths

3.1LoadConditionsandLoadPaths

VerticalLoadsGravityloadsActinthesamedirectionasgravity(i.e.,downwardorvertically)VerticalLoadsGravityloadsIncludedeadloadsliveloadssnowloadsWindupliftforcesVerticalLoadsGravityloadsstaticinnatureuniformlydistributed

load/concentratedloadThus,determiningagravityloadonabeamorcolumnisarelativelysimpleexercisethatusestheconceptoftributaryareas從屬面積toassignloadstostructuralelements.Tributaryarea=SLsq.mLoadonbeam=wS

kg/mFloorload=wkg/sq.mLSSSS=SpaninshortdirectionL=SpaninlongdirectionThetributaryareaistheareaofthebuildingconstructionthatissupportedbyastructuralelement,includingthedeadload(i.e.,weightoftheconstruction)andanyappliedloads(i.e.,liveload).Tributaryarea=SLsq.mLoadonbeam=wS

kg/mFloorload=wkg/sq.mLSSSS=SpaninshortdirectionL=SpaninlongdirectionForexample,thetributarygravityloadonafloorjoistwouldincludetheuniformfloorload(deadandlive)appliedtotheareaoffloorsupportedbytheindividualjoist.Tributaryarea=SLsq.mLoadonbeam=wS

kg/mFloorload=wkg/sq.mLSSSS=SpaninshortdirectionL=SpaninlongdirectionCast-in-placewithspanratiom=S/L<0.5One-waySlabTributaryareaOne-waySlabLongspan(AB):

Floorload=qKN/m2

Tributaryarea=SL/2-S2/4=m2

LoadonbeamKN/mShortspan(BC):

FloorloadqKN/m2

Tributaryarea=S2/4m2

Loadonbeam=qS/4qS/3KN/m雙向板Two-waySlab45o45o45o45oADCBSLSpanratiom=S/LBCBCWindupliftforcesaregeneratedbynegative(suction)pressuresactinginan

outwarddirectionfromthesurfaceoftheroofinresponsetotheaerodynamics

[7ZErEudai5nAmiks]空氣動力特性ofwindflowingoverandaroundthebuilding.Windpressuresactperpendiculartothebuildingsurface(notinthedirectionofgravity)andthatpressuresvaryaccordingtothesizeofthetributaryareaanditslocationonthebuilding,particularlyproximitytochangesingeometry(e.g.,eaves,corners,andridges).影響風(fēng)荷載大小的因素：

風(fēng)速建筑物的高度、形狀周圍環(huán)境風(fēng)載體型系數(shù)μs：風(fēng)荷載與建筑體型的關(guān)系風(fēng)壓分布系數(shù)迎風(fēng)面的風(fēng)壓力在建筑物的中間偏上為最大，兩邊及底下最?。粋?cè)風(fēng)面一般近側(cè)大，遠(yuǎn)側(cè)小，分布也極不均勻；背風(fēng)面一般兩邊略大，中間小。風(fēng)荷載體型系數(shù)是指風(fēng)作用在建筑物表面所引起的壓力(吸力)與原始風(fēng)速算得的理論風(fēng)壓的比值。LateralLoadsTheprimaryloadsthatproducelateralforcesonbuildingsareattributableto可歸因于forcesassociatedwithWindseismicgroundmotionsoil

Lateralforcesfromwindaregeneratedbypositivewindpressuresonthewindwardfaceofthebuildingandbynegativepressuresontheleewardfaceofthebuilding,creatingacombinedpush-and-pulleffect,andresultinguplifting,rackingorslidingofbuilding.rackingload：Aloadappliedintheplaneofanassemblyinsuchmannerastolengthenonediagonalandshortentheother.

Seismiclateralforcesaregeneratedbyastructure’sdynamicinertial慣性的

responsetocyclicgroundmovement.Themagnitudeoftheseismicshearloaddependsonmagnitudeofthegroundmotionbuilding’smassdynamicstructuralresponsecharacteristics(i.e.,dampening,ductility,naturalperiodofvibration,etc.).Forlow-risestructures,asimplifiedseismicloadanalysisemploysequivalentstaticforcesbasedonfundamentalNewtonianmechanics(F=ma)withsomewhatsubjective(i.e.,experience-based)adjustmentstoaccountforinelastic,ductileresponsecharacteristicsofvariousbuildingsystems.LateralLoadsLoadPathofaMaonryStructureTheVerticalLoadPathDeadload:alwayspresentLiveloads：transient;atonlyafractionoftheirdesignloadCurrentdesignloadstandardsgenerallyallowformultipletransientloadreductio