《土木工程專業(yè)英語 第2版》 翻譯版 課件全套 魯正 Unit 1 Introduction to Reinforced Concrete Design-Unit 5 Composite Construction

Unit1IntroductiontoReinforcedConcreteDesignEnglishforCivilEngineering——Unit1IntroductiontoReinforcedConcreteDesign1.1Concrete,ReinforcedConcrete,andPrestressedConcrete（混凝土，鋼筋混凝土，以及預(yù)應(yīng)力混凝土）1.2StructuralForms（結(jié)構(gòu)形式）1.3Loads（荷載）1.4Serviceability,Strength,andStructuralSafety（可用性，強(qiáng)度以及結(jié)構(gòu)安全性）1.4.1VariabilityofLoads（荷載變異性）1.4.2Strength（強(qiáng)度）1.4.3StructuralSafety（結(jié)構(gòu)安全性）1.5DesignBasis（設(shè)計基礎(chǔ)）1.1Concrete,ReinforcedConcrete,andPrestressedConcreteConcreteisastonelikematerialobtainedbypermittingacarefullyproportionedmixtureofcement,sandandgravelorotheraggregate,andwatertohardeninformsoftheshapeanddimensionsofthedesiredstructure.Thebulkofthematerialconsistsoffineandcoarseaggregate.Cementandwaterinteractchemicallytobindtheaggre-gateparticlesintoasolidmass.Additionalwater,overandabovethatneededforthischemicalreaction,isnecessarytogivethemixturetheworkabilitythatenablesittofilltheformsandsurroundtheembeddedreinforcingsteelpriortohardening.混凝土的組成stonelike像石頭一樣的

cement水泥

gravel砂礫aggregate骨料

coarse粗糙的workability和易性1.1Concrete,ReinforcedConcrete,andPrestressedConcreteConcreteisastonelikematerialobtainedbypermittingacarefullyproportionedmixtureofcement,sandandgravelorotheraggregate,andwatertohardeninformsoftheshapeanddimensionsofthedesiredstructure.Thebulkofthematerialconsistsoffineandcoarseaggregate.Cementandwaterinteractchemicallytobindtheaggre-gateparticlesintoasolidmass.Additionalwater,overandabovethatneededforthischemicalreaction,isnecessarytogivethemixturetheworkabilitythatenablesittofilltheformsandsurroundtheembeddedreinforcingsteelpriortohardening.混凝土是一種把水泥、砂和石礫或者其他骨料、以及水按比例混合并硬化成所需結(jié)構(gòu)的形狀和尺寸的石頭狀的材料。這種材料大部分由粗細(xì)骨料組成。水泥和水通過化學(xué)作用把骨料顆粒凝結(jié)為固體質(zhì)量。超過化學(xué)作用所需的額外的水用來提供混合物的和易性，使之在硬化之前能夠填入模板以及包圍嵌入的鋼筋。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteConcreteswithawiderangeofpropertiescanbeobtainedbyappropriateadjustmentoftheproportionsoftheconstituentmaterials.Specialcements(suchashighearlystrengthcements),specialaggregates(suchasvariouslightweightorheavyweightaggregates),admixtures(suchasplasticizers,air-entrainingagents,silicafume,andflyash),andspecialcuringmethods(suchassteam-curing)permitanevenwidervari-etyofpropertiestobeobtained.特種混凝土property

特性

constituent構(gòu)成的

admixture外加劑plasticizer塑化劑air-entrainingagent加氣劑silicafume硅粉flyash粉煤灰

steam-curing蒸汽養(yǎng)護(hù)1.1Concrete,ReinforcedConcrete,andPrestressedConcreteConcreteswithawiderangeofpropertiescanbeobtainedbyappropriateadjustmentoftheproportionsoftheconstituentmaterials.Specialcements(suchashighearlystrengthcements),specialaggregates(suchasvariouslightweightorheavyweightaggregates),admixtures(suchasplasticizers,air-entrainingagents,silicafume,andflyash),andspecialcuringmethods(suchassteam-curing)permitanevenwidervari-etyofpropertiestobeobtained.通過調(diào)整組成部分的比例，可獲得各種強(qiáng)度的混凝土。特殊的水泥（比如早強(qiáng)水泥），特殊的骨料（比如各種輕骨料或者重骨料），外加劑（比如增塑劑和加氣劑）和特殊的養(yǎng)護(hù)方法（比如蒸汽養(yǎng)護(hù)）可以得到更多種類的特性。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteThesepropertiesdependtoaverysubstantialdegreeontheproportionsofthemix,onthethoroughnesswithwhichthevariousconstituentsareintermixed,andontheconditionsofhumidityandtemperatureinwhichthemixismaintainedfromthemomentitisplacedintheformsuntilitisfullyhardened.Theprocessofcontrollingconditionsafterplacementisknownascuring.Toprotectagainsttheunintentionalproductionofsubstandardconcrete,ahighdegreeofskillfulcontrolandsupervisionisnecessarythroughouttheprocess,fromtheproportioningbyweightoftheindivid-ualcomponents,throughmixingandplacing,untilthecompletionofcuring.混凝土的制作與養(yǎng)護(hù)substantial實質(zhì)的

thoroughness充分性

intermix混合humidity濕度

curing養(yǎng)護(hù)1.1Concrete,ReinforcedConcrete,andPrestressedConcreteThesepropertiesdependtoaverysubstantialdegreeontheproportionsofthemix,onthethoroughnesswithwhichthevariousconstituentsareintermixed,andontheconditionsofhumidityandtemperatureinwhichthemixismaintainedfromthemomentitisplacedintheformsuntilitisfullyhardened.Theprocessofcontrollingconditionsafterplacementisknownascuring.Toprotectagainsttheunintentionalproductionofsubstandardconcrete,ahighdegreeofskillfulcontrolandsupervisionisnecessarythroughouttheprocess,fromtheproportioningbyweightoftheindivid-ualcomponents,throughmixingandplacing,untilthecompletionofcuring.這些特性很大程度上依賴于混合比例，不同組成部分?jǐn)嚢璧某浞中?，以及混合物在澆注后直到硬化前的濕度和溫度?？刂七@些條件的過程叫養(yǎng)護(hù)。為了避免次品混凝土，整個過程需要嚴(yán)格的技術(shù)控制和檢查。這個過程從不同組分按重量配比，到混合、澆注，直到養(yǎng)護(hù)完成。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteThefactorsthatmakeconcreteauniversalbuildingmaterialaresopronouncedthatithasbeenused,inmoreprimitivekindsandwaysthanatpresent,forthousandsofyears,startingwithlimemortarsfrom12,000to6000BCEinCrete,Cyprus,Greece,andtheMiddleEast.Thefacilitywithwhich,whileplastic,itcanbedepositedandmadetofillformsormoldsofalmostanypracticalshapeisoneofthesefactors.Itshighfireandweatherresistanceisanevidentadvantage.混凝土的歷史與優(yōu)點(diǎn)pronounced顯著的

primitive原始的

limemortars水泥砂漿facility容易

plastic塑性的deposited放置mold模具1.1Concrete,ReinforcedConcrete,andPrestressedConcreteThefactorsthatmakeconcreteauniversalbuildingmaterialaresopronouncedthatithasbeenused,inmoreprimitivekindsandwaysthanatpresent,forthousandsofyears,startingwithlimemortarsfrom12,000to6000BCEinCrete,Cyprus,Greece,andtheMiddleEast.Thefacilitywithwhich,whileplastic,itcanbedepositedandmadetofillformsormoldsofalmostanypracticalshapeisoneofthesefactors.Itshighfireandweatherresistanceisanevidentadvantage.混凝土應(yīng)用如此普遍，有一個顯然的原因便是其已經(jīng)使用了上千年了。早在公元前12000年到6000年間克里特島、塞浦路斯、希臘以及中東便開始使用混凝土，盡管是以水泥砂漿這樣一種更原始的方式在使用。當(dāng)混凝土處于塑性狀態(tài)時，它可以很容易地澆注并填充到任何形式的模板或磨具中。它具有高抗火性和耐候性的優(yōu)點(diǎn)。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteMostoftheconstituentmaterials,withtheexceptionofcementandadditives,areusuallyavailableatlowcostlocallyoratsmalldistancesfromtheconstructionsite.Itscompressivestrength,likethatofnaturalstones,ishigh,whichmakesitsuitableformembersprimarilysubjecttocompression,suchascolumnsandarches.Ontheotherhand,againasinnaturalstones,itisarelativelybrittlematerialwhosetensilestrengthissmallcomparedwithitscompressivestrength.Thispreventsitseconomicaluseinstructuralmembersthataresubjecttotensioneitherentirely(suchasintie-rods)oroverpartoftheircrosssections(suchasinbeamsorotherflexuralmembers).混凝土組成材料的特性additive添加劑

constructionsite施工現(xiàn)場

compressivestrength抗壓強(qiáng)度tensilestrength抗拉強(qiáng)度

1.1Concrete,ReinforcedConcrete,andPrestressedConcreteMostoftheconstituentmaterials,withtheexceptionofcementandadditives,areusuallyavailableatlowcostlocallyoratsmalldistancesfromtheconstructionsite.Itscompressivestrength,likethatofnaturalstones,ishigh,whichmakesitsuitableformembersprimarilysubjecttocompression,suchascolumnsandarches.Ontheotherhand,againasinnaturalstones,itisarelativelybrittlematerialwhosetensilestrengthissmallcomparedwithitscompressivestrength.Thispreventsitseconomicaluseinstructuralmembersthataresubjecttotensioneitherentirely(suchasintie-rods)oroverpartoftheircrosssections(suchasinbeamsorotherflexuralmembers).除了水泥之外的組成材料，大部分都可在當(dāng)?shù)鼗蚴┕がF(xiàn)場就近以很低廉的價格獲得。像天然的石頭一樣，它的抗壓強(qiáng)度很高，所以適合于做受壓構(gòu)件，如柱和拱。另一方面，與石頭一樣，它是相對較脆的材料，其抗拉強(qiáng)度低于抗壓強(qiáng)度。這使得它用在整體受拉（如系桿）或截面部分受拉（如梁或其他受彎構(gòu)件）的結(jié)構(gòu)構(gòu)件時不經(jīng)濟(jì)。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteTooffsetthislimitation,itwasfoundpossible,inthesecondhalfofthenineteenthcentury,tousesteelwithitshightensilestrengthtoreinforceconcrete,chieflyinthoseplaceswhereitslowtensilestrengthwouldlimitthecarryingcapacityofthemember.Thereinforcement,usuallyroundsteelrodswithappropriatesurfacedeformationstoprovideinterlocking,isplacedintheformsinadvanceoftheconcrete.將鋼材引入到混凝土中（即鋼筋混凝土）capacity承載力rod棒，桿interlocking咬合作用1.1Concrete,ReinforcedConcrete,andPrestressedConcreteTooffsetthislimitation,itwasfoundpossible,inthesecondhalfofthenineteenthcentury,tousesteelwithitshightensilestrengthtoreinforceconcrete,chieflyinthoseplaceswhereitslowtensilestrengthwouldlimitthecarryingcapacityofthemember.Thereinforcement,usuallyroundsteelrodswithappropriatesurfacedeformationstoprovideinterlocking,isplacedintheformsinadvanceoftheconcrete.為了彌補(bǔ)這種限制，19世紀(jì)中葉時，人們發(fā)現(xiàn)可以把高抗拉強(qiáng)度的鋼筋應(yīng)用于混凝土，尤其是用于因混凝土的低抗拉強(qiáng)度從而限制了構(gòu)件承載力的部位。鋼筋通常為圓形，外表通常帶有適當(dāng)變形以提供咬合力，并以利于混凝土的形式放置。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteWhencompletelysurroundedbythehardenedconcretemass,itformsanintegralpartofthemember.Theresultingcombinationoftwomaterials,knownasreinforcedconcrete，combinesmanyoftheadvantagesofeach:therelativelylowcost,goodweatherandfireresistance,goodcompressivestrength,andexcellentformabilityofconcreteandthehightensilestrengthandmuchgreaterductilityandtoughnessofsteel.Itisthiscombinationthatallowsthealmostunlimitedrangeofusesandpossi-bilitiesofreinforcedconcreteintheconstructionofbuildings,bridges,dams,tanks,reservoirs,andahostofotherstructures.鋼筋混凝土優(yōu)點(diǎn)hardened變硬的formability可成形性toughness韌性reservoirs水庫1.1Concrete,ReinforcedConcrete,andPrestressedConcreteWhencompletelysurroundedbythehardenedconcretemass,itformsanintegralpartofthemember.Theresultingcombinationoftwomaterials,knownasreinforcedconcrete，combinesmanyoftheadvantagesofeach:therelativelylowcost,goodweatherandfireresistance,goodcompressivestrength,andexcellentformabilityofconcreteandthehightensilestrengthandmuchgreaterductilityandtoughnessofsteel.Itisthiscombinationthatallowsthealmostunlimitedrangeofusesandpossi-bilitiesofreinforcedconcreteintheconstructionofbuildings,bridges,dams,tanks,reservoirs,andahostofotherstructures.當(dāng)被硬化的混凝土完全包裹后，鋼筋變成構(gòu)件整體的一部分。兩種材料的結(jié)合，被稱為鋼筋混凝土，它結(jié)合了各自的許多優(yōu)點(diǎn)：混凝土的低成本，高耐候性和抗火性，高抗壓強(qiáng)度和高成型性；鋼筋的高抗拉強(qiáng)度，高延性和韌性。正是這種聯(lián)合作用，使得鋼筋混凝土有著近乎無限的應(yīng)用范圍和可能，可以用于房屋，橋梁，大壩，水池，水庫和很多其他的結(jié)構(gòu)。1.1Concrete,ReinforcedConcrete,andPrestressedConcreteAspecialwayhasbeenfound,however,tousesteelsandconcretesofveryhighstrengthincombination.Thistypeofconstructionisknownasprestressedconcrete.Thesteel,intheformofwires,strands,orbars,isembeddedintheconcreteunderhightensionthatisheldinequilibriumbycompressivestressesintheconcreteafterhard-ening.Becauseofthisprecompression,theconcreteinaflexuralmemberwillcrackonthetensionsideatamuchlargerloadthanwhennotsoprecompressed.Prestressinggreatlyreducesboththedeflectionsandthetensilecracksatordinaryloadsinsuchstructures,andtherebyenablesthesehigh-strengthmaterialstobeusedeffectively.預(yù)應(yīng)力混凝土prestressed預(yù)應(yīng)力的wire網(wǎng)strand串bar棒equilibrium平衡precompression預(yù)壓力1.1Concrete,ReinforcedConcrete,andPrestressedConcreteAspecialwayhasbeenfound,however,tousesteelsandconcretesofveryhighstrengthincombination.Thistypeofconstructionisknownasprestressedconcrete.Thesteel,intheformofwires,strands,orbars,isembeddedintheconcreteunderhightensionthatisheldinequilibriumbycompressivestressesintheconcreteafterhard-ening.Becauseofthisprecompression,theconcreteinaflexuralmemberwillcrackonthetensionsideatamuchlargerloadthanwhennotsoprecompressed.Prestressinggreatlyreducesboththedeflectionsandthetensilecracksatordinaryloadsinsuchstructures,andtherebyenablesthesehigh-strengthmaterialstobeusedeffectively.然而，已經(jīng)發(fā)現(xiàn)了一種特殊的方法來將鋼筋與高強(qiáng)度混凝土組合起來，這種形式的結(jié)構(gòu)就是預(yù)應(yīng)力混凝土。鋼筋的形式通常是鋼線或鋼絞線，有時是鋼筋，在超張拉后埋入混凝土中，通過硬化后的混凝土的受壓應(yīng)力保持平衡。由于預(yù)先受壓，受彎構(gòu)件的混凝土在受拉部位的開裂荷載比未受預(yù)壓的得以提高。預(yù)應(yīng)力大大減小了這些結(jié)構(gòu)在普通荷載下的變形和受拉開裂，使這些高強(qiáng)材料得以有效使用。1.2StructuralFormsFloorsupportsystemsforbuildingsincludethemonolithicslab-and-beamfloorshowninFig.1-1,theone-wayjoistsystemofFig.1-2,andtheflatplatefloor,withoutbeamsorgirders,showninFig.1-3.TheflatslabfloorofFig.1-4,frequentlyusedformoreheavilyloadedbuildingssuchaswarehouses,issimilartotheflatplatefloor,butmakesuseofincreasedslabthicknessinthevicinityofthecolumns,aswellasflaredcolumntops,toreducestressesandincreasestrengthinthesupportregion.Thechoiceamongtheseandothersystemsforfloorsandroofsdependsuponfunc-tionalrequirements,loads,spans,andpermissiblememberdepths,aswellasoncostandestheticfactors.樓層支撐體系monolithic整體的warehouse倉庫vicinity臨近flared向外展開的esthetic審美的1.2StructuralFormsFig.1-3Flatplatefloorslab,carrieddirectlybycolumnswithoutbeamsorgirders.(PortlandCementAssociation.)Fig.1-1One-wayreinforcedconcretefloorslabwithmonolithicsupportingbeams.(PortlandCementAssociation.)Fig.1-2One-wayjoistfloorsystem,withcloselyspacedribssupportedbymonolithicconcretebeams;transverseribsprovideforlateraldistributionoflocalizedloads.(PortlandCementAssociation.)Fig.1-4Flatslabfloor,withoutbeamsbutwithslabthicknessincreasedatthecolumnsandwithflaredcolumntopstoprovideforlocalstressconcentrationofforces.1.2StructuralFormsFloorsupportsystemsforbuildingsincludethemonolithicslab-and-beamfloorshowninFig.1-1,theone-wayjoistsystemofFig.1-2,andtheflatplatefloor,withoutbeamsorgirders,showninFig.1-3.TheflatslabfloorofFig.1-4,frequentlyusedformoreheavilyloadedbuildingssuchaswarehouses,issimilartotheflatplatefloor,butmakesuseofincreasedslabthicknessinthevicinityofthecolumns,aswellasflaredcolumntops,toreducestressesandincreasestrengthinthesupportregion.Thechoiceamongtheseandothersystemsforfloorsandroofsdependsuponfunc-tionalrequirements,loads,spans,andpermissiblememberdepths,aswellasoncostandestheticfactors.建筑樓蓋支撐體系包括如圖1-1所示的整體板梁樓蓋，圖1-2所示的單向托梁體系，圖1-3的無梁樓蓋。圖1-4所示的平板樓蓋經(jīng)常在荷載較大的建筑中使用，如倉庫。它與無梁樓蓋相似，但增大了柱邊緣樓板的厚度以及柱端部的承載面積，從而減小了應(yīng)力，增大了支撐區(qū)域的強(qiáng)度。支撐體系的選擇取決于功能要求，以及荷載，跨度，構(gòu)件尺寸，成本和審美等因素。1.2StructuralFormsWherelongclearspansarerequiredforroofs,concreteshellspermituseofextremelythinsurfaces,oftenthinner,relatively,thananeggshell.ThefoldedplateroofofFig.1-5issimpletoformbecauseitiscomposedofflatsurfaces;suchroofshavebeenemployedforspansof200ftandmore.ThecylindricalshellofFig.1-6isalsorelativelyeasytoformbecauseithasonlyasinglecurvature;itissimilartothefoldedplateinitsstructuralbehaviorandrangeofspansandloads.ShellsofthistypewereoncequitepopularintheUnitedStateandremainpopularinotherpartsoftheworld.混凝土殼roof屋頂shell殼cylindrical圓柱形的curvature曲率；彎曲1.2StructuralFormsFig.1-5Foldedplateroofof125ftspan,inadditiontocarryingordinaryroofloads,carriesthesecondflooraswellfromasystemofcablehangers;thegroundflooriskeptfreeofcolumns.Fig.1-6Cylindricalshellroofprovidingcolumn-freeinteriorspace.1.2StructuralFormsWherelongclearspansarerequiredforroofs,concreteshellspermituseofextremelythinsurfaces,oftenthinner,relatively,thananeggshell.ThefoldedplateroofofFig.1-5issimpletoformbecauseitiscomposedofflatsurfaces;suchroofshavebeenemployedforspansof200ftandmore.ThecylindricalshellofFig.1-6isalsorelativelyeasytoformbecauseithasonlyasinglecurvature;itissimilartothefoldedplateinitsstructuralbehaviorandrangeofspansandloads.ShellsofthistypewereoncequitepopularintheUnitedStateandremainpopularinotherpartsoftheworld.當(dāng)屋頂凈跨度較大時，利用混凝土殼可以采用厚度極薄的材料。圖1-5所示的折板屋頂比較容易建造，因為它是由平面構(gòu)成；這樣的屋頂已經(jīng)被用在跨度200英尺或更大的結(jié)構(gòu)上了。圖1-6所示的圓柱形殼也比較容易建造，因為它只有一個曲率；它的結(jié)構(gòu)性能以及可接受的跨度和荷載均類似于折板屋頂。這種類型的殼曾一度在美國非常流行，現(xiàn)在在世界其他地區(qū)也依舊流行。1.2StructuralFormsCylindricalconcretetanksarewidelyusedforstorageofwaterorinwastepurifi-cationplants.ThedesignshowninFig.1.11isproofthatasanitaryengineeringfacilitycanbeestheticallypleasingaswellasfunctional.Cylindricaltanksareoftenpre-stressedcircumferentiallytomaintaincompressionintheconcreteandeliminatethecrackingthatwouldotherwiseresultfrominternalpressure.圓柱形混凝土水箱storage儲存purifi-cation凈化sanitary衛(wèi)生的esthetically審美地circumferentially圓周地internal內(nèi)部的1.2StructuralFormsFig.1-11CircularconcretetanksusedasapartofthewastewaterpurificationfacilityatHowden,England.(NorthumbrianWaterAuthoritywithLuderandJones,Architects.)1.2StructuralFormsCylindricalconcretetanksarewidelyusedforstorageofwaterorinwastepurifi-cationplants.ThedesignshowninFig.1-11isproofthatasanitaryengineeringfacilitycanbeestheticallypleasingaswellasfunctional.Cylindricaltanksareoftenpre-stressedcircumferentiallytomaintaincompressionintheconcreteandeliminatethecrackingthatwouldotherwiseresultfrominternalpressure.圓柱形混凝土水箱廣泛應(yīng)用在儲存水以及污水處理站方面。圖1-11所示的設(shè)計展示了一個衛(wèi)生工程設(shè)施既可以在審美上滿足要求，也可以在功能上滿足。圓柱體水箱通常是圓周地設(shè)置預(yù)應(yīng)力，以使得混凝土一直保持為壓力，防止內(nèi)力產(chǎn)生裂縫。1.3LoadsDeadloadsarethosethatareconstantinmagnitudeandfixedinlocationthroughoutthelifetimeofthestructure.Usuallythemajorpartofthedeadloadistheweightofthestructureitself.Thiscanbecalculatedwithgoodaccuracyfromthedesigncon-figuration,dimensionsofthestructure,anddensityofthematerial.Forbuildings,floorfill,finishfloors,andplasteredceilingsareusuallyincludedasdeadloads,andanallowanceismadeforsuspendedloadssuchaspipingandlightingfixtures.Forbridges,deadloadsmayincludewearingsurfaces,sidewalks,andcurbs,andanallowanceismadeforpipingandothersuspendedloads.恒載deadloads恒載magnitude幅值plasteredceiling灰泥吊頂piping管道系統(tǒng)suspendedload懸掛荷載sidewalk人行道curb路邊1.3LoadsDeadloadsarethosethatareconstantinmagnitudeandfixedinlocationthroughoutthelifetimeofthestructure.Usuallythemajorpartofthedeadloadistheweightofthestructureitself.Thiscanbecalculatedwithgoodaccuracyfromthedesigncon-figuration,dimensionsofthestructure,anddensityofthematerial.Forbuildings,floorfill,finishfloors,andplasteredceilingsareusuallyincludedasdeadloads,andanallowanceismadeforsuspendedloadssuchaspipingandlightingfixtures.Forbridges,deadloadsmayincludewearingsurfaces,sidewalks,andcurbs,andanallowanceismadeforpipingandothersuspendedloads.恒載是指那些在結(jié)構(gòu)生命周期中大小和位置均不變的荷載。恒載通常主要為結(jié)構(gòu)自重。這通常能通過結(jié)構(gòu)的設(shè)計布置，結(jié)構(gòu)尺寸，材料密度來較精確地計算得到。對于建筑來說，恒載通常還包括樓板填塞層，地板裝修以及吊頂，還應(yīng)對管道系統(tǒng)以及照明裝置等懸掛荷載留余。對于橋梁，恒載包括磨損面，人行道以及臨邊小路，同樣也應(yīng)對管道系統(tǒng)等懸掛荷載進(jìn)行留余。1.3LoadsLiveloadsconsistchieflyofoccupancyloadsinbuildingsandtrafficloadsonbridges.Theymaybeeitherfullyorpartiallyinplaceornotpresentatall,andmayalsochangeinlocation.Theirmagnitudeanddistributionatanygiventimeareuncer-tain,andeventheirmaximumintensitiesthroughoutthelifetimeofthestructurearenotknownwithprecision.Theminimumliveloadsforwhichthefloorsandroofofabuildingshouldbedesignedareusuallyspecifiedinthebuildingcodethatgovernsatthesiteofconstruction.活載occupancy使用distribution分布1.3LoadsLiveloadsconsistchieflyofoccupancyloadsinbuildingsandtrafficloadsonbridges.Theymaybeeitherfullyorpartiallyinplaceornotpresentatall,andmayalsochangeinlocation.Theirmagnitudeanddistributionatanygiventimeareuncer-tain,andeventheirmaximumintensitiesthroughoutthelifetimeofthestructurearenotknownwithprecision.Theminimumliveloadsforwhichthefloorsandroofofabuildingshouldbedesignedareusuallyspecifiedinthebuildingcodethatgovernsatthesiteofconstruction.活載主要由建筑使用荷載以及橋梁交通荷載組成。它們可能整體或局部分布，也可能完全沒有，也可能改變作用位置。對于給定的時間，它們的大小以及分布是不確定的，甚至結(jié)構(gòu)的整個壽命周期中活載的最大值也是無法準(zhǔn)確知道的。建筑樓板以及屋頂?shù)淖钚≡O(shè)計活載可在相關(guān)場地建筑設(shè)計規(guī)范中查得。1.3LoadsEnvironmentalloadsconsistmainlyofsnowloads,windpressureandsuction,earthquakeloads(i.e.,inertiaforcescausedbyearthquakemotions),soilpressuresonsubsurfaceportionsofstructures,loadsfrompossiblepondingofrainwateronflatsur-faces,andforcescausedbytemperaturedifferentials.Likeliveloads,environmentalloadsatanygiventimeareuncertaininbothmagnitudeanddistribution.Thebook,MinimumDesignLoadsforBuildingsandOtherStructures,containsmuchinformationonenvironmentalloads,whichisoftenmodifiedlocallydepending,forinstance,onlocalclimaticorseismicconditions.環(huán)境荷載suction吸力subsurface表面下的ponding積水differential差別1.3LoadsEnvironmentalloadsconsistmainlyofsnowloads,windpressureandsuction,earthquakeloads(i.e.,inertiaforcescausedbyearthquakemotions),soilpressuresonsubsurfaceportionsofstructures,loadsfrompossiblepondingofrainwateronflatsur-faces,andforcescausedbytemperaturedifferentials.Likeliveloads,environmentalloadsatanygiventimeareuncertaininbothmagnitudeanddistribution.Thebook,MinimumDesignLoadsforBuildingsandOtherStructures,containsmuchinformationonenvironmentalloads,whichisoftenmodifiedlocallydepending,forinstance,onlocalclimaticorseismicconditions.環(huán)境荷載主要由雪荷載，風(fēng)壓力與風(fēng)吸力，地震荷載（即地震運(yùn)動引起的慣性力），土對結(jié)構(gòu)地面以下部分的壓力，平板的積水荷載，溫度差異引起的荷載組成。與活載類似，環(huán)境荷載在給定的時間上也無法準(zhǔn)確得知其大小與分布。建筑及其他結(jié)構(gòu)最小設(shè)計荷載這本書包含了許多環(huán)境荷載的信息，這些信息通常根據(jù)當(dāng)?shù)匦畔?，如?dāng)?shù)貧鉁匾约暗卣鹎闆r等進(jìn)行了修正。1.4Serviceability,Strength,andStructuralSafetyToserveitspurpose,astructuremustbesafeagainstcollapseandserviceableinuse.Serviceabilityrequiresthatdeflectionsbeadequatelysmall;thatcracks,ifany,bekepttotolerablelimits;thatvibrationsbeminimized;etc.Safetyrequiresthatthestrengthofthestructurebeadequateforallloadsthatmayforeseeablyactonit.Ifthestrengthofastructure,builtasdesigned,couldbepredictedaccurately,andiftheloadsandtheirinternaleffects(moments,shears,axialforces)wereknownaccurately,safetycouldbeensuredbyprovidingacarryingcapacityjustbarelyinexcessoftheknownloads.However,thereareanumberofsourcesofuncertaintyintheanalysis,design,andconstructionofreinforcedconcretestructures.結(jié)構(gòu)的可用性，強(qiáng)度以及結(jié)構(gòu)安全性collapse倒塌serviceability可用性foreseeably可預(yù)知地1.4Serviceability,Strength,andStructuralSafetyToserveitspurpose,astructuremustbesafeagainstcollapseandserviceableinuse.Serviceabilityrequiresthatdeflectionsbeadequatelysmall;thatcracks,ifany,bekepttotolerablelimits;thatvibrationsbeminimized;etc.Safetyrequiresthatthestrengthofthestructurebeadequateforallloadsthatmayforeseeablyactonit.Ifthestrengthofastructure,builtasdesigned,couldbepredictedaccurately,andiftheloadsandtheirinternaleffects(moments,shears,axialforces)wereknownaccurately,safetycouldbeensuredbyprovidingacarryingcapacityjustbarelyinexcessoftheknownloads.However,thereareanumberofsourcesofuncertaintyintheanalysis,design,andconstructionofreinforcedconcretestructures.為了達(dá)到這個目的，結(jié)構(gòu)必須足夠安全以抵抗倒塌，并在使用時可供使用?？捎眯砸笞冃巫銐蛐?；任何裂縫都要控制在可接受的范圍內(nèi)；振動要盡量減小等等。安全性要求結(jié)構(gòu)的強(qiáng)度要足以抵抗可預(yù)見的所有荷載。如果荷載以及他們的內(nèi)力（彎矩，剪力，軸力）已經(jīng)準(zhǔn)確知道的話，可以僅提供比已知荷載稍大的承載力來保證安全性。然而，在分析，設(shè)計以及建造混凝土結(jié)構(gòu)時均有一系列不確定性問題。1.4.1VariabilityofLoadsSincethemaximumloadthatwilloccurduringthelifeofastructureisuncertain,itcanbeconsideredarandomvariable.Inspiteofthisuncertainty,theengineermustprovideanadequatestructure.Aprobabilitymodelforthemaximumloadcanbedevisedbymeansofaprobabilitydensityfunctionforloads,asrepresentedbythefre-quencycurveofFig.1.14a.Theexactformofthisdistributioncurve,foranyparticulartypeofloadingsuchasofficeloads，canbedeterminedonlyonthebasisofstatisticaldataobtainedfromlarge-scaleloadsurveys.Anumberofsuchsurveyshavebeencom-pleted.Fortypesofloadsforwhichsuchdataarescarce,fairlyreliableinformationcanbeobtainedfromexperience,observation,andjudgment.荷載概率模型randomvariable隨機(jī)變量distributioncurve分布曲線scarce缺乏的1.4.1VariabilityofLoadsSincethemaximumloadthatwilloccurduringthelifeofastructureisuncertain,itcanbeconsideredarandomvariable.Inspiteofthisuncertainty,theengineermustprovideanadequatestructure.Aprobabilitymodelforthemaximumloadcanbedevisedbymeansofaprobabilitydensityfunctionforloads,asrepresentedbythefre-quencycurveofFig.1.14a.Theexactformofthisdistributioncurve,foranyparticulartypeofloadingsuchasofficeloads，canbedeterminedonlyonthebasisofstatisticaldataobtainedfromlarge-scaleloadsurveys.Anumberofsuchsurveyshavebeencom-pleted.Fortypesofloadsforwhichsuchdataarescarce,fairlyreliableinformationcanbeobtainedfromexperience,observation,andjudgment.因為結(jié)構(gòu)生命周期里可能出現(xiàn)的最大荷載不確定，因此它可以被考慮為一個隨機(jī)變量。盡管存在這一不確定性，工程師應(yīng)該提供足夠的結(jié)構(gòu)強(qiáng)度。最大荷載的概率模型可以通過荷載的概率密度方程的形式來獲得，如圖1.14a所示的頻率曲線。對于任意一種荷載，如辦公室荷載，其分布曲線的確切形式應(yīng)以大規(guī)模荷載調(diào)查得到的統(tǒng)計數(shù)據(jù)為基礎(chǔ)進(jìn)行確定。大量的調(diào)查已經(jīng)完成。對于數(shù)據(jù)比較稀缺的荷載類型，可以根據(jù)經(jīng)驗，觀察以及判斷來得到較為可信的信息。1.4.2StrengthThestrengthofastructuredependsonthestrengthofthematerialsfromwhichitismade.Forthispurpose,minimummaterialstrengthsarespecifiedinstandardizedways.Actualmaterialstrengthscannotbeknownpreciselyandthereforealsoconsti-tuterandomvariables.Structuralstrengthdepends,furthermore,onthecarewithwhichastructureisbuilt,whichinturnreflectsthequalityofsupervi-sionandinspection.Membersizesmaydifferfromspecifieddimensions,reinforce-mentmaybeoutofposition,poorlyplacedconcretemay