土木工程英語(yǔ)論文

StructureofBulidingsAbuildingiscloselyboundupwithpeople,foritprovidespeoplewiththenecessaryspacetoworkandlivein.Asclassifiedbytheiruse,buildingsaremainlyoftwotypes:industrialbuildingsandcivilbuildings.Industrialbuildingsareusedbyvariousfactoriesorindustrialproductionwhilecivilbuildingsarethosethatareusedbypeoplefordwelling,employment,educationandothersocialactivities.Theconstructionofindustrialbuildingsisthesameasthatofcivilbuildings.However,industrialandcivilbuildingsdifferinthematerialused,andinthestructureformsorsystemstheyareused.Consideringonlytheengineeringessentials,thestructureofabuildingcanbedifinedastheassemblageofthosepartswhichexistforthepurposeofmaintainingshapeandstability.Isprimypurposeistoresistanyloadsappliedtothebuildingandtotransmitthosetotheground.Intermsofarchitecture,thestructueofabuildingisanddosemuchmorethanthat.Itisaninseparablepartofthebuildingformtovaryingdegreesisageneratorofthatform.Usedskillfully,thebuildingstructurecanestablishorreinforceordersandrhythmsamongthearchitecturevolumesandplanes.Itcanbevisuallydominantorrecessive.Itcandevelopharmoniesorconflicts.Itcanbebothconfiningandemincipating.And,unfortunatelyinsomecases,itcannotbeingored.Itisphysical.Thestructuremustalsobeengineeredtomaintainthearchitectureform.Theprinciplesandtoolsofphysicsteandmathematicsprovidethebasisfordifferentiatingbetweenrationalandinrationalformsintermsofconstruction.Artistscansometimesgenerateshapesthatobviateanyconsiderationofscience,butarchitectscannot.Thereareatleastthreeitemsthatmustbepresentinthestructureofabuilding:stabily,strengthandstiffness,economy.Takingthefirstofthethreerequiements,itisobviousthatstabilityisneededtomaintainshape.Anunstablebuildingstructureimpliesunbalancedforcesoralackofequilibriumandaconsequentaccelerationofthestructureoritspieces.Therequirementofstrengthmeansthatthematerialsselectedtoresistthestressesgeneratedbytheloadsandshapesofthestructure(s)mustbeadequate.Indeed,a“factorofsafety”isusuallyprovidedsothatundertheanticipatedloads,agivenmaterialisnotstressedtoalevelevenclosetoitsrupturepoint.Thematerialpropertycalledstiffnessisconsideredwiththerequirementofstrength.Stiffnessisdifferentformstrengthinthatitdirectlyinvolveshowmuchastructurestrainsordeflectsunderload.Amaterialthatisverystrongbutlackinginstiffnesswilldeformtoomuchtobeofvalueinresistingtheforcesapplied.Economyofabuildingstructurereferstomorethanjustthecostofthematerialused.Constructioneconomyisacomplicatedsubjectinvovlingrawmaterials,fabrication,erection,andmaintenance.Designandconstructionlaborcostsandthecostsofenergyconsumptionmoney(interest)areconsumptionmustbeconsiedered.Speedofconstructionandthecostofmoney(interest)arealsofactors.Inmostdesignsituations,morethanonestructuralmaterialrequiresconsideration.Completivealternativesalmostalwaysexist,andthechoiceisseldomobvious.Apartformthesethreeprimaryrequirements,severalotherfactorsareworthyofemphasis.First,thestructureorsuctructuralsystemmustrelatetothebuilding’sfunction.Itshouldnotbeinconflictintermsofform.Forexample,alinearfunctiondemandsalinearstructure,andthereforeitwouldbeimpropertoroofabowlingalleywithadome.Similarly,atheatermusthavelarge,unobstructedspansbutafinerestaurantprobablyshouldnot.Statedsimply,thestructuremustbeappropriatetothefunctionitistoshelter.Second,thestructuremustbefire-resistant.Itisobviousthatthestructuralsystemmustbeabletomaintainitsintegrityatleastuntiltheoccupuantsaresafelyout.Buildingcodesspecifythenumberofhoursforwhichcertainpartsofabuildingmustresisttheheatwithoutcollapse.Thestructuralmaterialsusedforthoseelementsmustbeinherentlyfire-resistantorbeadequentlyprotectedbyfireproofingmaterials.Thedegreeoffireresistancetobeprovidedwilldependuponanumberofitems,includingtheuseandoccupancyloadofthespace,itsdimensions,andthelocationofthebuilding.Third,thestructureshouldintegratewellwiththebuilding’scirculationsystems.Itshouldnotbeinconflictwiththepipingsystemsforwaterandwaste,theductingsystemsforair,or(mostimportant)themovementofpeople.Itisobviousthatthevariousbuildingsystemsmustbecoordinatedasthedesignprogresses.Onecandesigninasequentialstep-by-stepmannerwithinanyonesystem,butthedesignofallofthemshouldmoveinaparallelmannertowardcompletion.Spatially,allthevariouspartsofabuildingareinterdependent.Fourth,thestructuremustbepsychologicallysafeaswellasphysicallysafe.Ahighriseframethatswaysconsiderablyinthewindmightnotactuallybedangerousbutmaymakethebuildinguninhabitablejustthesame.Ligheweightfloorsystemsthataretoo“bouncy”canmaketheusersveryuncomfortable.Largeglasswindows,uninterruptedbydividingmotions,canbuquitesafebutwillappearveryinsecuretotheoccupantstandingnexttoon40floorsabovethestreet.Sometimesthearchitectmustmakedeliberateattemptstoincreasetheapparentstrengthorsolidnessofthestructure.Thisapparentsafetymaybemoreimportantthanhonestlyexpressingthebuilding’sstructure,becausetheuntrainedviewercannotdistinguishbetweenrealandperceivedsafety.Thebuildingdesignerneedstounderstandthebehaviorofphysicalstructuresunderload.Anabilitytointuitor“feel”structuralbehaviorispossessedbythosehavingmuchexperienceinvolvingstructuralanalysis,bothqualitativeandquantitative.Theconsequentknowledgeofhowforces,stresses,anddeformationsbuildupindifferentmaterialsandshapesisvitaltodevelopmentofthis“sense”.Structuralanalysisistheprocessofdeterminingtheforcesanddeformationsinstructuresduetospecifiedloadssothatthestructurecanbedesignedrationally,andsothatthestateofsafetyofexistingstructurescanbechecked.Inthedesignofstructures,itisnecessarytostartwithaconceptleadingtoaconfigurationwhichcanthenbeanalyzed.Thisisdonetomemberscanbesizedandtheneededreinforcingdetermined,inorderto:a)carrythedesignloadswithoutdistressorexcessivedeformations(serviceabilityorworkingcondition);andb)topreventcollapsebeforeaspecifiedoverloadhasbeenplacedonthestructure(safetyorultimatecondition).Sincenormallyelasticconditionswillprevailunderworkingloads,astructuraltheorybasedontheassumptionsofelasticbehaviorisappropriatefordeterminingserviceabilityconditions.Collapseofastructurewillusuallyoccuronlylongaftertheelasticrangeofthematerialshasbeenexceededatcircalpoints,sothatanultimatestrengththeorybasedontheinelasticbehaviorofthematerialisnecessaryforarationaldeterminationofthesafetyofastructureagainstcollapse.Neverthelese,anelastictheorycanbeusedtodetermineasafeapproximationtothestrengthofductilestructures(thelowerboundapproachofplasticity),andthisapproachiscustomarilyfollowedinreinforcedconcretepractice.Forthisreasiononlytheelastictheoryofgtructureispursuedinthischapter.Lookedatcritically,allstructuresareassembliesofthree-dimensionalelements,theexactanalysisofwhichisaforbddingtaskevenunderidealconditionsandimpossibletocontemplateunderconditionsofprofessionalpractice.Forthisreason,animportantpartoftheanalyst’sworkisthesimplificationoftheactualstructureandloadingconditionstoamodelwhichissusceptibletorationalanalysis.Thus,astructuralframingsystemisdecomposedintoaslabandfloorbeamswhichinturnframeintogirderscarriedbycolumswhichtransmittheloadstothefoundations.Sincetraditionalstructuralanalysishasbeenunabletocopewiththeactionoftheslab,thishasoftenbeenidealizedintoasystemofstripsactingasbeams.Also,long-handmethodshavebeenunabletocopewiththree-dimensionalframingsystems,sothattheentirestructurehasbeenmodeledbyasystemofplannersubassemblies,tobeanalyzedoneatatime.Themodernmatrix-computermethodshaverevolutionizedstructuralanalysisbymakingitpossibletoanalyzeentriesystems,thusleadingtomorereliablepredictionsaboutthebehaviorofstructuresunderloads.Actualloadingconditionsarealsobothdifficulttodetermineandtoexpressrealistically,andmustbesimplifiedforpurposesofanalysis.Thus,trafficloadsonabridgestructure,whichareessentiallybothofdynamicandrandomnature,areusuallyidealizedintostaticallymovingstandardtrucks,ordistributedloads,intendedtosimulatethemostsevereloadingconditionsoccurringinpractice.Similary,continuousbeamsaresometimesreducedtosimplebeams,rigidjointstopin-joints,fillers-wallsareneglected,shearwallsconsideredasbeams;indecidinghowtomodelastructuresoastomakeitreasonablyrealisticbutatthesametimereasonablysimple,theanalystmustrememberthateachsuchidealizationwillmakethesoulationmoresuspect.Themorerealistictheanalysis,thegreaterwillbetheconfidencewhichitinspires,andthesmallermaybethesafetyfactor(orfactorofignorance).Thus,unlesscodeprovisionscontrol,theengineermustevaluatetheextraexpenseofathoroughanalysisascomparedtopossiblesavingsinthestructure.Themostimportantuseofstructureanalysisisasatoolinstructuraldesign.Assuch,itwillusuallybeapartofatrial-and-errorprocedure,inwhichanassumedconfigurationwithassumeddeadloadsisanalyzed,andthemembersdesignedinaccordancewiththeresultsoftheanalysis.Thisphaseiscalledthepreliminarydesign;sincethisdesignisstillsubjecttochange,usuallyacrude,fastanalysismethodisadequate.Atthisstage,thecostofthestructureisestimated,loadsandmemberpropertiesarerevised,andthedesignischeckedforpossibleimprovements.Thechangesarenowincorporatedinthestructure,amorerefinedanalysisisperformed,andthememberdesignisrevised.Thisprojectiscarriedtoconvergence,therapidityofwhichwilldependonthecapabilityofthedesigner.Itisclearthatavarietyofanalysismethods,rangingfrom“quickanddirtytoexact”,isneededfordesignpurposes.Anefficientanalystmustthusbeincommandoftherigorousmethodsofanalysis,mustbeabletoreducethesetoshortcutmethodsbyappropriateassumptions,andmustbeawareofavailabledesignandanalysisaids,aswellassimplificationpermittedbyapplicablebuildingcodes.Anup-to-dateanalystmustlikewisebeversedinthebasesofmatrixstructuralanalysisanditsuseindigitalcomputersaswellasintheuseofavailableanalysisprogramsorsoftware.建筑結(jié)構(gòu)建筑物與人類有著親密的關(guān)系，它能為人們?cè)谄渲泄ぷ骱蜕罟?yīng)必要的空間。依據(jù)其功能不同，建筑物主要有兩大類：工業(yè)建筑和民用建筑。工業(yè)建筑有各種工廠或制造廠，而民用建筑指的是那些人們用以居住、工作、教化或其他社會(huì)活動(dòng)的場(chǎng)所。工業(yè)建筑的建立與民用建筑相同，但兩者在選用的材料、結(jié)構(gòu)形式或體系方面是有差別的。就工程的實(shí)質(zhì)而言，建筑結(jié)構(gòu)可定義為：以保持形態(tài)和穩(wěn)定為目的的各個(gè)基本構(gòu)件的組合體。其基本目的是反抗作用在建筑物上的各種荷載并把它傳到地基上。從建筑學(xué)的角度來(lái)講，建筑結(jié)構(gòu)并非僅僅如此。它與建筑風(fēng)格是不行分割的，在不同程度上是一種建筑風(fēng)格的體現(xiàn)。如能奇妙地設(shè)計(jì)建筑結(jié)構(gòu)，則可建立或加強(qiáng)建筑空間與建筑平面之間的格調(diào)與節(jié)奏。它在直觀上可以是顯性的或是隱性的。它能產(chǎn)生和諧體或比照體。它可能既局限又開(kāi)放。不幸的是，在一些狀況下，它不能被忽視。它是實(shí)際存在的。結(jié)構(gòu)設(shè)計(jì)還必需與建筑風(fēng)格相吻合。物理學(xué)和數(shù)學(xué)的原理及工具為區(qū)分在結(jié)構(gòu)上的合理和不合理的形式供應(yīng)了依據(jù)。藝術(shù)家有時(shí)可以不必考慮科學(xué)就能畫(huà)出圖形，但建筑師卻不行。在建筑結(jié)構(gòu)中至少應(yīng)包括三項(xiàng)內(nèi)容：穩(wěn)定性、強(qiáng)度和剛度，經(jīng)濟(jì)性。在上述三種要求中，首先是穩(wěn)定性。它在保持建筑物形態(tài)上是必不行少的。一座不穩(wěn)定的建筑結(jié)構(gòu)意味著有不平衡的力或失去平衡狀態(tài)，并由此導(dǎo)致結(jié)構(gòu)整體或構(gòu)件產(chǎn)生加速度。強(qiáng)度的要求意味著所選擇的結(jié)構(gòu)材料足以承受由荷載產(chǎn)生的應(yīng)力并且結(jié)構(gòu)形態(tài)必需適當(dāng)。事實(shí)上，通常都供應(yīng)一個(gè)平安系數(shù)以便在預(yù)料的荷載作用下，所運(yùn)用材料的應(yīng)力不會(huì)接近破壞應(yīng)力。被稱為剛度的材料的特性，需與強(qiáng)度要求一起考慮。剛度不同于強(qiáng)度，因?yàn)樗婕昂奢d作用下結(jié)構(gòu)應(yīng)變的大小和變形的程度。具有很高強(qiáng)度，但剛度較低的材料，在外力作用下會(huì)因變形過(guò)大而失去其運(yùn)用價(jià)值。建筑結(jié)構(gòu)的經(jīng)濟(jì)性指的不僅僅是所用材料的費(fèi)用。建筑經(jīng)濟(jì)是一個(gè)困難的問(wèn)題，其中包括原材料、制作、安裝和修理。必需考慮設(shè)計(jì)和施工中人工費(fèi)及能源消耗的費(fèi)用。施工的速度和資金成本（利息）也是須要考慮的因素。對(duì)大多數(shù)設(shè)計(jì)狀況，不能僅僅考慮一種建筑材料，常常存在一些有競(jìng)爭(zhēng)性的其他選擇，而具體應(yīng)當(dāng)選擇哪種并不明顯。除了這三種最基本要求之外，其他幾種因素也值得重視。首先，結(jié)構(gòu)或結(jié)構(gòu)體系必需和建筑物的功能相吻合而不應(yīng)當(dāng)與建筑形式相沖突。例如，線性功能要求線性結(jié)構(gòu)，所以把保齡球場(chǎng)的頂部蓋成圓形是不合適的。同樣劇院必需是大跨度、中間沒(méi)有障礙的結(jié)構(gòu)，而高檔飯店或許不是這樣。簡(jiǎn)而言之，結(jié)構(gòu)形式必需與所圍護(hù)空間的功能相適應(yīng)。其次，結(jié)構(gòu)必需防火。很明顯，至少始終到內(nèi)部人員平安撤離為止，結(jié)構(gòu)體系必需能保持完整。建筑規(guī)范具體規(guī)定了建筑物的某些構(gòu)件反抗熱量而不倒塌的時(shí)間。用于那些構(gòu)件的結(jié)構(gòu)材料自身必需具有防火性或者用耐火材料加以適當(dāng)愛(ài)護(hù)。所規(guī)定的防火等級(jí)將取決于一系列因素，它包括建筑空間的占有量和運(yùn)用狀況、建筑物的尺寸及建筑物的位置。第三，結(jié)構(gòu)應(yīng)與建筑物的循環(huán)系統(tǒng)很好的結(jié)合。它不應(yīng)與給排水管道、通風(fēng)系統(tǒng)或人的活動(dòng)空間相沖突（這是最重要的）。很明顯，各種建筑系統(tǒng)在設(shè)計(jì)時(shí)必需相互協(xié)調(diào)。對(duì)任何單個(gè)系統(tǒng)的設(shè)計(jì)，可以有依次的一步一步的進(jìn)行，而對(duì)全部系統(tǒng)的設(shè)計(jì)則采納并行方式來(lái)完成。從空間上來(lái)講，在一座建筑物的全部構(gòu)件之間都是相互依存的。第四，結(jié)構(gòu)在心理上及外觀上必需給人一種平安感。在風(fēng)荷載作用下晃動(dòng)猛烈的高層框架雖然沒(méi)有危害，但仍舊不相宜居住。彈性太大的輕質(zhì)樓蓋系統(tǒng)可能給居住者很不舒適的感覺(jué)。沒(méi)有窗欞的巨大玻璃窗戶盡管是相當(dāng)平安的，但對(duì)居住在樓房里的人來(lái)說(shuō)，特殊是當(dāng)他站在臨街40層高樓的大玻璃窗前時(shí)，總會(huì)感極很擔(dān)心全。有事建筑師必需有意實(shí)行主動(dòng)措施來(lái)增加建筑結(jié)構(gòu)外表的強(qiáng)度和堅(jiān)實(shí)性。外觀的平安性或許比真實(shí)表達(dá)建筑結(jié)構(gòu)更重要，因?yàn)闆](méi)有受過(guò)訓(xùn)練的人是不能分清真實(shí)的和感覺(jué)中的平安性的。建筑設(shè)計(jì)師須要理解荷載作用下實(shí)際結(jié)構(gòu)的性能。在結(jié)構(gòu)定性和定量