土木工程英語論文

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.建筑結構建筑物與人類有著親密的關系，它能為人們在其中工作和生活供應必要的空間。依據其功能不同，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、教化或其他社會活動的場所。工業(yè)建筑的建立與民用建筑相同，但兩者在選用的材料、結構形式或體系方面是有差別的。就工程的實質而言，建筑結構可定義為：以保持形態(tài)和穩(wěn)定為目的的各個基本構件的組合體。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。從建筑學的角度來講，建筑結構并非僅僅如此。它與建筑風格是不行分割的，在不同程度上是一種建筑風格的體現(xiàn)。如能奇妙地設計建筑結構，則可建立或加強建筑空間與建筑平面之間的格調與節(jié)奏。它在直觀上可以是顯性的或是隱性的。它能產生和諧體或比照體。它可能既局限又開放。不幸的是，在一些狀況下，它不能被忽視。它是實際存在的。結構設計還必需與建筑風格相吻合。物理學和數學的原理及工具為區(qū)分在結構上的合理和不合理的形式供應了依據。藝術家有時可以不必考慮科學就能畫出圖形，但建筑師卻不行。在建筑結構中至少應包括三項內容：穩(wěn)定性、強度和剛度，經濟性。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)定的建筑結構意味著有不平衡的力或失去平衡狀態(tài)，并由此導致結構整體或構件產生加速度。強度的要求意味著所選擇的結構材料足以承受由荷載產生的應力并且結構形態(tài)必需適當。事實上，通常都供應一個平安系數以便在預料的荷載作用下，所運用材料的應力不會接近破壞應力。被稱為剛度的材料的特性，需與強度要求一起考慮。剛度不同于強度，因為它涉及荷載作用下結構應變的大小和變形的程度。具有很高強度，但剛度較低的材料，在外力作用下會因變形過大而失去其運用價值。建筑結構的經濟性指的不僅僅是所用材料的費用。建筑經濟是一個困難的問題，其中包括原材料、制作、安裝和修理。必需考慮設計和施工中人工費及能源消耗的費用。施工的速度和資金成本（利息）也是須要考慮的因素。對大多數設計狀況，不能僅僅考慮一種建筑材料，常常存在一些有競爭性的其他選擇，而具體應當選擇哪種并不明顯。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，結構或結構體系必需和建筑物的功能相吻合而不應當與建筑形式相沖突。例如，線性功能要求線性結構，所以把保齡球場的頂部蓋成圓形是不合適的。同樣劇院必需是大跨度、中間沒有障礙的結構，而高檔飯店或許不是這樣。簡而言之，結構形式必需與所圍護空間的功能相適應。其次，結構必需防火。很明顯，至少始終到內部人員平安撤離為止，結構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件反抗熱量而不倒塌的時間。用于那些構件的結構材料自身必需具有防火性或者用耐火材料加以適當愛護。所規(guī)定的防火等級將取決于一系列因素，它包括建筑空間的占有量和運用狀況、建筑物的尺寸及建筑物的位置。第三，結構應與建筑物的循環(huán)系統(tǒng)很好的結合。它不應與給排水管道、通風系統(tǒng)或人的活動空間相沖突（這是最重要的）。很明顯，各種建筑系統(tǒng)在設計時必需相互協(xié)調。對任何單個系統(tǒng)的設計，可以有依次的一步一步的進行，而對全部系統(tǒng)的設計則采納并行方式來完成。從空間上來講，在一座建筑物的全部構件之間都是相互依存的。第四，結構在心理上及外觀上必需給人一種平安感。在風荷載作用下晃動猛烈的高層框架雖然沒有危害，但仍舊不相宜居住。彈性太大的輕質樓蓋系統(tǒng)可能給居住者很不舒適的感覺。沒有窗欞的巨大玻璃窗戶盡管是相當平安的，但對居住在樓房里的人來說，特殊是當他站在臨街40層高樓的大玻璃窗前時，總會感極很擔心全。有事建筑師必需有意實行主動措施來增加建筑結構外表的強度和堅實性。外觀的平安性或許比真實表達建筑結構更重要，因為沒有受過訓練的人是不能分清真實的和感覺中的平安性的。建筑設計師須要理解荷載作用下實際結構的性能。在結構定性和定量