土木工程英语论文.docx

土木工程英语论文.docx

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土木工程英语论文

StructureofBulidings

Abuildingiscloselyboundupwithpeople,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.

Themostimportantu