外文翻译建筑物的组成及高层结构.docx

外文翻译建筑物的组成及高层结构.docx

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外文翻译建筑物的组成及高层结构

ComponentsofABuildingandTallBuildings

Materialsandstructuralformsarecombinedtomakeupthevariouspartsofabuilding,includingtheload-carryingframe,skin,floors,andpartitions.Thebuildingalsohasmechanicalandelectricalsystems,suchaselevators,heatingandcoolingsystems,andlightingsystems.Thesuperstructureisthatpartofabuildingaboveground,andthesubstructureandfoundationisthatpartofabuildingbelowground.

Theskyscraperowesitsexistencetotwodevelopmentsofthe19thcentury:

steelskeletonconstructionandthepassengerelevator.SteelasaconstructionmaterialdatesfromtheintroductionoftheBessemerconverterin1885.GustaveEiffel（1832-1932）introducedsteelconstructioninFrance.HisdesignsfortheGaleriedesMachinesandtheTowerfortheParisExpositionof1889expressedthelightnessofthesteelframework.TheEiffelTower,984feet（300meters）high,wasthetalleststructurebuiltbymanandwasnotsurpasseduntil40yearslaterbyaseriesofAmericanskyscrapers.

ThefirstelevatorwasinstalledbyElishaOtisinstalledthefirstelevatorinadepartmentstoreinNewYorkin1857.In1889;EiffelinstalledthefirstelevatorsonagrandscaleintheEiffelTower,whosehydraulicelevatorscouldtransport2,350passengerstothesummiteveryhour.

Load-CarryingFrame.Untilthelate19thcentury,theexteriorwallsofabuildingwereusedasbearingwallstosupportthefloors.Thisconstructionisessentiallyapostandlinteltype,anditisstillusedinframeconstructionforhouses.Bearing-wallconstructionlimitedtheheightofbuildingsbecauseoftheenormouswallthicknessrequired；Forinstance,the16-storyMonadnockBuildingbuiltinthe1880’sinChicagohadwalls5feet（1.5meters）thickatthelowerfloors.In1883,WilliamLeBaronJenney（1832-1907）supportedfloorsoncast-ironcolumnstoformacage-likeconstruction.Skeletonconstruction,consistingofsteelbeamsandcolumns,wasfirstusedin1889.Asaconsequenceofskeletonconstruction,theenclosingwallsbecomea“curtainwall”ratherthanservingasupportingfunction.Masonrywasthecurtainwallmaterialuntilthe1930’s,whenlightmetalandglasscurtainwallswereused.Aftertheintroductionofbuildingscontinuedtoincreaserapidly.

AlltallbuildingswerebuiltwithaskeletonofsteeluntilWorldWarⅡ.Afterthewar,theshortageofsteelandtheimprovedqualityofconcreteledtotallbuildingbeingbuiltofreinforcedconcrete.MarinaTower（1962）inChicagoisthetallestconcretebuildingintheUnitedStates；Itsheight—588feet（179meters）—isexceededbythe650-foot（198-meter）PostOfficeTowerinLondonandbyothertowers.

Achangeinattitudeaboutskyscraperconstructionhasbroughtareturntotheuseofthebearingwall.InNewYorkCity,theColumbiaBroadcastingSystemBuilding,designedbyEeroSaarinenin1962,hasaperimeterwallconsistingof5-foot（1.5meter）wideconcretecolumnsspaced10feet（3meters）fromcolumncentertocenter.Thisperimeterwall,ineffect,constitutesabearingwall.Onereasonforthistrendisthatstiffnessagainsttheactionofwindcanbeeconomicallyobtainedbyusingthewallsofthebuildingasatube；theWorldTradeCenterbuildingisanotherexampleofthistubeapproach.Incontrast,rigidframesorverticaltrussesareusuallyprovidedtogivelateralstability.

Skin.Theskinofabuildingconsistsofbothtransparentelements（windows）andopaqueelements（walls）.Windowsaretraditionallyglass,althoughplasticsarebeingused,especiallyinschoolswherebreakagecreatesamaintenanceproblem.Thewallelements,whichareusedtocoverthestructureandaresupportedbyit,arebuiltofavarietyofmaterials:

brick,precastconcrete,stone,opaqueglass,plastics,steel,andaluminum.Woodisusedmainlyinhouseconstruction；Itisnotgenerallyusedforcommercial,industrial,orpublicbuildingbecauseofthefirehazard.

Floors.Theconstructionofthefloorsinabuildingdependsonthebasicstructuralframethatisused.Insteelskeletonconstruction,floorsareeitherslabsofconcreterestingonsteelbeamsoradeckconsistingofcorrugatedsteelwithaconcretetopping.Inconcreteconstruction,thefloorsareeitherslabsofconcreteonconcretebeamsoraseriesofcloselyspacedconcretebeams（ribs）intwodirectionstoppedwithathinconcreteslab,givingtheappearanceofawaffleonitsunderside.Thekindoffloorthatisuseddependsonthespanbetweensupportingcolumnsorwallsandthefunctionofthespace.Inanapartmentbuilding,forinstance,wherewallsandcolumnsarespacedat12to18feet（3.7to5.5meters）,themostpopularconstructionisasolidconcreteslabwithnobeams.Theundersideoftheslabservesastheceilingforthespacebelowit.Corrugatedsteeldecksareoftenusedinofficebuildingsbecausethecorrugations,whenenclosedbyanothersheetofmetal,formductsfortelephoneandelectricallines.

MechanicalandElectricalSystems.Amodernbuildingnotonlycontainsthespaceforwhichitisintended（office,classroom,apartment）butalsocontainsancillaryspaceformechanicalandelectricalsystemsthathelptoprovideacomfortableenvironment.Theseancillaryspacesinaskyscraperofficebuildingmayconstitute25%ofthetotalbuildingarea.Theimportanceofheating,ventilating,electrical,andplumbingsystemsinanofficebuildingisshownbythefactthat40%oftheconstructionbudgetisallocatedtothem.Becauseoftheincreaseduseofsealedbuildingwithwindowsthatcannotbeopened,elaboratemechanicalsystemsareprovidedforventilationandairconditioning.Ductsandpipescarryfreshairfromcentralfanroomsandairconditioningmachinery.Theceiling,whichissuspendedbelowtheupperfloorconstruction,concealstheductworkandcontainsthelightingunits.Electricalwiringforpowerandfortelephonecommunicationmayalsobelocatedinthisceilingspaceormaybeburiedinthefloorconstructioninpipesorconduits.

Therehavebeenattemptstoincorporatethemechanicalandelectricalsystemsintothearchitectureofbuildingbyfranklyexpressingthem；Forexample,theAmericanRepublicInsuranceCompanyBuilding（1965）inDesMoines,Iowa,exposesboththeductsandthefloorstructureinanorganizedandelegantpatternanddispenseswiththesuspendedceiling.Thistypeofapproachmakesitpossibletoreducethecostofthebuildingandpermitsinnovations,suchasinthespanofthestructure.

SoilsandFoundations.Allbuildingaresupportedontheground,andthereforethenatureofthesoilbecomesanextremelyimportantconsiderationinthedesignofanybuilding.Thedesignofafoundationdependsonmanysoilfactors,suchastypeofsoil,soilstratification,thicknessofsoillaversandtheircompaction,andgroundwaterconditions.Soilsrarelyhaveasinglecomposition；Theygenerallyaremixturesinlayersofvaryingthickness.Forevaluation,soilsaregradedaccordingtoparticlesize,whichincreasesfromsilttoclaytosandtograveltorock.Ingeneral,thelargerparticlesoilswillsupportheavierloadsthanthesmallerones.Thehardestrockcansupportloadsupto100tonspersquarefoot（976.5metrictons/sqmeter）,butthesoftestsiltcansupportaloadofonly0.25tonpersquarefoot（2.44metrictons/sqmeter）.Allsoilsbeneaththesurfaceareinastateofcompaction；thatis,theyareunderapressurethatisequaltotheweightofthesoilcolumnaboveit.Manysoils（exceptformostsandsandgavels）exhibitelasticproperties—theydeformwhencompressedunderloadandreboundwhentheloadisremoved.Theelasticityofsoilsisoftentime-dependent,thatis,deformationsofthesoiloccuroveralengthoftimewhichmayvaryfromminutestoyearsafteraloadisimposed.Overaperiodoftime,abuildingmaysettleifitimposesaloadonthesoilgreaterthanthenaturalcompactionweightofthesoil.Conversely,abuildingmayheaveifitimposesloadsonthesoilsmallerthanthenaturalcompactionweight.Thesoilmayalsoflowundertheweightofabuilding；Thatis,ittendstobesqueezedout.

Duetoboththecompactionandfloweffects,buildingstendsettle.Unevensettlements,exemplifiedbytheleaningtowersinPisaandBologna,canhavedamagingeffects—thebuildingmaylean,wallsandpartitionsmaycrack,windowsanddoorsmaybecomeinoperative,and,intheextreme,abuildingmaycollapse.Uniformsettlementsarenotsoserious,althoughextremeconditions,suchasthoseinMexicoCity,canhaveseriousconsequences.Overthepast100years,achangeinthegroundwaterleveltherehascausedsomebuildingstosettlemorethan10feet（3meters）.Becausesuchmovementscanoccurduringandafterconstruction,carefulanalysisofthebehaviorofsoilsunderabuildingisvital.

Thegreatvariabilityofsoilshasledtoavarietyofsolutionstothefoundationproblem.Wherefirmsoilexistsclosetothesurface,thesimplestsolutionistorestcolumnsonasmallslabofconcrete（spreadfooting）.Wherethesoilissofter,itisnecessarytospreadthecolumnloadoveragreaterarea；inthiscase,acontinuousslabofconcrete（raftormat）underthewholebuildingisused.Incaseswherethesoilnearthesurfaceisunabletosupporttheweightofthebuilding,pilesofwood,steel,orconcretearedrivendowntofirmsoil.

Theconstructionofabuildingproceedsnaturallyfromthefoundationuptothesuperstructure.Thedesignprocess,however,proceedsfromtheroofdowntothefoundation（inthedirectionofgravity）.Inthepast,thefoundationwasnotsubjecttosystematicinvestigation.Ascientificapproachtothedesignoffoundationshasbeendevelopedinthe20thcentury.KarlTerzaghiofth