ComponentsofABuildingandTallBuildingsMaterialsandstructuralformsarecombinedtomakeupthevariouspartsofabuilding,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.KarlTerzaghioftheUnitedStatespioneeredstudiesthatmadeitpossibletomakeaccuratepredictionsofthebehavioroffoundations,usingthescienceofsoilmechanicscoupledwithexplorationandtestingprocedures.Foundationfailuresofthepast,suchastheclassicalexampleoftheleaningtowerinPisa,havebecomealmostnonexistent.Foundationsstilhreahiddenbutcostlypartofmanybuildings.Althoughtherehavebeenmanyadvancementsinbuildingconstructiontechnologyingeneral,spectacularachievementshavebeenmadeinthedesignandconstructionofultrahigh-risebuildings.Theearlydevelopmentofhigh-risebuildingsbeganwithstructuralsteelframing.Reinforcedconcreteandstressed-skintubesystemshavesincebeeneconomicallyandcompetitivelyusedinanumberofstructuresforbothresidentialandcommercialpurposes.Thehigh-risebuildingsrangingfrom50to110storiesthatarebeingbuiltallovertheUnitedStatesaretheresultofinnovationsanddevelopmentofnewstructuralsystems.Greaterheightentailsincreasedcolumnandbeamsizestomakebuildingsmorerigidsothatunderwindloadtheywillnotswaybeyondanacceptablelimit.Excessivelateralswaymaycauseseriousrecurringdamagetopartitions,ceilings,andotherarchitecturaldetails.Inaddition,excessiveswaymaycausediscomforttotheoccupantsofthebuildingbecauseoftheirperceptionofsuchmotion.Structuralsystemsofreinforcedconcrete,aswellassteel,takefulladvantageoftheinherentpotentialstiffnessofthetotalbuildingandthereforedonotrequireadditionalstiffeningtolimitthesway.Inasteelstructure,forexample,theeconomycanbedefinedintermsofthetotalaveragequantityofsteelpersquarefootoffloorareaofthebuilding.Thegapbetweentheupperboundaryandthelowerboundaryrepresentsthepremiumforalllateralloads.Thegapbetweentheupperboundaryandthelowerboundaryrepresentsthepremiumforheightforthetraditionalcolumn-and-beamframe.Structuralengineershavedevelopedstructuralsystemswithaviewtoeliminatingthispremium.Systemsinsteel.Tallbuildingsinsteeldevelopedasaresultofseveraltypesofstructuralinnovations.Theinnovationshavebeenappliedtotheconstructionofbothofficeandapartmentbuildings.Frameswithrigidbelttrusses.Inordertotietheexteriorcolumnsofaframestructuretotheinteriorverticaltrusses,asystemofrigidbelttrussesatmid-heightandatthetopofthebuildingmaybeused.AgoodexampleofthissystemistheFirstWisconsinBankBuilding(1974)inMilwaukee.Framedtube.Themaximumefficiencyofthetotalstructureofatallbuilding,forbothstrengthandstiffness,toresistwindloadcanbeachievedonlyifallcolumnelementscanbeconnectedtoeachotherinsuchawaythattheentirebuildingactsasahollowtubeorrigidboxinprojectingoutoftheground.Thisparticularstructuralsystemwasprobablyusedforthefirsttimeinthe43-storyreinforcedconcreteDeWittChestnutApartmentBuildinginChicago.Themostsignificantuseofthissystemisinthetwinstructuralsteeltowersofthe110-storyWorldTradeCenterbuildinginNewYork.Column-diagonaltrusstube.Theexteriorcolumnsofabuildingcanbespacedreasonablyfarapartandyetbemadetoworktogetherasatubebyconnectingthemwithdiagonalmembersintersectingatthecenterlineofthecolumnsandbeams.ThissimpleyetextremelyefficientsystemwasusedforthefirsttimeontheJohnHancockCenterinChicago,usingasmuchsteelasisnormallyneededforatraditional40-storybuilding.Bundledtube.Withthecontinuingneedforlargerandtallerbuildings,theframedtubeorthecolumn-diagonaltrusstubemaybeusedinabundledformtocreatelargertubeenvelopeswhilemaintaininghighefficiency.The110-storySearsRoebuckHeadquartersBuildinginChicagohasninetubes,bundledatthebaseofthebuildinginthreerows.Someoftheseindividualtubesterminateatdifferentheightsofthebuilding,demonstratingtheunlimitedarchitecturalpossibilitiesofthislateststructuralconcept.TheSearstower,ataheightof1450ft(442m),istheworld'stallestbuilding.Stressed-skintubesystem.Thetubestructuralsystemwasdevelopedforimprovingtheresistancetolateralforces(windorearthquake)andthecontrolofdrift(lateralbuildingmovement)inhigh-risebuilding.Thestressed-skintubetakesthetubesystemastepfurther.Thedevelopmentofthestressed-skintubeutilizesthefacadeofthebuildingasastructuralelementwhichactswithactswiththeframedtube,thusprovidinganefficientwayofresistinglateralloadsinhigh-risebuildings,andresultingincost-effectivecolumn-freeinteriorspacewithahighratioofnettogrossfloorarea.Becauseofthecontributionofthestressed-skinfacade,theframedmembersofthetuberequirelessmass,andarethuslighterandlessexpansive.Allthetypicalcolumnsandspandrelbeamsarestandardrolledshapes,minimizingtheuseandcostofspecialbuilt-upmembers.Thedepthrequirementfortheperimeterspandrelbeamsisalsoreduced,andtheneedforupsetbeamsabovefloors,whichwouldencroachonvaluablespace,isminimized.Thestructuralsystemhasbeenusedonthe54-storyOneMellonBankCenterinPittsburgh.Systemsinconcrete.Whiletallbuildingsconstructedofsteelhadanearlystart,developmentoftallbuildingsofreinforcedconcreteprogressedatafastenoughratetoprovideacompetitivechallengetostructuralsteelsystemsforbothofficeandapartmentbuildings.Framedtube.Asdiscussedabove,thefirstframedtubeconceptfortallbuildingswasusedforthe43-storyDeWittChestnutApartmentBuilding.Inthisbuilding,exteriorcolumnswerespacedat5.5-ft(1.68-m)centers,andinteriorcolumnswereusedasneededtosupportthe8-in.-thick(20-cm)flat-plateconcreteslabs.Tubeintube.Anothersysteminreinforcedconcreteforofficebuildingscombinesthetraditionalshearwallconstructionwithanexteriorframedtube.Thesystemconsistsofanouterframedtubeofverycloselyspacedcolumnsandaninteriorrigidshearwalltubeenclosingthecentralservicearea.Thesystem(Fig.2),knownasthetube-in-tubesystem,madeitpossibletodesigntheworld'spresenttallest(714ftor218m)lightweightconcretebuilding(the52-storyOneShellPlazaBuildinginHouston)fortheunitpriceofatraditionalshearwallstructureofonly35stories.Systemscombiningbothconcreteandsteelhavealsobeendeveloped,anexampleofwhichisthecompositesystemdevelopedbySkidmore,Owings&Merrillinwhichanexteriorcloselyspacedframedtubeinconcreteenvelopsaninteriorsteelframing,therebycombiningtheadvantagesofbothreinforcedconcreteandstructuralsteelsystems.The52-storyOneShellSquareBuildinginNewOrleansisbasedonthissystem.出處：《土木工程專業(yè)英語(yǔ)》，段兵廷主編，武漢理工大學(xué)出版社建筑物的組成及高層結(jié)構(gòu)材料和不同的結(jié)構(gòu)形式組成建筑物各類不同部份，包括繁重框架、夕卜殼、樓板和隔墻。在建筑物內(nèi)部還有機(jī)械和電氣系統(tǒng)，例如電梯、供暖和冷卻系統(tǒng)、照明系統(tǒng)等。地面以上的部份是建筑物的上部結(jié)構(gòu)，地面以下部份為建筑物的基礎(chǔ)和下部結(jié)構(gòu)。摩天大樓的顯現(xiàn)應(yīng)歸功于19世紀(jì)的兩大進(jìn)展：鋼骨架結(jié)構(gòu)和載人電梯。鋼材作為一種建筑材料，是從1855年貝西默煉鋼法被第一次介紹后開(kāi)始應(yīng)用的。古斯塔?艾菲爾(1832~1923)第一次將鋼結(jié)構(gòu)引入法國(guó)。1889年的巴黎國(guó)際展覽會(huì)的塔和他為Galeriedes機(jī)械的設(shè)計(jì)表現(xiàn)了鋼結(jié)構(gòu)的靈活性。艾菲爾鐵塔高300米，是那時(shí)人類建造的最高建筑物，直到40年后才由美國(guó)的摩天大樓超過(guò)其高度。第一部電梯是1857年ElishaOtis給紐約的一家百貨公司所安裝的。1889年，艾菲爾在艾菲爾鐵塔上安裝了第一部大型電梯，它每小時(shí)能夠輸送2350位乘客抵達(dá)塔頂。繁重框架。直到19世紀(jì)后期，建筑物的外墻被用做繁重墻來(lái)支撐樓層，這種結(jié)構(gòu)是本質(zhì)上是一種梁柱模型，它還被用在框架結(jié)構(gòu)衡宇中。因?yàn)樗鑹w的厚度專門大，繁重墻結(jié)構(gòu)限制了建筑物的高度；例如，建于19世紀(jì)80年代的芝加哥16層高的MonadnockBuilding，在較低的樓層墻體厚度已達(dá)到1.5米。1883年，WillianLeBaronJenney(1832~1907)用鑄鐵柱來(lái)支撐樓層的方式以形成籠狀結(jié)構(gòu)。在1889年，框架結(jié)構(gòu)第一次由鋼梁和鋼柱組成。由于骨架結(jié)構(gòu)，圍墻變成了一種〃幕墻”。磚石一直是〃幕墻”的要緊材料，直到20世紀(jì)30年代輕金屬和玻璃幕墻的問(wèn)世為止。自從鋼框架第一次推出，建筑物的高度一直在迅速增加。在第二次世界大戰(zhàn)前，所有的高層建筑都是鋼結(jié)構(gòu)。戰(zhàn)爭(zhēng)終止以后，鋼材的缺乏和混凝土質(zhì)量的改良，增進(jìn)了鋼筋混凝土高層建筑的進(jìn)展。芝加哥的MarinaTowers(1962)是美國(guó)最高的混凝土建筑；它的高度是588英尺即179米，不久以后被倫敦的高達(dá)650英尺即198米的郵政大廈和其它的塔所超越。在關(guān)于摩天大樓構(gòu)造觀點(diǎn)的改變恢復(fù)了繁重墻的利用。在紐約，由EeroSaarinen于1962年設(shè)計(jì)的哥倫比亞廣播公司大樓，由1.5米寬，柱與柱的中心間距為3米的混凝土柱組成的環(huán)形墻。這種圍護(hù)墻有效地組成了建筑物的繁重墻。這種趨勢(shì)進(jìn)展的緣故是建筑物的墻作為一個(gè)筒體能夠超級(jí)經(jīng)濟(jì)的取得抗風(fēng)作用的足夠強(qiáng)度；世貿(mào)大樓是另一個(gè)筒體法的例子。相較之下，剛性框架或垂直的桁架通經(jīng)常使用于提供側(cè)向穩(wěn)固性。夕卜殼。一個(gè)建筑的外殼由透明元素（窗戶）和不透明元素（墻）組成。窗戶采納傳統(tǒng)上的玻璃作為材料，盡管塑料正在被利用，專門在學(xué)校，破損產(chǎn)生了一個(gè)保護(hù)問(wèn)題。用來(lái)覆蓋結(jié)構(gòu)和起支撐作用墻，它是由各類的建筑材料組成：磚、預(yù)制構(gòu)件、石頭、不透明的玻璃、塑料、鋼材和鋁材。木頭是過(guò)去建造衡宇的要緊材料；因?yàn)樗字?，因此不?jīng)常使用于商業(yè)的、工業(yè)的和公共建筑。樓板。一幢建筑的樓地面結(jié)構(gòu)取決于它所利用的大體結(jié)構(gòu)框架。在鋼框架建筑中，樓地面或是鋼梁上的混凝土樓板，或是由波紋鋼配有混凝土骨料組成的凹板。在混凝土結(jié)構(gòu)中，樓板或是混凝土梁上的混凝土樓板或是一系列緊密散布于混凝土梁在方向上端的薄混凝土樓板，在它的下面提供了一個(gè)多余的空寂間。這種類型的板取決于支撐柱之間的距離或墻間的跨度和空間的功能性。在一棟公寓大樓中，例如，墻和柱間距在3.7米到5.5米，最多見(jiàn)的結(jié)構(gòu)是無(wú)梁實(shí)心混凝土樓蓋。樓蓋的下表面能夠作為基層空間的天花板。辦公大樓中常利用波紋鋼地板，這是因?yàn)椴y鋼地板的波紋當(dāng)由另一塊金屬板蓋上時(shí)，能夠形成線和電線管道。機(jī)械和電力系統(tǒng)。一個(gè)現(xiàn)代建筑不僅包括必要利用空間（辦公室，教室，公寓）而且也包括機(jī)械、電力系統(tǒng)等的輔助空間，以便營(yíng)造一個(gè)舒適的生活環(huán)境。這些輔助空間可能占摩天大樓總建筑面積的25%。在一個(gè)辦公大樓中，供暖、通風(fēng)、電力和衛(wèi)生設(shè)備系統(tǒng)的預(yù)算額占實(shí)際建筑總預(yù)算額的40%，顯示了它們?cè)诮ㄖ械闹匾浴Ｒ驗(yàn)樵S多建筑是密封的，窗戶不能被打開(kāi)，因此由機(jī)械系統(tǒng)提供了通風(fēng)設(shè)備和空氣調(diào)劑設(shè)備。新鮮空氣從中央換氣室由空氣調(diào)劑器用管道輸入。通風(fēng)管和操縱照明設(shè)備單元由懸掛在上面樓層結(jié)構(gòu)下面的天花板遮住了。提供動(dòng)力的電力線路和通信線路也可能在天花板里或也可能在樓地面結(jié)構(gòu)層中的管道或?qū)Ь€管里。咱們?cè)鴩L試性地把機(jī)械、電力系統(tǒng)加入建筑物的建筑學(xué)中去。例如在愛(ài)荷華州首府的美國(guó)共和保險(xiǎn)公司大樓，管道和樓地面的結(jié)構(gòu)層有組織的、優(yōu)美的懸掛在天花板上。這種型的方式使得建筑物的花費(fèi)盡可能的減少了而且使結(jié)構(gòu)有了創(chuàng)新，例如在結(jié)構(gòu)間足昉面。土地和地基。所有的建筑物都是靠土層支撐在地面上的，因此土的特性成為建筑設(shè)計(jì)時(shí)極為重要的考慮因素。基礎(chǔ)的設(shè)計(jì)取決于土的許多因素，例如土的類型，土分層的情形，土層的厚度和它的密實(shí)度，和地下水的情形等。土層很少有一個(gè)單一的成份；他們一般是厚度轉(zhuǎn)變的混合狀態(tài)土層。據(jù)評(píng)定，土層的品級(jí)是依照土分子的大小來(lái)劃分，從小到大依次是淤泥、粘土、沙、石子、巖石。通常，較大分子的土支撐的荷載要大。最堅(jiān)硬的巖石能夠支撐的荷載大約是每平方米100噸，而最軟的淤泥僅能夠支撐的荷載大約是每平方米0.25噸。所有地表以下的土都處于受壓狀態(tài)，說(shuō)得更精準(zhǔn)些，這些土經(jīng)受與作用在其上的土柱重量相等的壓力。許多土顯示出彈性的性質(zhì)——在荷載作用下受壓變形，當(dāng)荷載解除后能夠回彈。土的彈性常隨時(shí)刻而改變，更精準(zhǔn)地說(shuō)，土層的變形在恒載作用下隨著時(shí)刻的增加而不斷地改變。過(guò)一段時(shí)刻后，若是加于土層上的荷載大于土自然壓緊狀態(tài)下的重量，那么建筑物會(huì)產(chǎn)生沉降。相反，那么會(huì)產(chǎn)生隆起，建筑物的重量可能會(huì)使本地貨生流動(dòng)；也確實(shí)是說(shuō)，常常會(huì)發(fā)生土被擠出。由于土受壓和流動(dòng)的阻礙，使建筑物發(fā)生沉降。不均勻沉降例如比薩斜塔，損壞的結(jié)果是建筑物發(fā)生傾斜，墻和隔墻可能顯現(xiàn)裂痕，窗戶和門可能產(chǎn)生變形，或乃至建筑可能倒塌。均勻沉降可不能如此嚴(yán)峻，盡管可能顯現(xiàn)危險(xiǎn)狀況，例如墨西哥城的一些建筑，顯現(xiàn)各類各樣的后果，在過(guò)去的一年里，地下水位發(fā)生了改變，致使一些建筑下沉了3米多。因?yàn)轭愃频臓顩r可能發(fā)生在建造時(shí)也可能是建造后，因此警惕處置建筑物下的土層是極為重要的。土層龐大的轉(zhuǎn)變使得解決地基問(wèn)題的方法多樣化。若是表面土層下的土為堅(jiān)硬土層，最簡(jiǎn)單的方法是采納混凝土基礎(chǔ)。假設(shè)是軟弱土層，加大柱的面積；假設(shè)如此的話，整個(gè)建筑就可采納筏板基礎(chǔ)。假設(shè)表面土層不能夠支撐建筑物的重量，木結(jié)構(gòu)建筑、鋼結(jié)構(gòu)建筑、或混凝土建筑應(yīng)建造在堅(jiān)硬土層上。建造一幢建筑物一樣是從基礎(chǔ)往上到上部結(jié)構(gòu)。但是設(shè)計(jì)的進(jìn)程是從屋頂開(kāi)始到基礎(chǔ)。在過(guò)去，地基處置不是一個(gè)系統(tǒng)的研究項(xiàng)目。在