土木工程专业毕业设计外文翻译.docx
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土木工程专业毕业设计外文翻译
High-RiseBuildings
Introduction
Itisdifficulttodefineahigh-risebuilding.Onemaysaythata
low-risebuildingrangesfrom1to2stories.Amedium-risebuilding
probablyrangesbetween3or4storiesupto10or20storiesormore.
Althoughthebasicprinciplesofverticalandhorizontalsubsystem
designremainthesameforlow-,medium-,orhigh-risebuildings,whenabuildinggetshightheverticalsubsystemsbecomeacontrollingproblemfortworeasons.Higherverticalloadswillrequirelargercolumns,
walls,andshafts.But,moresignificantly,theoverturningmoment
andthesheardeflectionsproducedbylateralforcesaremuchlargerand
mustbecarefullyprovidedfor.
Theverticalsubsystemsinahigh-risebuildingtransmitaccumulated
gravityloadfromstorytostory,thusrequiringlargercolumnorwall
sectionstosupportsuchloading.Inadditionthesesamevertical
subsystemsmusttransmitlateralloads,suchaswindorseismicloads,tothefoundations.However,incontrasttoverticalload,lateralloadeffectsonbuildingsarenotlinearandincreaserapidlywithincreaseinheight.Forexampleunderwindload,theoverturningmomentatthebaseofbuildingsvariesapproximatelyasthesquareofabuildingsmayvaryasthefourthpowerofbuildingsheight,otherthingsbeingequal.Earthquakeproducesanevenmorepronouncedeffect.
Whenthestructureforalow-ormedium-risebuildingisdesignedfordeadandliveload,itisalmostaninherentpropertythatthecolumns,walls,andstairorelevatorshaftscancarrymostofthehorizontalforces.Theproblemisprimarilyoneofshearresistanee.Moderateadditionbracingforrigidframesin“short”buildingscaneasilybe
providedbyfillingcertainpanels(orevenallpanels)withoutincreasingthesizesofthecolumnsandgirdersotherwiserequiredforverticalloads.
Unfortunately,thisisnotisforhigh-risebuildingsbecausetheproblemisprimarilyresistaneetomomentanddeflectionratherthanshear
alone.Specialstructuralarrangementswilloftenhavetobemadeandadditionalstructuralmaterialisalwaysrequiredforthecolumns,
girders,walls,andslabsinordertomadeahigh-risebuildingssufficientlyresistanttomuchhigherlateraldeformations.
Aspreviouslymentioned,thequantityofstructuralmaterialrequiredpersquarefootoffloorofahigh-risebuildingsisinexcessofthatrequiredforlow-risebuildings.Theverticalcomponentscarryingthegravityload,suchaswalls,columns,andshafts,willneedtobestrengthenedoverthefullheightofthebuildings.Butquantityofmaterialrequiredforresistinglateralforcesisevenmoresignificant
Withreinforcedconcrete,thequantityofmaterialalsoincreasesas
thenumberofstoriesincreases.Buthereitshouldbenotedthattheincreaseintheweightofmaterialaddedforgravityloadismuchmoresizablethansteel,whereasforwindloadtheincreaseforlateralforce
resistaneeisnotthatmuchmoresincetheweightofaconcretebuildingshelpstoresistoverturn.Ontheotherhand,theproblemofdesignforearthquakeforces.Additionalmassintheupperfloorswillgiverisetoagreateroveralllateralforceundertheofseismiceffects.
Inthecaseofeitherconcreteorsteeldesign,therearecertainbasicprinciplesforprovidingadditionalresistancetolateraltolateralforcesanddeflectionsinhigh-risebuildingswithouttoomuchsacrifire
ineconomy.
1.Increasetheeffectivewidthofthemoment-resistingsubsystems.
Thisisveryusefulbecauseincreasingthewidthwillcutdowntheoverturnforcedirectlyandwillreducedeflectionbythethirdpowerofthewidthincrease,otherthingsremainingcinstant.However,thisdoesrequirethatverticalcomponents
ofthewidenedsubsystembesuitablyconnectedtoactuallygainthisbenefit.
2.Designsubsystemssuchthatthecomponentsaremadetointeract
inthemostefficientmanner.Forexample,usetrusssystems
withchordsanddiagonalsefficientlystressed,placereinforcingforwallsatcriticallocations,andoptimizestiffnessratiosforrigidframes.
3.Increasethematerialinthemosteffectiveresisting
components.Forexample,materialsaddedinthelowerfloors
totheflangesofcolumnsandconnectinggirderswilldirectlydecreasetheoveralldeflectionandincreasethemoment
resistaneewithoutcontributingmassintheupperfloorswheretheearthquakeproblemisaggravated.
4.Arrangetohavethegreaterpartofverticalloadsbecarried
directlyontheprimarymoment-resistingcomponents.Thiswillhelpstabilizethebuildingsagainsttensileoverturningforcesbyprecompressingthemajoroverturn-resistingcomponents.
5.Thelocalshearineachstorycanbebestresistedbystrategicplacementifsolidwallsortheuseofdiagonalmembersinaverticalsubsystem.Resistingtheseshearssolelybyverticalmembersinbendingisusuallylesseconomical,sinceachievingsufficientbendingresistaneeinthecolumnsandconnecting
girderswillrequiremorematerialandconstructionenergythan
usingwallsordiagonalmembers.
6.Sufficienthorizontaldiaphragmactionshouldbeprovidedfloor.
Thiswillhelptobringthevariousresistingelementstowork
togetherinsteadofseparately.
7.Createmega-framesbyjoininglargeverticalandhorizontaicomponentssuchastwoormoreelevatorshaftsatmultistoryintervalswithaheavyfloorsubsystems,orbyuseofverydeep
girdertrusses.
Rememberthatallhigh-risebuildingsareessentiallyverticalcantileverswhicharesupportedattheground.Whentheaboveprinciplesarejudiciouslyapplied,structurallydesirableschemescanbeobtainedbywalls,cores,rigidframes,tubularconstruction,andotherverticalsubsystemstoachievehorizontalstrengthandrigidity.Someoftheseapplicationswillnowbedescribedinsubsequentsectionsinthe
following.
Shear-WallSystems
Whenshearwallsarecompatiblewithotherfunctionalrequirements,theycanbeeconomicallyutilizedtoresistlateralforcesinhigh-risebuildings.Forexample,apartmentbuildingsnaturallyrequiremanyseparationwalls.Whensomeofthesearedesignedtobesolid,theycanactasshearwallstoresistlateralforcesandtocarrytheverticalloadaswell.Forbuildingsuptosome20storise,theuseofshearwallsiscommon.Ifgivensufficientlength,suchwallscaneconomicallyresistlateralforcesupto30to40storiesormore.
However,shearwallscanresistlateralloadonlytheplaneofthe
walls(i.e.notinadiretionperpendiculartothem).Therefore,it
isalwaysnecessarytoprovideshearwallsintwoperpendiculardirectionscanbeatleastinsufficientorientationsothatlateralforceinanydirectioncanberesisted.Inaddition,thatwalllayoutshouldreflect
considerationofanytorsionaleffect.
Indesignprogress,twoormoreshearwallscanbeconnectedtofromL-shapedorchannel-shapedsubsystems.Indeed,internalshearwallscanbeconnectedtofromarectangularshaftthatwillresistlateralforcesveryefficiently.Ifallexternalshearwallsarecontinuouslyconnectedthenthewholebuildingsactsastube,andconnected,thenthewholebuildingsactsasatube,andisexcellentShear-WallSeystemsresistinglateralloadsandtorsion.
Whereasconcreteshearwallsaregenerallyofsolidtypewithopeningswhennecessary,steelshearwallsareusuallymadeoftrusses.Thesetrussescanhavesinglediagonals,“Xdiagonals,or“K'arrangementsAtrussedwallwillhaveitsmembersactessentiallyindirecttensionorcompressionundertheactionofview,andtheyoffersomeopportunityanddeflection-limitationpointofview,andtheyoffersomeopportunity
forpenetrationbetweenmembers.Ofcourse,theinclinedmembersoftrussesmustbesuitableplacedsoasnottointerferewithrequirementsforwiondowsandforcirculationservicepenetrationsthoughthesewalls.
Asstatedabove,thewallsofelevator,staircase,andutilityshafts
formnaturaltubesandarecommonlyemployedtoresistbothverticalandlateralforces.Sincetheseshaftsarenormallyrectangularorcircularincross-section,theycanofferanefficientmeansforresistingmomentsandshearinalldirectionsduetotubestructuralaction.Butaprobleminthedesignoftheseshaftsisprovidedsufficientstrengtharounddoor
openingsandotherpenetrationsthroughtheseelements.Forreinforcedconcreteconstruction,specialsteelreinforcementsareplacedaroundsuchopening」nsteelconstruction,heavierandmorerigidconnectionsarerequiredtoresistrackingattheopenings.
Inmanyhigh-risebuildings,acombinationofwallsandshaftscan
offerexcellentresistaneetolateralforceswhentheyaresuitably
locatedantconnectedtooneanother.Itisalsodesirablethatthestiffnessofferedthesesubsystemsbemore-or-lesssymmertricalinalldirections.
Rigid-FrameSystems
Inthedesignofarchitecturalbuildings,rigid-framesystemsfor
resistingverticalandlateralloadshavelongbeenacceptedasan
importantandstandardmeansfordesigningbuilding.Theyareemployedforlow-andmediummeansfordesigningbuildings.Theyareemployedfor
low-andmediumuptohigh-risebuildingperhaps70or100storieshigh.
Whencomparedtoshear-wallsystems,theserigidframesbothwithinandattheoutsideofabuildings.Theyalsomakeuseofthestiffnessinbeamsandcolumnsthatarerequiredforthebuildingsinanycase,butthecolumnsaremadestrongerwhenrigidlyconn