High-RiseBuildingsIntroductionItisdifficulttodefineahigh-risebuilding.Onemaysaythatalow-risebuildingrangesfrom1to2stories.Amedium-risebuildingprobablyrangesbetween3or4storiesupto10or20storiesormore.Althoughthebasicprinciplesofverticalandhorizontalsubsystemdesignremainthesameforlow-,medium-,orhigh-risebuildings,whenabuildinggetshightheverticalsubsystemsbecomeacontrollingproblemfortworeasons.Higherverticalloadswillrequirelargercolumns,walls,andshafts.But,moresignificantly,theoverturningmomentandthesheardeflectionsproducedbylateralforcesaremuchlargerandmustbecarefullyprovidedfor.Theverticalsubsystemsinahigh-risebuildingtransmitaccumulatedgravityloadfromstorytostory,thusrequiringlargercolumnorwallsectionstosupportsuchloading.Inadditionthesesameverticalsubsystemsmusttransmitlateralloads,suchaswindorseismicloads,tothefoundations.However,incontrasttoverticalload,lateralloadeffectsonbuildingsarenotlinearandincreaserapidlywithincreaseinheight.Forexampleunderwindload,theoverturningmomentatthebaseofbuildingsvariesapproximatelyasthesquareofabuildingsmayvaryasthefourthpowerofbuildingsheight,otherthingsbeingequal.Earthquakeproducesanevenmorepronouncedeffect.Whenthestructureforalow-ormedium-risebuildingisdesignedfordeadandliveload,itisalmostaninherentpropertythatthecolumns,walls,andstairorelevatorshaftscancarrymostofthehorizontalforces.Theproblemisprimarilyoneofshearresistance.Moderateadditionbracingforrigidframesin“short”buildingscaneasilybeprovidedbyfillingcertainpanels(orevenallpanels)withoutincreasingthesizesofthecolumnsandgirdersotherwiserequiredforverticalloads.Unfortunately,thisisnotisforhigh-risebuildingsbecausetheproblemisprimarilyresistancetomomentanddeflectionratherthanshearalone.Specialstructuralarrangementswilloftenhavetobemadeandadditionalstructuralmaterialisalwaysrequiredforthecolumns,girders,walls,andslabsinordertomadeahigh-risebuildingssufficientlyresistanttomuchhigherlateraldeformations.Aspreviouslymentioned,thequantityofstructuralmaterialrequiredpersquarefootoffloorofahigh-risebuildingsisinexcessofthatrequiredforlow-risebuildings.Theverticalcomponentscarryingthegravityload,suchaswalls,columns,andshafts,willneedtobestrengthenedoverthefullheightofthebuildings.Butquantityofmaterialrequiredforresistinglateralforcesisevenmoresignificant.Withreinforcedconcrete,thequantityofmaterialalsoincreasesasthenumberofstoriesincreases.Buthereitshouldbenotedthattheincreaseintheweightofmaterialaddedforgravityloadismuchmoresizablethansteel,whereasforwindloadtheincreaseforlateralforceresistanceisnotthatmuchmoresincetheweightofaconcretebuildingshelpstoresistoverturn.Ontheotherhand,theproblemofdesignforearthquakeforces.Additionalmassintheupperfloorswillgiverisetoagreateroveralllateralforceundertheofseismiceffects.Inthecaseofeitherconcreteorsteeldesign,therearecertainbasicprinciplesforprovidingadditionalresistancetolateraltolateralforcesanddeflectionsinhigh-risebuildingswithouttoomuchsacrifireineconomy.1.Increasetheeffectivewidthofthemoment-resistingsubsystems.Thisisveryusefulbecauseincreasingthewidthwillcutdowntheoverturnforcedirectlyandwillreducedeflectionbythethirdpowerofthewidthincrease,otherthingsremainingcinstant.However,thisdoesrequirethatverticalcomponentsofthewidenedsubsystembesuitablyconnectedtoactuallygainthisbenefit.2.Designsubsystemssuchthatthecomponentsaremadetointeractinthe...
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