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1TallBuildingStructureTallbuildingshavefascinatedmankindfromthebeginningofcivilization,theirconstructionbeinginitiallyfordefenseandsubsequentlyforecclesiasticalpurposes.Thegrowthinmoderntallbuildingconstruction,however,whichbeganinthe1880s,hasbeenlargelyforcommercialandresidentialpurposes.Tallcommercialbuildingsareprimarilyaresponsetothedemandbybusinessactivitiestobeasclosetoeachother,andtothecitycenter,aspossible,therebyputtingintensepressureontheavailablelandspace.Also,becausetheyformdistinctivelandmarks,tallcommercialbuildingsarefrequentlydevelopedincitycentersasprestigesymbolsforcorporateorganizations.Further,thebusinessandtouristcommunity,withitsincreasingmobility,hasfuelledaneedformore,frequentlyhigh-rise,citycenterhotelaccommodations.Therapidgrowthoftheurbanpopulationandtheconsequentpressureonlimitedspacehaveconsiderablyinfluencedcityresidentialdevelopment.Thehighcostofland,thedesiretoavoidacontinuousurbansprawl,andtheneedtopreserveimportantagriculturalproductionhaveallcontributedtodriveresidentialbuildingsupward.Ideally,intheearlystagesofplanningabuilding,theentiredesignteam,includingthearchitect,structuralengineer,andservicesengineer,shouldcollaboratetoagreeonaformofstructuretosatisfytheirrespectiverequirementsoffunction,safetyandserviceability,andservicing.Itisdifficulttodefineahigh-risebuilding.Onemaysaythatalow-risebuildingrangesfrom1to2stories.Amedium-risebuildingprobablyrangesbetween3or4storiesupto10or20storiesormore.Althoughthebasicprinciplesofverticalandhorizontalsubsystemdesignremainthesameforlow-,medium-,orhigh-risebuildings,whenabuildinggetshightheverticalsubsystemsbecomeacontrollingproblemfortworeasons.Higherverticalloadswillrequirelargercolumns,walls,andshafts.But,moresignificantly,theoverturningmomentandthesheardeflectionsproducedbylateralforcesaremuchlargerand2mustbecarefullyprovidedfor.Theverticalsubsystemsinahigh-risebuildingtransmitaccumulatedgravityloadfromstorytostory,thusrequiringlargercolumnorwallsectionstosupportsuchloading.Inadditionthesesameverticalsubsystemsmusttransmitlateralloads,suchaswindorseismicloads,tothefoundations.However,incontrasttoverticalload,lateralloadeffectsonbuildingsarenotlinearandincreaserapidlywithincreaseinheight.Forexampleunderwindload,theoverturningmomentatthebaseofbuildingsvariesapproximatelyasthesquareofabuildingsmayvaryasthefourthpowerofbuildingsheight,otherthingsbeingequal.Earthquakeproducesanevenmorepronouncedeffect.Whenthestructureforalow-ormedium-risebuildingisdesignedfordeadandliveload,itisalmostaninherentpropertythatthecolumns,walls,andstairorelevatorshaftscancarrymostofthehorizontalforces.Theproblemisprimarilyoneofshearresistance.Moderateadditionbracingforrigidframesin“short”buildingscaneasilybeprovidedbyfillingcertainpanelswithoutincreasingthesizesofthecolumnsandgirdersotherwiserequiredforverticalloads.Unfortunately,thisisnotisforhigh-risebuildingsbecausetheproblemisprimarilyresistancetomomentanddeflectionratherthanshearalone.Specialstructuralarrangementswilloftenhavetobemadeandadditionalstructuralmaterialisalwaysrequiredforthecolumns,girders,walls,andslabsinordertomadeahigh-risebuildingssufficientlyresistanttomuchhigherlateraldeformations.Aspreviouslymentioned,thequantityofstructuralmaterialrequiredpersquarefootoffloorofahigh-risebuildingsisinexcessofthatrequiredforlow-risebuildings.Theverticalcomponentscarryingthegravityload,suchaswalls,columns,andshafts,willneedtobestrengthenedoverthefullheightofthebuildings.Butquantityofmaterialrequiredforresistinglateralforcesisevenmoresignificant.Withreinforcedconcrete,thequantityofmaterialalsoincreasesasthenumberofstoriesincreases.Buthereitshouldbenotedthattheincreaseintheweightofmaterialaddedforgravityloadismuchmoresizablethansteel,whereasforwindloadtheincreaseforlateralforceresistanceisnotthatmuchmoresincetheweightofaconcretebuildings3helpstoresistoverturn.Ontheotherhand,theproblemofdesignforearthquakeforces.Additionalmassintheupperfloorswillgiverisetoagreateroveralllateralforceundertheofseismiceffects.Inthecaseofeitherconcreteorsteeldesign,therearecertainbasicprinciplesforprovidingadditionalresistancetolateraltolateralforcesanddeflectionsinhigh-risebuildingswithouttoomuchsacrifireineconomy.⒈Increasetheeffectivewidthofthemoment-resistingsubsystems.Thisisveryusefulbecauseincreasingthewidthwillcutdowntheoverturnforcedirectlyandwillreducedeflectionbythethirdpowerofthewidthincrease,otherthingsremainingcinstant.However,thisdoesrequirethatverticalcomponentsofthewidenedsubsystembesuitablyconnectedtoactuallygainthisbenefit.⒉Designsubsystemssuchthatthecomponentsaremadetointeractinthemostefficientmanner.Forexample,usetrusssystemswithchordsanddiagonalsefficientlystressed,placereinforcingforwallsatcriticallocations,andoptimizestiffnessratiosforrigidframes.⒊Increasethematerialinthemosteffectiveresistingcomponents.Forexample,materialsaddedinthelowerfloorstotheflangesofcolumnsandconnectinggirderswilldirectlydecreasetheoveralldeflectionandincreasethemomentresistancewithoutcontributingmassintheupperfloorswheretheea