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ConcreteACI31808 page
C t D iConcreteDesignPresentedby:SeanDang,P.E.
Date:April2011
Createdby:SeanDang,P.E.
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ConcreteACI31808 page
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ConcreteACI31808 page 1
h l dd d h f l fThisisnewlyaddedtotheSCOPEforclarificationpurposes.TheStrengthEvaluationofExistingStructureshasalreadybeenimplementedinChapter20ofthe2005ACICode.
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ConcreteACI31808 page 2
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ConcreteACI31808 pageFromACICommentaryFromACICode
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y
L NPiles,caissons,etciftheysupportastructureassignedtoSeismicDesignCategoriesD E andFaregovernby
LecturesNotes
CategoriesD,E,andFaregovernbyACI.AllothersareregulatedbytheBuildingCode(ie.Chapter18&19).
Example:Micropilesbeneathaforparkinglot
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ConcreteACI31808 pageFromACICode
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Deformedsteelfibers(nextfewpages)Headedshearstuds(seebelow)
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ConcreteACI31808 pageForRef.Only:nochangeinSec.11.11.4
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y g 4
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ConcreteACI31808 pageConcreteACI31808FromACICode
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Sec.7.7.5specifiestheamountofconcretecoverforshearstudreinforcementcoverforshearstudreinforcement.
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ConcreteACI31808 pageMainlyforslabsFromACICode
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yVerygoodtopreventshearcracks
TheCodedoesNOTmentionthisreinforcementanywhereelseagain.y gTherearenodesignparametersforthismaterial.Mixturecontent?Fibervs.ConcreteNoadditionalrebars required??
Deformedsteelfibers Deformedsteelfiberscastinconcrete
Noadditionalrebars required??Requiredthicknessoftheslab???
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ConcreteACI31808 pageFromACICode
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ConcreteACI31808 pageConcreteACI31808C Becautious whenitis
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Cusedtoterminateverticalrebarforboundaryelementsofashearwall ashearwall.Theengineerneedstocheckthedevelopmentlengthincompression.
T
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ConcreteACI31808 page 10
TherequirementsofStructuralIntegrityisnotnew,however,therequirementstogainstructuralintegrityhasbeenrevised.
ForSlabs,atleastonebottombartopassthruthecolumncore
ForPerimeter Beams,atleasttwobarstopassthruthecolumncore
InteriorBeamswillbediscussedlater
DenotesNeworChangesinACI31808
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ConcreteACI31808 pageConcreteACI31808ForPerimeterBeams
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Theamountofbeamreinforcementtorequiredforstructuralintegritydidnotq g ychange.
Oldcodejustaskfortwocontinuousbarswithoutanyotherrequirements.
Newcoderequirescontinuousbarstopassthroughtheregionboundedbythel it di l i f t fth longitudinalreinforcementofthecolumnColumn
C lColumn
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ConcreteACI31808 pageConcreteACI31808StructuraldetailshowingabeamthatForPerimeterBeams(continue)
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giswiderthanthesupportingcolumn.
Notetheamountofrebarpassingthruthecolumncoreforstructuralintegrity.
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ConcreteACI31808 pageConcreteACI31808ForRef only:nochangeinthe
ForPerimeterBeams(continue)
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ForRef.only:nochangeinthedevelopmentlength
OldcodeallowedClassUstirrups
OldcodeallowedClassAOldcodeallowedClassAsplice.NewcoderequiresClassBsplice.Seeabove.??
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ConcreteACI31808 pageConcreteACI31808ForPerimeterBeams(continue)
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Thisisnew!
OldcodeallowedClassUstirrups
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ConcreteACI31808 pageConcreteACI31808ForPerimeterBeams(continue) FromACICommentary
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ThisconcernfortorquestressesisalsothereasonforrequiringaportionofthelongitudinalreinforcementswithinthePerimeterBeams(andnotforinteriorbeams),topassh h l f i l i
Transversereinforcementwithinaperimeterbeam.
thruthecolumncoreformoretorsional resistance.
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ConcreteACI31808 pageConcreteACI31808ForRef.only:nochangeinpunchingForInteriorBeams
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y g p gshearrequirements
Column
Caution!OthersectionslikePunchingShearmaystillrequirethelongitudinalreinforcementtopass throughtheregionreinforcementtopass throughtheregionboundedbythelongitudinalreinforcementofthecolumn.
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ConcreteACI31808 pageTheACIintroducesaLightweight
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TheACIintroducesaLightweight
Concretemultiplier thruouttheCodewhereeverisused.
Doyounoticeanythingdifferentabovethisdevelopmentlengthabovethisdevelopmentlengthequation?
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ConcreteACI31808 page 18
Thisischanged!
Inthe2005Codelambda=1.3Inthe2008Code,lambda=0.75
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ConcreteACI31808 pageConcreteACI31808Review
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Elastic:capableofreturningtoitsoriginallength,shape,etc.,afterbeingstretched deformed ie Elastic
NonlinearAnalysis??
stretched,deformed,ie.ElasticDisplacement,Deformation.
Inelastic:NOTreturningtoitsoriginalLinearAnalysis??
g gform.Duetocracks,rebarslippage,etc..InelasticDisplacement,Deformation.Ie.inelasticdisplacement,inelasticdeformation.
D ili i j ifi d i hYield:changefromelastictopermanentdeformationbuthasNOTnot collapse.
Ductilityisjustifiedwithtesting
Brittle:astiffelementthatfractureseasily
Ductile:aseriesofcyclicrotationinitsyieldedstateandstillabsorbingenergy.
Brittle:astiffelementthatfractureseasily
Collapse:Youshouldknowthis.
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ConcreteACI31808 page 20
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ConcreteACI31808 pageConcreteACI31808FromSection8.8.2: ThisisNew!
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Checkbuildingswayingunderwindl diloading:
Columns:1.4x0.70Ig =0.98IgBeams:1.4x0.35Ig =0.60Ig4 35 g gWalls:1.4x0.35Ig =0.60Ig
ThisismainlyfortallslenderOCCUPIEDBuildingsorhighrisestructures.
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ConcreteACI31808 page 22
Thestrengthreductionfactorforspiralreinforcementhaschangedfrom0 90toreinforcementhaschangedfrom0.90to0.75
Inthe2008Code,thefactorwasincreasedto0.60from0.55.Notsurehowthisisused,butinLACityi f t i i db freinforceconcreteisrequiredbecauseof
SeismicityZone.
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ConcreteACI31808 pageConcreteACI31808ThisisNew!
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Transversereinforcementshallnotexceedfy =80,000psiEXCEPT:
SpiralreinforcedcolumnsSpiralreinforcedcolumnsSpecialMomentFramesSpecialStructuralWalls(shearwalls)
Highstrengthtiescanhelpalleviaterebarcongestion(moreonthislater).
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ConcreteACI31808 pageConcreteACI31808Eqn:(1010)willbefromacomputer
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q ( ) panalysis.Duetotheinelasticstorydrift.Forhandcalculationsitwouldbeeasiertoassumenotbracedagainstsideswaytoassume notbracedagainstsidesway ascheckforSlendernessEffect.
Thisprocedurehasnotchangedfromtheoldcode,exceptthatthecontenthasbeenreorganized.
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ConcreteACI31808 pageConcreteACI318082008ACInowprovidesanalternativeway
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p ytodetermineswayornonswaycolumns.
Thisisnew!Butdifficulttousewithoutacomputer.Seepreviousslidesforhandcalc.alternative.
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ConcreteACI31808 pageConcreteACI31808Thisisnew! FromACICommentary
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y
SecondordermeansPdeltaeffects
Pv m
hh
P m+
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ConcreteACI31808 pageConcreteACI31808Nochangeintheprescriptivevaluesforh d d f
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thereducedmomentofinertia.
Thisisnew!The2008Codeprovidesalternativeequationstodeterminethereducedequationstodeterminethereducedmomentofinertia
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ConcreteACI31808 pageSec.14.8.3Slenderwalldesign ACICommentary
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4 3 g y
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ConcreteACI31808 page 29
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ConcreteACI31808 page 30
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ConcreteACI31808 pageThisisnew!
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Thisisnew!
Severalsectionshavebeenaddedtothischapter.
Wewillnotbediscussingtheseitems.
Itisashortchapterwith5pages.Itisashortchapterwith5pages.
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ConcreteACI31808 page 32
21.1.1.3 StructuresassignedtoSeismicDesignCategoryAshallsatisfyrequirements LACityAmendment.DesignCategoryAshallsatisfyrequirementsofChapters1to19and22;Chapter21doesnotapply. StructuresassignedtoSeismicDesignCategoryB,C,D,EorFalsoshallsatisfy21.1.1.4through21.1.1.8,asapplicable.ExceptforstructuralelementsofplainconcretecomplyingwithSection1908.1.8oftheCaliforniaBuildingCode,structural Languageaddedtoprohibitplain(noni f d)theCaliforniaBuildingCode,structuralelementsofplainconcreteareprohibitedinstructuresassignedtoSeismicDesignCategoryC,D,EorF
reinforced)concrete.
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ConcreteACI31808 page 33
21.1.1.7 StructuralsystemsdesignatedaspartoftheseismicforceresistingsystemshallberestrictedtothosepermittedbyASCE7.Except LACityAmendmentforSeismicDesignCategoryA,forwhichChapter21doesnotapply,thefollowingprovisionsshallbesatisfiedforeachstructuralsystemdesignatedaspartoftheseismicforce
LACityAmendment.
resistingsystem,regardlessoftheSeismicDesignCategory:(a)Ordinarymomentframesshallsatisfy21.2.(b)OrdinaryreinforcedconcretestructuralwallsandordinaryprecaststructuralwallsneednotsatisfyanyprovisionsinChapter21.(c)Intermediatemomentframesshallsatisfy21.3.
ThisisthefirsttimeACIprovidesdesignparametersfor:OrdinaryMomentFrames
(d)Intermediateprecaststructuralwallsshallsatisfy21.4.(e)Specialmomentframesshallsatisfy21.5through21.8. OrdinaryMomentFrames
OrdinaryShearwallsIntermediateMomentFrames
(f)Specialstructuralwallsshallsatisfy21.9.
(g)Specialstructuralwallsconstructedusingprecastconcreteshallsatisfy21.10.
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ConcreteACI31808 pageN h f i d
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Nochangefrompreviouscode.NoideawhatASTM706isbuttherearenoqualifyingconditionsassociatedwiththismaterial.Buttheconditions(a)&(b)onlyappliestoASTMA615Grades40andGrades60reinforcement.
( h ll d hi l b Thishaschanged.Forinspectors:ThenewcodedoesNOTallowaretest.
(retestsshallnotexceedthisvaluebymorethananadditional3000psi)
Useoflongitudinalreinforcementwithstrengthsubstantiallyhigherthanthatassumedindesignwillleadtohighershearandbondstressesatthetimeofdevelopmentofyieldindesignwillleadtohighershearandbondstressesatthetimeofdevelopmentofyieldmoments.Theseconditionsmayleadtobrittlefailuresinshearorbondandshouldbeavoided.
So,isStrongeralwaysbetter?Theplanscallsoutforfy =40ksi andthecontractorinstallsfy =60ksi rebar.ThisisNOTacceptable.
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ConcreteACI31808 page 35
Thisisnew!ThenewcodeallowsALL confinementreinforcementtonotexceed100,000psi.
InthepreviouscodelimitedAllconfinementreinforcementtonotconfinementreinforcementtonotexceed60,000psi(Sec.21.2.5)
Thisisnew!Thenewcodelimitsallshearreinforcementto60 000psi Thereinforcementto60,000psi.Thepreviouscodedidnothaveanyrestrictions.
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ConcreteACI31808 pageConcreteACI31808Thisisnew!
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ThenewcodeprovidesdesignparametersforOrdinary momentframes.
21.3.3 isthecolumndesignforIntermediatemomentframes.( )
ThislimitationforuseinSDCBisfoundinthe
(nextslide)
Basically,ifthecolumnheightislessthan5xC1thenitis
CommentarySectionandnottheCode.
5consideredashortcolumnwhichistypicallycontrolledbyshearfailure.
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ConcreteACI31808 pageConcreteACI31808ForReferenceonly:
d f
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NonewdesignparametersforIntermediatemomentframes.NOTpermittedinSDCD,E,&F.
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ConcreteACI31808 pageConcreteACI31808 38Thisisnew!ThenewcodeprovidesdesignparametersThenewcodeprovidesdesignparametersforSpecialmomentframes.
Caution!!TheCodelanguagedoesnotmatchthediagram.ButasoftheThirdPrinting(October
C2and0.75C1ButasoftheThirdPrinting(October
2009)thiserrorhasbeenfixed.0.75 C
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ConcreteACI31808 pageConcreteACI31808AfewChangesin:
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gTheSpecialMomentFrames
Thi i !Thisisnew!
10/4=2.5whichisthevaluefor.
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ConcreteACI31808 pageConcreteACI31808 40Longbeamspanningbetweentwostiffwall.LikeamomentframeSec.21.5
Shortbeamspanningbetweentwostiffwall,therefore,shearwillcontrol
Thisisnew!Aclarification:ThebeamwillbehavelikeaMomentFrameBeam,therefore,useSec.21.5.2through21.5.4.
FromACICommentary:FromACICommentary:Experimentsshowthatdiagonallyorientedreinforcementiseffectiveonlyifthebarsareplacedwithalargeinclination.Therefore,di ll i f d li b diagonallyreinforcedcouplingbeamsarerestrictedtobeamshavingaspectratioln/h>4.The2008editionofthisCodewaschangedgtoclarifythatcouplingbeamsofintermediateaspectratiocanbereinforcedaccordingto21.5.2through21.5.4.
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ConcreteACI31808 pageConcreteACI31808 41
Thisisnew!Thepreviouscodedidnothaveanyspecialrequirements
Thisisnew!Inotherwords,twoormorelayersof:
anyspecialrequirements.
, yaminimumfourbarcage.
Thepreviouscodeonlyrequiresaminimumof4barswithtiesminimumof4barswithties.
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ConcreteACI31808 pageConcreteACI31808Thisisnew! FromACICommentary
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Section21.9.7.4(d)describesasecondoptionforconfinementofthediagonalsintroducedinthe2008Code(Fig.R21.9.7(b)).Thissecondoptionistoconfinetheentirebeampcrosssectioninsteadofconfiningtheindividualdiagonals.Thisoptioncanconsiderablysimplifyfieldplacementofhoops,whichcanotherwisebeespecially
Option#1likethepreviousCode,
p p ychallengingwherediagonalbarsintersecteachotherorenterthewallboundary.
requiresthediagonalbarstobeenclosed.
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ConcreteACI31808 pageConcreteACI31808 43
Again,designersmustprovideproperconfinementwhereeverplastichingearetooccur Thiswillcreateaductilesystemtoabsorbseismicenergy tooccur.Thiswillcreateaductilesystemtoabsorbseismicenergy.
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ConcreteACI31808 pageConcreteACI31808 44
LACityLACityAmendment
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ConcreteACI31808 pageConcreteACI31808N t h iti
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Notsurewhyitisplainconcretewhenrebars arerequired.q
LACityAmendment
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ConcreteACI31808 pageConcreteACI31808 46
LACityLACityAmendment
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ConcreteACI31808 pageConcreteACI31808 47
LACityLACityAmendment
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ConcreteACI31808 pageConcreteACI31808 48
TheEnd
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