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PLACINGANDTYINGREINFORCINGSTEEL

Beforeyouplacereinforcingsteelinforms,allformoilingshouldbecompleted.Oilonreinforcingbarsshouldbeavoidedbecauseitreducesthebondbetweenthebarsandtheconcrete.Useapieceofburlaptoremoverust,millscale,grease,mud,orotherforeignmatterfromthebars.Alightfilmofrustormillscaleisnotobjectionable.

Barsaremarkedtoshowwheretheywillfit.Youmayworkaccordingtoeitheroneofthetwomostusedsystemsformarkingbarshowever,thesystemyouuseshouldagreewiththemarkingsystemwhichappearsontheengineeringorassemblydrawings.Thetwomarkingsystemsusedareasfollows:

1.Allbarsinonetypeofmemberaregiventhemarkofthatmember.Thissystemisusedforcolumnbars,beambars,footingbars,andsoon.

2.Thebarsaremarkedingreaterdetail.Thesemarksshowexactlywherethebaristobeplaced.Inadditiontothetypemember(thatis,beam(B),wall(W),column(C),andsoon),themarksshowtheflooronwhichthebarsaretobeplacedandthesizeandindividualnumberofeachparticularbar.Insteadofshowingthebarsizebyitsdiametermeasurement,themarkshowsthebarsizeincodebyeighths.Theexamplesshownbelowshowthesecondtypeofmarkingsystem.

2138052=secondfloorB=beammember8=8/8or1inch(2.5cm)squarebar05=partofthesecondfloorplandesignatedbythenumber5

21306052=secondfloorB=beammember06=6/8or3/4inch(1.9cm)roundbar05=partofsecondfloorplandesignatedbythenumber5

Tiewireisusedtoholdrebarinplacetoensurethatwhenconcreteisplacedthebarsdonotshiftoutofposition.Sixteengaugewireisusedtotie

Table76.Multishearing

reinforcingbars.About12pounds(5.4kg)ofwireisrequiredtotieanaverageton(0.9tome)ofbars.NOTE:Tiewireaddsnothingtothestrengthofthesteel.

Anumberofdifferenttypesoftiescanbeusedwithreinforcingbarssomearemoreeffectivethanothers.Figure717showssixtypesoftiesthatareidentifiedbelowaccordingtothelettersofthealphabetusedtoshowindividualties.

FastSettingMortarIdealforuseinhightrafficareaswherequickrepairiscritical!

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A.SNAPTIEorSIMPLETIE.Thewireissimplywrappedoncearoundthetwocrossingbarsinadiagonalmannerwiththetwoendsontop.Thesearetwistedtogetherwithapairofsidecuttersuntiltheyareverytightagainstthebars.Thenthelooseendsofthewirearecutoff.Thistieisusedmostlyonfloorslabs.

B.WALLTIE.Thistieismadebygoingabout11/2timesaroundtheverticalbar,thendiagonallyaroundtheintersection,twistingthetwoendstogetheruntiltheconnectionistight,butwithoutbreakingthetiewire,thencuttingofftheexcess.Thewalltieisusedonlightverticalmatsofsteel.

C.DOUBLESTRANDSINGLETIE.Thistieisavariationofthesimpletie.Itisespeciallyfavoredforheavywork

D.SADDLETIE.Thewirespasshalfwayaroundoneofthebanoneithersideofthecrossingbarandarebroughtsquarelyordiagonallyaroundthecrossingbarwiththeendstwistedtogetherandcutoff.Thistieisusedonspeciallocations,suchasonwalls.

E.SADDLETIEWITHTWIST.Thistieisavariationofthesaddletie.Thetiewireiscarriedcompletelyaroundoneofthebars,thensquarelyacrossandhalfwayaroundtheother,eithersideofthecrossingbars,andfinallybroughttogetherandtwistedeithersquarelyordiagonallyacross.Thesaddletiewithtwistisusedforheavymatsthataretobeliftedbyacrane.

F.CROSSTIEorFIGUREEIGHTTIE.Thistypeoftiehastheadvantageofcausinglittleornotwistinthebars.

Theproperlocationforthereinforcingbarsisusuallygivenondrawings(table77).Inorderforthestructuretowithstandtheloadsitmustcarry,placethesteelinthepositionshown.Securethebarsinpositioninsuchawaythatconcreteplacingoperationswillnotmovethem.Thiscanbeaccomplishedbytheuseofthereinforcingbarsupportsshowninfigures718,719,and720.

Figure717.Sixtypesofties.

Figure718.Reinforcementbaraccessories.

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Thepropercoverageofbarsintheconcreteisveryimportanttoprotectthebarsfromfirehazards,possibilityofcorrosion,andexposuretoweather.Whennotspecified,minimumstandardsgivenbelowandinfigure721shouldbeobserved.

FOOTINGS3inchesatthesideswhereconcreteiscastagainsttheearthandonthebottomsoffootingsorotherprincipalstructuralmemberswhereconcreteisdepositedontheground.

Figure719.Precastconcreteblockusedforrebarsupport.

WALLS2inchesforbarslargerthanNo.5,whereconcretesurfaces,afterremovalofforms,wouldbeexposedtotheweatherorbeincontactwiththeground11/2inchesforNo.5barsandsmaller3/4inchfromthefacesofallwallsnotexposeddirectlytothegroundortheweather.

COLUMNS11/2inchesoverspiralsandties.

BEAMSANDGIRDERS11/2inchestothenearestbarsonthetop,bottom,andsides.

JOISTSANDSLABS3/4inchonthetop,bottom,andsidesofjoistsandonthetopandthebottomofslabswhereconcretesurfacesarenotexposeddirectlytothegroundortheweather.

NOTE:Allmeasurementsarefromtheoutsideofthebartothefaceoftheconcrete,NOTfromthemainsteel,unlessotherwisespecified.

Footingsandotherprincipalstructuralmembersthatareagainstthegroundshouldhaveatleast3

Figure720.Rebarhunginplace.

inches(76.2mm)ofconcretebetweenthesteelandtheground.Iftheconcretesurfaceistobeincontactwiththegroundorexposedtotheweatherafterremovaloftheforms,theprotectivecoveringofconcreteoverthesteelshouldbe2inches(50.8mm).Itmaybereducedto11/2inches(38.1mm)forbeamsandcolumnsand3/4inch(19.5mm)forslabsandinteriorwallsurfaces,butitshouldbe2inches(50.8mm)forallexteriorwallsurfaces.Thismeasurementistakenfromthemainrebar,notthestirrupsortheties.

NOTE:Wheresplicesinreinforcingsteelarenotdimensionedonthedrawings,thebarsshouldbelappednotlessthan30timesthebardiameternorlessthan12inches(table77).Thestressinatensionbar

Table77.LengthofLapSplicesinReinforcingSteel

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Figure721.Minimumcoverageofrebarinconcrete.

canbetransmittedthroughtheconcreteandintoanotheradjoiningbarbyalapspliceofproperlength.

Tolapweldwirefabric/wiremesh,youcanuseanumberofmethods,twoofwhicharetheendlapandthesidelap.Intheendlapmethod,thewiremeshislappedbyoverlappingonefullmesh,measuredfromtheendsofthelongitudinalwiresinonepiecetotheendsofthelongitudinalwiresintheadjacentpiece,andthentyingthetwopiecesat1foot6inch(45.0cm)centerswithasnaptie.Inthesidelapmethod,thetwolongitudinalsidewiresareplacedonealongsideandoverlappingtheotherandthenaretiedwithasnaptieevery3feet(.9m).

Reinforcingbarsareintensionandthereforeshouldneverbebentaroundaninsidecornerbeams.Theycanpullstraightthroughtheconcretecover.Instead,theyshouldoverlapandextendtothefarfaceforanchoragewith180degreehooksandproperconcretecoverage(fig.723).

Thebarscanalsobesplicedbymetalareweldingbutonlyifcalledforintheplansandspecifications.Forbarswhichareplacedinaverticalposition,abuttweldispreferred.Theendofthebottombariscut

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Figure723.CorrectandIncorrectplacementofreinforcementforaninsidecorner.

square,andtheendofthetopbarrestingonitiscutinabevelfashion,thuspermittingabuttweld.Forbarswhichwillbearaloadinahorizontalposition,afilletweldispreferred.Usually,thetwobarsareplacedendtoend(ratherthanoverlapping),andpiecesofflatbar(orangleiron)areplacedoneitherside.Filletweldsarethenmadewherethemetalsjoin.Theweldsaremadetoadepthofonehalfofthebardiameterandforalengtheighttimesthebardiameter.

Theminimumcleardistancebetweenparallelbarsinbeams,footings,walls,andfloorslabsshouldeitherbe1inch(25.4mm)or11/3timesthelargestsizeaggregateparticleintheconcrete,whicheverdistanceisgreater.Incolumns,thecleardistancebetweenparallelbarsshouldbenotlessthan11/2timesthebardiameteror11/2timesthemaximumsizeofthecoarseaggregate.Alwaysusethelargerofthetwo.

Thesupportforreinforcingsteelinfloorslabsisshowninfigure724.Theheightoftheslabbolsterisdeterminedbytherequiredconcreteprotectivecover.Concreteblocksmadeofsandcementmortarcanbeusedinplaceoftheslabbolster.Woodblocksshouldneverbeusedforthispurpose.Highchairs(fig.718)canbeobtainedinheightsupto6inches(15cm).Whenaheightgreaterthan6inchesisrequired,makethechairoutofNo.0,soft,annealedironwire.Toholdthebarsfirmlyinposition,youshouldtiethebarstogetheratfrequentintervalswheretheycrosswithasnapat.

Steelforcolumntiesmaybeassembledwiththeverticalsintocagesbylayingtheverticalbarsforonesideofthecolumnhorizontallyacrossacoupleofsawhorses.Thepropernumberoftiesareslippedoverthebars,theremainingverticalbarsareadded,andthenthetiesarespacedoutasrequiredbytheplacingplans.Allintersectionsarewiredtogethertomaketheassemblyrigidsothatitmaybehoistedandsetasaunit.Figure725showsatypicalcolumntieassembly.

Afterthecolumnisraised,itistiedtothedowelsorreinforcingsteelcarriedupfrombelow.Thisholdsitfirmlyinpositionatthebase.Thecolumnformiserectedandthereinforcingsteelistiedtothecolumnformat5foot(4.5m)intervals,asshowninfigure726.

Theuseofmetalsupportstoholdbeamreinforcingsteelinpositionisshowninfigure78.Notethepositionofthebeambolster.Thestirrupsaretiedtothemainreinforcingsteelwithasnaptie.Whereverpossibleyoushouldassemblethestirrupsandmainreinforcingsteeloutsidetheformandthenplacetheassembledunitinposition.Precastconcreteblocks,asshowninfigure727,maybesubstitutedformetalsupports.

Thehorizontalandverticalbarsarewiredsecurelytoeachotheratsufficientlyfrequentintervalstomakearigidmat.Tyingisrequiredateverysecondorthirdintersection,dependinguponthesizeandspacingofbars,butwithnotlessthanthreetiestoanyonebar,and,inanycase,notmorethan4to6feetapartineitherdirection.

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Figure724.Steelinplaceinafloorslab.

Figure725.Columnassembly.

Figure726.Methodofholdingcolumnsteelinplaininformwork.

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Figure727.Steelinplaceinafooting.

Figure728.Steelinplaceonawallform

Steelinplaceinawallisshowninfigure728.ThewoodblockisremovedwhentheformhasbeenfilleduptotheleveloftheblockForhighwalls,tiesinbetweenthetopandbottomshouldbeused.

Steelisplacedinfootingsverymuchasitisplacedinfloorslabs.Stones,ratherthansteelsupports,maybeusedtosupportthesteelattheproperdistanceabovethesubgrade.Steelmatsinsmallfootingsaregenerallypreassembledandplacedaftertheformshavebeenset.Atypicalarrangementisshowninfigure727.Steelmatsinlargefootingsareconstructedinplace.

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