Placing and Tying Reinforcing Steel
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Order this information in Print Order this information on CDROM Download in PDF Format Click here to make tpub.com your Home Page Page Title: PLACING AND TYING REINFORCING STEEL Back | Up | Next tpub.com Updates Search Web www.tpub.com Home Information Categories .... Administration Advancement Aerographer Automotive Aviation Combat Construction Diving Draftsman Engineering Electronics Food and Cooking Math Medical Music Nuclear Fundamentals Photography Religion USMC Products Educational CDROM's Printed Manuals Downloadable Books PLACING AND TYING REINFORCING STEEL Before you place reinforcing steel in forms, all form oiling should be completed. Oil on reinforcing bars should be avoided because it reduces the bond between the bars and the concrete. Use a piece of burlap to remove rust, mill scale, grease, mud, or other foreign matter from the bars. A light film of rust or mill scale is not objectionable. Bars are marked to show where they will fit. You may work according to either one of the two mostused systems for marking bars; however, the system you use should agree with the marking system which appears on the engineering or assembly drawings. The two marking systems used are as follows: 1. All bars in one type of member are given the mark of that member. This system is used for column bars, beam bars, footing bars, and so on. 2. The bars are marked in greater detail. These marks show exactly where the bar is to be placed. In addition to the type member (that is, beam (B), wall (W), column (C), and so on), the marks show the floor on which the bars are to be placed and the size and individual number of each particular bar. Instead of showing the bar size by its diameter measurement , the mark shows the bar size in code by eighths. The examples shown below show the second type of marking system. 213805 2 = second floor B = beam member 8 = 8/8 or 1 inch (2.5 cm)square bar 05 = part of the second floor plan designated by the number 5 2130605 2 = second floor B = beam member 06 = 6/8 or 3/4inch (1.9 cm)round bar 05 = part of second floor plan designated by the number 5 Tie wire is used to hold rebar in place to ensure that when concrete is placed the bars do not shift out of position. Sixteen gauge wire is used to tie Table 76.Multishearing reinforcing bars. About 12 pounds (5.4 kg) of wire is required to tie an average ton (0.9 tome) of bars. NOTE: Tie wire adds nothing to the strength of the steel. A number of different types of ties can be used with reinforcing bars; some are more effective than others. Figure 717 shows six types of ties that are identified below according to the letters of the alphabet used to show individual ties. Fast Setting Mortar Ideal for use in high traffic areas where quick repair is critical!
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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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