Rebar Tips 2002

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JLC bull JULY 19

The steel reinforcing that we all knowas ldquorebarrdquo is a critical component of

quality concrete construction Byenabling concrete to resist bendingforces rebar allows concrete to be usedfor overhead spans like freewayoverpasses or multilevel parking garagesIn residential use rebar enables slenderconcrete foundation walls to resisthorizontal soil pressures and gives piersgrade beams and slabs the strength tosupport the weight of a home

Anyone whorsquos had to break out aconcrete structure knows that a slab orwall poured without steel is much easierto demolish than one with even a fewpieces of rebar Itrsquos no coincidence thatbomb shelters and missile silos are madeof steel-reinforced concrete It is steelreinforcing that makes concrete such avaluable and versatile building material

Rebar SpecsEngineers design strength into a

concrete structure by specifying a

certain size and grade of rebar placin specific ways Rebar specs are usuadetailed on the blueprints

Sizes Rebar comes in a rangediameters numbered 3 through 11 Tnumbers denote the diameter of the bin 18-inch increments Thus 3 bar38 inch in diameter 4 bar is 48 (or 1

inch 5 bar is 58 inch and so on Tsize most commonly used in residentconstruction is 4 though 5 and 6 bare used often in hillside constructi

(see ldquoHillside Foundationsrdquo 393) Reblarger than 6 will sometimes be fouin large retaining walls or in largdiameter deep piers but in residentwork these larger bars are rare Paslabs garage floors walkways podecks steps and simple landings aoften made with 3 bar The 38-inch sis also used in stirrups or cage ties whialso contain an assembly of larger b(see Figure 1 next page)

Grades Besides a variety of bdiameters rebar is graded in tw

REBAR TIPSby Greg Casorso

Reinforcing steel enables

concrete to resist bendingforces mdash but you have to

place it and tie it correctly

Cont ents Home Search Results



primary grade classifications commonknown as grade 40 and grade 60 Gra40 is more malleable and easier bend Grade 60 is stiffer and does nbend as easily Generally grade 40found in 3 and 4 bar and grade 60 5 and larger

Lengths When yoursquore orderirebar you should be aware that i

manufactured in standard lengthDepending on the mill itrsquos usualavailable in 20-foot 30-foot an60-foot lengths with 20-foot the mocommon So if you order prebent rebin an odd length the supplier has cut some off The remnants gcollected and recycled but you pay fthem anyway To cut your own costry to work in lengths that divievenly into 20 30 or 60 feet

Proper Use of Reinforcing Bar

To get the full benefit of steel inconcrete structure the rebar must handled and installed properly Awith any other material the corretechniques become a habit wiexperience

Handling Specs usually call frebar to be clean and free from rust practice the thin film of rust you oftsee on rebar isnrsquot a problem If tmaterial sits on the job site for four six weeks or so it will still be fine Wdonrsquot even cover it on the sitOccasionally however sandblastingrequired to clean the rust off rebar thhas been exposed for too long Rebthat is old and has rusted extensiveshould not be used

Keeping the rebar clean is a mocommon problem Mud and dirt othe steel will prevent the concrefrom bonding to it and reduce effectiveness Rebar can easily gmuddy as itrsquos dragged around a job siWe take care to keep the mud off it

Cutting To cut 5 or larger rebyou really need an oxygen acetylecutting torch (Figure 2) which yocan buy at welding supply stores torch also makes cutting smaller sizeasier) The torch costs about $35and then you have to rent bottles oxygen and acetylene Oxyacetyletorches are dangerous mdash anyowhorsquos handling one should be trainto use it properly

Rebar sizes 4 and smaller can both cut and bent with a cutterbend

JLC bull JULY 1994

Figure 1 For deepconcrete piers theauthor uses steel cagesmade from 3 rebarspirals with 5 rebar inthe middle The cageshown here will helpsupport the brickchimney in a

foundation

underpinning job

Figure 2 The author uses an oxyacetylene torch to cut large-diameter rebar (left) while 3 and4 can be cut and bent with a combination cutting and bending tool (right)




tool The tool is readily available atmost concrete supply stores also forabout $350

Bending We bend 3 and 4 bar onsite with the bending tool but thelarger sizes are practically impossible to

work on site I always order the largersizes bent by the supplier and deliveredto the site ready for installation Neverbend rebar by heating it with a torchmdash this makes the steel brittle and easyto break defeating its structuralpurpose of resisting flex

Placing Rebar has to be buried atleast 3 inches deep in the concreteunless otherwise specified Goodconcrete cover is essential mdash otherwisewater will get to the rebar rust thesteel and eventually cause failure To

hold rebar off the ground or away fromthe forms we use concrete spacerblocks called ldquodobiesrdquo (Figure 3)Dobies come in many sizes 1 inch2 inch 3 inch and larger Three-inchdobies are the most common because

3-inch concrete coverage is theindustry standardTying Rebar should be tied together

with tie wire at every intersection(Figure 4 next page) The wire iswrapped around the bars and twisted justlike the tie wrap on a loaf of bread Therebar should be held in place firmly andsecurely by the tie wire mdash on larger wallswe tie the rebar so securely that we canactually climb up the bars

Tie wire comes in rol ls or inbundles of precut lengths We like to

JLC bull JULY 19

Figure 3 Concrete ldquodobies are used tohold rebar off the ground or away from

forms ensuring adequate concrete coveragand preventing rust

Concrete has tremendous compressive strengthmdash anywhere from 3500 psi to 6000 psi But ithas almost no tensile strength mdash tension forcescan easily pull it apart Steel rebar on the otherhand is very strong in tension

When a sideways load is applied to a concreteretaining wall tension develops on the pressure-bearing side and compression on the side awayfrom the load Concrete readily resists thecompression while the steel carries the tensionand prevents the structure from breaking andtoppling

The retaining wall drawn here is from a job mycompany did recently The engineer called for 6 bar to be placed vertically on 6-inch centers3 inches from the pressure-bearing face of thewall tied to horizontal courses of 5 rebar every16 inches on-center to the top of the wallPrebent 10 bar provided the crucial link betweenthe wall and the spread footing below

In this case steel rebar not only provides thenecessary tensile strength for the pressure-bearingvertical face of the wall but it also provides vitaltensile strength at the joint between the wall andthe spread footing Without the continuous steerunning from footing to wall that joint would failcausing failure of the entire structure

Retaining walls should be designed byexperienced design professionals Each case isdifferent and there is no ldquocookbook solutionrdquothat works for all walls Also different engineerswill find different ways to solve the sameproblem The concrete contractor must place the

steel where the engineer says to (industrystandards allow a 14-inch tolerance for error) Ifyou put the steel in the wrong place yoursquoveentered lawsuit country

mdash GC

How Rebar Works in aRetaining Wall

The compressive strength of concrete and the tensile strength of steel worktogether to resist lateral soil pressures in this retaining wall




use the roll-type that comes on aspecial spool that can be worn on awork belt The spool convenientlydispenses the t ie wire as neededwithout tangles We tie the wire withspecial spring-loaded linesmanrsquos pliersthat gently open by themselvesmaking it easy to grasp wrap twistand cut

Installers who work with precutbundles of looped wire use a specialtool that twists the wire up with a fewsnaps of the wrist Irsquove found that thisis an efficient method if you have acresof slab to tie where there are a lot of intersections that are easy to get atBut the reel-and-pliers method is moreversatile for smaller jobs because itrsquosgood for working in tight spaces

Splicing Be sure to splice the rebaras specified by the engineer Forexample if you are using 4 bar andthe engineer calls for splices of 28 bardiameters then you know that youneed at least a 14-inch overlap whentwo bars are spliced together Theoverlap should be tied with wire in atleast two places

The pour When you place theconcrete make sure that it fills incompletely around the rebar and bondsto the steel tightly You should spray

release agents on the forms beforeplacing the rebar but donrsquot get anyrelease agent on the rebar or theconcrete wonrsquot bond to the steel as well

Use a mechanical vibrator to workthe concrete in and around the rebarPay special attention to corners where there is often lots of rebar Thevibrator works air out of the concrete

and allows a better concrete-to-rebbond But donrsquot rest the vibrator heon the rebar That causes the rebar pulsate and reduces the bond betwethe concrete and the rebar

Safety Exposed rebar ends are vedangerous There is a very real risk falling on the sharp steel A man wkilled recently in my area when htripped and fell from a grade beaform He didnrsquot fall from a height he just tripped and fell down andpiece of rebar punctured his heart

OSHA now requires that all rebends be covered with high-visibiliplastic safety caps (Figure 5) Thisone rule that I strongly support Itworth making the ef fort to trapeople to put those caps on and to

aware of the risk We take the caoff when the concrete gets poureand caps come off by accident toAt any given time there are probabsome exposed ends around I just tto stay continuously vigilant anmake sure my workers remember put the caps on and keep them on s

Greg Casorso is the owner of CasorConstruction in Lafayette Califspecializing in foundation constructiorepair and drainage

JLC bull JULY 1994

Figure 5 The exposed ends of rebar cancause fatal accidents OSHA regulations call

for rebar ends to be covered with high-visibility protective caps

Figure 4 The author ties the rebar at every intersection Precut wire can be bought in bundlesand twisted with a special swiveling tool (top right) but the authorrsquos crew prefers to use a pairof spring-loaded linesmanrsquos pliers and a roll of wire on a spool (right)




primary grade classifications commonknown as grade 40 and grade 60 Gra40 is more malleable and easier bend Grade 60 is stiffer and does nbend as easily Generally grade 40found in 3 and 4 bar and grade 60 5 and larger

Lengths When yoursquore orderirebar you should be aware that i

manufactured in standard lengthDepending on the mill itrsquos usualavailable in 20-foot 30-foot an60-foot lengths with 20-foot the mocommon So if you order prebent rebin an odd length the supplier has cut some off The remnants gcollected and recycled but you pay fthem anyway To cut your own costry to work in lengths that divievenly into 20 30 or 60 feet

Proper Use of Reinforcing Bar

To get the full benefit of steel inconcrete structure the rebar must handled and installed properly Awith any other material the corretechniques become a habit wiexperience

Handling Specs usually call frebar to be clean and free from rust practice the thin film of rust you oftsee on rebar isnrsquot a problem If tmaterial sits on the job site for four six weeks or so it will still be fine Wdonrsquot even cover it on the sitOccasionally however sandblastingrequired to clean the rust off rebar thhas been exposed for too long Rebthat is old and has rusted extensiveshould not be used

Keeping the rebar clean is a mocommon problem Mud and dirt othe steel will prevent the concrefrom bonding to it and reduce effectiveness Rebar can easily gmuddy as itrsquos dragged around a job siWe take care to keep the mud off it

Cutting To cut 5 or larger rebyou really need an oxygen acetylecutting torch (Figure 2) which yocan buy at welding supply stores torch also makes cutting smaller sizeasier) The torch costs about $35and then you have to rent bottles oxygen and acetylene Oxyacetyletorches are dangerous mdash anyowhorsquos handling one should be trainto use it properly

Rebar sizes 4 and smaller can both cut and bent with a cutterbend

JLC bull JULY 1994

Figure 1 For deepconcrete piers theauthor uses steel cagesmade from 3 rebarspirals with 5 rebar inthe middle The cageshown here will helpsupport the brickchimney in a

foundation

underpinning job

Figure 2 The author uses an oxyacetylene torch to cut large-diameter rebar (left) while 3 and4 can be cut and bent with a combination cutting and bending tool (right)












JLC bull JULY 19









mdash GC

















JLC bull JULY 1994















JLC bull JULY 19









mdash GC

















JLC bull JULY 1994


















JLC bull JULY 1994





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Rebar Tips 2002