I agree hokie, he is probably referring to tying the rebar. For a slab typically the top mat gets every third, known as the hi-rise tie. Bottom mat might even see less...Most people that are not in the loop, or are not ironworkers, try to push for every other bar...
When you say tie are you referring to shear reinforcement?
ACI318-08 Cl.11.4.6.1 says 'A minimum area of shear reinforcement Av,min shall be provided in all reinforced concrete flexural members (prestressed and nonprestressed) where Vu exceed 0.5*?*Vc'. (Vu=Shear force; Vc=Shear capacity of the concrete)
Very similarly, AS3600-09 Cl.8.2.5 says 'Where V*<=0.5*?*Vc, no shear reinforcement is required, except where the overall depth of the beams exceeds 750mm. (V*=Shear force; Vc=Shear capacity of concrete).
Typically the beam shear or one-way shear in a slab is very low and peaks in regions around the supports which will have thickenings to satisfy punching shear requirements. You can read a recent thread about one-way shear and two-way shear in a recent thread thread507-268971.
Close ties are provided in torsion strips as punching shear reinforcement. Personally, I have never seen this done and I have read some literature explaining why this reinforcement can be in-effective against punching shear.
Only once have I seen shear reinforcement detailed in a slab for one-way shear at the face of a column. It was for a transfer slab and my opinion was that the shear reinforcement was not necessary.
By Tie i mean tying rebars and required maximum spacing between tying of rebar. Sorry for not explaining the term clearly. Actually i have rebar contractor tying rebars at only two locations at end no matter how long is rebar and even at one end for 5 to 8 ft long bar
Thanks
Your contractor's method is definitely not adequate, and he knows it. Your country should have a reinforcement practice manual to cover this issue. The bars will certainly not stay where intended during placement by big-footed concreters unless both top and bottom bars are adequately tied.
Wire ties are intended to prevent displacement prior to and during concrete placement. If you step on a bar, and it deflects, but then returns to position, you are OK.
Frequency of tying is dependent on bar size and support locations. If the mat is placed on carrier (bury) bars, which are supported on chairs, then ties can be very infrequent.
As a rule, tying every 4th or 5th intersection is a good place to start. Stagger ties on a diagonal. Ties on #5 bars spaced at 12" might be 4 feet apart, which is usually fine.
John Turner CSP PE
CRSI Greater Southwestern Regional Manager
I agree with TXStructural, while I said every third is probably what should be done. If you are constructing a mat on standees and carry bars and space the the carry bars farther apart you sometimes have to tie more to make it more rigid. The contractor and thus the inspector also has to see how the concrete is being placed. If their will be pump hose dragged on the mat, be sure to have enough ties or the hose will be sure to break the few ties that are there. Some agencies are specific about their requirements, NJDOT spec requires every intersection for bars spaced at 12", every other for anything less.
We occasionally run into agencies that require tying every intersection, and the only explanation is that they want to pay more for the work. There is no need for such a waste of time and money. But if this is an agency's written requirement, the bidders should have known in advance and included that cost in the bid.
