Reinforced SOG CCJ Spacing
Reinforced SOG CCJ Spacing
(OP)
All,
I need to increase to joint spacing for a reinforced SOG and not follow Table 9.9 from ACI 360 for plain concrete. Has anyone used the drag formula (eq. 6-3 from ACI 360) to back into a joint spacing? This procedure is noted in Section 9.9 but was wondering how others look at this situation.
TIA
I need to increase to joint spacing for a reinforced SOG and not follow Table 9.9 from ACI 360 for plain concrete. Has anyone used the drag formula (eq. 6-3 from ACI 360) to back into a joint spacing? This procedure is noted in Section 9.9 but was wondering how others look at this situation.
TIA






RE: Reinforced SOG CCJ Spacing
RE: Reinforced SOG CCJ Spacing
RE: Reinforced SOG CCJ Spacing
where As is the amount of reinforcing in sq. in. per lin. foot slab width
F = coefficient of friction between base and slab (typically 1.5)
L = slab length between free ends, feet, in the direction of the steel
w = weight of the concrete slab, psf (usually 12.5 psf per inch of thickness)
fs = allowable steel stress, psi 24,000 psi for 60 grade steel
RE: Reinforced SOG CCJ Spacing
RE: Reinforced SOG CCJ Spacing
RE: Reinforced SOG CCJ Spacing
RE: Reinforced SOG CCJ Spacing
If I remember right, the subgrade drag equation does not result in enough steel to permit increasing joint spacing. If you do try to increase the joint spacing by using reinforcing, you won't prevent random cracking in between control joints. The steel will just hold the cracks that do develop more or less tightly together. More tightly if you have a lot of steel.
Regarding control joints not functioning as intended, this sounds like they are being cut too late. We use the Soff-Cut saw, and they can be on the slab cutting about 2 hours after finishing is completed. That way, the slab is cut while still green and before random cracks start to develop. We have had excellent results with this saw.
RE: Reinforced SOG CCJ Spacing
At your sawed crack control joints are you allowing all the reinforcing to run across the joint or do you cut every other bar or use some other procedure. I've seen it both ways and was wondering if you got onto the slab early enough then precutting bars would be eliminated. Any thought?
STR04
RE: Reinforced SOG CCJ Spacing
However, sometimes we do put rebar in if there are unusual conditions or heavy loads, or whatever. In these conditions, we don't have any rebar going across the joint. That way, each slab panel has less restraint to shrinkage, and therefore, will be less likely to crack. In my opinion having all of the rebar go thru the joint renders the joint ineffective. If for structural reasons you do want some continuity between the slab panels and you can tolerate some cracking, then I would go with having every other bar go through. That way, you get at least partial benefit because you still have a plane of weakness where the shrinkage forces can be relieved.
You can also reduce the probability for the slab to have random cracks by using the largest practical coarse aggregate. We also use a w/cm of 0.45 max, and frequently use fly ash or ground granulated blast furnace slag, and have had good results.