Minimum Shear and Torsion Reinf per ACI 318-11
Minimum Shear and Torsion Reinf per ACI 318-11
(OP)
I have a condition where I need to provide minimum shear steel in a beam, and I also need to provide shear steel for torsion. The amount of steel I need to provide for torsion is greater than the 50*bw*s/fy minimum. I believe that I am therefore covered for the minimum shear steel as well per 11.5.5.2. Would you agree?






RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
Since the torsion and shear share the same reinforcing, you need to make sure you have enough to resist both simultaneously. Regardless of individual levels. At least that is my opinion.
RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
The issue I see is once the torsion sets in (you obviously have an appreciable amount of it) the section will crack, the torsion failure cracks are extremely similar to shear cracks and therefore the available Vc goes out the window in my mind.
The force in your stirrups would be a sum of the torsion and shear stress on one leg and a difference of the stresses on the other leg. Therefore your reinforcing has to be capable of taking T and V/2 in a single leg. Can yours do that?
Maybe I'm being over-conservative... wouldn't be the first time.
RE: Minimum Shear and Torsion Reinf per ACI 318-11
then added them together....This might be conservative but I'm not sure if ACI ever comments on this.
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RE: Minimum Shear and Torsion Reinf per ACI 318-11
If you wanted to trim down on the total reinforcing you could determine the reinforcing required to resist both your torsional and shear stresses and as long as that required amount is more than the minimums than I think it's ok.
RE: Minimum Shear and Torsion Reinf per ACI 318-11
I decided to just provide the minimum for shear plus that required for torsion. I think 318 would let me just provide that steel required for torsion, but it feels wrong. When in doubt throw in some more steel.
RE: Minimum Shear and Torsion Reinf per ACI 318-11
I would probably start by determining the torsion spacing and size, then tighten the spacing up to some multiple of 4" or 6". Then recheck for the combined stresses.
RE: Minimum Shear and Torsion Reinf per ACI 318-11
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RE: Minimum Shear and Torsion Reinf per ACI 318-11
RE: Minimum Shear and Torsion Reinf per ACI 318-11
1) As you've identified, torsion is really just additional shear, differently distributed.
2) The aims of the minimum steel requirements, as stated in the commentary, have nothing to do with resisting a particular load. So there's little cause to suppose that additional load equates to additional minimum steel.
Given the spirit of the minimum steel provisions, I could imagine a case where neither the shear nor torsion demand, considered separately, warranted minimum steel but the combination of the two would.
This seems like a good thread for TXStructual. Hopefully he surfaces.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.