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Punching shear on slab on grade

Punching shear on slab on grade

Punching shear on slab on grade

(OP)
Consider an existing, 4" thick, unreinforced slab on grade that must support a new concentrated load. I want to check punching shear with the equation Vc = 4*(sqrtf'c)*bo*d (base plate is square). My question is what do I use for d? The ACI code defines d in this case as the effective depth, but I'm assuming the slab is not reinforced. Because the slab is on grade, can I take d as the full depth? Any feedback would be much appreciated.

RE: Punching shear on slab on grade

RE: Punching shear on slab on grade

Well, technically ACI 318 requires a minimum thickness for footings which is more than 4" so your slab can't serve as a footing.

But if this is a minor loading, not part of a major load carrying column, then a check for punching shear might be referenced through the "Plain Concrete" section 22 of 318.

Short of that I'd use 0.8T to 0.6T to be conservative.
But with no reinforcing, I'd stick to what Chapter 22 of
ACI says.

RE: Punching shear on slab on grade

(OP)
Got it.  Equation (22-10) from ACI Chapter 22 is what I was looking for.  Good thing because the punching shear capacity I got from using the equations in Chapter 11 was adequate, and that would have been wrong in this case.  Thanks a lot!    

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