punching shear capacity of piled slabs

[oneintheeye]

checking punching shear of piles, does anyone use the two layers of steel as the area of rebar? I have always used the one layer (in tension zone). seems to be a bit of disagreement in speaking to people on whether 2 layers can be used. i.e. have same rc in top and bottom of slab continuing over pile head.

 

[apsix]

I can see some logic but I'm not convinced yet, if the definition of shear failure is when cracking first commences, rather than at complete separation.

 

[oneintheeye]

thats one reason i'm not convinced since if it cracks and 'puches' through then the slab has already failed and the top reinforcent is out of the equation anyway, the only thing holding the slab together would be the bottom steel. Then again if shear is enhanced by the doweling nature of the rebar then surely the concrete is affected by both the top and bottom?