SOG Punching Shear

Is there an accurate method for figuring punching shear for slabs on grade?? I have a few concrete slab books "Concrete Floors on Ground", "Slab Thickness...", etc.; but I haven't seen an analysis procudere for checking this.

The problem seems to stem from the fact that "punching" is dependant on the subgrade below the slab. To truely get "punching" through of the slab the subgrade below has to complete settle out. The key, as I see it, is to determine the amount of settlement AND at what point the settlement becomes excessive.

I do a lot of work with SOG design and analysis and I'ld like to find a more "engineered" method then what is in my current books. Right now I feel like my solutions are overly-cautious....which isn't necessarily bad.

Any thoughts are appreciated.

 

[dlew]

Pouring,

I believe that the punching shear in a slab on grade could be analized in the same way we do in spread footings. Instead of the column base plate or pedestal, I would use the footprint of the concentrated load.

Normally, unless the slab is very thin or the concentrated load very heavy, punching shear does not control the design of the slab. Generally the design is controlled by the bending stresses.

AEF

 

[suqlainUK]

I would tend to agree with dlew's assertions.
Punching shear check may be critical for a slab supporting high bay storage racking systems, or slabs with mezz columns......but the design approach for punching shear is the same for any slab, be it on grade, suspended , or for a pad base.

 

[DaveAtkins]

I agree with everyone, but I would advise using the punching shear formula for PLAIN (UNREINFORCED) concrete, in Section 22.5.4 of ACI 318-95 (unless your slab has at least minimum reinforcement per Code).

 

Thanks!! I know how to apply it in that case!!

FYI - I usually have to analyze adding equipment in buildings which get placed on SOG. Hence, the reason why I need to check punching shear (and one way shear when applicable).