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Re: thin structural slab design

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It fails in punching shear, ductility and deflection and there is nothing you can do to make it work in this configuration.. I have never seen a 2way column supported flat slab with a single layer of reinforcement. It just does not work, let alone the fact that the slab is far too thin even if it was reinforced at both faces.

You can make a 7" slab reinforced on both faces work for everything but punching shear. But normal design rules preclude the use of punching shear reinforcement in slabs shallower than 8". You might be able to justify a structural steel shear head in the 7" slabs.

At 07:01 AM 8/07/2006, you wrote:
I am designing a thin elevated slab for an entry area on a condo project.  The slab is six bays long (17? each) by one bay wide (13?).  Due to some restrictions on thickness, I started analyzing a 5? thick slab with one mat of rebar bearing on 8? diameter concrete piers.  Punching shear is giving me fits.  Is there any merit to simply adding some additional horizontal rebar over the columns and calculating shear friction to resist the punching shear?  In a 5? slab and with the construction budget, hoops or stud rails are probably not an option.
Bruce D. Holcomb, PE, SE
Butler, Rosenbury & Partners

Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd. (ABN 84 003 163 586)
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