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RE: IBC Special inspection for Slab-on-Grade supporting HVAC unit.

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A slab-on-grade is generally NOT a structural stab.  I typically refer to these slabs as "indoor paving", wearing surfaces that are almost entirely dependant on the subgrade for strength and stiffness.  Exceptions might arguably include stiffened slabs-on-grade designed to resist differential movement, and certain industrial slabs designed for specific wheel loads or other significant concentrated loads.
A slab-on-air is always a structural slab.
You might consider this simple rule-of-thumb:  If you design the slab to resist loads in shear and flexure, it is structural.  Otherwise, it is not.
Stan R. Caldwell, P.E.
Dallas, Texas
Protons have mass? I didn't even know they were Catholic!

From: Elias Hahn [mailto:ehahn(--nospam--at)]
Sent: Friday, May 27, 2005 2:59 PM
To: seaint(--nospam--at)
Subject: RE: IBC Special inspection for Slab-on-Grade supporting HVAC unit.

I tend to agree, but I can’t find anything to cite.  There are only four exceptions given in the IBC – Isolated spread footings (under 3 stories), Continuos footings (some requirements), “non-structural slabs supported directly on the ground…” and some foundation walls.


So, my follow-up question – what differentiates a structural slab and a non-structural slab?