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

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From: Elias Hahn [mailto:ehahn(--nospam--at)]
Sent: Tuesday, May 31, 2005 12:49 PM
To: seaint(--nospam--at)
Subject: RE: IBC Special inspection for Slab-on-Grade supporting HVAC unit.

I’m sorry, I didn’t realize my second question was a stupid one.  I got an answer to it, although I did get insulted (AWESOME!  Makes me want to continue to use this list to learn!).  I still have nothing to cite that says “ A slab on grade is nonstructural”, and since this was a little bit of an argument, it’s better to have literature to site than someones word, especially the word of someone who calls me a code monkey.


Anyways, thanks to those who helped, I appreciated that. 



Though Gail expounded on it in her usual (abrasive) way, she is nevertheless correct.


IN GENERAL, a SOG is NOT a structural element. (You may take "in general" to mean on the order of 95% of the time--and most of the rest, many would argue, are not even SOGs at all).


As ACI puts it (paraphrasing here), "the SOG does not transmit loads laterally to any other portion of the structure," meaning (I've always assumed) that nothing "spans;" that there is no real "load path" to consider.


However, there are exceptions, or at least elements that are neither fish nor fowl. And many of them occur with some regularity, such as PT SOGs which are prevalent in the Southwest.


I contend that HEAVILY LOADED SOGs, such as you encounter in the design of storage facilities such as warehouses, or in industrial environments, are in that "in between" region. Certainly, when you have appreciable moments induced in a slab such that you can effectively cut down on the slab thickness by adding structurally active reinforcing, I would contend you are "transmitting forces laterally to other parts of the structure."


This is the approach that Ringo and Anderson describe in their manual "Designing Floor Slabs On Grade," the kind of publication that I find to be worth gold. I have lots of textbooks on various subjects, such as hot-rolled and cold-formed steel design, designing for dynamic loading, etc. But all too few examples exist of "cookbook"-style design guides that give you the benefit of an experienced engineer's insights into problems that are not typically encountered in engineering school, but are ever-present in the workplace (and thus get "done wrong" all too often).


Instead of working so hard to "overcategorize," so we can breathe a sigh of relief in the mistaken belief that someone ("code monkeys," code officials, et al) has done the thinking for us so we don't have to, we ought to share our own insights into things we've done, and seen, and experienced both positive and negative.


That's what I get most out of SEAINT. I stay here because of folks like Harold Sprague and Dennis Wish and Bill Allen and so many others--to numerous to mention--who have very often solved a problem for me that I didn't even know I had (a scarey thought, but hey, it happens).

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