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

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-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com] 
Sent: Saturday, May 28, 2005 4:16 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: IBC Special inspection for Slab-on-Grade supporting HVAC
unit.

Actually, I don't think the "environment" is why 318 does not cover
non-structural slabs on grade.

-----/Original Message-----

I didn't say it was "why." I said the unique environment of the SOG may
be one reason ACI 318 doesn't cover it.

After all, if it were so "open and shut" as to why, this would not be
one of the perennial subjects on SEAINT, along with ASD vs. LRFD,
politics and religion (in that order). 

> If the differences were only based on the environment, the code
> could be written to accommodate such differences. 

It IS written to accommodate environmental differences--but it purposely
excludes SOGs nonetheless.

There are doubtless many reasons why this is, among them the safety
aspects which you mention. In the end, I think the reason comes down to,
as my professor said, "majority rules." The majority of structural
engineers don't see why ACI 318 ought to cover SOGs.

Then they turn around and form, e.g., Committee 360.

SOGs are important, including to structural engineers. But they simply
aren't subject to the same criteria as "structural concrete elements"
covered by ACI 318, by acclamation.

FWIW, Boyd Ringo, the guy I quoted regarding the waiver of the 3" clear
cover requirements for SOGs, was the chairman of ACI Committee 360.

Also, not all slabs on grade are on vapor retarders, the prepared
surface will likely still have more variation than a formed surface, and
workers may still step on the rebar while placing concrete, depressing
it further towards the ground surface.  Thus, I still question the idea
of reducing concrete cover over rebar just because the concrete element
is not code governed - although I do think that an argument can be made
to reduce cover a little where a vapor retarder is used. 

William C. Sherman, PE
(Bill Sherman)
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

-----Original Message-----
From: Polhemus, Bill [mailto:bill.polhemus(--nospam--at)tyson.com] 
Sent: Saturday, May 28, 2005 1:16 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: IBC Special inspection for Slab-on-Grade supporting HVAC
unit.

-----Original Message-----
From: Sherman, William [mailto:ShermanWC(--nospam--at)cdm.com]
Sent: Saturday, May 28, 2005 2:05 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: IBC Special inspection for Slab-on-Grade supporting HVAC
unit.

I've never understood this argument - how does the rebar know it's in a
slab on grade vs a structural foundation? Why does corrosion only attack
bars in structural foundations but not slabs on grade? 

-----Original Message-----

The notion here is that, unlike say a footing cast against earth, with a
SOG you are going to have a prepared subgrade. Typically, you will have
a vapor retarder of some kind underneath the slab. You are NOT nearly as
likely to have moisture migration to anywhere near the extent as you
would a "structural" foundation.

These are likely some of the reasons that SOGs are not covered by ACI
318. The assumptions as to the environment are very different.


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