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

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Bil-

Thanks for doing a much better job of making the point I had in mind.

btw what is the client's desired service life of this slab?

Bob

On 5/28/05, Polhemus, Bill <bill.polhemus(--nospam--at)tyson.com> wrote:
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
> Sent: Friday, May 27, 2005 10:26 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: IBC Special inspection for Slab-on-Grade supporting HVAC
> unit.
> 
> My point was that a SOG with wheel loads is still technically not a
> structural slab (which you seem to agree with).  It _STILL_ needs to be
> designed properly.
> 
> -----Original Message-----
> 
> 'Sfunny this thread should crop up now. It so happens I've been
> designing a SOG for parked chicken trailers. I have the weight data for
> the typical trailer, and I note that the load on the front legs (when
> the tractor is disengaged, props the trailer up in front) is really
> pretty large.
> 
> I typically refer to Boyd Ringo's "Designing Floor Slabs on Grade" for
> this kind of thing. Using the "modified" PCA Method that Ringo
> describes, I come up with a required minimum slab thickness of a little
> over nine inches.
> 
> Ringo goes further to describe a design method that turns the empirical
> PCA data into design moments for which you can derive the required
> reinforcement using the flexural design procedure of ACI 318.
> 
> In my case I came up with an "optimum" design of 8 inch slab thickness
> with #5 bars @ 12" Top and Bottom. (Interesting also to note that Ringo
> recommends a bottom bar clear cover of no more than an inch or so; his
> rationale is that the 3" clear cover requirements of ACI 318 don't apply
> because SOGs aren't covered by ACI 318).
> 
> When I mentioned this to my "boss," he objected. "We would only use a
> single layer of rebar, say #4 @ 16" for an 8" slab!" I pointed out that
> my design would not require expansion joints, because the reinforcement
> would handle stresses due to movement, and he still objected. "Just put
> in the joints, it's cheaper."
> 
> Well, he's right in one sense, because it IS cheaper. But by how much?
> 
> Using the current R. S. Means "Building Construction Cost Data", I
> calculated that it costs about $3,000 more for this 2,500 S.F.
> slab--$1.20/S.F. added cost--to do it my way. But I insist that the slab
> will perform far better.
> 
> This area is expected to be "washed down" pretty frequently, and we are
> even designing in trench drains going to a commercial septic tank to
> settle out fecal solids, etc. To my mind, this is NOT an environment
> where you want joints and "purposely cracked" concrete.
> 
> So we've agreed to disagree--he's the client and he'll get his way, but
> to me this is being penny-wise and pound-foolish.
> 
> In the end, "structural" is in the eye of the beholder. To me, this is a
> structural slab because of the service and the way you want (or rather,
> "I want") the slab to perform. To him it's just a plain ol' SOG, no
> different than a highway pavement. But they don't frequently wash down
> highway pavements to get rid of fecal wastes into a trench drain system
> ('round here, buzzards and crows do all the waste disposal for highway
> pavements).
> 
> 
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