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RE: Minimum steel in slabs on ground

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The construction quality in many of the non-industrial and non-commercial jobs leaves much to be desired. Typically, a WWF or rebar grid is laid on the soil, concrete placed and the rebar grid is lifted from a few points. The final location of rebar is anybody's guess. Unfortunately, this practice is followed at some industrial sites as well!
That said, reinforced or unreinforced 4" slab or even a 2" slab (used in side walks) has a place, if one can live with periodic maintenance problems.

Harold Sprague <spraguehope(--nospam--at)> wrote:
Check the rebar cover for a 4" slab. That is where you can run into 

Harold Sprague

>From: "Ed Tornberg" 
>Subject: RE: Minimum steel in slabs on ground
>Date: Fri, 15 Oct 2004 08:48:04 -0700
>I too find the PCA vs ACI vs WRI vs etc. methods "difficult" to sort
>out. The only conclusion I can make is that slab design is an "art".
>Well, no, it really is a science, but it borders on art because there
>are nearly infinite variables involved in determining whether the slab's
>cracking (cracking is when and how, not if) will be adverse enough to
>irritate the owner.
>Why do the design manuals shy away from addressing the classic 4" slab
>that seems to be poured quite often? I know they're really interested
>in rack loading, wheel loading, etc. for industrial use, but for your
>standard office/light commercial slab that the contractor wants to do as
>4", the manuals virtually ignore it. Example: ACI 360 Table 9.9 for
>joints for plain slabs (which happens to be a PCA table) - the minimum
>slab thickness is 5". If we as engineers allow a 4" slab, have we
>violated something?
>Ed Tornberg
>Tornberg Consulting, LLC
>-----Original Message-----
>From: Jim Wilson [mailto:wilsonengineers(--nospam--at)]
>Sent: Thursday, October 14, 2004 6:31 PM
>To: seaint(--nospam--at)
>Subject: Re: Minimum steel in slabs on ground
>Thanks for remembering Gail. I found this buried in the old sent items
>folder, so here it is.
>I just received my copy of PCA's "Designing Floor Slabs on Grade"
>thinking it would resolve some floor slab design questions. But it
>brought up even more questions about minimum steel requirements.
>They present three different methods for determining minimum steel:
>'subgrade drag' (which has been discussed here before) which nets around
>.4% - .5% minimum steel, 'temperature method' and 'equivalent strength
>method'. When running numbers for the second two methods, I come up
>with anywhere from 4%-6% steel based on area (assuming a moderate
>temperature differential during exposure). These numbers seem to be
>excessively high, especially when compared to the first method and even
>a 1% minimum by rule of thumb.
>The PCA notes for a Type B slab with shrinkage control reinforcement say
>these slabs usually take steel designed by the subgrade drag equation.
>Yet the notes under the 'temperature method' section say it is "more
>desirable" than the subgrade drag method.
>These comments don't exactly conflict with themselves, but they sure
>don't point the reader in a clear direction.
>Any better thoughts on these last two methods? Are the units in the
>book off? I am inclined to stick with the 1% minimum and be happy.
>From what I've seen, even 15" airport slabs should only require a
>moderate weight mesh...
>Jim Wilson
>Stroudsburg, PA
> _____
>Do you Yahoo!?
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