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RE: Minimum steel in slabs on ground

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An interior slab cast over a vapor barrier over a smoothly compacted
base is neither "cast against... earth" nor even "exposed to weather",
interpreting the intent of the code commentary.  So I see no cover
problem with #3 or #4 bars EW in a 4" slab.  This is a code-compliant
opinion.  I welcome anyone's practical experience comments, of course.

Ed Tornberg
Tornberg Consulting, LLC
503-551-4165

-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com] 
Sent: Friday, October 15, 2004 10:26 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Minimum steel in slabs on ground

Check the rebar cover for a 4" slab.  That is where you can run into 
problems.

Regards,
Harold Sprague


>From: "Ed Tornberg" <etornberg(--nospam--at)comcast.net>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>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
>503-551-4165
>-----Original Message-----
>From: Jim Wilson [mailto:wilsonengineers(--nospam--at)yahoo.com]
>Sent: Thursday, October 14, 2004 6:31 PM
>To: seaint(--nospam--at)seaint.org
>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.
>
>Seaint,
>
>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...
>
>Thanks,
>Jim Wilson
>wilsonengineers(--nospam--at)yahoo.com
>Stroudsburg, PA
>   _____
>
>Do you Yahoo!?
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><http://us.rd.yahoo.com/mail_us/taglines/aac/*http:/promotions.yahoo.co
m
>/new_mail/static/ease.html>  Mail Address AutoComplete - You start. We
>finish.

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