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Re: Minimum steel in slabs on ground

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Padmanabhan Rajendran wrote:

Exactly!
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. Rajendran

*/Harold Sprague <spraguehope(--nospam--at)hotmail.com>/* wrote:

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

    Regards,
    Harold Sprague


    >From: "Ed Tornberg"
    >Reply-To:
    >To:
    >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!?
    >Yahoo!
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Sure, if it's a sidewalk, you can "live with it."

But what if it is the floor slab to your $300,000 home?

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