Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Concrete Code Interpretation

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Thomas,

I am going to disagree with you some.  Section 10.5.4 is NOT aimed at
a slab-on-grade that "only people walk on".  ACI 318 DOES NOT apply at all
to typical slabs-on-grade with some very limited exceptions in chapter 21.

Take a look at the commentary for section 10.5.4.  It specifically states
that section 10.5.4 applies to structural slabs-on-grade that DO transfer
vertical loads from other parts of the of the structure to soil.  It
further states that mat foundations and "other slabs that help support the
structure vertically should meet the requirements of this section."  Thus,
it would appear that the intent of this section is for flexural members
that also happen to be supported by soil, such as mat foundations, spread
footings, strip footings, grade beams (somewhat debatable admittedly),
etc., BUT not your typical slab-on-grade (also take a look at section
1.1.6 of ACI 318 for this issue).

HTH,

Scott
Ypsilanti, MI

On Thu, 26 Sep 2002 THunt(--nospam--at)absconsulting.com wrote:

> Jim,
>
> I am not sure your interpretation of the code is quite correct.  The
> 200bd/fy requirement can be easily derived and is the minimum amount of
> rebar that can resist the equivalent moment capacity of a plain
> (non-reinforced) section and applies to all moment resisting elements.
> Anything less and you can have a sudden failure as your concrete is loaded
> and begins to crack.
>
> The following sections are tweaks and exceptions to the above rule for
> specific applications.  Section 10.5.3 give you a slight break if you have
> a large cross section due to other than structural requirements (extra
> mass for buoyancy, etc).  Section 10.5.4 gives a break if you have a slab
> on grade that does not transmit vertical loads from other parts of the
> structure to the soil.  The feeling being that since the slab is on grade
> if it fails it is not going anywhere like the second floor of a parking
> structure might.  ACI has always had a rather weak interpretation of
> "structural slabs" and "footings".  To them a footing is a blob of
> concrete under a column with minimum or no moment and a structural slab on
> grade is something only people walk on.  I am being a little facetious but
> you need to look close at the types of loads applied to the slab and the
> level of shear and moment developed from those loads.
>
> Thomas Hunt, S.E.
> ABS Consulting
>
>
>
>
>
> "Lutz, James" <JLUTZ(--nospam--at)earthtech.com>
> 09/25/2002 05:23 PM
> Please respond to seaint
>
>
>         To:     seaint(--nospam--at)seaint.org
>         cc:
>         Subject:        Concrete Code Interpretation
>
>
> In ACI-318, section 10.5, if flexural steel ratio provided is less than
> 200/fy, you can only use 75% of the computed moment capacity. However, in
> paragraph 10.5.4, a lower minimum steel ratio is provided for slabs and
> footings per section 7.12. My question is this, can you ignore the 200/fy
> requirement and still use the full computed moment capacity for a slab on
> grade as long as you meet the minimums in 7.12? I am reviewing an
> existing,
> lightly-reinforced thick concrete pad for possible mounting of some heavy
> equipment. It computes if I can avoid taking the discount for the low
> steel
> ratio.
>
> Jim Lutz, P.E., S.E.
> Earth Tech, Inc.
>
> 10800 NE 8th Street - 7th Floor
> Bellevue, WA 98004
> (425) 455-9494
> (425) 453-9470 FAX
>
>
>
> ******* ****** ******* ******** ******* ******* ******* ***
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
> *
> *   This email was sent to you via Structural Engineers
> *   Association of Southern California (SEAOSC) server. To
> *   subscribe (no fee) or UnSubscribe, please go to:
> *
> *   http://www.seaint.org/sealist1.asp
> *
> *   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
> *   send to the list is public domain and may be re-posted
> *   without your permission. Make sure you visit our web
> *   site at: http://www.seaint.org
> ******* ****** ****** ****** ******* ****** ****** ********
>
>
>



******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********