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Re: Foundation Min. reinforcement

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Ed,

You are correct in that if you provide 1/3 more steel than required by
analysis then the minimum steel for flexural contained in 10.5.1 of ACI
318-99 (the greater of 3sqrt(f'c)*bw*d/fy or 200*bw*d/fy) or 10.5.2 of ACI
318-99 (similar to 10.5.2) need be provided.  This is provision is contain
in section 10.5.3 of ACI 318-99.

Additionally, as others have pointed out, there is section 10.5.4 of ACI
318-99.  This basically states that for structural slabs (i.e. supported
slabs not slabs-on-grade) and footings (i.e. spread footings) only need to
have minimum steel as specified in section 7.12 of the ACI code
(temperature steel).  This would not include slabs-on-grade since ACI 318
does not apply to slabs-on-grade except for a few special seismic
conditions (see section 1.1.6 of the ACI 318-99).  This also would not
include a grade beam, IMHO (but not a strip footing).  As others have
pointed out, a grade beam will either be to laterally tie footings
together for lateral loads, which would means that it is basically going
to be acting like a column, or it will be a flexural beam (i.e. loaded
flexurally and maybe axially) that happens to be sitting on the soil.
OTOH, a strip footing should have next to nothing in bending along its
length unless you have wide variations in soils conditions, but
potentially some serious bending perpendicular to its length depending on
its width.

HTH,

Scott
Ypsilanti, MI


On Thu, 14 Mar 2002, Ed Najjarine wrote:

> First, thank you all for your informative response, For Flexural Members,
> it's stated in the 97 UBC page 2-117, Sec. 1910.5.3 that as long as you
> provide 30% more Tensile reinforcement than required( which in my case a
> whole lot less than the minimum 200/Fy), the minimum reinforcement
> requirement does not apply. Any comments?
>
> Ed Najjarine, P.E.
>
>
>
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