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Re: Foundation Min. reinforcement

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Actually, I don't believe that is true.  Section 10.5.3 (the 1/3 higher by
analysis) still is an exception even for flexural members in special
moment frames...at least according to ACI 318-99.  Section 21.3.2.1
states:

"At any section of a flexural member, except as provided in 10.5.3, for
top as well as for bottom reinforcment, the amount of reinforcement shall
not be less than that given by Eq. (10-3) but not less than 200bw*d/fy,
and the reinforcement ratio (rho) shall not exceed 0.025.  At least two
bars shall be provided continuously both top and bottom"

This section is basically repeating the requirements of section 10.5.1 and
the exception permitted by section 10.5.3.

Now, all of this may have changed in 318-02...I haven't taken a close look
at it to see if anything in this area has changed.

HTH,

Scott
Ypsilanti, MI

On Fri, 15 Mar 2002, Syed A Masroor wrote:

> Ed,
> Scott is absolutely right however, 33% higher is not applicable to:
> Beams in  high seismic category
> In slabs/footings, where temp. reinforcement (0.0018bh) governs
> IMHO, minimum temperature reinforcement should also be required in beams where
> 33% higher value will still fall short of 0.0018bh. Such conditions are often
> encountered when architecture dictates larger beam sizes.
>
> S A Masroor
> Consulting Structural Engineer
> Karachi, Pakistan
>
>
> Scott Maxwell wrote:
>
> > 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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