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RE: Minimum area of steel in concrete column

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Mark:

If I recall correctly, the minimum steel ratio for compression members
does not directly apply to caissons.  The rationale for this is that
caissons will already have some confinement from the earth that surrounds
them.  In addition, section 1.1.5 states that ACI 318 does not govern the
design of concrete piles, drilled piers, and caissons...at least the
portion embedded in the ground...except in high seismic zones (i.e.
provisions in chapter 21).

This does not mean that you cannot use the columns provisions at a
reasonable first starting point.  But this assumes that you need steel at
all.  If I recall correctly, many drilled piers only have steel in the
first third or so (in low seismic zones) and some may not have any steel
at all.

HTH,

Scott
Adrian, MI


On Fri, 15 Oct 2004, Eli Grassley wrote:

> Mark -
>
> I agree completely with the first two parts of your question.  Long live
> decent logic!  I'm curious what other list-ers think.  I don't know about
> caissons.
>
> Eli Grassley
> PSM Engineers
> Seattle
>
>
> -----Original Message-----
> From: Mark L. Puccio [mailto:mpuccio(--nospam--at)ramaker.com]
> Sent: Friday, October 15, 2004 12:13 PM
> To: Seaint List (E-mail)
> Subject: Minimum area of steel in concrete column
>
> I have a 3part question to settle some differences of opinion in our office
> regarding the minimum area of steel required for a concrete column that is
> not in a high seismic region.
>
> Section 10.9.1 states that the area of longitudinal reinforcement shall be
> not less than 1% of the gross area. Section 10.8.4 states it shall be
> permitted to base the minimum reinforcement and strength on a reduced
> effective area not less than one-half the total area.
>
> My interpretation is that you can design a column with a minimum area of
> steel of 1% and if (and only if) that works you can increase the total area
> of concrete up to twice the "design" area without adding anymore area of
> steel. So if 1% doesn't work (for the original design area) you have to
> increase the steel even if using that area and increasing your d gives you
> the strength required. My argument here is that you can't simply design a
> column based on 0.5% steel.  Correct?
>
> The second part of this question is with regard to the commentary for
> 10.8.4, it states ...simply add concrete around the designed section... I
> would say it is okay to put the steel you designed for the smaller column
> out toward the larger column perimeter. Do you all agree?
>
> Third question do all of these requirements apply to caissons.
>
> Thanks in advance
>
> Mark L. Puccio P.E.,S.E.
>
>
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