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RE: Minimum area of steel in concrete column

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I agree with your general interpretations. Section 10.8.4 is not well worded
as a code requirement, as it does not tell you how to calculate the reduced
effective area, it only gives a limit for the reduction. Regarding locating
the reinforcement, I think that it should be located where it is most
effective - at the perimeter of the cross-section. 

There are occasions where it makes sense to provide a column with dimensions
larger than required specifically for strength. This provision allows for a
lower steel percentage when that is the case. This is often done "by
judgment" when the larger column with 0.5% steel clearly has much excess
capacity, but technically you should be able to show that a smaller column
with 1% steel would work. 

The column requirements do not specifically apply to drilled piers, but I
would use judgment as to whether these requirements make sense to apply to
drilled piers for some applications. 

William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Mark L. Puccio [mailto:mpuccio(--nospam--at)ramaker.com] 
> Sent: Friday, October 15, 2004 1:13 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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