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Re: Concrete Column Design -Plastic Centroid vs. Centroid

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Wontae,

I don't know what the most current edition states...I don't have it.  And,
FWIW, James Wight is now the primary author of that book as Jim MacGregor
is kind of retired (he is still list as the second author and still works
with Jim Wight on the book, I believe).  I know this cause Jim Wight was
my concrete professor in school and he and I are still in touch.

At to the edition that I _DO_ have, I did not see that exact phrasing (I
looked on the page number that you cited plus or minus some pages).  There
is mention of taking the moments about the centroid or the geometric
centroid.

In general, it should not matter which point you use to determine Mn.
Using _ANY_ point to sum the moments to determine Mn should work...it is
just that some points make life "easier" than others (i.e. pick the
"right" point and some of the forces drop out cause they act through that
point).

Regards,

Scott
Adrian, MI


On Tue, 30 Aug 2005, Wontae Kim wrote:

> Hi, everybody!
> {After posting this question, I have never received any response.}
>
> According to "Reinforced Concrete - Mechanics and Design, 2nd Ed." by J. G. MacGregor,
> "The moment capacity M_n for the assumed strain distribution is found
> by summing the moments of all internal forces about the centroid of the column.
> ...In the 1950s and 1960s moments were sometimes calculated about the plastic centroid,
> ...[P. 410]
>
> Is this true?
> All books are using P.C. instead of centroid
>  to calculate moment capacity of columns.
> Why did Dr. MacGregor say that?
>
> Does the latest edition of his book  contain the same statement?
>
>
>
>
> ****Wontae Kim****
> Unistress Corp.
> Pittsfield, MA 01201
> (Tel)  413-629-2031
> (Fax) 413-499-0824
>
>
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