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Re: Brace Connection Moment from Eccentricity

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See below for my comments
 
Scott A. Dunham, PE
Dunham Engineering Services
Dothan, AL
334-678-6948
 
----- Original Message -----
From: <j.grill(--nospam--at)attbi.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, January 08, 2003 6:38 PM
Subject: Brace Connection Moment from Eccentricity

> My questions are these.  In the explanation for the special case (page 7-109)
> the moment to the column is listed as Mc=2*V*ec.  Example 22 and on page 7-110
> the moment is listed as V*ec/2.  The first equation in the paragraph on page 7-
> 109 appears to be a typo.  Right?
You are correct.  I have the Second Printing, and it was corrected.  Also, an errata dated 12/1/93 notes this correction.  Also, the equations for a and b on page 7-109 are incorrect and were corrected in an errata dated 1/1/94.
 
> My next question is this.  For the column moment to be V*ec/2 the brace
> location must be at the mid-height of a column.  Right/wrong?  And if the
> brace is at the top of a column the column moment would be Vc*ec. 
> Right/wrong?  I seem to be questioning my own mechanics today, and I believe
> the text is kind of over-generalizing, unless I just need to go home.
 
I don't think that the calculation of Mc is a function of the location of the connection to the base of the column.  My only question is why Mc = ½*V*ec instead of Mc = V*ec based on the fact that V acts at a distance of ec from the column centerline.  I don't have a copy of Dr Thornton's paper from the 1991 NSCC proceedings that presents the development of the method, but it has appeared unchanged in subsequent AISC publications (read = LRFD) so I've just accepted it.
 
HTH