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Re: Brace Connection Moment from Eccentricity

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Scott,
Thanks for the reply.  I still need to pursue the thread somewhat though.  It's funny that you have a copy of the Second Printing and the equation differences were corrected.  I have a copy of the Third Printing and they are still again showing differences.  Interesting?  With that information, and your mention of the equations for alpha and beta on page 7-109, I would ask for a copy of the errata you are talking about, or where can I get a copy?  I wasn't given one when I purchased my copy of the text.  Maybe there are other things in the text that a person should be aware.
 
As far as the column moment goes.  I looked in "Blodgetts" book at his list of beam equations near the end of the book.  For a beam loaded with a concentrated moment at the mid-span the moment to the beam is M/2 which makes sense with the
(Vc*ec)/2.  Also, example 22 is not located at the top of the column (looking at the sketch anyway).  The induced moment to the beam, however, is at the end of the beam and is equal to the induced moment of Hb*eb.  If the brace were located at the mid-span of the beam, would the induced moment then become Hb*eb/2 or remain Hb*eb.
 
I'm not saying I'm certain I'm right, but can't justify the 1/2 factor in the moment calculation from the mechanics as I see them.  A factor of 2 is a big difference in some of my columns at this point.
 
Once again, thanks,
 
Joseph R. Grill, PE
----- Original Message -----
Sent: Thursday, January 09, 2003 12:47 PM
Subject: Re: Brace Connection Moment from Eccentricity

See below for my comments
 
Scott A. Dunham, PE
Dunham Engineering Services
Dothan, AL
334-678-6948
 
----- Original Message -----
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