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RE: Single or Double angle bending member

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Jordan,
That is how I decided to look at it also.  I have purchased Mathcad as Bill
and Will, but I haven't had the time to get into it yet and start learning.
One of these days.....
Thanks for the replies.
Joe

Joseph R. Grill, P.E. (Structural)
Shephard - Wesnitzer, Inc.
Civil Engineering and Surveying
1146 W. Hwy 89A Suite B
Sedona, AZ  86340
PHONE (928) 282-1061
FAX (928) 282-2058
jgrill(--nospam--at)swiaz.com
 


-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com] 
Sent: Tuesday, April 26, 2005 5:22 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Single or Double angle bending member

Will Haynes wrote:

> I think it is a single angle problem. The angles can't buckle in 
> lateral torsional mode together like they can in a back-to-back double 
> angle section. How does one angle know there is another angle on the 
> other side of the wall?
>
> I see these angles a lot in cmu walls, with the tips of the angles 
> facing each other. A guy told me the following method before and I 
> suspect this is probably what a lot of engineers use. You figure out 
> the section modulus of only the vertical legs of the angles, add these 
> together, then limit the stress to 0.6 Fy based on this section 
> modulus only. I don't know how accurate this technique actually is, 
> probably not very.
>
> To begin doing it correctly, I think sections 5.1 and 5.2 of the LRFD 
> single angle spec would apply, specifically section 5.1.1. I don't 
> think checking the LTB equation in section 5.1.3 is  correct, since 
> each angle is forced to rotate about it's shear center (leg 
> intersection) and this rotation is being resisted by the wall. 
> So neither angle can buckle as a unit in lateral torsional mode. I am 
> going to think about this some more tomorrow, I would really like to 
> know if this is the correct approach.
>
> Will
>
I would agree with you on the lack of LTB - the rotation is resisted by 
the masonry and/or the opposing angle.  In a perfect world, the load 
would be shared equally and the induced moment about the shear center 
would be equal and opposite for the two angles.

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