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Re: Single or Double angle bending member

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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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