Torsional Stresses

[scanf1027]

I am trying to use the torsional stresses reported by Risa to compare to the AISC Design Guide #9 Example 5.1 for checking torsion. It seems the warping stresses reported by Risa are reverse of what I should be seeing at midspan. Risa shows the max warping stress (for top and bottom) at beam ends, when it should be at midspan. The shear stress reported by Risa is correct; max at midspan and zero at beam ends. Maybe I'm missing something.

 

[JoshPlumSE]

RISA's implementation of torsional warping criteria is approximate. It is based on Case2 (torsionally "fixed") of the AISC design guide whereas that example (5.1) is based on a torsinally pinned boundary condition.

This would account for the difference in what your hand calculations show and what RISA provides.

For what it's worth, the stress values in RISA should be conservative.... Though perhaps a bit too conservative. If you find this to be the case, then you can run the RISA analysis without considering warping effects at all. This can be done by using the checkbox on the global parameters.