Allowable Torsion Strees on Steel

I believe Roark's Formulas for Stress and Strain has an equation for maximum shear stress in a rectangular section under torsion.

Depending on the geometry, you could get into stability problems above the basic shear stress calculation.

There is no allowable torsion stress, thinking of it as being different from flexural or shear. The reason is torsion adds to the flexural and shear stressed, it doesn't create its own independent stress. What you should do is for each load combination, find the maximum total shear and total flexural (normal) stress on the section due to the combinations of torsional shear stresses (warping and pure) and direct shear stress and the combination of torsional normal stress amd flexural normal stress. Compare these then with the allowables for flexural and shear stresses.

drpink,

This is a complicated issue, and you should really find a good text on torsion design before you try and do anything.

Regards

Csd72

As with all steel issues, check out Blodgett's Design of Welded Structures.