The problem is that the nice closed form solutions rely on the assumption that plane sections remain planar, which is only true for circular sections
>I am currently trying to find the shear stress of an "L" shaped bar
> >due to torsion. The bar is loaded in a cantilevar fashion, fixed at
> >one end and loaded with a torque at the other. I have not been able
> >to find a solution that is clear. Every formula and solution seems to
> >lead toward circular cross sections or for very common noncircular
> >cross sections. Maybe if I knew how the formulae were derived for
> >variables such as "Q". As in Max Shear Stress = Torque/Q. Q being a
> >function of the cross sectional area of the shape.
>
> The American Institue of Steel Construction publishes a guide to torsional
> analysis of rolled sections of various shapes. Look on their website
>
formatting link
for details.
>
> Roark's Formulas for Stress and Strain also has formulas that will solve your
> problem. Look on page 407 ofthe seventh edition.
>
>
>
> David Duerr, P.E.
> Houston, Texas