How is Warping Torsion in RISA-3D calculated?
RISA-3D’s torsion calculations are based on the AISC publication Torsional Analysis of Steel Members. The program currently only models warping fixed conditions. The program does not model a warping pinned condition. (A warping pin is restrained against twist, but free to warp) RISA-3D models all warping conditions as a CASE 2 as shown in the AISC publication. This is correct for columns of buildings, and any other case where torsional loads are applied only at the ends of the member. For the cases where internal torque loads are applied as nodal torques, the solution given by RISA-3D will be conservative for the maximum warping stresses at the ends of the members. If an accurate solution is required (as opposed to a conservative solution) for a point torque or a distributed torque on a member, then it is recommended that the engineer combine RISA-3D’s direct stresses with the warping stresses obtained from a hand solution. The above mentioned AISC publication on torsion contains chart
