Warping torsion occurs in the cross sections that are not free to warp, if the warping of the end cross-sections is restrained. The non-free-to-warp cross-sections include especially the open thin-walled steel cross-sections. On the other hand, a circle, a circular ring and a square hollow cross-section with the constant wall thickness, are free-to-warp cross-sections.
The warping torsion analysis can be carried out using the RF‑/STEEL Warping Torsion module extension of RF‑/STEEL EC3 as well as using the RF‑/FE‑LTB add‑on module. It is possible to perform lateral‑torsional (flexural-torsional) buckling analyses of members according to the second‑order theory with 7 degrees of freedom and application of imperfections with regard to mode shapes.