Torsion and its interaction with other internal forces in EN 1993‐1‐1 – a new approach

This paper presents and clarifies the treatments included in EN 1993‐1‐1 [1] relating to checking the resistance of steel cross‐sections under torsion and its interaction with other internal forces. Specifically, the origin of the formulations for shear‐torsion interaction, which has not been found in the literature, is presented. Furthermore, a very simple formulation based on the expressions used for shear‐torsion interaction is developed in order to take into account bending‐warping torsion interaction for symmetrical I‐sections (IP and HE steel profiles). Such a formulation overcomes the overly conservative approach given in EN 1993‐1‐1 [1] for class 1 and class 2 cross‐sections (plastic and compact cross‐sections). Finally, a rigorous method for determining the bending resistance of cross‐sections is proposed considering the interaction with shear and torsion. The proposal is well suited to the concept of cross‐section class and is perfectly consistent with the approaches set out to consider bending‐shear and bending‐warping torsion interactions.