On the Capacity of Beams with U Cross Section Subjected to Bending and Torsion

Beams with singly symmetric U cross sections are often subjected to bending about the strong axis and simultaneously to scheduled torsion, since the shear center is outside the section geometry. The member capacity of such sections, which is strongly influenced by effects of lateral torsional buckling, can therefore hardly be represented with the common design regulations based on reduction factors χ_LT of EN 1993‐1‐1. However, numerical approaches allow analyzing deeply the structural behavior of corresponding beams. In the present study, different numerical finite element simulations (GMNIA) including simplified numerical models based on the plastic zones theory are incorporated to determine member capacities and to derive corresponding reduction factors for simplified verifications. As the load‐bearing capacity of members susceptible to stability is strongly influenced by imperfections, the straightness according to manufacturing tolerances as well as approaches for the acquisition of structural imperfections (residual stresses) are considered in the numerical analyses. The investigations are carried out for selected structural systems with different sets of parameters, such as for the member lengths and cross section types. Concluding, a capacity curve is derived and compared to different reduction factors χ_LT specified in EN 1993‐1‐1.