NUMERICAL EVALUATION OF THE DISTORTIONAL-GLOBAL INTERACTION PHENOMENON IN COLD-FORMED STEEL HAT-SECTION BEAMS UNDER NON-UNIFORM BENDING

Abstract

Cold-formed steel profiles exhibit high structural efficiency; however, their reduced thickness renders them highly susceptible to interaction between buckling modes, particularly distortional and global modes. This work investigates the behavior of hat-section beams subjected to uniform and non-uniform bending, a loading condition still insufficiently addressed by current regulatory formulations. The geometries were selected through elastic buckling analysis using the GBTUL program, while finite element models were developed in ABAQUS software, employing the Riks method for nonlinear buckling and post-buckling analyses. A total of 960 numerical models were evaluated, considering varying bending moment gradients, boundary conditions, and distortional slenderness levels. The results demonstrate that non-uniform bending significantly alters the redistribution of longitudinal stresses, expanding the post-critical reserve and modifying the beam's resistant mechanism, with asymmetrical responses depending on the loading orientation relative to the principal axes of inertia. Although the general trend is compatible with the Direct Strength Method (DSM) predictions, the observed scatters highlight limitations in the direct application of this regulatory procedure to hat-sections under moment gradients. The findings contribute to the understanding of the distortional-global interactive phenomenon and provide relevant data for the calibration of future design models.