Behavior and DSM design of cold-formed steel “S" type beams experiencing distortional failure

Abstract

The present work reports a numerical analysis investigation about the buckling and post-buckling behavior, ultimate strengthand Direct Strength Method (DSM) design predictions applied to cold formed steel beams with “S” type and lipped channels (plane and stiffened) sections experiencing distortional buckling. The analyzed beams (i) are single-span members, (ii) are simply supported but they exhibit different end support conditions regarding warping and minor-axis flexural rotations and (iii) present different cross-section dimensions and buckling lengths, which provide a wide range of geometrical relations that help understanding their behavior. It is assured that all analyzed beams (i) present “purely” distortional buckling modes and (ii) cover a wide range of yielding stresses, enabling the investigation on a great amount of distortional slenderness. The post-buckling equilibrium paths and ultimate bending moments exhibited in this work are extracted from shell finite element non-linear elastic and elastic-plastic analysis through the software ANSYS. The results obtained in this work evidence that current codified DSM distortional curveis unable to estimate safely and accurately the ultimate bending moments for the selected beams.