Resistência de perfis "Z" formados a frio sob flexão não-uniforme e colapso distorcional

Abstract

This work presents results of a numerical-computational analysis applied to cold-formed Z-sections beams whose failure mode is the distortional, when subjected to non-uniform oblique bending. The goal is to evaluate the buckling and post-buckling behavior, as well as the Direct Strength Method (DSM) design predictions, set out in Annex C of the Brazilian Standard NBR 14762: 2010 and AISI S100-16 Specification. Buckling modes and their ultimate strength and lengths of the bars are determined through eigenvalue analyses, using the Finite Element Method (FEM) and Generalized Beam Theory (GBT). The analyzed beams (i) are single-span members, (ii) are simply supported, however, which different end support conditions regarding warping and minor-axis flexural rotations (totally free or prevented), (iii) present Z stiffened crosssection and miscellaneous buckling lengths and (iv) submitted the three moment gradients (including the uniform bending for comparison purposes). Assured that all the 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 results were used to evaluate the merits of the current dimensioning curves of the DSM (checking for significant overestimation) and of the curves adapted, from these, by other authors.