Flambagem distorcional de perfil formado a frio seção rack sob flexão uniforme e não-uniforme - Análise numérica e MRD

Abstract

Due to the wide variety of cross-sections and their good mass/strength ratio, coldformed steel (CFS) components are gaining prominence among steel structures, although this material is more susceptible to local, distortional, and global buckling. The design procedure based on the direct strength method (DSM) presented in some codes as the Brazilian (NBR), the American Iron and Steel Institute (AISI), and the Australia/New Zealand (AS/NZS), have been well accepted for estimating simply and safely the moment capacity of beams subject to distortional buckling for many situations. However, more recent studies show that DSM design can lead to unsafe moment capacity for beams with a high slenderness factor of distortional buckling. This study analyzes the behavior from 768 models developed using the finite element analyses (FEA) with the ABAQUS software. The selection of the specimens in which the distortional buckling mode is predominant (modal participation analysis) was performed through a linear stability analysis using the GBTUL software. The finite element (FE) models used in nonlinear elastoplastic analyses included geometrical initial imperfections and material nonlinearity. A parametric study was developed to investigate the influence of the slenderness factor of distortional buckling (λdist) on CFS Rack beams' moment capacity. The FEA results were compared with DSM results to verify the accuracy of this method to predict distortional moment capacity. It is shown that, for CFS Rack beams subject to uniform and non-uniform bending and distortional buckling with slenderness factor of distortional buckling higher than 1.0 – 1.5, the DSM overestimates the moment capacity. Modifications were proposed in the DSM in order to improve the accuracy in predicting the moment capacity for the analyzed conditions.