Inelastic Lateral-Torsional Buckling Strength Validation for Non-Principal Axis Bending Using Numerical Methods
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The current design specification for point-symmetric cold-formed steel members in North America (AISI S100) has long applied a conservative simplification for elastic lateral-torsional buckling. This report aims to provide additional validation of a recently proposed design approach. The validation involves a series of numerical analyses designed to assess the accuracy of proposed changes for lateral-torsional buckling behavior of point-symmetric section bent about a non-principal axis. Using a set of 14 lipped Zee sections with sharp corners, numerical analysis was carried out for elastic buckling using the finite strip method, and shell finite element method, and in addition inelastic shell finite element collapse analysis was conducted to determine the expected strength. As reference, analytical equations from previous research (Glauz, 2017) are also used to validate the elastic lateral-torsional buckling simulations. Nominal flexural capacity was predicted by three design methods: AISI S100-16 approximate approach, AISI S100-16 linear interaction approach, and a new method considering direct bi-axial bending. The simulation results are compared with the proposed provisions for both stability and strength determination. The level of conservatism in the strength predictions is high for the selected members based on the assessment of the data, especially for those members with higher global slenderness. The assessment in this report focused primarily on the global inelastic buckling range, where it was found that the method considering direct bi-axial bending is preferred.