Lateral-torsional Buckling of Web-tapered I-Beams. 1D and 3D FEM Approach

This paper deals with lateral-torsional buckling of web-tapered I-beams with doubly symmetric cross-section. A governing system of two differential equations for lateral-torsional buckling of prismatic beams (developed by Vlasov) has been modified for the case of web-tapered I-beams. At first, there was used a simplification of considering small angle between a flange axis and a beam axis (as used by some authors), and afterwards this simplification was not used. A Rayleigh-Ritz variant from the weighted-residual methods was chosen to solve obtained differential equations. To validation of the equations and their solutions a parametric study of results with various other programs based on 1D beam approach (LTBeam, Eta_KI, RF FE LTB) was done. Then, the results from 1D beam based programs were compared to the ones from ANSYS using the 3D shell-element approach. Because of the assumption used in the beam model, namely rigidity of a cross-section in its plane, inclusion of special diaphragms was chosen to reduce a local and distortional buckling occurrence in global lateral-torsional buckling modes.