Higher buckling and lateral buckling strength of unrestrained and braced thin-walled beams: Analytical, numerical and design approach applications

Abstract

The present study investigates the flexural-torsional struts buckling and beam lateral buckling analyses. In the highlight of braced structures, analytical solutions are derived for higher 3D buckling modes of simply supported struts with arbitrary cross-sections. Closed-form solutions are also investigated for lateral buckling strength of beams with doubly symmetric cross-sections. For more general cases, the finite element approach is adopted. In presence of torsion, warping is of primary importance. For this aim, 3D beams with 7 degrees of freedom (DOFs) per node are adopted in the analysis. The model is able to carry out higher buckling modes of bars under compression or lateral buckling modes of beams initially in bending. The analytical and the numerical results of the present model are compared to some available benchmark solutions of the literature and to finite element simulations of some commercial codes (Abaqus, Adina). The efficiency of the closed form solutions and the numerical approach is successfully verified. Applications of higher buckling modes in design of braced structures are considered according to Eurocode 3 code. A particular attention is pointed out to torsion and flexural-torsional buckling modes not considered in bar strength. At the end, some solutions are proposed in order to cover the full strength of columns and beams in presence of instabilities. This proposal makes steel structures more performant and attractive when effects of instabilities are limited at a minimum.