A proposal based on the effective section factor for the lateral-torsional buckling of beams with slender I-shaped welded sections

Abstract

Abstract The lateral-torsional buckling of steel beams with welded slender I-shaped sections, or Class 4 sections according to Eurocode 3 classification, is investigated in this paper. While the response of non-Class 4 section beams has been extensively studied in the literature, welded slender section beams have received less attention to date. Finite element (FE) models for non-linear analyses were developed and validated against 64 experimental tests available in the literature considering both material and geometrical imperfections. Subsequently, an extensive parametric study covering a wide range of sections and member geometries was carried out. The existing rules from Eurocode 3 and a proposal based on a consistent derivation of the Ayrton-Perry formulation, developed for compact and semi-compact sections (sections of Class 1, 2 and 3), were presented and their accuracy was then evaluated using the numerical data generated. As demonstrated, due to high width-to-thickness ratio of section's constituent plates, the coupled interaction between the local buckling and the lateral-torsional buckling affects the stability of the beams, but the design provisions deliver insufficient account of said interaction thus resulting in highly scattered predictions when compared against the numerical results, mostly yielding lower values of resistance than that obtained numerically. To improve this condition, a novel concept, named the effective section factor (E.S·F.), was further developed to account with the coupled interaction by grouping the behaviour of beams with Class 4 sections into different ranges of E.S·F. Finally, enhanced design formulae for the estimation of the ultimate strength of the beams was proposed based on the developed E.S.F. concept, providing more accurate capacity prediction.