Local buckling of RHS members with small-to-large corner radii subject to combinations of axial force and biaxial bending

This paper presents an in-depth study on the critical local buckling behavior of thin-walled rectangular hollow section (RHS) members subjected to combined axial load and biaxial bending, which accounts for the influence of web-flange interaction and small-to-large corner radii. The calculation of the half-wavelength leading to the minimum critical bifurcation load is performed by means of a Generalized Beam Theory specialization, developed taking advantage of the assumption that the stress resultants are uniform along the member length. This assumption makes it possible to obtain semi-analytical solutions, adopting half-wave sinusoidal amplitude functions for the GBT cross-section deformation modes, and leads to an implementation that (i) is able to quickly solve a large number of cases and (ii) provides physical insight into the critical buckling mode mechanics, through a shell-like stress resultant-based energy criterion, as well as the modal decomposition features of the GBT semi-analytical solution. The critical buckling coefficients obtained in this work are compared with those provided by available analytical expressions and/or currently included in steel design codes, namely Eurocode 3 and the North American Specification for Cold-Formed Steel Members.