Explicit expressions are developed for the buckling analyses of rectangular (long) plates: for ‘linearly varying axial load’ the known results for hinged supports are corrected and new results are presented for built-in and constrained edges; for ‘shear load’ new results are presented for constrained edges; for ‘uniform compression’ new results are presented when the longitudinal edges are rotationally constrained by stiffeners. The results are based on the Rayleigh—Ritz method.

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Local buckling analysis of thin-walled open or closed section fiber-reinforced plastic beams is presented. In the analysis, the web is modeled as a long orthotropic plate with rotationally restrained edges. Explicit expressions were developed for the buckling analyses of rectangular (long) plates in a companion paper. These results are applied to develop explicit expressions for the calculation of the web buckling of beams with thin-walled cross sections. At last, the applicability of the method is demonstrated by numerical examples and the results are verified by finite element calculations.

Approximate expressions to determine the lowest buckling load of short and long composite plates are presented. The plate is subjected to uniaxial compressive load. All the four edges of the plate are elastically restrained by springs or stiffeners. Explicit expressions for the calculation of the lowest buckling load are presented as a function of the plate’s length. The derived expressions were compared to numerical solutions investigating the entire parameter range.

Local buckling analysis of thin walled composite beams is presented, where the flanges are stiffened at their free edges. The web and the flanges are modelled by rotationally restrained long orthotropic plates. Explicit expressions are developed for the calculation of the lowest buckling load. For the stability of the flange distortional buckling, plate buckling (or local buckling) and their interaction are considered, while the stabilizing effect of the web is taken into account by elastic constraint. Web buckling is modelled with a long plate, whose edges are constrained by stiffeners with warping stiffness. The accuracy of the method is demonstrated through numerical examples.