Buckling in Steel U-Shaped Beams

Coupled behavior of overall and local buckling of U-shaped beams subjected to uniform bending moment is presented. A finite strip method is applied to the coupled buckling analysis and the inelastic buckling is analyzed including the residual stresses of the cross section. The buckling tests are carried out with seven welded steel U-beams. Load-deformation behavior, failure modes, the ultimate bending strength and the stiffening effects by the intermediate knee braces and diaphragms are investigated. Interaction of the lateral buckling of compression flanges and the overall buckling of U-beams are made clear both theoretically and experimentally. The lateral buckling strength of laterally unbraced compression flanges can be estimated by tbe approximate method based on the equivalent T-column. The overall buckling strength is primarily affected by the ratio of the span length to spacing of webs.