Inelastic Lateral Buckling of Determinate Beams

Present methods for the design of laterally unbraced steel I-beams are reviewed, and the need for improvements in the treatment of beams of intermediate slenderness is demonstrated. A simple method, which makes due allowance for the type of loading, of estimating the inelastic buckling load of a single span beam is proposed. A design curve is proposed which makes use of the fully plastic moment and either the elastic or the inelastic critical moment. The position of this curve is determined by using available test data. This approach is more consistent than previous methods, particularly in the inelastic range where better allowance is made for the type of loading. A method of dealing with the interaction between adjacent segments of laterally continuous beams that buckle in the inelastic range is also proposed. Comparisons show that the method gives conservative results that are more accurate than those of existing approximate methods.