Buckling approximations for laterally continuous elastic I-Beams

An approximate method for determining the elastic flexural-torsional buckling loads of laterally continuous structures is developed. The method is a refinement of that proposed by Nethercot and Trahair and can be applied to structures loaded at braced points. The braces and supports are assumed to prevent lateral deflection and twisting. The procedure locates a critical segment and adjacent restraining segments which together form a substructure. The elastic critical load is obtained by determining the effective length of the critical segment. Charts of effective length factors, k, are presented and are shown to depend on the end restraint parameters, G_A and G_B the segment beam parameter, K, and the end moment ratio, ß. The proposed method is applied to a number of worked examples. The results are in close agreement with accurate numerical solutions.

The paper has been written with the design engineer in mind and does not presuppose a detailed knowledge of buckling theory.