Simplified method for lateral‐torsional buckling of beams with lateral restraints

Selected, extended paper from the SDSS 2019 special session ECCS/TC8 – Structural Stability This paper discusses the simplified method for the lateral‐torsional buckling design of I‐shaped beams with discrete lateral restraints. This popular method, also adopted in Eurocode 3, Part 1‐1:2005, consists of verifying the resistance of the compressed “flange” of the beam subjected to major‐axis bending. In this case the compressed flange is considered to be composed of the flange itself plus 1/3 of the compressed part of the web. This paper summarizes the analytical derivation of the simplified method and its key assumptions. It then presents inconsistencies arising if the simplified method is compared with the more generally applicable design methods for lateral‐torsional buckling given in Eurocode 3, Part 1‐1:2005. In addition, the design methods are compared with numerical simulations to reveal the lack of conservatism in the simplified method in some cases. The final part of the paper discusses how the simplified method may be modified in order to ensure a sufficient level of safety.