Design of cross‐sections for local buckling based on a mechanical model

Abstract

An alternative design method, capable of predicting the local buckling capacity of thin‐walled steel cross‐sections of arbitrary shape, is presented. Unlike currently codified approaches (i.e. the Effective Width Method and the Direct Strength Method) which are based on empirical curve‐fitted equations, the new approach is anchored in the structural mechanics of plate buckling. This requires a description of the highly nonlinear post‐local buckling range, which is obtained by simplifying the governing Föppl‐von Kármán equations using Vlasov‐type assumptions. A failure criterion inspired by von Kármán's effective width approach is added. Approximate yet highly accurate closed‐form solutions to the resulting equation can be constructed in the particular cases of plates with four simply supported edges, and simply supported plates with one longitudinal free edge. In the former case, the results agree eminently well with the Winter equation. A finite element scheme is developed to treat the general case of a randomly shaped cross‐section. Validation against test results reveals excellent agreement, with an average ratio of the predicted capacity to the experimental value of 0.96 and a standard deviation of merely 2.9%.