Design of cold-formed steel built-up sections with web perforations subjected to bending

The flexural behaviour including the moment capacities and failure modes of cold-formed steel built-up sections with circular web holes was investigated. Finite element analysis was performed on a wide range of cold-formed steel built-up section beams with different sizes of perforations under four-point bending. The built-up sections included both I-shaped open sections assembled from two lipped channels back-to-back and box-shaped closed sections assembled from two plain channels face-to-face. Finite element (FE) models have been developed to simulate the simply-supported cold-formed steel built-up section beams. The FE models for the built-up open sections and built-up closed sections were verified against the test results that have been conducted by the authors. The validated models were employed to carry out extensive parametric studies on cold-formed steel built-up section beams with various section slenderness and hole sizes. The beam strengths obtained from the numerical analysis together with the available test data were compared with the design strengths calculated from the current direct strength method (DSM). The critical elastic local and distortional buckling moments including the influence of holes that are required in DSM calculation were determined by rational finite strip analysis. It is shown that the DSM formulae in the North American Specification AISI S100-16 are capable for predicting the design strengths of the built-up open section beams with holes, while are quite conservative for the closed section beams with holes. Modifications are proposed for the DSM formulae for built-up closed section beams with holes. In this study, the current DSM was extended to cover the cold-formed steel built-up open and closed section beams with holes.