Web crippling design of modular construction optimised beams under interior-two-flange (ITF) loading

Modular construction is gaining prominence for its sustainability, speed of assembly, reduced material waste, and cost-effectiveness. Cold-formed steel (CFS) beams, such as the Modular Construction Optimised (MCO) beam, play a vital role in these structures due to their lightweight characteristics, high strength-to-weight ratio, and ease of fabrication. However, the thin-walled geometry of CFS beams introduces challenges in structural design, particularly due to complex buckling and failure modes. The structural behaviour of the MCO beam remains insufficiently explored, with no prior research focusing on its web crippling performance under interior two-flange (ITF) loading. Existing design codes provide equations for estimating web crippling capacity. However, these provisions have been shown to underestimate the actual capacity of complex CFS sections, resulting in overly conservative designs and inefficient material use. To address these limitations, this study investigates the web crippling behaviour of the MCO beam using finite element analysis (FEA). Numerical models were developed and validated against experimental web crippling data from similar beam types. A parametric study involving 162 FE models was conducted to assess the influence of key geometric parameters displaying an average reduction of 27% due to corner radius effects. All models assumed unfastened flanges, reflecting common modular construction practices. Based on the results, new design equations were proposed to improve the accuracy of web crippling capacity predictions, providing a mean value of 1.00 and COV value of 0.08 and 0.07. These findings support the development of more efficient design practices, reduce material overuse, and contribute to the optimisation of lightweight modular steel structures.