Jack Lifsey

Cold-formed steel (CFS) has become increasingly prominent in modular construction owing to its high strength-to-weight ratio, formability and sustainability advantages. The recently developed Modular Construction Optimised (MCO) beam, featuring a hollow triangular-flange cross-section, may offer improved flexural efficiency and material savings compared with conventional CFS profiles. However, MCO beams remain vulnerable to localised failures such as web crippling, particularly under concentrated Interior-Two-Flange (ITF) loading typical of modular stacking, transportation and temporary support conditions. The inclusion of large circular web openings (40–80% of the clear web height, d _wh /d ₁ ) for service integration further complicates design, while current standards provide limited specific guidance for such configurations. This study presents a purely numerical investigation into the web crippling behaviour of MCO cold-formed steel beams with circular web openings under Interior-Two-Flange (ITF) loading. A comprehensive finite-element (FE) programme comprising 648 models (486 perforated and 162 plain-web beams) was developed and validated against existing experimental data for comparable cold-formed steel sections, achieving strong agreement (mean = 1.00, COV = 0.06). The parametric analyses examined the effects of hole size, web thickness, bearing length, corner radius and yield strength. Results indicated mean reductions of 11%, 19% and 26% in web-crippling capacity for 40%, 60% and 80% openings, respectively, with reductions most sensitive to web thickness, corner radius and bearing length. A modified reduction-factor equation, incorporating web-thickness and corner-radius parameters not considered in existing design provisions, is proposed, achieving excellent agreement with FE predictions (mean = 1.00, COV = 0.04) and a corresponding resistance factor of 0.92. The proposed formulation enables a preliminary design approach for MCO beams with service penetrations, addressing a major limitation of existing codes. Future experimental and independent validation is required before practical application. The study enhances understanding of web-crippling mechanisms in optimised CFS geometries and supports the safe and material-efficient use of MCO beams in modular construction.

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.