Influence of circular web openings on the web crippling performance of modular construction optimised cold-formed steel beams under ITF loading

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/d₁) 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.