Equivalent thickness-based elastic buckling design of perforated CFS sections under web crippling

Cold-formed steel (CFS) lipped channel sections with web holes are widely used in modular and light steel construction. However, their elastic buckling behaviour under web crippling—particularly for two-flange loading conditions—remains insufficiently understood. This study introduces, for the first time, an equivalent thickness approach to estimate the elastic buckling loads of CFS sections with unstiffened circular web holes subjected to end-two-flange (ETF) and interior-two-flange (ITF) loading. A validated finite element (FE) modelling framework was used to conduct an extensive parametric study involving 4775 configurations, systematically varying web geometry, hole size, and bearing length. The data pool included CFS channels with plain webs (no holes) and unstiffened circular web holes. Results show that increasing the web hole ratio can reduce the elastic buckling load by up to 54%, a trend not captured by existing design formulae. To address this, the study proposes refined elastic buckling coefficient expressions and a novel equivalent reduced thickness method. Both approaches demonstrated high predictive accuracy and consistency across a wide range of parameters. The equivalent thickness method, in particular, offers a practical and computationally efficient alternative to full numerical simulations. These findings advance the Direct Strength Method (DSM) and Continuous Strength Method (CSM) design frameworks for perforated CFS members and provide a foundation for extending equivalent thickness concepts to other localised failure modes.