Structural behaviour of cold-formed steel channels with unstiffened and edge-stiffened web holes under combined compression and bending

Cold-formed steel (CFS) channel sections with web openings are widely used to accommodate services in light-frame construction. However, their structural performance under combined axial compression and bending, particularly when openings are either unstiffened or edge-stiffened, remains poorly understood. This study develops a validated nonlinear finite element model that accounts for material nonlinearity and initial imperfections to assess the behaviour of such sections under eccentric loading. A comprehensive parametric study involving 3078 simulations was conducted to quantify the effects of slenderness, width-to-thickness ratio, hole configuration (number, size, location), stiffener ratio, and eccentricity about both principal axes. Results show that unstiffened web holes can increase the axial–bending interaction ratio by up to 60 % beyond the limits of AISI S100 and AS/NZS 4600, while edge stiffeners effectively limit this increase and improve capacity by 15 % on average. The detrimental effects of unstiffened holes diminish with increasing eccentricity and become negligible beyond specific eccentricity thresholds. Based on the simulation results, new design equations are proposed to account for geometric and loading parameters explicitly. These equations reduce prediction error by 20 % and address key conservatism and non-conservatism issues in current design standards, offering a pathway toward safer and more economical CFS member design.