Flexural behaviour and design of modular construction optimised CFS beams with circular web openings

Modular Construction Optimised (MCO) beams, cold-formed steel sections with rigid hollow-flanges tailored for prefabricated floor systems, require clear guidance when incorporating large unstiffened circular web openings (>38% of clear web height). This study fills that gap by: (1) developing and validating detailed nonlinear finite-element (FE) models against thirteen experimental tests (mean FE/exp = 1.01, COV = 0.02 for plain and web-perforated sections); (2) conducting a systematic parametric study of 288 FE models varying section dimensions, material yield (300–600 MPa), and opening ratios (0.4–0.8); (3) quantifying that openings up to 60% reduce ultimate moment capacity (Mu) by < 5%, while 80% openings incur a 10% average reduction; and (4) deriving simple reduction-factor equations that predict Mu with mean = 1.00 and COV = 0.03. Comparative analyses demonstrate that MCO beams with 80% openings outperform equivalent unperforated Lipped Channel Beams by an average of 32% in Mu, highlighting their strength-to-weight advantage despite large hole sizes. These findings provide engineers with validated design rules and practical equations for integrating large service openings into modular cold-formed steel floors. • Comprehensive flexural study of MCO beams with unstiffened circular-web openings. • 288 FE models assessed design variables: opening ratio, thickness, yield strength. • 80% opening ratio beams experienced approximately 10% Mu reduction. • Proposed Mu reduction equations provide mean accuracy=1.00, COV=0.03. • Flexural performance of plain and perforated MCO sections outperformed LCB.