Numerical Evaluation of Failure Modes in Perforated Beams with Hexagonal Openings

Abstract

Perforated and castellated steel beams are widely used due to their high structural efficiency; however, the presence of web openings introduces complex failure modes, such as Vierendeel bending and web-post buckling, which are not observed in solid-web sections. In this study, the influence of geometric parameters on the load-bearing behavior and failure mechanisms of perforated beams with hexagonal openings was systematically investigated. Nonlinear finite element analyses were performed on eleven models, including ten perforated beams with varying opening angles (ranging from 40° to 63°) and numbers of openings, as well as a solid-web reference beam. The numerical modeling approach was validated against experimental data from the literature to ensure the reliability of the results. All models were designed with a constant overall depth, allowing the effects of opening geometry to be isolated from those associated with increased section depth in conventional fabrication methods. The analysis results indicate a direct correlation between beam geometry and failure mode. The primary parameter controlling the transition from ductile, high-capacity flexural failure to brittle, low-capacity shear failure (Vierendeel bending or web-post buckling) is the dimensionless ratio 2dt/dg, where dt is the net section depth and dg is the total beam depth. Models with higher 2dt/dg ratios (such as 0.50 and 0.42) reached 86–92% of the capacity of the solid-web beam by developing a ductile flexural mechanism. In contrast, models with a lower 2dt/dg ratio (0.33) exhibited early brittle failure through the Vierendeel mechanism at 72–79% of the reference capacity, independent of opening angle. The opening angle (θ) was determined to be a secondary parameter. It is concluded that optimizing the 2dt/dg ratio is essential for achieving ductile failure in perforated steel beams and avoiding premature Vierendeel failure.