Progressive Collapse Resistance of Steel Frames with Reduced Beam Sections and Web Openings

Progressive collapse represents a critical failure scenario in steel moment-resisting frames, especially when beam sections are intentionally weakened through flange cuts or web openings. While previous studies reported that circular openings were the most effective configuration among various shapes, the present study investigates whether semi-circular openings, when combined with reduced beam sections (RBS), can provide superior performance. A finite element model was developed in ABAQUS/Explicit v2016 and validated against experimental results to ensure reliability. Parametric analyses considered both circular and semi-circular openings with diameters of 80 mm and 110 mm, placed at various distances from the RBS centerline (L = 0, 65, 140, and 180 mm). The results show that openings located too close to the RBS zone (L = 0 mm and L = 65 mm) significantly
reduced strength and suppressed catenary action. Conversely, larger spacings (L = 140 mm and L = 180 mm) enhanced load capacity and ductility by promoting stress redistribution. Importantly, semi-circular openings consistently outperformed circular ones in the present investigation. In particular, the SC3-140-110 specimen achieved the highest peak load (248.7 kN) and the strongest catenary action contribution (227.6 kN), demonstrating superior robustness against progressive collapse. These findings highlight the technical advantage of semi-circular openings as an effective detailing strategy for improving the collapse resistance of steel moment frames.