Effect of torsion on the mobilisation of alternate load paths in double-span reinforced concrete edge beams subjected to progressive collapse

This study introduces a novel, integrated framework that combines numerical simulation, large-scale experimental testing, and detailed strut-and-tie modelling to quantify the impact of torsion on the mobilisation of Alternate Load Paths (ALP) in double-span reinforced concrete (RC) edge beams subjected to progressive collapse. Unlike previous studies [1–5] that examined these phenomena in isolation or with simplified assumptions, this framework synergistically integrates these techniques to capture the complex interactions between torsion, flexure, and shear. Initially, a numerical analysis was performed to establish torsion demand scenarios reflective of actual design conditions. Subsequently, two specimens with varying torsion demands were tested under combined flexure-shear-torsion loading and compared against a torsion-free control specimen. Experimental results revealed that while the control specimen effectively mobilised compressive arch action and catenary action, torsion in the other specimens induced premature failures through distinct torsion-bending and torsion-shear interactions, severely compromising ALP mobilisation. Detailed analyses of load-displacement responses, twisting profiles, reinforcement strains, and displacement behaviour provided new insights into how torsion disrupts critical ALP mechanisms. Furthermore, sectional analyses using strut-and-tie models elucidated the contributions of key structural components to torsional failure. These findings underscore the significant detrimental impact of torsion on progressive collapse resistance and inform design recommendations to enhance reinforcement strategies and optimise force transfer in torsionally loaded RC beams.