CFRP Strengthening for Progressive Collapse Mitigation of RC Flat Slabs

This study evaluates different strengthening arrangements of externally bonded carbon fibre-reinforced polymer (CFRP) strips for mitigating progressive collapse of reinforced concrete flat slabs following column failure. Using a well-calibrated three-dimensional numerical model based on the Applied Element Method, parameters including CFRP strip position, width, length, spacing, multiplicity, and fibre orientation were systematically investigated to evaluate their influence on flat slab strength, compressive membrane action, tensile membrane action, punching resistance, catenary action, deflection at peak catenary load, energy dissipation, residual strength, strain distribution, and contribution of slab column and middle strips in resisting progressive collapse. This study highlighted that CFRP strengthening arrangements can modify stress and strain redistributions and load-transfer mechanisms, leading to transforming the slab behaviour from a localized slab–column connection resistance into a global slab-wide load-resisting mechanism capable of mobilizing alternative load paths overarching a larger portion of the slab area to mitigate progressive collapse. Under the adopted ideal-bond assumption, the 100 mm-wide strip-length series increased peak catenary load by up to 89.92% and load-deflection energy to peak catenary load by up to 153.51% relative to the unstrengthened control. The findings also demonstrated that optimizing strengthening arrangement was primarily a load-transfer path problem rather than a material-quantity problem, where strategically configured arrangement can optimally enhance the flat slab resistance mechanism to progressive collapse. Overall, this study provides new insights into the mechanistic role of strengthening arrangement parameters in controlling the transformation from localized slab–column connection resistance to a more robust global slab-wide resistance mechanism capable of mitigating flat slab progressive collapse.