Issue 78

D. D. Joshi et alii, Fracture and Structural Integrity, 78 (2026) 315-345; DOI: 10.3221/IGF-ESIS.78-19

adopted by researchers to improve the progressive collapse performance of RC structures is discussed in the following sections. Externally bonded FRP systems Bao et al. [11] investigated the effectiveness of externally bonded basalt fiber reinforced polymer (BFRP) sheets in enhancing the progressive collapse resistance of RC deep flexural members. Quasi-static tests were conducted on four one-third (1/3) scale specimens under a middle column removal scenario, including uncorroded, corroded and BFRP-strengthened corroded specimens. Vertical downward load was applied at the location of the removed column using a hydraulic actuator. Corrosion in the specimens was induced using an electrochemical accelerated corrosion technique, in which the specimens were immersed in a rectangular tank containing a 5% NaCl solution as the electrolyte. Two different BFRP strengthening configurations were applied around the beam-column joint region in addition to longitudinal BFRP strips at beam soffit. The results indicated that BFRP strengthening significantly enhanced the progressive collapse resistance of the specimens, with notable improvements in catenary action, load-carrying capacity, ductility and energy dissipation. The maximum enhancement of 39.31% in the ultimate capacity of BFRP strengthened specimen was observed at catenary stage. The effectiveness of carbon fiber reinforced polymer (CFRP) based strengthening schemes for enhancing the progressive collapse resistance of non-seismically designed RC frames was examined by Liang et al. [12]. A total of seven one-half (1/2) scale sub-frame specimens were tested under a middle column removal scenario. Five different CFRP strengthening configurations were employed around the beam-column joints and end column stubs, with the objective of enhancing compressive arch action (CAA), catenary action (CA), or a combination of both mechanisms. The experimental results demonstrated that the proposed strengthening schemes significantly enhanced the load carrying capacity of the specimens during both the compressive arch action (CAA) and catenary action (CA) phases, with maximum increases of 23.8% and 66.7%, respectively. Li et al. [13] conducted experimental investigations on one-third (1/3) scale, two-story, four-bay planar RC frame specimens under a central column removal scenario. The damaged frame was subsequently retrofitted using CFRP wraps and retested to evaluate the efficacy of the proposed technique. The retrofitting process involved removing the damaged concrete near the beam-column joints, followed by straightening or replacing the reinforcing bars. The affected regions were then filled with high-strength cementitious grout and strengthened using CFRP wraps. The results indicated that the proposed retrofitting technique effectively restored the capacity of the damaged RC frame to its original capacity. In addition, numerical models were developed and validated against the experimental results. Based on these findings, the authors proposed a design approach for retrofitting damaged RC structures using CFRP wraps. Qian and Li [14] employed CFRP strengthening to enhance the progressive collapse resistance of RC flat slabs constructed with low and medium reinforcement ratios. Experimental investigations were carried out on six one-third (1/3) scale RC flat slab specimens, considering two control and four strengthened specimens, under a corner column removal scenario. Externally bonded CFRP laminates were applied on the top surface of the slabs in two configurations, namely orthogonal and diagonal orientations, with a spacing of 500 mm center-to-center in both directions. A vertical downward load was applied using a hydraulic jack at the location of the corner column stub. The results demonstrated that CFRP strengthening significantly improved the progressive collapse performance of the flat slabs, with diagonally oriented CFRP laminates exhibiting higher effectiveness. The failure of the strengthened specimens was primarily governed by debonding of the CFRP laminates. The authors recommended the use of fiber or mechanical anchors, to address these debonding issues and further enhance the effectiveness of CFRP strengthening. The effectiveness of CFRP retrofitting in improving progressive collapse resistance of existing reinforced concrete structures under extreme loading conditions was examined by Maxy et al. [15] using the Applied Element Method (AEM). Three different CFRP retrofitting schemes including column jacketing, CFRP strips on slab and a combination of both were considered for the numerical study. The results showed that externally bonded CFRP systems enhance load redistribution and delay collapse progression, demonstrating the potential of CFRP retrofitting as an effective mitigation measure against progressive collapse of damaged structures. Among the different techniques considered, jacketing of concrete column was found most effective to mitigate the pancake effect during progressive collapse. Chen et al. [16] explored the use of nano-CFRP for strengthening RC frames against progressive collapse. Experimental investigations were conducted on two half-scale, four-bay RC frame specimens under a central column removal scenario. The beam ends were strengthened using two 150 mm wide U-shaped nano-CFRP sheets, spaced with a non-strengthened area of 50 mm. A vertical load was applied at the location of the removed central column using an actuator. The results showed that nano-CFRP strengthening increased the load-carrying capacity by 18.5% and enhanced ductility by 3.09 times compared to the control specimen. In addition, the strengthening effectively delayed the shear failure in the joint region. Scalvenzi et al. [17] highlighted that research on the development and investigation of retrofit strategies for mitigating progressive collapse of structures remains limited. The authors conducted numerical investigations to assess the impact of

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