Issue 78

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

CFRP retrofitting on the progressive collapse performance of a five-storey RC frame subjected to middle and corner column removal scenarios. The results indicated that CFRP strengthening of beams and columns helped in preventing premature brittle failures and enhanced alternative load path mechanisms, thereby increasing resistance to progressive collapse. Furthermore, the findings emphasized the importance of multi-hazard retrofit strategies, wherein seismic strengthening measures can simultaneously improve progressive collapse performance. Esfandiari and Latifi [18] evaluated the progressive collapse behaviour of a five-storey RC building under three column removal scenarios through numerical studies. The beams and slab bottom were strengthened with externally applied CFRP sheets. The results indicated that CFRP strengthening improved the structural response by reducing displacement, cracking and stress levels, thereby enhancing the resistance of the building against progressive collapse. Qian and Li [19] investigated the effectiveness of glass fiber reinforced polymer (GFRP) strengthening in enhancing the progressive collapse performance of flat slabs. A total of seven specimens of one-quarter (1/4) scale multi-bay flat slab substructure were tested, including three control specimens and four specimens strengthened with GFRP strips. The GFRP strips were applied as horizontal ties on the top surface of the slabs in both longitudinal directions at a spacing of 500 mm. In three strengthened specimens, fiber anchors were provided at the intersections of orthogonal GFRP strips. A 12-point distributed load was applied using a hydraulic jack and the structural response was evaluated. The results showed a significant improvement in initial stiffness, yield strength, crack resistance and first peak resistance, indicating the effectiveness of GFRP strengthening in enhancing progressive collapse resistance during the pre-failure stage. However, at large deformations in the post-failure stage, the effectiveness of GFRP strips was limited due to significant debonding at the concrete interface, even in the presence of fiber anchors. Feng et al. [20] investigated the progressive collapse behaviour of GFRP strengthened RC beam-slab sub-assemblages under a corner column removal scenario. Experiments were conducted on one-half (1/2) scale beam-slab specimens subjected to quasi-static loading. The sub-assemblages were strengthened using two techniques: externally bonded reinforcement (EBR) with GFRP laminates and near surface-mounted (NSM) GFRP bars. In the EBR scheme, GFRP laminates were applied orthogonally on the top surface of the slab. The influence of laminate width was examined by considering two different widths of laminates, 145 mm and 70 mm. For the NSM technique, 6 mm diameter GFRP bars were placed at a spacing of 200 mm in both directions. Vertical loads were applied at the location of the removed corner column using two hydraulic actuators and the structural response of test specimens was measured. The experimental results indicated that both strengthening techniques effectively enhanced the progressive collapse resistance of the specimens with an increase in peak load capacity by 10.81% to 24.83%. It was further observed that, the NSM technique demonstrated superior overall performance compared with EBR strengthening. In addition, the authors developed finite element models to perform FE analysis, which showed good agreement with the experimental results. The effectiveness of FRP strip retrofitting for RC beam-column and beam-slab-column substructures under a column removal scenario was evaluated by Zhang et al. [21] through numerical studies. The authors developed 81 full-scale FE models to investigate the influence of strip thickness, configuration and placement on progressive collapse resistance. Study demonstrated that optimized FRP schemes significantly enhanced collapse resistance at large deformations by improving tensile contributions and catenary action. Provision of FRP strips parallel and perpendicular to the beam axis, improved collapse resistance of RC beam-column substructure by 53.6% at large deformations. For beam-column-slab substructure, a scheme of orthogonal and diagonal FRP strips applied at the bottom of the slab was found effective, with a 15.3% increase in collapse resistance of the substructure. Furthermore, an analytical approach for predicting ultimate collapse resistance of FRP retrofitted substructures with equal spans and idealized boundary conditions, was proposed based on the findings of the study. Innovative hybrid strengthening techniques Effectiveness of hybrid Textile-Reinforced Mortar (TRM) and Near-Surface-Mounted (NSM) reinforcement in enhancing the progressive collapse resistance of existing RC frames was examined by Vieira et al. [22]. Experimental studies were conducted on four one-half (1/2) scale beam-column assemblies under a middle column removal scenario. Quasi-static loading was applied at the location of the removed middle column using a hydraulic actuator. For NSM strengthening, 6 mm diameter stainless-steel bars were employed. In the TRM technique, two types of textile fibers, namely light carbon and heavy carbon were used. The results indicated that both TRM and NSM strengthening techniques significantly improved load resistance during the compressive arch action phase, with increases of 1.44 and 1.42 times, respectively compared to the unstrengthened specimens. Qin et al. [23] evaluated the progressive collapse resistance of RC beam-column assemblies strengthened using engineered cementitious composites (ECC) at the beam bottoms and hybrid reinforcement including BFRP bars, steel rebars and their combination. Experimental and numerical investigations were carried out on four reduced (1/3) scale test specimens under column removal scenario. Pseudo-static loading was applied at the top of removed middle column in displacement-

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