Issue 78

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

analyses, it was observed that retrofitting only the perimeter beams was ineffective particularly during interior column failure scenarios. The authors further suggested the need for additional studies to assess the applicability and effectiveness of the proposed retrofitting schemes for high-rise buildings with varying column sizes along the height as well as for buildings located in high seismic regions. Kim and Shin [37] retrofitted six-storey and ten-storey RC model structures using external prestressing tendons provided along floor girders to enhance progressive collapse performance. Tendons were placed in two different configurations i.e., X-shaped and parallel along the beam length. Progressive collapse potential of control and retrofitted building models were evaluated by performing nonlinear static and nonlinear dynamic analysis under column removal scenario. The analysis results revealed that the building model without any retrofitting measure was vulnerable to progressive collapse. However, provision of external prestressing tendons improved the progressive collapse resistance of building models. The effectiveness of retrofitting increased with an increase in the initial tension and cross-sectional area of tendons. It was further observed that, in addition to progressive collapse resistance, external prestressing tendons effectively enhanced seismic performance of RC building models. Ali et al. [38] investigated the effectiveness of various retrofitting strategies including different bracing systems, viscous dampers and CFRP wrapping to enhance the progressive collapse resistance of a thirteen-storey RC moment-resisting frame. Nonlinear dynamic analysis was performed by simulating the removal of an interior column at the first, sixth and thirteenth storeys. Three types of bracing systems, namely, X-bracing, inverted V-bracing and diagonal bracing were considered for the study. Viscous dampers were installed at different locations, including the central bay, inner bays and selected storeys of inner bays, while CFRP wraps were applied to the bottom and side faces of beams. The results indicated that retrofitting schemes improved the progressive collapse resistance of the structure. The study further recommended the combined use of these techniques to achieve enhanced structural performance and more effective force redistribution under column removal scenarios. Huang et al. [39] employed a novel sector friction damper (SFD) to enhance the progressive collapse resistance of reinforced concrete (RC) frames. The study first developed a theoretical model of the SFD, followed by numerical analysis to assess the influence of key parameters on its mechanical performance. The damper was then installed at beam-column joints of an RC frame and its progressive collapse behaviour was investigated under column removal scenarios. The results demonstrated that the inclusion of SFD effectively enhanced the structural performance, with increase of 16.4% in static resistance, 15.6% in dynamic resistance, 17.7% in ductility and 69.7% in energy dissipation capacity. Furthermore, an analytical model was proposed to predict the load-bearing capacity of SFD strengthened RC frames during the compressive arch action phase, highlighting the effectiveness of energy-dissipation based retrofit strategies in mitigating progressive collapse. Abruzzo et al. [40] identified key progressive collapse mitigation strategies of RC building structure, which included the alternate load path method, tie force provisions and enhancement of structural continuity and redundancy. Authors reported that buildings which satisfy codal requirements of ACI and UFC related to integrity and tie forces, can remain vulnerable to progressive collapse when subjected to the loss of interior columns. It was emphasized that more realistic and performance based assessment of structural response, focused on load redistribution mechanisms is essential for improving collapse resistance in reinforced concrete buildings. Adaros and Smilowitz [41] discussed the challenges associated with retrofitting existing structures to resist progressive collapse. A case study of five-storey building was presented, which was retrofitted using high-strength steel rods that suspend the floors from a steel transfer girder placed at the roof level. Nonlinear dynamic analysis under column removal scenarios was performed to examine the influence of concrete tensile strength and the contribution of existing reinforcement on the failure mechanism. Alogla et al. [42] proposed a mitigation scheme that involves providing additional reinforcement in the mid-layer of RC beams to improve resistance against progressive collapse. Experimental investigations were conducted on four RC beam-column subassemblies under quasi-static loading. The results showed that the proposed scheme significantly enhanced both ductility and collapse load under column removal scenarios. The load-carrying capacity increased by 5% to 12% during the compressive arch action stage and by approximately 52% to 109% during the catenary action stage. Based on the experimental findings, the authors also developed a simplified model to predict load capacity during catenary action, incorporating reinforcement fracture. Based on the available literature, it is observed that a considerable number of studies have been conducted proposing a wide range of strengthening techniques to enhance the progressive collapse resistance of RC structures. These investigations encompass experimental, numerical and analytical approaches. The reported studies consider diverse structural configurations, including beam-column assemblies, typically comprising two-span beams and three columns with a removed middle column, multi-bay and multi-storey planar frames and three-dimensional frames with single or multiple bays in both directions and varying storey levels. In addition, strengthening of beam-slab sub-assemblages, beam-slab-column substructures and flat slab systems has also been investigated. Experimental investigations have been conducted on specimens of varying scales, ranging from full-scale to one-quarter (1/4) scale, under different column removal scenarios, including middle, corner, edge and penultimate column removal. A graphical representation of the various strengthening

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