Issue 78

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

Qiu et al. [30] used external steel cables installed beneath each beam span as a retrofitting measure against progressive collapse. The effectiveness of this technique was evaluated through experiments conducted on five one-quarter (1/4) scale beam-column assembly specimens under a middle column removal scenario. Two cable diameters, 10 and 14 mm, were considered to examine the influence of cable size on progressive collapse resistance. A monotonic vertical load was applied at the location of the removed middle column using a hydraulic actuator and the structural response of the specimens was measured. The experimental results indicated a significant enhancement in ultimate load carrying capacity, ranging from 90% to 255% for the retrofitted specimens. Furthermore, the authors proposed a simplified model to estimate the ultimate resistance of the beam-column sub-assemblages retrofitted using external steel cables. Izadi and Ranjbaran [31] proposed a progressive collapse mitigation technique using vertical cables suspended from the top of the building. In this approach, the beam ends are connected to vertical cables aligned parallel to the columns. These cables are anchored to a hat braced frame at the roof level, which helps redistribute loads to adjacent structural members during column removal scenarios. A ten storey regular building was studied under nine independent column removal cases at the first, fifth and tenth storeys. The results showed that the proposed scheme was effective in mitigating progressive collapse of building considered. Steel plate systems Elsanadedy et al. [32] used bolted steel plates to strengthen RC beam-column assemblies of non-seismically designed frames under a column removal scenario. Numerical analyses were carried out on ten two-dimensional (2D) FE models to investigate the influence of steel plate thickness, steel grade and strengthening location on progressive collapse response. The results demonstrated that bolted steel plate strengthening significantly enhanced load-displacement response and stiffness of RC assemblies, thereby improving progressive collapse resistance. During the flexural phase, strengthened specimens exhibited up to 25% higher load-carrying capacity, compared to the control specimen. However, the authors highlighted the need for further investigations on three-dimensional frame assemblies incorporating slabs and transverse beams, under a column removal scenario to better represent realistic structural behaviour. The use of corrugated steel plates to enhance the progressive collapse resistance of RC frames under column removal scenarios was proposed by Ramin et al. [33]. The plates were installed at beam ends to shift the plastic hinge region away from beam-column joint regions. The tensile behaviour of corrugated plates with varying geometries, thicknesses and wave configurations was characterized through experimental testing and validated using numerical simulations. Subsequently, the performance of retrofitted beam-column assemblies under a middle column removal scenario was evaluated through finite element analyses. The results indicated that the proposed retrofitting scheme, particularly with a three-wave corrugated plate, significantly improved structural performance in terms of ultimate load-carrying capacity, energy dissipation, stress distribution in reinforcement and catenary action. Load-carrying capacity of strengthened specimens was enhanced by 48.7%, while energy absorption was increased by 44.38% to 67.49% compared to the control specimen. Building level measures Garg et al. [34] evaluated the effectiveness of three strengthening strategies i.e., addition of a perimeter beam, addition of a shear wall and a combination of both, for improving the progressive collapse performance of flat slab buildings. A simulation model of a four-storey, three-bay by three-bay building structure was developed for the analysis. The Demand Capacity Ratio (DCR) and vertical displacements at the top of the removed columns were determined for different column removal scenarios, including corner, edge and interior columns, in accordance with GSA guidelines. Both static and dynamic responses of the structural models were assessed under alternate, simultaneous and sequential column removal cases. The results indicated that the proposed strengthening schemes significantly enhanced the progressive collapse resistance of flat slab building structures by reducing the DCR of critical columns by up to 67%. Furthermore, Garg et al. [35] investigated the progressive collapse behaviour of a five-storey RC flat slab building strengthened by introducing perimeter beams. Nonlinear dynamic analysis was carried out under corner and edge column removal scenarios. Various strengthening configurations were examined by altering the size and reinforcement detailing of the perimeter beams. The results demonstrated that the inclusion of perimeter beams significantly enhanced progressive collapse resistance by increasing structural stiffness and facilitating effective load redistribution. The authors also evaluated sustainability aspects in terms of cost and CO ₂ emissions for different strengthening schemes. Accordingly, a scheme of varying beam sizes at all storeys was proposed as an optimized configuration which showed a balanced performance between progressive collapse resistance and sustainability considerations. Structural robustness of existing buildings through retrofitting of roof level beams for progressive collapse mitigation was investigated by Rueda-Garcia et al. [36]. The study evaluated performance of low-rise RC and steel structures, by increasing the roof beam depth to two and four times that of the existing beams. Three different retrofit configurations were examined i.e., strengthening of all perimeter beams, all beams in the X-direction and all beams in the Y-direction. Based on numerical

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