Issue 78

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

overall integrity and robustness of the precast substructure. The proposed strengthening scheme increased load-carrying capacity by 115% to 142% compared to the control specimen. Enhancement was also observed in other parameters, including displacement, stiffness, energy absorption and reduced separation between precast elements. Externally bonded CFRP sheets applied along the side faces of the beam, combined with hybrid FRP anchors were employed by Pan et al. [49] to enhance progressive collapse resistance of precast RC frames. Experimental investigations were conducted on two one-half (1/2) scale precast RC frame sub-assemblages subjected to a middle column removal scenario. Displacement controlled loading was applied at the location of the removed column to simulate the progressive collapse scenario. The results indicated that CFRP strengthening was particularly effective in enhancing load resistance during the catenary action stage, thereby improving the robustness of the precast frame at large deformations. The proposed strengthening scheme could not significantly enhance the load-carrying capacity during flexural action and compressive arch action phases. The authors recommended the use of multiple CFRP layers or a composite strengthening approach combining externally bonded reinforcement (EBR) and near-surface mounted (NSM) techniques for improved strengthening efficiency. An analytical model and practical construction recommendations were also proposed, while emphasizing the need for additional experimental data to refine and validate predictive models for progressive collapse mitigation. Zhang et al. [50] studied influence of FRP strengthening on progressive collapse performance of RC and precast frame substructures. Detailed numerical models were developed considering bond-slip of rebars as well as FRP strips, bond failure between precast and cast-in-place concrete and loss of cross-sectional area of rebars. Effectiveness of different strengthening schemes was examined for beam column assemblies under column removal scenario. Results of study indicated that applying longitudinal FRP strips at beam surfaces and U-shaped transverse FRP strips in plastic hinge regions increases progressive collapse resistance at large deformations by 49.5% and 48.1%, for RC and precast concrete substructure respectively. However, the improvement in collapse resistance at small deformations level was not significant in RC structures as compared to precast concrete structures. Pan et al. [51] examined Carbon Fiber Rope (CFR) for strengthening precast beam column assemblies subjected to a progressive collapse scenario. Experimental studies were conducted on three one-half (1/2) scale assemblies under a middle column removal condition. Two strengthening schemes were adopted, namely implanting CFR and binding CFR. In addition, pull-out tests and knot tests were performed to evaluate the performance of rope for the both schemes. The load displacement responses and observed failure modes indicated that both strengthening techniques significantly enhanced the ultimate load capacity during the catenary action stage. The use of carbon fiber rope was found to improve the safety and redundancy of precast assemblies, thereby meeting the strengthening requirements under column removal conditions. Furthermore, the authors proposed analytical models based on semi-empirical and semi-theoretical equations to predict the load-carrying capacity of precast frames subjected to column removal. Practical construction recommendations, including location of drilling points, chamfering requirements, suitable knot types etc., for improved performance, were also provided for both implanting and binding CFR schemes. Hybrid techniques A hybrid strengthening technique incorporating bolted steel plates and CFRP strips to improve the progressive collapse resistance of precast beam-column assemblies was evaluated by Zhang et al. [52]. Four different strengthening configurations were proposed and examined through finite element analysis. In addition to bolted steel plates and CFRP strengthening, effect of important parameters such as top and bottom longitudinal reinforcement ratio of beam, strength of steel plates, concrete compressive strength, yield strength of reinforcing bars and span-to-depth ratio on the progressive collapse resistance of precast assemblies were studied. The findings of study indicated that the combined application of bolted steel plates and CFRP strips effectively improved progressive collapse performance of precast reinforced concrete systems. The ultimate load-carrying capacity of strengthened specimens was enhanced by 386% compared to the control specimens. Elsanadedy et al. [53] assessed the effectiveness of combining near ‑ surface mounted (NSM) steel rebars and externally bonded CFRP sheets to mitigate progressive collapse of precast RC beam-column joints under a column removal scenario. Experimental studies were conducted on three one-half (1/2) scaled specimens. Each specimen was comprised of two span beam and three columns. A dynamic vertical load was applied at the top of middle column to simulate column removal condition. The proposed strengthening scheme was found effective, with enhancement in ultimate collapse load and energy dissipation observed as 16.9 times and 12.4 times, respectively, compared to the control specimen. Three dimensional (3D) FE models were also developed incorporating rate dependent material nonlinearity and bond behavior at FRP to concrete interface, to compare experimental results. Subsequently, FE models were used to perform parametric study. The effect of different parameters were studied such as end anchorage of CFRP sheets at outer joints, area of NSM reinforcement and thickness of CFRP sheets. The experimental and numerical findings suggested that, the proposed strengthening scheme, was effective to enhance progressive collapse resistance during flexural action phase. However, due

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