Issue 78

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

Accordingly, various international codes and guidelines recommend ensuring structural integrity and continuity of reinforcement across joints of precast structures to mitigate progressive collapse. In line with other standards, the Indian Standard for Building Design and Erection Using Prefabricated Concrete IS: 15916-2020 [43] also recommends that precast structures should be designed with adequate structural integrity and continuity of reinforcement across joints to reduce the probability of progressive collapse. Similarly, the Indian Standard on Criteria for Structural Safety of Tall Concrete Buildings IS: 16700-2023 [44] emphasizes that progressive collapse should be mitigated by ensuring alternate load transfer paths through appropriate design and detailing. Hence, it becomes important to evaluate the progressive collapse potential of existing high-rise structures constructed using precast technology. Many existing multi-storey precast buildings may require strengthening to enhance their resistance against progressive collapse. Furthermore, IS: 15916-2020 [43] depicts that “adequate strengthening of external joints of precast structure is important and should be kept in mind for ensuring stability of precast / prefabricated structures”. As discussed in the previous section, substantial research has been carried out on strengthening reinforced concrete (RC) structures to enhance their resistance against progressive collapse. Various retrofitting strategies and design recommendations have been proposed by researchers to mitigate collapse of RC structures under column removal scenarios. However, comparatively limited studies are available on the strengthening and retrofitting of precast concrete frame systems subjected to progressive collapse. Therefore, this section presents a review of the existing studies focusing on strengthening techniques for precast frames under progressive collapse scenarios. Bolted steel plates Al-Salloum et al. [45] investigated the effectiveness of bolted steel plates in enhancing the progressive collapse resistance of precast beam-column assemblies. Experimental studies were conducted on three one half (1/2) scale specimens comprising of two-span beams and three columns. A vertical cyclic load was applied at middle column to simulate a column removal scenario. The results demonstrated that the use of bolted steel plates significantly improved the collapse resistance, with the ultimate load capacity increasing by up to 29 times compared to the control specimen under column removal condition. In addition, a section analysis approach was adopted to estimate the theoretical collapse load by incorporating effects such as strain compatibility, material nonlinearity, strain rate and possible failure modes. The efficacy of bolted steel plate strengthening was further examined by Elsanadedy et al. [46] through numerical studies. Detailed finite element models were developed and validated using available experimental results from previous studies. Subsequently, a comprehensive parametric study was performed to examine the influence of steel plate thickness, steel grade and anchorage detailing within the compression zone on the structural response of precast assemblies under column removal situation. Additionally, parameters related to peak load, energy efficiency and strengthening effectiveness were proposed to facilitate comparison between strengthened precast frames and equivalent monolithic frames. The study also provided design recommendations for steel grade, plate thickness, bolt diameter and edge distance to improve the progressive collapse performance of precast assemblies strengthened with bolted steel plates. Kim et al. [47] experimentally investigated the progressive collapse behavior of one-third (1/3) scale wet precast beam column assemblies under a middle-column removal scenario. Three steel tendon strengthening configurations, namely, embedded, exterior and penetrating tendons were considered for the study. Concrete and bearing crushing were observed in all specimens, while tendon fracture occurred in the specimens strengthened using embedded and penetrating tendons. For, exterior type tendons anchorage bond failure was observed in addition to concrete and bearing crushing. Overall, steel tendons enhanced the progressive collapse performance of the precast beam-column assemblies. Embedded tendon system was effective at compressive arch action phase with improved joint flexural resistance and axial force transfer, whereas exterior tendons primarily enhanced the catenary action response. Improved performance was observed at both compressive arch action and catenary action phase for penetrating tendon system. FRP materials Qian and Li [48] evaluated the effectiveness of externally bonded GFRP strengthening for multi-panel precast beam column-slab substructures. Experiments were conducted on reduced one-third (1/3) scale test specimens comprising of beam-column-slab substructures under column removal scenario. Precast elements were connected using bolted dry connections. The proposed strengthening scheme consisted of 80 mm wide GFRP strips applied orthogonally in both directions on the top and bottom faces of the slab. At the top surface, strips were placed locally around the beam-column slab interface, oriented perpendicular to the beam axis, to improve the anchorage. At the bottom surface, strips were applied continuously across the entire slab length to enhance the performance of substructure at large deformations. The results of the experimental studies demonstrated that the proposed GFRP strengthening configurations significantly improved the

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