Issue 78

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

of drilling locations, chamfering requirements and suitable knot types can significantly influence the effectiveness of the strengthening system. Similarly, techniques involving NSM reinforcement or other intrusive strengthening methods may provide effective load transfer and improved structural performance, but their application requires adequate access and modification of the existing concrete, which may pose practical challenges in existing structures. Overall, although a number of studies have investigated strengthening of RC and precast structures and connections, most available studies have been conducted using reduced-scale specimens representing simplified beam-column assemblies under a middle-column removal scenario. The effects of transverse beams and floor slabs were generally not considered and the beams were not extended beyond the exterior columns, limiting the development of catenary action. Therefore, the findings cannot be directly generalized to system-level strengthening of RC and precast structures without further investigation. However, these studies provide useful insights into the structural behavior and load redistribution mechanisms of strengthened RC and precast systems under progressive collapse scenarios. Comparison between strengthening of RC and precast systems A comparative assessment of RC and precast structures indicates significant differences in the extent and nature of research related to strengthening against progressive collapse. A substantial number of studies are conducted and reported for RC systems, whereas investigations on precast structures, particularly in the context of strengthening against progressive collapse, remain limited. In terms of similarities, commonly adopted strengthening techniques for both RC and precast systems include, externally bonded fiber-reinforced polymer (FRP) wrapping, bonded steel plates and hybrid retrofitting approaches. These techniques primarily aim to improve the ability of structural members to redistribute loads and develop alternate load paths under progressive collapse scenario. However, key differences exist in their application and effectiveness. Most precast related studies are primarily limited to component level investigations on beam-column subassemblies, while comprehensive studies on three-dimensional systems, including effect of slabs, transverse beams and multi-storey buildings, are not explored in great detail. Existing studies on progressive collapse strengthening of precast structures are predominantly limited to beam-column connections, with limited attention given to connections between other structural components, namely, column-to-column, beam-to-beam, beam-to-slab, slab-to-wall as well as system-level strengthening. Several strengthening techniques, including nano-CFRP sheets, use of dampers, steel bracing and hanging cables from the roof have been investigated for RC structures but remain unexplored for strengthening precast structures against progressive collapse. Strengthening of RC and precast systems to enhance progressive collapse resistance involves several practical and technical challenges, which are more pronounced in precast structures. In RC structures, challenges are generally associated with accessibility, surface preparation and ensuring adequate bond performance for externally applied materials. However, due to monolithic construction, achieving continuity and effective load redistribution is relatively feasible. In contrast, precast systems face certain challenges related to the strengthening applications due to different connection types, which govern overall behaviour of precast structures. Strengthening of dry connections or connections having a presence of corbel is particularly difficult, as the application of externally bonded reinforcement or wrapping techniques is often limited by interface discontinuity and compatibility between existing elements and strengthening materials. Constructability constraints, such as restricted access to connection regions and the need to avoid disturbance of existing precast joints, further complicate strengthening implementation. These challenges highlight the need for specialized, connection-focused strengthening strategies for precast systems, in contrast to the relatively more straightforward approaches applicable to RC structures. As discussed, researchers have employed a variety of structural strengthening techniques to enhance the progressive collapse resistance of RC and precast structures. These measures include the use of bolted steel plates, FRP composites, as well as hybrid strengthening approaches. Among these, externally bonded FRP systems using GFRP, CFRP, BFRP and their hybrid configurations have been widely adopted. However, FRP materials exhibit brittle failure and debonding issues. In addition, their performance under elevated temperatures, particularly during fire events, remains a concern. Stainless Steel Wire Mesh (SSWM) has emerged as a potential alternative strengthening material, owing to its local availability and cost-effectiveness compared with FRP materials. However, its application for structural strengthening has not been extensively explored. The following section presents a review of studies investigating the feasibility of SSWM for structural strengthening, together with an overview of its fundamental characteristics.

335