Retrofitting damaged reinforced concrete beam-column joints with carbon and basalt FRCM

This paper presents an experimental investigation of full-scale reinforced concrete exterior beam-column joints retrofitted with Fabric-Reinforced Cementitious Matrix (FRCM) composites. Four specimens were designed to fail in joint shear and subjected to a two-phase testing protocol simulating realistic retrofit scenarios. Initially, all specimens were cyclically loaded to approximately 85% of their estimated capacity to induce controlled damage in the joint panel representative of moderate seismic events. Following crack documentation, retrofitting with either carbon or basalt FRCM was applied, and specimens were tested to failure under the same cyclic loading protocol. The experimental program investigated two key parameters: the presence or absence of transverse reinforcement in the joint panel, and the influence of fiber type (carbon versus basalt). Experimental results show that FRCM repair substantially restored and enhanced structural capacity, with average strength increases ranging from 116% to 162% compared to pre-damage levels. Joints originally lacking transverse reinforcement exhibited greater relative gains (144–162%) than reinforced counterparts (116–128%), demonstrating higher repair efficiency for poorly detailed elements. Additional performance improvements included lower stiffness degradation during cyclic loading, and reduced damage accumulation. Instrumentation revealed significant fiber exploitation in both horizontal wrapping and vertical layers, indicating active participation in resisting shear demands. Carbon and basalt reinforcement performed comparably at the structural level, with carbon demonstrating slightly higher capacity enhancement. These findings validate FRCM repair as an effective retrofitting technique for beam-column connections, offering particular advantages for poor joints characteristic of aging structures requiring seismic upgrading.