CFRP-based structural repairing and strengthening of deficient cast-in-place RC foundation-column joints

The foundation–column joint (FCJ) is a critical structural component in moment-resisting reinforced concrete (RC) frames. Field observations from recent seismic events have shown that exterior or corner cast-in-place RC FCJs without transverse reinforcement were prone to damage, impairing the seismic performance of the entire structural system. Such joints, commonly found in Türkiye and other seismically active regions with inadequate construction and inspection practices, experienced concrete cover crushing, followed by buckling of the longitudinal reinforcement. This study investigated the cyclic response of a deficient and carbon fiber-reinforced polymer (CFRP)-strengthened exterior RC FCJ, along with the repair of a pre-damaged FCJ using CFRP, through a combined experimental and numerical approach. A code-compliant FCJ with proper transverse reinforcement was also tested as a reference, which primarily exhibited a flexural hinge at the column base. The deficient FCJ exhibited failure due to concrete crushing and longitudinal bar buckling within the foundation panel—consistent with post-earthquake field evidence. CFRP repair of the pre-damaged FCJ effectively mitigated further panel deterioration. Additionally, the CFRP strengthening scheme applied prior to damage significantly improved both the strength and displacement capacities of the deficient FCJ, outperforming even the code-compliant specimen. The results confirmed that CFRP application to joint panel was highly effective in enhancing the cyclic performance of exterior FCJs lacking transverse reinforcement. • Evaluating seismic performance of deficient cast-in-place RC FCJs. • Experimental results align with field observations of severe damaged deficient FCJs. • Innovative CFRP repair scheme restores function in damaged RC FCJs. • Proposing a scalable retrofit method for vulnerable RC FCJs. • Validated numerical models replicate observed failure mechanisms.