Experimental Evaluation of Reinforced Concrete Beam-Column Joints Strengthened With CFRP Grid

The failure of reinforced concrete (RC) beam–column joints during seismic events can precipitate the progressive collapse of structures. This failure mechanism, predominantly observed in structures constructed prior to the 1970s, is primarily attributed to suboptimal design and inadequate reinforcement detailing. Recent experimental investigations have sought to enhance the performance of beam–column joints—in terms of strength, ductility, and failure mode—using externally bonded fiber-reinforced polymer (FRP) techniques. However, even with the necessary initial bonding for installation, the reliance on epoxy adhesives in these methods has raised concerns regarding debonding and diminished performance under high-temperature and humid conditions. To address these long-term limitations, this study introduces a cementitious matrix as the primary, durable alternative to epoxy for the strengthening system. RC beam–column joint was retrofitted using a carbon fiber-reinforced polymer (CFRP) grid encased in engineered cementitious composites (ECC). The original dimensions of the retrofitted specimens were maintained by removing the concrete cover from the joint region where the cementitious matrix was applied. Experimental results indicate that this retrofitting approach effectively modifies the failure mode by redistributing the load from the joint to the beam. Additionally, the specimens demonstrated enhanced strength and ductility, thereby delaying the onset of failure.