Integrated NSM and GFRP-reinforced ECC/UHPC techniques for strengthening deficient RC columns

The integrity of the structure and load capacities of reinforced concrete (RC) columns are severely impacted by corrosion-induced reinforcing steel losses. This study examines an innovative strengthening technique incorporating near-surface mounted (NSM) steel or glass fiber-reinforced polymer (GFRP) bars, combined with an external layer of engineered cementitious composite (ECC) or ultra-high-performance concrete (UHPC) reinforced with a GFRP mesh. The experimental results demonstrated that UHPC provided superior confinement compared with ECC jackets, leading to the highest load capacity enhancement. Incorporating NSM steel bars with ECC (Group 3 (G3)) significantly improved performance, increasing ultimate load capacity by 25%-32%, with energy absorption increasing up to 3.9 times compared with the control column. The combination of NSM bars with external jacketing proved to be the most effective, particularly when NSM GFRP bars were used alongside UHPC, resulting in a 49% increase in load capacity and a substantial improvement in energy absorption. Additionally, finite element models were developed and showed good agreement with the experimental findings, further validating the proposed strengthening technique. The model was extended for a parametric study examining the effect of main reinforcement diameter. The results highlight the important role of the reinforcement diameter in enhancing column strength. Increasing the reinforcement diameter led to progressive strength improvements, but the efficiency of additional reinforcement decreased at larger diameters.