Lateral strength and ductility of reinforced concrete columns strengthened with NSM FRP rebars and FRP jacket

Abstract

Fiber-reinforced polymer (FRP) wrapping of reinforced concrete (RC) columns is an effective way to improve their shear capacity and ductility and prevent buckling in their longitudinal reinforcements. Another strengthening method called the near surface mounted (NSM) reinforcement has been proven effective in improving the flexural strength of RC columns. In this research, the strengthening of RC columns with the combined use of NSM rebars and FRP jacket was studied using a finite element modeling approach. After validating the numerical models with the existing experimental data, a comprehensive parametric study was performed to determine the effect of axial load, implementing the FRP confinement around the base or over the entire height of the column, the number of plies of FRP jacket, the type of jacket fiber, the ratio of NSM reinforcement, and the compressive strength of the concrete on the behavior of the strengthened RC columns. The results show that the optimum number of plies of jacket for reaching a desirable level of ductility can be determined by setting the maximum compressive strain in the confined concrete, εccu, to 0.008. Increasing the ratio of NSM reinforcement from 0.16% of the total cross-sectional area to 1% led to approximately 28% increase in the lateral strength and 50% decrease in the ductility factor.