Repair and strengthening of reinforced concrete columns with CFRPs

In this study, seismic retrofitting of undamaged and moderately damaged RC columns with CFRP was investigated. The experimental program was conducted on five RC columns with inadequate tie spacing, 90-degree hooks at tie ends, and plain (undeformed) reinforcing bars. Columns were tested under a constant axial load of 27% of axial capacity and under reversed lateral cyclic loading. The primary objective of this study was to investigate the influence of sustained axial load during repairing, damage, and corner-rounding radius of CFRP wraps on the seismic performance of RC columns. Improved performance in terms of ductility, dissipated energy, and secant-stiffness degradation was observed for the CFRP strengthened columns. Reducing the corner-rounding radius deteriorated the seismic behavior of the columns, while the stiffness degradation response remained unaffected. The sustained axial load during repairing had only minor effect on column behavior. After CFRP repairing, the increase in yield drift ratio and curvature was observed to be in proportion with the corresponding consumed ductility values during damage cycles. A drift-based design equation for FRP repaired columns was proposed that considers the damage amount and axial load level as the major parameters as consistent with the experimental results.