Seismic FRP Retrofit of Bond-Critical Regions in Circular RC Columns: Validation of Proposed Design Methods

Abstract

This study experimentally evaluates the effect of fiber-reinforced polymer (FRP) confinement on the seismic response of circular reinforced concrete columns with spliced reinforcement at the critical hinging regions. A general expression previously was derived and verified for designing the thickness of external FRP jackets required for bond strengthening of spliced reinforcement within the critical hinging region of rectangular column sections. The current study applies the corresponding design expression for circular column sections. Full-scale circular columns with spliced reinforcement were tested under lateral load reversals. Findings show that all of the unconfined columns suffered premature splitting bond failure leading to almost total strength and stiffness degradation. Confining the splice zone with external FRP jackets within the range of thicknesses predicted by the proposed design expression substantially improved seismic performance. The mechanism by which the FRP confinement improves the bond strength of spliced bars in circular columns is similar to that in rectangular columns. Compared with other proposed design methods, the equation under consideration predicts a realistic and conservative jacket thickness and accounts for all parameters that are known to influence the splice strength of steel bars in tension.