Experimental and Numerical Studies of Debonding Monitoring of FRP Shear-Strengthened Beams Using EMI Technique

Fiber-reinforced polymer (FRP) is commonly used to strengthen or retrofit reinforced concrete (RC) structures. FRP debonding may initially occur around tiny cracks and then propagate to other parts of the structure, ultimately leading to the brittle failure of the strengthened structure. Therefore, the secure bonding of FRP onto the strengthened structure should be closely monitored using a reliable approach. In this study, an electromechanical impedance (EMI) technique is applied to monitor early FRP debonding in FRP shear-strengthened RC beams through experimental and numerical studies. Lead zirconate titanate (PZT) patches and strain gauges were bonded onto the surface of the FRP. The admittance and strain data were then collected and used to assess the FRP bonding condition. As the loads were increased, the beams began cracking, leading to FRP debonding and subsequent brittle failure of the beams. A root-mean square deviation index was adopted to quantify the debonding severity. The admittance data of the PZT patches were found more advantageous than the strain data and visual inspection to detect the debonding initiation. The EMI technique was then simulated through finite-element analysis. The FRP-concrete interface was modeled using a bond-slip model. Infinite elements were used to eliminate wave reflections at boundaries. The experimental and numerical results validate the effectiveness of the EMI technique in monitoring FRP debonding.