Closed-form solution to the debonding of embedded Through-Section FRP bar-to-concrete joints with interfacial defects

Abstract

The Embedded Through-Section (ETS) technique has recently received significant attention in strengthening existing reinforced concrete (RC) structures through the use of fibre-reinforced polymer (FRP) bars inserted into predrilled holes in concrete using adhesive. Interfacial bond defects are easily observed in practical applications of ETS FRP bar-to-concrete joints due to poor construction or environmental deterioration, resulting in degradations in both local bond behavior and global performance of ETS-strengthened concrete systems. This paper presents a closed-form analytical solution to evaluate the effect of interfacial defects on the debonding response of ETS- FRP bar-to-concrete joints and examine the interfacial defect criticality from size and location aspects. A set of closed-form solutions for the load-slip curve, debonding load, interfacial bond stress, tensile stress as well as effective bond length are derived throughout the debonding process. After validating the analytical solutions with self-conducted test results and existing experimental and numerical data, a parametric analysis is performed to quantify the influence of interfacial defects on the load responses. The results show that the analytical predictions can accurately describe the debonding behavior of ETS FRP bar-to-concrete joints with different defect lengths and locations. It is revealed that bond defects adversely affect both the debonding load and maximum load; however, enhancing the bond strength and embedded length can alleviate such a detrimental impact. Furthermore, defects near the loading point in short joints or close to the embedded end in long joints can maximize the load-bearing capacity. These findings emphasize the critical role of interfacial defects in the debonding analysis and practical design of RC beams strengthened with FRP bars using the ETS technique.