Introduction of critical stress state criterion to predict bond strength between FRP and concrete substrate

The technique of externally bonded FRP to existing concrete structures has been rapidly growing in the civil engineering field. In general, the performance of the strengthened structures depends on the bond between FRP and concrete. The development of conceptual predicting expression for the bond strength capturing the debonding initiation and behavior is needed. Prediction models are developed as a function of material properties of structures with empirical and mathematical coefficients and parameters. Analyzing and understanding the debonding mechanism enables the FRP strengthening technique more wide-use and application. Study of debonding behavior is the main focus of this research.;A simple criterion for the FRP debonding initiation is proposed. Using the elasticity theory, the critical stress state on a finite element in the vicinity of the bond interface is considered to develop an analytical solution. The shear-slip behavior at the bond interface is described with the developed analytical solution based on mechanics of materials. The adhesive material properties are successfully implemented as well as the properties of FRP and concrete substrate. The fracture depth and the strength factor are established from a single pull-off test. The proposed criterion and the analytical solution are then applied to the experiment conducted in this study and existing experimental data from literature (totally 342 data points), to predict the bond strength. The comparison between predicted values and experimental data shows good agreement providing a relatively high correlation factor. In addition, comparison between the existing models and the proposed model verifies the validity of the proposed criterion and the predicting expressions.