Prediction of debonding behavior of externally bonded FRP-to-concrete joints with bond defects: Analytical approach and experimental validation

• Development of analytical model for FRP-to-concrete joints with a single bond defect. • Derivation of closed-form solutions for full-range debonding process of defective joints. • Validation against experimental data shows good agreement with IAE values below 15%. • Increasing defect ratio from 10% to 30% causes over 50% drop in minimum load and over 15% loss in peak capacity. • Defects near loaded end cause unstable load drops while those near free end exhibit stable debonding and better capacity. Externally bonded (EB) fiber-reinforced polymer (FRP) composites are widely used to strengthen reinforced concrete (RC) structures. FRP-to-concrete interfaces often contains randomly distributed bond defects resulting from imperfect installation or service-related deterioration. However, most existing analytical models fail to consider the effect of such defects. This paper presents a closed-form analytical model for predicting the debonding performance of defective FRP-to-concrete joints with a single bond defect of arbitrary size and location. The model is formulated using a bilinear cohesive material law (CML) and is validated against experiments from the literature. The predictions agree well with the experimental load-slip responses, with Integral Absolute Error (IAE) values below 15% for the first peak load, the minimum load, the second peak load, and the maximum load. A parametric study quantitatively evaluates the effects of defect size and location on the load-slip response and critical load values. It is found that increasing the defect ratio from 10% to 30% causes over a 50% drop in the minimum load and more than a 15% loss in maximum load. Defects near the loaded end cause unstable responses with significant load drops, whereas those near the free end result in more stable debonding propagation and enhanced load-bearing performance.