Semi-empirical model for load-slip response of externally bonded FRP strengthened reinforced concrete structures

Understanding the interfacial bond behavior between externally bonded fiber-reinforced polymer (EB-FRP) and concrete is essential for the effective strengthening of civil structures. Various bond-slip models exist, but most analytical models are too complex for practical engineering, and empirical models lack flexibility across diverse configurations. Furthermore, existing models are generally based on small-scale tests that do not adequately represent real-world construction conditions. This study presents a semi-empirical bond-slip model that integrates experimental observations with fracture mechanics principles to predict debonding behavior. Strain distributions and debonding mechanisms were captured using digital image correlation (DIC) in 24 large-sized EB-FRP strengthened reinforced concrete (up to 915 mm in length, 2 mm in thickness) subjected to single-lap shear tests. The model applies an interfacial analytical approach based on fracture mode II (sliding shear) and uses multi-variable nonlinear regression to account for key bond indicators. Validation of the model against a dataset of 1659 single-lap shear tests reported in the literature confirms the accuracy in predicting load-slip responses. The proposed bond-slip model offers a practical and scalable tool for calculating the debond capacity efficiently, making it valuable for both research and industry applications in large-sized EB-FRP systems.