A nonlinear FEM approach for predicting concrete cover separation and FRP debonding in RC beams externally reinforced with FRP

This study presents a novel framework for the analysis of reinforced concrete (RC) structures externally bonded (EB) with fiber-reinforced polymer (FRP) sheets or plates. The proposed framework is designed to simulate the behavior of RC beams from the onset of loading up to failure, capturing the main brittle failure mechanisms: debonding of the FRP reinforcement or detachment of the concrete cover (cover separation). The framework is based on a nonlinear total Lagrangian Finite element Method (FEM), which naturally accounts for large displacements and rotations when necessary. The FRP coupling strategy is originally presented in this study and combines a J2 continuous damage model with high aspect ratio coupling elements (J2-HARc). To complete the brittle failure modeling of RC structures, it also employs high aspect ratio (HAR) elements specifically designed to simulate cracked concrete, formulated within a mixed-mode continuous damage strategy that incorporates both Mode I and Mode II fracture behaviors through a single damage variable. The framework was validated through numerical examples, with results compared against experimental data. The findings demonstrate that the framework is capable of accurately reproducing the structural behavior of FRP-strengthened RC beams, successfully capturing the main brittle failure mechanisms. Additionally, numerical studies were conducted to investigate the influence of FRP thickness and concrete cover on the structural response of the strengthened beams, providing insights into the design and optimization of FRP strengthening systems.