Modeling of the Cyclic Bond Behavior of FRP Strengthening Applied to Concrete Elements

Fiber Reinforced Polymer (FRP) materials are widely used as strengthening systems for concrete and masonry structures. Typically applied to the external surfaces of structural elements they enhance the structural strength and, in some cases, ductility, by relying on the bond developed between the FRP and the substrate. The bond behavior of FRPs has been extensively investigated through experimental tests and numerical models, with most studies focusing on monotonic bond behavior. However, relatively few experimental and numerical studies address the cyclic bond behavior of FRPs, despite its significant importance in the context of seismic actions. In this context, this paper proposes a simplified nonlinear model for the numerical simulation of the cyclic bond behavior of FRP systems externally applied to concrete elements. Specifically, the proposed model incorporates distinct loading and unloading behaviors based on the level of damage at the interface between the FRP and the concrete substrate. The developed model is implemented in MATLAB within a finite element framework. Numerical analyses are conducted using experimental data from literature. The results demonstrate the model’s capability to accurately replicate the experimental cyclic behavior of FRP applied to concrete elements.