The damage effect on the dynamic characteristics of FRP-strengthened reinforced concrete structures

The present work aims to assess the modal properties of reinforced concrete structures strengthened with FRP-based systems subjected to progressive damage. In particular, an integrated numerical fracture model, based on a cohesive crack approach and an embedded truss model, has been used to simulate the damage phenomena of such kinds of structures under quasi-static loading conditions. Subsequently, at predefined damage levels, the dynamic response, in terms of natural vibration frequencies, has been obtained by solving the problem of small amplitude free oscillations and then compared with the numerical and experimental results. The comparisons show the beneficial strengthening effect of the FRP system on both static and dynamic structural response, in terms of load-carrying capacity and natural vibration frequency degradation, highlighting the applicability of the proposed numerical model in the framework of model-based damage identification methods for FRP-strengthened concrete structures.