Three-dimensional contact-damage coupled modeling of FRP reinforcements - Simulation of delamination and long-term processes

In recent years FRP (Fiber Reinforced Polymer) technology has been developed to repair damaged concrete structures. This work proposes to investigate the complex mechanism of stress–strain evolution at the FRP interface until complete debonding as well as when long-term loads are accounted for. The study has been performed by means of a fully three-dimensional approach within the context of damage mechanics, to appropriately catch transverse effects and normal stresses, developing a realistic and comprehensive study of the delamination process. The adhesion properties have been reconstructed through a contact model incorporating an elastic-damaged constitutive law, relating inter-laminar stresses acting in the sliding direction. A F.E. research code (FRPCON3D) has been developed, including a numerical procedure accounting for Mazars’ damage law inside the contact algorithm. The code is also able to describe the delamination process when considering the effects from different concrete surface preparations. Additionally, it has been upgraded to describe the long-term behaviour of composite structures by means of two visco-elastic formulations: (i) Bazant’s B3 law has been considered for the concrete component, where creep effect is composed by three different terms, i.e. the elastic part, basic creep and drying creep; (ii) for FRP’s fibres and matrix a micromechanical approach has been implemented. The numerical results have been calibrated and validated against available experimental evidences.