A numerical insight into the response of masonry reinforced by FRP strips. The case of perfect adhesion

In this study a heterogeneous model at the meso-scale is presented, suitable to interpret delamination phenomena of FRP strips glued to masonry. Both mortar and bricks are modeled independently in tension and compression, through different isotropic damage variables and activation criteria. Reference is made to a masonry pillar, constituted by three Italian standard bricks interspersed by two mortar joints, reinforced by a perfectly-adherent FRP external sheet. The overall response and the collapse mechanism are investigated, induced by different boundary conditions and mechanical properties of constituent materials. Numerical predictions are compared to those provided by the Italian design code, with the aim of assessing pros and cons of simplified formulae. As a valid alternative for practitioners, the recourse to a numerical database is proposed, generated by combining FE predictions and best fitting, suitable to specify closed-form interface laws with brick and mortar compressive strengths as entries.