Corotational beam-interface model for stability analysis of reinforced masonry walls

Under horizontal loadings, such as seismic actions, buckling phenomena can strongly affect the bearing capacity of masonry walls to gravity loads. Indeed, due to the low tensile strength of the mortar, when vertically loaded masonry members are subjected to bending moments induced by load eccentricity, out-of-plane collapse mechanisms often prevail on compressive vertical crushing. This work presents a two-dimensional micromechanical approach relying on force-based beams and nonlinear interface elements for the out-of-plane stability analysis of regular brick/block masonry walls under eccentric vertical compressive loads. The elastic beams model the horizontal brick courses, while interfaces describe the bed mortar joints and reinforcing layer nonlinear behavior. A damage-plastic constitutive relationship is adopted for the mortar and a piece-wise linear damage-based law is proposed for the reinforcing layer. A corotational formulation is considered for both the beams and interface elements to account for large nodal displacements and P-Delta effects occurring during instability phenomena. Hence, the response of eccentrically loaded masonry walls, both reinforced and unreinforced, is reproduced, comparing the numerical results with experimental data.