A microporomechanical model to predict nonlinear material behavior of masonry

The microporomechanics theory, which combines the mean-field homogenization method and linear fracture mechanics theory, has been successfully adopted to study the nonlinear behavior of compositelike materials, such as alloy, rocks and concretes. The application of such theory is however mainly limited to the isotropic quasi-brittle materials and the study of crack propagation in an initially anisotropic materials, as masonry, has received limited attention. This paper aims to derive the nonlinear material behavior of masonry by adopting microporomechanics theory. In this study, masonry is treated as a composite material, made of bricks, mortar joints and microcracks. At constituents’ level, cracks are idealized as three orthotropic families of penny-shaped inclusions, which are then embedded in an undamaged effective masonry matrix formed by bricks and mortar joints. A crack density variable, containing the information of each crack family (e.g., crack radius), is adopted to define the damage state of masonry. The propagation of each crack family is governed by the energy release rate and its critical value. The results shows that the microporomechanics theory can successfully derive the nonlinear behavior of masonry (e.g., the tensile softening). The proposed model allows using limited input parameters mainly related to properties of constituents, and elastic modulus and tensile strength of the composites. However, it should be mentioned that the model developed in this study only considers the cohesive mechanics by modelling the propagation of open cracks, while the friction on the lips of closed microcracks is not taken into consideration and it will be objective of further study.