An orthotropic damage model for masonry structures

An orthotropic damage model specifically developed for the analysis of brittle masonry subjected to in-plane loading, is described. Four independent internal damage parameters, one in compression and one in tension for each of the two natural axes of the masonry, are defined so allowing to consider the stiffness recovery at crack closure as well as the different inelastic behaviour along each natural axis. The damage field of the material is defined in terms of four equivalent stresses and results, in the space of the in-plane effective stresses, in a double pyramid with a rectangular base where the slopes of the faces correspond to the internal friction angle of the material. The equivalent stresses control also the growth of the damage parameters. The returning path from the effective to the damaged stresses is given by multiplication by a fourth rank damage effect tensor, which is function of the damage parameters and of the effective stress state. Mesh size regularisation is achieved by means of an enhanced local method taking into account of the finite element size. Good agreement has been found in the comparison between numerical results and experimental data both for masonry shear panels as well as for a large-scale masonry holed wall.