An orthotropic damage model for masonry structures

An orthotropic damage model speci cally 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 de ned allowing the sti ness recovery at crack closure as well as the di erent inelastic behaviour along each natural axis to be considered. The damage eld of the material is de ned in terms of four equivalent stresses and results, in the space of the in-plane e ective 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 also control the growth of the damage parameters. The returning path from the e ective to the damaged stresses is given by multiplication by a fourth-rank damage e ect tensor, which is a function of the damage parameters and of the e ective stress state. Mesh size regularization is achieved by means of an enhanced local method taking into account the nite element size. Good agreement has been found in the comparison between numerical results and experimental data both for masonry shear panels and for a large-scale masonry holed wall