Failure behaviour of brick masonry

The case of biaxially stressed masonry occurs in a large number of walls subjected to complex systems of in-plane loads. Masonry is a material which exibits distinct directional properties, so a failure criterion, because of the material anisotropy, cannot be postulated in terms of principal stresses, like the failure of an isotropic material. In the case of biaxial stress it is necessary to take into account the reference to the effect of a third variable, the orientation of the bed joints relative to the direction of principal stresses. Hence, to define a failure criterion for masonry in a plane stress state, a three-dimensional surface is required in terms of the principal stresses and their respective directions relative to the bed joints. The main objective of this paper is to present and discuss a surface of this type, in which a Mohr-Coulomb behaviour is considered, involving a friction tensor, to take into account the material anisotropy. Experimental tests on masonry specimens, performed by means of the Casagrande box for the identification of the model, are explained in detail.