Anisotropic yield behaviour of adobe masonry

Earth is one of the most diffused building materials all over the world. Adobe constructions of different type can be found in large areas belonging to developing countries and in some cases are part of Cultural Heritage. The peculiar material characteristics with particular regard to fragility of the blocks together with the strong anisotropy have been experimentally studied, and numerical analyses have been performed in order to design optimal retrofitting techniques. In general classical constitutive models have been applied in this case. This paper proposes an approach to a constitutive model for this material, developed in the framework of rate independent softening plasticity, involving a yield criterion in which anisotropic friction and cohesion tensors are considered. It turns out to be generally useful for materials characterized by ultimate behaviour which varies according to the direction, such as the adobe masonry. A geometrical representation of the limit domain in the case of plane stress, together with the comparison with results of laboratory tests on adobe masonry is presented and discussed. It is shown that the framework of plasticity with internal variables provides a coherent description of the softening problem to represent the behaviour of adobe masonry.