ABSTRACT
As reported in literature (Hamid & Drysdale 1980, Samarasinghe & Hendry 1980), the orientation of the mortar joints to the applied stresses takes a major role in the ultimate strength and failure modes of masonry under in-plane stress state. The influence of mortar joints acting as a plan of weakness on the composite behavior of masonry is even more relevant in case of strong unit-weak mortar joint combinations, which are characteristic of ancient stone masonry. Two basic failure modes can occur at the level of the unit-mortar interface: tensile failure (mode I) associated to stresses acting normal to joints and leading to the separation of the interface, and shear failure (mode II) corresponding to a sliding mechanism of the units or shear failure of the mortar joint.
