Masonry Failure Criterion under Biaxial Stress State

Masonry is a material that exhibits distinct directional properties because the mortar joints act as planes of weakness. To define failure under biaxial stress, a 3D surface in terms of the two normal stresses and shear stress (or the two principal stresses and their orientation to the bed joints) is required. This paper describes a method to define a general anisotropic (orthotropic) failure surface of masonry under biaxial stress, using a cubic tensor polynomial. The evaluation of strength parameters is performed using existing experimental data through a least-squares approach. The validity of the method is demonstrated by comparing the derived failure surface with classical experimental results. The ability to ensure the closed shape of the failure surface, the unique mathematical form for all possible combinations of plane stress, and the satisfactory approximation with the results of the real masonry behavior under failure conditions are some of the advantages of the proposed method.