The boundary conditions that would cause bending and shear stress in a post and lintel structure, in a curved structure cause just axial stress in the unit elements. Indeed, according to Professor de:Jacques Heyman, in the case of masonry curved structures (he referred especially to Gothic architecture), the assumptions of unlimited compressive resistance, null tensile and shear resistance and under the hypothesis of small displacements, it can be assumed that a structure is safe and stable until the funicolar polygon stays within the middle third of the cross section. This method has been widely used in the past because of its simplicity and effectiveness. However it is still studied by some scholars, and adapted to the three-dimensional case for double curvature.