Cyclic behavior of masonry walls strengthened by tie rods

This preliminary work is aimed at investigating numerically the behaviour of unreinforced masonry walls strengthened through the use of metallic tie rods. In the first part, the improvement of strength is studied by evaluating the increase in shear resistance for low vertical action values, which is the most critical state for unreinforced masonry. Tie rods are placed along diagonals of the walls, as to maximize their effect on the overall strength and on recentering capabilities of piers. Subsequently, by using non-linear dynamic analyses carried out on a masonry wall, the importance of the axial forces acting on retrofitted piers during a seismic event is highlighted. It is shown that this becomes particularly important in the presence of a significant vertical component due to seismic actions. All the analyses are carried-out with non-linear material models, as to investigate the capacity in post-elastic field. Finally, the recentering capabilities and cyclic response of strengthened piers using tie rods are evaluated, on the basis of the residual transversal displacements measured at the end of numerical simulations. Results show improvements on the shear-displacements cyclic behaviour of reinforced piers, including better recentering capabilities, enhancing masonry performance under seismic conditions.