Seismic improvement of slender masonry tower by using hysteretic devices and partial prestressing technique

An innovative system for seismic improvement of slender masonry towers by using hysteretic devices and partial prestressing technique was developed and applied to a case study. The proposed technique consists in a low level of prestressing of the upper part of the tower in order to localize in the un-prestressed lower part of the tower, i.e. a limited zone near the basement, the vertical displacements due to the cracking of masonry under seismic action. The positioning of dissipative devices, such as the Buckling-Restrained Axial Dampers, across the localization zone allows a significant contribution in terms of damping for hysteretic dissipation. The main effect of such an intervention is the reduction of the seismic demand to the tower and consequently the reduction of the top displacement as well as of the level of damage of the masonry. Both numerical analyses and experimental tests on a scale model of a Venetian bell tower were carried out showing the efficiency and reliability of the proposed technique.