Seismic vulnerability enhancement of medieval and masonry bell towers externally prestressed with unbonded smart tendons

Medieval and masonry bell towers are highly vulnerable to suffer strong earthquake damage due to the mechanical and physical characteristics of masonry and other important factors. An approach for the seismic vulnerability reduction of masonry towers with external prestressing is proposed. The devices are vertically and externally located in order to be removable when needed. The characteristic flexural failure mode of medieval towers and the shear mechanism of bell towers are simulated. Both failure modes are in agreement with earthquake damage in similar towers. Medium prestressing level enhances force capacity of towers failing by bending without reducing ductility. High prestressing level slightly reduces the displacement capability of towers failing ductile. In case of belfry failure, both prestressing levels permit to increase displacement but lower force than towers failing by bending. The proposed medium prestressing level is the optimal for masonry towers and other slender structures failing by bending and shear.