Redesign of Strengthening Interventions on Historical Buildings. The Case Study of an Earthquake-Damaged Bell Tower

In the case of degraded building material and developing cracks, steel tie-rods allow for a fast, relatively simple, and very effective strengthening intervention, especially for high rise masonry structures such as medieval bell towers. However, their design has a high impact on the external aesthetic of the structure; thus, they are generally not considered as an acceptable definitive solution. Here, several designs are proposed for the replacement of such a pre-existing reinforcement system with less invasive options. These candidates are then compared considering multiple factors such as the conservation of the architectural design, the uncertainties in terms of geometric and mechanical properties, the nonlinear behaviour of the damaged masonry walls, and the required level of structural safety. The placement of these alternative strengthening interventions along the tower height is also optimised according to the specific crack pattern - reflected in a subdivision of the calibrated Finite Element Model in of macroelements - and the most probable collapse mechanism. Their viability is finally assessed and ranked.