Sensing hardware optimization and automated condition assessment of a monumental masonry bell-tower

Vibration-based structural health monitoring systems have the potential of enabling automated condition assessment of slender structures with a limited number of sensors, leading to a cost-effective optimization of maintenance activities. Nevertheless, the development of SHM systems able to early alert about the occurrence of a structural damage is still quite a challenge due to the weak correlation that typically exists between global dynamic behavior and structural conditions. Methods of multivariate statistical analysis, such as principal components analysis and novelty detection, can be a solution to this issue, but documented validations of their effectiveness at damage detection in full-scale structures are not yet available. This work presents the design and implementation of a vibration-based SHM system, recently installed by the authors on a monumental masonry bell-tower: the bell-tower of the Basilica of San Pietro in Perugia, Italy. The tower, about 61.50 m high, is considered one the symbols of the city of Perugia and was recently restored after a strong earthquake. The monumental tower and its historical background are presented, at first. Then, the results of experimental and analytical dynamic investigations are discussed, including: (i) ambient vibration tests and output-only modal identification using various types of sensors, deployed with different layouts, (ii) remote automated frequency tracking, (iii) numerical modeling, (iv) damage sensitivity analysis and (v) algorithmic strategy for health assessment. The results presented in the paper aim to demonstrate the potential of vibration-based SHM systems for applications to cultural heritage structures, owing to their fully non-destructive and non-invasive character.