Continuous Dynamic Monitoring to Enhance the Knowledge of a Historic Bell-Tower

The results of the long-term vibration monitoring program, carried out on the bell-tower of Santa Maria del Carrobiolo in Monza (Italy), are reported in the paper. The dynamic monitoring was motivated by the weak structural layout of the historic building, with two fronts of the tower being supported by the load-bearing structures of the apse and South aisle of the adjacent church. Furthermore, closely spaced modes with similar mode shapes were clearly identified from ambient vibration tests, hence, the modal parameters of the bell-tower significantly differ from those obtained in past experimental studies of similar masonry structures. The continuous dynamic monitoring was mainly aimed at enhancing the knowledge of the historic structure, checking the possible evolution of the key resonant frequencies and assessing the effects of changing temperature on the dynamic characteristics of the bell-tower. The main results of the dynamic monitoring for a period of two years highlight distinctive behavior of the bell-tower, such as the frequency veering exhibited by the lower modes with increased temperature. Subsequently, in order to mitigate the effects of the environmental factors on resonant frequencies, the application of the multiple linear regression (MLR) and the principal component analysis (PCA) tools have been investigated.