A recent survey of the historic complex of ''Santa Maria del Carrobiolo'' in Monza (Italy) highlighted that two sides of the bell-tower are directly supported by the load-bearing walls of the apse and South aisle of the neighbouring church. After the discovery of the weak structural arrangement of the building, a network of 10 displacement transducers, integrated by five temperature sensors, was installed in the tower to check the opening variation of the main cracks. Subsequently, ambient vibration tests were performed and closely spaced modes with similar mode shapes were clearly identified: since the dynamic characteristics of the tower are quite different from those obtained in past experimental studies of similar structures and conceivably related to the construction sequence, a simple dynamic monitoring system was installed in the tower to complete the health monitoring aimed at the preservation of the historic structure. The paper-after a brief description of the tower and a summary of selected evidences provided by on-site survey, historic research and static monitoring-focuses on the dynamic characteristics identified in the preliminary ambient vibration tests and the main results of 1-year dynamic monitoring. In order to assess the effects of changing temperature on the natural frequencies of the investigated tower, especially in view of the removal of those effects needed for an effective performance assessment, simple correlation studies between modal frequencies and temperature are presented and discussed.

The Milan Cathedral, whose main structures were erected between 1386 and 1813, is one of the largest masonry monuments ever built. Within the traditional collaboration between Politecnico di Milano and Veneranda Fabbrica del Duomo di Milano  the historic Institution established in 1387 and responsible for the preservation and development of the Cathedral  a structural monitoring system was recently designed and implemented with the twofold objective of assisting the condition-based structural maintenance of the Cathedral and creating a large archive of experimental data, useful to improve the knowledge of the monument. The new monitoring system, fully computer based and with efficient transmission of the collected data, includes static and dynamic measurements. The static monitoring system consists of: (a) bi-axial tilt-meters installed at the top of selected piers and at 3 levels of the Main Spire; (b) vibrating wire extensometers mounted on the iron tie-rods which are characterized by the higher tensile stress; (c) temperature and humidity sensors for the measurement of internal and external environmental parameters. The dynamic monitoring is performed through seismometers (electro-dynamic velocity sensors) installed at the top of 14 selected piers and at 3 levels of the Main Spire. After a concise historic background on the Milan Cathedral and the description of the sensing devices installed in the church, the paper focuses on the results obtained during the first months of monitoring (since October 16th, 2018) and the lessons learned in view of the Structural Health Monitoring (SHM) of the monument.

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