Video-Based Dynamic Monitoring of Ancient Masonry Structures: The Case Study of Santa Maria Della Quercia Bell Tower

Historic masonry structures, originally designed centuries ago to primarily bear vertical loads, have demonstrated significant vulnerability to natural events like earthquakes, soil movement, and their own degradation over time. To safeguard these structures and facilitate timely retrofitting interventions, various Structural Health Monitoring (SHM) methodologies have been developed, particularly in the realm of cultural heritage preservation. Among these, dynamic monitoring is notably prominent, as it enables the non-invasive assessment of structural health by evaluating the fundamental frequency of the building. Vibration-based SHM, utilizing operational modal analysis (OMA), allows for the extraction of modal parameters, including the fundamental frequency, mode shape, and damping ratio. However, the effectiveness of these techniques is heavily influenced by the number and placement of sensors on the structure. Recently, video-based vibration analysis, which allows to capture imperceptible motions in a video sequence, has emerged as an appealing alternative due to its convenience and cost-effectiveness. This approach employs advanced image processing techniques, in which pixels function as motion sensors, effectively replacing traditional mechanical sensors. This paper aims to explore the potential of vision-based technologies in the context of cultural heritage health dynamic monitoring, by comparison with traditional vibration-based SHM. The bell tower of Santa Maria della Quercia, a 15th-century Renaissance-style church in Viterbo, Italy, is used as a case study for this investigation.