Detecting earthquake-induced changes in the dynamic response of a historical belfry under short training data

Built heritage represents an invaluable asset, but its preservation poses significant challenges to modern civil engineering, particularly in assessing the health state of historical structures. Among these, masonry bell towers hold a prominent place in the Italian architectural landscape, yet they are especially vulnerable to earthquakes. This study deals with vibration-based Structural Health Monitoring of the bell tower of Civitacampomarano, in Southern Italy, by means of a simple and cost-effective monitoring system composed of high-sensitivity accelerometers. Automated Operational Modal Analysis was employed to track the fundamental modal parameters of the belfry that have been further elaborated for anomaly detection. A distinctive aspect of this case study was the occurrence of an earthquake about two weeks after the beginning of continuous monitoring, which poses a challenge in establishing a reliable baseline. To distinguish earthquake-induced changes from those induced by environmental variability, a data normalization methodology was adopted, focusing on temperature effects on the tower natural frequencies. Results demonstrate how a simplified monitoring strategy, like the one considered in the present study, can contribute to timely detect earthquake-induced changes in the dynamic behavior of historical towers even in the case of limited training data availability.