Antonella Saisi¹, Carmelo Gentile², and Antonello Ruccolo²
1)  Dept. of Architecture, Built environment and Construction engineering (ABC), Politecnico di Milano
Piazza Leonardo da Vinci, 32, 20133, Milano, Italy
antonella.saisi@polimi.it
2)  Dept. of Architecture, Built environment and Construction engineering (ABC), Politecnico di Milano
Piazza Leonardo da Vinci, 32, 20133, Milano, Italy
carmelo.gentile@polimi.it, antonello.ruccolo@polimi.it

Keywords: Continuous dynamic monitoring, Environmental effects, Masonry, Towers.

Abstract. Masonry towers are very common Cultural Heritage buildings in Italy, where churches and bell-towers were built even in smaller towns and a large number of defensive towers dates back to Middle Age. Since ancient towers exhibit a cantilever-like dynamic behaviour and are usually sensitive to ambient excitation, such as micro-tremors and wind, a successful dynamic monitoring of these structures can be obtained by permanently installing a few high-sensitivity accelerometers in the upper part of the building. Hence, the idea of performing cost-effective vibration-based Structural Health Monitoring (SHM) of historic towers has been taking shape recently. On the other hand, the use of a limited number of sensors and automated operational modal analysis in SHM often implies the choice of resonant frequencies as damage sensitive features, although modal frequencies are also affected by factors other than structural changes in a way that is likely more significant than variations induced by a small damage. In order to highlight the possible effects of changing temperature on the dynamic characteristics of masonry towers, especially in view of the removal of those effects needed for an effective performance assessment, the paper focuses on selected results obtained by continuously monitoring the dynamic response of three historic towers in Italy.