Automated Modal and Structural Identification of a Stone-Masonry Bell-Tower for SHM

The bell-tower of the San Vittore church in Arcisate has been studied by Politecnico di Milano since 2007. After a brief description of past operational modal tests and FE modeling, the paper focuses on the results provided by a simple dynamic monitoring system installed inside the tower for several months. The modal identification from continuously recorded acceleration data has been performed using an automated operational modal analysis procedure, based on the covariance-driven Stochastic Subspace Identification method. Since the identified natural frequencies revealed cyclic evolution over short- and long-time periods, mainly due to thermal effects, two methods aimed at detecting the structural anomalies were adopted: (1) the first one is based on the use of appropriate statistical models to predict the modal frequency fluctuation; (2) the second one consists in the continuous update of the FE model based on the temperature de-trended frequencies.