Operational modal testing and analysis: an effective tool for the assessment of masonry towers

This paper presents the results of a recent research on the dynamic behaviour of an historic bell-tower, built in stonework masonry. The first part of the investigation involved: (a) an accurate survey of the tower geometry and of the crack pattern; (b) ambient vibration testing under wind, micro-tremors and swinging of bells; (c) modal identification; (d) FE modelling and model tuning. Since the amplitude of the excitation seems to affect the modal behaviour of the structure, a permanent dynamic monitoring system was recently installed inside the tower in order to investigate the changes in the modal parameters and the possible correlation with damage