Dynamic monitoring of a masonry tower

Ambient vibration tests were conducted on a historic masonry bell-tower, about 37.0 m high, to evaluate its dynamic characteristics. The modal parameters identified under different levels of ambient excitation (low wind and micro-tremors, swinging of the bells) turned out to exhibit a slight dependence of the vibration level; hence, a simple dynamic monitoring system (consisting of 3 accelerometers with high sensitivity) was installed inside the tower for several months with the main objective of investigating the variation of natural frequencies and the possible correlation with damage and environmental effects. The paper, after a brief overview of the preliminary tests, summarizes the first results of the dynamic monitoring and especially the dependence of natural frequencies on temperature is highlighted.