Ambient vibration testing of historic masonry towers for structural identification and damage assessment

The results of the ambient-vibration based investigations carried out to assess the structural conditions of a masonry bell-tower are presented. The tower, dating back to the XVII century and about 74 m high, is characterised by the presence of major cracks on the western and eastern load-bearing walls. The assessment procedure includes full-scale ambient vibration testing, modal identification from ambient vibration responses, finite element modelling and dynamic-based identification of the uncertain structural parameters of the model. A good match between theoretical and experimental modal parameters was reached for relatively low stiffness ratios in the most damaged regions of the tower. Furthermore, the model identification, carried out by using two different methods, provided consistent structural parameters which are also in close agreement with the available characterization of the materials.