A new numerical procedure for assessing the dynamic behaviour of ancient masonry towers

The paper presents a new numerical procedure for the modal analysis of masonry structures implemented in the finite element code NOSA-ITACA, which models masonry as a nonlinear elastic material with zero tensile strength and infinite or bounded compressive strength. The procedure, which allows for taking into account the effects of the stress field and crack distribution within a structure on its natural frequencies and mode shapes, is applied to assess the dynamic behaviour of a medieval bell tower in Lucca. Data recorded by the monitoring system installed on the tower have been processed via suitable modal identification algorithms, which have enabled calculating the tower's modal frequencies, mode shapes and damping ratios. Then, the tower has been analysed via the NOSA-ITACA code and model updating techniques applied to fit the data measured on the tower. The results of the standard modal analysis have been compared to those of modal analyses conducted on the structure subjected to its own weight while taking into account the corresponding crack distribution.