Modal parameters identification on environmental testd of ancient bell towers and validation of their numerical models

Masonry towers are quite widespread in Europe and represent an important portion of the built heritage that must be preserved, especially in high-seismicity regions. Very often, such masonry towers exhibit unique peculiar morphologic and typological characteristics, which might affect their different structural behaviors under horizontal loads. For this reason, accurate knowledge of their dynamical parameters is useful for seismic assessment and the design of risk mitigation interventions. In this work, the opportunities provided by dynamic identification techniques for the non-destructive evaluation of heritage structures are discussed with a focus on different bell towers, located in the Marche region (Italy). All of them were stricken by a long seismic sequence (Center Italy earthquakes between August and October 2016), and are investigated in detail in order to have an insight into their dynamic behavior. Furthermore, the experimental investigations and the operational modal analysis results are presented, and they are useful for defining the Finite Element (FE) model of the towers with a continuum approach. The monitoring system consists of several elements adequately connected. Many operative problems have conditioned the positioning of the instrumentation due to the limited accessibility of the structure, not only to the primary access but also to reach the top. However, it has been possible to identify with certain confidence the first three frequencies of the towers and their corresponding mode shapes. The results carried out after the updating procedure may be considered very good. The material data values estimated in this way will constitute an important reference for the evaluation of the state of the building.