Rocking analysis of masonry bell towers

The most recent earthquakes that hit Italy, including L'Aquila (2009), Emilia-Romagna (2012), Central Italy (2016), and Ischia (2017), have highlighted the high seismic susceptibility of ecclesiastical masonry complexes. Bell towers are slender masonry structures that frequently belong to ecclesiastical structures. Their presence represents a point of vulnerability as they could cause partial collapse; their loss of capacity is often caused by aging and neglect. In fact, bell towers require preliminary analysis to assess their vulnerability. The assessment of their structural behaviour is crucial when considering the masonry aggregate as a whole [1,2], especially when retrofit interventions are involved. Accurate analysis and modelling of ecclesiastical structures and aggregate buildings generally are challenging [3]. They comprise different structural parts, determining a complex global behaviour that is not always easy to understand and describe. Different methodologies to analyse the dynamic response of bell towers exist and generally require knowledge of a significant number of parameters. This work considers several approaches to analyse the dynamic behaviour of the bell tower emerging from a masonry building. The goal is to provide a preliminary stability estimation, furnishing a risk index evaluation with a quick procedure before more accurate ones. The proposed method is block-based and combines the rocking of the bell tower [4] with the sliding motion of the underlying building by applying different friction coefficients. The result is a double-block analysis compared with a single-block model subjected to the floor spectrum. The influence of the masonry complex being calculated using only its total mass and soil friction coefficients has demonstrated that the proposed quick method is suitable for a preliminary evaluation of the bell tower's stability without requiring a strong computational effort, unlike a FEM modelisation of the whole complex.