Dynamic identification and evaluation of the seismic safety of a masonry bell tower in the south of Italy

Many countries, especially in southern Europe, are greatly exposed to seismic hazard, which is the cause of severe damage in historical buildings or even destruction in the case of strong earthquake ground motions. The recent experience of Italian seismic events (Umbria and Marche 1997, Puglia and Molise 2002, Abruzzo 2009, Emilia 2012) has highlighted the behavior, the damage and the intrinsic vulnerability of monumental buildings. Historical and monumental constructions are characterized by an inherent vulnerability to seismic action, due to the circumstance that most of them frequently lack basic seismic features and/or were never fitted with adequate provisions against earthquake actions. This entails the need to define urgent strategies for the protection of cultural heritage from seismic hazard. This paper deals with the structural monitoring and seismic assessment of a unique masonry tower in a Apulia region in southern Italy: the bell tower of “Santa Maria di San Luca” in the city of Valenzano. This monument was monitored by means of full-scale environmental vibration testing. Measured responses were then used for modal identification. The assessment procedure includes morphological and structural knowledge, full-scale ambient vibration testing, modal identification from ambient vibration responses, finite element modeling, dynamic-based identification of the model. A satisfactory improvement in modal parameters is so obtained, resulting in a close agreement between the modal properties observed in dynamic tests and those calculated from a numerical model. Nonlinear dynamic analysis allows to identify the potential collapse mechanisms and those dangerous structural weak points which may play a fundamental role in the seismic vulnerability of the towers.