Assessment of the seismic vulnerability of a masonry bell tower by non-destructive experimental techniques

The recent experiences of Italian seismic events have pointed out the necessity of a deep knowledge of the behavior, the damage mechanisms 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 were not designed according to basic seismic rules. Moreover, for old masonry monuments, reliable structural analyses are fundamental in order to identify specific and not invasive retrofitting interventions. In this framework towers are very interesting case-studies due to their high vulnerability to horizontal actions and to their peculiar typological characteristics. This paper deals with the vibration measurement, the structural identification and the seismic risk assessment of a unique masonry tower in Apulia region in Southern Italy: the bell tower of "Santa Maria di San Luca" in the city of Valenzano. The assessment procedure includes: historical and morphological knowledge; non-destructive diagnostic investigation; full-scale ambient vibration testing; structural identification from environmental vibration measurements; finite element modeling; nonlinear dynamic analysis. The analysis shows the importance of reliable finite element models in order to identify the potential collapse mechanisms of the monument and those dangerous structural weak points deeply affecting the seismic vulnerability. At this aim it emerges the effectiveness of a suitable combination of dynamic identification techniques and non-destructive diagnostic investigations.