Analysis of damage mechanisms suffered by Italian fortified buildings hit by earthquakes in the last 40 years

This paper presents an empirical approach to studying the seismic behaviour of fortified buildings, including castles, fortresses, and citadels. The first step for a focused preventive intervention on this building typology, characterised by the presence of towers, defensive walls and other particular elements, is to identify recurring vulnerabilities. Over 750 castles and 7 seismic events which have hit Italy in recent decades have been considered, including the earthquakes in Central Italy in August and October 2016. For each seismic event, the characteristics of the earthquake have been described by means of shake maps, while the castles in the area have been identified and inserted in a specifically formulated geographic information system. Subsequently, a thorough archival and bibliographical research on the damage suffered by the most significant case histories allowed the comparison of the damage observed in the castles with different characteristics in terms of soil, materials, building typologies and conservation status. A previously proposed table of damage mechanisms was adopted and verified on a larger number of castles, suggesting some modifications. Lastly, statistical analysis on these data was conducted in order to inspect possible connections between building features, peak ground acceleration and damage mechanisms. The results have shown a good agreement with the existing vulnerability curve and the small amount of numerical analyses proposed in the literature for the same building typology.