The seismic response of five cultural heritage towers erected between the 9th and 10th century AD are investigated herein. Firstly, their architectural and modal characteristics were studied in the light of seismic events that hit the monuments. There exist several historical reports of strong earthquakes, as well as damaged structures and collapses. The limit analysis is adopted to examine the post-elastic behavior of the towers up to collapse due to out-of-plane failure. Recurrent damage modes were collected from recent earthquakes and a classification of four possible collapse mechanisms in towers and slender masonry structures is here proposed: overturning, separation of perpendicular walls, diagonal cracking, and dislocation of the belfry. A thorough examination of the towers under investigation verified the proposed damage classification. The capacity curves were derived combining the capacity curves of each of the collapse mechanisms. Damage thresholds were defined on these curves in correspondence with damage states. The studied group of structures is representative of a wider typology. A statistical approach was adopted to describe damage with seismic intensity, and vulnerability curves were generated. The results of this study will improve the understanding of the performance and the collapse mechanisms of slender masonry structures under seismic loading and provide a characterization of seismic vulnerability for the studied cultural heritage types of towers.

This paper deals with the seismic vulnerability of monumental unreinforced masonry (URM) towers, the fragility of which has not yet been sufficiently studied. Thus, the present paper fills this gap by developing models to investigate the seismic response of URM towers up to collapse. On mount Athos, Greece, there exist more than a hundred medieval towers, having served mainly as campaniles or fortifications. Eight representative towers were selected for a thorough investigation to estimate their seismic response characteristics. Their history and architectural features are initially discussed and a two-step analysis follows: (i) limit analysis is performed to estimate the collapse mechanism and the locations of critical cracks, (ii) non-linear explicit dynamic analyses are then carried out, developing finite element (FE) simulations, with cracks modelled as interfacial surfaces to derive the capacity curves. A meaningful definition of the damage states is proposed based on the characteristics of their capacity curves, with the ultimate limit state related to collapse. The onset of slight damage-state is characterised by the formation and development of cracks responsible for the collapse mechanism of the structure. Apart from these two, another two additional limit states are also specified: the moderate damage-state and the extensive one. Fragility and vulnerability curves are finally generated which can help the assessment and preservation of cultural heritage URM towers.