Issue 51

F. Clementi et alii, Frattura ed Integrità Strutturale, 51 (2020) 313-335; DOI: 10.3221/IGF-ESIS.51.24 318 The bell tower consists of a first level of about 9 m, composed by smooth stones on the outer side and is based 15 cm in the wall thickness. Additionally, a second floor is based at 19 m, allowing to access the bell cell from the elevation of the tower. The upper part of the bell tower is about 5 m high and it rises on four rectangular piers with dimensions of 0.90 x 0.80 m. In fact, the cell bell presents single arched windows on each of the four façades, which have equal pairwise sizes. The civic tower is characterised at its top by a pavilion wooden roof, so as not to overload the masonry walls. The cell bell and the wooden roof of the civic tower of Amatrice actually collapsed under the destructive actions of the shocks occurred during the Central Italy seismic sequence of 2016. In fact, as reported in Fig. 6, the initial rotation of the piers of the arches began with the first main event of 24 th August 2016 then evolved over time under the major shock of the 26 th October 2016, until its total collapse due to the strongest event of 30 th October 2016. Moreover, these shocks produced relevant failures of both the annex and the vertical development of the civic tower, but without other important collapses of other parts of the masonry structure. Figure 6 : Views of the damaged civic clock tower of Amatrice (Rieti, Italy) after the main shocks of the Central Italy seismic sequence of 2016. D ISTINCT ELEMENT METHOD FOR HISTORICAL MASONRY ncient masonry structures exhibit complex behaviours, due to the heterogeneity and irregularities of their elements and the various material properties that compose them. Hence, for the conservation of the cultural heritage, rich of historical masonry, it becomes crucial to perform accurate modelling and exhaustive assessment of these existing structures. For this reason, the numerical analyses of masonry buildings are widespread and numerous, according to different approaches. In fact, the most used is macro-modelling, i.e. continuum medium, which takes homogenisation technique into account. However, to recreate the real geometry, with the interaction between distinct blocks, the use of micro-models is the more appropriate, like the Non-Smooth Contact Dynamics Method (NSCD). In fact, this method permits to assess the dynamic global behaviour of the masonry through the local behaviour. Moreover, the interfaces between blocks contain the contact points that allow having frictional behaviour of joints, which are regulated by the Coulomb’s law and Signorini’s impenetrability. Hence, to apply the discrete modelling, the LMGC90 © open source software was used in this work, which implements the Non-Smooth Contact Dynamics method, with implicit time integration and implicit contact solvers. A