Issue 51

F. Clementi et alii, Frattura ed Integrità Strutturale, 51 (2020) 313-335; DOI: 10.3221/IGF-ESIS.51.24 315 Moreover, the ancient masonry structures may be considered as discontinuous structural systems, which are composed of units (e.g. bricks, stones, blocks, etc.), bonded together with or without mortar [13,14]. Thus, for a numerical model to adequately represent the behaviour of a real structure, both the constitutive model and the input material properties must be selected carefully by the modeler to take into account the variation of masonry properties and the range of stress state types that exist in masonry structures [15–20]. For this reason, the iconic crumbling of the civic bell tower belongs to Amatrice [21], in the province of Rieti in Italy (Fig. 1) is numerically investigated in this study by means of the Non-Smooth Contact Dynamics method (NSCD) which is implemented on a distinct element code [22–24], namely LMGC90 © . The NSCD method was applied on advanced numerical models to survey both the dynamical behaviour of the ancient masonry bell tower subject to strong nonlinear dynamic actions and the modalities of progressive collapse mechanisms. Consequently, this characteristic masonry structure inside the epicentral area of the Centre Italy seismic sequence of August and October 2016 was discretized in very detailed 3D models. These models were achieved through rigid blocks bounded together by points of contacts, which follow the Signorini's law, about the impenetrability condition, and the Coulomb's law, relative to dry-friction [25]. Thus, this approach pointed out discontinuous nonlinear dynamics of the structure, allowing to investigate them, exploring the influence of the main mechanical parameters used in the NSCD method, namely the friction coefficient, on the dynamical global behaviour of the structure under the action of the four different sets of ground motions related to most recent Central Italy seismic sequence of 2016. S TRUCTURAL CHARACTERISTICS OF THE A MATRICE ’ S C IVIC T OWER he civic clock tower of Amatrice is the symbol of the city and it is located in the main city’s square, namely Cacciatori del Tevere, at the intersection of Via Roma and Corso Umberto I, which are the main streets of the centre (Fig. 2). In fact, there are the Municipal Palace, right in front of the bell tower, and the Church of San Giovanni overlooking the same square and preserving precious frescoes of XV century. Figure 2 : Location of the civic clock tower inside the historic center of Amatrice (Rieti, Italy) (a), photos of the tower in the past (b), before (c) and after (d) the Central Italy seismic sequence of 2016 T