Issue 51

F. Clementi et alii, Frattura ed Integrità Strutturale, 51 (2020) 313-335; DOI: 10.3221/IGF-ESIS.51.24 325 D ISCUSSION OF THE NUMERICAL RESULTS he major results concerning the nonlinear dynamic analyses of the civic tower of Amatrice are introduced in Fig. 12, where the main failure mechanisms at the final step of the cumulative simulations of both models are presented, with and without the steel chains, for a friction values µ=0.30 for the masonry of the bell cell and µ=0.50 for the remaining masonry of the elevation and annex. In Fig. 12 and moreover in Fig. 13 it clearly appears the effect of steel chains on the masonry arched windows of the bell cell , resisting to the outwards thrust of the arches and the overturning of the piers. Obviously, the multi-leaf masonry of the upper part of the cell bell, made by small stones and mortar with bad quality (µ = 0.30), led to considerable dislocations and rotations of the blocks also in the case of the arches with steel chains. Moreover, in Fig. 13 is also possible to grasp the impact of the sequence of the strong motion on the masonry structures and their failure mechanisms, with the increment (cumulation) of the numerical damages over time, as in the real collapse. Furthermore, it is important to highlight the influence of previous damages on the dynamical response of the structure and on its capacity to resist to consecutive dynamic actions. Figure 13 : Numerical cumulative damages of the civic clock tower of Amatrice (Rieti, Italy) under the four main shocks recorded in the village during the Central Italy seismic sequence of 2016 for both configurations, with and without the steel chains, and with the friction coefficient equal to 0.30 in the bell cell and 0.50 in the other parts. The sensitivity of the dynamic response at varying the friction coefficient Furthermore, to better investigate the dynamic response of the civic masonry tower of Amatrice, sensitivity analyses were performed by varying the value of the friction coefficient of the bell cell by steps of 0.05 until the µ=0.50. The main results relative to the civic tower of Amatrice and its nonlinear dynamic simulations are reported in Fig. 14, in which are plotted the principal failure configurations at the last step for each of the five seismic analyses at varying the friction coefficient of the masonry of the bell cell with and without steel chains. As expected, the models with the steel chains exhibit a better dynamic behaviour of the whole bell cell than the tower without the boundary effect of chains, showing less and less damage to the increased friction coefficient of the masonry. T