Issue 51

F. Clementi et alii, Frattura ed Integrità Strutturale, 51 (2020) 313-335; DOI: 10.3221/IGF-ESIS.51.24 326 Figure 14 : Numerical cumulative damages of the civic 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, at varying of the friction coefficient on the bell cell. Hence, as visible in the enlargement reported in Fig. 15, the model without the steel chains introduces an early overturning of the piers of the masonry arches, with prevalent dislocations for lower values of the friction, i.e. µ = 0.30 and µ = 0.35, and with major rotations and complete overturning mechanisms for higher values of the friction, i.e. µ = 0.40, µ = 0.45 and µ = 0.50. Moreover, it is important to highlight that the failure of the annex is very similar to the existing crack pattern observed in reality and reported for comparison in Fig. 6. Additionally, to better understand these failure mechanisms and to appreciate the amplification of the deformations due to the various friction values, it is necessary to know the displacements of the control point #1 over time plotted in Fig. 16, i.e. related to the upper part of the cell bell of the Amatrice civic tower. In fact, the displacements Time Histories (THs) present the results of the analyses at varying of the friction coefficient for both configurations, with and without the steel chains (respectively namely C, indicated by the solid line, and NC, marked by the dashed line). It confirms the early collapse of the model without chains, for all friction values. At the same time, it is clearly shown how the increasing of the friction, combined with the resistance of the steel chains, improves the capacity of the bell cell to resist mainshock and aftershocks. Furthermore, this model without steel chains and with a friction coefficient equal to 0.30, during the three initial shocks, shows displacements of circa 18÷20 cm and, by increasing the coefficient until 0.50 the displacements are contained in the range of 6÷8 cm.