PSI - Issue 64

Carmelo Gentile et al. / Procedia Structural Integrity 64 (2024) 677–684 Author name / Structural Integrity Procedia 00 (2019) 000–000

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the red lines) closely aligns with (and even surpasses) the SLO and SLD spectra in the low-period range, indicating more significant structural susceptibility to the effects of a subsequent earthquake.

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Fig. 8. Elastic spectra (SLO and SLD) vs. response spectra: (a) N-S direction and (b) E-W direction.

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Fig. 9. Comparison of the stabilization diagrams: (a) before and (b) after the 2020 earthquake, (c) before and (d) after the 2021 earthquake.

A quantitative and immediate evaluation of the earthquakes’ effects on the monument is obtained by comparing the modal parameters identified before and after the seismic event. Figure 9 illustrates this comparison via stabilization diagrams: examining these diagrams reveals that the frequency corresponding to stable pole alignments remains practically unchanged after the first event (Figs. 9a-b). Conversely, a slight frequency decrease is observed after the second, conceivably related to temperature fluctuations. 6. Conclusions After a brief overview of the dynamic monitoring system installed in the Milan Cathedral, selected results obtained in the first 5 years of monitoring are presented and discussed. The conclusions drawn from the results presented in the paper are as follows: