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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Fig. 3. Milan Cathedral: selected mode shapes (17/10/2018, h 12:00-13:00).

3. Results from the continuous monitoring The following outcomes from the ongoing dynamic monitoring span a period of over 5 years, from 16/10/2018 to 31/10/2023. As previously stated, SHM projects usually involve the measurement of environmental parameters that might affect the structural response. Fig. 4 exemplifies the evolution in time of the measured outdoor temperature (weather station) during the investigated monitoring period: it should be noticed that the outer temperature ranges between − 3.3°C and +36.9°C.

Fig. 4. Variation of the outdoor temperature measured from 16/10/2018 to 31/10/2023.

The statistics of the modal parameters identified during the first year of monitoring (i.e., from October 16th, 2018 to October 15th, 2019) are summarized in Table 1. In more detail, Table 1 reports the identification rate, the average value (f ave ), standard deviation (  f ), and extreme values (f min , f max ) of each frequency, the average (MAC ave ) and minimum (MAC min ) value of the MAC. It should be noticed that the average and minimum value of the MAC suggests very low variation of mode shapes and no appreciable fluctuations associated with the environmental effects. On the other hand, the evolution in time of the lower six natural frequencies over 5 years (Fig. 5) reveals that the frequency fluctuations after the first year of monitoring are very similar to the ones observed during the first year.