PSI - Issue 64

Marco Pirrò et al. / Procedia Structural Integrity 64 (2024) 669–676 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 3. Baixo Sabor dam: stabilization diagram (SSI-COV) obtained from data collected on 01/12/2015 00:00 – 00:30.

f 1 = 2.738 Hz

f 2 = 2.918 Hz

f 3 = 3.852 Hz

f 4 = 4.470 Hz

f 5 = 5.306 Hz

f 6 = 6.226 Hz

Fig. 4. Baixo Sabor dam: reference natural frequencies and mode shapes identified from data collected on 01/12/2015 00:00 – 00:30 (black points refer to the modal ordinates, while blue lines are obtained using “spline” interpolation in Matlab).

Fig. 5a shows the evolution of the natural frequencies of the dam during the first two years of monitoring (i.e., from 01/12/2015 to 01/12/2017) and clearly suggests that the variation in time is influenced mostly by water level (Fig. 5c): as water level tends to increase, all the natural frequencies decrease, and vice-versa. The dependency between natural frequencies and temperature is less evident (Fig. 5b), but it’s worth highlighting that as temperature increases, natural frequencies increase. It is also interesting to observe that the coefficients of determination between the frequencies identified in the first two years of monitoring range between 0.86 and 0.99 (Table 1). Table 2 summarizes the mean value ( f mean , ξ mean ) and the standard deviation ( s f , s ξ ) of frequency and damping estimates, as well as the identification rate (Id. Rate).

Table 1. Coefficients of determination R 2 between the natural frequencies identified from 01/12/2015 to 01/12/2017. R 2 f 1 f 2 f 3 f 4 f 5 f 6 f 1 1 0.992 0.979 0.983 0.921 0.877 f 2 - 1 0.983 0.985 0.934 0.880 f 3 - - 1 0.977 0.945 0.874 f 4 - - - 1 0.940 0.884 f 5 - - - – 1 0.866 f 6 - - - – – –