16 Empirical Models for the Health Monitoring of High-Rise Buildings: The Case of Palazzo Lombardia 173 Fig. 16.4 Trend of f est 2 and f exp 2 with the corresponding confidence intervals (95% confidence level) Fig. 16.5 Trend of f est 1 and f exp 1 Finally, it is noticed that the use of the root square for the terms related to A(see Eq. (16.2)) is able to properly describe the sudden drops of the eigenfrequency values due to an increase of vibration related to an increase of the wind action (see, as an example, the peaks downward in Fig. 16.5). The model of Eq. (16.2) for the two eigenfrequencies of Table 16.1 has then been used to predict the values of fi (f pre i in the following) according to the values of the I and Aindexes measured from November 2016 to April 2017 which were not previously used to derive the model (see the next section). A significant difference betweenf pre i and f exp i could, indeed, indicate a structural change.
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