Issue 51

C. Ferrero et alii, Frattura ed Integrità Strutturale, 51 (2020) 92-114; DOI: 10.3221/IGF-ESIS.51.08

Eigenvalue analysis and model updating A first eigenvalue analysis was carried out to obtain the natural frequencies and modes shapes of the three different models prepared for “Pietro Capuzi” school. The results obtained in terms of the first three global frequencies are similar for the three models. In particular, the first three frequencies range from 5.63 Hz to 6.00 Hz for model A, from 5.57 Hz to 5.92 Hz for model B and from 5.51 Hz to 5.80 Hz for model C. Figure 12 shows the mode shapes for the first three global modes identified for model A, B and C. For all the models, the first mode corresponds to a translational mode in the Y direction of the building, while the second mode is a torsional mode. With respect to the third mode, it is characterized by a translational movement of body B in the X direction for models A and B, while it is associated to a torsional movement of body A for model C.

Model A

Mode 1 (5.63 Hz)

Mode 2 (5.78 Hz)

Mode 3 (6.00 Hz)

Model B

Mode 1 (5.57 Hz)

Mode 2 (5.77 Hz)

Mode 3 (5.92 Hz)

Model C

Mode 1 (5.51 Hz)

Mode 2 (5.70 Hz)

Mode 3 (5.80 Hz)

Figure 12: Numerical mode shapes obtained for model A, B and C.

In order to identify which model better simulated the real behavior of the structure, the numerical frequencies and mode shapes were compared with the ones derived from the dynamic identification tests performed by CESI S.p.A [9]. For the first three global modes identified, the comparison between numerical and experimental results was performed in terms of frequency error and modal assurance criterion (MAC). The latter is a statistical indicator that is normally used to compare the mode shapes obtained from analytical or numerical models with the ones identified experimentally [24], and it was calculated according to the following relation [25]:

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