PSI - Issue 62

S. Anastasia et al. / Procedia Structural Integrity 62 (2024) 1061–1068 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The signals were processed using the in-house software code MOVA and MOSS (Enrique García-Macías F. U., 2020) with a filtering sequence involving the elimination of anomalous peaks through the Hanning window, moving average detrending (time window = 0.08 s) and a fourth-order Butterworth band-pass filter with cut-off frequencies of 0.1 and 35 Hz. Finally, decimation of the data at 70 Hz. This approach allows the automated interpretation of the stabilization diagrams in the subsequent continuous OMA. The broad frequency band of interest is between 4 and 20 Hz, where some clear resonance peaks are observed. Specifically, four resonance peaks are identified at frequencies of 4.52, 6.04, 8.81 and 12.80 Hz (as see Fig. 2 c,d,e,f) and the corresponding graph of the MAC matrix is given in. These correspond, respectively, to a first-order torsional mode for S3 and S4, a first-order flexural mode for S3 and S4 (hyperstatic heads), a first-order torsional mode for spans S1,S2,S5 and S6 . Finally, a first-order flexural mode for spans S1, S2, S5 and S6.

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Fig. 2.(a) Dynamic identification of the Quisi bridge using SSI-COV in MOVA (cluster diagram) (b) MAC matrix graph. Experimentally identified natural frequencies: (c) T1h first-order torsional mode for S3 and S4, (d) F1(z) first-order flexural mode for S3 and S4 (hyperstatic heads), (e) T1i first-order torsional mode for spans S1,S2,S5 and S6 (isostatic heads) . Finally, (f) F1i first-order flexural mode for spans S1, S2,S5 and S6. The time series of tracked frequencies is visually represented in Fig. 3a, illustrating the outcomes of the continuous monitoring of the resonance frequencies of the Quisi bridge. These modes, identified through the automated OMA procedure, distinctly align with the stable pole columns in the stabilization diagram Errore. L'origine riferimento non è stata trovata. a and the peaks of the singular values within the spectral matrix. The Modal Assurance Criterion (MAC) matrix plot in Fig. 2b further reveals that the majority of identified modes exhibit high independence, with MAC values approaching zero in most off-diagonal terms. To prevent classification errors, the comparison is selectively conducted for groups of poles adhering to well-defined tolerances in terms of natural frequencies. This meticulous approach ensures precision in the assessment and classification of the identified modes.