PSI - Issue 78

780 A. Romanazzi et al. / Procedia Structural Integrity 78 (2026) 777–784 maximum output acceleration admitted in such segment. Therefore, ARX fitting is performed at first on the pre seismic segment of the SISO data, which allows to estimate the first natural frequency, thus the natural period 1 of the structure prior to possible damage. Details about the fitting procedure as well as on the model order are provided in Section 2.2. The value of the first natural period is subsequently considered to establish the minimum length for admissible segment as: = × 1 (9) Where is a user integer multiplier to take into account the minimum time instants required to identify the first period. The rest of the SISO time series is segmented by conducting recursively and iteratively ARX fitting, and the first natural period is identified for each segment. Subsequently, for the post-seismic scenario, the algorithm is structured to allow a priori selection of the time window, thus the ARX fitting is performed on the final section of the SISO data and the post-seismic dynamics properties are inferred. Finally, the natural periods in the pre-, post- and during the seismic event are collected to analyse the stepwise time-variant dynamic properties of the structure.

Fig. 1. Overall algorithm workflow chart

2.2. Segmentation procedure The algorithm on the ARX fitting of the pre-seismic section and post-seismic section are following described in detail. At first, the iteration over the model order is initialised as =0 . After the individuation of the initial and final