PSI - Issue 84

Lorenzo Sangiuliano et al. / Procedia Structural Integrity 84 (2026) 1326–1333

1330

damping ratios of the first nine modes, derived using the PolyMAX and Stochastic Subspace Identification (SSI) algorithms, are listed in Table 1.

Table 1: first nine vibration modes

Frequence [Hz]

Damping [%]

Mode

Type

PolyMax

SSI

PolyMax

SSI

1 2 3 4 5 6 7 8 9

I lateral flexural I vertical flexural

--

3.07 3.64 4.11 8.36 8.98

--

10.35

3.63 4.13 8.37

1.5 1.9 1.6 1.7 2.1 1.8 1.4 1.9

1.4 1.7 2.6 2.4 2.0 2.2 2.5 2.1

I torsional

8.944

II vertical flexural

9.93

10.00 10.55 11.06 14.33

10.57 11.22 14.36

II torsional

Further modal identification, based on free vibration recordings following train passage, revealed that high-speed trains tend to predominantly excite the symmetric vertical modes identified under ambient excitation. As highlighted in Chellini's thesis, the experimental findings confirmed the presence of elastic interaction between adjacent spans and informed the refinement of numerical models. In addition, measurements collected during high speed train crossings facilitated the development and calibration of mechanical models for train–structure dynamic interaction. 3.3. 3.3 Application of the automated workflow to the case study structure The proposed method was applied to the Sesia Viaduct, selected as a representative case study. The structural geometry was defined parametrically, and the finite element model was calibrated to accurately reproduce the first two flexural and torsional modes of vibration within an acceptable error range. Traffic monitoring data from the Turin–Milan high-speed line enabled the identification of two main ETR500Y train configurations: Type 1 (two power cars and twelve passenger cars) and Type 2 (two power cars and eight passenger cars), as illustrated in Figure 3. These data were processed through a numerical procedure that automatically determined train speed and length, subsequently used to generate the corresponding load time histories.

Figure 3: types of ETR500Y crossing the bridge