PSI - Issue 84

Donato Fiore et al. / Procedia Structural Integrity 84 (2026) 417–424

422

Table 1. Primary modal shapes.

Modal shape 1

2

3

4

5

6

7

8

9

10

11

Freq. Hz

0.60 0.80 1.19 1.59 2.00 2.48 3.26 3.80 6.42 6.86 10.27

The measured frequencies showed variability (±7-8%), influenced by temperature and traffic load, and deviations greater than 10% are suggested as indicators of structural anomaly. Accelerometric monitoring showed good consistency with radar data, but complete identification requires synchronized and automated signal analysis. Figure 8 shows the FEM obtained from the accelerometers.

Fig. 8. Calculate FEM using the accelerometers and interferometric data. The mode shapes are not mixed forms: they are indeed either vertical or horizontal forms. The complete bridge model presents mode shapes related to both the deck/arch interaction and the arch alone. The frequencies of the two models show partial agreement, with differences attributable to both variations in stiffness of the structural system and the additional mass introduced by the deck. If we consider the relationship for a simple harmonic oscillator, the frequency would be a function of the square root of the stiffness ( k ) and mass ( m ):