PSI - Issue 64

Maciej Kulpa et al. / Procedia Structural Integrity 64 (2024) 1673–1680 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1679

7

-600 -500 -400 -300 -200 -100 0 100

P01 P02 P03 P04 P05 P06 P07 P08 P09 P10 P11 P12 P13 P14 P15 P16

Strain [ μɛ]

16.08.2021 r. | CH 010

0

2

4

6

8 1012141618202224

Span lenght [m]

Fig. 9. Distribution of axial strains along the length of the upper face laminate after placing individual load slab (P01-P16)

0 10 20 30 40 50 60 70 80

DFOS Reference FEM

Displacement [mm]

0

2

4

6

8

10 12 14 16 18 20 22 24

Span length [m]

Fig. 10. Distribution of vertical displacements along the length of the span measured by the DFOS system and reference method compared to the design value calculated by FEM.

3.2. Dynamic test The dynamic identification test included a series of dynamic excitations of the footbridge to record its dynamic response. Excitations included, among others: natural passing, synchronised passing, running, and jumping of a group of people (1, 2, 3, 4, 12, and 30). A group of 12 and 30 people correspond to a load density of 0.2 and 0.5 person/m 2 of the deck area, respectively. In total, 29 individual dynamic loading schemes were performed (Fig. 8b). During the dynamic test, the DFOS system measured strains in selected sensors with a frequency of up to 250 Hz. Using the obtained strain versus time function, parts of the plots were isolated when the structure vibrated freely. On the basis of this data, the Fast Fourier Transform (FFT) was performed, and the natural frequencies of the structure were identified from the obtained spectrum. Furthermore, to verify the dynamic measurements performed using the DFOS monitoring system, the typical acceleration gauges PCB393A03 were mounted in ½ and ¼ of span length to compare both measurement methods. The first natural frequency measured using the DFOS system (3,45 Hz) and the reference acceleration gauges (3,56 Hz) were very similar to each other, and the slight difference is because these values were determined with different types of excitations. Furthermore, the first natural measured frequency was almost identical to the calculated design value (3,47 Hz), which showed that the FEM model correctly simulated the behaviour of the FRP composite structure.