PSI - Issue 64

Ge-Wei Chen et al. / Procedia Structural Integrity 64 (2024) 724–731 Ge-Wei Chen, Xinghua Chen, Piotr Omenzetter / Structural Integrity Procedia 00 (2019) 000–000

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The damping ratios (Columns 9 to 14) were between 0.5% to 2.9%, i.e., as expected for similar bridge structures, cf., e.g., Ntotsios et al. (2009). The relative differences in the damping ratios identified by the different algorithms from either the AVT or HVT data are markedly larger than those for the corresponding identified natural frequencies. These discrepancies reach up to 0.5% in the AVT and up to 0.8% Hz in the HVT, respectively. The bigger scatter in experimental damping ratios has widely been reported in literature, see, e.g., Mao et al. (2019). We will curtail further descriptions and discussions of the results at this point and direct the interested reader to Chen et al. (2020), where other aspects such as the identification of mode shapes and balancing the accuracy and computational cost of the various system identification methods are covered in depth.

Table 1. Comparisons of modal frequencies and damping ratios from FEM, AVT and HVT.

Mode

Natural frequencies (Hz)

Damping ratios (%)

FEM

AVT

HVT

AVT

HVT

AR

ERA OKID

SSI data

AR

ERA OKID

SSI data

AR

ERA OKI D (10)

SSI data (11)

AR

ERA OKID

SSI data (14)

(1) V1 V2 V3 V4 V5 V6 L1 L2 L3 L4 L5 L6 L7 L8 L9

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9) 0.7 1.1

(12)

(13)

3.18 3.99 4.17 4.77 5.70 6.89 8.65 1.87 2.65 3.69 4.12 4.34 5.49 6.45 7.63 9.30

3.17 3.85

3.17 3.85

3.15 3.81

3.16 3.87 4.16 4.73 5.62 7.13 1.87 2.58 3.78 4.12 4.25 5.50 6.67 7.64 9.35 −

3.16 3.87 4.16 4.73 5.62 7.13 1.87 2.58 3.78 4.28 5.50 6.69 7.66 9.34 −

3.16 3.87 4.17

0.7 0.9

0.5 0.7

1.4 1.7 1.5 2.5 2.4 1.2

1.0 1.4 1.5 2.9 2.3 1.3 1.0 1.2 2.1 1.9 1.6 1.6 2.2 1.4 1.3 −

1.0 1.0 0.7

− − − − − −

− − − − − −

− − − − − −

− − − − − −

− − − − − −

− − − − − −

− −

− −

7.12

0.9

V7/T1

−

−

−

1.87 2.58 3.76 4.13 4.25 5.53 6.59 7.50 9.36

1.0

1.1 1.2 2.9 2.3 2.6 2.1 2.5 2.2 1.9

2.64 3.75 4.13 4.26 5.52 6.62 7.64 9.35

2.64 3.74 4.12 4.27 5.52 6.63 7.63 9.35

2.62 3.72 4.12 4.24 5.50 6.60

1.8 2.1 2.5 2.6 1.9 2.7 2.2 1.5

1.9 2.2 2.3 2.4 2.0 2.6 2.0 1.7

1.6 1.9 2.4 2.2 1.6 2.9 1.7 1.3

1.3)

2.1 2.0 1.8 1.8 2.0 1.5 1.5

4.11

7.585

9.33

6. Conclusions HVT was conducted on a post-tensioned concrete bridge with 11 spans. A broad-band linear chirp excitation was applied, which was generated by two light, portable exciters, to augment the already-present environmental excitations. For modal system identification, three OMA algorithms were adopted, i.e., the classical SSI-data and the AR and ERA-OKID methods. The effectiveness and accuracy of the system identification results from the HVT were compared to the those of AVT and the FEM. Enhancing the environmental excitations using the shakers enabled identifying four more higher-order vertical modes and the fundamental lateral mode compared to AVT. Nevertheless, several higher-order modes predicted by the FEM were still missing, e.g., the first vertical-torsional mode. The natural frequencies identified by AR, ERA-OKID and SSI-data from the HVT agreed well, most of them within 0.03 Hz. This confirmed the reliability and robustness of these output-only identification algorithms when used with both AVT or HVT response data (for the modes that they managed to reveal). The modal damping ratios estimated from either the AVT or HVT showed a more noticeable scatter amongst the different identification algorithms of up to 0.8%, but this is common in in-situ testing.