PSI - Issue 5

Xu Min et al. / Procedia Structural Integrity 5 (2017) 325–331 Xu Min, Luís O. Santos/ Structural Integrity Procedia 00 (2017) 000 – 000

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Due to the high density of reinforcement steel, for the concrete weight density was taken 25.4 kN/m 3 . The remaining dead load of 16.6 kN/m was also considered. Thus, the total weight of the structure is about 282 000 kN.

5.2. Dynamic tests

Dynamic tests were performed to obtain experimentally the dynamic characteristics of the structure, namely, the vibration frequencies, mode shapes and damping ratios. In June 2016, the dynamic tests of the São João Bridge were carried out in nine set-ups. During these tests the 7 uniaxial accelerometers placed in the deck and the main pier D1. The records at each set-up had a time length of about 60 minutes, using a sampling rate of 500 Hz. The structural modal parameter identification was performed with the software ARTeMIS (SVS, 2005), using the technique of Enhanced Frequency Domain Decomposition (EFDD). A total of 30 vibration modes were identified based on measured response only. Some identified mode shapes are illustrated in Fig. 8. The developed FE model was used to validate the experimental results of the dynamic tests. The natural frequencies and mode shapes computed by the updated FE model were compared to the modes identified from the tests, as illustrate in Fig. 8 and Table 1. In general, a very good accordance was achieved.

1 st tranversal mode (f=0.405 Hz)

1 st vertical mode (f=0.770 Hz)

2 nd tranversal mode (f=0.675 Hz)

2 nd vertical mode (f=1.605 Hz)

3 rd tranversal mode (f=0.823 Hz)

3 rd vertical mode (f=2.004 Hz)

identified mode shape

calculated mode shape

Fig. 8. Identified and calculated mode shapes of the São João Bridge

Table 1. Dynamic characteristics of the São João Bridge Modes identified from transverse accelerations

Modes identified from vertical accelerations

DMS 

Test 

FEM f (Hz) 0.413 0.662 0.817 1.185 1.534 1.917

DMS 

Test 

FEM f (Hz) 0.771 1.225 1.659 1.894 2.238 2.326

Mode

Mode

f (Hz) 0.406 0.656 0.825 1.195 1.529 2.085

f (Hz) 0.405 0.675 0.823 1.193 1.530 2.089

f (Hz) 0.772 1.217 1.608 2.009 2.389 2.570

f (Hz) 0.770 1.223 1.605 2.004 2.395 2.576

 (%)

 (%)

 (%)

 (%)

V.1 L.1 V.2 V.3 V.4 V.5

T.1 T.2 T.3 T.4 T.5 T.6

0.07 0.08 0.07 0.09 0.25 0.27

1.96 1.26 1.05 0.73 0.95 0.66

0.08 0.49 0.22 0.14 0.17 0.17

1.08 1.86 0.85 0.90 0.61 0.61

T – Transverse mode; V – Vertical mode; L – Longitudinal mode.