PSI - Issue 62

E. Tomassini et al. / Procedia Structural Integrity 62 (2024) 903–910 Author name / Structural Integrity Procedia 00 (2019) 000–000

909

7

Automated modal identification of time histories recorded between February 20, 2023, and June 29, 2023, was performed for each subgroup using the same SSI-cov parameters and stability parameters as defined for the reference identification. Subsequently, frequencies were tracked throughout the entire period. Frequency tracking plots for each subgroup are presented in Figure 4 (a), (b), (c), (d), from which a pretty large success ratio in modal identification points out. Statistical pattern recognition for removal of environmental effects involved proposing a different Multi Linear Regression (MLR) model for each subgroup of channels. Since the two available temperature sensors were non positioned on the bridge deck, the correlation between the frequencies and the temperature recordings was not very pronounced. Nevertheless, a negative correlation was noted between the frequencies and maximum RMS values of the accelerations of the channels in each subgroup, which conceivably reflects the effects of traffic on the structure providing dynamic identification (larger RMS values of acceleration) and added mass of vehicles (resulting in a reduction in natural frequencies). The cross-correlation between Mode 1 and mode 6 of Subgroup 3 and channels 32 and 48 are reported in Fig. 3(b). Note that Mode 1 and 6 of Subgroup 3 are mainly transversal and vertical bending Table 1. Modal identification results. FDD Reference identifications through SSI-cov algorithm Whole bridge Subgroup 1 Subgroup 2 Subgroup 3 Subgroup 4 Mode id [Hz] [Hz] [%] [Hz] [%] [Hz] [%] [Hz] [%] 1 2.656 4.471 4.972 4.457 3.002 2.649 1.365 4.308 3.987 2 2.950 4.763 7.413 4.992 1.722 2.938 1.623 4.761 0.863 3 3.242 6.534 3.2739 5.915 2.498 3.292 2.198 5.301 2.339 4 4.589 11.837 2.3701 6.555 2.429 4.288 3.729 6.565 2.985 5 4.766 12.340 1.5323 8.608 1.294 4.495 1.905 12.671 1.700 6 5.449 14.191 1.3460 9.128 1.167 4.909 6.375 14.839 0.496 7 5.938 18.150 5.0108 10.231 0.643 5.303 3.168 8 6.563 11.812 0.346 5.943 2.689 9 15.807 0.478 6.492 2.925 10 17.293 1.93 9.515 3.603 11 9.855 0.810 12 12.740 0.386 13 14.753 0.606 14 17.568 2.570

Fig. 4. Frequency tracking of Subgroup 1 (a), 2 (b), 3 (c) and 4 (d). Control charts of Subgroup 1 (e), 2 (f), 3 (g) and 4 (h).