PSI - Issue 5

C.A. Prato et al. / Procedia Structural Integrity 5 (2017) 332–339 C.A. Prato/ Structural Integrity Procedia 00 (2017) 000 – 000

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on the bridge axis, and ii) Eccentric truck path. The amount of eccentricity was defined rather arbitrarily to comply with the details of the numerical model. For the eccentric path, the ratio of the maximum computed acceleration at center-span section turned out to be 1.45, instead of the ratio of 1.7 obtained with the tests, suggesting that the effective path eccentricity needed to produce the observed ratio was somewhat larger than that used in the calculations. In any event the dominant peak of response obtained with the numerical model shows a peak at a frequency close to 7 Hz, whereas that of the experimentally recorded response is at approximately 3.1 Hz, which corresponds to the lowest torsional-flexural mode. Figure 7 shows the computed acceleration response at mid-span for both centered and eccentric (offset) paths. The maximum acceleration for the centered path is approximately 0.40 m/s 2 while that for the eccentric paths is about 0.57 m/s 2 . At this point it is worth recalling that the mean measured peak acceleration given in Table 4 for both sensors is 0.85 m/s 2 for the ideally centered path chosen for the tests, while the maximum predicted acceleration by the numerical model for the centered load is 0.40 m/s 2 , that is with a ratio of 2.12 between measured and predicted according to the IAP-11. Figure 8 shows the Fourier amplitude spectra of the complete computed accelerations response for centered and eccentric paths. Both cases present two dominant peaks of response at the fundamental bending frequency of the bridge at about 2 Hz, and one or two peaks of response at about 7 Hz. Figures 9 and 10 show the Fourier amplitude spectra of a complete record (continuous line) and that of only the peak (dashed line), both for computed and measured accelerations, respectively. The spectrum of the peak response in Figure 9 is approximately at 7 Hz, while that Figure 10 is at 3.1 Hz, showing a significant difference in the dominant frequency of the computed and measured peaks of acceleration. -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0 2 4 6 8 10 12 a [m/s2] t [s]

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Fig. 7. Computed accelerations for V = 60 km/h.

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Fig. 8. Computed acceleration spectra at sidewalk for V = 60 km/h.

Fig. 9. Fourier amplitude spectra of accelerations of computed response for centered path