Assessment of the Bill Emerson Memorial Bridge - FTP Directory ...

The FE model of the bridge was validated with field measurements in terms of modalparameters. For this purpose, the acceleration time histories recorded during anearthquake that occurred at 12:37:32 (UTC) on Sunday, 1 May 2005, were taken andanalyzed.5.4.1. Calibration by natural frequencyThe numerically calculated frequencies and the experimentally identified frequencies arecompared in Table 5.8 for 19 modes of vibration up to 12.86 Hz. The relative error in thiscomparison is also given in the table. As one can see, the maximum error is less than10%. Most calculated frequencies match their corresponding measured frequencies verywell. This level of accuracy is generally acceptable, considering the complexity and scaleof the cable-stayed bridge.It should be noted that the 4 th and the 7 th modes of the FE model are not included in Table5.8. This is because the mass participations for these two modes are very small. All thecomputed and measured frequencies are plotted in Figure 5.39 to see their correlation. Ingeneral, the computed frequency agrees fairly well with the measured data.Table 5.8Comparison of calculated and measured natural frequenciesNo. Mode FE model Measured Error (%)1 1 0.339 0.338 0.302 2 0.400 0.438 -8.573 3 0.484 0.500 -3.204 5 0.602 0.588 2.475 6 0.625 0.650 -3.856 8 0.689 0.713 -3.307 9 0.740 0.775 -4.528 10 0.828 0.825 0.369 12 0.853 0.850 0.3510 96 1.182 1.075 9.9511 115 1.237 1.338 -7.5512 181 1.651 1.725 -4.2913 303 2.167 2.038 6.3314 366 2.303 2.338 -1.5015 568 3.187 3.263 -2.3316 1751 7.870 7.625 3.2117 1961 8.834 8.775 0.6718 2277 10.76 10.85 -0.8019 2528 12.86 12.01 7.0571