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Modal response identification of a highway bridge under traffic loads using frequency domain decomposition (FDD)

Mehmet Akköse, Hugo C. Gomez, Maria Q. Feng



In this study, a four-span, 224m long, post-tensioned concrete box girder bridge supported on single column piers was subject to a series of controlled vehicle tests. Bridge acceleration response datasets were used to study the effect of truck speed and a sudden stop, on the modal identification of the bridge structure. Natural frequencies and mode shapes of the bridge were determined using the frequency domain decomposition technique for all datasets. The passing of the truck rendered difficult to identify the first bridge frequency. Conversely, the vehicle tests improved the identification of higher vibration modes. This is because the truck preferentially excites the bridge vertical response, which is associated with higher modes of vibrations, especially when a sudden stop of the vehicle occurs. Thus, carefully conducted vehicle-crossing tests provide detailed information about the bridge structure dynamics in the vertical direction. However, to identify lower modes, no vehicle on the bridge is preferred.


box girder bridge; modal identification; frequency domain decomposition; traffic loads

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