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Open channel bridge over a railway line

This two-span footbridge crosses a railways line in Cornwall, England. The main span is 14m and the deck width is about 1.5m. The U-shaped cross section is made of pultruded elements. The bridge was built in 2007 and it is the first FRP structure on the UK rail network. Photos of the bridge are shown in Figure 1.

Modal testing

Frequency response function (FRF) based modal testing was conducted to determine modal properties of this bridge. The input force was generated using an instrumented hammer and the vertical vibration response was measured at 18 points on the bridge deck to determine the vertical/torsional vibration modes. The fundamental natural frequency of the first vertical flexural mode was 11.9Hz, and the damping ratio 1.6%. Figure 2 shows photos taken during modal testing.

Response measurements

Acceleration response was measured due to human- and train-induced excitation, as illustrated in Figure 3. Data analysis is currently under way and it will be reported in a journal paper in near future.

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