The dynamic response of the Berwick-upon-Tweed bypass bridge

The Al trunk road bridge over the River Tweed upstream from Berwick-upon-Tweed was monitored as part of the routine condition monitoring strategy. This paper presents details of the principal inspection report, traffic count, vehicle speed, and axle weight data derived from in situ induction loops and weigh-in-motion sensors, followed by data arising from the non-destructive testing of the bridge. The NDT used the random dynamic traffic loading to excite the bridge's natural frequency response, which was detected by accelerometers mounted under the deck. Modal analysis was then used to draw conclusions about the amplitudes, frequencies and modes of vibration of the bridge, especially with respect to the effect of the bearings and the expansion joints which were potentially problematic and as such, would be subject to rigorous inspection. Data presented here established a baseline case for future condition monitoring. The main theme of the research was to use modal analysis to determine the bridge's dynamic response.