Using GPS to monitor the Forth Road Bridge
Roberts, Gethin, Chris Brown and Xiaolin Meng
The use of GPS to monitor the deflections of large bridges has been an ongoing topic of research between the University of Nottingham and Brunel University for about a decade. In February 2005, an extensive survey was carried out on the Forth Road Bridge in Scotland. The suspension bridge itself has a main span length of 1,005m long, and is designed to withstand large movements. During the field trials, 46 hours of continuous GPS data was gathered using Leica 500 series GPS receivers at a rate of 10Hz. GPS receivers were located upon the bridge deck at 5 locations and on top of the two southern towers. These data were then all post processed relative to two reference GPS receivers located adjacent to the bridge as well as data that was downloaded from the Ordnance Surveyys Active Station Network in the area. In addition to this, a weather station was used to record the wind speed, direction, temperature, pressure and relative humidity. During the majority of the trials, normal traffic flow was observed, however, during the second night, two lorries with a combined weight of 80 tonnes were hired and were driven across the bridge in a variety of maneuvers. During the maneuvers, the bridge was closed to other traffic. The known traffic loading and wind loading were therefore known, and this data used to compare the GPS results to a Finite Element Model of the structure.
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