The Use of GNSS to Monitor the Deflections of a Motorway Viaduct

Research into the use of GPS and GNSS to monitor the deformations and deflections of large suspension bridges, such as the Humber Bridge and Forth Road Bridge, has been ongoing by the authors for over a decade. These bridges have movements of the order of tens of centimetres, to even a couple of metres, and the use of carrier phase GNSS positioning is able to pick up such movements quite easily. Further to this, due to the fact that GNSS receivers output data at rates of typically 10 or 20Hz, with a precise time, it is possible to change the 3D coordinates with corresponding time into the frequency of the movements of the bridge.
This paper focuses on trials that were carried out on a motorway viaduct. A two day assessment and feasibility trial for GPS monitoring of a concrete Viaduct with a main span length of 173.7m was conducted on the 29th and 30th of November 2007.
Five dual frequency GPS receivers were attached to the railings on the main span of the bridge at strategic locations and occupied for set durations at different times of the day. The GPS receivers were set to record data at 10Hz and 20Hz, and used light-weight choke ring antennas in order to mitigate multipath.
The paper outlines the configuration of a number of receivers placed on the structure, as well as provisional results, showing the feasibility of GPS for such monitoring.