Monitoring the movements of bridges by GPS

Real time On-The-Fly (OTF) kinematic GPS will allow a multitude of monitoring, navigation and engineering applications scenarios to become reality. Applications include real time deformation and movement monitoring, real time centimetric navigation and real time automated plant control. The use of state of the art dual frequency GPS receivers, UHF data links and high speed portable processors allow real time processing and navigation to centimetre level. In a low dynamic environment, with a short baseline length, it is possible to position a roving receiver to an approximate accuracy of less than 5 mm within a few seconds of the start of the ambiguity search. One Engineering application is the monitoring of the movement of cable suspension bridges. Such structures are capable of movements of up to a few metres under adverse wind conditions or heavy traffic loads. The use of relative OTF positioning at strategic points upon the bridge would allow close monitoring of the bridge's movement. Such real time monitoring could be used to warn of dangerous bridge movements and calculate deformation and long-term deterioration factors for the bridge. Future bridge designs and traffic management schemes could also benefit from the monitoring system. Real time GPS tests have been carried out at strategic points on three different bridges, the Humber Bridge, the Nottingham Clifton Bridge and the Dee Bridge. This paper describes tests carried out under different traffic loads and varying wind speeds and directions, and demonstrates the potential of the technique with results from the Humber and Clifton bridges.