Monitoring the deflections of suspension bridges using 100 Hz GPS receivers

The University of Nottingham has been researching deformation monitoring of structures for more than 10 years. To date the GPS receivers used will gather data at a 10 Hz data rate, which is not fast enough to identify high frequency bridge dynamics. A hybrid system of GPS and accelerometers was investigated to overcome the problems of both systems and also to allow high frequency dynamics to be identified.

Recently two Javad JNS100 receivers, which output raw GPS observations and positions at a rate of up to 100 Hz without interpolation, were purchased by the IESSG. These receivers have been used to increase the range of detectable frequencies with GPS only data, which is a research interest for bridge deformation monitoring.

This paper outlines initial trials undertaken to investigate the precision obtainable from the JNS100 receivers. Zero baseline and static trials were conducted and the results are compared to those obtained from a high quality survey grade receiver (Leica Geosystems system 500 single frequency receiver) measuring at a 10 Hz data rate. In a kinematic environment, bungee test rig trials and also a bridge trial are conducted. In these cases, as well as comparing the results to a survey grade GPS receiver, they are also compared to a closely located accelerometer. Initial frequency analysis is conducted, using FFTs of the bridge data, both from the JNS100 receiver and the accelerometer. Higher bridge frequencies are identified with the JNS100 data than has ever been possible with GPS before.