Comparing L1 GPS with displacement transducers and accelerometers in monitoring applications of bridges.

Abstract

The Department of Transportation of São Carlos Engineering School, Brazil, has been researching about deflections monitoring of large structures, mainly bridges, with Global Positioning System (GPS), since year 2000. This work had technical support from researches of the Timber Wood Laboratory of Sao Carlos Engineering School and researches of the Department of Geodesy and Geomatics Engineering from the University of New Brunswick, Canada. The experiments had the objective to compare the measurements of two geotechnical conventional instruments, displacement transducer and accelerometer, with L1 GPS receiver measurements. The evaluation with the displacement transducer was performed at a cable stayed timber bridge, measuring the amplitude and frequency of its dynamic displacements induced by the stepping of pedestrians. The comparison with the accelerometer consisted in applying a periodic vertical movement by means of an electro-mechanical device. GPS results were obtained by Phase Residual Method (PRM). As this method is not based on coordinate determination, it is very useful for measuring short-lived oscillations at millimeter level. The PRM is not susceptible to multipath-induced position errors (which can be up to several centimeters) and there are minimal satellite visibility constraints. By analyzing results with the different techniques, repeated tests results were obtained which indicate the precision and accuracy of GPS.