Analysis of Bridge Deformations using Continuous GPS Measurements

In this presentation we describe the application of a continuously operating GPS monitoring system to determine the short term deformations of the suspension bridge at Tulln/Austria. Two experiments were carried out using stable reference stations at the embankment and monitoring points placed at the top of the pylon and directly at the bridge deck close to the steel cables. The results clearly show that the bridge point is not well suited for high precision GPS measurements due to the shading and diffraction effects caused by the steel cables. The attainable precision of position for the bridge point is about 1-2cm, and even worse for the height component. However, the experiments yielded a precision of 2mm for the position of the pylon point, with a time resolution of a few seconds. Diurnal variations of the top of the pylon can clearly be correlated with temperature variations. Our experimental data demonstrate the real time capability of GPS monitoring to determine load dependent (e.g., temperature dependent) behaviour of the pylon points of a bridge. We suggest to use GPS as the basis of a bridge monitoring system which yields long term deformation information related to structural fatigue and thus safety of the bridge.