Monitoring of structures using the global positioning system

Previous work has described the application of the Global Positioning System (GPS) to the measurement of movements of large structures (such as darns); the effectiveness of validated finite-element modelling in the prediction of the behaviour of structures under a wide range of loading conditions is well known. This paper describes the use of the GPS in a specific application to the validation of a finite-element model of the Humber Bridge, The Humber Bridge has been in successful operation since its completion and opening in 1981, and the finite-element model was developed for the continued inservice monitoring of the bridge under increased traffic loads or other similar changes. Using the GPS, the deflections of the bridge were measured under known loading conditions, and compared to those predicted by the model. Extremely close agreement was obtained. Rather less expected was the ability of the GPS to determine the resonant frequency of the structure. Careful analysis of the outcome of the validation tests shows that remarkably good experimental data can be obtained from GPS signals, and that these data can be processed to give resonant frequencies of the structure. Close agreement is again obtained between these measured frequencies, the natural frequencies measured by more conventional methods and the natural frequencies predicted by the finite-element model. It is concluded that the technique can be applied to the monitoring of structures with displacements of much smaller amplitude than those of a suspension bridge, and hence that the on-line monitoring of major structures might be readily achieved using GPS-based techniques.