MONITORING AND ANALYSIS OF DEFORMATION OF IKPOBA RIVER BRIDGE, BENIN CITY, EDO STATE, USING GLOBAL POSITIONING SYSTEM

Safety is the primary and most important reason for monitoring the deformations of engineering structures. It could also help in improving our knowledge of the mechanical behaviour of engineering structures. Engineering structures are subject to deformation due to factors such as changes of ground water level, traffic load changes, tidal and tectonic
phenomena. The Ikpoba River Bridge in Benin City whose traffic load has increased was monitored using GPS technology. The bridge was investigated as a result of carrying more load than usual due to the expansion of the road and dredging activities that had taken place in the river in 2008. One reference station and six monitoring points were involved in the monitoring of the bridge. The regularity of the survey was thirty days, and six observation epochs were used. Each monitoring point was occupied for about thirty minutes during the observation. The observation data were processed with compass software. The processed coordinates were adjusted with least squares adjustment technique. The standard deviation of unit weight for the weighted observations (óo) was computed for each observation epoch and was less than 1cm. The observation epochs were compared consecutively by finding the difference between successive observation results. The maximum differences in coordinates of the successive epochs were all less than 1mm. It was seen from the results that the bridge was stable and did not undergo any displacement/movement within the period of study. It is recommended that the results of the six monitored points on the bridge should be further analyzed using other appropriate model of adjustment technique.