Measuring the Displacements of a Rigid Footbridge Using Geodetic Instruments and an Accelerometer

Systematic experimental studies have shown the potential of geodetic instruments (GPS, Robotic Theodolites-RTS) with high sampling rate (up to 10Hz) to measure dynamic displacements of relatively rigid structures (oscillation frequency > 1Hz). Based on these results, we used a dense measuring network including GPS instruments, robotic theodolites and an accelerometer to measure the dynamic response of a 40m-long, stiff steel footbridge in Athens, Greece, excited by synchronized vertical jumps of pedestrians. Spectral analysis of the accelerometer, GPS and RTS recordings defined the bridge oscillation frequency on the vertical axis to be 4.3-4.4Hz. Furthermore analysis of the GPS and RTS measurements indicated a mean vertical dynamic displacement of 3.9 mm for the GPS instrument and 3.5 for the RTS. The results of this study indicate that geodetic instruments are able to directly measure the displacements of a wide variety of engineering structures, making them a very useful tool for structural health monitoring.

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