Establishment of Infrastructure Monitoring System using High-accuracy Laser Dopper Vibrometers and its Application to Real Infrastructure

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The objective of this research is to develop vibration measurement system using three laser Doppler vibrometers, which makes possible to measure three-dimensional behavior of an object high accurately and spatially high densely. At first, to validate the measurement principle, fundamental system was developed. Then, for the application to on-site measurement, three-dimensional vibration measurement system allowing a scanning and an arbitrary setting was developed. Because developed system can clarify the three-dimensional local deformation of structures caused by train/traffic-induced vibration, it can contribute to the preventive maintenance and the improvement of functionality in existing infrastructures.The developed system is applied to study the effect of train-induced vibrations and the train speed on local stresses at each part of the steel box girder bridge by field measurement. The measurement clarified the non-stationary dynamic response characteristics of a railway bridge subjected to train-induced vibrations. The data acquired were analyzed to identify the natural frequencies and the changes based on the retrofit in the mode shapes of the railway bridge. The results show that vibrations at the lower flange of the main girder increased the local stresses causing damage. Furthermore, the study shows that the vibration depends on the cyclic external load induced by train speed.