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

本研究的目的是开发利用三台激光多普勒测振仪的振动测量系统，使高精度、空间高密度地测量物体的三维行为成为可能。首先，为了验证测量原理，开发了基本系统。然后，为了应用于现场测量，开发了允许扫描和任意设置的三维振动测量系统。由于所开发的系统可以明确由火车/交通引起的振动引起的结构的三维局部变形，因此可以为现有基础设施的预防性维护和功能改进做出贡献。应用所开发的系统，通过现场实测研究了列车振动和列车速度对钢箱梁桥各部分局部应力的影响。测量结果明确了铁路桥梁在列车振动作用下的非稳态动力响应特性。通过对采集到的数据进行分析，确定了铁路桥梁的固有频率和模态振型在改造后的变化。结果表明，主梁下翼缘处的振动增加了局部应力，造成了损伤。此外，研究表明，列车的振动与列车速度引起的循环外载荷有关。

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.