Abstract
At a railway steel box girder bridge, damage was observed on the web of a main girder at the bottom end of a welded vertical stiffener. The objective of this paper is to clarify the cause of the damage. In order to meet the objective, the following steps were taken: 1) A vibration measurement system using laser doppler vibrometers was developed. 2) Local vibration modes were identified based on the ambient vibration measurement using the measurement system with and without stiffeners at the bottom end of a welded vertical stiffener. 3) Relations between local stress, local vibration and train speed were investigated in detail. As a result, it was made clear that the cause of the damage was local vibration of the lower flange on the main girder induced by the cyclic passage of the train bogies. Lastly, a simple analytical model using measurement data explained the phenomena of train-induced vibration and predicted the effect of train speed to the local vibration accurately.
