MONITORING OF A STEEL PLATE GIRDER RAILROAD BRIDGE WITH FIBER BRAGG GRATING SENSORS

초록

This study investigates an existing steel plate girder railroad bridge after superstructure rehabilitation in order to monitor static and dynamic responses using fiber Bragg grating (FBG) sensors. This paper also presents an experimental technique to estimate the vertical deflection of the bridge using FBG sensors. Seven FBG sensors are multiplexed in a single optical fiber and installed in parallel pairs along the length of the bridge, with one set at the top flange and the other at the bottom flange. In addition to the FBG sensors, a conventional electric strain gauge and a LVDT are installed at the mid-span of the bridge for comparison. A test train consisting of one locomotive is placed at the center of the bridge to produce the maximum static effect. The train passes over the bridge at different speeds, ranging from 10 km/h to 90 km/h, so as to monitor the dynamic response of the bridge. The measured strains using the FBG sensor compare well with the readings from the electric strain gauge. The results also show that the proposed instrumentation technique is capable of estimating the vertical deflection of the bridge for various loading conditions, which is crucial in structural health monitoring.