Comparison of natural frequencies of vibration for a bridge obtained from measurements with new sensor systeme

Deterioration and aging of bridges structures and damage caused by strong earthquakes might be conducive to collapse of the bridge, sometimes with catastrophic consequences. Therefore, investigation of structural condition of bridges is necessary for secure safe road operations. This paper presents a prototype of piezoelectric-cable sensor for vibration monitoring system that permits easy evaluation of the bridge structure integrity. For this study, a bridge located at Yurihonjo city, Japan was chosen as a target structure. The structure is a continuous beam type bridge with steel beams of various sections and lengths and reinforced concrete slabs to support the asphalt carpet. The bridge comprises seven spans with total length of 256 m. Experimental measurements were taken of the first span near the left abutment. Quantitatively, the natural period of vibration is obtainable from signals recorded using the proposed data acquisition system. Subsequently, results obtained from the proposed system are compared with those obtained from common accelerometers. A piezoelectric sensor emits a signal when a change in the stress condition occurs. Therefore, the sensor was set up at the support of the bridge where large changes in the stress level are expected to occur. The target bridge was also subjected to moving loads. Its vibration response was also obtained. The experiment was performed using a track of 19 t of equivalent weight. Responses were captured appropriately using the proposed system. They are comparable to responses obtained using accelerometers. Although the general response pattern is obtained appropriately, it is necessary to improve the accuracy of the proposed system to gather more reliable data. As presented herein, the general outline of the proposed system is described, mentioning the main specifications and assessing possible means to improve the data acquisition system to permit stable and accurate monitoring of bridge structures.