10. Structural performance evaluation of existing bridges by acceleration monitoring

Some of Shinkansen bridges have been observed to have significant vibration due to resonance caused by passing trains.
The maintenance of existing bridges is generally conducted only by visual inspection, while quantitative data such as deflection and reinforcing bar stress are periodically required to accurately evaluate structural performance such as train running performance and fatigue safety, posing issues of increased labor and cost.

Therefore, we have developed a method to estimate the deflection and reinforcing bar stress when a train passes by with high accuracy, using the records of acceleration sensors installed on the bridge.
The accuracy of acceleration sensors is decreased in the low-frequency range due to noises. To solve this problem, we have developed an algorithm that replaces the low-frequency component of the acceleration waveform with a waveform based on vibration theory and integrates it into the deflection waveform, as well as an algorithm that estimates the stress waveform of reinforcing bars from the deflection waveform without performing detailed cross-sectional calculations, by considering the increase in stress on reinforcing bars due to cracks in the concrete (Fig. 1). This has made it possible to evaluate the train running performance, such as riding comfort due to deflection, and fatigue failure due to reinforcing bar stress, from the measured acceleration waveform of the bridge. This method can estimate the deflections and stresses with an estimation error of less than 10% for an existing standard concrete girder by high-speed processing of less than one second. The validity of this method has been verified by comparing it with numerical experiments and stress measurements on actual bridges.

By applying this algorithm to acceleration monitoring, which is small and can be installed permanently, it is possible to evaluate the structural performance quantitatively and determine the need for repair or reinforcement of bridges that, for example, resonate when a train passes by without much labor (Fig. 2).