Identification of Cause of Displacement-Induced Fatigue in Steel Bridges Based on Displacement Measurements Using High-Performance Micro-electromechanical Systems Sensor

It is important to know the displacement response of steel bridges under live loads to ensure that they are properly maintained.In particular, with regard to fatigue damage, if the bridge deformation can be determined based on the displacement response measured at multiple locations, the cause of displacement-induced fatigue can be identified, and appropriate repairs and reinforcements can be implemented as a countermeasure against fatigue damage.In recent years, accelerometers based on micro-electromechanical systems (MEMS) have been proposed to measure the displacement response of bridges to external forces because they are inexpensive and easy to install.However, it is difficult to choose an appropriate accelerometer for this task because the signal-to-noise (S/N) ratio that is required to accurately determine the bridge deflection from the measured acceleration has not been clarified.In the present study, to clarify the dominant frequency range of the displacement of a bridge under live loads, field measurements of two bridges in service were conducted using laser displacement gauges and accelerometers.Next, to clarify the required S/N ratio at the dominant frequency range of bridge displacement, constant-amplitude vibration tests using 10 different accelerometers consisting of nine MEMS accelerometers and a servo-type accelerometer were conducted.By conducting the field measurement of a bridge in service, the bridge displacement responses at multiple points were determined using high-performance MEMS accelerometers.Finally, by analyzing the correlation between the bridge deformation determined from multiple displacement responses obtained using the MEMS accelerometers and the stress at a location where cracks are likely to develop, the cause of displacement-induced fatigue was identified.