Evaluation of a railway bridge using distributed and discrete strain sensors

Abstract

With over 100,000 rail bridges in North America, of which many are over 100 years old, railway corporations are interested in developing ever more effective condition assessment and monitoring strategies for their structures. In general, strain gauges have been a common and reliable sensing tool as they can provide low-noise measurements at high sampling frequencies (greater than 100 Hz). However, fully distributed sensors, in the form of fibre optics strain sensors, have the potential to compliment discrete sensors by providing a more complete understanding of structural behaviour under loading. In this paper, a sensor system including fibre optics sensors on the rail and strain gauges on the rail and bridge members was used to measure the strain experienced during train passage on the Newmarket Bridge, located in North Bay, Canada. The test span is a typical open deck through plate girder (TPG) with a floor system consisting of stringers and floor beams. Four locations on the continuously welded rail, an intermediate floor beam supporting two bays, the bottom lateral bracing system in two bays as well as a 4 m length of rail were instrumented with strain gauges and fibre optic sensors. The research objectives were to (i) understand the load path from wheel to rail to bridge and (ii) quantify the stress states of the instrumented bridge members under service traffic. Conclusions drawn from this research will assist the assessment of railway bridge behaviour and improve future monitoring and reinforcement techniques.