Hybrid reference-free total displacement for railroad bridge campaign monitoring

Abstract

According to railroad managers in North America, measuring bridge displacements under service traffic can assist in quantifying the reliability and safety of an aged railroad network. Railroad bridge campaign monitoring consists of collecting as much information as possible annually to inform decisions related to safety and for maintenance, repair, and replacement (MRR). However, acquiring displacement data without a stationary reference frame in the field is often challenging during railroad bridge campaign monitoring. This research proposes a hybrid reference-free sensing technology to enable the collection of bridge displacements under service traffic during inspections. This technology fuses two sensing systems: the estimated pseudostatic displacement from an accelerometer pair and the measured direct dynamic displacement from a passive-servo-electro-magnetic-induction (PSEMI) sensing system. Researchers designed a cantilever column in the laboratory representing a timber bridge pier model in order to validate the effectiveness of the hybrid sensing system. This technique used an Euler–Bernoulli cantilever beam model to translate the pier tilt from the accelerometer pair to pseudostatic displacement. Researchers used a shake table to excite the laboratory model with real bridge displacement collected in the field under a train crossing. The pseudostatic displacement was obtained by applying a low-pass filter to the accelerometer data, and the dynamic displacement was obtained by using a high-pass filter on the PSEMI data. The total reference-free transverse displacements acquired through the fusion of the pseudostatic and dynamic components were compared to the LVDT measurements. The comparison results showed that the proposed hybrid sensing system measures the reference-free total bridge displacements accurately and reliably without the need for postprocessing dynamic displacement. The authors conducted this comprehensive laboratory testing to support the suitability of this system for railroad bridge campaign monitoring in railroad bridge environments.