Field investigation of bicycles for indirect bridge structural health monitoring

Indirect structural health monitoring (iSHM) for bridges typically utilises motorised vehicles. A large number of pedestrian and cycle bridges worldwide cannot practically be accessed by these vehicles. Nevertheless, such bridges are equally susceptible to ongoing accumulation of defects. This paper reports field investigation of using bicycles as exciters and sensor carriers for identifying bridge modal parameters. Data are gathered simultaneously from the moving bicycle and the subject bridge to reduce ambiguity. Bridge modal frequencies estimated using bicycle-mounted sensors are compared to baseline properties estimated using ambient and pedestrian heel drop inputs. Changes in baseline modal frequencies are observed to be correlated with varying temperature, a known cause of environmental and operational variation (EOV). The possible pollution of recorded signals due to human-bicycle interaction dynamics is considered. The combined rider-bicycle-bridge system is observed to exhibit nonstationary frequency behaviour during freewheeling traversals, and bridge resonance due to harmonic pedalling forces is demonstrated. Increased pedalling cadence is correlated with reduced frequency nonstationarity for the combined system. It is suggested that this could be due to an increase in the rider-bike subsystem fundamental frequency caused by rider posture. Collectively, these observations suggest the potential for the use of fleets of bicycles for iSHM, while highlighting the need for greater understanding of potential confounding due to rider-bicycle and rider-bicycle-bridge interaction dynamics as a source of EOV.