Indirect Frequency Identification of Footbridges with Pedestrians Using the Contact-Point Response of Shared Scooters

As an essential element of a smart city, rapid health assessment of transportation infrastructure, including footbridges, is crucial. This study proposes a method for identifying the frequencies of a footbridge with pedestrians using the vibrations of a shared scooter. To simulate a rider and a scooter, a novel finite-element (FE) model with four degrees of freedom (DOFs) is proposed. One of the key challenges in identifying the frequency of footbridges is the impact of pedestrians, which can result in complex vehicle–footbridge–pedestrian interaction (VFPI) processes. The contact-point (CP) response is further deduced from the 4-DOF model’s accelerations to eliminate its self-frequencies. The influence of road roughness is weakened by employing the residual CP response of the two wheels, which highlights the frequencies of the footbridge. The results indicate that pedestrians can play a “positive” role in indirectly identifying the footbridge’s fundamental frequency even with poor road roughness classes (B and C in this study). The effects of the environmental noise, footbridge damping, and tire damping were examined.