Pedestrian-sensed indirect footbridge frequency identification

While indirect bridge monitoring has been widely investigated using vehicles and, more recently, micromobility devices, the use of pedestrian response for footbridge frequency identification has yet to be systematically studied. To fill this gap, this paper proposes a new pedestrian-sensed indirect monitoring method for identifying the natural frequencies of footbridges, in which pedestrians themselves serve as low-cost moving sensors rather than requiring a dedicated sensing system on the footbridge. The key novelty lies in demonstrating the feasibility of extracting footbridge modal information directly from pedestrian vibration responses under various pedestrian activities. Numerical simulations of pedestrian–footbridge interaction are carried out for three representative activities, namely standing, jumping, and walking, to examine the feasibility of capturing footbridge modal information in pedestrian responses. The results show that footbridge frequencies can be observed from pedestrian vibrations in all three scenarios. The high damping of pedestrians suppresses their own frequencies, which helps highlight footbridge frequencies, with the pedestrian acting as a weak “low-pass filter”. For walking cases, both footbridge frequencies and walking excitation frequencies appear in the pedestrian response, and the higher footbridge frequencies exhibit a “camel hump phenomenon” due to the moving-sensor effect. Finally, the influences of pedestrian mass, walking speed, environmental noise, footbridge frequency, and footbridge damping are investigated to assess the robustness and limitations of the proposed method.