Dynamic Response of a Lively Footbridge Under Walking Pedestrians

The paper analyzes the dynamic response of a lively footbridge, 107 m long, overpassing the river Lambro near Milano (Italy). Ambient vibration tests (AVTs), performed in 2016 as a part of proof tests, detected the first flexural frequency at 1.75 Hz, within the critical range of vibration for walking pedestrians. In a previous numerical and experimental work, a FE model accurately reproduced the first frequency but showed a poor match of the second one, corresponding to a torsional mode. In onsite tests, groups of up to twelve pedestrians, adopted as vibration exciters, crossed the footbridge with step frequency and spatial configurations exciting mainly the first mode. To overcome these limitations, in this study AVTs were performed to repeat the identification of the second mode. The FE model was updated subsequently. Onsite tests were repeated with a group of five pedestrians, each walking alone. Walking paths and step frequencies were chosen to excite both the first and the second mode. The pedestrians' vertical acceleration was recorded using a mobile phone. The experimental data concerning both footbridge response and pedestrians' acceleration are analyzed to detect the correlation between the two.