Vibration Serviceability Issues of Slender Footbridges: Fid-Bau Portal

Vibration Serviceability Issues of Slender Footbridges

Setareh, Mehdi

Three important issues related to vibration serviceability were investigated in this study using a slender steel footbridge: (1) the evaluation of footbridge vibrations by passive people (standing still on the footbridge) and active people (pedestrians); (2) the increase in vibrations when a group of people walk/run on a footbridge compared with a single pedestrian crossing the structure; and (3) the modal damping ratios for vibration analysis of footbridges. Using the results of a number of dynamic tests, relationships between various evaluation parameters were established, and more reliable and consistent limits based on the vibration dose values (VDVs) are proposed. In addition, a simplified method of computing the acceptable level of peak acceleration based on average number of footbridge crossings per day for the performance-based (usage-based) serviceability design of footbridges is suggested. The investigation on the group effects showed results consistent with those of past studies when the pedestrians crossed the footbridge at the average normal speed of 2 steps/sec. However, the footbridge vibrations resulting from a group of people increased less than the reported value in the literature when people walked randomly and more than the reported value when they moved at the first-mode resonance frequency of the structure. Based on the results of the dynamic field testing of the footbridge, a modal damping ratio of 0.6–0.8% for steel footbridges with timber decking is recommended.