Vertical Vibrations of Footbridges Due to Group Loading: Effect of Pedestrian–Structure Interaction

Paweł Hawryszków,Roberto Pimentel,Rafaela Silva,Felipe Silva

doi:10.3390/app11041355

Abstract

The vibration serviceability of footbridges has evolved from the adoption of a single pedestrian crossing in the resonance condition to load cases in which several pedestrians cross the structure simultaneously. However, in spite of this improvement, pedestrians continue to be considered as applied loads in codes of practice. Recent research has pointed out that modeling pedestrians as dynamic systems is a step further in the search for a more realistic design approach. This is explored in this paper, focusing on the case of vertical vibration. A two-span cable-stayed test structure was selected, and accelerations were measured from single and group crossings, both at the structure and at a pedestrian’s waist. Numerical simulations considering the pedestrians modeled as loads only and also as dynamic systems were implemented, and numerical and experimental time response vibration signatures were compared. Reductions of up to 25% and 20% in peak and RMS acceleration, respectively, were obtained when pedestrians were modeled as dynamic systems, in comparison with the less realistic model of pedestrians as loads only. Such reductions were shown to depend on the number of pedestrians involved in the group. The results, thus, highlight that pedestrian–structure interaction is an asset for the vibration serviceability design of footbridges.

Highlights

Introduction published maps and institutional affilFootbridges are designed for the conveyance of pedestrians
The following investigations carried according this sequence of loadsteps: DLF of each pedestrian from singlewere crossings; (c)out comparing thetoresults for group (a) obtaining the structural damping ratio (so as to use it in obtaining the ings between measurements and simulations; and (d) investigating the effect of the of each pedestrian from single crossings; (c) comparing the results for group loadings number of pedestrians on the two modeling approaches (force-only and dynamic sysbetween measurements and simulations; and (d) investigating the effect of the number of tems)
A collection of damping ratios collection of damping ratios obtained from several crossings are shown in Figure 6, takobtained from several crossings are shown in Figure 6, taking as a reference the value ing as aacceleration reference theamplitude value of the acceleration amplitude at theofbeginning the region of of the at the beginning of the region the decayof signal that was the decay signal that was employed for the respective calculation

Summary

Introduction

Introduction published maps and institutional affilFootbridges are designed for the conveyance of pedestrians. Two major groups of such structures can be distinguished: the group in which footbridges presented excessive vibration in the lateral direction [1,2,3,4,6], and the other group presenting excessive vibration in the vertical direction [1,5,6,7,8]. In the former, the lateral natural frequencies of such lively footbridges are within the usual range of half of pedestrian pacing rates. This is because a complete cycle of body movement in the lateral direction requires two steps to be taken

Objectives

Methods

Results