Change in Mass and Damping on Vertically Vibrating Footbridges Due to Pedestrians

Abstract

Pedestrian-induced footbridge vibrations are an issue that bridge designers often have to contend with. A plethora of research in recent years has led to the development of load models and procedures that allow for the determination of footbridge response. Nonetheless, measured footbridge responses often deviate from those predicted. One of the main deficiencies of the existing models and guidelines is the exclusion of the effect of changes in the footbridge's dynamic properties due to the presence of pedestrians. More specifically, any change in mass and/or damping that a pedestrian might introduce to a bridge will affect the bridges overall dynamic response. This effect is an element of what is often referred to as human-structure interaction. In this paper, the results of an experimental study to determine the change in mass and damping of a vertically vibrating footbridge due to traversing pedestrians are presented.

Characterization of stationary and walking people on vertical dynamic properties of a lively lightweight bridge

“…Besides, the natural frequency of the occupied structure decreases as the number of walking people on the structure increases, that is, the first bending frequency of the bridge decreases from 2.83 ( N = 1) to 2.74 Hz ( N = 7) for cases of walking at 1.88 Hz, as shown in Figure a. The results are in line with those reported elsewhere for groups of walking people . The decrease in natural frequency and increase in structural damping can be partly attributed to the existence of human–structure interaction, which is usually observed in stationary people scenarios.…”

“…Compared to stationary people, the knowledge about how moving pedestrians affect the dynamic properties of vertically vibrating structures is very limited, especially for multipedestrian traffic. Previous works are representative studies toward clarify the mechanism of this issue. In particular, Shahabpoor et al systematically reviewed the efforts to date to simulate walking HSI in the vertical direction and highlighted the key areas that need further investigation.…”

Interaction between Walking Humans and Structures in Vertical Direction: A Literature Review

“…Several studies in the past have noted the increase of damping and/or changes of the natural frequencies of structures when they are occupied by stationary (standing or sitting) people [26][27][28][29][30]. However, studies are rare concerning changes in dynamic properties of the structure due to moving (e.g., walking and running) people in the vertical direction [11,31,32].…”

“…Georgakis and Jorgensen [32] did a series of forced vibration tests on a purposefully built test footbridge to quantify the effects of walking pedestrians on the mass and damping of the structure. The footbridge was a simply supported 16 m long double U-beam steel structure with the mass of 5,224 kg, natural frequency of 2.23 Hz, and amplitude-dependent damping of 0.25-0.58%.…”

Dynamic assessment of a FRP suspension footbridge through field testing and finite element modelling

“…Greater damping was recorded during the stamping tests than during following walking for both of the vertical modes examined. This is usually the case for lightweight footbridges, due to the higher level of vibration caused by stamping or jumping compared to walking, together with the contribution of the people remaining on the bridge during the decay response (Georgakis andJørgensen 2013, Sachse et al 2003). In the present study one extra person remained on the footbridge following the stamping tests, whereas only the operator of the signal analyser was present on the bridge during the decay phase following the walking tests.…”