Human-induced vibration of a bridge and its mechanism

报道了在极度拥挤的情况下，对一座实际人行天桥的人为引起的大幅度横向振动进行了观测。对摄像机记录的行人行走动作进行分析。研究发现，20%或更多的行人行走与梁的横向振动同步。在这种同步作用下，行人对主梁的总侧向力明显增大，并对主梁的横向振动产生共振力。为了弄清在实际桥梁中观察到的行人引起的横向振动的原因，采用横向振动楼板进行了人体行走实验。实验的目的是为了弄清楚在地板的横向运动下行走特性的变化。人体颈部的横向运动用加速度计测量，行走时施加的侧向力用压力计测量。证实了人体行走与地板运动的同步性，发现行走时的横向运动随着地板震动幅度的增大而增大。根据这些实验结果，指出桥梁的横向振动是通过人向地面行走的同步产生的。采用人步行的两足刚性摇摆模型，研究了行人引起的桥梁横向振动。用该模型计算了行走时的侧向力，与实验数据吻合较好。选取了一座观测到横向振动的桥梁作为研究实例。在假定人的运动与行走力存在相位滞后的前提下，利用该模型研究了人的行走与梁的相互作用。计算出的梁幅值与该桥的幅值相同。根据这些结果，讨论了行人诱发振动的机理，认为这是人与梁相互作用的结果。

Observation of human-induced large-amplitude lateral vibration of an actual pedestrian bridge in an extremely congested condition is reported. Walking motions of pedestrians recorded by a video camera are analyzed. It is found that walking among 20% or more of the pedestrians was synchronized to the girder lateral vibration. With this synchronization, the total lateral force from the pedestrians to the girder is evidently increased and it acts as a resonant force on the girder lateral vibration.An experiment on human walking is carried out using laterally shaking floor in order to clarify causes of pedestrian-induced lateral vibration observed in an actual bridge. The purpose of the experiment is to make clear the changes of characteristics of walking under the lateral motion of the floor. Lateral motion of the neck of the human body is measured by an acceleration meter, while the lateral force exerted by walking is measured by pressure meters. Synchronization of human walking to the floor motion is confirmed and it is found that the lateral motion during walking increases as the amplitude of the floor shaking increases. According to these experimental results, it is pointed out that lateral vibration of a bridge occurs through synchronization of human walking to the floor.Pedestrian-induced lateral vibration of a bridge is studied using a two-legs rigid rocking model for human walking. Lateral force exerted by walking is calculated by this model and is found to agree with the experimental data. A bridge where lateral vibration is observed is chosen as a case study. Interaction between human walking and the girder is studied using the model under the assumption that there is a phase lag between human motion and walking force. The calculated amplitude of the girder is as the same order as of that bridge. According to these results, the mechanism of pedestrian-induced vibration is also discussed as an interaction of human and girder.