Human-induced vibration of a bridge and its mechanism

对一座实际人行天桥在极端拥挤状态下的人为振动进行了观测。分析了摄像机记录的行人的行走运动。结果表明，20%或更多的行人的行走与主梁的横向振动同步。为了研究桥梁横向振动产生的原因，利用横向振动地板进行了人步行试验，并对试验结果进行了分析。实验的目的是为了明确地板横向运动下的步行特性的变化。人体颈部的横向运动由加速度计测量，而行走所施加的横向力由压力计测量。人的步行同步地板运动被证实，它被发现，在步行过程中的横向运动增加的地板振动的幅度增加。根据这些实验结果，指出桥梁的横向振动是通过人与桥面的同步行走而产生的，并利用人的两腿刚性摇摆模型研究了行人引起的桥梁横向振动。用该模型计算了步行时的侧向力，与实验结果吻合较好。选择一座有横向振动观测的桥梁作为案例研究。在人体运动与行走力之间存在相位滞后的假设下，利用该模型研究了人体行走与主梁之间的相互作用。主梁的计算振幅与该桥的振幅同阶。在此基础上，还讨论了人-梁相互作用引起主梁振动的机理。

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.