不同交通流下车辆对桥梁涡振稳定性影响的试验研究

Experimental study of the impact of the vehicular transportation and traffic on the vortex-induced vibration of bridges in different traffic currents

涡激振动是桥梁风致振动中最常见的现象,通常在较低的风速下发生,且对结构气动外形的变化很敏感,车辆行驶在桥梁上势必会改变桥梁断面的外形,因此,研究不同交通流下车辆对桥梁涡激振动的影响非常必要。为了考虑实际运营中车辆对桥梁涡振的影响,基于自由悬挂节段模型试验系统,分别对无车、自由车流和繁忙车流3种交通流状态下车辆对桥梁涡振振动的影响进行了风洞试验。测试了涡振响应和涡振频率,分析了车辆对桥梁涡振响应的影响及机理。结果表明,由于车流显著改变了主梁的气动外形,并且增加了系统质量,不同交通流下车辆对桥梁涡激振动起到了抑制作用。偏于安全考虑,实际桥梁的涡激振动试验可以不用考虑车辆的影响。

This paper intends to make an investigation of the impacts of the vehicles on the vortex-induced vibration of bridges under different traffic flows for the safety of bridges and transportation system. For this purpose, we have conducted a series of wind tunnel tests to imitate the vehicle effects on the vortex-induced vibration of the bridges via a free-attaching section model test, in which a scale of 1：60 section was adopted with the length of 1.54 m for the wind tunnel test. Based on the practical situations of the traffic, the wind tunnel test was oriented to investigate the three types of traffic situations, that is, Type I ： no vehicles moving on the bridge deck, Type ：2 ： free flow of the vehicles; and Type 3： busy vehicle flow. Furthermore, we have examined the three different attack angles of 0°,±3° under each flow situation. We have also simulated the weight of the vehicles in accordance with the similarity criteria of the wind tunnel test. Under each test condition, the test tries to measure the vibration signals and the vibration frequency, with the amplitude of the vortex induced vibration converted into the real bridge level according to the modal modification factors. Furthermore, we have investigated the mechanism of the effects of the vehicle movement on the vortex-induced vibration to0. The results of the experimental study reveal that the section model displays much better performance of the vortex induced vibration under - 3° attack angle with no vehicles on the bridge deck. However, with the increase of the attack angle from - 3° to ＋ 3°, the vibration performance turns to be worse. This may account for the traffic flow induced change to the aerodynamic configuration of the bridge deck and in turn lead to the remarkable increment of the system mass. Thus, the wind tunnel test results tend to prove that the different kinds of traffic flow can suppress the vortex induced vibration of the bridge to some extent, which can be expected to be useful for the serviceability and safety of the bridge. And, from the point of view of the bridge maintenance, there is no need to consider the effect of the vehicles on the vortex-induced vibration of the real bridge when a wind tunnel test study is done.