Experimental analysis of additional aerodynamic effects caused by wind-driven rain on bridge main girder

Abstract

To study the additional aerodynamic effect on a bridge girder under the action of wind-driven rain, the rainfall similarity considering raindrop impact and surface water is first given. Then, the dynamic characteristics and the process of vortex and flutter generation of the segment models under different rain intensities and angles of attack are tested by considering several typical main girder sections as examples. The test results indicate that the start and end wind speeds, interval length and number of vortex vibrations remain unchanged when it is raining, rainfall will reduce the wind-induced vortex response. When test rain intensity is large, the decrease of amplitude is obvious. However, after considering the rain intensity similarity in this study, all of actual maximum rain intensities after conversion approach the domestic extreme rain intensity of approximately 709 mm/h. It can be observed that rainfall has a limited influence on the dynamic characteristics of the structure and vortex vibration response. When the test rain intensity is 120 mm/h, the critical wind speed of the model flutter increases by 20%–30%. However, after considering the rain intensity similarity ratio, the influence of rainfall on the wind-induced flutter instability of the bridge girder may be ignored.

摘要

针对风驱雨作用下桥梁主梁的附加气动效应问题,首先,依据风驱雨作用和主梁振动特点,给出了分别考虑雨滴冲击和表面积水后的降雨相似关系。然后,以几类典型主梁截面为例,实现了不同雨强和攻角下的节段模型动力特征与涡振、颤振发生过程测试。试验结果表明:随着雨强的增大,结构振动频率降低,但即使试验雨强达到120 mm/h,改变量也仅在3%左右;阻尼比随雨强增加而增大,但增加量较小;降雨时的起振和结束风速、区间长度和数目不变,有雨时涡振振幅小于无雨时结果,试验雨强较大时减小明显,但考虑本文的雨强相似关系后,其均接近700 mm/h左右的国内短时极值雨强,可知降雨对结构动力特性和涡振响应的影响非常有限。随着雨强的增大,主梁截面的颤振气动导数变化无明显规律,各导数的变化量值相当,随风速增加,降雨引起的导数变化有所加大,但基本没有改变其随风速变化的整体趋势,在试验雨强120 mm/h时,模型颤振临界风速会有20%∼30%的提高,但考虑雨强相似比后可以认为降雨对桥梁主梁的风致颤振失稳特征的影响基本可以忽略。