栏杆透风率对主梁涡振特性影响的风洞试验
Wind tunnel experimental on influence of railing ventilation rate on？？characteristics of vortex？？induced vibration of main girder

为了研究栏杆透风率对箱形钢主梁涡激振动特性的影响，通过不同的封闭栏杆方案改变外侧栏杆的透风率，并在试验模型表面布置测压孔道，进行测振、测压风洞试验。采取2种封闭形式，一封三空和一封二空方案，即比原方案的透风率分别降低25%和33%。在不同的透风率工况下，同步测量主梁断面风速与振幅的关系及模型表面各测点的风压时程，分析模型表面各测点的平均压力系数、脉动压力系数及功率谱密度随栏杆透风率的变化情况。研究结果表明：降低栏杆透风率可有效抑制主梁的涡激振动；不同工况下，主梁表面压力系数的分布规律一致，仅在数值上有所差异，这是由阻风面积改变造成；封闭栏杆方案较原方案的脉动压力系数在分布规律及数值上均有显著差异；原方案绝大部分测点的涡脱频率集中在模型的竖弯和扭转频率，且能量较大，而封闭栏杆方案的涡脱频率仅有小部分集中在竖弯和扭转频率，且能量较小，栏杆透风率的降低改变气流的绕流，有效打散了能量在竖弯及扭转频率上的集中，因此未能激起结构的显著振动；涡激振动对栏杆透风率具有敏感阈值，栏杆透风率降低25%是对该桥竖弯涡振影响的阈值。
To study the influence of railing ventilation rate on characteristics of vortex？？induced vibration of main girder in box？？shaped steel, ventilation rate of outside railing with different sealing strategies on railings were changed， and manometric holes were arranged on the surface of model, the vibration measurement and manometric method in the wind tunnel experiment were conducted. The railings were sealed in two ways, in the one？？sealed three？？open plan(a sealed segment was arranged between every three open segments) and in the one？？sealed two？？open plan (a sealed segment was arranged between every two open segments), the ventilation rate of two ways were reduced by 25% and 33%, respectively, compared to the original plan. The relationship of the air speed on the section of main girder and its amplitude were measured based on the different vibration rates, and the change history of the average pressure coefficient, the pulsating pressure coefficient, and the power spectral density were analyzed on the tested holes which located on the surface of model. The results show that the reduce of railing vibration rate could restrain the vortex？？induced vibration of the main girder effectively, and with different operating conditions, pressure coefficient distributes coherently on the surface of the main girder, the only difference caused by changing choke proportion lies on numerical values. Compared with the original plan, there are significant differences in railing sealing plan on distribution and values of pulsating pressure coefficient. The vortex？？shed frequency on the majority of tested points concentrates on vertical bending and torsional frequency of the model, and the energy is larger, in the original plan, while there is only a small part of the vortex？？shed frequency concentrates on he vertical bending and torsional frequency and the energy is small in the railing sealing plan, thus the reduce of railing ventilation rate changes the turbulent flow of air, effectively distributes the concentration of energy on the vertical bending and torsional frequency, therefore undoes the dramatic