基于精确阻尼调控的桥梁竖弯涡振Sc数影响

Effect of Sc Number on Vertical Vortex-induced Vibration of Bridges Based on Precise Damping Adjustment

在桥梁气动外形和来流风场确定的条件下,Sc数(Scruton number)是影响大跨度桥梁涡振响应大小的关键因素.为了开展Sc数对大跨度桥梁竖向涡振影响的精细化研究,首先研制了适用于桥梁节段模型风洞试验的永磁式板式电涡流阻尼器,可为弹性悬挂节段模型系统提供可连续调节的、理想线性黏滞阻尼.然后以带风嘴的开口断面钢混组合梁桥为研究对象,针对+3°、0°和-3°三个风攻角和不同的Sc数开展了节段模型竖向涡振试验.根据试验结果,总结了节段模型涡振振幅的风速变化曲线随名义阻尼比的变化规律,分析了最大涡振振幅随Sc数变化规律的函数拟合,并对桥梁高阶模态涡振响应进行了预测.研究发现不同风攻角下主梁竖向涡振的锁定风速区间都随Sc数的增大而缩小,最大振幅都随Sc数的增加而降低,但变化曲线有显著差别;通过对三组及以上不同Sc数的节段模型风洞试验结果进行函数拟合,可以较好地预测节段模型最大涡振振幅随Sc数的变化规律;在模态阻尼比相同的条件下,大跨度悬索桥各阶竖弯模态的涡振振幅基本相同,高阶模态涡振更容易出现不满足规范限值的情况.研究成果为大跨度桥梁竖弯涡振响应的精细化预测提供了重要方法.

Under the condition that the aerodynamic shape of the bridge and the incoming wind field are determined,the Sc number is one of the key factors affecting the vortex-induced response of long-span bridges.In order to conduct a refinement study on the effect of Sc number on vertical vortex-induced vibration(VVIV)of long-span bridges,firstly a permanent magnet plate eddy current damper was developed,and it was utilized to provide linear and adjustable viscous damping for the spring-suspended sectional model system.Then wind tunnel test for a section model of a steel-concrete composite girder bridge with wind fairings was conducted under three different wind attack angles of+3°,0°and-3°,respectively,and several different Sc number.Based on the experiments,the variation of VVIV displacement with the wind velocity for different nominal damping ratio was obtained,the maximum displacement of the VVIV versus Sc number relationship was analyzed by curve fitting,and the higher-order modal vortexinduced vibration response of the bridge was predicted.It is found that the lock-in wind speed region as well as the maximum amplitude decrease with the increase of Sc number under all the three wind attack angles,though their varying tendencies are significantly different.The maximum amplitudes for different Sc numbers can be well predicted by curve fitting of the results of wind tunnel tests for at least three different Sc numbers.On the assumption of the same modal damping ratio,the vortex-induced vibration amplitudes of all vertical bending modes of long-span suspension bridges are almost the same.As a result,the vortex-induced vibration amplitudes of higher-order modes are more difficult to meet the specification limits.The research results provide a novel method for refinement prediction of VVIV response of long-span bridges.