斜拉桥正常运营条件下振动特性的变异性

由于环境与运营条件的变化，桥梁结构的振动行为是时变的，桥梁振动动力特性的变异性是基于振动的健康监测技术难以实际应用的原因之一。利用徐浦大桥环境振动监测数据，研究斜拉桥在正常运营条件下动力特性的变化。结果表明：即使在较为稳定的风与温度环境下，该桥整体振动的频率在一天内可以发生接近1％的变化；各振型模态幅值与各测点模态挠度的变化不大；但模态阻尼比对大桥振动强度较敏感，尤其当振动加速度均方根值超过某一水平时，模态阻尼迅速增大。

Variability in Dynamic Properties of Cable- stayed Bridge under Routine Traffic Conditions

The variability in the dynamic properties of a cable-stayed bridge under routine traffic conditions is investigated.First,ambient vibration test was conducted on the bridge under a relatively steady wind and temperature environment and normal traffic conditions.Totally 24 h acceleration response time histories were recorded.Then the data are divided in sequence of time into twelve segments with each data segment containing 2 h measurements.Thereby the modal variability due to changing traffic loading is investigated in both amplitude and frequency domains.It is indicated that the natural frequencies of almost all of the global modes vary within 1%.The variations of the modal amplitudes of each mode as well as of the modal deflection at each measurement position are negligible.However,the damping ratios are sensitive to the vibration intensity,especially when the deck vibration exceeds a certain level.