桥梁工作模态分析中阻尼比识别的离散性研究

准确识别阻尼比一直是桥梁结构模态参数识别的难题。为研究工作模态分析中识别的阻尼比离散性问题,总结了现有的代表性的频域、时域和时频分析的阻尼比识别方法,指出了各种方法导致识别结果不准确的原因。以一个预应力混凝土连续梁桥的工作模态分析为例,分析了阻尼比识别的结果,研究了减小识别的阻尼比离散性的方法。结果表明:相对频率而言,阻尼比识别结果离散程度较高;在混合自由振动响应的情况下,通过增加采样时间,能改善阻尼比识别离散较大的问题,提高识别精度;利用振动水平较低的随机振动响应识别的阻尼比离散性较小。

Study on the Discreteness of Damping Ratio Identified from Operational Modal Analysis of Bridge Structure

The precise identification of the damping ratio of a bridge structure is generally challenging. The existing representative damping ratio identification methods in the frequency domain, time domain and time-frequency analysis are summarized in order to study the discrete problem of identifying damping ratios using operational modal analysis (OMA). Reasons for incorrect results in each method are investigated. Then, the identified damping ratios are analyzed by using the OMA of a continuous pre-stressed concrete bridge as an example. Finally, a method to reduce the discreteness of the identified damping ratios is studied. The results show that the damping ratios have higher dispersion than that of the natural frequencies. This problem can be relieved by increasing the sampling time when combining the free vibration response, so the accuracy of the damping ratios would improve. The damping ratios extracted from the ambient vibration responses with lower vibration levels show lower discreteness.