识别中低高度桥墩自振频率的冲击振动试验法

Impact Vibration Test Method for Identifying the Natural Vibration Frequency of Piers with Middle and Low Heights

在分析既有频率识别方法的基础上,对利用冲击振动试验识别中低高度桥墩频率的方法进行研究。桥墩在白噪声冲击荷载作用下的速度响应频谱非常复杂,往往出现多个卓越频率,如果仅一个卓越频率对应180°相位角,则可明确判定其为桥墩的自振频率,其他卓越频率可能为相邻梁或桥墩的自振频率,可通过分析它们自身响应频谱的方法进行频率认定。如果出现桥墩响应频谱中多个卓越频率对应180°相位角的情况,需要结合相位曲线特征进行频率识别:满足相位曲线连续横跨180°线的卓越频率是桥墩的自振频率,相位曲线在其后出现突降的卓越频率仍就是相邻梁或墩的干扰频率。用冲击振动试验法可以对桥墩响应频谱中的干扰频率进行鉴别,准确识别出中低高度桥墩的自振频率。

On the basis of the detailed analysis of existing frequency identification methods, the trequency identification of piers with middle and low heights by impact vibration test method is studied. The study indicates that the velocity response spectra of piers under white-noise impact load are complex, in which many dominant frequencies emerge. In the event that only one dominant frequency accords with the 180° phase, it can he definitely judged as the natural frequency of the pier. Other dominant frequencies may be the natural frequencies of adjacent beams or piers, which can be ascertained by analyzing their own response spectra. If many dominant frequencies, at which the phase is 180°, emerge in the response spectra of piers, the frequency identification can be conducted according to the phase curve characteristics. The dominant frequencies, at which the phase curves stride over the 180° line continuously, are the real natural frequencies of piers, while those dominant frequencies, after which the phase curves mutate, are still the disturbance frequencies of adjacent beams or piers. By the impact vibration test method, the disturbance frequencies in the response spectra of piers can be differentiated and the natural frequencies of piers with middle and low heights can be identified precisely.