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研究液化场地和非液化场地上地表地震加速度记录的时频曲线,提出频率下降率概念和计算方法,给出液化场地和非液化场地频率下降率的分界值。加速度时频曲线采用零交法进行分析,非液化场地包含软土场地和除去软土场地后的一般非液化场地。结果表明:①所定义的频率下降率的概念和计算方法,能够反映液化和非液化场地地表加速度时频响应特征和变化规律;②峰值前,在平均意义上液化场地与一般非液化场地平均频率相差不大,软土场地上的平均频率远小于一般非液化场地和液化场地;③峰值后,在平均意义上一般非液化场地加速度平均频率最高,软土场地居中,液化场地最低;④软土场地与液化场地峰值后平均频率范围有交叉,如以加速度时频曲线绝对变化量为判断标准,软土场地和液化场地会出现混淆;⑤液化场地和非液化场地的加速度频率下降率的分界值为0.5,以此可正确区分出液化场地与非液化场地以及液化场地与软土场地。
The time-frequency curve of surface seismic acceleration recorded on liquefied ground and non-liquefied ground is studied. The concept and calculation method of frequency descent rate are proposed, and the cut-off value of frequency descent rate of liquefied ground and non-liquefied ground is given. The time-frequency curve of acceleration is analyzed by the zero-crossing method. The non-liquefied site contains the soft soil site and the general non-liquefied site after the soft soil site is removed. The results show that: (1) The definition and calculation method of frequency descent rate can reflect the time-frequency response characteristics and variation law of surface acceleration of liquefied and non-liquefied sites; (2) Before the peak value, the mean frequency of liquefaction site and general non-liquefied site The average frequency of soft soil is far less than that of general non-liquefaction and liquefaction sites; ③ After peak, the average frequency of acceleration of general non-liquefied sites is the highest in average, and the lowest is in soft soil; ④ Soft soil The average frequency range of the site after the peak of the liquefaction site crosses. If the absolute variation of the time-frequency curve of the acceleration is used as the judgment standard, confusion will occur between the site of the soft soil and the site of liquefaction. ⑤ The cutoff value of the rate of decline of the acceleration frequency of the liquefied site and the non-liquefied site Is 0.5, which can correctly distinguish liquefied and non-liquefied sites and liquefied sites and soft sites.