基于现场记录的液化和非液化场地加速度时频曲线对比分析
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摘要
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 histories of acceleration records on liquefied and non-liquefied sites are analyzed.The concept and the calculation method of frequency decreasing ratio are proposed;and the division between the liquefied and non-liquefied sites is presented.The zero-crossing method is employed to analyze the time-frequency curves of acceleration records.The non-liquefied sites include the soft sites and the ordinary non-liquefied sites.The results indicate:① The concept and calculation method of frequency decreasing ratio proposed in this paper can describe the characteristics and regulations of time-frequency on liquefied and non-liquefied sites.② Before PGA,the difference of the average frequencies of acceleration on liquefied and non-liquefied sites is not obvious;and the average frequency of acceleration on soft sites is smaller than that either on liquefied or non-liquefied sites.③ After PGA,the average frequency of acceleration on ordinary non-liquefied sites is the highest of the three types of sites,that of soft sites is the middle and that of liquefied sites is the smallest.④ If the absolute change of the time-frequency is used as the criteria,it will be confused between soft sites and liquefied sites.⑤ The threshold of frequency decreasing ratio is 0.5 between liquefied and non-liquefied sites,which can distinguish the liquefied sites,non-liquefied sites and soft sites correctly.
The time-frequency histories of acceleration records on liquefied and non-liquefied sites are analyzed.The concept and the calculation method of frequency decreasing ratio are proposed;and the division between the liquefied and non-liquefied sites is presented.The zero-crossing method is employed to analyze the time-frequency curves of acceleration records.The non-liquefied sites include the soft sites and the ordinary non-liquefied sites.The results indicate:① The concept and calculation method of frequency decreasing ratio proposed in this paper can describe the characteristics and regulations of time-frequency on liquefied and non-liquefied sites.② Before PGA,the difference of the average frequencies of acceleration on liquefied and non-liquefied sites is not obvious;and the average frequency of acceleration on soft sites is smaller than that either on liquefied or non-liquefied sites.③ After PGA,the average frequency of acceleration on ordinary non-liquefied sites is the highest of the three types of sites,that of soft sites is the middle and that of liquefied sites is the smallest.④ If the absolute change of the time-frequency is used as the criteria,it will be confused between soft sites and liquefied sites.⑤ The threshold of frequency decreasing ratio is 0.5 between liquefied and non-liquefied sites,which can distinguish the liquefied sites,non-liquefied sites and soft sites correctly.
引文
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[2]刘汉龙,周云东,高玉峰.砂土地震液化后大变形特性试验研究[J].岩土工程学报,2003,24(2):142-146.LIU Han-long,ZHOU Yun-dong,GAO Yu-feng.Study on the behavior of large ground displacement of sand due to seismic liquefaction[J].Chinese Journal of Geo-technical Engineering,2003,24(2):142-146.
[3]王志华,刘汉龙,陈国兴.基于随机地震反应的桥墩-群桩-土相互作用研究[J].岩土力学,2006,27(3):71-75.WANG Zhi-hua,LIU Han-long,CHEN Guo-xing.Study on pier-pile group-soil interaction based on stochastic seismic response[J].Rock and Soil Mechanics,2006,27(3):71-75.
[4]孙恒矗,周小文,蔡元林.建筑物下砂土地震液化分区特征数值模拟研究[J].岩土力学,2007,28(Supp.):748-752.SUN Heng-chu,ZHOU Xiao-wen,CAI Yuan-lin.Numerical simulation of sandy soil liquefaction zoning for unfree field under earthquake[J].Rock and Soil Mechanics,2007,28(Supp.):748-752.
[5]孙锐,袁晓铭.液化对设计反应谱和场地分类的影响[J].地震工程与工程振动,2003,23(5):46-52.SUN Rui,YUAN Xiao-ming.Effect of soil liquefaction on design response spectrum and site classification[J].Earthquake Engineering and Engineering Vibration,2003,23(5):46-52.
[6]KOSTADINOV M V,TOWHATA I.Assessment of liquefaction-inducing peak ground velocity and frequency of horizontal ground shaking at onset of phenomenon[J].Soil Dynamics and Earthquake Engineering,2002,(22):309-322.
[7]胡聿贤,张郁山,梁建文.应用HHT方法从竖向地震动记录识别场地液化的物理过程[J].地震工程与工程振动,2004,24(3):1-11.HU Yu-xian,ZHANG Yu-shan,LIANG Jian-wen.Identification of physical process of site liquefaction from vertical seismic recordings via the method of HHT[J].Earthquake Engineering and Engineering Vibration,2004,24(3):1-11.
[8]公茂盛,谢礼立.HHT方法在地震工程中的应用之初步探讨[J].世界地震工程,2003,19(3):39-43.GONG Mao-sheng,XIE Li-li.Discussion on the application of HHT method to earthquake engineering[J].World Earthquake Engineering,2003,19(3):39-43.
[9]孙锐,袁晓铭.非均等固结下饱和砂土孔压增量简化计算公式[J].岩土工程学报,2005,27(9):1021-1025.SUN Rui,YUAN Xiao-ming.Simplified incremental formula for estimating pore water pressure of saturated sands under anisotropic consolidation[J].Chinese Journal of Geotechnical Engineering,2005,27(9):1021-1025.
[10]ISHIHARA K,YASUDA S.Sand liquefaction under random earthquake loading condition[C]//Proceedings of 5th Word Conference on Earthquake Engineering.Rome:[s.n.],1973.
[11]孙锐,袁晓铭.液化土层对地表加速度反应谱的影响[J].世界地震工程,2004,20(3):33-38.SUN Rui,YUAN Xiao-ming.Effect of soil liquefaction on response spectrum of surface acceleration[J].World Earthquake Engineering,2004,20(3):33-38.
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