【摘要】 利用有限元数值方法模拟不同类型砂土在多向地震荷载输入条件下的动单剪试验,采用弹塑性边界面模型,通过室内动单剪试验实测结果确定模型参数,计算分析地震动特性对砂土震陷的影响。研究结果表明:地震波加载次序、不对称性、加载方向、地震波类型、加载维数对砂土变形影响显著。当大的应力脉冲出现时,砂土竖向应变明显增大,其增量的大小受到大波出现的时刻和次序影响明显;在其他条件相同时,地震波不对称性越明显,砂土竖向应变越大;反向加载对砂土具有向下压应力作用,提高竖向应变值,正向加载效应则与此相反;现有的一些规范方法取20周作为转换后的等幅应力波的标准作用次数进行震陷定量计算,其对于振动型和冲击型地震波输入等效性结果差别较大;Tokimatsu和Seed(1987)震陷分析方法按2倍单向水平地震动引起的砂土震陷简化确定多向地震动引起的砂土震陷,其结果尚待商榷。更多还原

【Abstract】 Dynamic simple shear tests on different types of sands under multidirectional earthquake loading were simulated with finite element method.Reduced order bounding surface model was employed to study the effect of characteristics of earthquake loading on the seismic compression of sands.The parameters of model were determined based on results obtained from laboratory dynamic simple shear tests.The study results show that the characteristics of earthquake loading such as loading sequence,asymmetry,loading direction,loading type and input loading dimension have great influence on seismic compression of sand.The vertical strain of sand increases dramatically when sand specimen is subjected to high stress pulse;also its increment is greatly influenced by time and sequence of stress pulse;the vertical strain of sands increases as the asymmetry of earthquake loading grows under identical conditions;negative loading results in increase of vertical strain of sand due to its compaction effect,which is opposite to positive loading effect;20 cycles were used simply as the number of equivalent cycle in some current codes for computation of seismic compression,whose equivalences for vibration-type and impact-type of seismic loading is greatly different;two times of seismic compression of sand induced by one component loading was taken as the sum of seismic compression of sand induced by actual multidirectional earthquake loading in Tokimatsu and Seed(1987) procedure,which is in doubt.更多还原