Evaluating nonlinear effective stress site response analyses using records from the Canterbury earthquake sequence

A widely used one-dimensional nonlinear effective stress site response analysis program is used to model the response of potentially liquefiable soils during strong shaking. Ground motion records from six events of the 2010–2011 Canterbury earthquake sequence and the extensive site investigation data that have been obtained for the Christchurch area provide the basis for the analyses. The results of the analyses depend significantly on the input motions and soil profile characterization, so these important aspects are examined. Deconvolved Riccarton Gravel input motions were generated, because recorded rock or firm layer motions were not available. Nonlinear effective stress seismic site response analyses are shown to capture key aspects of the observed soil response through the comparison of acceleration response spectra of calculated surface motions to those of recorded surface motions; however, equivalent-linear and total stress nonlinear analyses capture these aspects as well. Biases in the computed motions compared to recorded motions were realized for some cases but they can be attributed primarily to the uncertainty in the development of the input motions used in the analyses.     

基于地震动参数的RC框架结构易损性分析

以某典型的12层钢筋混凝土框架结构作为研究对象,研究基于非线性动力时程分析和地震动参数的RC框架结构易损性分析方法。首先采用静力pushover分析判定结构薄弱层,并确定结构性能(capacity)参数;然后应用非线性动力时程分析估计结构地震反应,研究以峰值加速度和基本周期加速度反应谱作为地震动参数结构反应的不确定性,并进一步分析结构地震需求(demand)参数与地震动参数的关系;在此基础上,分别建立该结构基于峰值加速度和加速度反应谱的易损性曲线,通过考虑场地条件对地震动特性的影响,研究场地条件对结构易损性的影响,结果表明不同场地条件下的结构易损性曲线有一定差异。应用本文方法,根据新一代地震区划图或地震安全性评价确定的地震动参数,可以直接估计结构在未来地震中出现不同破坏的概率,这在结构的抗震性能评估和地震损失预测中有一定意义。     

土层结构对油气管线工程地震动峰值加速度区划图的影响研究

油气管线工程是生命线工程的重要组成部分,工程跨度通常超越几十甚至几千公里,从而导致横穿地区覆盖层中土层结构存在明显差异,对地震动峰值加速度(PGA)产生较大影响,进而影响区划结果。本文采用分区拟合放大系数的方法,对华北平原地区某大型管线进行研究,给出研究区不同土层结构条件下场地放大系数KS-基岩PGA拟合函数结果,得到沿线附近10km范围内的PGA区划图结果,并与第四代和第五代中国地震动参数区划图提出的场地系数公式的计算结果进行比较。三种计算方法的结果表明,研究区内50年超越概率10%条件下实际场地放大系数为1.30~1.45,50年超越概率5%条件下实际场地放大系数为1.15~1.30,均高于我国第四代和第五代区划图对场地系数的建议值。50年超越概率10%下的PGA区划图结果显示,局部区域在第四代和第五代地震动参数区划图场地系数的结果中位于0.15g或0.20g区,由于KS的提高,其实际计算结果会提升为0.20g或0.25g分区,这说明场地系数对峰值加速度区划图结果具有较大影响。     

黄土丘陵河谷场地地震动特征研究

研究黄土丘陵河谷场地在地震作用下强地面运动特征的变化情况,可以揭示强震对该类场地上震害的触发机理。结合黄土高原的地貌特征,建立具有代表性的动力数值分析模型,通过输入不同幅值、频谱特性和持续时间的地震波,对起伏地形和覆盖黄土层共同影响下的黄土河谷场地进行地震反应分析。结果表明:黄土层和地形耦合作用控制了地表的PGA变化,使其趋于复杂,在同一输入波不同振幅作用下,与基岩河谷各测点相比,黄土覆盖河谷场地的地震动频谱幅值均有所增加,并且频谱主峰均向高频移动。在不同地震波输入下,场地不同部位的固有频率受地形高程和土层影响;而地震动大小和频谱幅值不仅与场地的基本频谱和地形起伏有关,也与输入地震波的频谱成分相关。输入波PGA与地震频谱特征都不变时,同一场地输出的地震频谱形状具有相似的特征,随着地震持时增长,能量向场地基本频率附近集中,从而可能导致场地上相应频率建筑物震动幅值增加,造成累积破坏。     

西昌断陷盆地场地地震动差异分析

以汶川地震中的非发震断层安宁河断裂带周边西昌地区所获取的加速度记录为依据,研究了这些记录在峰值、频谱之间的差异,并通过这些地区的局部场地条件差异进行了初步解释。在此基础上通过数值模拟方法,利用基于显式有限元和局部透射人工边界的二维有限元模型对该地区的地面运动进行了模拟。数值试验结果表明：这些简单的理想化模型对这一地区地震动的本质特征进行重现,并对产生地面运动差异的机理进行合理解释。通过分析,初步揭示了由深部断层构造所控制的断陷盆地对地震动影响显著。     

A numerical study on the 2D behavior of clayey basins

In this numerical study the effects of basin edge on the dynamic behavior of the clayey basins are investigated. For this purpose a range of bedrock inclinations at the valley sides from slighter 10° and 20° to steeper 30° and 40°, and three types of stiff, medium plasticity and soft clay materials are selected. The results of the 2D analyses show that not only the amplification pattern of different clay types is different, but also it differs for each material type under different motion intensities. Also, the frequency domain results show that different parts of the valleys are sensitive to different periods. It was seen that under two-dimensional conditions the amplification of clay types other than soft clay could be higher. Finally, the results of this research show the important effect of motion intensity on the 2D behavior of valleys.     

四川数字测震台网震级偏差分析

为了提高震级测定值的稳定性,保证地震资料产出质量,利用四川数字测震台网2008年10月-2012年4月 MS ≥4．0近震记录,分析造成震级偏差的原因,并总结四川测震台网单台震级偏差分布特征。     

Ground motion record simulation for structural analysis by consideration of spectral acceleration autocorrelation pattern

A novel approach is introduced to generate simulated ground motion records by considering spectral acceleration correlations at multiple periods. Most of the current reliable Ground Motion Record(GMR) simulation procedures use a seismological model including source, path and site characteristics. However, the response spectrum of simulated GMR is somewhat different when compared with the response spectrum based on recorded GMRs. More specifi cally, the correlation between the spectral values at multiple periods is a characteristic of a record which is usually different between simulated and recorded GMRs. As this correlation has a signifi cant infl uence on the structural response, it is needed to investigate the consistency of the simulated ground motions with actual records. This issue has been investigated in this study by incorporating an optimization algorithm within the Boore simulation technique. Eight seismological key parameters were optimized in order to achieve approximately the same correlation coeffi cients and spectral acceleration between two sets of real and simulated records. The results show that the acceleration response spectra of the synthetic ground motions also have good agreement with the real recorded response spectra by implementation of the proposed optimized values.     

土层剪切波速测试中的不确定性对场地地震动参数的影响分析——以Ⅲ类场地为例

本文选取山东地区2个Ⅲ类场地的工程地质勘探及土层剪切波速等资料,将土层厚度按5个深度段,每个分段给出了4个土层剪切波速的改变量,通过改变不同深度段土层剪切波速,建立了19种土层地震反应分析模型,分析了不同深度段,不同概率水平下土层剪切波速的变化对场地地震动参数的影响。研究表明,不同深度段土层剪切波速的变化对场地地震动参数的影响有差异。具体表现为,土层剪切波速的改变在1—10m、11—40m和地震输入界面处三个深度段对地震动加速度峰值影响较大;其中,41—70m和71—100m两个深度段剪切波速的改变对地震动加速度峰值影响小;在土层深度1—10m时,剪切波速降低,峰值变大,剪切波速的改变与峰值的改变呈负相关;在其它深度段,剪切波速降低,峰值变小,剪切波速的改变与峰值的改变呈正相关。剪切波速的改变在1—10m和11—40m两个深度段对地震加速度反应谱影响较大;在41—70m、71—100m和地震输入界面三个深度段对地震加速度反应谱影响很小。