沙牌坝址基岩场地地震动输入参数研究

重大水利水电工程地震动输入参数必须根据专门的地震危险性分析结果来确定。目前由地震危险性分析得到的一致概率反应谱具有包络的意义,不能反映实际地震的频谱特性,输入"一致概率反应谱"可能导致地震作用偏大;拟合设计反应谱人工生成地震动加速度时程的频率非平稳性也没有得到很好解决。为了解决这些问题,得到与坝址地震危险性一致、具体地震的输入参数,结合沙牌大坝提出了一套适用于重大水利水电工程基岩场地地震动输入参数确定方法:通过以有效峰值加速度为参数的概率地震危险性计算分析,确定坝址不同超越概率下的有效峰值加速度及对坝址贡献最大的潜在震源区;在最大贡献潜在震源内利用震级空间联合分布概率最大法确定坝址设定地震,依据加速度反应谱衰减关系确定与坝址设定地震对应的设计反应谱;根据设定地震结果和时变功率谱模型参数衰减关系确定时变功率谱,将时变功率谱和最小相位谱按三角级数叠加法进行强度和频率非平稳地震加速度时程合成。在对沙牌坝址区域的地震活动性及地震构造环境分析评价的基础上,采用上述方法,得到了坝址基岩场地不同超越概率下的有效峰值加速度、设计反应谱、强度和频率非平稳地震加速度时程等地震动输入参数。

Study of ground motion input parameters of Shapai dam rock site

There are many limitations for important hydraulic project’s rock site at present, such as envelopment effects of probability-consistent response spectrum, and frequency stationarity in acceleration time history, etc.. In order to overcome those shortcomings, a new method of determination of ground motion input parameters for important hydraulic project’s rock site has been put forward in this study. The effective peak acceleration with different exceeding probability, as well as the dominant potential seismic source which had the largest contribution to the site, have been determined by using probabilistic seismic hazard analysis, which based on effective peak acceleration. The magnitude of scenario earthquake within the dominant potential earthquake sources is determined by the largest probability of magnitude-spatial joint distribution,and the corresponding design response spectra is determined by the attenuation relationship of acceleration response spectra. Then evolutionary power spectrum is gained according to scenario earthquake and the attenuation relationships of evolutionary power spectrum model parameters, and the amplitude and frequency non-stationary acceleration time history at dam site are synthesized by using trigonometric series superposition method, which based on evolutionary power spectra and minimum phase spectrum. In a case study of Shapai dam site, based on the evaluation of regional seismic activities and seismotectonic environment, ground motion input parameters at dam rock site with different exceeding probability, including the effective peak acceleration, design response spectra, amplitude and frequency non-stationarity acceleration time history, are determined.