近断层地区抗震设计谱研究

预测近断层地区的抗震设计谱可以为该地区工程结构的抗震设计提供依据.通过对28条具有明显方向性效应特征的近断层地震动峰值速度、速度脉冲周期的统计分析,给出了估计近断层方向性效应脉冲地震动峰值速度和脉冲周期的经验关系式.对2种场地上脉冲地震动ATv/V的研究表明,岩石场地上的ATv/V值明显大于土层场地的ATv/V.基于近断层地震动的这一特征,建议了岩石和土层场地的等效脉冲地震动模型.基于脉冲地震动参数的经验关系式和简单的脉冲地震动模型给出了近断层地区岩石和土层场地上考虑方向性效应影响的设计谱.与规范设计谱的比较结果表明,我国设计谱的取值偏低,尚需考虑近断层脉冲型地震动的影响.

Study on seismic design spectra of near-fault region

To develop seismic design spectra for the near-fault region,parameters such as peak ground velocity(V) and period of the velocity pulse(Tv) in the velocity-time history of 28 near-fault forward-directivity ground motions are analyzed.Empirical relationships at rock and soil sites are developed for estimating the pulse velocity and pulse period of the forward-directivity motions.Ratio of ATv/V is utilized to characterize the effect of locate site on near-fault ground motions.The ATv/V ratio of near-fault motions is evidently larger for rock site than those for soil site.Then,near-fault ground motions are represented by two equivalent pulses,whose characteristics are defined by a small number of parameters.Using the predictive relationships of parameters and simple pulses,preliminary model for the acceleration design spectra of the near-fault region that includes site dependence is developed.Comparison between developed design spectra and code design spectra shows that Chinese code spectra are lower than predicted spectra,indicating the need for consideration of the near-fault effect in earthquake-resistant design.