我国Ⅰ、Ⅱ、Ⅲ类场地上PGA归一化加速度反应谱特征统计研究

Statistical Study on Characteristics of Spectral Accelerations Normalized by PGA on Site Classifications I,II and III in China

近30年来全球强震动记录,尤其是大震记录的数量显著增加,有必要对近40年前基于仅300余条强震动记录获得的地震动加速度反应谱特征进行检验与修正。基于NGA-West2数据库中全球范围内3584条强震动记录的统计发现,我国场地类别划分标准下Ⅰ、Ⅱ、Ⅲ类场地上地面峰值加速度(PGA)归一化反应谱(阻尼比5%)与地震震级密切相关,与震源距离、地震动强度等因素的相关性相对较弱;我国现行抗震规范中设计谱低估了地震震级对反应谱谱型的影响,第4段的直线下降模式也与统计特征不符;在主要受大震控制的地区,设计谱特征周期取值过小而偏于冒险。参考中欧美抗震规范中的设计谱规准化原则,给出了适用于我国Ⅰ、Ⅱ、Ⅲ类建筑场地上的设计谱修正建议,主要改变为延长了受大震控制地区设计地震动分组的特征周期,并调整了下降段的下降模式与衰减指数,以更可靠地反映地震动反应谱的中长周期特性。

Global strong-motion records,particularly those obtained in great earthquakes,increased significantly in the last three decades,which made it necessary to verify and rectify the statistical characteristics of ground motion spectral accelerations obtained about forty years ago based on only about 300 sets of strong-motion records.Based on statistics of 3584 strong-motion records worldwide in NGA-West2 database,it was found that the spectral accelerations(damping ratio=0.05)normalized by peak ground acceleration(PGA)on site classifications I,II and III in China's site classification standards,are closely correlated to earthquake magnitudes,while the correlation with factors such as source distances or ground motion strengths is relatively weak.The current Chinese seismic codes underestimated the impacts of earthquake magnitude on the shapes of spectral accelerations,and the linear descent pattern in the fourth segment was also inconsistent with statistical characteristics.In areas mainly controlled by large earthquakes,the characteristic periods(i.e.the ending period of the constant spectral acceleration segment)were underestimated and tended to be risky.Referring to the standardization principals of design spectra in seismic codes of China,EU and US,suggestions for modifying design spectra applicable to site classifications I,II and III in China were proposed.The major changes included extending the characteristic periods of design ground motion groups in areas controlled by large earthquakes,and adjusting the descent mode and attenuation exponentials of the descent segments to more reliably reflect the medium to long period characteristics of ground motion spectral accelerations.