基于等损伤的主余震序列型地震动PGA放大系数谱研究

大地震发生后往往会伴随强余震发生，强烈余震会加重结构的破坏程度，在抗震设计及结构损伤评估中考虑余震的影响是一重要课题。采用NGA-West2数据库建立主余震序列型地震动记录数据集，基于损伤等效思想定义主余震作用下PGA放大系数α,针对单自由度体系结构，通过动力时程分析建立不同相对强度、不同场地条件下平均PGA放大系数谱，进一步通过回归分析构建PGA放大系数谱的预测方程，分析统计结果的离散性。结果表明：PGA放大系数谱受场地条件影响较小，受主余震相对强度影响显著；放大系数谱值随周期增大而减小。谱预测方程能够提供目标损伤下结构的主震PGA放大需求，并可以作为设计谱调整系数使用，以实现在结构抗震设计及结构损伤评估中考虑余震的影响。

PGA amplification factor spectrum of mainshock-aftershock sequence-type ground motions based on equal damage

Strong aftershocks often occur after earthquakes, increasing the extent of structural damage. Thus, the influence of aftershocks on structures in seismic design and structural damage assessment is an important topic. In this study, the NGA-West2 database was used in establishing the date set of mainshock-aftershock sequence-type ground motions. Based on damage equivalence theory, the peak ground acceleration (PGA) amplification factor under mainshock-aftershock ground motions was defined. Then, the average PGA amplification factor spectra of the structure with a single degree of freedom system under different relative intensities and different site conditions were obtained through dynamic time-history analysis. The prediction equation of the PGA amplification factor spectrum was constructed through regression analysis, and the discreteness of the statistical results was analyzed. Results show that the PGA amplification factor spectrum is less affected by site conditions but affected by the relative intensity of mainshock-aftershock ground motions, and the value of the amplification factor spectrum decreases with increasing period. The spectral prediction equation can provide the PGA amplification requirement of the mainshock under target damage, and it can be used as the adjustment coefficient of a design spectrum. In addition, this equation considers the influence of aftershocks in a seismic design and structural damage assessment of a structure.