水平旋转不变平均持时特征分析
Analysis of Characteristics of Horizontal Rotation-invariant Mean Duration

地震动持时对结构低周疲劳、破坏累积效应以及非弹性破坏具有显著影响，合理确定地震动持时至关重要。基于汶川地震记录资料，分析旋转不变平均持时与测点记录持时的大小比值关系和相关性，探讨其随断层距的空间变化规律。结果表明：旋转不变平均持时在数值上不恒等于测点记录持时、两水平分量持时的算术平均值及矢量和时程持时的任一量。旋转不变平均能量持时和相对Bolt持时将随断层距的增大而增加，旋转不变平均绝对Bolt持时则将随断层距的增大而减小。旋转不变平均持时与测点记录持时具有强相关性；相比较而言，90%能量持时的相关性强于70%能量持时；绝对Bolt持时的相关性强于相对Bolt持时；能量持时的相关性强于Bolt持时。
Determining ground motion duration is an important factor in the seismic analysis of structures as it has a significant impact on low-ycle fatigue, the cumulative effect of damage, and the inelastic failure of structures. In this paper, after determining the significant and Bolt durations, we introduce the concept of rotation-invariant mean duration. Then, based on Wenchuan seismic records, we discuss the spatial variability law of rotation-invariant mean duration with changes in the fault distance. Lastly, we analyze the ratio of the rotation-invariant mean duration and record-based duration of the measuring points as well as their correlation. The results indicate that the rotation-invariant mean duration is not equal to the single record-based duration. The rotation-invariant mean energy duration and relative Bolt duration increase with increased fault distance, whereas the rotation-invariant mean absolute Bolt duration decreases with increased fault distance. The rotation-invariant mean duration and record-based duration are highly correlated. By comparing different definitions of duration, we found that the correlation between rotation-invariant mean duration and a record-based duration of 90% energy is stronger than that of 70% energy. Furthermore, the correlation with the absolute Bolt duration is more significant than that with the relative Bolt duration, and the correlation with energy duration is more significant than that with the Bolt duration.