液化与非液化场地加速度反应谱对比

通过对2011年新西兰发生的6.3级地震中获取的硬土场地、软土场地和液化场地强震记录实测资料进行分析，研究包括3种类型场地的地震动特征及其相互关系。分析的强震记录为震中距小于50 km，且峰值大于0.05g的23个场地上的加速度记录，其中含3个硬场地、11个软场地和9个液化场地。3种类型场地上的放大系数谱对比分析表明，硬土场地、软土场地和液化场地上的地震动特征具有明显区别，三者层次清晰，差别显著，从地震动表现上液化场地已构成一个与常规场地并列的独立单元；液化场地减少地震动高频分量但同时对低频分量显著放大，与非液化场地相比，液化场地可使其上短周期结构反应减小一半，但同时可使其上长周期结构反应放大2.5～5.0倍；土层的液化对此次地震中克莱斯特彻奇市中心CTV大楼的破坏应有很大影响，大楼自振周期约为0.7 s，地震中土层液化使场地加速度反应谱卓越周期由0.1～0.3 s增到0.5～1.0 s，与大楼的自振周期趋于吻合，加重了大楼震害。以此为鉴，按现有规范中地震动的设计方法，如遇液化场地将对长周期结构给出明显危险的结果，因此从振动角度今后进行结构抗震设计时，可液化场地上的地震动应给予特殊考虑。

Comparison between acceleration response spectra on liquefaction and non-liquefaction sites

By analyzing the records from stiff sites, soft sites and liquefied sites in 2011 Ms 6.3 New Zealand earthquake, the characteristics and relationship of ground motion on 3 types of sites including the liquefied sites are investigated. The seismic acceleration records at 23 seismic stations whose epicenter distances are less than 50 km and PGA great than 0.05g are collected, in which 3 stiff sites, 11 soft sites and 9 liquefied sites are included. The comparison results of amplification coefficient spectra from 3 types of sites indicate that there are obvious distinction among the stiff sites, soft sites and liquefied sites. From the view of ground motion, the liquefied sites can become an independent type. On the liquefied sites the high frequency component of ground motion decreases and meanwhile the low frequency component significantly amplifies. Compared with non-liquefied sites, the response of the short period structure on the liquefied sites will be reduced by half; but at the same time, the response of long period structure on the liquefied sites will be amplified by 2.5-5.0 times. The influence of liquefaction on the damage of CTV building in Christchurch City in the earthquake is significant because the predominant period of acceleration spectra increased to 0.5-1.0 s from 0.1-0.3 s, which is tallied with the natural period of the building about 0.7 s; and the response of the building increases as the consequence. As a result, the existing structure design method would be dangerous for the structures with long period in the liquefiable sites and the seismic ground motion in the liquefiable sites should be specially considered from the viewpoint of vibration.