地震动场地放大效应的时频特性分析

Time-frequency analysis on amplification of seismic ground motion

为了详细研究均质及复杂非均质场地中地震动的放大效应,通过大型振动台试验获得原始试验数据,再采用傅立叶变换、时频分析与分段时频分析相结合的手段,对试验数据进行分析和处理。通过对试验结果的对比分析,发现当地震动沿竖直方向传播时,不仅地震动时程曲线的峰值会随场地高度的增加而逐步放大,其频率成分含量、主频段的频谱形状,以及整体地震动能量在时频平面上的分布,均会随着场地高度及各分层介质的不同而发生较大变化。与此同时,场地表面的倾斜程度、软弱夹层的厚度等因素也均对地震动的放大效应具有显著影响。通过以上研究,得到了一系列与地震动竖向传播放大效应相关的研究规律(包括PGA峰值特性、频谱特性、时频面上能量谱的分布特性等)。

A large scale shaking table test has been carried out to investigate the amplification effect of ground motion in homogeneous and complex heterogeneous sites. After that, a Fourier transform, time frequency analysis method and subsection time-frequency analysis method are combined to analyze the experimental data. By comparing the experimental results,, the peak of the time curve of the ground motion will be gradually enlarged with the increase of the height of the site when the local vibration propagates in the vertical direction. The frequency component content, the frequency spectrum of the main frequency band, and the distribution of the whole ground motion energy on the time-frequency plane will change greatly with the height of the site and the different layers. The above study concludes a series of PGA peak characteristics, spectral characteristics, distribution characteristics of energy spectrum on time-frequency plane.