基于随机地震反应的桥墩-群桩-土相互作用研究

考虑地震动的随机性，利用复反应分析技术，采用随机地震反应计算方法对某一特大型桥梁群桩基础与土动力相互作用效应进行了数值试验研究。将土与群桩体系视为一个整体进行有限元离散，采用等效线性化方法考虑土体的动力非线性性能。将桥墩-群桩-土相互作用体系与自由场随机地震反应进行比较，结果表明：相互作用效应的影响与桩土模量差异以及土体与群桩基础距离有关；软土层剪应变水平及分布发生了显著变化，群桩基础两侧附近土域剪应变呈现明显的弧形分布；地表及浅层土体最大地震加速度反应有所减小，但覆盖层中下部土体加速度反应峰值明显增大，增幅达5 %～30 %左右；此外，地震地面运动的频谱成分存在显著差别。桥梁桩基础抗震设计中应充分考虑桥梁结构-群桩-土相互作用效应。

Study on pier-pile group-soil interaction based on stochastic seismic response

Dynamic interaction effects of a giant pier-pile group-soil system are investigated by a stochastic seismic response method. A complex response technique is employed in this method. The interaction system as an integrality is modeled by some finite elements and the dynamic nonlinearity of soils is considered through the equivalent linearity method. Stochastic seismic analysis of the free ground and the interaction system are carried out respectively; and their results are compared. The comparisons indicate that the effects of interaction are related to the modulus variance of pile and soil, and the distance of soil and pile foundation. The dynamic shear strains of soft soils have significant difference. The distributions of shear strains near the both boundaries of pile group appear to be curved. The peak acceleration values of ground surface and superficial layer obtained from seismic interaction analysis are smaller than that obtained from seismic free ground analysis. But, the peak acceleration values of deep layers have increases of 5%-30%. In addition, the frequency components of ground surface motions have marked difference for seismic responses of free ground and interaction system. Therefore, the dynamic bridge structure-pile group-soil interaction should be considered properly for the seismic design of bridge foundations.