结构-群桩基础地震响应离心振动台模型试验

为研究桥梁群桩基础的大质量承台和外露桩基对桩-土动力相互作用效应的影响，分别对低承台（与土接触）和高承台群桩基础进行了离心振动台模型试验。试验中地基土采用了黏质粉土，上部结构简化为质点和杆构件，基础形式包括单桩和群桩。为模拟地震剪切波作用下土层运动效应，采用叠环式层状剪切箱实现土体的层状自由剪切，箱内壁设置橡胶膜以消除边界反射效应。在加速度为5.0g的离心环境中，选取Chi-Chi地震波作为基底激励输入，在不同输入峰值加速度下，分析了结构-群桩基础的地震响应。试验结果表明：与低承台群桩基础相比，高承台形成的群桩外露会增加上部结构和承台的惯性效应，改变桩身峰值弯矩的分布，表现为承台与桩接触处的桩身峰值弯矩下降，但桩身最大峰值弯矩改变较小。

Model test on seismic response of superstructure and pile group

Centrifuge shaking table tests about the bridge pile groups with embedded cap and elevated cap were carried out to investigate the effect of bridge group foundation with massive cap and exposed piles on the dynamic pile-soil interaction. Clayey silt was chosen as the test soil, the superstructure was simplified as mass point and connecting column and the foundation types included both the single pile and pile group. To simulate the soil movement under earthquake shear wave excitations, the laminar shear box was adopted for the free shear motion of layer soil and corresponding reflection at its boundary was further eliminated by using the rubber film on the inner wall of shear box. In the 50g centrifugal acceleration environment, the Chi-Chi seismic wave was selected as the input motion, and the seismic responses of structure-pile group were analyzed at different input peak acceleration of waves. The results show that, compared with the embedded cap pile groups, the exposure of the bridge pile groups with elevated cap increases the inertia effect of superstructure and cap, and the distribution of peak bending moments along the pile shaft are also changed, i.e., the peak bending moment is significantly decreased at the connection of pile and cap, while the values of maximum peak bending moments along the pile shaft only have a small change.