沉箱加桩复合基础地震响应离心试验

Centrifuge tests for seismic response of caisson-pile composite foundation

针对沉箱加桩复合基础地震响应问题开展动力离心试验研究。采用砂质粉土作为地基土,上部结构简化为质点和柱体,基础类型包括单桩、沉箱、沉箱加桩复合基础,利用层状剪切模型箱消除边界反射,以上海人工中波为输入波,在50 g离心加速度场下进行水平地震试验。根据基础形式的不同进行3组试验,试验结果表明:对于刚度较小的土,地震波向上传播过程中具有加速度衰减的特征;沉箱底部加桩对于降低基础和结构地震响应有积极的效果,有利于增强其抗震能力;地表、基础、结构的地震响应频率特性各不相同,这取决于其各自不同的自振特性;土与基础、基础与结构之间均会发生地震相互作用,但只有与相互作用对象自振频率均较接近的地震频域分量才能引起明显的相互作用。

Dynamic centrifuge tests are carried out to study seismic response of caisson-pile composite foundation. With Shanghai sandy silt chosen as test soil, laminar shearing box used to eliminate reflection at the boundary, and Shanghai artificial middle wave is taken as the input motion, three tests with different foundation types are conducted under the centrifuge acceleration of 50g. Single pile, caisson and caisson-pile composite foundation are the foundation types for those three tests, and all the superstructures in these tests are simplified as mass points and connecting columns. Test results indicate that, for soil with low stiffness acceleration decays in the process of earthquake wave propagating upwards;adding piles under the caisson could decrease the earthquake responses of both the foundation and structure, so the reinforcement of the system in resisting earthquakes is expected;frequency characteristics of the responses at soil surface, foundation and structure are all different from each other depending on their own natural vibration characteristics;and for the interaction between soil and foundation, or foundation and structure, only the earthquake component with similar frequency with both interacting sides can cause remarkable earthquake interaction.