通过群桩-土-偏心结构振动台试验分析群桩与地基的响应

Response analysis of group pile and foundation by using shaking table test on pile groups-soil-eccentric structure interaction system

通过对群桩-土-偏心结构相互作用体系振动台试验,分析了结构偏心效应对相互作用体系自振特性、地基振动和桩基变形的影响规律。试验结果表明:地基土的加入使得相互作用体系前两阶自振频率相差增大,平扭振动耦联程度降低,体系阻尼比明显增加;结构偏心效应增大了角桩的加速度响应,高出同深度边桩测点10～15%,桩身振动频率特性较场地土有明显差别;角桩变形幅度较边桩更为突出,桩长范围内角桩应变峰值始终大于边桩测点,两者相差在桩顶附近达到最大;桩间土承担了部分扭转效应,角桩较边桩应变增幅约为对应位置筏板位移增幅的一半;土的动力放大特性与以往研究规律相近,结构偏心效应对地基整体振动产生的影响不很明显;桩土界面动力响应与筏板平动位移时程相对应,且随深度的增加而逐步增大。

To improve the computational efficiency of nonlinear dynamic problem of large-complicated structures, based on the characteristic of structures, in which local plastic regions exist, the mixed linear-nonlinear constrained mode synthesis method is presented. The basic idea is to define the component which is hardly to get into nonlinear stage as a linear substructure, while the local component which will definitely get into plastic deformation stage as a nonlinear substructure. Degree of freedom of linear substructures is reduced by coordinate transformation and will be synthesized with nonlinear substructures. Subsequently we shall solve the mixed equation and obtain the dynamic responses. The proposed method is effective for solving the nonlinear dynamic problem of large-complicated structures as it could decrease the computational cost and could take account of the nonlinear material feature of structures reasonably. In addition, the mode cut-off criterion based on potential energy criterion for constrained mode synthesis method is also presented. The suitable mode cut-off number of substructure is obtained on the basis of the convergence of potential energy criterion. Finally, the mixed linear-nonlinear constrained mode synthesis method and potential energy criterion are adopted to solve the nonlinear seismic response of soil and multi-story building interaction problem. Comparison with the results of direct-finite-element-method shows that the proposed method has high efficiency and precision, and the proposed potential energy criterion is also effective for the mixed constrained mode synthesis method.