变刚度地基上隔震结构群桩基础动力响应试验研究

Experimental study on the dynamic characteristics of the pile group foundation of a base-isolated structure on variable stiffness groud

通过控制输入地震动持时压缩比和强度的方法,提出了变刚度地基上桩基基础隔震结构振动台模型试验方法,并结合已完成的不同地基上桩基基础隔震结构系列振动台模型试验,分析了地基刚度变化对隔震结构群桩基础动力学特性的影响规律。结果表明,结构-土体相对刚度比和输入地震动强度显著影响隔震结构群桩基础弯矩反应,强震下结构-土体相对刚度比越大,隔震结构群桩基础中间桩体上部弯矩反应幅值增大越显著,而中间桩体下部弯矩幅值较小。当输入加速度峰值和结构-土体相对刚度比R大于一定限值时,群桩基础震陷显著增加,群桩基础承台转动反应强烈,同时群桩基础桩顶水平位移在主震后出现明显的单边累积水平位移,说明强震作用下地基刚度变化过程中隔震结构群桩基础上部更易出现地震破坏,而群桩基础震陷与基础承台强烈转动反应的共同作用可能是导致隔震结构群桩基础上部弯矩骤增的主因。

By controlling the intensity and duration of input ground motions,a shaking table test method was proposed for the pile group foundation isolated structure on a variable-stiffness groud.On this basis,integratedly considering the results of the completed shaking table model tests of isolated structures on different kinds of grouds,the influence of the groud stiffness change on the dynamic characteristics of the pile group foundation of the isolated structure was analyzed.The results show that the relative stiffness ratio of structure to soil and the strength of the input ground motion significantly affect the bending moment response of the pile group foundation of the isolated structure.With the increase of the relative stiffness ratio of structure to soil under strong earthquake motion,the bending moment response amplitude at the upper part of the middle piles in the pile group foundation of the isolated structure grow remarkably,while the bending moment response amplitude at the lower part of the middle piles is relatively small.When the peak acceleration of the input motion and the relative stiffness ratio of structure to soil are greater than a certain limit,the seismic settlement of the pile group foundation increases significantly,and the rotation response of the pile group foundation cap is strong.Meanwhile,the horizontal displacement of the pile top of the pile group foundation appears obvious unilateral cumulative horizontal displacement after the main earthquake.It indicates that the pile top of the pile group foundation of the isolated structure tends to occur earthquake damage during the process of response stiffness change.The joint action of the seismic settlement of the pile group foundation and the strong rotation reaction of foundation cap may be the main reason for the sharp increase of the bending moment at the upper part of piles.