Vibration model of pile foundation considering nonlinearity of soil

本研究的目的是在考虑土体刚度和阻尼非线性的情况下，提出复合刚度和输入运动作为桩基动力特性的评价方法，建立适用于抗震设计的桩基振动模型。本学期的研究结果总结如下：对于地基的非线性响应分析，采用有效应力分析。指出了南部地震等强烈地震作用下填土地基的响应特征；水平加速度沿地表方向分布减小，最大曲率响应发生的深度与桩的弯曲断裂发生的深度相对应，考虑循环迁移率可以得到更精确的地面滞回线。采用薄层单元法分析了桩基建筑的地震反应。这一分析掌握了以下几点。即土体刚度越减小，输入水平加速度越减小，土体的隔震作用越明显。通过各种研究，发现该方法采用薄层单元法，采用等效线性化程序考虑土体非线性，可用于桩基础的非线性地震反应分析。在有地下室的建筑物的响应分析中，将其替换为圆柱管，并将其下地面假设为土柱。该方法采用薄层单元法，根据土体非线性取等效刚度和阻尼。通过对地震观测结果与分析结果的对比研究，证明该分析方法适用于有地下室的建筑物的地震反应分析。

The purpose of this research is to present the evaluation method of complex stiffness and input motion as dynamic properties of pile foundation considering the non-linearlity with respect to rigidity and damping of soil and to present the vibration model of pile foundation applicable to earthquake resistant design. Results obtained in this term are summarized as follows.1. Concerning the nonlinear response analysis of ground, effective stress analysis is adopted. The characteristics of response of filled ground under drastic earthquake such as Hyogoken Nanbu Earthquake are pointed out as follows ; Distribution of the horizontal acceleration reduces towards ground surface, the depth where the maximum curvature response occurs corresponds to the depth where the bending fracture of pile happens and more accurate hysteresis loop of ground can be obtained when the cyclic mobility is considered.2. Earthquake response of buildings with pile foundation is analyzed by thin layred element method. The followings are grasped by this analysis. i.e.the more the rigidity of the soil reduces, the more the input horizontal acceleration is reduced and the isolation effect of ground is develops. Through various investigations, this method using the thin layred element method and considering the soil nonlinearity by equivalent linealization procedure is found to be useful for the non linear earthquake response analysis of pile foundation.3. For the response analysis of building with basements, it is replaced by cylindrical tube and the ground beneath it is assumed as a soil column. This method uses the thin layred element method and takes equivalent rigidity and damping corresponding to the soil non-linearity. From the comparative study of observed results of earthquake and analytical results, this analysis method is justified to be useful for earthquake response analysis of building with basements.