Development of Earthquake Response Analysis for Whole Structural System Consisting of Ground, Piles and RC Structures

本研究的目的是通过静、动载试验，对地下钢筋混凝土桩的响应特性进行试验和分析。模型试件被固定在土箱的底部，假定地基上固定了一根真实的RC桩，土箱中填满了砂子。在地震荷载作用下，桩头承受反向循环水平荷载。试验参数为桩头轴力，包括桩基摇摆产生的交变轴向力和桩头连通性条件。通过试验和分析得出以下结论：1)随着桩头轴力的增大，桩顶响应出现较大的滞回曲线，等效阻尼系数也变大。2)桩的最大损伤长度与桩的轴向荷载水平无关，仅与桩与周围土体的相对刚度有关。交变轴向荷载作用下桩的响应特性取决于桩在最大和最小恒定轴向荷载作用下的响应特性。3)为了评价包括桩基础在内的混凝土结构体系的整体抗震性能，在三维有限元分析的基础上，提出了考虑桩土分离的反应分析方法。用该方法给出的分析结果与实验结果吻合良好。

The objective of this research is to investigate experimentally and analytically the response behavior of reinforced concrete piles under ground by the static and dynamic loading tests. The model specimens of RC piles were fixed to the bottom of the soil box assuming that a real RC pile is fixed at foundations, and the soil box was filled with sand. The pile head was subjected to reversed cyclic lateral loading as seismic load. The experimental parameters were the axial force on the pile head, including the alternative axial force due to rocking behavior of footing, and the connectivity condition at the pile head. The followings are derived conclusions from the experiment and analysis.1) With the increase of the axial force on the pile head, the larger hysteresis loops were observed in the response behavior, and the equivalent damping factor also became high. Additionally, a remarkable reduction of restoring force from its maximum value after yielding of the pile was observed in the case of high axial force.2) The maximum damaged length is independent on the axial load level of the pile and dependent only on the relative stiffness between pile and surrounding soil. The response behavior of the pile with the alternative axial load is determined by the behavior under the maximum and minimum constant axial load. Therefore, the most important point is to evaluate the possible range of axial load on the pile under seismic excitation.3) In order to evaluate the seismic behavior of the whole system of concrete structures including pile foundation, the response analysis method considering the separation of pile and soil was developed, based on 3-dimensional finite element analysis. Analytical results given by the developed method have good agreement with the experimental results.