Seismic Behavior of RC Structures considering the Interaction between Soil and Foundation

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The objective of this research are, 1) to develop the response analysis method of the RC structural system considering the interaction between the foundation and the surrounding ground, 2) to verify the method by the result of the model loading test of RC pile in soil, and 3) to consider the seismic behavior of RC structure affected by the response of the piles and soil. Finally, the fruits from these considerations will be made good use for improving the seismic design method of RC structures.In this year, the static and dynamic loading tests of RC model piles in soil are performed. The specimens are fixed on the bottom of the steel soil box, to model the condition at the base in real case. The soil box with pile specimen is filled by the dry sand of which the material properties are clear. The reversed cyclic load or the dynamic sine wave load is acted at the pile top, modeling the seismic load transmitted from footing to pile. In addition, the response analyses of RC structural system, consists of surrounding ground, piles, footing, pier and superstructure, are performed using 3-dimensional elasto-plastic finite element method. From these results, the following points are clarified ; (1) The plastic area of RC pile, i.e. plastic hinge, spreads to lower due to reversed cyclic loading. Additionally, the behavior of the pile is affected by the stiffness of surrounding ground, but not by the shape of the cross section of the pile. (2) The settlement of the ground is observed at the surface around the pile top due to the reversed cyclic loading. This phenomenon causes the compaction of the ground around the pile and the damage of the pile proceeds with the increment of stiffness of surrounding ground. (3) The analytical method used in this research can evaluate the behavior of RC pile in ground to some extent.