Numerical Prediction of the Dynamic Behaviors of an RC Group-Pile Foundation

ABSTRACT

In a major earthquake, it is reasonable to assume that the mechanical behavior of a pile foundation and the surrounding ground is nonlinear. It is commonly accepted that the dynamic behavior of a group-pile foundation is not only related to its own mechanical properties, but also to the upper structure supported by the foundation, and to the surrounding ground. It is recommended, therefore, that a full system, which consists of superstructures, foundation and ground, be considered in the dynamic analysis because of the merit that relatively few assumptions are adopted. The most important thing in the dynamic analysis, however, is that the individual nonlinear behavior of soils and piles should be properly evaluated. In this paper, a new beam theory is proposed for a reinforced concrete material (RC material). The theory is based on a weak form in which the axial-force dependency in the nonlinear moment-curvature relation is considered. Its validity is verified by experimental results of an RC cantilever beam. Then, an elevated bridge with a 12-pile foundation is analyzed using a three-dimensional elastoplastic finite element analysis (DGPILE-3D). The piles are cast-in-place reinforced concrete and have a diameter of 1.2 m. Meanwhile, the ground soil is simulated with a tij subloading model in which the concepts of kinematic hardening and subloading are adopted. The purpose of the paper is to provide an accurate numerical way of evaluating the dynamic behavior of a pile foundation during an earthquake.