Forces in Pile Foundations under Seismic Loading

Abstract

The purpose of this paper is to study the relative significance of kinematic and inertial interaction on the magnitude of forces induced in pile foundations by a seismic disturbance. The structure is modeled as a single-degree-of-freedom (SDOF) oscillator and the foundation is a typical pile group embedded in a homogeneous half-space. A three-dimensional Green's function-based formulation, which rigorously models the pile-soil-pile interaction, is used to calculate the forces in the piles during the seismic kinematic- and inertial-interaction phases. Different structures, represented by their aspect ratios and natural frequencies, and different pile foundations, characterized by their pile rigidities and spacings, are considered in this study. The results show that the seismic shear force and bending moment in a pile are strongly contributed by the kinematic seismic interaction, except in a band approaching the natural frequency of the pile-soil-structure system. In this frequency band, the inertial interaction dominates the pile forces. The extent of contribution from the inertial interaction is governed by the damping of the foundation.