Seismic Response of Pile Foundations

Keywords: Seismic Response Analysis, Dynamic Loads, Soil-Structure, Pile Foundations, Boundary Element Methods, Pile-Soil Interaction, and Green's Function.

Abstract: A boundary element formulation is presented to analyze the seismic response of a single pile. The piles are modeled by compressible beam-column elements and the soil as a hysteretic elastic half-space. A new Green's function corresponding to dynamic loads in the interior of a semi-infinite solid is developed for this study. The governing differential equations of motion for the pile domain have been solved exactly for distributed periodic loading intensities. These solutions were then coupled with a numerical solution for the motion of the soil domain by satisfying equilibrium and compatibility at the pile-soil interface. The responses were evaluated over wide ranges of the parameters involved to vertically and obliquely incident P, SV and SH-waves. Results are presented as dimensionless graphs and the pile-soil interaction is studied. It is observed that the existence of the pile produces a filtering of the waves, reducing the amplitude of motion as a function of frequency. Also, the filtering effects, pile motions and amplitudes are found to be dependent on the slenderness ratio, stiffness ratio and angle of incidence. Finally, an actual transient analysis is performed to study the response of piles to seismic waves in the time domain.