ABSTRACT:

Semi-empirical methods are widely used in the seismic response analysis of pile foundations because the complexity of the problem precludes 3-D dynamic finite element analysis. The most common approach for the analysis of pile foundations is the use of nonlinear Winkler springs and dashpots to simulate the interaction between piles and soil. The properties of these springs are specified by p-y curves. The most widely used curves are those recommended by the American Petroleum Institute. In order to include the effects of inertial interaction with the superstructure, a very simplified foundation-superstructure model is employed in the analysis. This paper evaluates the effectiveness of p-y curves and the simplified foundationsuperstructure model in simulating the response of pile foundations. The p-y curve approach is shown to be potentially unreliable. The simplified model is shown to work very well provided the pile foundations undergo very little rotation of the pile cap and the pile foundation is analyzed using a simplified nonlinear continuum model of the soil-foundation system.

INTRODUCTION

Seismic soil-structure interaction analysis involving pile foundations is one of the more complex problems in geotechnical earthquake engineering. The analysis involves modelling pile-soil-pile interaction, the effects of the pile cap, nonlinear soil response and inertial interaction with the superstructure. Commercial structural analysis programs can not include the pile foundations directly. Therefore in the seismic analysis of bridges and buildings on pile foundations, various semi-empirical procedures are widely used. Dynamic nonlinear finite element analysis in the time domain using the full 3-dimensional wave equations is not feasible for engineering practice at present because of the time needed for the computations. However, by relaxing some of the boundary conditions associated with a full 3D analysis, it is possible to get reliable solutions for nonlinear response of pile foundations with greatly reduced computational effort.

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