Analysis of a Yielding Pile-Column in Nonlinear Soil


Modelling of pile foundations to account for the structural yielding is hardly a trivial operation, in view of the already complex nonlinear soil response. Continuum-based models, implemented through finite–element or finite–difference discretisation of both the pile and the surrounding soil, are not necessarily effective, let alone efficient, in modelling such 3D pile–soil interaction problems. By contrast, modelling soil reaction through nonlinear “p–y” springs is a versatile approach, in effect rendering the soil–pile interaction problem as 1–dimensional.

The NL−PILE code, developed by Gerolymos & Gazetas (2005) utilises the expanded Bouc−Wen model to describe both the soil “p–y” response and the pile flexural behaviour. Nonlinear phenomena such as separation between soil and pile, and sliding along their cylindrical interface can be (indirectly but quite realistically) simulated.

Successful application of the model will stem from its proper calibration through lateral pile load tests in the field (medium–scale or large–scale models) or in the laboratory (small–scale or medium–scale models). An explicit finite–difference formulation is implemented in NL−PILE to solve in the time domain the governing system of differential equations. This will be extended and applied to column–pile–soil systems. A parametric investigation will then be conducted to shed light into this significant earthquake problem. The interplay between plastic hinging in the pile and in the column will be explored.