Nonlinear Dynamic Stiffness of Piles: Fid-Bau Portal

Nonlinear Dynamic Stiffness of Piles

D. C. Angelides / J. M. Roesset

The effect of nonlinear soil behavior, without slippage or gapping, on the dynamic response of piles is explored. This research uses a finite element model for the soil region adjoining the pile; a consistent boundary matrix at some distance to reproduce radiation effects; and an iterative, equivalent linearization technique to estimate the variation of soil properties with level of strain. A cylindrical region of soil, surrounding the pile is discretized using toroidal finite elements. The pile is modeled as a series of beam segments attached through rigid links to the finite element nodes. The results consider hollow, floating piles with aspect ratio (length over diameter) equal to 45. The top of the pile is assumed to be free. Comparing the results of this analysis with those obtained using the p-y curves, it seems that the main difference is due to the lack of tension capacity in the soil and the appearance of gaps for larger forces. The results for the horizontal case indicate that as the level of force increases, there is an increase in internal soil damping, but a decrease in radiation. When both effects are combined, the effective damping ratio tends to increase.