Seismic analysis of pile foundations for bridges

This thesis deals with the seismic response of bridges supported on pile foundations. A substantial portion of thesis is devoted in developing a better understanding of the seismic behavior of the pile foundations and their effects on the overall response of the bridge structure. Current methods for modeling the pile foundations are evaluated and some deficiencies are identified. New methods are developed that model better the seismic behavior of the pile foundations.; Case studies based on the recorded response of a two span bridge under ambient vibration and strong earthquake shaking showed that the behaviour of the bridge foundations under strong shaking is highly nonlinear. A new lumped parameter model consisting a set of nonlinear springs and dashpots was developed to reproduce the nonlinear behaviour of the pile foundations during strong shaking. The nonlinear stiffnesses and damping ratios of the pile foundation are determined using an existing Quasi-3D finite element model. One finding was that it was the relative stiffness of the foundation and the superstructure that controlled seismic response of the bridge.; A new method was developed for determining the dynamic impedances of bridge abutments using simplified models of the abutments. Studies showed that the impedances of the abutments change significantly during strong shaking and that these changes should be taken into account.; The Winkler model of a single pile is widely used in practice for the analysis of pile foundations. A comprehensive program for the dynamic analysis of a single pile using a Winkler model was developed which included the currently available methods. This method was then used to evaluate the Winkler model and the use of p-y curves recommended by the American Petroleum Institute (API) by simulating a centrifuge test on a single pile under low level and strong shaking. Analyses using the API p-y curves gave poor estimates of the response of the pile under strong shaking. Studies showed that the extrapolation of the group behavior from the behavior of single pile using a group factor should consider both pile-to-pile interaction and the effects of superstructure-foundation interaction.; An effective stress method was developed for the dynamic analysis of pile foundations in potentially liquefiable soils by incorporating a pore water pressure generation model into the Quasi-3D finite element method. The effective stress method was extensively verified using centrifuge test data on a single pile and (2 x 2) and (3 x 3) pile groups under low-level and strong shaking. (Abstract shortened by UMI.)...