Nonlinear response of pile foundation-superstructure systems

In this research, the problem of nonlinear pile foundation-superstructure interaction is addressed by utilizing a substructure approach and developing appropriate time-domain methodologies for the analysis of each subsystem, as well as procedures for the subsequent integrated analysis of the system. The need for nonlinear modeling and the importance of foundation dynamics to overall system response is established first by studying the response of the Painter Street Bridge to the Petrolia Earthquake of 1994. Subsequently, the problem of a yielding superstructure on a linear foundation is studied in which the superstructure is modeled by a simple two degree-of-freedom system with a Bouc-Wen model to simulate nonlinear behavior. Two different solution methods are proposed for the system governing equations. The first method models the restoring force from the foundation by means of a convolution of the velocity history of the foundation relative motion and the dynamic relaxation stiffness of the foundation while the second utilizes a state-space representation. Both methods are validated at the linear limit by comparing time with frequency domain analyses.; A time-domain procedure is then presented to compute nonlinear axial dynamic response of pile groups under inertial loading using a nonlinear winkler foundation model for the soil-pile interface and utilizing linear wave propagation theory to compute pile-to-pile interaction. It is used in the modeling of two sets of field data obtained for single piles and subsequently to provide equivalent linear stiffnesses and damping. It is found that there is a significant deviation from linear behavior for single piles and pile-groups at high load amplitudes. The effect of pile yielding on overall system behavior is studied with the help of a new model which incorporates a bilinear hysteretic moment curvature relationship for the pile cross-section into a nonlinear soil-pile interaction model for lateral motion. This one-dimensional finite element model is shown to be a promising tool in analyzing foundation-structure interaction under earthquake strong motion, especially for CIDH pile shaft foundations.