The Research On Simplified Analysis Methods About Lateral Nonlinear Dynamic Responses Of Single Piles

The lateral dynamic responses of pile-foundation in the earthquake are generally divided into lateral inertial response and kinematic seismic response. Most of the simplified analysis methods for dynamic responses of pile-foundation adopt the dynamic Winkler foundation models (the dynamic p~y curves methods) based on the linear visco-elastic hypothesis. However, the linear analysis is only within the limits of the small displacement gradient, whereas nonlinear stress- and displacement-field in the vicinity of the pile will be generated due to stress concentration and the interface of the soil-pile leaded to separation and the dynamic response of pile-foundation also presented intense non-linearity in the strong seismic motion. Therefore, the simplified analysis methods based on the linear visco-elastic dynamic theories cannot satisfactorily describe the nonlinear dynamic responses of pile-foundation. Responses of the lateral nonlinear dynamics of single piles are studied in this dissertation. First, a 3-D finite element model, which can reflects a lot of influences of the non-linear factors, is constructed using a large finite element analysis software ANSYS. With this model, this dissertation gives a relatively complete analysis the lateral nonlinear dynamic responses of the single piles and has a comparative detailed discussion about the influences resulted from the geometrical and physical parameters and the nonlinear factors over the lateral nonlinear dynamic responses of single piles. Second, Based on the predicted results of the 3-D finite element numerical simulation and the principal characteristics of the dynamic interactions of the soil-pile foundation-superstructure system, using the basic theory of the random vibration for the hysteretic nonlinear systems, e.g. Bouc-Wen model, a newer simplified model which can be truthfully reflect the main characteristics of the lateral nonlinear dynamic responses of the single piles is established. The nonlinear Winkler-Kelvin sub-grade model is adopted in this simplified model and the complicated 3-D problems of the soil-single piles dynamic interaction are simplified to the 1-D, that is to say, the lateral nonlinear acting force of the soil to the pile shift is simulated with thehorizontal nonlinear springs which have the continuous uniform distribution, while the nonlinear spring restoring force is described by the deteriorated Bouc-Wen model; the radiation damping and material damping due to the energy dissipation and inner friction in the soil are displayed with the dashpots which are in parallel with the horizontal nonlinear springs. The influences of the material non-linearity, such as, the yielding, the hysteretic effects, the mechanical property deterioration of the soil surrounding the piles, and state non-linearity, such as no continuous conditions of the soil-pile interface, etc, on the behaviors of the lateral dynamics of the single piles are taken into consideration in this model. The whole process of the nonlinear deformation from elastic to plastic of the soil surrounding the pile can also be described with this simplified model. The simplified model is applicable in various geological conditions. Only two model parameters have to be calibrated by fitting experimental data and using current design codes. Finally, with the developed methods, calibrated model and the concepts of the kinematic response factors, the lateral nonlinear inertial responses and kinematic seismic responses of the single piles are studied respectively. It is also studied that the influences of various kinds of the systematic parameters and nonlinear factors over the lateral dynamic responses of the single piles. The predicted results show that the simplified model developed in this dissertation can simulate the lateral nonlinear dynamic responses of single piles effectively.