Numerical Modeling Of Soil-Pile-Structure Dynamic Interaction Under Seismic Excitation

Pile foundation has been used to consolidate soft ground for a long history, and it is also one popular means to be used to improve foundation today. Many pile foundations are damaged seriously during the past major earthquakes. Large amount of cost will be paid to remedy the defect of pile foundation undergoing earthquakes, so it is a significant value for both academic and concrete project to study the subject of numerical modeling of Soil-Pile-Superstructure Dynamic Interaction under seismic loading.Based on the review of past research work, a state-of-art with respect to Soil-Pile-Superstructure Dynamic Interaction, which includes pile analysis models, pile group efficiency, analysis methods, is presented firstly. Research field of Soil-Pile-Superstructure Dynamic Interaction under seismic loading is a complicated program involving many subjects, and also concerned by many departments. To meet the different requirements of structure anti-seismic design, it is necessary to develop both rigorous model and simplified model. Research work is conducted along two parallel lines of both simplified method and Finite Element Method analysis as follows:To model nonliearity and hysteretic character of soil under seismic loading, the p-y curve of single pile under monotonic loading is used as the skeleton curve and modified Ramberg-Osgood model theory is employed to construct the hysteretic loop for single pile dynamic p-y curve. The improved model is used in the Dynamic Beam on Nonlinear Winkler Foundation method. Both material and hysteretic damping of soil are taken into consideration. The governing equation of motion is set up combining with theory of FEM, and a Fortran code is written based on above theory. An orthogonal test parametric sensitivity analysis including three dimensionless factors, earthquake input level. slenderness ratio of pile and modulus ratio of pile to soil, is performed for soil-pile system under seismic loading. A comprehensive parametric study is also done for shear type structure supported by a single pile.Based on the lumped masses model developed by Penzien, the Soil-Pile-Structure Dynamic Interaction analysis model is constructed by a set of bend-shear lumped masses representing the structure and pile group, springs, dashpots which represent surrounding soil. The shear stiffness and damping characteristic of equivalent soil layers are taken into consideration. Calculation methods of interaction parameters are put forward. Approximation method of equivalent linear iteration is employed to obtain solution of the governing equation. Comparison analysis has been done for a structure supported by single pile with different models, results indicate that two models coincide each other very welland effect of equivalent soil is not significant on structure with single pile seismic response. Comparison analyses also have been done for compliance and stiff structure with pile group foundation. Results show that dynamic interaction plays an important role in seismic response for stiff structures.The single surface constitutive model developed by Desai and his co-workers is introduced systematically, the image stress point method similar to Bounding Surface Model is employed to calculate the plastic soil modulus undergo cyclic load. Methods of determination parameters of model by conventional experiments are put forward, and approximate scales of parameters are given, and parametric study is also conducted. Finite Element analysis model of Soil-Pile-Superstructure Dynamic Interaction is constructed, in which 8-node iso-parametric elements are used to model surrounding soil, and incompatible elements are employed to model pile. Comprehensive parametric analysis is performed for single piles and pile groups with Fortran code written by author. Discussion of effect of elevator pile free length on seismic response is done for an elevator pile foundation The calculation results show that it is necessary to take soil plasticity into consideration and the free length is an important value for fr...