Numerical Analysis Of Pile-Soil-Structure Dynamic Interaction

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 were damaged seriously during the past major earthquakes. Large amount of cost have been paid for the remedy of pile foundation after earthquakes .The code for seismic design of pile only made some details of seismic design, the lack of gender. Significant testing and analysis found in the role of the earthquake, the interaction between the foundation and structure occur. So it is a significant value for both academic and concrete project to study the subject of numerical modeling of pile - soil -superstructure dynamic interaction under seismic loading.Based on the review of past research work, a state-of-art with respect to pile-soil-superstructure dynamic interaction, which includes piles earthquake disaster characteristics and damage forms, pile-soil-structure interaction analysis methods, is presented firstly. Research field of pile-soil-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. Because of this, with the method of whole dynamic finite element, the study will simplify the system for the horizontal model, through a comparative analysis, and examined the pile-soil-structure interaction system for dynamic characteristics and laws for the following:(1) The suitable constitutive equation for pile-soil-structure is selected, and the practical analysis model of the finite element method is adopted in the study of pile-soil- structure dynamic interaction. The elastic constitutive model is used for the superstructure, and the elastic-plastic constitutive model based on Drucker-Prager yield criterion is used for the soil, then the parameters for these constitutive models are computed .The solution of motion equation, the finite element, the boundary of soil, the dimension of mesh and the gravity load of system are discussed in this paper.(2) Pile-soil dynamic interaction under the different seismic wave and site conditions, multiple factors and levels parametric sensitivity analysis of pile-soil system, Pile-Soil dynamic interaction under seismic dynamic load and the elastic-plastic property of soil have been discussed. Then under the same siteconditions and the same peak value of seismic accelerated speed, the seismic response of the pile-soil dynamic interaction is different if the shape of the seismic wave differs. The harder the upper soil is, the more the displacement and accelerated speed of the pile are decreased. But it affects less to the deep pile. Among these factors, pile soil stiffness ratio, pile slenderness ratio and earthquake design level are taken into consideration. The calculation results indicate that the pile soil stiffness ratio is the most sensitive one among three factors. In the same elastic parameters of soil, when the elastic-plastic property of soil has been considered, the displacement, accelerated speed and the shear of the pile are decreased probably. Under the horizontal seismic action, the single-deck soil damaged turns to be sheared;multi-layer soil turns to be curved scissors. Because of pile existence, the displacement, accelerated speed of pile-surrounding soil would be greatly reduced.(3) In the pile-soil-superstructure dynamic interaction analysis, it emphasizes the seismic response on the pile in liquefiable site. With the deepening of the liquefiable soil, the inherent vibration periodic time, peak value of horizontal displacement in the pile and the peak value of moment and shear on the top of pile are increasing. At the meantime, influence of seismic response on piles due to pile-surrounding soil and spacing between adjacent piles was studied. The peak value of horizontal displacement in the pile appears to the top of pile. When the thickness of the upper soft soil layer is little ,the internal force of the pile body at the top of pile section would reach the maximum value .When the thickness of the upper soft soil layer reach a certainty value, the internal force of the pile body at soil-hard demarcation section would reach the maximum value. The internal force peak value of pile body would be decreased with reducing spacing of the pile. At the same time, these infer force on the pile section at the first movement of the soft soil and hard soil is largely increasing. With increasing of stiffness of superstructure, the inherent vibration periodic time is decreased, and the peak value of horizontal displacement in the pile and the peak value of moment and shear on the top of pile are increasing. Pile soil stiffness ratio, pile slenderness ratio and earthquake design level are the three factors of the sensitivity. At last, two-dimension seismic and the interaction have been discussed. It is discovered that the value of decrease for the story drift, relative displacement, the shear force and axial force of column are different. So the same decrease of the value for different those parameters in the Code for seismic design of buildings is not reasonable.In the anti-seismic design of buildings, not only should pile-raft foundations anchoring and details of seismic design be noticed, but also special attention should be paid to the pile section's moment of resistance steel and shear of resistance steel at the first movement of the soft soil and hard soil in order to prevent it from curved scissors damaging.