Seismic Response Analysis Of Bridge Foundation Based On Pile-soil Interaction

Earthquakes are burst-mode natural disasters with strong destructive.Strong earthquakes can cause destruction to buildings and bridges in very short-time,even can make them collapsed in serious situation.In 1976,Tangshan earthquake made the whole Tangshan city destroyed,lots of buildings and bridges fell down.Economic loss is more than 10 billion RMB.In 1995,all kinds of losses of Osaka God earthquake in japan are more than 100 billion dollars.Wenchuan earthquake took place in 2008 May 12th in Sichuan province.The number of damaged bridges reachs 5560,direct economic losses are several tens of billion RMB.The direct economic losses resulted from earthquakes are great.On the other hand,bridge engineering is the throat of transportation.When the earthquake occurs,bridge enginneering is the lifeline of the rescue after disasters.In 2008 Wenchuan earthquake,many bridges got destroyed,and roads can not get access.It have great influence on earthquake relief.Therefore,the indirect losses caused by interruption of transportation resulted from bridges destroyed after earthquakes are much more unpredictable.Bridge seismic is very important to life and property safety of the people.Therefore,it is of great significance to carry out the research on bridge structure seismic theory and design method.Although some rules about design of part bridges are made in bridge seismic specifictions of our country,but the checking calculation of bridge structures in earthquake response in the specifictions are all used pile-soil consolidation model.In pile-soil consolidation model,the coupling effect is not taken into consideration.flexury rigidity of the foundation is easily centralized to the bottom of bridge piers.According to a series of engineering practice,people realize that there is great difference between the results calculated by pile-soil consolidation model and test results.When structures are bearing earthquake,superst structure,pile and soil are one organic whole of cooperative work.Pile and soil consolidation treatment artifically can lead to the phenomenon of uncomformable between structure anlysis and actual datas.Pile-soil coupling interaction appear to be obvious nonlinear.There are complex nonlinear behaviors,such as relative slip, separation and friction between Pile-soil interface. Nonlinear coupling deformation considering pile-soil coupling interaction is of great significance to seismic design of bridge structures. Because of the randomness of the earthquake, pile-soil structure interaction, soil nonlinearity, so seismic response analysis of the pile - soil interaction is very complicated. Existing theoretical methods and practical engineering applications there are still some way away, there are still no effective analytical model. Based on this situation,it is necessary to carry out the mechanism of pile-soil interaction studies and the earthquake response of bridge foundation analysis method.Winkler foundation beam lumped parameter model is used widely among the pile - soil interaction simplified model. The piles are regarded as beams in soil media in this method,and dynamic impedance of the soil around the pile to the piles is instead of continuous distribution of independent springs and dampers.Dynamic Winkler model can be further consideration of non-uniform soil changing with the depth of soil and even the nonlinear nature. However, the pile-soil coupling interaction appears significant nonlinear characteristics,and there are complex nonlinear behaviors,such as relative slip, separation and friction between Pile-soil interface. Nonlinear coupling deformation considering pile-soil coupling interaction is of great significance to seismic design of bridge structures.Dynamic Winkler model has not fully consider the nonlinear properties of pile-soil coupling interaction.A comprehensive study of dynamic Winkler model in the pile - soil interaction analysis is carried out.An improved dynamic Winkler model for large deformation conditions, considering the pile - soil nonlinear deformation characteristics, ie complex nonlinear behavior,such as relative slip, separation, soil yielding and friction exist in the pile-soil interface, is proposed in this paper.Finally, as an example of a single pile, the seismic time history analysis is done,and the validity of this model was verified. The results showed that compared with traditional dynamic Winkler model, this model can be more reasonably reflect the mechanism of pile-soil interaction and work status. Mainly research work as following:1.From the basics of dynamic analysis, the pile-soil interaction mechanism is discussed.Motion equations considering the pile-soil structure interaction is established by using finite element analysis method.Based on the pile - soil interaction mechanism and the characteristics of the motion equations,basic solution procedure of motion time history analysis method is formed.2. Depth analysis of nonlinear characteristics of the pile-soil interaction is done.Based on the the nonlinear characteristic of pile-soil interaction, contact element used to simulate the nonlinear pile-soil contact surface. The basic principles and methods of the contact element simulating pile-soil contact interface are analyzed. Based on the contact elements, finite element solid model of pile - soil interaction is established by the finite element method. Finally, a pile-soil interaction seismic response simulated.3. the basic principle of discrete model of the pile - soil interaction analysis is analyzed in this chapter,and the analysis course is defined. seismic response analysis of pile - soil interaction system is carried out by using Winkler model.Analysis results are compared with analysis results of finite element model based on contact element4.An improved dynamic Winkler model for large deformation conditions, considering fully the pile - soil nonlinear deformation characteristics, ie complex nonlinear behavior,such as relative slip, separation, soil yielding and friction exist in the pile-soil interface, is proposed in this paper.The results are compared with the calculation in Chapter 3 and Chapter 4 to verify the validity of this model.