| The design of pile-raft foundation, in a long time, has been carried on according to routine pile foundation'design due to have no efficient computing method. The carring capacity of soil can't get fully used. The distance between routine piles foundation is oversized in order to use soil's supporting capacity and think over the pile-soil's combined supporting capacity. This pile foundation is called composite pile foundation (thinned pile foundation). Now the mechanics of composite foundation is not very clear, this article is mainly on composite foundation combined action.On the basis of related literature at home and abroad, this paper puts emphasis on studying the problem by finite element. In the analysis of raft, Kichhoff's thin plate theory is important. With the building are getting higher, the thickness of raft is getting more thick too and the shape is getting irregular. To this raft, if rectangle thin plate is still used will has limitation. So the elastic material is used to simulate the piles, raft and superstructure, and the nonlinear elasticity Duncan-Chang model is used to simulate soil as well as interface element method is introduced in between piles and soil. The finite element method is used to analyze the superstructure, and the stiffness matrix is condensed from top to bottom. Using 2D 8-node iso-parameter bending element, 3D 20-node iso-parameter and 3D 16-node interface element, a coupled non-linear numerical approach for the piled raft system is set up. The Object-Oriented programming of finite element software with VC++ is developed.This simplified spatial program is worked out on the base of this article's theory, and analyzed some main parameter's influence. Some regular conclusion is gotten.Case study show that the object-oriented model presented in this dissertation is correct and feasible, and the result is also satisfying.
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