Study On The Effect Of Superstructure On The Behaviour Of A Pile-raft Foundation

In conventional design methods, the interactions between superstructures and foundations are not considered, and the constraint of superstructure towards foundations (i.e. the contribution of the rigidity of superstructure) are neglected, which lead to over-large bending moments and buckling of foundations and conservative foundation design.In this paper, the simplified analysis method of pile-raft foundations considering interactions of soil-pile-raft and the basic principles of the Finite Element Method are explained. Simplified analytical method is adopted to analyze the interactions between soil and foundations, three-dimensional finite element method is used to analyze the interactions between superstructures and foundations, the effect law of superstructures towards the internal force of foundations is discussed through a simple frame model, and the insufficiency of conventional method is demonstrated.To simplify the analysis, a simplified analytical method considering the interactions of the rigidity of superstructures is put forward in this paper. The action of superstructures towards foundations is simplified as a series of distributed springs, so as to simulate the bending resistant and shear resistant action of structures such as columns, shear walls and hulls. The differences are studied among calculation results by finite element method, simplified method and the method not considering the effect of superstructure respectively, and the simplification method is indicated to possess the advantages of simple and convenient analysis and have more reasonable results compared with the method not considering the effect of superstructure. Through the numerical example, the effect law of superstructure rigidity towards thedeformation and internal force of stake-raft foundation is analyzed.At last, the influence of superstructure is analyzed in a practical case with the method submitted in this paper.