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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 102
PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by:
Paper 196

Simulating Piled Rafts in Layered Media using Finite Element - Boundary Element Formulations

D.B. Ribeiro1 and J.B. Paiva2

1Polytechnic School of the University of São Paulo, Brazil
2Structural Engineering Department
São Carlos Engineering School of the University of São Paulo, Brazil

Full Bibliographic Reference for this paper
D.B. Ribeiro, J.B. Paiva, "Simulating Piled Rafts in Layered Media using Finite Element - Boundary Element Formulations", in , (Editors), "Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 196, 2013. doi:10.4203/ccp.102.196
Keywords: layered media, pile, raft, boundary elements, finite elements.

Summary
The objective of this paper is to present formulations developed by the authors for soil-structure interaction analysis. The soil is modeled with the boundary element method (BEM) as a layered solid infinite for radial directions. Cylindrical piles are modeled with the finite element method (FEM) using one dimensional elements. The raft is also modeled with the FEM, but with two dimensional elements. The analysis is static and all materials are considered homogeneous, isotropic, elastic and with linear behavior.

Kelvin fundamental solutions are used in the BEM and an alternative multi-region technique is employed. Establishing relations between the displacement fundamental solutions of the different domains, the alternative technique here used allows analyzing all the domains as one unique solid, not requiring equilibrium or compatibility equations. Infinite boundary elements (IBEs) are employed for the far field simulation, allowing computational cost reduction without compromising the result accuracy. The IBE formulation is based on a triangular boundary element instead of the quadrilateral IBEs usually found in the literature.

In the one dimensional elements used for the piles, displacements and tractions along the shaft are approximated by polynomial functions. The triangular three-node finite element employed for the raft is obtained by superposing plate and membrane effects, totalling six degrees of freedom per node. For the FEM-BEM coupling, the BEM tractions are considered as nodal reactions between the contact surfaces. The coupling is established using equilibrium and compatibility equations, obtaining a single system of equations that represents the complete pile-raft-soil problem.

The proposed formulation is applied into two examples and it is concluded that it may be considered a practical and attractive alternative in the field of soil-structure interaction simulation.

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