Exact formulation of interface stiffness matrix for axisymmetric bodies under non-axisymmetric loading

Based on the concept of the zero-thickness joint element, a new and accurate formulation of the stiffness matrix for an axisymmetric interface element is presented. This element was formulated to model soil-structures interfaces in semi-analytical analysis of axisymmetric solids of revolution subjected to non-axisymmetric loading. The advantages of the closed-form solution of the interface stiffness matrix are manifold. First of all, it is exact and accurate under all conditions. Secondly, it can be easily used in a finite element code. This formulation requires only the angle of the interface element inclination, thus eliminating the need for numerical integration for each orientation of interface element. Thirdly, it is compatible with the commonly used continuum isoparametric elements such as the six-noded triangle or the eight-noded quadrilateral elements. Two example problems involving a rigid footing and a pile subjected to lateral loading are used to show the advantages of using this new exact formulation.