Exact Formulation of Axisymmetric‐Interface‐Element Stiffness Matrix

A new and accurate formulation of the stiffness matrix for an axisymmetric interface or joint element is presented. This element is formulated to model rock joints and soil-soil and soil-structure interfaces in the finite element analysis of axisymmetrical solids of revolution. The formulation is done in the local coordinate system and the closed-form solution of the interface stiffness matrix is obtained. The advantages of the new formulation are: (1) It is exact and accurate under all conditions, versus the various approximate forms; (2) it can be easily used in a finite element code; and (3) the planar interface element is a special case of the new interface element. As such, the stiffness matrices of the planar and axisymmetric interface elements can now be expressed in a unified form, thus eliminating the need for two different types of interface elements. An example problem involving a rigid footing is used to show the advantage of using the new formulation in modeling axisymmetric interface behavior.