EPAS-finite element program for analysis of nonlinear behavior of nuclear power piping

The purpose of this paper is to discuss the alternative technique to connect the different kinds of elements using the fictitious elements without occupied volume, so that one can considerably reduce the number of unknowns in the simultaneous equation regarding the finite element method without any troublesome preparation of input data. In other words, superior elements typified by the isoparametric solid elements are arranged only at such an important regions as near crack parts in the whole structure, while the other part of the structure is discretized with the use of one- or two-dimensional lower class of elements, e.g. the beam, plate and shell elements. The connection of the different types of elements is pursued with the help of the fictitious elements placed between the real elements, the characteristics of which are determined by employing the Lagrange multiplier concept. Unknowns of the resulting simultaneous equation consist of usual nodal displacements of the whole structure together with the generalized coordinates regarding the Lagrange multipliers for the fictitious elements. (orig.)