This paper is devoted to the construction and evaluation of mass and stiffness matrices of elastodynamic four and five node infinite elements with united shape functions (EIEUSF), recently proposed by the author. Such elements can be treated as family elastodynamic infinite elements appropriate for multi-wave soil-structure interaction problems. The common characteristic of the proposed infinite elements is the so-called united shape function, based on finite number of wave shape functions. The idea and the construction of the united shape basis are described in brief. This element belongs to decay class infinite elements. It is shown that by appropriate mapping functions the formulation of such an element can be easily transformed to a mapped form. The results obtained using the proposed infinite elements are in a good agreement with the superposed results obtained by series of standard computational models. The continuity along the finite/infinite element (artificial boundary) line in two-dimensional substructure models is also discussed in brief. In this type of computational models such a line marks the artificial boundary between the near and the far field of the model.
