Predicting the dynamic behavior of complex structures is possible by the use of high accurate numerical models. Generally, structural systems are modeled using methods such as finite element method (FEM), finite difference method (FDM) or boundary element method (BEM). The scaled boundary finite element method (SBFEM) is a semi-analytical boundary method that does not requires the knowledge of a fundamental-solution to make possible its formulation and it is based on FEM. Using in-plane and out of plane motion structural dynamic problems and discretizing the boundary with three nodes quadratic line finite element, in this work the derivation of the frequency response function (FRF) by SBFEM is presented. From the FRFs, the natural frequencies and mode shapes can be obtained by performing a theoretical modal analysis. Numerical studies considering various assumptions for the scaled boundary finite element method are presented and the results obtained are compared with FEM Ver menos