The graduation thesis deals with seismic design according to European standard EN 1998 (EC 8), examining the case of existing eight-storied office-residential building in Maribor that was designed in 1999 according to existing regulations. The subject matter splits the research into three parts. Part one presents the designing of the building, done according to EC 8: the information on structure is given, the structure’s ductility class set and the actions on structure are defined. Linear elastic modal analysis of the spatial model was conducted with the computer program EAVEK. The first part also shows the designing of two critical structural members, one for each transversal structural direction. Shear resistance and bending resistance were verified and so the detailing for assured local ductility is presented. In addition, reinforcement plans for the both two structural members are drawn. The second part compares the existing regulations and standard EC 8. The comparison was made with the same computational models, the only difference being that according to EC 8 cracked sections has to be taken into consideration. Due to quite some differences in the manner of designing, the results of the analysis offer big discrepancies. The differences in structure’s mode shapes are shown, as well as the arrangement of internal forces in the structure as a whole and in its individual structural members. It was examined out on two structural members, whether the reinforcement calculated according to existing regulations also suffices for shear and bending resistance according to EC 8. In the last part of the research the comparison between different models of structure is presented. By comparing its mode shapes and the arrangement of structure’s internal forces, as well as shear and bending resistance of the two structural members, this thesis shows the effect of considering cracked sections and considering wall flanges, as well as the structure’s behaviour in the Ljubljana region with high seismic intensity.