The research results contribute to the knowledge in the field of earthquake engineering and, in their final consequence, help to reduce human and material losses due to strong earthquakes. The most important contribution is the development of a simplified method for non-linear seismic analysis of structures (N2 method) which has been implemented in the European standard for design of earthquake resistant structures Eurocode 8. In the period 1999-2003, the method has been formulated in the AD format. Its applicability has been extended to asymmetric structures and to infilled frames. Important results, published in international literature, are also contributions to the understanding of non-lienar seismic behaviour of asymmetric structures and to the structural modeling based on results of pseudo-dynamic tests, development of a simplified method for seismic risk estimation, contributions to simplified seismic analysis of viaducts, and development of new devices for semi-active seismic isolation.