Mestrovic - Professor, Faculty of Civil Engineering, Structural Department, University of Zagreb, Kaciceva ۲۶, Zagreb
Stanilovic - Graduate Student, Faculty of Civil Engineering, Structural Department, University of Zagreb, Kaciceva ۲۶ Zagreb, Croatia

Basic about earthquake as phenomenon is given – how and why are earthquakes generated, measurement of earthquake intensity and general about seismic zones. Focus of article is comparison between different methods of obtaining seismic forces as the height of structure is increasing. Article analyzes simple twostory, five stories and ten stories reinforced concrete buildings which are situated in seismically active region in Croatia. Each structure is modeled as a simple plane frame. Several different calculations are made (pseudo static, spectrum analysis, non-linear time history and pushover). Pseudo-static analysis is made according to Croatian regulations. Structure is also analyzed using spectrum analysis according to EC8 (for this type of analysis both elastic and design spectrum are computed and discussed). Non-linear time history analysis is made using two synthetic accelograms that represent earthquake in this region. Based on available digitized accelograms, two earthquakes were selected according to their magnitudes: earthquake occurring in Petrovac (Montenegro) on April 15, 1979, with magnitude M=6.8 and earthquake occurring on April 9, 1979, in Ulcinj (Montenegro) with magnitude M=5.3. Finally, seismic capacity of structure is tested by pushover analysis. Results obtained by regulations, time history and pushover analysis are compared and discussed. Conclusion about different methods for seismic design is given in relation to height of the frame.