Assistant professor, Department of Civil Engineering, Lorestan Univercity.Iran.
PhD student in Azad University, South Tehran Branch.Iran
Developments in the field of Structure and Earthquake Engineering and also consequences of earthquakes have been led to develop some continually changes and improvement of seismic regulations around the world. In regards to seismicity of Iran, it is necessary and also possible to review and edit the Seismic Regulations of Iran and compare it with the other countries; so it seems that a comparative study of relations of the fundamental period based on various regulations is required. This debate is regarded to change all kinds of structures; for example, here the irregular structures with varieties of irregularities on height can be mentioned. The irregular structures are more observable than the other ones because of their unique form and creative ideas of architectures. Then, in regards to extend and grow of usage these structures around the country we shall collect and present a correct study based on an accurate planning because investigation of the fundamental period of irregular steel frames on height is required. By this research the investigation of the fundamental period of three-opening irregular steel frames with divergent bracing along with irregularities on height is studied. Models of three-bay frames with 2-15 storeys have been modeled by Etabs Software; also a series of short, middle and high frames have been modeled by Opensses Software, and then they are compared together, finally the analyzed periods have been compared with the different relations in Regulation; then by the use of MATLAB-2013 Software some coefficients of formula of the fundamental period have been determined for three-bay frames with one-sided-stepped on the height and divergent bracing.