Amir Masoud SANAYEI - M.Sc. Grad uate, Sahand University of Technology, Tabriz, Iran
Behzad RAFEZY - Associate Pro fessor, Sahand University of Technology, Tabriz, Ira n
Reza KAMGAR - Ph.D. Candidate, ShahidBahonar University, Kerman, Iran

Different seismic regulations provide different definitions related to irregular criteria in buildings. In addition, these regulations categori ze the buildings into two kinds: regular and irregular buildings. Seismic regulations neglect the effect of sy mmetry on the seismic behavior of irregular buildings as a factor against irregular buildings in plan; therefore, in this paper the effect of symmetry on th e behavior of unparallel systems is studied. For this purpose, 6, 10 and 15 storey concrete buildings des igned based on Design Regulation of Iran are used. In adddition, the conventional software ETABS 9.5. 0 and capacity spectral method are used to determine oper ation point of models. The paper concluded that in ten storey buildings, the wedge-shaped models show critiical behavior rather than trapezoidal -shaped, asymmetric models.

Symmetric Irregular Bu ilding, Dissymmetric Irregular Building, Conc rete Building, ATC-40, Capacity Spectral Method