en Structure-Earthquake Structure-Earthquake Research Paper Research Paper Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers. Progressive collapse, Symmetric and asymmetric reinforced concrete mid rise and tall buildings, Story drift 30 44 http://ijce.iust.ac.ir/browse.php?a_code=A-10-365-2&slc_lang=en&sid=1 S. Karimiyan s.karimiyan@iiees.ac.ir 180031947532846009538 180031947532846009538 No Int’l Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran A. Moghadam moghadam@iiees.ac.ir 180031947532846009539 180031947532846009539 Yes Int’l Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran A. . Husseinzadeh Kashan : a.kashan@modares.ac.ir 180031947532846009540 180031947532846009540 No Department of Industrial Engineering, Faculty of Engineering, Tarbiat Modares University, Tehran, Iran M. Karimiyan 180031947532846009541 180031947532846009541 No Applied Science and Technology University, Tehran, Iran