The aim of the study is to compare and evaluate structural response obtained from nonlinear static analysis that is Pushover analysis procedures recommended in ATC 40. Three-dimensional low-rise moments resisting RC buildings with vertical irregularity are investigated. Two types of vertical irregularities, that is, mass and stiffness, as specified in the IS 1893- 2002 are considered in this study. In order to determine nonlinear behavior of the buildings under lateral loads, the base shear-roof displacement relationships i.e. capacity curves are obtained by Pushover analysis. The effects of mass irregularity (MI) and stiffness irregularity (KI) were investigated and discussed in terms of the height-wise distribution of story drift, storey shear, Storey Displacements. The performance point and structural performance level of mass and stiffness irregularities were determined using Pushover analysis. The mass irregular buildings were observed to experience larger storey shear whereas stiffness irregular buildings experienced lesser storey shear force than regular counterpart. The storey shear is increased by 25% at fifth floor for mass irregular structure compared to regular counterpart, whereas the stiffness irregular building experience lesser storey shear. Storey drifts were maximum for the stiffness irregular buildings; the drifts were increased by 94% than regular building. The storey displacements were decreased for mass irregular structures at the floor of irregularity, but the storey displacements were increased at bottom storey. The displacements at bottom storey were increased by 40%. The storey displacement for stiffness irregular buildings is increased by 97% compared to regular structure. The capacity curve of regular building is found less than mass irregular buildings, but the capacity curves of regular building is more than stiffness irregular buildings. The structural performance level of mass irregular building was found under “collapse” level, where as the structural performance level of stiffness irregular structure was under “Life of Safety “level
