Structural damage assessment during earthquakes has always been a challenging problem for earthquake engineers. Evaluation of buildings vulnerability and determination of damage can be an important step taken for rehabilitation. Dissipated energy and deformation in an earthquake are the most important parameters in vulnerability of buildings. In this research, effects of elements nonlinear deformation on vulnerability and damage of irregular steel structures in different earthquake hazard levels has been assessed in three dimensions which have not been considered in recent studies done on seismic vulnerability. The buildings have been considered in different floors with irregular plans. The buildings were modeled in three dimensions with considering panel zone. It is concluded that nonlinear deformation of beams is 70% more than column in life safety performance and nonlinear deformation of columns is 20% more than beams in collapse prevention. Severe damage and collapse due to these parameters occurred in the initial stories of low-rise buildings and in middle stories of high-rise buildings.