Composite Reinforced Concrete-Steel (RCS) frames which consist of Reinforced Concrete (RC) columns and Steel (S) beams were represented to combine the advantages of pure RC and steel frames. This system permits the primary steel beam to run continuous through the reinforced concrete column. This paper evaluates seismic performance of RCS frames based on FEMA-356, considering plastic rotations as acceptance criteria. The effect of joint deformations on overall behavior of RCS frames is studied through nonlinear static analysis (Pushover) that is performed in OpenSees software. It is concluded that the RCS joint behavior increases lateral load capacity of frame. Additionally, 3 RC frames are compared to RCS frames with columns similar to those of RC frames. The results show a great improvement on overall behavior since steel beams is used instead of RC beams.