Nonlinear dynamic analysis of reinforced concrete structures requires a thorough understanding of behavior of structural elements for all levels of performance, especially collapse. Main reason is that reinforced concrete is a mixed material having complicated nonlinear behavior, each element having several coupled degradation modes that influence the entire structure and can change its collapse mechanism. Therefore, using oversimplified models can lead to misleading results. This paper presents a numerical study on the relation among the non-simulated failure modes of the structural elements of non-ductile RC frames and their collapse mechanism; this study reports on the so-called