Publisher Summary Evaluation of the seismic performance of moment resisting steel frames is usually carried out assuming the elastic-perfectly-plastic type of hysteresis model for plastic zones. This type of model is associated with conventional ultimate plastic rotations giving indication of the maximum deformation beyond which strength degradation is likely to occur. This methodology leads to conservative results, and the elastic-perfectly-plastic type of hysteresis model is definitely adequate to obtain reliable information on deformation demands when the maximum values presented in this chapter are not exceeded. However, the safety of the frame at collapse remains unknown. The analyses presented in the chapter show that safety margins on the global collapse of the structure can be predicted only by considering more realistic hysteresis behaviors. Finally, aiming at obtaining more rational structures—that is, structures satisfying both the serviceability and ultimate limit states with the same level of confidence, some possible solutions are proposed and discussed in the chapter.