In the present research, the difference between elastic and inelastic modeling of concrete superstructures resting on Triple Concave Friction Pendulum (TCFP) isolators is investigated. In order to attenuate the effects of earthquake on structures, the use of isolation systems provides an effective solution for addressing seismic excitations. Seismic isolators are designed in such a way to end up with a relatively rigid superstructure design with low relative displacements. In the study of isolated structures, it is usual to model the superstructure elastically. However, numerous studies have indicated that the structure behavior may extend to inelastic region in earthquakes of large intensity upon which the isolator reaches its ultimate displacement capacity. As such, TCFP isolators (which are among the newest variants of friction isolators) and three-, six-, and nine-story concrete structures resting on the isolators were selected for the present investigation. In this study, investigating plastic joints in reinforced concrete structures, we found that the structure was yet to enter nonlinear zone, meaning that all of the results obtained from linear analysis coincide to those of nonlinear analysis. In order to understand the behavior of superstructure when it enters the nonlinear region, the isolator displacement was reduced to the level mentioned in the respective design code followed by reanalyzing the six-story superstructure in linear and nonlinear modes. The obtained results were indicative of increased roof acceleration when displacement capacity of the isolator is below the allowed threshold according to the code.