In this research, Concentrically Braced Frames coupled with an elastic truss as a strong back system are analysed. The elastic system has the scope of reducing the permanent residual lateral displacement of steel frames subjected to strong ground motion. Responses of this system are compared with those of the buckling restrained braced frame without elastic truss. All members of the vertical truss, including the diagonal members, should remain in the elastic range during the earthquake, while other braces, that are buckling restrained braces (BRB), come into the plastic zone in severe earthquakes and provide the system with ductility and energy dissipation. Frames are initially designed according to current design codes and then the results are studied by nonlinear time history analysis subjected to the maximum considered earthquake level records and static nonlinear analysis. For the structures under study, the amount of residual inter-story drift ratio decreased on average from 1.33 percent to 0.58 percent, due to the use of an elastic truss in the BRB.
