Abstarct: Acceleration and large deformation are main reason of damages during the strong earthquakes, hence providing ductility and decreasing displacement results in a decrease in structural damages, specially for deficient structures that were designed with earlier codes. In recent decades, for improving the structural behavior, researchers have innovated and suggested many retrofit methods.These methods are mainly baxsed on strengthening the structural elements which in turn leads to the increased stiffness and decreased period of the structure. In this study, a new retrofit procedure, baxsed on a different strategy is introduced. The procedure has two main stages. At the first stage the stiffness of the structure is reduced in order to reduce the seismic demand. This stage, called structural weakening, as expected usually results in large displacements. Hence, in the second stage of the retrofit, additional damping is provided by adding proper dampers for controlling the displacements. The main advantage of this procedure is reducing the seismic demend and reducing the peak building acceleration. In this thesis the performance of proposed retrofit method for steel structures is investigated. For this purpose three moment frxames steel structurs with different heights are considered and nonlinear dynamic analysis (time history) and push over analysis were carried out to evaluate the behavior of the structures including performance level and performance point of structures. Numerical simulations (with seven historical strong motion records) show that despite increasing the displacement in the first stage, the overall performance of the suggested method is desirable and in most cases a reduction in the acceleration, baxse shear and displacement is achived. In addition, the performance level of structures was improved and even in some cases the performance level changed from collapse to a linear limit. Accordingly, the proposed retrofit method causes damage reduction in both structural and nonstructural elements and equipments simultaneously, and can be endorsed specially for situations such as hospital, laboratories and advanced technology centers where the protection of the 'secondary systems' are vital.