Abstarct: One of the new methods of seismic rehabilitation of structures, is using of mextallic damper which due to its many advantages compared to other energy absorber equipments, is appropriate for steel and concrete frxames Strengthening. Therefore in this study performance of frxames equipped by triangular mextallic plate dampers (TADAS) installed on chevron braces inside the span of the frxame, and the structural response to earthquake force before and after the Strengthening to this type of damper is studied. To this end three moment frxames with 5, 10 and 15 stories and with 3 and 5 spans in both directions in plan were selected. Also to increase the accuracy of non-linear static analysis, and determination of structural capacity curve and the target displacement and performance point of studied three dimensional frxames, Sap2000 program was used. Also parameters affecting the behavior factor (R) and seismic performance of structure were determined. Comparing the values obtained, shows the reduction of roof displacement and lateral forces imposed on the building floors and increase of behavior factor, stiffness, damping, strength and ability of dissipation the input energy to Strengthening structure, and using this damper will cause the structure to achieve the level of Life Safety (LS) performance level. The obtained results prove that using this method to improve buildings, will cause in reducing seismic response and increasing ductility and energy acceptance of structures and reduce buildings vulnerability against earthquakes and prevent casualties and financial losses a lot. The use of this Strengthening system despite its advantages has economic justification and additional costs related to buying and installing this type of mextallic damper equipment would be covered.