This paper describes an experimental evaluation of viscous dampers used to reduce seismic motion in reinforced concrete moment-resisting building structures. Common practice in Taiwan is to use lightly reinforced concrete exterior walls and interior partition walls, which not considered for their contribution of stiffness and strength in the design process. As these additional walls greatly reduce relative story displacement and velocity, it has been suspected that the effectiveness of supplemental dampers would be very limited. However, the test results show that a new displacement multiplying mechanism, the toggle brace damper system, is effective even with a small relative story drift in the seismic response control of the structure. Dampers produce significant force and displacement reduction in the moment-frame structures that were investigated.