Abstract: Amounts of seismic damage investigation results show that the concentration of a cumulative hysteretic energy distribution in a weak story is almost inevitable in ordinary reinforced concrete (RC) frames under strong earthquakes, leading to the collapse of those structures. A nonlinear viscous fluid damper, as a type of widely-used device in structural seismic engineering, has good ability of dissipating input-energy by earthquakes without changing the stiffness of an original structure. RC frames with and without nonlinear viscous fluid dampers were designed by the current Chinese aseismic design code for building structures. The two types of structures were calculated by a nonlinear time-history analysis method and their cumulative hysteretic energy distribution modes were compared. Besides, the structural collapse-resistant capacities and safety margins against collapse were quantitatively evaluated, with collapse fragility analysis based on an incremental dynamic analysis (IDA). The analysis results show that the energy dissipation mechanism is improved and the damage degrees of structural members are reduced in the frames with dampers, resulting in obviously increased collapse-resistant capacity of a structure.