Empirical equation for estimating seismic response of the stiffness-degrading inelastic SDOF structures with fully elasto-plastic dampers are applied to 6- and 3-story reinforced concrete building structures with or without bearing walls. Fully elasto-plastic dampers are designed based on the nonlinear pushover analysis result for the bare frames. Nonlinear time history analysis is performed for the building models with dampers, and their ductility demands and spectral accelerations are transformed to those of SDOF structures, and compared with the response estimated using empirical equations for inelastic SDOF structures. Empirical equations estimates the ductility demands with reasonable accuracy, but the spectral accelerations have errors unacceptable for design purposes due to higher mode effects, which requires further improvement.