Simplified theories are proposed for seismic response evaluation and preliminary design of RC building structures added with elasto-plastic dampers. They are based on the single-degree-of-freedom (SDOF) idealization of multistory building, and produce the control performance curve expressing the peak responses as a function of stiffness of all components, based on spectral characteristics of the earthquake. Against the target peak response, a rule to convert the SDOF design to multistory design, with consideration to distribute damper stiffness over the building height, is also presented. Accuracy of the approach is demonstrated by passive control design and time history simulations on two RC buildings.