This paper describes the passive control method of mid-story isolation buildings designed to mitigate seismic response in the substructure. An equivalent two degree of freedom system consisting of both the substructure and the super structure is introduced. Optimal parameters of the isolation are formulated for the building subjected to white noise ground motions. The equivalent frequency and the damping factor of the equivalent single degree of freedom (SDOF) system are defined based on the random vibration theory. The practical estimation methods of maximum responses are proposed with the combination of the SDOF model and the response spectrum method. Finally, performance curve diagrams are presented.
