The Coupling Coefficients Method for Seismic Design of Mid‐Story Isolated Structures

This study proposes a new seismic design procedure for mid‐story isolated structures that reduces design complexity, computational effort, and time. In the proposed procedure, referred to as the coupling coefficients (CCs) method, the isolated superstructure and the substructure are initially treated as decoupled and analyzed separately. CCs are then used to capture the interaction effects among seismic isolation, substructure, and superstructure. We first derived the CCs in closed form using basic concepts of modal analysis. Then, we validate these analytical expressions using statistical results obtained through comprehensive numerical simulations. We described the dynamic problem using mass and stiffness ratios. For stiffness ratios () limited to , and stiffness‐to‐mass ratios ( t ) limited to , simplified expressions for modal periods, masses, participation factors, and damping ratios are developed. A reduced damping in the first mode captures the amplification effects of the substructure on the isolated superstructure. An increased damping in the second mode captures the tuned mass damper effects of the isolated superstructure on the substructure. For small stiffness ratios, the seismic demand of the isolation system can be approximated by that of the independent isolated superstructure on the ground, and the demand of the substructure can be approximated by that of the independent substructure, with adjustments made only for the viscous damping effects.