This paper focuses on use of supplemental stiffness and damping to reduce seismic responses of one-story torsionaly coupled structural systems having uni-axial stiffness eccentricities. Adding stiffness to minimize stiffness eccentricity can most directly reduce the torsional response, but increases translational acceleration and corresponding lateral force. In contrast, adding damping in a manner to produce “damping eccentricity” controls both the torsional and translational responses, by increasing the system damping ratio. Combining both approaches can lead to effective and economical solution. The response prediction rule for such a non-proportional damping system using real-valued modes was proposed earlier by the writers, and is modified to be more simple and accurate in this paper. Using the rule, performance curves clarifying relationship between structural parameters and response parameters are proposed. The curve can determine required supplemental stiffness and damping to reduce both torsional and translational responses, and is extremely useful for sizing and horizontally distributing dampers in the system.
