Seismic control mechanism of tuned viscous mass damper (TVMD) outriggers

This study investigates the seismic control mechanism of tuned viscous mass damper (TVMD) outriggers in a core wall-frame system, which can be regarded as providing frequency-dependent equivalent stiffness and damping. Closed-form formulas for equivalent stiffness and damping of TVMD outriggers are derived based on a distributed-parameter model that represents the core-wall frame system. As the frequency increases, the equivalent stiffness transitions from negative to positive values and asymptotically decays to the spring stiffness of TVMD outriggers at infinite frequency. Simultaneously, the equivalent damping increases from the TVMD damping coefficient to a maximum value as the frequency increases from zero to the tuning frequency, and then asymptotically decays to zero along with the increasing frequency. A modal response mitigation ratio is defined and calculated, revealing that equivalent damping plays a dominant role over equivalent stiffness in the control mechanism. An analysis of equivalent damping-frequency curves elucidates that the control mechanism of TVMD outrigger, i.e., tuning effect for the targeted mode and damping supplement effect for the lower-order modes. Finally, seismic control performance of TVMD, viscous damper (VD), and negative stiffness damper (NSD) outriggers is compared based on a 140-m tall core wall-frame structure. Seismic response analysis demonstrates that TVMD, VD and NSD outriggers reduce the maximum inter-story drifts by 26%, 10%, and 17%, and the maximum floor accelerations by 27%, 12%, and 18%, respectively.