An enhanced base isolation system equipped with optimal tuned mass damper inerter (TMDI)

In seismic base isolation, most of the earthquake-induced displacement demand is concentrated at the isolation level, thereby the base-isolation system undergoes large displacements. In an attempt to reduce such displacement demand, this paper proposes an enhanced base-isolation system incorporating the inerter, a 2-terminal flywheel device whose generated force is proportional to the relative acceleration between its terminals. The inerter acts as an additional, apparent mass that can be even 200 times higher than its physical mass. When the inerter is installed in series with spring and damper elements, a lower-mass and more effective alternative to the traditional tuned mass damper (TMD) is obtained, ie, the TMD inerter (TMDI), wherein the device inertance plays the role of the TMD mass. By attaching a TMDI to the isolation floor, it is demonstrated that the displacement demand of base-isolated structures can be significantly reduced. Due to the stochastic nature of earthquake ground motions, optimal parameters of the TMDI are found based on a probabilistic framework. Different optimization procedures are scrutinized. The effectiveness of the optimal TMDI parameters is assessed via time history analyses of base-isolated multistory buildings under several earthquake excitations; a sensitivity analysis is also performed. The enhanced base-isolation system equipped with optimal TMDI attains an excellent level of vibration reduction as compared to the conventional base-isolation scheme, in terms not only of displacement demand of the base-isolation system but also of response of the isolated superstructure (eg, base shear and interstory drifts); moreover, the proposed vibration control strategy does not imply excessive stroke of the TMDI.