Improving the dynamic performance of base-isolated structures via tuned mass damper and inerter devices: A comparative study

The dynamic performance of base-isolated buildings can be improved by introducing a tuned mass damper (TMD) at basement, below the isolation floor where most of the earthquake-induced displacement demand is concentrated. In order to enhance the effectiveness of the TMD without simultaneously amplifying the relevant mass ratio, the use of supplemental inertial mass dampers has been envisaged by the authors and other authors in earlier studies. These schemes exploit the mass-amplification effect of the inerter, a two-terminal device whose generated force is ideally proportional to the relative acceleration between its terminals. In this paper, we present a review along with a systematic comparative study of six different strategies proposed in the literature, each one featuring a specific combination of mass-spring-dashpot elements arranged in series or in parallel with an inerter for the displacement mitigation of base-isolated structures. Frequency-response functions of each model are derived in closed form. Optimal design is based on a common strategy, considering a white-noise random process as seismic input, by minimization of the displacement variance but with an eye also for the superstructure acceleration (associated with forces arising in the superstructure) and for the TMD stroke. Then, the seismic performance of the six systems is assessed considering an ensemble of 52 natural earthquake ground motions, by comparing several response indicators including TMD stroke, deformation of the base-isolation floor, superstructure acceleration, interstory drifts, base shear, and reactions associated with spring, oil damper, and inertial damper supporting the TMD, which are significant for outlining preliminary economic assessments.