A variant design of Tuned Mass Damper Inerter for reducing displacements of base isolated structures

In this study an innovative passive control strategy, referred to as New Tuned Mass Damper Inerter (New TMDI), coupled with a base isolation system (BI), is presented with the aim of reducing displacements in base isolated structures subject to seismic actions. The proposed New TMDI employs the synergetic benefits of a recently developed non-traditional Tuned Mass Damper (known as New TMD) and an inerter device to achieve higher control performances in isolated structures. Specifically, the New TMD is a secondary mass system connected to the BI system by a spring and to the ground by a dashpot. In addition, in the New TMDI configuration, the inerter device is placed in parallel with the damper. The New TMDI optimal parameters are determined by performing a simplified approach which provides simple closed-form formulae as a quick tool to design the examined device. The reliability of the proposed approach is assessed by a comparison with a more accurate and computationally complex numerical optimization procedure. Further, the performance of a base-isolated multi-degree-of-freedom structure equipped with a New TMDI is investigated taking into account different recorded ground motions as base excitation. Results from time history analyses assess the mitigation effect due to the optimal New TMDI on the response of base-isolated structures, also in comparison with those of a conventional Tuned Mass Damper Inerter (TMDI). On this base, the proposed New TMDI might be considered as preventive conservation strategy for applications also in historic buildings, where general constraints require limited space for the base displacements.