A novel nonlinear isolated rooftop tuned mass damper-inerter (IR-TMDI) system for seismic response mitigation of buildings

This paper conceptualizes a novel passive vibration control system comprising a tuned mass damper-inerter (TMDI) contained within a seismically isolated rooftop and investigates numerically its effectiveness for seismic response mitigation of building structures. The working principle of the proposed isolated rooftop tuned mass damper-inerter (IR-TMDI) system relies on the yielding of typical elastomeric isolators (e.g. lead rubber bearings) under severe earthquake ground motions to create a flexible rooftop which, in turn, increases the efficacy of the TMDI for seismic vibrations suppression. Herein, a nonlinear mechanical model is considered to explore the potential of IR-TMDI whereby the primary building structure is taken as linear damped single-mode system, while the Bouc–Wen model is used to capture the nonlinear/hysteretic behaviour of the rooftop isolators. An equivalent linear system (ELS), derived through statistical linearization, is used to expedite the optimal IR-TMDI tuning for different isolated rooftop properties, inertance, and primary structure natural period. To this aim, white noise excitations with different intensities as well as Kanai–Tajimi excitations for different soil conditions are considered. It is found that tuning for maximizing TMDI seismic energy dissipation is more advantageous than tuning for minimizing primary structure displacement or acceleration response since it lowers deflection and force demands to the isolators and to the inerter. Further, significant primary structure displacement and acceleration reductions are achieved as the effective rooftop flexibility increases through reduction of the nominal strength of the isolators, which verifies the intended working principle of the IR-TMDI. This is also confirmed through response history analyses to the nonlinear model under benchmark recorded ground motions. Moreover, for IR-TMDI with sufficiently flexible isolators, improved seismic structural performance with concurrent reduced deflection and force demands at the isolators is shown for all considered stochastic excitations as the inertance scales-up, which is readily achievable technologically. Thus, it is concluded that the IR-TMDI mitigates effectively structural seismic response without requiring the inerter to span several floors, as suggested in previous studies, thus extending the TMDI applicability to both existing and low-rise new-built structures.