Experimental seismic performance assessment and numerical modelling of nonlinear inerter vibration absorber (IVA) - equipped base isolated structures tested on shaking table

In recent years, inerter vibration absorbers (IVAs), such as the tuned mass damper inerter (TMDI), attracted much attention in the literature for reducing seismic displacement demands of base isolated structures (BISs). Several theoretical studies reported reduced BIS seismic demands with increasing inertance endowed by a grounded inerter element but adopted mostly idealized linear dynamical models. Herein, the potential of TMDI-configured IVAs for seismic response reduction of BISs modelled as single-mass structures is assessed under the combined effects of nonlinear inerter and structural behavior. To this aim, experimental data from a shaking table testing campaign are considered utilizing a custom-built flywheel rack-and-pinion grounded inerter prototype with vari- able inertance along with high damping rubber bearings in the isolation layer and in the BIS-to-absorber link. White noise excitation and an ensemble of six ground motions (GMs) with different frequency content are used in the tests for which bearings exhibit softening nonlinear behavior. Experimental results demonstrate improvement of BIS nonlinear seismic response in terms of dis- placement and base shear with increasing inertance for nonlinear and nonoptimally designed TMDIs. It is found though that nonoptimally tuned IVAs may be detrimental to BIS acceleration response depending on the GMs time-varying frequency content signatures as captured by the continuous wavelet transform spectrogram. Last, it is concluded that representing the inerter device by a simplified linear dissipative model as opposed to a nonlinear model with friction and gear backlash suffices to trace the BIS response with acceptable accuracy and, thus, can be used for optimal seismic TMDI design.