## 5 Experimental Results  
### Dynamic Tests  
The dynamic response and system properties of the tested structures were obtained through analysis of the experimental pseudo-frequency response functions, PFRFs, in the case of white noise input. The tests were repeated at different intensities to investigate possible emerging nonlinear effects due to the insertion of the non-conventional TMD via inter-story isolation with HDRBs. The experimental PFRFs of the absolute acceleration and relative displacement at the support level are depicted in Figure 8a,b, respectively, for the F3S configuration at a given input intensity (F3S, black curve) and for the FTMD configuration at three increasing input intensities (green WN01 = 0.002 g, blue WN05 = 0.008 g, and red WN12 = 0.025 g curves, respectively). Focusing the attention first on F3S, the uncontrolled configuration, five main amplifications are observed in the acceleration response (Figure 8a), evidencing additional modes due to asymmetric base boundary conditions. In the displacement response (Figure 8b), instead, three peaks are visible. For both responses, the first mode always has highest amplification, the following being less amplified. By observing in the figures the responses obtained with the FTMD configuration, focusing the attention on the curve at the lowest intensity it is possible to observe that in both responses the first mode splits into two smaller amplitude modes of frequencies smaller and greater than the first uncontrolled one, respectively, dramatically reducing the first amplification of the three-story frame structure (black curve). Observing more in detail, for the acceleration response (Figure 8a), the first two modes have similar amplitudes, whereas for the displacement (Figure 8b), the first one is always greater than the second. The subsequent modes instead are modestly attenuated, without varying appreciably the frequencies with respect to the uncontrolled case. By increasing the input intensity, it is possible to notice that the first two amplifications move to the left, evidencing the softening behavior induced in the structure by the presence of the HDRB isolators; moreover, the first amplification attenuates, while the second one increases. This result is connected to the damping effect and energy exchange between the two modes that, by increasing the intensity, increase for the first mode and decrease for the second one. In any case, the control action induced by the TMD is always effective in a sufficient wide range of frequencies centered on the first uncontrolled one. \begin{table}
\begin{tabular}{c c c} \hline
**Earthquake** & **PGA (g)** & **RMS (m/s2)** \\ \hline \multirow{4}{*}{Kobe} & 0.05 & 0.07 \\  & 0.18 & 0.25 \\  & 0.23 & 0.32 \\  & 0.3 & 0.42 \\ \hline \multirow{4}{*}{Northridge} & 0.06 & 0.05 \\  & 0.23 & 0.22 \\  & 0.28 & 0.27 \\  & 0.29 & 0.28 \\ \hline \multirow{4}{*}{El Centro} & 0.05 & 0.06 \\  & 0.16 & 0.2 \\  & 0.26 & 0.3 \\  & 0.3 & 0.35 \\ \hline \multirow{4}{*}{Hachinohe} & 0.05 & 0.07 \\  & 0.13 & 0.2 \\ \cline{1-1}  & 0.16 & 0.26 \\ \cline{1-1}  & 0.19 & 0.32 \\ \cline{1-1}  & 0.25 & 0.37 \\ \hline \end{tabular}
\end{table} 
Table 3: Natural earthquakes’ characteristics. The experimental PFRFs of the fourth floor absolute acceleration and relative displacement are depicted in Figure 8c,d, respectively, for the F4 configuration (black curve) at a given reference intensity in comparison with the same responses obtained with the FTMD configuration at three input increasing intensities. In this comparison, the F4 configuration represents the non-segmented structure before the inter-story isolation has been implemented as control strategy. Concerning F4 configuration, in the acceleration response (Figure 8c), six amplifications are observed, evidencing additional modes due to asymmetric base boundary conditions. In the displacement response (Figure 8d), instead, only three peaks are visible.