## 5 Experimental Results
### Dynamic Tests
Specifically, in the figure, it is possible to notice that the time history applied increasing in the first  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Frequencies (Hz)**} \\  & & \multicolumn{4}{c}{**Mode**} \\ \hline RMS (g) & 1 & 2 & 3 & 4 & 5 & 6 \\
0.002 & 2.995 & 6.053 & 12.173 & 17.159 & 17.772 & 20.927 \\
0.005 & 2.766 & 5.182 & 12.051 & 17.122 & 17.727 & 20.889 \\
0.010 & 2.618 & 4.822 & 11.966 & 17.018 & 17.627 & 20.782 \\
0.020 & 2.446 & 4.592 & 11.905 & 16.931 & 17.549 & 20.696 \\
0.040 & 2.168 & 4.380 & 11.818 & 16.768 & 17.450 & 20.579 \\ \hline \hline \multicolumn{8}{c}{**Damping Factors (\%)**} \\   RMS [g] & 1 & 2 & 3 & 4 & 5 & 6 \\
0.002 & 4.814 & 12.406 & 1.038 & 0.516 & 0.474 & 0.413 \\
0.005 & 7.420 & 10.790 & 0.830 & 0.590 & 0.540 & 0.420 \\
0.010 & 10.991 & 9.105 & 0.775 & 0.653 & 0.556 & 0.457 \\
0.020 & 12.487 & 7.187 & 0. 150 s and decreasing in the last 150 s is not perfectly symmetrical due to nonlinearities introduced by the HDRB isolators. The corresponding resonances observed with increasing and decreasing sine sweep are indicated in Figure 11 with the same symbols. It is possible to observe that the amplifications are slightly different. Figure 11: SS. FTMD configuration absolute acceleration at first floor for increasing and decreasing sine sweep. Stars, squares, circles, triangles, \(\times\) represent same resonances at increasing and decreasing sweep respectively. Figure 10: (**a**) First two identified frequencies for FTMD configuration versus the RMS of the base excitation (experimental values and interpolating curves), dotted lines: first frequency of F3S and F4 configuration, respectively, (**b**) first two identified damping factors for FTMD configuration versus the RMS of the base excitation (experimental values and interpolating curves), dotted line: \(\overline{\eta}\) mean value of the first two identified damping factors versus the RMS of the base excitation. Figure 12a-d show the time histories with increasing SS of absolute acceleration at the support level, relative displacement at the support level, absolute acceleration at the fourth floor, and relative displacement at the fourth floor, respectively. Six resonance frequencies are visible from the support level absolute acceleration time history (Figure 12a), as was observed with the PFRF in Figure 8a. Three resonance frequencies are visible from the relative displacement at the support level (Figure 12b), as observed with the PFRF in Figure 8b, and the absolute acceleration at the fourth floor (Figure 12c), as indicated with the PFRF in Figure 8c. However, only the first two frequencies are visible from the relative displacement at the fourth floor (Figure 12d), as observed with the PFRF in Figure 8d. Figure 13 reports details of the time history of the inter-story drift between the TMD mass and the support plane overlapped to the support level relative displacement time history, in the range where the first two resonance frequencies of the structure in the FTMD configuration appear. In the figure, the first two frequencies of the FTMD configuration and the first frequency of the F3S configuration are reported as well. It can be observed that when the structure vibrates with the first resonance frequency (f\({}_{1}\)-FTMD = 2.25 Hz), the inter-story drift of the TMD (TMD, blue curve in Figure 13) is higher and in phase with respect to the relative displacement of the substructure (the support level displacement, red curve in Figure 13). Differently, when the structure vibrates with the second resonance frequency (f\({}_{2}\)-FTMD = 4.25 Hz), the TMD drift is lower and out of phase with respect to the relative displacement of the substructure. By representing more in detail the signals around the three frequencies indicated in Figure 13, it is possible to have an idea of the first two modes of vibration of the FTMD configuration examined in Figure 14a-c.