## 5 Experimental Results
### Further Considerations on the TMD Effectiveness  
Some further comments concerning the TMD seismic effectiveness can also be deduced from the observation of the PFRFs obtained with WN input, reported in Figure 8. With respect to a non-segmented structure, F4 configuration, the implementation of inter-story isolation and realization of a non-conventional TMD produced a great attenuation of the dynamic structural response at all the frequencies (see Figure 8c,d), proving that it is a smart control strategy useful for enhancing structural vibration mitigation. The enhancement is especially evident for the acceleration response, which possesses high amplifications not only around the first modes, as is typical for relative displacement (Figure 8d), but also at higher ones. All the amplifications are effectively reduced by the non-conventional TMD implementation (Figure 8c).  
Figure 15: NE—response indices based on maximum values (\(J_{n}\)) and RMS values (\(I_{n}\)), \(n\) = 1–6, varying the input intensity for near-fault earthquakes: (**a**,**b**) Kobe, (**c**,**d**) Northridge.  
The F3S configuration, instead, in this comparison can be viewed as a three-story primary structure without control. With respect to the F3S configuration, the introduction of a TMD with a large mass ratio (FTMD configuration) produced its control action mainly around the first mode, with a great attenuation of the dynamic response in a wide range of frequencies centered on the first uncontrolled mode. Subsequent modes instead were only modestly influenced by the TMD (Figure 8a,b).  
The preliminary indications obtained with WN input were confirmed when the configurations were tested with multi-frequency actions as the earthquake signals.  
The results are synthetically reported for two exemplificative response quantities, the maximum values of the third floor displacement D\({}_{3}\) and the base shear T\({}_{\text{b}}\) in Figure 17a,b, respectively, in the case of Kobe earthquake at different intensities, comparing the FTMD configuration with F4 and F3S configurations. In the case of F4 and F3S configurations, the responses have a linear trend, whereas in the case of the FTMD configuration the responses are modestly nonlinear. It is possible to notice that the insertion of the TMD is effective if applied to both cases for each response. In addition, the maximum effectiveness is obtained by implementing inter-story isolation from an original non-segmented structure (FTMD vs. F4 configuration).  
Figure 16: NE–response indices based on maximum values (\(I_{n}\)) and RMS values (\(I_{n}\)), \(n=1\)–\(6\), varying the input intensity for far-field earthquakes: (**a,b**) El Centro; (**c,d**) Hachinohe.  
In Figure 18a,b, as an exemplificative case, the time history of the base shear is reported in the case of the Kobe earthquake at a PGA level of 0.18 g, comparing FTMD with the F4 configuration, and FTMD with the F3S configuration, respectively. The base shear is evidently reduced with respect to both configurations considered. The response time history is attenuated from the very first pulses and has almost null oscillations after the first decades of seconds. In addition, observing the time history, the maximum effectiveness of the TMD applied to an original non-segmented structure with inter-story isolation is confirmed (Figure 18a).