## 2 Description of the Physical Models  
The original physical model is a 1:5 scale model steel frame structure (\(\lambda_{L}=5\)). It consists of a four-story frame structure, with plan dimensions of 636 mm \(\times\) 670 mm, an inter-story height of 600 mm, and made of L cross-section beams joined in order to form a T cross-section. The rectangular columns have dimensions of 80 mm \(\times\) 8 mm, and the slabs are made by plates of dimensions 576 mm \(\times\) 580 mm. The floor mass for each story is m\({}_{i}\)= 131 kg (\(i\) = 1, 4). Horizontal plates with two welded vertical orthogonal plates are bolted to the table realizing the base constraints of each rectangular column. The columns are bolted to the base constrains at one side only (Figure 2a). As a result, the columns are not symmetrically constrained. A picture of the physical model is shown in Figure 2a, whereas the model dimensions (plane and elevation) are reported in Figure 2b,c. Base motion is applied in the direction of minor inertia of the columns. The four-story frame structure represents the first configuration tested, named F4 (Table 1).  
Configuration F4 is segmented into a three-story substructure and a one-story superstructure, which is converted into tuned mass (Table 1). A support plane, indicated with subscript \"S\", is built on the top of the three-story frame and connected by two cross bracings in the motion direction in order to realize a rigid slab to place the isolators. The three-story structure with the support plane, named F3S, represents the second intermediate configuration tested, and it is indicated in Table 1, where the detail of the cross bracings and the rigid support plane are evidenced. The non-conventional TMD is realized by placing the one-story mass, which represents the superstructure, on two high damping rubber bearings (HDRB) placed in series, positioned in the center of the support plane (Figure 3b). The three-story structure with a rigid support plane controlled by the non-conventional TMD implemented via inter-story isolation, named FTMD, is the third configuration tested (Table 1, depicted in Figure 3a). It has total height of 2.48 m, floor masses m\({}_{1}\) = m\({}_{2}\) = 131 kg and m\({}_{3}\) = 133 kg, a support plane mass m\({}_{\rm S}\) = 17 kg, and a TMD mass m\({}_{\rm TMD}\) = 100 kg. Model dimensions are reported in Figure 3c.  
The HDRB isolators, realized according to the TMD design described in Section 3, consist of two bearings made by 27 layers, 2 mm thick, and 26 steel shims, 1 mm thick. The total rubber thickness is 54 mm, the height of the bearing is 80 mm, and the total diameter is 58 mm, including 53 mm of shim diameter and 5 mm of cover (Figure 4). A truss structure connected at the base of the support floor by four spherical bearings (see Figure 3b) is realized in order to avoid flexural behavior of the isolators, which sustain only shear strain. The threaded rods are braced in the direction of the motion.  
The configurations tested are summarized in Table 1: (1) F4--the reference four-story structure, (2) F3S--the three-story structure with the rigid support plane, (3) FTMD--the three-story structure equipped with the non-conventional TMD. Concerning the investi  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & Configurations & & \\ \hline F4 & F3S & FTMD \\ \hline  
\hline \end{tabular}
\end{table}
Table 1: Configurations tested in gation of the dynamic structural response, the FTMD configuration is compared with the two reference cases: F4, the four-story structure, and F3S, the three-story structure with the support plane.