## 4 Configuration for Shake Table Testing
### Examination of the Test Specim  
The experimental setup included two identical single-bay, single-story reinforced concrete frames, as shown in Figure 4. One frame acts as the control specimen, while the other has a diagonal TnT brace for enhancement. The frames will be called Specim 1 (Bare Frame) for the control and Specim 2 (TnT-retrofitted Frame) for the reinforced variant. Both are scaled models, reduced to one-third of the original dimensions, following the similitude rule in Table 1. \begin{table}
\begin{tabular}{l c} \hline \hline
**Physical Quantity** & **Scale Factor** \\ \hline Length, \(l_{r}\) & 3 \\ Modulus of elasticity, \(E_{r}\) & 1 \\ Time, \(t_{r}\) & 1.732 \\ Gravitational acceleration, \(g_{r}\) & 1 \\ Strain, \(\varepsilon_{r}\) & 1 \\ Acceleration, \(a_{r}\) & 1 \\ Frequency, \(\omega_{r}\) & 0.577 \\ Velocity, \(v_{r}\) & 1.732 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Calculated physical quantities for shake table tests. The structural simulations involved columns with a rectangular cross-section of 100 mm width and 150 mm height, spaced 1350 mm apart. Each column had four longitudinal reinforcement bars of 8 mm diameter, the smallest available locally. The height of the columns was 950 mm from the foundation to the slab underside. As illustrated in Figure 5, transverse reinforcement included 8 mm diameter bars spaced 100 mm apart, with stirrups featuring 90-degree hooks, indicating suboptimal detailing. Additionally, 8 mm bars were used at 100 mm intervals in the slab's upper and lower sections. The foundation's longitudinal reinforcement consisted of 16 mm bars, with 10 mm stirrups spaced at 150 mm intervals. The top slab measured 1450 mm long, 450 mm wide, and 50 mm thick. A foundation beam, measuring 1950 mm long, 600 mm wide, and 400 mm deep, was anchored to the shake table with 50 mm diameter bolts. Specimen 2 was created as a replica of the first specimen but included a TnT brace, as presented in Figure 4. The seismic retrofit aimed to enhance the strength and stiffness of the original RC frame, surpassing its initial load-bearing capacity. TnT bracing system features a Tube-in-Tube design with a circular hollow structural section (HSS) of 42 \(\times\) 1.5 mm made of S235 JRH steel, encased in a 48.4 \(\times\) 2.0 mm outer tube. This structure incorporates an outer tube as a buckling restraint that is split into two segments, while a single load-bearing tube connects the end plates. The assembly begins with an 8 mm-thick ring-shaped stopper plate attached to a 1235 mm load-bearing tube via fillet welding. Two 595 mm outer tubes are then welded to this stopper plate. The load-bearing tube is connected to 8 mm-thick rectangular end plates at both ends through fillet welding, with an intentional 18 mm gap included  
Figure 4: Shake table test setup for two specimens. Figure 5: (a) Reinforcement detailing, (b) Cross-sectional views of beam and column elements. between the outer tube and end plates for accommodating potential tube shortening under compression. This design ensures effective performance in both compression and tension, as the outer tube's contribution to compressive strength is disregarded. The clearance dimensions were based on expected brace deformations. Finally, 75 \(\times\) 75 mm end plates were connected to the pre-welded end plates on gusset assemblies using four M12 grade 8.8 bolts to prevent end rotations, thereby enhancing stability, reinforced by stiffeners at key locations as supported by scholarly references [47; 48; 57; 58]. It should be mentioned that incorporating bracings, either buckling or non-buckling, in an existing RC frame in particular is a challenge for several reasons. One of the major difficulties was taking accurate measures to produce shop drawings required for the fabrication of the TnT bracing and its connections. To overcome the erection tolerance issues, small tolerances that existed in the bolted connections were accommodated by the repair mortar injected between the steel reinforcing plates and the existing frame.