# Development of a New Rubber Buckling-Restrained Brace System for Structures
## 4 Fabrication of RBRB  
Based on the pre-designed experimental results of material, a RBRB prototype has been fabricated. The fabrication of the RBRB prototype involves 11 steps, as shown in Figure 14: (1) providing steel material such as steel plates and hollow section, (2) cutting the assumed steel core dimensions and supports for steel core sections, (3) preparing a steel tube restrainer from the steel hollow section, (4) welding the core element to support plates, (5) covering the steel core with cardboard, (6) cutting the rubber components, (7) casting the UHPFRC inside the half steel tube restrainer, (8) grinding and leveling the concrete surface after 28 days, (9) inserting rubber components, (10) fastening the BRB device by putting the core element inside the steel tube restrainers, and (11) assembling and attaching the RBRB in a dynamic actuator setup frame. Figure 14: RBRB fabrication steps. Figure 13: UHPFRC testing setup and result. (**a**) Compressive strength cube test. (**b**) Average strength of UHPFRC. Table 4 represents the details and specifications of the RBRB model. It consists of a 300 mm\({}^{2}\) core with a total length of 1500 mm. The RBRB dimensions can be seen in Figure 15.  
All steel components of RBRB have been manufactured based on the initial design details. As shown in Figure 16, the steel core segment was covered with 2 mm-thick cardboard to create a sufficient gap, allowing the steel core to slide smoothly inside the concrete during testing. Additionally, plastic foam was used to create gaps within the concrete for the insertion of rubber blocks after casting. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Brace** & **Steel** & **Core** & **Compaction** & **Concrete** & **Steel Tube** & **Total Device** & **Rubber Element** \\
**Type** & **Restrainer** & **Dimension** & **(mm)** & **Type** & **Length (mm)** & **Length (mm)** & **(mm)** \\ \hline RBRB & \(150\times 150\times 6\) & 300 & 2 & UHPC & \(1140\) & \(1500\) & \(100\times 100\times 150\) \\ \hline \end{tabular}
\end{table} 
Table 4: RBRB dimensions. Figure 15: RBRB dimensions and model. (**a**) Side view of steel core and rubber component. (**b**) Side view of steel tube restrainer. (**c**) Top view of steel tube restrainer. (**d**) Assembly shape of steel core and rubber component in restrainer. The UHPFRC concrete, as specified in Table 4, was utilized for molding in the RBRB. The procedure started by pouring the concrete into one-half of the steel tube restrainer, followed by positioning the steel core, wrapped in cardboard, within the fresh concrete to create the intended gap for the core element. The same process was repeated for the other half section. Figures 17 and 18 depict the molded concrete prior to surface grinding and leveling. To ensure maximum strength, the molded concrete was covered with a plastic sheet, as UHPFRC requires a 28-day curing period. After a 28-day curing period, the concrete surface was ground and leveled to facilitate the insertion of the core, as shown in Figure 19. A grinding machine was used to smooth the concrete surface, ensuring seamless sliding of the steel core within the concrete during the device's operation. Figure 16: RBRB steel components and covers. Figure 17: RBRB steel tube restrainer gap forming. Figure 18: RBRB steel tube restrained cast concrete. After preparing the concrete surface, the steel core was reinserted into the steel tube restrainer. The two half sections were then aligned and stacked together, followed by assembling the device to evaluate the assembly's efficiency and the steel core's movement, as illustrated in Figure 20.  
Following the successful testing of the core's smooth movement, the prototype was dismantled and moved to the testing actuator frame setup. To achieve this, one-half of the steel restrainer, along with the steel core, was mounted in the frame setup by bolting the steel core's support heads to the supports, forming a fixed joint.