# Buckling-Restrained Bracing System with Ultra-High-Performance Fiber Concrete
## 4 Experimental Test of BRB with UHPFRC Concrete
### BRB Fabrication Procedure  
The fabrication of the BRB prototype involved nine steps, as shown in Figure 22: (1) providing steel material such as steel plates and hollow sections, (2) cutting the steel core to the assumed dimensions and preparing supports for the steel core, (3) creating 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) casting UHPFRC inside half of the steel tube restrainer, (7) after a curing period of 28 days for concrete, grinding and leveling the surface of UHPFRC to achieve a smooth and even finish, (8) assembling the BRB device by inserting the core element into the steel tube restrainers and (9) assembling and attaching the BRB device to the dynamic actuator setup frame. \begin{table}
\begin{tabular}{c c c c c c} \hline  & & **Maximum** & **Maximum** & **Maximum** & **Maximum** \\  & & **Force** & **Displacement** & **Stress in** & **Maximum** \\  & & **(kN)** & **(mm)** & **Compression** & **Strain (\%)** \\ \hline BRB & Tension & 89 & 26 & & \\ (Low Grade) & Compression & 56 & 45 & 186 & 3 \\ \hline BRB & Tension & 86 & 27 & & \\ (Medium Grade) & Compression & 64 & 31 & 218 & 2.06 \\ \hline BRB & Tension & 90 & 26 & & \\ (High Grade) & Compression & 68 & 23 & 226 & 1.7 \\ \hline \end{tabular}
\end{table} 
Table 10: BRB result in tension and compression for low-grade, medium-grade and high-grade concretes. Figure 21: BRB Hysteresis curves for (**a**) low-grade concrete, (**b**) medium-grade concrete, (**c**) high-grade concrete. To fabricate the BRB prototype, steel materials were cut and assembled based on the dimensions provided in Table 1. The length ratio of the plastic core was set to 0.44 (840 mm), as is indicated in Figure 2[29]. The main body of BRB consists of a steel tube restrainer with a thickness of 6 mm, a cross section of 150 \(\times\) 150 mm, and a length of 1160 mm, as shown in Figure 23. The steel tube was cut into two halves to facilitate the casting of concrete inside each half section and allow for inspection of the core condition after conducting the experimental test. Figure 23: Half cut steel tube restrainer. Figure 22: Fabrication steps of BRB. Figure 24 illustrates the support heads that were designed for both ends of the core. These support heads were fabricated by creating bolt holes according to the sizes specified for the support and actuator head. The design allows the prototype to be securely fixed to the experimental setup. In addition, two steel belts were employed, as is indicated in Figure 25 to enhance the strength of the device during the test. These belts were used to restrain the BRB and prevent any out-of-plane movement. The experimental test was conducted using a Shimadzu dynamic actuator with a 300 kN load capacity at UPM structural laboratory. As shown in Figure 26, the steel core segment was covered with a 2 mm-thick cardboard to create a predetermined gap between the steel core and concrete. This gap allows the smooth sliding of the steel core inside the concrete during the test. Figure 24: BRB steel heads. Figure 25: BRB assembly belt. The UHPFRC concrete was used as the filler material for BRB. The casting process began by pouring the concrete into one of the half sections of steel tube restrainer. Subsequently, the steel core, covered by cardboard, was positioned inside the wet concrete to create the determined gap for the core. The same procedure was repeated for the other half section to ensure uniformity in the casting process. Figure 27 shows the cast concrete before grinding and leveling of the surface. To allow the UHPFRC concrete to reach its maximum strength, the cast concrete was covered with a plastic sheet and cured for 28 days. After 28 days, the concrete surface was ground and leveled in preparation for inserting the core, as indicated in Figure 28. A grinder machine was utilized to achieve a smooth concrete surface, allowing the steel core to move sufficiently inside concrete during the test.