# Buckling-Restrained Bracing System with Ultra-High-Performance Fiber Concrete
## 3 Finite Element Analysis Results for UHPFRC and Conventional Concrete Filler
### BRB Hysteretic Response Result for UHPFRC and Conventional Concrete Filler  
A cyclic test was conducted to investigate the behavior of the BRB model filled with conventional concrete and UHPFRC concrete under applied displacement amplitudes, which is indicated in Figure 1. The maximum resistance force was calculated on one node  
Figure 19: BRB steel tube restrainer, (**a**) BRB (G40) displacement steel tube, (**b**) BRB (UHPFRC) displacement steel tube restrainer, (**c**) BRB (G40) strain steel tube restrainer, (**d**) BRB (UHPFRC) strain steel tube restrainer, (**e**) BRB (G40) stress steel tube restrainer, (**f**) BRB (UHPFRC) stress steel tube restrainer.  
at the applied load side of both BRB models along the horizontal direction. The outline of the hysteresis curve was observed to be smooth and responded elastically.  
As is illustrated in Table 9, the maximum displacement and force values in the BRB filled with conventional concrete and UHPFRC under tension are nearly identical. This observation suggests that changes in filler material do not have a significant effect on the tensional performance of BRB. In contrast, in compression, resistance force in BRB filled with UHPFRC was observed to increase compared to the model filled by conventional concrete. This increase in resistance force is attributed to the superior confinement capability of UHPFRC. Consequently, the maximum stress experienced by the core element of BRB filled with UHPFRC was increased by approximately 28%.  
As can be seen in Figure 20, based on the material properties of G40 concrete, the core is more prone to have local buckling, which results in more displacement. However, UHPFRC exhibits advanced behavior, providing improved restraint to the core element in BRB. This enhanced restraining ability of UHPFRC reduces the risk of global buckling in BRB, thereby contributing to its improved overall performance and stability.  
Previous experimental studies conducted by [PERSON] (2023) confirmed that using steel fibers in conventional concrete enhances the load capacity of the BRB system up to 25% [27]. Additionally, [PERSON] et al. (2011) proved that using concrete with a compressive strength exceeding 30 MPa provides sufficient confinement for the core and improves the performance of BRBs [31]. These findings highlighted the advantages of using UHPFRC as a filler material in the BRB device. These advantages include increased confinement of  
Figure 20: BRB hysteresis curves.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**BRB** & \multirow{2}{*}{**Max Force (kN)**} & \multirow{2}{*}{**Maximum Dis**} & \multicolumn{2}{c}{**Stress at**} & **Strain at** \\
**(Conventional Concrete)** & & & **(mm)** & **Maximum Load** & **Maximum Load** \\ \hline Tension & 90.8 & 25.8 & & **(MPa)** & **(\%)** \\ Compression & 58 & 33.6 & & 213 & 2.3 \\ \hline
**BRB (UHPFRC concrete)** & \multirow{2}{*}{**Max Force (kN)**} & \multirow{2}{*}{**Maximum Dis**} & \multicolumn{2}{c}{**Stress at**} & **Strain at** \\
**(mm)** & & & **maximum load** & **maximum load** \\  & & & **(MPa)** & **(\%)** \\ \hline Tension & 92.2 & 25.5 & & **(MPa)** & **(\%)** \\ Compression & 70 & 25.6 & & **(MPa)** & **(\%)** \\ \hline \end{tabular}
\end{table}
Table 9: BRB results in tension and compression.  
the steel core, higher resistance forces, reduced occurrence of local buckling, and overall enhanced performance and behavior of BRB under compression loads.