## 4 Parametric Study
### Effect of Concrete Strength  
The comparison of beams reinforced with different types of fibers in Section 4.1 indicates that concrete beams reinforced with steel-BFRP composite bars have both good ductility and ultimate capacity. The following numerical simulation studies focus on the variable parameters based on beams reinforced with steel-BFRP composite bars.  
In order to better compare the test beam specimens, the numerical simulation in Sections 4.2 and 4.3 adopt the mechanical properties of the tested materials verified in Section 3.1 into the simulation model. In the model, BFRP original fiber is 2400 tex, and its mechanical performance parameters are shown in Table 6 The load-horizontal displacement curve of the S12B50 beam is analyzed by changing the strength of concrete. The strength values are 30 MPa, 50 MPa and 70 MPa, respectively.  
Figure 16 shows the influence of different concrete strength values on load-horizontal displacement curve of S12B50\" beams. It can be seen that the curves coincide at the pre-yield stage, indicating that the change in concrete strength has a very limited impact on the strength and horizontal displacement of specimens at the initial elastic stage. However, the peak load and the post-yield stiffness increased gradually with the increase in concrete strength at the post-yield stage. As a result, when the concrete strength value is more than doubled, the seismic ultimate capacity of the beam increases by only 10% and the horizontal displacement at FRP fracture point decreased by only 2.7%, that is, the ductility did not change significantly.  
Figure 17 shows the influence of concrete strength and fiber content on the seismic ultimate capacity and corresponding drift ratio of the component. The range of BFRP bundles in composite bars is from 50 to 90. As shown in Figure 17a, it is concluded that with the increase in concrete strength, the seismic ultimate capacity of concrete beam with different fiber content increases significantly. Figure 17b shows the effect of concrete strength on the ultimate drift ratio, with the increase in concrete strength, the drift ratio at the BFRP fracture point decreases gradually. Due to the elastic behavior of the FRP, all curves are linear to the fiber content. Under the same concrete strength, the ultimate drift ratio decreases more obviously with the increase of the fiber area in composite bars. However, the overall variation range is from 3.6 to 4.4, showing good ductility. It indicates that increasing the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fiber Types** & \begin{tabular}{c} **Original Fiber** \\ **Strength (MPa)** \\ \end{tabular} & \begin{tabular}{c} **Fiber Ultimate Strength** \\ **in SFCBs (MPa)** \\ \end{tabular} & \begin{tabular}{c} **Original Fiber** \\ **Elongation (\%)** \\ \end{tabular} & \
\begin{tabular}{c} **Elongation** \\ **in SFCBs (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Area** \\ **(mm2/bundle)** \\ \end{tabular} \\ \hline BFRP (2400 tex) & 2250 & 1540 & 2.5 & 2.2 & 0.833 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Mechanical and physical properties of BFRP fibers in OpenSees.  
Figure 16: Effect of concrete strength on the load-displacement pushover curve.  
concrete strength of components blindly can improve the seismic ultimate capacity, but also reduce the ductility of components.