## 3 Analysis of Factors Affecting Shear Behavior of Reinforced Concrete Beams
### Effect of the Amount of FRP Grid Reinforcement
#### 3.1.2 Effect of the Spacing of the FRP Grid  
To investigate the effect of the spacing of the FRP grid on the shear behavior of strengthened beams, taking the strengthened beam B-1 as the reference, keeping the original parameters unchanged, the spacing was adjusted to 75, 100, 125, and 150 mm. The specific parameters are shown in Table 3. Figure 9 is a comparison diagram of the load-midspan deflection curves of the unstrengthened beam and the strengthened beams with different grid spacings. The detailed data and comparison are listed in Table 5. As the grid spacing increases, the ultimate load of the strengthened beam gradually decreases and the effective strain of the FRP grid increases significantly, which intuitively reflects that the spacing is negatively correlated with the shear behavior capacity and positively correlated with the grid strain. Compared with the reference beam B-1, the reinforcement amount of beam B-II decreased from 1.33% to 0.89%, a reduction of 33%, and the ultimate bearing capacity only decreased by 6.3 kN, while the effective strain increased from 0.0054 to 0.0104, an increase of 93%, indicating that the grid efficiency of beam B-II was more fully exerted. In Figure 9, except for beams B-1 and B-II, the beams have obvious descending sections. The author believes that the reason is the same as that in Section 3.1.1. As the spacing increases, the failure characteristics of the strengthened beam and the corresponding failure curves gradually approach those of the unstrengthened beam. When approaching the ultimate load value of the unstrengthened beam, there is a clear divergence in the load-midspan deflection curves. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Beam** \\ **ID** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Thickness** \\ **(mm)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Cross-** \\ **Sectional** \\ **Area (mm\({}^{2}\))** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Strengthening** \\ **Amount (\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Ultimate** \\ **Load (kN)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Change** \\ **Rate (\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **FRP Grid** \\ **Effective** \\ **Strain** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Change** \\ **Rate (\%)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Failure** \\ **Mode** \\ \end{tabular} } \\ \hline B-1 & 5 & 50 & 1.33 & 328.27 & & 0.0054 & & SF \\ B-T1 & 7 & 70 & 1.87 & 329.02 & 0.23 & 0.0045 & \(-\)17.14 & SF \\ B-T2 & 6 & 60 & 1.60 & 328.83 & 0.17 & 0.0050 & \(-\)7.80 & SF \\ B-T3 & 4 & 40 & 1.07 & 323.84 & \(-\)1.35 & 0.0083 & 53.70 & SF \\ B-T4 & 3 & 30 & 0.80 & 314.92 & \(-\)4.07 & 0.0128 & 138.59 & SF \\ B-T5 & 2 & 20 & 0.53 & 300.77 & \(-\)8.38 & 0.0153 & 185.27 & SF \\ B-T6 & 1 & 10 & 0.27 & 274.37 & \(-\)16.42 & 0.0173 & 221.18 & SF \\ \hline \hline \end{tabular} Note: SF represents the shear–compression failure; the judgment criterion is that the stirrups reach the yield strength first, then the strain of the concrete in the shear span zone reaches the ultimate compressive strain; the strain of the FRP grid selected is the actual maximum tensile strain of the grid when the strengthened beam fails, which is customarily referred to as the effective strain, and the same below; the change rate of the ultimate load = (the ultimate load of each strengthened beam – the ultimate load of the reference beam)/the ultimate load of the reference beam, and the same below; and the change rate of the FRP grid strain = (the strain of each strengthened beam – the strain of the reference beam)/the strain of the comparison beam \(\times\) 100%, and the same below.  
\end{table} 
Table 4: Effect of FRP grid thickness on reinforced beams.