# Experimental Study on Shear Strengthening of RC Beams with an FRP Grid-PCM Reinforcement Layer
## 3 Experimental Study on Reinforcement Amount  
### Test Programme  
According to the test results from the last section, better performance was obtained on concrete beams with I-shaped profile, especially in the ultimate state, when using reinforcement of CFRP grid -PCM layer along both the web and the haunch regions. Other bonding tests of FRP grid-PCM and concrete blocks have been previously conducted by authors, and these research results suggested that the bonding behavior between the existing concrete and the CFRP grid with PCM shotcrete was sufficient, while the essential number of grid points in one plane was at least three [44; 64]. Thus, seven types of beam specimens with larger dimensions and full range reinforcement (i.e., both web and haunch), Series B, were prepared and then tested. In this series, the reinforcement amount of the CFRP grids is considered as the main test variable to investigate their influence on RC beams strengthened by CFRP grid-PCM layer in shear, as indicated in Table 5. In terms of the existing portion, the stirrups spaced intervals of 250 mm were Grade HRB 300 steel bars with diameter of 10 mm, while the compressive and tensile steel bars were Grade HRB 335 with diameter of 35 mm. The shear span ratio is 2.93 in all beam specimens. For strengthened beams, in addition to control beam N0\({}^{\prime}\) with no reinforcement, all of strengthened beams are reinforced along the web and the haunch: the RHWP specimen reinforced by PCM only, specimens RHWC4, RHWC6, and RHWC8 reinforced with PCM and CFRP grids of different types (named as CR4, CR6 and CR8). The RHWC4' specimen includes a grid type CR4, but with vertical spacing of 50 mm, which is 1/3 of the others (150 mm). The remaining specimen, RHWC64, is special because it is reinforced by a combination of CR4 and CR6 types, layered in horizontal and vertical directions, respectively. Some design principles and construction methods are almost the same as the previous Series A tests, including design concepts, manufacture process, standards for test methods, instrumentation, and testing procedure. Hence, these are not introduced again, and all related measured results are summarized in Tables 6 and 7, while the geometrical dimensions of specimens and the installation placement of the strain gauges are shown in Figure 8. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type** & **Type of CFRP** & \begin{tabular}{c} **Grid Interval** \\ **(Vertical \(\times\) Horizontal, mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Reinforcement** \\ **Range** \\ \end{tabular} &
\begin{tabular}{c} **Thickness of** \\ **PCM, mm** \\ \end{tabular} \\ \hline N0/ & - & - & - & - \\ RHWP & - & - & Haunch + Web & 20 \\ RHWC4 & CR4 & \(150\times 50\) & Haunch + Web & 20 \\ RHWC6 & CR6 & \(150\times 50\) & Haunch + Web & 20 \\ RHWC8 & CR8 & \(150\times 50\) & Haunch + Web & 20 \\ RHWC4\({}^{\prime}\) & CR4 & \(50\times 50\) & Haunch + Web & 20 \\ RHWC64 & CR6\&CR4 & \(150\times 50\) & Haunch + Web & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Material properties of concrete and PCM. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Types** & **Materials** & \(A_{\text{w1}}\)**, mm2** & \(f_{\text{w}}\)**, MPa** & \(f_{\text{y}}\)**, MPa** & \(E_{\text{o}}\)**, Gpa** \\ \hline D35 & tensile steel bars & 956.6 & 578 & 386 & 200 \\ \hline D10 & Stirrups & 71.33 & 573 & 363 & \\ \hline CR4 & & 6.6 & 1400 & - & 100 \\ \hline CR6 & CFRP grids & 17.5 & 1400 & - & 100 \\ \hline CR8 & & 26.4 & 1400 & - & 100 \\ \hline \hline \end{tabular} Note: \(A_{\text{w1}}\) is the cross-sectional areas of single steel bar or FRP grid;\(f_{\text{w}}\),\(f_{\text{y0}}\) are the mean values of the ultimate and yielding strengths, respectively.  
\end{table} 
Table 7: Material properties of steel bars and CFRP grids.