## 3 The Shear Sliding Test of the Composite Timber Column's Interface
### Test Results and Discussion
#### 3.2.2 Parameter Analysis  
The peak load, as measured by the universal press, is defined as the ultimate load of the shear sliding of the interface. The shear strength of the interface is calculated by the application of Equation (24):  
\[\tau=\frac{P}{A} \tag{24}\]  
where \(P\) is the ultimate load of the shear sliding of the interface and \(A\) is the sum of the areas of the interface. The shear strengths of the interfaces of the different test groups are shown in Table 2. The average value curves of the shear stress-displacement curve of each group of test results were used to represent this group. The shear stress-displacement curves of the interfaces of the different test groups are shown in Figure 11. Figure 12a shows the fitting curves between the number of iron hoops and the shear strength of the interfaces. Figure 12b shows the fitting curves between the inclination angles and the shear strength of the interfaces. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Specimen Number** & **Parameter Value** & **Ultimate Shear Load** & **Shear Strength \(\tau\)/kPa** & **Average Shear Strength \(\tau\)/kPa** \\ \hline \multirow{8}{*}{Number of iron hoops} & G1-1 (a) & & 1.651 & 32.474 & \multirow{8}{*}{33.975} \\  & G1-1 (b) & 1 & 1.762 & 34.657 & \multirow{8}{*}{58.424} \\  & G1-1 (c) & & 1.769 & 34.795 & \\ \cline{2-5}  & G1-2 (a) & & 2.896 & 56.962 & \multirow{8}{*}{58.424} \\  & G1-2 (b) & 2 & 3.004 & 59.086 & \\  & G1-2 (c) & & 3.011 & 59.224 & \\ \cline{2-5}  & G1-3 (a) & & 4.569 & 89.686 & \multirow{8}{*}{85.751} \\  & G1-3 (b) & 3 & 4.385 & 86.249 & \\ \cline{2-5}  & G1-3 (c) & & 4.125 & 81.135 & \\ \cline{2-5}  & G1-4 (a) & & 5.183 & 101.945 & \multirow{8}{*}{404.574} \\  & G1-4 (b) & 4 & 5.232 & 102.909 & \\ \cline{2-5}  & G1-4 (c) & & 5.535 & 108.869 & \\ \hline \multirow{8}{*}{Spacing of iron hoops} & G2-1 (a) & & 2.389 & 46.990 & \multirow{8}{*}{56.398} \\  & G2-1 (b) & 0 mm & 2.898 & 57.001 & \\ \cline{1-1}  & G2-1 (c) & & 3.315 & 65.203 & \\ \cline{1-1} \cline{2-5}  & G2-2 (a) & & 3.196 & 62.863 & \multirow{8}{*}{65.360} \\ \cline{1-1}  & G2-2 (b) & 170 mm & 3.309 & 65.085 & \\ \cline{1-1}  & G2-2 (c) & & 3.464 & 68.134 & \\ \cline{1-1} \cline{2-5}  & G2-3 (a) & & 2.896 & 56.962 & \multirow{8}{*}{58.424} \\ \cline{1-1}  & G2-3 (b) & 260 mm & 3.004 & 59.086 & \\ \cline{1-1}  & G2-3 (c) & & 3.011 & 59.224 & \\ \hline \multirow{8}{*}{Inclination angle} & G3-1 (a) & & 4.125 & 81.135 & \multirow{8}{*}{85.751} \\  & G3-1 (b) & 0° & 4.385 & 86.249 & \\ \cline{1-1}  & G3-1 (c) & & 4.569 & 89.868 & \\ \cline{1-1} \cline{2-5}  & G3-2 (a) & & 4.280 & 84.184 & \multirow{8}{*}{89.245} \\ \cline{1-1}  & G3-2 (c) & & 4.467 & 87.862 & \\ \cline{1-1} \cline{2-5}  & G3-2 (c) & & 4.865 & 95.690 & \\ \cline{1-1} \cline{2-5}  & G3-3 (a) & & 4.452 & 87.567 & \\ \cline{1-1} \cline{2-5}  & G3-3 (b) & 3.55° & 4.567 & 89.829 & 91.684 \\ \cline{1-1}  & G3-3 (c) & & 4.965 & 97.657 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Shear strength of the interfaces. Figure 11: Shear stress–displacement curves of different test groups. (**a**) The number of iron hoops; (**b**) the spacing of iron hoops; (**c**) the inclination angle of the interface. (1)  
It can be seen from Figure 11a that the shear stress of the interface increased with the increase in the number of iron hoops under the same displacement. At the beginning of loading, the shear stress of the interface increased linearly, but with the increase in the number of iron hoops, the shear strength of the interface did not increase by any multiple. By analyzing the data that are provided in Table 2, it was found that when the number of iron hoops \(n\) = 2, 3 and 4, the average shear strength of the interface was 1.72 times, 2.52 times and 3.10 times that of when the number of iron hoops \(n\) = 1, respectively, indicating that increasing the number of iron hoops can effectively improve the shear strength of the interface.