## 3 The Shear Sliding Test of the Composite Timber Column's Interface
### Test Results and Discussion
#### 3.2.2 Parameter Analysis
The average shear strength of G1-3 (\(n\) = 3) is the sum of that of the G1-1 (\(n\) = 1) and G1-2 (\(n\) = 2), with an error of 7.8%. Therefore, the specimen with 3 iron hoops can be regarded as the superposition of the specimen with 1 and 2 iron hoops. The reason for the above is that the effect of the iron hoops on the interface is related to its position. When the spacing of the iron hoops is within a certain range, the effect of each iron hoop can be superimposed independently. When the spacing exceeds this range, the effect of the iron hoops on the interface will not increase. Figure 12a shows that the shear strength of the interface is positively correlated with the number of iron hoops. When there is a greater number of iron hoops there is a greater level of shear strength in the interface. The fitting equation between the number of iron hoops and the shear strength of the interface can be expressed by Equation (25). \[\tau=10.9+23.912n \tag{25}\]  
where \(\tau\) is the shear strength of the interface and \(n\) is the number of iron hoops. (2)  
According to the data in Table 2, when the iron hoop spacing d = 170 mm (i.e., G2-2), the average shear strength of the interface increased by 15.9% compared with that of G2-1 (d = 0 mm), while that of G2-3 (d = 260 mm) increased only by 3.6% compared with G2-1 (d = 0 mm). This indicates that, when the spacing is less than 170 mm, the effect of the iron hoops on the interface increases with the increase in the iron hoops' spacing, but it is opposite when the spacing is more than 170 mm. Compared with G1-1, the average shear strength of the interface of G2-1 (d = 0 mm), G2-2 (d = 170 mm) and G2-3 (d = 260 mm) had increased by 66.0%, 92.4% and 72.0%, respectively. When the iron hoop spacing d = 170 mm (G2-2) was used, the shear strength of the interface increased the most, this is a result which  
Figure 12: Fitting curves of shear strength. (**a**) The number of iron hoops; (**b**) the inclination angle of the interface. can be regarded as the most reasonable arrangement of the iron hoops. The reason of this is that the iron hoop is too close to the edge of the wooden column when the iron hoop spacing exceeds 170 mm and the constraint range of the iron hoops on the interface is narrower than the width of the side block, which leads to the decline of the constraint effect of the iron hoops. Therefore, it can be considered that there is a most reasonable spacing of the iron hoops and that the shear strength of the interface cannot be effectively improved when the spacing is too large or too small. The Effect of the Inclination Angle of the Interface  
The shear stress-displacement curves of the interface under different inclination angles are shown in Figure 11c. Figure 11c demonstrates that, under the same displacement, the shear stress of the interfaces of G3-2 (\(\theta\) = 2.79\({}^{\circ}\)) and G3-3 (\(\theta\) = 3.55\({}^{\circ}\)) were greater than that of G3-1 (\(\theta\) = 0\({}^{\circ}\)), indicating that the existence of the inclination angle increases the shear strength of an interface. Figure 12b pinpoints that the shear strength is positively correlated with the inclination angle of the interface. The shear strength of the interface increases with the increase in the inclination angle. The fitting equation between the inclination angle and the shear strength of the interface can be expressed by Equation (26). \[\tau=85.603+93.987\theta \tag{26}\]  
where \(\theta\) is the inclination angle of the interface.