# Shear Behavior of Superposed Perfobond Connectors Considering Lateral Constraints
## 3 Experimental Results
### Test Parameter Analysis  
#### 3.5.1 Shear Capacity  
It can be seen from the comparison between Specimens P-1 and P-4 in Figure 14a and Table 4 that when the number of holes changes from 1 to 2, the shear capacity of the connectors increases by 57.1%. However, the shear capacity of the double-hole connector is not a simple superposition of that of the single-hole one, owing to the stress complexity of multi-hole perfobond connectors.  
As shown in Figure 14, by combing this with the data in Table 4, when the concrete strength was increased from 42.82 to 72.20 MPa, the connectors without a perforating rebar and with 16 and 20-mm-diameter perforating rebars exhibited shear capacity increases of 48.0%, 32.0% and 12.0%, respectively. The concrete strength increase not only enhances the shear contribution of the concrete dowel itself but also the concrete wrapping force in the lateral constraint. Therefore, increasing the concrete strength can markedly improve the shear bearing capacities of perfobond connectors.  
Figure 14a,b separately depict the effects on the shear strength of the perforating rebar in connectors under two concrete strengths, corresponding to the data in Table 4. For C60 concrete grade perfobond connectors, the diameters of the perforating rebars in groups P-1, P-2 and P-3 were 16, 20 and 0 mm (no rebar), respectively; compared with the results of P-3, the shear capacity of P-1 and P-2 increased by 65.9% and 75.8%, respectively. For C40 concrete grade perfobond connectors, the diameters of the perforating rebars in groups CP-1, CP-2 and CP-3 were 20, 16 and 0 mm (no rebar). When the diameter of the perforating rebar increased from 0 to 16 and 20 mm, the shear capacities of Specimens CP-1 and CP-2 were 85.7% and 132.7% higher than that of CP-3. It can be concluded that increasing the diameter of the perforating steel bar not only enhances the shear pin force but also strengthens the lateral constraints of the concrete dowel along the axial direction, thereby improving the shear capacity.  
Figure 15 shows the impact of stirrup forms in the concrete slabs of perfobond connectors. The data in Table 4 indicate that the stirrup forms of Specimens SP-1, P-1 and NP-1 are segmental, conventional, and \"no stirrups,\" respectively. Compared with the shear capacities of NP-1, the results of SP-1 and P-1 increased by 60% and 34.1%, respectively. Clearly, the presence and increase of transverse reinforcement number enhances the lateral constraints on the concrete dowel, thereby significantly increasing the specimen's shear capacity.  
Figure 14: Effect of perforating rebar concrete grade on load–slip curves: (a) C60 concrete; (b) C40 concrete.  
Figure 16 compares the load-slip curves of connectors with different hole shapes and areas. The hole areas of Specimens P-5, LP-1 and HP-1 were all 2900 mm\({}^{2}\), 8.4-13.4% higher than that of Specim P-1, which had a 1963.5 mm\({}^{2}\) hole area. It can be concluded that the shear contribution of the concrete dowel mainly depends on the area of the concrete dowel. Therefore, the larger the opening area, the stronger the bearing capacity of the perfobond connector.  
Figure 16: Effect of hole shape and size on load–slip curves.  
Figure 15: Effect of stirrup form on load–slip curves.