# Experimental Study of Perfobond Rib Shear Connector under Lateral Force
## 4 Results Discussion
### Rib Hole Diameter  
The specimen groups BH-1 versus BH-3, BH-2 versus BH-4, and BH-5 versus BH-7 are discussed. BH-1 and BH-3 specimens both have the same reinforcement of 16 mm diameter and 20 mm thick steel plates, and the only difference is that BH-1 specimens have 60 mm diameter holes in the rib and BH-3 specimens have 75 mm diameter holes in the rib. Therefore, these two specimens are compared in Figure 6. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Specimen** & **Rib Holes Diameter** & **Transverse Rebar Diameter** & **Rib Thickness** & **Transverse Stress** & \(P_{u}\)**/**kN** & \(\delta_{u}\)**/mm** \\  & **(mm)** & **(mm)** & **(mm)** & **(MPa)** & **(MPa)** & **(\(\delta_{u}\)**/mm** \\ \hline BH-1 & 60 & 16 & 20 & 0 & 313.3 & 11.9 \\ BH-2 & 60 & 20 & 20 & 0 & 386.1 & 13.6 \\ BH-3 & 75 & 16 & 20 & 0 & 377.2 & 10.4 \\ BH-4 & 75 & 20 & 20 & 0 & 433.3 & 15.7 \\ BH-5 & 75 & 25 & 20 & 0 & 562.8 & 20.7 \\ BH-6A & 75 & 25 & 20 & 3 & 450.0 & 38.0 \\ BH-6 & 75 & 25 & 20 & 2 & 466.7 & 24.2 \\ BH-6P & 75 & 25 & 20 & 0 & 525.0 & 10.5 \\ BH-7 & 75 & 25 & 20 & 1 & 550.0 & 20.7 \\ BH-8 & 75 & 25 & 20 & \(-2\,^{*}\) & 672.2 & 35.4 \\ BH-9 & 75 & 25 & 24 & 0 & 688.9 & 29.6 \\ BH-10 & 90 & 25 & 20 & 0 & 625.0 & 32.0 \\ BH-11 & 90 & 28 & 20 & 0 & 669.4 & 33.1 \\ \hline \hline \end{tabular}
*: minus sign represents compressive forces.  
\end{table} 
Table 2: Push-out test results. Figure 5: Steel structure. As demonstrated in Figure 6, BH-3 specimens obviously have better ultimate resistance. While the specimen properties and the reinforcement steel bars are the same, the larger rib hole diameter in BH-3 specimen provides better shear resistance (about 20% improvement) by means of more concrete dowel action. The tested specimens were broken up and structural components were analyzed immediately after the tests to examine the deformation and failure modes, as demonstrated in Figures 7 and 8. In Figures 7 and 8, the BH 1-1 specimen had a reinforcement failure, whereas the BH 3-2 specimen had a concrete dowel failure. Therefore, the reinforcement bars in the BH 1-1 specimen had more deformation than the same reinforcement bars in the BH 3-2 specimen. This is because the smaller rib holes trapped a smaller amount of concrete to provide shear resistance and, consequently, the reinforcement bars have to deform more to provide shear resistance. On the other hand, if the openings in the steel ribs are large enough, like in the BH 3-2 specimen, the concrete dowel will provide the majority of the shear resistance and the concrete inside of the steel rib will fail before the reinforcement bars fail. Figure 6: Load–slip relationship. Figure 7: Rib plate and reinforcement of the BH 1-1 specimen after the test: (a) Deformation form of reinforcement; (b) Deformation form of rib plate. Similarly to BH-1 and BH-3 specimens, BH-2 and BH-4 specimens both have the same reinforcement diameter of 20 mm and thickness of 20 mm, but BH-2 specimens have 60 mm diameter rib holes, whereas BH-4 specimens have 75 mm diameter rib holes. The bond-slip relationships of these two specimens are plotted in Figure 9.  
Different from BH-1 and BH-3 specimens, BH-2 and BH-4 specimens almost have the same bond-slip relationship and resistance. This can be explained by considering the difference that BH-1 and BH-3 specimens have 16 mm diameter reinforcement bars, whereas BH-2 and BH-4 specimens have 20 mm diameter reinforcement bars. The larger diameter reinforcement bars would provide adequate shear resistance, such that the increase in the amount of concrete dowel action from the larger rib hole specimens will not play such an important role any more. More detailed analysis is made possible by examining the failure modes of the reinforcement bars, concrete dowel, and rib plates in Figures 10-12. Figure 8: Rib plate and reinforcement of the BH 3-2 specimen after the test: (**a**) Deformation form of reinforcement; (**b**) Deformation form of rib plate. Figure 9: Load–slip relationship.