## 3 Experimental Results  
### Overall Behavior and Failure Modes  
The failure modes of all the specimens can be classified into two types. One is the steel bar connector failure and the other is steel bar rupture failure. For the specimens of steel bar connector failure, take specimen M4-D12-7.5d (No. 2 specimen) as an example. At the early stage of loading, few visible cracks are generated at the concrete surface and the specimens undergo the elastic deformation stage. As the load increases, the steel bars yield and the specimens change from elastic deformation stage into elastic-plastic deformation stage. After that, the diagonal cracks are generated between the two heads among all the specimens and part of the specimens generate the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & \(f_{cu}\) **(MPa)** & \(f_{e}\) **(MPa)** & \(f_{y}\) **(MPa)** & \(f_{u}\) **(MPa)** & \(E_{c}\) **or \(E_{s}\)** & \(v\) \\ \hline C30 concrete & 31.9 & 19.7 & / & / & 28.9 & 0.212 \\ \(\Phi\)6 stirrup & / & / & 463.4 & 613.7 & 209.2 & / \\ \(\Phi\)10 stirrup & / & / & 472.5 & 637.0 & 195.4 & / \\ \(\Phi\)12 headed bar & / & / & 448.6 & 617.2 & 199.0 & / \\ Head steel plate & / & / & 250.7 & 407.3 & 209.3 & 0.282 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of concrete and steel. Figure 5: Measurement system (**a**) Measurement of slip; (**b**) Strain gauge layout. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Grade** & **Water to** & **Water** & **Cement** & **Fine Aggregate** & **Coarse** & **Superplasticizer** & **Fly Ash** \\
**Binder Ratio** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & **Aggregate** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** \\ \hline C30 & 0.40 & 153 & 300 & 710 & 1110 & 7.6 & 80 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Concrete mixture ratio. horizontal cracks which develop from the edge side to the inner side of the concrete. It should be noted that the diagonal cracks may generate at a single side of the specimens and it results in the uneven bar stress among the four headed bars, which can lead to the rotation of specimens consequently. In addition, since the four headed bars cannot yield simultaneously, it can also result in uneven bar stress among the four headed bars as well as the undesirable rotation of specimens. As it reaches peak load, the diagonal and horizontal cracks are developed and the cracks are clearly visible at the concrete surface (Figure 6). During the post-peak stage, new vertical cracks are generated and they develop fast along with the rotation of the specimens becoming obvious and the stress nonuniformity of the headed bars also increases rapidly (Figure 7). Besides, for the specimens without horizontal cracks before, horizontal cracks are generated and develop fast with the increase in rotation of the specimens. It can be inferred that the horizontal cracks are generated due to the rotation of the specimens. Additionally, multiple cracks are generated and develop fast at the side of the concrete surface and eventually, the side concrete blows out. It should be noted that while CHBC is applied in the structure members such as shear walls or beams, the rotation due to the uneven bar stress is limited by the concrete and reinforcement inside the structure members and the mentioned side concrete blow-out failure can be prohibited. Loading ceases before the harmful rotation of the specimens is too large and any loading unsafety is possible. For the specimens of steel-bar rupture failure, take specimen M8-D12-7.5d (No. 6 specimen) as an example. Similarly, few cracks generate before the headed bars are yielding. During the hardening deformation stage, diagonal cracks are observed at the concrete surface between the two heads and part of the specimens generate horizontal cracks (Figure 8). As it reaches peak load, the headed bars stresses are closed to ultimate tensile strength and one of the headed bars ruptures soon after the local necking of the steel bar is evident.