## 4 Analysis of Experimental Results
### Flexural Strength and Ductility  
To test the reliability of the experimental results, this study compared the maximum flexural strength of specimens to the ACI318-19 code [21]. The equation from ACI318-19 is as follows.  
\[M_{n}=P_{n}\cdot e=0.85 ab\left(\frac{h}{2}-\frac{a}{2}\right)+\sum_{i=1}^{n} \left(A_{sif}f_{y}\right)\left(\frac{h}{2}-d_{i}\right) \tag{1}\]  
As shown in Table 2, the maximum flexural strength of specimens was, on average, 1.8 times the flexural strength of specimens predicted based on ACI318-19, and the coefficient of variation was approximately 3%, thus demonstrating the reliability of the experimental results. The configuration of transverse reinforcement, axial force ratio, and yield strength of transverse reinforcement did not affect the comparison between experimental results and analysis.  
Figure 8: Strain distributions of transverse reinforcement: (**a**) NH20; (**b**) NH30; (**c**) UH20; (**d**) UH30; (**e**) NS20; (**f**) NS30; (**g**) US20; (**h**) US30.  
This study calculated curvature at yield and maximum flexural strength using Equation (2) [22]. The curvature of specimens was obtained from the strain gauge bonded to the critical sections.  
\[\phi=\frac{\epsilon_{sc}+\epsilon_{st}}{d} \tag{2}\]  
As shown in Table 2 and Figure 9, the curvature ductility factor of specimens (\(\phi_{u}/\phi_{y}\)) was 1.1 to 2.2 times higher for the S-series than for the H-series, with the exception of US20. Here, \(\phi_{y}\) represents the curvature ductility at yield of longitudinal tension reinforcement, and \(\phi_{u}\) is the curvature ductility at flexural failure. The difference in curvature ductility factor in relation to configuration of transverse reinforcement was larger at higher axial force ratio, and the curvature ductility factor of US30, with high-strength transverse reinforcement, was 2.2 times greater than that of UH30. Compared to the H-series, the proposed S-series transverse reinforcement was thus found to exhibit outstanding ductility due to effective lateral confinement of core concrete and longitudinal reinforcement under high axial force, except the NS30 specimen. Such ductile behavior improved with increasing yield strength of transverse reinforcement.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Specimens**} & \multicolumn{2}{c}{\(V_{y,exp}\)} & \multicolumn{2}{c}{\(V_{x,exp}\)} & \multicolumn{2}{c}{\(M_{y,exp}\)} & \multicolumn{2}{c}{\(M_{w,exp}\)} & \multicolumn{2}{c}{\(M_{w,exp}\)} & \multicolumn{2}{c}{\(M_{w,exp}\)} & \multicolumn{2}{c}{\(M_{w,exp}\)} & \multicolumn{2}{c}{\(M_{w,exp}\)} \\  & \(V_{y,exp}\) & **Drift** & \(V_{x,exp}\) & **Drift** & \(M_{y,exp}\) & **Drift** & \(\phi_{y}\) & **Drift** & \(\phi_{u}\) & **Drift** & \(\phi_{y}\) & **Drift** & **Drift** \\  & **(kN-m)** & **angle (\(\Delta_{y}\))** & **(kN)** & **Angle (\(\Delta_{y}\))** & **(kN-m)** & **\(\phi_{y}\)** & **(kN-m)** & **\(\phi_{u}\)** & **Drift** & **Drift** & **Drift** \\ \hline NH20 & 81 & \(0.5\%\) & \(101\) & \(1.3\%\) & \(18.8\) mm & \(61\) & \(7.2\times 10^{-6}\) & \(76\) & \(2.2\times 10^{-5}\) & \(3.1\) & \(62\) & \(1.23\) \\ NH30 & 102 & 0.6\% & \(117\) & \(1.0\%\) & \(77\) & \(6.3\times 10^{-6}\) & \(88\) & \(2.2\times 10^{-5}\) & \(3.4\) & \(77\) & \(1.14\) \\  & & (8.6 mm) & \(105\) & \(1.3\%\) & \(68\) & \(6.0\times 10^{-6}\) & \(79\) & \(4.1\times 10^{-5}\) & \(6.8\) & \(62\) & \(1.27\) \\ UH20 & 90 & \(0.5\%\) & \(121\) & \(1.1\%\) & \(77\) & \(5.9\times 10^{-6}\) & \(91\) & \(2.1\times 10^{-5}\) & \(3.4\) & \(77\) & \(1.18\) \\ UH30 & 102 & \(0.5\%\) & \(121\) & \(17.0\) mm & \(77\) & \(5.9\times 10^{-6}\) & \(91\) & \(2.1\times 10^{-5}\) & \(3.4\) & \(77\) & \(1.18\) \\ NS20 & 84 & \(0.5\%\) & \(99\) & \(1.2\%\) & \(63\) & \(3.1\times 10^{-6}\) & \(74\) & \(1.4\times 10^{-5}\) & \(3.8\) & \(62\)