# Behavior of an Internally Confined Hollow Reinforced Concrete Column with a Polygonal Cross-Section
## 3 Verification
### Behavior of Polygonal ICH RC According to Parameters
#### 3.2.1 Rectangular Cross-Section  
The behavior of the rectangular ICH RC columns was analyzed according to the change in concrete strength and inner tube thickness. Table 2 shows the material properties of the concrete and reinforcements used in the representative section and column members, as well as information on columns. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Cross-Section** & \multicolumn{2}{c}{**Properties**} \\ \hline  & \(d_{h}\)(mm) & 13 \\ \cline{2-3}  & \(d_{v}\)(mm) & 19 \\ \cline{2-3}  & \(s\)(mm) & 50 \\ \cline{2-3}  & \(f_{c}^{\prime}\)(MPa) & 20, 25, 30 \\ \cline{2-3}  & \(t\)(mm) & 1, 2, 4, 6 \\ \cline{2-3}  & \(f_{yh}\)(MPa) & 237.6 \\ \cline{2-3}  & \(f_{yv}\)(MPa) & 237.6 \\ \cline{2-3}  & \(H\)(mm) & 2500 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cross-section and specification of the rectangular ICH RC column. Figure 10: Results of comparisons between references and analyses. * Analysis of the axial load-bending moment  
Figures 11 and 12 show the results of axial load-bending moment analysis of the rectangular ICH RC columns according to the parameters. Since the ICH RC columns of the rectangular cross-section have different lengths in transverse (\(x\)) and longitudinal (\(y\)) directions, the results of each analysis are separately derived by the applied load directions. In addition to the cases of concrete strengths of values 20, 25, and 30 MPa, shown in Table 2 above, the case where the 20 MPa concrete is not confined is analyzed for confirming the confining effect. The inner tube thickness of the cases changing the strength of the concrete is set to 3 mm, and the concrete strength of the case changing the inner tube is 25 MPa. It is assumed that there is no initial axial load. The results of the P-M interaction above show that the resistance against the axial force and bending moment increases in both directions when the confining effect of concrete occurs. The maximum axial load and bending moment of confining concrete in the \(x\) direction are found to be 126% and 133% of the unconfined concrete, respectively. In addition, as the concrete strength increases, the maximum axial load and bending moment increase as well. In the case of varying inner tube thickness, it is confirmed that the resistance capacity of the rectangular ICH RC column with respect to the maximum axial force and bending moment also increases in both directions as the inner tube thickness increases. In the directional comparison of the ICH RC columns with the rectangular cross-section, it can be found that the maximum bending moment with respect to the direction of the longer length in the two directions is larger. * Analysis of the lateral load-displacement  
Figure 11: P-M interaction curves according to concrete strength (rectangular cross-section). Figure 12: P-M interaction curves according to the inner tube thickness (rectangular cross-section). Figures 13 and 14 show the results of the lateral load-displacement analysis of the rectangular ICH RC columns according to the parameters. As with the P-M interaction analysis, the analytical results for each direction are separately derived. In the lateral load-displacement analysis, according to the change in the concrete strength, the lateral load increases in both directions when the confining effect of concrete occurs. The maximum lateral load of the confined 20 MPa concrete is 150% and 140% of the unconfined 20 MPa concrete in \(x\) and \(y\) directions, respectively. In addition, an increase in the maximum lateral load of the rectangular ICH RC columns increases the concrete strength. In the cases of varying the inner tube thickness, the maximum lateral force is increased in both \(x\) and \(y\) directions as the thickness is increased. The minimum inner tube thickness for avoiding the yield failure and bending failure is calculated as 1.89 and 0.47 mm, respectively. As shown in Figure 14, when the inner tube thickness is 1 mm, the lateral force of the column decreases sharply after a certain lateral displacement.