# Seismic Performance of Ductile Column with Rectangular Hollow Cross-Section in RC Building
## 2 Experimental Program
### Specim Details  
Figure 1 shows the specimen details, and Table 1 summarizes the specimen properties. Material characteristics are listed in Tables 2 and 3. The specimens are about 1/3 scale, assuming columns at the lower level of a high-rise residential building (about 20-story). Per the AIJ standard [24], more than 4 longitudinal bars should be placed in RC columns, and the reinforcement ratio should be more than 0.8%. For the transverse reinforcement, the reinforcement ratio should be larger than 0.2%, and its spacing should be less than 100 mm, within the range from column ends to 1.5\(D\), where \(D\) is the cross-section height of the column. 135 or 180 degree hooks are also required for transverse reinforcement. Figure 1: Specim details: (a) N-series; (b) S-series. The specimens were scaled down and designed according to the AIJ standard. The hollow parts consist of square and taper sections, as can be seen in Figure 1, to reduce the stress concentration. The hollow section ratio (\(r\)) of the specimen was set around 0.8, as shown in Table 1. For the N-series with the axial force ratio of 0.16, two specimens were fabricated, which are a solid-sectioned specimen (CM1) and a hollow-sectioned specimen (CM2). In the S-series with the axial force ratio around 0.3, three specimens were fabricated: one solid-sectioned specimen (CM11) and two hollow-sectioned specimens (CM12 and CM13). The difference between the two hollow-sectioned specimens was the tip position of taper sections. In CM12, the tip position started from both column ends. However, in CM13, the tip position was planned at 0.75\(D\) away from both column ends. As explained later, CM13 was planned after the experiment of CM12, because of an unexpected failure, a concrete compressive failure, had developed in the plastic hinge region near the column end of CM12. The higher strength concrete was used for hollow-sectioned specimens so that the axial force ratios of solid and hollow-sectioned specimens became almost the same. The concrete mix proportion is shown in Table 4, where the water-cement ratio of solid-sectioned specimens was 36% and that of hollow-sectioned specimens was 28%. The concrete mix proportion, generally employed for high-rise building construction in Japan, was used. Although the hollow section reduces the moment of inertia and thus the flexural stiffness, higher strength concrete usually has a higher Young's modulus. As a result, hollow-sectioned specimens have an equivalent flexural stiffness to solid-sectioned specimens. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Series**} & \multirow{2}{*}{**Specimen**} & \multicolumn{2}{c}{**Cross-Section**} & \multirow{2}{*}{**Tip Position**} & \multirow{2}{*}{**Longitudinal**} & \multirow{2}{*}{**Transverse**} & \multirow{2}{*}{**Axial Force (kN)**} \\  & & & **Gold/ Hollow** & & **of Taper *b** & & **Reinforcement** & **Reinforcement** \\ \hline \multirow{2}{*}{N} & CM1 & solid & 1.00 & & 8-D13 & U9.0\#30 & \multirow{2}{*}{1400 (0.16)} \\ \cline{2-2} \cline{6-6}  & CM2 & hollow & 0.81 & 0\(D\) & (SD490) & (SBPD1275) & & \\ \hline \multirow{2}{*}{S} & CM11 & solid & 1.00 & & & & 1800 (0.28) \\ \cline{2-2} \cline{6-6}  & CM12 & & & 0\(D\) & (SD490) & D6 \(\times\) 2@30 & \multirow{2}{*}{1800 (0.30)} \\ \cline{2-2} \cline{6-6}  & CM13 & & & 0.75\(D\) & & & 1800 (0.28) \\ \hline \hline \end{tabular}  
* \(r\): Hollow section ratio.
* Distance from column end.  
\end{table} 
Table 1: Specim properties.