# Seismic Performance of Ductile Column with Rectangular Hollow Cross-Section in RC Building
## 3 Experiment Results
### Failure Process and Hysteresis Curve of S-Series (\(\eta\) = 0.3)  
In the solid-sectioned CM11, with relatively high axial force, the flexural cracks were found at \(R\) = +0.1%, and their propagation was initiated from this drift angle. At around 1.0% loading, a flexural-shear crack developed, and the maximum strength was recorded with the cover concrete spalling near the column ends. During +1.0% loading, the yielding of compression reinforcement was found at \(R\) = +0.66%, and that of tensile reinforcement was confirmed at \(R\) = +1.0%. After that, the load-bearing capacity seemed to gradually decrease, and at the final drift peak of +5.0%, it dropped to 67% of the maximum strength. However, it should be noted that such a reduction in strength can be attributed to the \(P\)-\(\Delta\) effect, which is plotted by a dot-line in Figure 6, and it was not caused by structural performance deterioration. The hollow-sectioned CM12 also had a flexural crack during +0.1% loading, and its initial stiffness was found to be substantially equivalent to that of the solid-sectioned CM11. Similar to CM11, the compression yielding of longitudinal reinforcement was found at \(R\) = +0.66%, and the maximum load was recorded at \(R\) = +0.91% with the covering concrete spalling. In addition, the yielding of tensile reinforcement was observed at \(R\) = +0.95% during +1.0% loading, and then the maximum strength at the negative loading was recorded at \(R\) = \(-0.90\%\). Although the total number of cracks was found to be slightly more than that for CM11, no significant change was observed in the hysteresis curve until the peak drift angle of the maximum strength. Nevertheless, at the second loading cycle of \(R\) = +2.0%, the sudden concrete crushing developed intensively at the position around 0.5\(D\) from the top end, where the hollow sections exist, and then the load-bearing capacity abruptly reduced, as shown in Figure 6. The ratio of calculations to experiments of the maximum strength was 1.00-1.01, and it showed good accuracy in the case of relatively high axial force. As explained, CM12 had almost the same load-deflection relationship as the solid-sectioned CM11 until the development of flexural failure. However, after that, the brittle failure was followed by sudden concrete compressive failure near the plastic hinge region, observed as approximately 0.5\(D\), and at this time, the shear reinforcement yielding did not occur. Because severe concrete crushing, which accelerated the partial loss of the cross-sectional area, developed at the flange of the hollow section, the damaged hollow section could not afford to sustain the high axial compression force. From this observation, the application of the hollow-sectioned column is found to have an important relationship with the compressive axial force level; therefore, the appropriate application scope will be also explained in the next section. Therefore, the hollow sectioned CM13 was designed to prevent such unexpected compressive failure under a high compressive axial force by replacing the tip position of taper sections at 0.75\(D\) away from both column ends, as mentioned earlier. During +0.1% loading, CM13 also had flexural cracks exhibiting, an equivalent initial stiffness with CM11 and CM12. Until 1.0% loading, the total number of cracks was found to be less than that for CM12, and the hysteresis curve was almost the same as for the solid-sectioned CM11. During +1.0% loading, the longitudinal reinforcement yielded, and the maximum strength was recorded at \(R\) = +0.96%, along with the cover concrete spalling near the column ends. After that, at \(R\) = \(-1.00\%\), the lateral strength reached its maximum at the negative loading. Although the load-bearing capacity seemed to gradually decrease due to the \(P\)-\(\Delta\) effect, 78% of the maximum strength was kept until the final drift peak of \(R\) = +5.0%, which is extremely large deformation.