# Seismic Performance of Ductile Column with Rectangular Hollow Cross-Section in RC Building
## 3 Experiment Results
### Failure Process and Hysteresis Curve of N-Series (\(\eta\) = 0.16)  
As shown in Figure 6, in the solid-sectioned CM1, the flexural cracks occurred at \(R\) = +0.1%, following which stiffness degradation was observed. After that, the yielding of tensile reinforcement was found at \(R\) = +0.76%, and that of compression reinforcement was confirmed at \(R\) = +0.95%. A shear crack was observed at around the peak drift angle of \(R\) = +1.0%, and the maximum strength was recorded with the spalling-off of cover concrete near the column ends. At the loading stage of \(R\) = \(-\)1.0%, an axial force that was about 10% larger than expected was introduced to the specimen; therefore, the peak strength at the negative loading was higher than the positive loading. After the maximum strength, no significant strength reduction was observed up to +5.0% loading. The hollow-sectioned CM2 also had an initial stiffness which was substantially equivalent to that of the solid-sectioned CM1, since higher strength concrete was employed in CM2. Flexural cracks occurred at \(R\) = +0.1% and, at 0.5% loading, a flexural-shear crack occurred in the tapered section near the column ends. Although a shear crack was observed earlier than CM1, there was no significant change in the load-deflection curve. At the loading stage of \(R\) = +0.82%, the tensile reinforcement yielded, and at \(R\) = \(-\)0.94%, the compression reinforcement yielded, and the yielding timing of the longitudinal reinforcement was found almost the same as CM1. The cover concrete was then slightly crushed near \(R\) = 1.0% and the maximum strength was recorded at \(R\) = +1.0% and \(-\)1.42%. After that, until the extremely large deformation state of \(R\) = +5.0%, no significant strength degradation was generated. The residual strength was maintained as larger than 80% of the maximum strength, and almost the same hysteresis curve as for CM1 was exhibited. As mentioned earlier, the maximum flexural strength (\(Q_{mu}\)) was calculated based on the cross-sectional analysis. As a result, the ratios of calculations to experiments of the maximum strength were found in the range of 1.03\(\sim\)1.06, and it was found that the ultimate flexural strength could be accurately evaluated from the plane-section assumption even in the case of hollow cross-sections. As can be seen in Figure 7, comparing the solid-sectioned CM1 and the hollow-sectioned CM2, flexural and shear cracks were likely to concentrate on the region from the column ends to 1.0\(D\) in both specimens, and the maximum flexural crack width occurred in the column ends. In CM1 and CM2, the maximum flexural crack widths at the loading peak were about 1.7 mm and 2.0 mm, and the maximum residual flexural crack widths were about 0.45 mm and 0.35 mm, respectively. Also, the maximum shear crack width was observed within 1.0\(D\) from the column ends, and there was no significant difference in both specimens. The crack numbers, as well as the cracks developing patterns, in both specimens, were found to be almost the same regardless of the presence of hollow sections. It should be noted that, in CM2, some vertical cracks were observed in the hollow-sectioned parts, which were considered to be induced by the axial compression force, as can be seen in Figure 7. However, their widths, less than 0.03 mm, were extremely small until the final loading peak, and they almost closed at the unloading stage.