## 4 Test Results Analysis  
### Hysteretic Behavior  
The characteristic points (namely, the yielding load \(P_{\mathrm{y}}\) and yielding displacement \(\Delta_{\mathrm{y}}\), peak load \(P_{\mathrm{u}}\) and peak displacement \(\Delta_{\mathrm{u}}\), ultimate load \(P_{\mathrm{f}}\) and ultimate displacement \(\Delta_{\mathrm{f}}\) ) of the specimens, which were defined on the skeleton curve, were listed in Table 2. The yield load \(P_{\mathrm{y}}\) corresponding to the yield displacement \(\Delta_{\mathrm{y}}\) was defined based on the criteria for equivalent elastic-plastic energy absorption. The peak displacement \(\Delta_{\mathrm{u}}\) referring to the peak load \(P_{u}\) was the maximum lateral load. The failure load \(P_{\mathrm{f}}\) was defined as the post-peak displacement corresponding to 85% of the peak strength. The hysteretic responses of torsion-twist and load-displacement for the specimens are shown in Figure 7a,b, respectively. The following observations could be summarized:  
(1) Both the two hysteretic curves of the torsion-twist and the load-displacement exhibited an \"S\" shape. Due to the asymmetry of section, the asymmetry of the hysteresis curves were observed. Before cracking, the specimen exhibited elastic behavior and the hysteresis curve was narrow with little residual deformation after unloading. After cracking, a drop of secant stiffness was observed and the envelope area increased. After the peak load, the slope of secant stiffness dropped rapidly. (2) Comparing with RCL-1 (_T/M_ = 0.36), RCL-5 (_T/M_ = 0.28), and RCL-6 (_T/M_ = 0.17), it was noted that _T/M_ ratio had a significant effect on the hysteretic behavior. For the relationship of torsion-twist, the slope of unloading stiffness and the degree of pinching increased with the increase of _T/M_ ratio. This was attributed to the increase of _T/M_ ratio that change the failure mode from the bending failure to torsion-shear failure. Therefore, the stiffness dropped rapidly and the pinching in the loops was relatively high. The plastic deformation of concrete also increases the ultimate rotation angle and hysteretic curve area. For hysteretic curves of lateral load-displacement, with the increase of _T/M_ ratio, ultimate bearing capacity and ductility decrease. In addition, the hysteretic loops of the RCL-2 (_T/M_ = 0) was plumper than these specimens under combined loading including torsion. It is indicated that the torsion had an adverse effect on seismic performance. (3) Axial compression ratio was another important effect on hysteretic behavior. In particular, with the decrease of the axial compression ratio, the twist increased and the flexural capacity reduced while the bending energy consumption and ductility increase slightly. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{**Loaling**} & \multicolumn{4}{c}{**Nield Point**} & \multicolumn{4}{c}{**Peak Point**} & \multicolumn{4}{c}{**Ultimate Point**} & \multirow{2}{*}{_Yo/\%_} & \multirow{2}{*}{_Yo/\%_} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} & \multirow{2}{*}{_\mu \(\mu\)_\#_0/0} \\ \cline{3-14}  & Direction & \(\mathbf{T_{3}}\) & \(\mathbf{\theta_{3}}\) & \(\mathbf{P_{5}}\) & \(\mathbf{\Delta_{y}}\) & \(\mathbf{T_{5}}\) & \(\mathbf{\theta_{6}}  
curve, are listed in Table 2. In the following part, all the comparsion of the characteristic value from Table 2 referred to the average value. (1) The skeleton curves were similar in shape. All the skeleton curves consisted of linear elastic stage, elastic-plastic stage, and descending stage. (2) It is noted that the specimen with bending failure exhibited a high bearing capacity and ductility. Besides, with the increase of _T/M_ ratio, the skeleton curve dropped gently in the descending stage.