## 4 Discussion of Test Results  
### Envelope Curves  
An envelope curve is made up of the connection of the maximum lateral resistance of each loading cycle, and it is commonly used in the analysis of seismic performance, because it can intuitively reflect the seismic performance characteristics of the specimens. Figure 8a shows the envelope curves of all specimens, and the positive and negative direction envelope curves of the specimens are drawn in the same direction by taking their absolute values, as shown in Figure 8b. Figure 8a shows that the flange in the specimens enhances the lateral resistance of the specimens, and it also increases the initial stiffness of a specimen. Considering the influence of prestressing technology, it could be observed that the prestressing technology improves the initial stiffness of all specimens. Moreover,  
Figure 7: Load–displacement curves of the specimens: (**a**) BMF, (**b**) BMFP, (**c**) BMFT, (**d**) BMFTP.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Direction**} & \multicolumn{3}{c}{**Crack State**} & \multicolumn{3}{c}{**Max State**} & \multicolumn{3}{c}{**Final State**} \\ \cline{3-10}  & & **Q** & \(\triangle\) & **DR** & **Q** & \(\triangle\) & **DR** & **Q** & \(\triangle\) & **DR** \\  & & **(kN)** & **(mm)** & **(\%)** & **(kN)** & **(mm)** & **(\%)** & **(kN)** & **(mm)** & **(\%)** \\ \hline \multirow{2}{*}{**BMF**} & + & +80 & +2.3 & +0.13 & +170 & +16.0 & +0.89 & +115 & +64.0 & +3.55 \\  & – & \(-\)70 & \(-\)1.5 & \(-\)0.09 & \(-\)154 & \(-\)16.0 & \(-\)0.89 & \(-\)94 & \(-\)64.0 & \(-\)3.55 \\ \hline \multirow{2}{*}{BMFP} & + & +100 & +2.2 & +0.12 & +182 & +16.0 & +0.89 & +98 & +68.0 & +3.78 \\  & – & \(-\)100 & \(-\)2.3 & \(-\)0.13 & \(-\)178 & \(-\)16.0 & \(-\)0.89 & \(-\)147 & -68.0 & \(-\)3.78 \\ \cline{1-1}  & + & +100 & +1.6 & +0.08 & +262 & +17.5 & +0.97 & +154 & +52.5 & +2.92 \\ \cline{1-1}  & – & \(-\)110 & \(-\)2.0 & \(-\)0.14 & \(-\)249 & +17.5 & \(-\)0.97 & \(-\)168 & \(-\)52.5 & \(-\)2.92 \\ \cline{1-1}  & + & +110 & +1.2 & +0.07 & +268 & +17.5 & +0.97 & +150 & +52.5 & +2.92 \\ \cline{1-1}  & – & -100 & \(-\)1.1 & \(-\)0.06 & \(-\)236 & \(-\)10.0 & \(-\)0.55 & \(-\)150 & \(-\)52.5 & \(-\)2.92 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Summary of displacements and measured loads.  
the lateral resistance in both the positive and negative direction of the specimen BMFP is higher than that of the specimen BMF at the same displacement, and the curves of the specimen BMFP decline more slowly than those of the BMF specimen, as shown in Figure 8b. A similar situation is observed in BMFT in the positive direction. However, the negative direction comparison results between the BMFT and BMFTP shows that the lateral resistance of BMFTP was lower and reached at the smaller drift than BMFT. This was due to the early occurrence of a severe diagonal crack. In spite of this, the prestressing technology has a beneficial effect on the initial stiffness and declining trend of the lateral capacity of the specimens. Furthermore, the larger plateau on the envelop curves around the max lateral resistance were observed at specimens with prestressing technology than those without, as showed in Figures 7 and 8. This demonstrated that the specimen with prestressing technology can keep the lateral resistance unchanged in a larger displacement range when the specimen reached max lateral resistance, and this also proved that the specimen with prestressing technology had better ductility. Nonetheless, the influence of the prestressing technology on the seismic performance of the specimens is related to the failure mode of the specimens, and a greater amount of supplementary testing is needed to support the analytical conclusions.