## 5 Conclusions  
This paper presents experimental and analytical research on retrofitted steel angle members under compression. Some conclusions can be drawn within the scope of the current study:  
1. Three failure modes of flexural-buckling mode, flexural-torsional buckling mode, and local buckling mode may occur for built-up steel angle members under axial compression. The width of the reinforcement plate has a significant impact on the failure mode. Failure of the local buckling mode can be avoided by reducing the clamp distance to the member end. 2. The bearing capacity of the reinforced steel angles is increased by 39-174%, indicating that the reinforcement effect of the proposed non-destructive method is significant. The increment ratio of bearing capacity is positively correlated with the slenderness \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{**Height/mm**} & \multirow{2}{*}{\begin{tabular}{c} **Effective** \\ **Length/mm** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Width of** \\ **Reinforcement** \\ **Plate/mm** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Tested** \\ **Result/kN** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Calculated** \\ **Result/kN** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Tested/Calculated** \\ **Result/kN** \\ \end{tabular} } \\ \hline LR1-1-1 & 790 & 1170 & 137 & 437.18 & 375.71 & 1.164 \\ LR1-2-1 & 1422 & 1802 & 137 & 345.33 & 322.85 & 1.070 \\ LR1-2-2 & 1422 & 1802 & 137 & 339.45 & 322.85 & 1.051 \\ LR1-3-1 & 1738 & 2118 & 137 & 312.26 & 291.42 & 1.072 \\ LR1-3-2 & 1738 & 2118 & 137 & 306.12 & 291.42 & 1.050 \\ LR1-3-3 & 1738 & 2118 & 137 & 303.45 & 291.42 & 1.041 \\ \hline \end{tabular}
\end{table} 
Table 6: Prediction result of method in AISC 360-16. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{**Height/mm**} & \multirow{2}{*}{\begin{tabular}{c} **Effective** \\ **Length/mm** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Width of** \\ **Reinforcement** \\ **Plate/mm** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Tested** \\ **Result/kN** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Calculated** \\ **Result/kN** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Tested/Calculated** \\ **Result/kN** \\ \end{tabular} } \\ \hline LR1-1-1 & 790 & 1170 & 137 & 437.18 & 248.59 & 1.759 \\ LR1-2-1 & 1422 & 1802 & 137 & 345.33 & 217.87 & 1.585 \\ LR1-2-2 & 1422 & 1802 & 137 & 339.45 & 217.87 & 1.558 \\ LR1-3-1 & 1738 & 2118 & 137 & 312.26 & 198.30 & 1.575 \\ LR1-3-2 & 1738 & 2118 & 137 & 306.12 & 198.30 & 1.544 \\ LR1-3-3 & 1738 & 2118 & 137 & 303.45 & 198.30 & 1.530 \\ \hline \end{tabular}
\end{table} 
Table 5: Prediction result of method in GB 50017.  
ratio, reflecting that the reinforcement method is more effective for slender members. The clamp types and clamp distance behave a slight effect on bearing capacity. 3. By analyzing the reinforcement mechanism of reinforced angle steel, it indicates that the reinforcement plate is not subjected to axial compression; namely, it does not participate in the distribution of vertical load and only balances the secondary bending moment through the squeezing force with the steel angle. 4. A simplified mechanical model of reinforced steel angle members (built-up steel angles) is established under bending instability. Moreover, a design method based on existing codes is proposed to predict the flexural-torsional capacity by considering the effect of the reinforcement plate. The verification result indicates that the design method based on AISC 360-16 has better agreement with the experimental results and could be used as a basis for calculating the flexural-torsional bearing capacity of reinforced steel angles. Conceptualization, J.L. and Q.S. ; methodology, J.L. and X.W. ; validation, J.L. and B.Y. ; data curation, J.L. and J.W. ; writing--original draft preparation, J.L. ; writing--review and editing, Q.S.