# Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method
## 5 Conclusions  
This study proposed a collaborative method to retrofit an RC beam by using a CFRP plate, a steel plate, and angle steel. A monotonic four-point bending test was conducted on six specimens to investigate the strengthening effect of the proposed method. The major conclusions are summarized as follows:  
(1) The three types of retrofitting materials can cooperate with each other during the whole process. The retrofitted beam demonstrates a larger load-bearing capacity and deformation capacity than those of the standard beam in terms of aspects such as crack resistance and durability failure. The crack load and ultimate load are improved up to \(84.9\%\) and \(4.41\) times, respectively.  
(2) The gap in the adhesive layer and the CFRP plate tends to delay the function of the steel unit. After the deformation of the beam increases to a certain extent, the steel plate and angle steel function with regard to both the load bearing and the anchorage of the CFRP plate. Finally, the CFRP plate contributes more to the ultimate bearing capacity after the steel units yield; thus, it can be considered as safety storage.  
(3) The retrofitting materials are recommended for continuous use, as the collaborative method can achieve the best improvement by limiting crack development and transferring the load from the midspan to the beam ends. Although the separated steel plate can enhance the flexural performance, it mainly functions as an anchorage of the CFRP plate and tends to concentrate more load at the midspan.  
(4) Based on the deformation capacity, a prediction method is proposed to calculate the ultimate flexural capacity of the beam retrofitted using the collaborative method. As the average error between the calculated and the experimental result is \(4.03\%\), the prediction can be regarded as valid.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Specimen No.** & \(M_{\bf u,exp}\) **(kN\(\cdot\)m)** & \(M_{\bf u,pre}\) **(kN\(\cdot\)m)** & **Error (\%)** \\ \hline L2-A & \(217.10\) & \(210.11\) & \(-3.22\) \\ L3-C & \(170.61\) & \(176.96\) & \(3.72\) \\ L4-Sf-A & \(320.00\) & \(297.31\) & \(-7.09\) \\ L5-C-St-A & \(340.57\) & \(334.32\) & \(-1.84\) \\ L6-C-Ss-A & \(298.42\) & \(285.66\) & \(-4.28\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Prediction verification.  
**Author Contributions:** Conceptualization, Y.W. and W.X.; methodology, Y.L. and Y.W.; formal analysis, Y.L.; investigation, Y.L., Z.G. and K.Z.; writing--original draft preparation, Y.L.; writing--review and editing, Y.W., Z.G. and K.Z.; supervision, Y.W. and W.X.; project administration, Y.W.; funding acquisition, Y.W. and Y.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China (Grant Nos. 52378244 and 52308257), the Natural Science Foundation of Jiangsu Province (Grant Nos. BK20231293 and BK2023039), and the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (Grant No. 23 KJB560019).  
**Data Availability Statement:** The original contributions presented in the study are included in the article, and further inquiries can be directed to the corresponding authors.  
**Acknowledgments:** The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China, Natural Science Foundation of Jiangsu Province, and Natural Science Foundation of the Higher Education Institutions of Jiangsu Province.  
**Conflicts of Interest:** The authors declare no conflicts of interest.