# Flexural Behavior of Reinforced Concrete Beams Retrofitted with Modularized Steel Plates
## 6 Conclusions  
The purpose of this study is to propose and examine a modularized steel plate retrofitting method resulting in improved structural performance and constructability. The details of retrofitting method were proposed based on the finite element analysis. The flexural test was conducted to evaluate the structural performance of concrete beams retrofitted with the proposed method. The main conclusions obtained from the study are as follows:  
1. In this study, the details and components of the modularized retrofitting method are proposed, with \(Z\)-shaped side plates, L-shaped lower plate, and bottom plate with vertical grid. Finite element analyses were carried out to investigate the effect of the bottom plate thickness, L-shaped lower plate thickness, Z-shaped side plate thickness, and the bolt spacing on the stress distribution. Details of the modularized steel plate retrofitting system were proposed based on the analysis results.
2. The maximum load increased as the thickness of the bottom plate increased, but it was found to be relatively lacking in ductility. Although the number of vertical grid did not significantly affect stiffness, the increase in that number improved the ductility. In addition, the flexural performance increased by about 1.17 times, depending on the presence of the vertical grid. The vertical grid attached to the bottom plate increased the confinement effect of the mortar and reduced spalling by acting as a flexural reinforcement.
3. The ductility and energy dissipation capabilities were compared and analyzed. Compared to non-retrofitted reinforced concrete beams, the ductility capacity increased by about 2.5 times, and the energy dissipation capacity increased by about seven times. This confirms that the application of the proposed retrofitting method can improve the structural performance of existing concrete members.
4. The experiment in this paper focused on the evaluation of the flexural capacity of retrofitted concrete beams. Further experimental research is needed on the shear behavior of concrete beams retrofitted with modularized steel plates. Moreover, a finite element model that can predict structural capacity is required for the design stage.  
Figure 18: Comparison between the numerical and the experimental results of load versus midspan deflection.  
**Author Contributions:** Conceptualization, M.S.K. and Y.H.L.; methodology, M.S.K.; validation, Y.H.L.; formal analysis, M.S.K.; investigation, M.S.K. and Y.H.L.; writing--original draft preparation, M.S.K.; writing--review and editing, Y.H.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2019R1A2C1090033).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The results presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.