# Strengthening of RC Beams with CFC Panels for Improving Impact Resistance
## 7 Conclusions  
In this study, both experimental and numerical analyses were carried out to investigate the reinforcement effect of applying CFC panels to improve the impact resistance of RC beams subjected to impact loading. For the analytical study, an analysis program using virtual particles that takes into account the characteristics of the adhesive in the SPH method was developed, and its accuracy was verified by comparing it with the results of the impact experiments. Subsequently, a parametric study was conducted using a validated analytical program to examine the relationship between the method of reinforcement with CFC panels and impact resistance performance. The main results of this study are summarized as follows. In the impact test, flexural cracks were observed in all the specimens; however, it was confirmed that reinforcement with the CFC panels significantly improved the impact resistance of the beams and suppressed the propagation of cracks throughout the beams. The strengthened specimens performed better in terms of recovery capability compared to the unstrengthened specimens, which was apparent after the first impact. The full bottom strengthening and the partial bottom and side surfaces strengthening acquired higher restitution coefficients compared to the unstrengthened RC beams by 151% and 32%, respectively. In particular, the specimens reinforced with CFC panels on the entire bottom and side surfaces showed the greatest improvement in impact resistance, as demonstrated by a higher restitution coefficient compared to the conventional RC beam for 225% after the first impact and being able to withstand up to three repeated impacts before reaching the failure condition. In terms of energy dissipation, the strengthened specimens had better performance compared to the conventional RC beam. The partial bottom and side surface strengthening was able to absorb energy over a wide area, which helped to reduce crack propagation. It was also found that the CFC panels were prone to interface delamination due to the fracture of the adhesive layer. An anchorage system is suggested to be applied to improve the interfacial bonding between the concrete and CFC panels, as well as the three layers of CFC panels. In the analytical study using the SPH method, a simple linear elastoplastic model, which combines the individual stress-strain relationships of carbon fiber and flexible board for the CFC panels, was employed, and it was confirmed that the model can easily and accurately reproduce the impact behavior of RC beams reinforced with CFC panels. It was also confirmed that the interfacial delamination of the CFC panels could be reproduced by placing adhesive particles between the CFC panels and concrete that bond the two and by setting the conditions for their failure. Figure 25: Results of parametric study on the effect of impact velocity: (**a**) displacement at midspan; (**b**) impact force at midspan; (**c**) relationship between cumulative residual displacement and impact velocity. From the parametric analysis results for the increasing impact velocity and the number of repeated impacts, it can be concluded that the ultimate performance to complete failure is improved by integrally reinforcing the bottom and sides of the beam rather than reinforcing only the bottom. Conceptualization, Y.S. ; methodology, Y.S., S.S. and C.L. ; software, S.S., C.L. and Y.S. ; validation, H.T. ; formal analysis, S.S. and Y.S; investigation, S.S.; resources, H.T. ; data curation, S.S.; writing--original draft preparation, S.S.; writing--review and editing, H.T., C.L. and Y.S. ; visualization, S.S.; supervision, Y.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data will be made available upon request. In this study, impact tests were conducted on specimens provided by Taisei Corporation. The authors would like to express their gratitude to Taisei Corporation for providing the specimens for this study.