## 4 Conclusions  
The primary objective of this study was to evaluate the influence of GFRP and CFRP strengthening materials on the static and dynamic behavior of R/C beams subjected to progressive damage. Four beams were strengthened in both the undamaged and pre-damaged states. Dynamic impact tests were performed on the beams in their undamaged states, as well as at different damage levels. Modal frequencies corresponding to the first three vibration modes in both vertical and horizontal directions were estimated using  
Figure 17: Modal frequency ratios in the horizontal direction for the (**a**) first, (**b**) second, and (**c**) third modes of all beams. the EFDD method, facilitating an evaluation of the beams' dynamic behavior before and after strengthening. The results show that CFRP significantly enhances the stiffness of R/C beams compared to GFRP. CFRP-strengthened beams exhibit a notable increase in load-bearing capacity but fail at lower displacement levels, suggesting less ductility compared to beams strengthened with GFRP, which display more ductile behavior under similar conditions. The improvement in stiffness provided by CFRP is particularly evident in dynamic tests, where modal frequencies revealed a more substantial increase in CFRP-strengthened beams, especially at lower damage levels. The first vibration mode, in both the vertical and horizontal directions, proves to be the most sensitive to progressive damage, while the second and third modes show more stability across damage levels. This finding is a natural consequence of the fact that the first modes in both directions have the highest participation in the dynamic responses of the beams. The results also indicate that while both materials are effective in improving the structural performance of undamaged and damaged beams, the specific choice of strengthening material depends on the required balance between load capacity and ductility. Beams strengthened with GFRP may be more suitable for applications where greater ductility is desired, while CFRP may be preferable when maximizing stiffness and load capacity is a priority. The absence of end anchorage in the study may have contributed to some degree of debonding, particularly in the CFRP-strengthened beams, where higher stiffness and load-bearing capacity were achieved but at the cost of reduced ductility. This highlights the potential for incorporating end anchorage in future experiments to further enhance the performance of FRP-strengthened beams, particularly for preventing early debonding and achieving greater structural efficiency. In addition, a more detailed investigation into the long-term performance of GFRP and CFRP under environmental factors such as temperature changes, moisture, and sustained loading would be valuable. Numerical simulations and analytical models may be developed to predict the behavior of R/C beams with different types and configurations of fiber-reinforced polymers under different loading conditions. The effects of GFRP and CFRP on the damage formation mechanisms of beams will be better understood by updating the pre-calibrated analytical model based on the modal parameters extracted from different damage levels of the strengthened beams. Exploring hybrid strengthening techniques that combine the benefits of both GFRP and CFRP may also lead to improved performance in terms of both stiffness and ductility. Conceptualization, O.O., U.Y., C.K. and E.D. ; methodology, O.O., U.Y., C.K. and E.D. ; experimental test, O.O., U.Y., C.K. and E.D. ; analysis, O.O. ; investigation E.D. ; writing--original draft preparation, O.O., U.Y., C.K. and E.D; writing--review and editing, O.O. and U.Y. ; visualization, O.O. ; supervision, O.O. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The datasets presented in this article are not readily available because the data are part of ongoing studies. Requests to access the datasets should be directed to the corresponding author.