## 3 Test Results  
### Static Test Results and Damage Observations  
During the quasi-static loading test of Beam_GFRP_PreStr, the first flexural crack appears in the midspan region when the load reached 23.89 kN (i.e., at 7.47 mm displacement), corresponding to approximately 46% of the ultimate load of 51.94 kN. As the load increased, additional flexural cracks formed, and at a load of 49.18 kN (i.e., at 18.44 mm displacement), the longitudinal steel reinforcement yielded. Note that the yielding displacements of all beams were determined based on the reduced stiffness equivalent elasto-plastic yield [50]. When the deflection reached 55.87 mm, the cracks in the concrete cover became more pronounced and propagated horizontally toward the right. A reduction in load values was observed during the third and fourth loading cycles (i.e., the D3 and D4 damage levels). At a displacement of 78.89 mm (i.e., at 44.45 kN load), the GFRP layer debonded from the concrete interface, leading to failure. At this stage, the concrete in the compression zone was fully crushed. As illustrated by the load-displacement curve in Figure 4, Beam_GFRP_PreStr exhibits a ductile flexural failure mechanism. The failure mode of Beam_GFRP_PreStr is shown in Figure 5. \begin{table}
\begin{tabular}{c c c} \hline
**Drift Ratio (\%)** & **Midspan Displacement (mm)** & **Damage Level** \\ \hline
0.00 & 0 & Undamaged State \\
1.00 & 30 & D1 \\
1.50 & 45 & D2 \\
2.00 & 60 & D3 \\
2.50 & 75 & D4 \\ \hline \end{tabular}
\end{table} 
Table 3: Drift ratios, corresponding midspan displacements, and damage levels. During the static loading test of Beam_CFRP_PreStr, the first flexural crack appeared in the tensile zone of the concrete when the applied load approached 24.51 kN (i.e., at 7.21 mm displacement), corresponding to approximately 37% of the ultimate load of 66.24 kN. As the load increased, numerous flexural cracks formed. These cracks were not concentrated in the midspan region but were distributed along the length of the beam. At a load of 58.12 kN (i.e., 21.34 mm displacement), the longitudinal steel reinforcement yielded. After the load reached a maximum of 66.24 kN, the cracks in the concrete cover became more pronounced and started to propagate toward the left. At a displacement of 37.65 mm (i.e., at 60.56 kN load), failure occurred due to the debonding of the CFRP strengthening material along with the concrete cover, resulting in a sudden drop in load and the termination of the test (see Figure 4). Although slight crushing was observed in the concrete compression zone, debonding happened before the beam reached its full flexural capacity. Compared to Beam_GFRP_PreStr, which was strengthened with GFRP, Beam_CFRP_PreStr failed at a lower displacement level while bearing a higher load value (see Figure 4). The failure mode of Beam_CFRP_PreStr is illustrated in Figure 6.  
As mentioned earlier, Beam_GFRP_PostStr and Beam_CFRP_PostStr, which were initially bare beams, were pre-damaged up to 30 mm displacement (i.e., D\({}_{1}\) damage level) and strengthened with GFRP and CFRP, respectively. The load-displacement  
Figure 4: Load–displacement curves for Beam_GFRP_PreStr and Beam_CFRP_PreStr. Figure 5: The failure mode of Beam_GFRP_PreStr. Figure 6: The failure mode of Beam_CFRP_PreStr. curves of Beam_GFRP_PostStr and Beam_CFRP_PostStr are presented in Figure 7. The pre-damaging procedure serves as a reference for the pre-strengthened beams, namely Beam_GFRP_PreStr and Beam_CFRP_PreStr. The first crack in the midspan region occurred at 18.83 kN (i.e., at 5.98 mm displacement) and 19.23 kN (i.e., at 6.18 mm displacement) for Beam_GFRP_PostStr and Beam_CFRP_PostStr, respectively. As the load increased, additional flexural cracks formed. The longitudinal steel reinforcement yielded at 42.61 kN (i.e., at 15.11 mm displacement) for Beam_GFRP_PostStr and 41.86 kN (i.e., at 15.23 mm displacement) for Beam_CFRP_PostStr.