# An Experimental Study on Repairing of Reinforced Concrete Beams Having Damaged Longitudinal Bars
## 3 Results and Discussion
### Load-Displacement Curves  
The load versus displacement curves for all the RC beam specimens are presented in Figure 10. The damaged reference beam showed an expected lower capacity, where the beam cracked almost immediately after loading due to the lack of middle reinforcement, having a maximum load of 7.89 kN and a maximum displacement of 27.8 mm. However, the specimen behaved in a ductile manner due to the presence of the upper reinforcement until failure. The undamaged reference specimen and specimens repaired with steel bars in Groups B and E (RB1-SNSM-S and RB7-EBR-S) showed similar load-displacement patterns until load capacity, with maximum capacities of 57.76 kN and 87.92 kN, respectively. The rigidity was characterized by a first linear stage until the first cracking of concrete, followed by a reduced rigidity stage due to concrete cracking until the yielding of the reinforced bars. Then, the final stage where the load gradually decreased until the failure point was reached, and the reference specimen (RefB) exhibited a high ductility, reaching a deflection of 140 mm, where the ductility of RB1-SNSM-S was about half of that. The RB8-EBR-G beam showed a sudden failure at an ultimate loading of 32.56 kN, which resulted from the debonding between the mortar layer and the concrete at a displacement of 9.2 mm. Specimens in Group D had similar rigidity in early stages as compared to other beams up until tensile cracking point of concrete. After that, the rate of increasing deflection was suddenly higher than in the previous stage, resulting in a sudden decrease in rigidity, with maximum capacities of 43.91 kN and 59.11 kN, at displacements of 15.8 mm and 33.3 mm for the RB5-EBR-CS and RB6-EBR-CS-U specimens, respectively. Figure 10: Load–displacement curves of all beam specimens. The maximum load point was much higher for the beam with a U boundary sheet (RB6-EBR-CS-U) with increased deformability until sudden failure, while the beam without the U boundary (RB5-EBR-CS) reached a lower peak load followed by separation of the sheet. The specimens that were repaired with GFRP bars showed the lowest load capacity performance in the two repair methods of Groups B and E. Prior to the first cracking, the two beams showed similar rigidity up until the point of decreasing rigidity in both beams. The EBR method used in Group E showed a higher capacity due to the increased beam depth. The peak point was reached at the point of complete separation of the added mortar layer followed by a sudden drop in rigidity, and the capacity was then being governed by the upper steel reinforcement. The RB2-SNSM-G beam showed more deformability with a maximum displacement of 43 mm up until peak loading of 26.54 kN, where a complete splitting of the bar from the mortar was followed by a drop in the rigidity. The general results of all tested beams are presented in Table 6, and further details about these results will be presented in subsequent sections. All beam specimens were loaded up to the failure point. Herein the symbols \(\mathrm{P_{cr}}\), \(\mathrm{P_{u}}\), \(\mathrm{\Delta_{y}}\), \(\mathrm{\Delta_{u}}\), \(\mathrm{\mu}\), K, and E refer to first crack and ultimate loads, yield and ultimate displacement, ductility, initial rigidity, and energy assumption of the beam specimens, respectively. The yield characteristic point was specified in a curve as the transition point entering the yield plateau phase. The ultimate characteristic point and energy assumption were designated where the load capacity decreased to 85% of the peak load. The percentage increase in the first cracking and ultimate load capacities, ductility, rigidity, and energy absorption values of the tested beam specimens are compared with the results of RefB and RefB-D specimens in Table 7. In Table 7, the positive values indicate an increase and negative values indicate a decrease in the value as compared to the reference specimens.