# An Experimental Study on Repairing of Reinforced Concrete Beams Having Damaged Longitudinal Bars
## 3 Results and Discussion
### Cracking Behavior and Failure Mode  
In this section, test observations primarily focusing on the failure modes and crack propagation are presented for all specimens, illustrated through photographs and schematic drawings in Figure 9.  
The cracking behavior of the undamaged (RefB) and the damaged (RefB-D) reference beams in Group A are shown in Figure 9a,b. The undamaged reference beam behaved similarly to a typical ductile reinforced concrete beam where bending cracks initiated in the lower section of the mid-span propagated upwards, followed by shear cracks when loading approached the yielding of the steel, and finally, compression crushing failure appeared in the top extreme fibers of the concrete. The damaged specimen behaved differently from the undamaged specimen, where a single crack was formed due to the lack of steel reinforcement in the damaged part. The crack width was large as compared to the undamaged specimen, and the crack propagated upwards until it reached the upper reinforcement layer where the crack split at the level of the upper reinforcement layer. The cracking behavior in the RB1-SNSM-S specimen repaired with steel bars in Group B was observed to be similar to that of the undamaged beam, with flexure cracks initiating at mid-span; however, the specimen experienced a formation of a wider crack in the damaged location, propagating upwards. The crack widened as the specimen was loaded, leading to crushing in the upper concrete fibers (Figure 9c). The RB2-SNSM-G specimen repaired with GFRP bars did not experience the same flexure cracks; instead, a single crack was formed in the damaged area and the GFRP bar was split from the mortar embedment, unlike the specimen repaired with steel bars (Figure 9d). The splitting caused the specimen to lose its load capacity. The beam was then primarily relying on the upper steel reinforcement layer, causing a horizontal crack in that location; a similar behavior was observed in the damaged reference specimen (RefB-D). The beams repaired with the NSM procedure by using GFRP rebars in Group C (RB3-NSM-G and RB4-NSM-G-U) showed behavior similar to that in the RB2-SNSM-G specimen. It was observed that the cracks with increasing width occurred at the edge of the gap in the middle of the beam, and the concrete in the concrete compression zone crushed at the last stage (Figure 9e,f). The beams repaired with the EBR procedure by using CFRP sheets in Group D formed a considerable crack in the damaged area, accompanied by some bending cracks until the failure of the bonding layer. This led to the separation of the lower sheets causing the U boundary sheet to hold the lower sheet in place; then, the middle crack propagated upwards causing some crushing of upper concrete fiber. On the other hand, the beam without the support of the U boundary sheet did not experience as many bending cracks or crushing in the upper section; instead, a single crack was formed in the damaged area and the failure was governed by the failure of the bonding surface and separation of lower FRP sheet (Figure 9g,h). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Loading** & **Displacement** & **Loading** & **Displacement** & **Loading** & **Displacement** \\ \hline
**Step** & **(mm)** & **Step** & **(mm)** & **Step** & **(mm)** \\ \hline
1 & 0.75 & 8 & 20.00 & 15 & 60.00 \\
2 & 1.50 & 9 & 25.00 & 16 & 70.00 \\
3 & 3.00 & 10 & 30.00 & 17 & 80.00 \\
4 & 6.00 & 11 & 35.00 & 18 & 90.00 \\
5 & 9.00 & 12 & 40.00 & 19 & 100.00 \\
6 & 12.00 & 13 & 45.00 & 20 & 110.00 \\
7 & 15.00 & 14 & 50.00 & 21 & 120.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The displacement values corresponding to each loading step. Figure 9: Photographs and schematic drawings of the damage to all beams. (**a**) RefB (Group A), (**b**) RefB-D (Group A), (**c**) RB1-SNSM-S (Group B), (**d**) RB2-SNSM-G (Group B), (**e**) RB3-NSM-G (Group C), (**f**) RB4-NSM-G-U (Group C), (**g**) RB5-EBR-CS (Group D), (**h**) RB6-EBR-CS-U (Group D), (**i**) RB7-EBR-S (Group E), (**j**) RB8-EBR-G (Group E).