# An Experimental Study on Repairing of Reinforced Concrete Beams Having Damaged Longitudinal Bars
## 1 Introduction  
It is necessary to ensure that buildings can withstand the horizontal loads exerted by earthquakes, especially in seismic active zones. In new structures, structural members can be designed to withstand such loads. However, in structures that have already been damaged by an earthquake, the affected structural elements need to be either repaired or demolished. Repairing existing structures is crucial for extending their service life and ensuring safety, particularly in seismic zones. Various factors affect the type of repair that can be used, including its economic viability, on-site practicality, and effect on the overall performance of the structure. Earthquake damage to reinforced concrete (RC) members and corrosion damage are the main reasons to use repairing techniques on RC members [1, 2, 3]. Other damage that might affect structural members can be accidental or intentional cuts during construction. Such intentional openings might be remedies for clashes between a structural element and a utility part. Examples of clashes might be a water or wastewater pipe, electrical cable ducts, ventilation ducts, or any other clashes with other mechanical or service equipment, as shown in Figure 1. The opening size and shape of these clashes are different for each situation. Main or transverse reinforcement might be affected by such openings, which require substantial consideration to prevent failure. The openings affect the cracking behavior of concrete members [4]. The created gap causes a significant decrease in the load-carrying capacity of the damaged element; therefore, it is important to repair these damaged elements. In recent years, various reinforcement materials have been explored to enhance the performance of concrete structures. These materials include synthetic fibers such as steel fibers (SFs) and plastic fibers (PLs), as well as natural fibers (NFs) like hemp, flax, and sisal. Steel fibers are well known for their strength and ability to increase the toughness and ductility of concrete, while plastic fibers, such as polypropylene (PP), are used to improve the workability, shrinkage control, and crack resistance of concrete. Additionally, natural fibers are gaining recognition for their sustainability, being derived from renewable sources, and offering an eco-friendly alternative to traditional synthetic fibers [5; 6]. In recent years, carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) reinforcing bars, sheets, and plates have been extensively used in repair due to their high strength, corrosion resistance, light weight, and durability [7; 8; 9; 10; 11]. These bars and sheets can be applied by the externally bonded reinforcement (EBR) technique from the outside of the beam or by embedment using the near-surface mounted (NSM) technique. Many researchers [12; 13; 14; 15; 16] have studied the effect of NSM and EBR techniques in strengthening concrete members. Both methods showed significant enhancements in the flexural [13; 17; 18; 19; 20; 21] and shear [22; 23; 24] behaviors of strengthened members, leading to better stiffness and capacity. Repairing complete damage in the main reinforcement, such as opening cuts, is rarely discussed in the literature. In the EBR method, the sheets can be adhered to the surface of the reinforced concrete element, whereas in reinforced bars it is mandatory to add an extra layer to embed the bars. The main disadvantage of this technique is that the FRP material causes premature separation damage from the reinforced concrete element [25; 26; 27; 28; 29; 30]. Such separation damage can limit the strength utilization and strengthening efficiency of the FRP material. The prevention of separation damage in RC strengthened beams has been extensively researched. In the literature, various anchorage applications have been developed to address this issue, and their effectiveness has been demonstrated [21; 31; 32; 33]. The NSM strengthening technique offers a practical alternative to the EBR method.