# Concrete Beams Reinforced with High Strength Rebar in Combination with External Steel Tape
## 1 Introduction
Comparative analysis [25] has also shown that RC beams strengthened with steel tapes tend toward more flattered crack development in the shear span. Therefore, when using the external tape reinforcement it is important to take into account the specifics of the stress-strain state, durability parameters, and limitations due to corrosion impacts, which was highlighted in the number of studies [26; 27; 28]. The effect of steel tapes as the strengthening material on fatigue characteristics was studied by [PERSON] et al. [29]. The work of [PERSON] et al. [30] was devoted to the flexural capacity of steel-concrete structures. An interesting study from [PERSON] et al. [31] included the theoretical calculation and analysis of steel-concrete beams. Article [32] describes results of the study of pre-stressed steel-concrete beams, analyzing a different ratio of steel tape and rebar in the zone of pure bending. Strengthening technology with the use of external steel tapes includes such operations as cutting a steel plate into strips, pasting them at a certain distance at the bottom edge of the structure, and anchoring at the end [33; 34; 35]. Reliable anchoring is an obligatory condition of optimal use of the strengthening system. As is stated in [36], the effective operation of the multi-layered beam structure requires reliable connection between layers. Similarly, in the study [37], it was noted, that the contact between different layers of the structural element is important from the point of view of the load-bearing capacity of the composite cross-section. Comparative study [38] has shown, that for both, externally applied CFRP tapes and steel tapes, the decisive parameter of failure was the peeling off at the steel-glue interface. For beams with an external reinforcement, adhesion between smooth tape reinforcement and concrete surface is ensured with the use of different anchoring systems, which prevent the sliding of steel tape. For example, additional adhesion between the tape and the concrete can be ensured with the use of steel bars welded to the tape. Among all types of anchors, the simplest in manufacturing are single bars, welded to tape in T-form. However, U-type anchors welded to the tape are more efficient. The load-bearing capacity of such anchors is determined by the resistance of the anchor to the bearing and strength of the concrete. Shear deformations depend on the level of stress in the concrete in the interphase zone of the anchor with tape reinforcement. The perforation anchoring system was approved by the authors [39] to be an effective way of ensuring joint work and the increase in the structures' load-bearing capacity by 10 % in comparison with loop anchors. In addition, the increase in the steel sheet thickness from 2 to 4 mm results in an increased load-bearing capacity from 17% to 38% [39]. It is important to note that the use of external tape reinforcement in combination with steel bars of usual strength does not provide reliable stiffness. Thus, the study of [40] has shown that such structures have higher deflection values than the concrete elements with fiber-reinforcement. In the industrial manufacturing conditions, high strength rebar is widely used in reinforced concrete structures. Among its advantages, high strength is the most important one, which enables the reduction of the amount of steel without decreasing the reliability. Another important parameter of the structural steel is its limit strain, which is higher for high strength reinforcement; it has a negative impact on the crack resistance of the structure. An interesting finding was presented in the study [41], according to which an additional prestressing of the tape and high-strength rebar can increase the ultimate moment by up to 19% and significantly reduce deflections under service loads. High strength reinforcement is mostly used in industrially-manufactured, prestressed, reinforced concrete structures, as the prestressing of steel bars is expensive and technologically complicated on the construction site.