## 2 Analysis of Previous Research  
The main reasons for the need to strengthen structures are a decrease in their bearing capacity or the need to increase their bearing capacity to manage a greater load. Defects occur in all structures during operation, and reduce the bearing capacity of RC structures. Most common are concrete defects in reinforced concrete beams [4] or columns [5]. The defects described in these works lead to a significant decrease in the bearing capacity of such structures. One of the reasons for the rapid spread of defects is the opening of cracks in the RC structure. In the study [6], it was established that the load level of the opening shear crack was 53% higher than the load level of the appearing bending cracks. This dependence was derived for prestressed reinforced concrete T-beams based on experimental data. An empirical expression for determining the projection of a dangerous shear crack and the necessary shear reinforcement has been obtained. The use of modern methods and devices for viewing and detecting cracks allows faster identification of their effects on the safe operation of structures with higher accuracy [7]. In the case of emergency dynamic loads, it is also important to research the shear crack resistance of concrete and the reinforced concrete elements of protective structures. The work [8] describes the influence of dynamic loads on protective structures, data about changing the shear crack resistance, and the calculation principles in this case. The appearance of corrosion or mounting holes in the structure decreases the strength of RC beams. In this regard, experimental research was conducted focused on different RC beams with a web opening, such as beams made from ultra-high-performance concrete (UHPC) with a web opening in the support area [9]. Developing methods for strengthening RC structures requires the improvement of calculation methodologies. To determine the necessary amount of reinforcement for structures, their residual bearing capacity needs to be known [10; 11]. Only by having the exact value of the residual strength is it possible to design economic strengthening of structures. Today, structures often need to be strengthened due to the demand to restore or increase the bearing capacity of elements. Classic methods of strengthening are improving and changing. For example, geopolymer concrete (GPC) is used with improved properties for jacketing [12]. In this case, there is a need to perform experimental investigations and improve the calculation methodology. The most effective way to increase the bearing capacity of bent elements is to strengthen the compressed zone of concrete and tensile reinforcement [13]. Strengthening was performed by using fine-grained or steel fiber concrete in the compressed area and glued carbon fibers in the tensile area. The overall strengthening effect was 32-69%, depending on the type of strengthening and the type of load (one-time or low-cycle). A study of various types of composites (Fiber-Reinforced Polymer (FRP) and Fiber-Reinforced Cemertitious Matrix (FRCM)) as systems for strengthening shear beams was conducted in the article [14]. It was established that the beams strengthened by the FRCM system showed a worse interaction than the samples strengthened by the FRP system. Research on the implementation of U wraps of the FRCM system is relevant [15]. In this case, the possibility of the practical application of such strengthening increases. Strengthening took place along the entire length of the beam and was performed in one or more layers. The reinforcement effect ranged from 21 to 56%, depending on the characteristics of the concrete and the number of layers of reinforcement material. The influence of the reinforcement numbers at different reinforcement ratios for longitudinal reinforcement for strengthened concrete beams by the FRP system showed the necessity to consider the specified reinforcement ratio and the importance of the quality performance of design works [16].