## 2 Analysis of Previous Research
The combination of different types of strengthening to increase the bearing capacity has been used more and more widely [17]. Experimental studies of two-span RC beams with strengthening frames from rebars and concrete with steel fibers have been conducted. Research [18] proposed a method of strengthening the concrete properties by laying a fibrous mesh in the top (mortar) layer of the concrete surface. Basalt fiber, aramid fiber, and carbon fiber mesh were selected as reinforcing materials to study the concrete's early cracking resistance and the mortar's early cracking characteristics. Another method is installing a polymer-cement coating on wall structures [19]. The influence on the durability and destruction of the tested wall elements was described. The need for reinforcement often arises in connection with an increase in the seismicity of the building or a change in code [20]. Research into reinforced concrete beams with different schemes and reinforcement principles for seismic impact is directed toward the most effective construction of RC beams. A particular type of strengthening increases the seismic resistance of the joints of reinforced concrete structures. A promising direction is their reinforcement with composite materials with significant strength and deformability, which can prevent the destruction and collapse of structures [21]. Long-term effects on structures also lead to the need to strengthen them [22]. As the service life increases, the mechanical characteristics deteriorate due to the properties of filled concrete that wear out over time. Another factor that is rarely taken into account is the level of load on the structure for which strengthening is performed [23]. An important aspect of the development of methods of strengthening reinforced concrete structures is their practical application, such as the strengthening of an RC tank [24]. According to results of a technical inspection, numerous defects were discovered, and a method of using steel external bandages was developed. However, to restore tightness and improve operational characteristics by installing reinforced concrete brackets [25]. The given examples of strengthening were carried out taking into account the existing defects and the real state of the structure. Expanding the application areas of FRCM systems requires appropriate design models. The paper [26] proposes a simplified modified compression field theory (SMCFT) for shear model calculation. According to this calculation model, the calculation accuracy was 0.96 (the ratio of theoretical data to experimental data) with a deviation of 0.14. The calculation of strengthening concrete T-beams reinforced in shear with FRCM composites based on the ACI549.4R-13 code is relevant [27]. The results of the calculations were significantly underestimated and require further refinement. For a high-quality calculation of RC structures, it is necessary to consider the nonlinear properties of materials and the deformation criteria for the exhaustion of the bearing capacity [28]. The same requirements apply to the calculation of constructions on the shear. The proposed method for determining the reliability of RC structures on shear allows optimal design decisions to be made, ensuring the specified level of construction reliability without overspending on materials [29]. Optimizing the design method is an urgent issue. This technique can be based on geometric parameters and structural features of systems [30]. This technique can be based on design features and systems' geometric parameters. Required reinforcements for beams with span-to-depth ratios varying from 10 to 20 were first determined in accordance with Eurocode 2. A probabilistic analysis using Monte Carlo simulations then revealed that doubling the span-to-depth ratio would not worsen the performance of the beams in terms of ultimate strength [31]. One of the effective methods of strengthening structures is their unification of pre-fabricated individual elements into a continuous spatial structure [32].