The article presents the results of experimental tests of a number of reinforced concrete eccentrically compressed structures reinforced with composite materials in the longitudinal and transverse directions. During the study, it was found that the composite external reinforcement does not work the same in reinforced concrete structures, but depends on the area of ​​​​the composite materials on the structure. This is due to different stress concentrations along the length of reinforced concrete structures from the action of bending moments and transverse forces. The consequence of this uneven stress state in composite materials is their premature delamination and an underestimation of the overall efficiency of the reinforcement system. This article presents the results of experimental data on the values ​​​​of relative deformations εf of composite materials of reinforced concrete pillars, flexibility λh = 10, tested at a large eccentricity of load application (e0 = 4 cm or 0.32h), going beyond the core of the section. This paper considers various options for composite reinforcement located both in the longitudinal and transverse directions. The deformations were recorded by strain gauges with a 2.0 cm base, at all load levels. As a result, the maximum relative deformations of composite materials were recorded, the most effective zones of transverse clamps location and places where deformation along the fibers did not develop were identified, therefore, the composite in the reinforcement system did not work. The obtained data make it possible to develop the most rational reinforcement options.

Keywords: concrete, reinforced concrete, composite material, carbon fiber, external reinforcement, deformations, compressed elements

This article presents a new method of strengthening reinforced concrete columns using metal and composite materials. The analysis of existing traditional and modern methods of strengthening of reinforced concrete compressed elements has been carried out and their main disadvantages have been identified, taking into account which a new reinforcement method has been developed. This study presents the results of testing the effectiveness of a new reinforcement method, describes in detail the basic schemes, technology and procedure for performing reinforcement work. The results of the conducted experimental studies are presented. The strength of the control samples was compared with the reinforced ones. Proposals have been developed to strengthen reinforced concrete columns with metal elements arranged longitudinally and composite materials glued in the form of clamps with fibers arranged in the transverse direction.

Keywords: steel, reinforced concrete, heavy concrete, test, rack, composite material

This article presents a new developed calculation methodology, which includes provisions for standard calculations and takes into account the peculiarities of the operation of eccentrically compressed reinforced concrete structures operating at large eccentricities of load application. Adjustments have been made to the calculation methodology to take into account the following factors: the standard methodology uses the maximum tensile strength of reinforcement; proposals have been developed to determine the actual resistance of tensile reinforcement, which, in fact, will be significantly lower than the limit. Proposals are given that take into account the limiting deformations of concrete, which, in turn, will be a key quantity for determining the resistance of tensile reinforcement in the cross section. The article also presents the results of experimental studies of a flexible reinforced concrete pillar operating with a load eccentricity equal to e0 = 0.32h. Theoretical calculations and experimental studies were analyzed and appropriate conclusions were drawn.A formula has been developed to determine the real resistance of the stretched metal reinforcement at the time preceding destruction. The calculation algorithm has been compiled. When comparing theoretical and experimental strength, the difference did not exceed 5%.

Keywords: steel, heavy concrete, reinforced concrete, testing, stand

This work is a continuation of a scientific study to determine the effectiveness of composite materials based on carbon fabric in the field of strengthening bending and compressed elements. The article is devoted to the determination of the geometric characteristics of prototypes, the description of the structure of the internal metal frame and the methodology for strengthening reinforced concrete samples. The importance of this scientific work lies in the fact that one of the most popular companies selling composite materials in Russia (“Gidrozo”) proposes to use a new technology for reinforcing reinforced concrete structures that differs from that recommended in the norms. However, according to the manufacturer's specialists, this technique not only ensures reliable adhesion and joint operation of reinforcement materials and structural concrete, but also significantly increases the efficiency of the composite material.

Keywords: steel, heavy concrete, reinforced concrete, composite material, reinforcement, carbon fiber, test, stand, beam, sample

This paper presents, developed by the authors of this scientific article, a method for calculating the strength of reinforced concrete out-of-center compressed racks according to the current regulatory methodology according to SP 63.13330.2018. The peculiarity of this technique is the condition that when calculating the strength, an external force is unknown, in turn, the normative methodology, on the contrary, is focused on calculating the cross-sectional area of metal reinforcement, provided that an external force is known in advance. The inverse problem is not provided for by the norms, since it is used mainly for scientific purposes. Consequently, the methodology developed by us is of great value for research work, where an important factor is the determination of the strength of samples for subsequent comparison with the strength of the corresponding reference samples and the development of new proposals for calculation methods. For the convenience of the reader, the developed calculation method is presented as an example of calculating the strength of one off-center compressed reinforced concrete sample, with explanations and references to the formulas of the normative literature. The calculated sample was actually manufactured and tested in the laboratory of the Department of Housing and Communal Services of DSTU and all its characteristics were found experimentally, therefore, the calculation method is based on comparison with the results of experimental studies.

Keywords: steel, heavy concrete, reinforced concrete, test, rack, eccentricity, strength, off-center compression

The results obtained during experimental studies of deflections of reinforced concrete struts of two flexibilities λh = 10 and 20 tested at three load application eccentricities e0=0; 2.0cm (0.16h) and 4.0cm (0.32h) are considered.Theoretical calculations of deflections were performed according to the current set of rules (SP 63.13330.2018). Based on experimental data and calculation results, it was found that the values of theoretical deflections differ significantly from experimental ones. The influence of the eccentricity of the load application and the flexibility of the samples on the convergence of the theoretical and experimental values of the deflections of the images was analyzed, possible causes of the discrepancy were considered and proposals for improving the calculation methodology were developed.

Keywords: "concrete, reinforced concrete, compressed elements, flexibility, eccentricity, the second group of limit states, deflection "

Construction practice shows that in addition to the need to strengthen the supporting structures of buildings and structures, there is a need for repair and restoration work of reinforced concrete power transmission line supports. With local damage, followed by corrosion of the internal reinforcement, which plays the most important role in containing the resulting bending moments, modern reinforcement methods are either expensive or impossible to perform. In this scientific work, a proposal is presented to strengthen such structures by replacing damaged metal rods with new ones, while new rods are connected to existing special ferrules. The reinforcement process ends with the sealing of damaged areas with high-strength putty. The paper presents the amplification technology and presents all the positive properties of the new amplification method.

Keywords: heavy concrete, power transmission line support, reinforced concrete, compressed elements, coupling, reinforcement

Reinforced concrete structures with prestressed reinforcement are a problem when it is necessary to restore or strengthen them, especially when the prestressed reinforcement is damaged or has significant corrosion. Typically, such structures have large dimensions or cover large spans. Given the scale of work to replace such structures, the development of options for strengthening or restoration is an urgent issue. One of the most complex structures with prestressed reinforcement is a high-rise power line support with an annular section. Its work in the natural environment is exposed to destructive factors that lead to the removal and destruction of prestressed reinforcement. This article is devoted to the development of a method for strengthening the damaged section of the reinforced concrete pylon of a power transmission line by replacing and prestressing the destroyed rod. The paper presents the technology of the amplification method and the main positive properties.

Keywords: heavy concrete, power transmission line support, reinforced concrete, compressed elements, threaded coupling, reinforcement

The results of the studies show that the manufacturer of composite materials for the consumption of reinforced concrete structures depends and produces materials for reinforcement, material properties and their quality. Such a thing requires the study of properties, fixing in the structure of materials. The article is devoted to the appeal. A program has been specially developed for influencing structures with unexplored, but the most popular composite materials in Russia, in particular, in the Rostov region. Certain parameters of reinforced structures that will be checked during the testing process. The program of the experiment was designed in such a way as to capture the most important reinforced concrete structures used in construction.

Keywords: concrete, reinforced concrete, composite material, carbon fiber reinforced plastic, external reinforcement, deformations, compressed elements

The choice of options for strengthening reinforced concrete structures is based on a large number of factors based on technical capabilities and economic efficiency. Modern construction requires new reinforcement methods that allow reducing labor costs and work time, while maintaining the aesthetic appearance of a building under construction or being restored. The stumbling block is the issue price and the reliability of new amplification methods. For this purpose, known and used reinforcement methods based on materials such as reinforced concrete and metal were compared with a fairly new reinforcement method used materials based on carbon fabric. This article provides examples and results of calculations for the reinforcement of a column with a reinforced concrete, metal and composite cage. Based on the results of the calculations, a technical and economic comparison of the existing reinforcement options was carried out.

Keywords: "concrete, reinforced concrete, composite material, carbon fiber reinforced plastic, external reinforcement, deformations, compressed elements

The use of composite materials for reinforcing reinforced concrete structures is very popular abroad, and in recent years they have gradually conquered the Russian building materials market. Insufficiently complete scope of research activities does not allow the full use of composite materials in the field of reinforcing reinforced concrete structures. In addition, there is no single product range in which composite materials from different manufacturers have the same properties. Given the difficult political situation in Russia, a number of composites manufacturing companies have stopped supplying their materials to the country. In this regard, there is a need to research new manufacturers and their reinforcement materials. Given the great responsibility placed on structural reinforcement projects, the behavior and properties of the reinforcement materials must be studied. This paper provides a comparison of materials and techniques for performing work to strengthen 2 different firms, the reliability and efficiency of one of them, BASF, was tested as a result of research and development, but this firm stopped working in Russia, another firm, Hydrozo - is the most common, but little studied. Also, the work presents all the positive and negative properties of the technologies for performing work, an analysis is made regarding the prospects for the use of reinforcement materials.

Keywords: concrete, reinforced concrete, reinforcement, carbon fiber reinforced plastic, composite material, reinforcement, carbon fiber

In recent decades, composite materials have been widely used in the reinforcement and fabrication of reinforced concrete structures. However, the volume of experimental and research work in Russia is not large enough to determine all the possibilities and real effectiveness of composite materials in this area. This paper presents proposals for improving the methodology for calculating the strength of reinforced concrete flexible eccentrically compressed struts reinforced with composite materials in the transverse direction. The developed proposals are based on the results of experimental studies. The proposals were developed in the field of determining the additional compressive strength of concrete from the action of composite materials located in the transverse direction. The paper describes the shortcomings of the normative calculation methodology and developed a coefficient that corrects the formula for determining the resistance of concrete reinforced with composite materials Rb3.

Keywords: concrete, reinforced concrete, composite material, carbon fiber reinforced plastic, external reinforcement, deformations, compressed elements

The work is devoted to a review of the study of a composite material based on CFRP in the field of reinforcing reinforced concrete structures. The main work on the study of the effectiveness of carbon fiber reinforced plastic in the reinforcement of bending elements along normal and inclined sections and compressed flexible elements are considered. The main achievements and conclusions are established, as well as the disadvantages of calculation methods and amplification technology are considered. The purpose of this paper is to review the areas already studied and identify promising topics for further study of composite material.

Keywords: concrete, reinforced concrete, composite material, carbon fiber reinforced plastic, external reinforcement, deformations, compressed elements

The results of experimental studies on the formation of cracks in reinforced concrete racks of two slenderness λh = 10 and 20, tested at three eccentricities of load application e0 = 0; 2.0cm (0.16h) and 4.0cm (0.32h). On the basis of the experimental data and the results of calculations on the formation of cracks, it was found that the values ​​of the theoretical moments of cracking of the experimental compressed elements differ significantly from the experimental ones. An analysis was made of the influence of the eccentricity of the load application and the flexibility of the samples on the convergence of the theoretical and experimental moments of cracking in the samples, and the possible reasons for the change in the bearing capacity of the samples were also considered.

Keywords: concrete, reinforced concrete, compressed elements, flexibility, eccentricity, crack, crack resistance

On the basis of experimental data, it was found that when calculating flexible reinforced concrete racks reinforced with composite materials in the transverse direction, the strength of the elements is underestimated by the norms. The influence of the composite reinforcement is not taken into account when calculating the stiffness D, the conditional critical force Ncrc and the slenderness coefficient η. Experimental data from the experiments carried out showed that the deflections of the reinforced struts were less than similar, not reinforced specimens, therefore, the influence takes place. Based on the analysis of the results of experiments, in the methodology of norms when calculating D, proposals were made that take into account the step of the transverse amplification at different eccentricities of the load application.

Keywords: Determination of the conditional critical force of flexible strengthened concrete struts reinforced with composite materials