The question of increasing the reliability and durability of reinforced concrete structures is a priority. One of the ways to increase the strength of concrete is using of dispersed reinforcement. The interest of using of fiber-reinforced concrete in Russia, as well as in Europe, Asia and the USA has increased significantly in recent ten years. The improvement of the physical and mechanical properties of concrete is noted to depend on the reinforcement parameters, such as the volume content of the fiber, the characteristics of the dispersed reinforcement, the structure of the concrete matrix, etc. Authors consider various types of fibers for dispersed concrete reinforcement, specifically polypropylene, polyethylene, nylon, acrylic, polyester, cotton, asbestos, glass, basalt, steel, carbon. Description of the main advantages and disadvantages of each type of fiber is given. Comparative characteristics are presented in terms of density, tensile strength, modulus of elasticity, elongation at fracture of the materials used to manufacture the fiber. The influence of fibers on crack strength of fiber-reinforced concrete under impact loads is studied. Analytical review of existing works found that it is possible to achieve a significant increase of strength of fiber-reinforced concrete in axial compression, tension, tension in bending, shear compared to ordinary heavy concrete.

The fiber-reinforced concrete finds more applications in modern construction. This material has improved strength and deformation characteristics. The fiber-reinforced concrete is considered to be one of the most promising building materials in the world practice. The experience of using this material in developed countries, such as the USA, UK, Japan, Germany, Italy, France, Australia, has shown the good technical and economic indicators in building constructions. Recently, the base of standards for preparation, calculation and design of such concretes has been prepared and introduced in Russia. The method of determination of the class of the fiber-reinforced concrete by residual tensile strength, the calculation of the strength of standard sections, the diagrams of the deformation is discussed in the article based on the new Code of Practice. The obtained results of analysis of the theory of calculation suggest further studies of the properties and physical characteristics.

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This article is devoted to the peculiarities of calculating compliance modifications of the timber elements on mechanical linkages. Here we analyze in detail the method of C M Kochenov using in the design standards of the Russian Federation. This method allows to determine accurately the number of links that are able to resist the shear force in the linkage, however, this method does not include analyzing of shear deformation in modifications. And it is a disadvantage. In this article the author considers another approach, based on the idea of determining the shear deformation of the mechanical linkage, installed in the connection. To calculate the shear deformations of connections in the linkage it is necessary to conduct a preliminary analysis of the construction, to establish the type of connection and thickness of the connected elements, to determine the number of shear planes, the number of established joints and the level load on the joint. After determining these values, structural analysis design is performed. This article describes in detail the theoretical aspects of this method, used assumptions and limitations. It is considered a test case for validation of the considered methods. The FEM joints model is investigated. The forces and displacements of the bonds obtained by the FEM model are compared with the result of the theoretical calculation.