The article presents proposals for the calculation of three-layer reinforced concrete slab structures, the outer layers of which are made of heavy concrete, the middle layer is made of lightweight expanded clay concrete. Experimental elements were calculated according to the compiled program of iterative calculation, which takes into account the concrete deformation diagram in an explicit form. The calculation program reflects a technique that allows you to determine the actual distribution of deformations in sections with a crack and in the areas between them. The results of the calculation of the prototypes indicate a close convergence of the theoretical values ​​of the breaking moments, deflections, deformations of the extreme fibers, and cracking forces with those directly recorded in experimental studies.

Keywords: concrete, reinforced concrete, expanded clay concrete, reinforcement, three-layer slab, prestressing, calculation methods, deformations, stresses, deflections

The article considers several types of reinforced concrete slabs: homogeneous monolithic slabs, waffle slabs, as well as prestressed joist and vault slabs. Its main characteristics, properties and advantages are also described. An evaluation of structural analysis is given with a determination of its effectiveness. Reticular slabs: they are made from a network of cross beams that form a grid, leaving gaps that can be filled with blocks of materials whose density does not exceed 900 kg / m3. Homogeneous monolithic slab: it is a slab composed of concrete and reinforcement. The rebars are located in both directions, according to the characteristics of the load. Prestressed joist slabs and vault: it is a structural system consisting of precast beams that are made of prestressed concrete and include hollows of various configurations, within which lighting elements can be placed.

Keywords: concrete, reinforcement, reinforced concrete, floor slabs, wafer plates, monolithic plates, precast monolithic plates

It is shown that the given ratio of the modulus of deformation and the initial modulus of elasticity of concrete depends not only on the type of the function ε = f(𝜎), and from the initial modulus of elasticity of the concrete, i.e. concrete with different values of initial modulus at equal strength, for example, with the introduction of the composition of concrete organo-mineral modifiers, the dependence of the ratio E𝜎/E0 from the loading level will vary. To describe the "stress-strain" or "modulus of deformation-level of loading" for concretes with organo-mineral modifiers, it is advisable to use The sargin diagram, taking into account the influence of modifiers on the main deformation constants: the initial modulus of elasticity, the coefficient of elasticity, the relative deformation corresponding to the short-term strength limit. The nature of deformation of concretes with organo-mineral modifiers at a loading level above 0.9 may differ from the known patterns for traditional concretes, in connection with which this issue requires special study.

Keywords: modulus of deformation, stress-strain diagram, modified concretes, loading level, modulus of elasticity

The article is devoted to the reduction of steel consumption in the compressed zone of reinforced concrete elements. Special attention is paid to the combined prestressing, in which the armature of the stretched zone is subjected to prestressing, and compressed – prestressing. The combined prestressing allows to reduce the steel consumption, and also to increase the performance of many technical characteristics by increasing the limit stresses in the high-strength reinforcement of the compressed and stretched zones

Keywords: the combined prestressing, compressed area, consumption of steel compressed fittings

The peculiarities of the deformation diagram under short-term central axial compression of concrete of the frame structure of class B60, obtained by immersing a large aggregate in a low-viscosity solution component, are revealed. The boundaries of microcrack formation of concrete are determined. A good correspondence of the main regularities of the change in the tensile strength and deformation properties of a concrete frame structure with some known data is shown. The possibility of an analytical description of the deformation diagram of a concrete frame structure known formula Sargine (Sargine) is confirmed. Data are presented on the change in the initial modulus of elasticity, the Poisson's ratio, the change in the volume of concrete and the propagation velocity of ultrasound in concrete, depending on the level of loading. The ratio of cubical and prismatic strength is given. The conclusion is made about the expediency of using concrete frame structure in reinforced concrete columns.

Keywords: concrete frame structure, tensile strength, modulus of elasticity, deformation diagram, parametric points, microcrack formation, superplasticizing additive

In this article, we consider ways to restore the operational reliability of reinforced concrete structures, the types of spacers, the method of reinforcing a reinforced concrete column with semi-circular steel sheets. The reinforcement of the elements by the biaxial transverse compression of concrete is also considered.

Keywords: concrete, reliability, reinforced concrete, structures, technologies, installation, reinforced concrete structures, struts, prestressing, columns, reinforcement, bearing capacity, reinforcement.

This article deals with the introduction of reinforced concrete structures with a variable pre-stress combined along the span. The identification of economic efficiency from replacement of reinforcement and prestressing is carried out.

Keywords: concrete, reinforced concrete, structures, technologies, installation, reinforced concrete structures, tension, prestress, beams, reinforcement, efficiency

Presented the general selection of external composite strengthening, based on the use of the above characteristics of the materials for the strengthened elements of the rectangular profile.

Keywords: concrete, reinforced concrete, composite strenghtening, steel, calculation method, strength, capacity

Have been given the substantiation of the need for preliminary testing of concrete beams on the transverse force. Their goal is to determine the effect of inclined cracks formed at the operating load levels, on the efficiency of the composite reinforcement in the near support sections.   The results of these tests, obtained with the shear span 1,5h0; 2h0 and 2,5 h0, that significantly affects the nature of inclined cracks. According to the results of an experiment formulated recommendations for the design of composite reinforcement.

Keywords: concrete, reinfrcement, reinforced concrete composite, CFRP, strengthening, crack, stress level, clamp, shear span, strength

The article is concerned with development of optimal reinforcement constructions of hollow-core slabs to ensure reliable recovery or increase the bearing capacity, safe operation of hollow-core slabs, safety operation of hollow-core slabs, cost and complexity inimisatrion.

Keywords: Hollow-core slab, reinforcement construction, optimization, safe operation, reinforcement, plot points, plot materials, rod, the center of gravity of the reinforcement

There are new options of reinforcement hollow core slab. The essence of the proposed solutions is to install the rod into the groove located below the voids of the slab. Describes the field of rational use, as well as design and fabrication of these options of reinforcement.

Keywords: reinforcement of building constructions, safety operation, hollow core slab, normal section

Presented and analyzed the data of the test results of concrete columns with the flexibility of λh=10 and λh=20, the strengthening of the external carbon fiber reinforcement. Borders impact of the various options strengthen influence on strength and deformability of columns and efficiency of composite materials installed.

Keywords: concrete, reinforcement, reinforced concrete composite, eccentricity, flexibility, capacity, strength, deformability, strengthening

The data on the bearing capacity of short reinforced concrete columns with the flexibility λh = 10 strengthened by CFRP, the action of axial load, eccentricity e0 = 4cm. Effectiveness of various options for strengthening was determined, provided the action force outside core-section.

Keywords: concrete, reinforced concrete, steel, rebar, composite, carbon fiber, strength, load-bearing capacity.

Presented and analyzed data on the results of tests of short reinforced concrete columns with the flexibility λh = 10 strengthened by CFRP for external applying force with an eccentricity e0 = 2 cm. The effect of strengthening on the bearing capacity and deformability of columns when a load is applied to the inside of the core-section.

Keywords: concrete, reinforced concrete, reinforcement, CFRP, load, strength, deformability.

The most promising technologies of concrete and reinforced concrete for the underground construction and transport. The studies with the inclusion of concrete and steel and polypropylene fibers. The factors affecting the strength and modulus of deformation materials. The conclusion about the need to study the effectiveness of the concrete with a combined reinforcement.

Keywords: Concrete and underground construction, fiber, strength, modulus of deformation