Layered reinforced concrete beams made of multi-modulus of elasticity concretes are increasingly used in engineering practice. The step-by-step iterative method in combination with numerical integration in the calculation of such structures using a nonlinear deformation model and real deformation diagrams is a rational solution, despite the currently lack of a generally recognized approach to assessing the stress-strain state of sections of layered beams.

Keywords: double-layer reinforced concrete beams, normal cross-sections, nonlinear deformation model, high-modulus concrete, neutral axis coordinate

Currently, a large amount of research is devoted to the use of polymer composite materials applied for increasing the strength and durability of reinforced concrete elements. In compressed reinforced concrete columns, the bearing capacity depends on the eccentricity of the external force application and the corresponding stress-strain state, as well as on the arrangement and quantity of composite materials bonded to the surface of the structure. The choice of the arrangement scheme of composite materials depending on the stress state of the structure is of current interest for researchers. At the same time, studies conducted on centrally compressed elements often have contradictory effects. The main purpose of this study is to perform numerical experiment of a digital model for the centrally compressed concrete column reinforced with composite materials. The calculation results for 3 short columns with different reinforcement schemes are presented. It is shown that the use of composite materials to reinforce structures increases the bearing capacity up to 10%. Based on the study results, recommendations on the optimal schemes of reinforcement with composite clamps of inflexible columns reinforced in the transverse direction are proposed.

Keywords: reinforced concrete columns, normal sections, finite element modeling, reinforcement with composite materials

As part of the work on the PhD thesis on the creation of new systems and calculation devices for the design of reinforced concrete tanks for the storage of liquefied natural gas, work was done to determine the properties of concrete mixtures used in the construction of tanks in Vietnam, namely in the Hanoi area. A feature of the materials used for the manufacture of concrete is the use of local rocks, which have distinctive properties, which affects the strength and deformation properties of concrete. The article presents the results of experimental studies of the properties of concretes made with Vietnamese materials. A relationship was established between the modulus of elasticity of concrete and its prismatic compressive strength. As part of the study, 16 formulas of concrete mixtures on different materials from Vietnam were compiled and studied. As a result of the conducted research, the dependence of the modulus of elasticity and the intended strength of concrete was revealed, which will later be used in the creation of calculation devices for the design of reinforced concrete structures.

Keywords: concrete, reinforced concrete, materials, structures, modulus of elasticity, prismatic strength of concrete, deformations

This article is devoted to determining the main characteristics and properties of concretes made from different concrete mixtures based on Vietnamese materials. A total of 16 formulas of concrete mixtures were studied. Concrete samples were tested to determine deformations under prolonged loading. Based on the data obtained, the main creep characteristics were determined, these are the creep measure C0 and the creep coefficient ϕ, as well as additional characteristics including prismatic strength and the initial modulus of elasticity of concrete. The main purpose of this study was to determine the dependencies of the prismatic strength of concrete Rpr, as its main indicator, in relation to the creep coefficient of concrete ϕ. In conclusion, experimental data on the creep coefficients of concrete ϕ were compared with the normative values found according to SP 63.13330 and conclusions were drawn on the effect of concrete creep on its prismatic strength of concrete Rpr made from concrete.

Keywords: concrete, reinforced concrete, structures, materials, creep, deflections, deformations, prolonged loading

This article discusses the comparative calculation of solid-stage and three-layer tubular structures with an assessment of the reliability of their application. To do this, their stress-strain state is investigated when exposed to a pulsed load on the wall. Pipeline structures currently occupy important positions in the infrastructures of many countries. Every year new safety requirements are added to the reliability indicators of these structures. Such important strategic facilities fulfill the task of providing people with energy, without which it is difficult to imagine modern life. For a solid-stage pipe, displacements in the nodes of the pipe wall, as well as longitudinal stresses (Nx) and annular stresses (Ny) in the elements of the pipe wall are determined. In a three-layer pipe, the displacements are determined at the nodes of the pipe wall.

Keywords: three-layer tubular structure, solid-walled pipe, load-bearing layer, pulse load, filler, displacement, voltage

The results of studies of two-layer reinforced concrete beams with a layer of various thicknesses of high-modulus concrete of the frame structure in the compressed zone and traditional heavy concrete in the rest of the section are presented. The stress-strain state of normal cross sections along the height of the beam was estimated by the values of relative deformations at the level of stretched and compressed reinforcement using the hypothesis of flat sections and actual compression and calculated tensile deformation diagrams of concrete. The influence of the thickness of a layer of high-modulus concrete on the nature of the stress-strain state between the layers is shown. The possibility of destruction of the beam on the concrete of the compressed zone was revealed due to the abrupt decrease in the actual height of the compressed zone due to the "shooting" of a layer of high-modulus concrete with its thickness less than 0.1 h0. The dependence of the relative actual thickness of the compressed concrete, i.e. the distance from the edge fiber of the compressed concrete to the neutral axis, in the studied beams on the magnitude of the bending moment is obtained. It is established that for single-layer beams, with a difference in the elastic modulus of concrete up to 20%, the dependences of the relative actual thickness of the compressed concrete layer on the bending moment are almost identical. In the studied beams, the limiting state of which is caused by the fluidity of the reinforcement, the thickness of the compressed concrete layer was 0.37 ...0.4 with a relative moment value of 0.5, and 0.33 ...0.36 with a maximum bending moment value.

Keywords: double-layer reinforced concrete beams, normal cross-sections, nonlinear deformation model, high-modulus concrete, neutral axis coordinate

Based on the research conducted by the authors, data on the stiffness and curvatures of reinforced concrete beams with a layer of various heights of concrete with frame structure are presented. Stiffness, curvature and deflections are given for cases of absence and presence of cracks in the tensile zone of beam. Formulas for describing changes in the stiffness and curvature of sections depending on the magnitude of the moment are obtained. The influence of the thickness of the layer of concrete with frame structure and the diameter of the working reinforcement on the change in the stiffness of the sections is established. The regularity of changing the position of the neutral axis for single and double-layer beams depending on the beam parameters.

Keywords: concrete of frame structure, stiffness, curvature, deflection, layered structures, bending moment, neutral axis

The method of determining crack-forming forces based on the normative approach is considered. Experimental and theoretical studies of reinforced concrete beams made of ordinary heavy concrete, self-compacting concrete with a modifier and concrete of a frame structure have been carried out. Formulas for determining the tensile strength and flexural strength depending on the compressive strength for each of the considered types of concrete are given. The calculated values of the ultimate extensibility of various concretes determined by various methods are given. Coefficients to the formula linking the reduced and initial elastic modulus of various types of concrete are obtained. The influence of the accuracy of the experimental determination of the moment of cracking on the change in the calculated dependencies is analyzed.

Keywords: cracking moment, flexural and tensile strength, frame structure concrete, self-compacting modified concrete

The work of reinforced concrete racks made of concrete frame structure is analyzed. The conclusion is made about the expediency of using concrete frame structure in reinforced concrete columns.

Keywords: concrete frame structure

The article discusses the most common types of modified columns in Mexico: composite section columns, high-strength concrete columns, prestressed concrete columns. The procedure for calculating columns and new proposals to improve construction efficiency is described. Columns are one of the most important elements of orthogonal frame buildings, so improving their designs requires special attention. In composite section columns, using high-strength concrete in the outer zone, the strength of the concrete located in the core increases 1.5 times more, which significantly increases the efficiency of the structure. Columns made of high-strength concrete have an increase in efficiency when used in high-rise buildings. Prestressed concrete columns are very effective because they have high resistance to load, they are able to withstand significant stresses.

Keywords: concrete, reinforcement, reinforced concrete, high-strength concrete, prestressing, columns, columns of composite section, eccentricity, stress, deformation

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 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.