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  • Experimental studies to determine the deformation properties of concretes under prolonged loading on materials from Vietnam

    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

  • Stress-strain state of a three-layer tubular structure under the influence of a uniformly distributed pulse load

    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

  • Features of the stress-strain state of normal sections of reinforced concrete beams with concrete of frame structure in a compressed zone

    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

  • Determination of stiffness and curvature of two-layer reinforced concrete beams with concrete of frame structure in the compressed zone

    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

  • To the problem of determination the crack resistance of reinforced concrete beams made of various types of concrete

    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

  • On the bearing capacity of columns made of concrete frame structure with central axial compression

    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

  • Effective reinforced concrete columns of frame-monolithic buildings

    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

  • Features of the deformation analysis of three-layer reinforced concrete slab structures

    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

  • Rational designs of reinforced concrete slabs of frame-monolithic buildings in Mexico

    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

  • On the dependence of "stress-strain" and "modulus of strain-loading level" for concretes with organomineral modifiers

    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

  • Deformation properties and parametrical points of concretes of frame structure

    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

  • On the issue of restoring experimental reliabilityreinforced concrete structures

    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.

  • Increasing the efficiency of reinforced concrete beams due to the use of variable prestressing

    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

  • Optimization of reinforcement constructions of hollow-core slabs

    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

  • New reinforcing constructions of hollow core concrete slabs

    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