Andrii Niedoriezov
Stress-Strain State of Reinforced Concrete Elements with Indirect Reinforcement
Donbas National Academy of Civil Engineering and Architecture
Abstract. The results of the analysis of the stress-strain state of reinforced concrete elements with indirect reinforcement under uniaxial compression, carried out numerical tests by using the software systems «Lira SAPR» and «ANSYS» are presented in this article. A physically nonlinear calculation of reinforced concrete samples of prisms was performed using the relations of the orthotropic dilatation model of concrete deformation. The criterion for the destruction of prismatic samples in the calculation was the achievement of the maximum values of stresses in concrete, taking into account the non-axial stress state according to the strength criteria of S. F. Klovanich – D. I. Bezushko and K. J. Willam – E. P. Warnke, as well as stresses in the longitudinal and transverse reinforcement of the yield strength of steel. In general, taking into account the physical nonlinearity of the deformation of materials allows us to estimate the deformations and the bearing capacity of the elements of samples-prisms with indirect reinforcement in the software complexes «Lira SAPR» and «ANSYS» with a sufficient degree of accuracy. The analysis results are consistent with the current regulatory documents. The relations of the volumetric stress state in concrete and the stresses in the grids of indirect reinforcement are determined, depending on the percentage of indirect reinforcement for the elements used in the work.
Keywords: concrete, indirect reinforcement, short centrally compressed element, volumetric stress state, strength, deformations, strength criteria, dilatation, concrete deformation models.
Uchkun Gaziev, Tuygun Shakirov, Shavkat Rakhimov
Selection of the Optimal Composition of Lightweight Concrete on Porous Filler from Quartz Porphyer
Tashkent Institute of Architecture and Civil Engineering
Abstract. The article presents the results of research work on the development of filling mixtures, porous aggregates; heat-insulating and structural-heat-insulating concretes using industrial waste. The optimal compositions, manufacturing technology and basic physical and mechanical characteristics of the developed building materials and concretes have been determined. It should be noted that the building materials industry is a construction industry for which the issues of resource conservation and the use of industrial waste are especially relevant. Today the construction industry uses hundreds of millions of tons of various mineral raw materials, and the share of raw materials costs in the cost of production is 25…50 %. Under these conditions, the attraction of millions of tons of industrial waste as a raw material can and does bring a significant national economic economic effect. Currently, large-scale industrial waste, which is of interest as a raw material for the production of building materials and concrete, is generated at the enterprises of dozens of organizations, companies and departments. At the same time, enterprises producing construction materials and products use no more than 10…12 % of all generated waste. In this regard, one of the most important problems at the moment is the maximum and comprehensive use of waste from various industries as raw materials for the production of efficient and cheaper building materials.
Keywords: lightweight concrete, optimal composition, porous aggregate, workability, cohesion, average density, strength, superplasticizer.
Volodymyr Korsun
Development of Methods for Calculation of Reinforced Concrete Constructions of Buildings and Structures for Temperature and Humidity Effect
Peter the Great St. Peterburg Politechnik University
Abstract. The results of the analysis of the effect of high temperatures on the main regularities of the formation of stress-strain state of reinforced concrete structures of buildings and structures are presented. The main possibilities and disadvantages of engineering methods for calculation of the specific characteristics of elements of reinforced concrete structures and a method for calculating using a nonlinear deformation model are presented. The possibilities and directions of further development of deformation models of reinforced concrete are considered in relation to normal and high-strength modified concretes in terms of taking into account the main specific properties of reinforced concrete – physical nonlinearity of deformation, long-term processes in concrete, work of reinforced concrete under conditions of non-uniaxial (one-, two-, triaxial) stressed states with cracks, nonuniformity of the properties of materials over the volume of the structure, the dependence of the characteristics of mechanical and rheological properties of concrete and reinforcement on the temperature and duration of heating, on the modes of force and temperature effects, on the scale factor.
Keywords: reinforced concrete structures, concrete, heating, mechanical and rheological properties, characteristics, calculation, engineering methods, deformation models, development.
Mark Panasiuk, Oleksandr Petrakov, Natalia Petrakova
Numerical Tests of Concrete Samples
Donbas National Academy of Civil Engineering and Architecture
Abstract. The results of numerical testing of concrete prisms and cubes by limit loads are presented. Strategy of testing is based on new calculation models of concrete as anisotropic material that have different strength under press and tension. The equations of the plastic state based on the hypotheses of the Flow Theory of Plasticity, unified for different materials, such as soil ground, concrete, metal, etc. are used. For all materials, the strength theory of Mises-Schleicher-Botkin is used. The strength characteristics of materials, determined by standard methods, are redefined for octahedral sites, for which they are invariants. The problem is solved by the finite element method (FEM). The computational model of the FEM is represented by singular finite elements (tetrahedral, triangular plates, rods). This increases the accuracy of the description of loading paths in finite elements and ensures a unique correspondence of the state equations to elementary volumes of the construction. The use of singular finite elements is associated with a large amount of RAM for storing the stiffness matrix of the system, which significantly limits the range of practically solvable problems. To eliminate this contradiction, an iterative Newton – SUR method has been accepted for solving equilibrium equations in the design of finite element structures. An iterative algorithm was used, which does not require an assembly of the system stiffness matrix for its implementation. The volume of operational information is proportional to the number of finite elements in the system. With the traditional approach, which requires the assembly of the system’s stiffness matrix, the amount of operational information is proportional to the square of the degree of kinematic indeterminacy of the system. When using the iterative algorithm, the size of the stiffness matrix is reduced and the time of solving the problem is significantly reduced. The results of a nonlinear analysis of concrete structures are presented. It is shown that the work of concrete on the descending branch is a property of the design of the sample, and not a property of the material. The downward branch of the concrete work is a consequence of the destruction of the material due to volumetric stretching and can be obtained outside the framework of dilatancy models.
Keywords: anisotropic model of concrete, theory of plastic flow, descending branch of concrete work.
Valentina Taran, Rostislav Kostrykin
Justification of the Choice of Organizational and Technological Solutions for the Construction of Frameless Buildings in the Winter Period in the Conditions of the Donbas by the Method of Prioritization
Donbas National Academy of Civil Engineering and Architecture
Abstract. The construction of vertical structures of frameless buildings in the winter period in the conditions of the Donbas is carried out taking into account the influence of the main factors considered in the article, which allow using the best technological solutions with the least labor and time costs. The article describes the procedure for assessing the quality of performance of functions by the method of prioritization. The selection criteria for the compared options are given. An algorithm for determining the complex priority of one of the options over all those compared by a set of criteria is presented. Digrams of the ranks of the criteria factors based on the results of expert surveys are presented. According to the considered criteria, the option with the greatest number of complex priorities is determined. Pairwise comparison using the algorithm based on the method of prioritization makes it possible to analyze and compare the main indicators for the material and labor intensity of the process of erecting load-bearing walls of frameless buildings in the winter period in the conditions of the Donbas.
Keywords: frameless buildings, brickwork, winter conditions, factor, criterion, priority, manufacturability.
Andrei Volkov
The Influence of the Scale Factor and the Effect of Elevated Temperatures up to +200 °C on the Characteristics of the Physico-Mechanical and Rheological Properties of High-Strength Modified Concrete
Donbas National Academy of Civil Engineering and Architecture
Abstract. The results of experimental studies of the influence of the scale factor (dimensions of concrete samples and module of an open surface), as well as the effect of temperatures elevated up to +200 °C on the physical-mechanical and rheological properties of high-performance modified concrete based on the energy industry waste Donbas are presented. The dependences of the characteristics of strength, deformability, initial modulus of elasticity, Poissant’s ratio, parametric levels of fracturing, shrinkage and creep deformations at different levels of continuous compression of high-strength concrete on the dimensions of the samples and the conditions of their drying have been obtained based on the experimental data, including when exposed to high temperatures. Analytical dependences on accounting for the influence of the scale factor on the physical, mechanical and rheological properties of high-strength modified concretes at normal and elevated temperatures are tested and proposed.
Keywords: high-strength modified concrete, exposure to elevated temperatures, scale factor, strength and deformation under axial compression, shrinkage, creep.