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Sabitov L.S.

Candidate of Engineering Sciences (Ph.D.), Associate Professor, Kazan (Volga region) Federal University, Russia

Stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements under the action of longitudinal and transverse forces

https://doi.org/10.58224/2618-7183-2024-7-1-3
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Abstract
Most wall panels in operating multi-storey residential buildings are in a complex stress-strain state under the influence of vertical and horizontal loads, such as their own weight, wind, etc. These features must be taken into account in the calculation in order to ensure operational safety. The combination of vertical and horizontal forces acting simultaneously for three-layer bending elements leads to the fact that the boundary between the compressed and tensile zones not only moves from one layer to another, but also has a different geometric shape depending on the ratio between the vertical and horizontal load. The stress-strain state during the formation of normal cracks in three-layer bendable reinforced concrete elements is caused by the impact on layers of different concretes. The formation of normal cracks occurs due to the achievement of ultimate tensile strength by the most stretched concrete under the influence of external loads. Since three-layer reinforced concrete elements consist of two outer layers (reinforced concrete) and a middle layer (lightweight concrete), when such an element bends, the outer layers are subject to compression, and the middle layer is subject to tension. The boundary of the compressed zone can be located either in one of the outer layers or intersect the middle layer, which falls into both the compressed and stretched zones. To analyze the stress-strain state during the formation of normal cracks, it is necessary to take into account the fol-lowing parameters: geometric characteristics of the element (dimensions and shape of the section, layer thickness, etc.), physical and mechanical properties of concrete (compressive and tensile strength, elastic modulus, Poisson's ratio, crack resistance coefficient, etc.), characteristics of reinforcement (class, diameter, pitch of bars, etc.) and its location in the section.
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Method for calculating the strength of massive structural elements in the general case of their stress-strain state (kinematic method)

https://doi.org/10.58224/2618-7183-2023-6-3-5-17
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 5-17 p.
Abstract
A variant of the kinematic method of the theory of limit equilibrium is proposed; massive structural elements are considered, the material of which, in the general case, is anisotropic.
A rigid-plastic model of a deformable solid body is adopted. It is assumed that massive structural ele-ments are destroyed by dividing into parts that deform relatively little (“absolutely rigid finite ele-ments”, ARFE) and have 6 degrees of freedom in three-dimensional space. The process of destruction of the material goes along infinitely thin generalized destruction surfaces (GDS), on which the work of all acting internal force factors (IFF) is taken into account – 9 forces and 9 moments. Bodies made of homogeneous isotropic materials that resist tension and compression in different ways are considered. The strength surfaces in the IFF space are described by the corresponding parametric equations.
Using the equilibrium equation in the Lagrange form and the Mises maximum principle, as well as the proposed parametric equations of the limiting surface, the problem of determining the minimum value of the possible kinematic parameter of the load is reduced to a standard linear programming problem (LP), which is solved using the simplex method.
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Method for calculating the strength of massive structural elements in the general case of their stress-strain state (parametric equations of the strength surface)

https://doi.org/10.58224/2618-7183-2023-6-2-104-120
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 104-120 p.
Abstract
In the mechanics of a deformable solid, there are rods (one overall dimension of which is significantly larger than the other two), plates and shells (one dimension of which is significantly smaller than the other two), arrays (all three dimensions of which are of the same order). The complexity of the corresponding calculation models grows in the same order: the calculation models for rods and rod systems are relatively simple, the most complex are the calculation models for massive structural elements.
In the work, parametric equations of the strength surface in the space of internal force factors (IFF) are obtained – 9 forces and 9 moments for homogeneous anisotropic bodies. As special cases, similar equations are given for isotropic bodies that resist tension and compression differently, for isotropic bodies that equally resist tension and compression. Algorithm A1 for constructing the desired sections of strength surfaces given by parametric equations is proposed. Algorithm A2 is proposed for deter-mining the safety factors for the bearing capacity, remaining in the space of the IFF. Some examples of calculations made using the proposed equations, algorithms and the corresponding computer programs compiled on their basis are given.
The proposed method for calculating massive bodies allows a more realistic assessment of the bearing capacity of massive structural elements.
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Сompositional analysis: the project of the III Communist International Monument (Tatlin Tower)

https://doi.org/10.58224/2618-7183-2023-6-1-74-83
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 74-83 p.
Abstract
The authors of the article broadcast information about the study of the compositional activity of architects of Soviet Russia in the 20s of the XX century. in line with the trend of "constructivism". The study of three-dimensional architectural composition is considered by the authors as the separation of the "indivisible whole" (integrity – the law of composition) and "unchangeable for further im-provement" (it is impossible to make changes without deterioration of the already created, completed composition) artificially created object – organism of universal laws and means. The authors believe that the study of high–class Heritage samples is based on the separation of formal (composite) ele-ments (contrast, plastic, texture, plane – volume, rhythm, modular divisions, construction, engineering materials, walls, floors, ceilings, fasteners, etc.) from an artificially created composite organism. The analysis allows you to develop compositional thinking, taste and teaches you to understand the course and origins of the Master's compositional thought. The study of the formal (compositional) sphere of the Heritage of the classics of modernity and past eras allows you to build the path of the author's work on the project, avoiding mistakes and disappointments.
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Compositional analysis: synthesis of abstract painting and architecture of the 20s of the XX century

https://doi.org/10.58224/2618-7183-2022-5-6-64-74
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 64-74 p.
Abstract
The authors broadcast information about the union of architecture and abstract painting and the identification, fixation of the laws and means of composition that were used in the creation of the well-known creative products of architecture, painting, design. The article analyzes the prerequisites for the emergence of an international style that easily integrates into any cultural environment, historical buildings, due to the presence in the products of this direction of the maximum formal sphere and almost complete leveling of the content part in an artificially created compositional form. The study of high-class Heritage samples allows you to develop taste and teaches you to understand the course and origins of the Master’s compositional thought. The study of the formal (compositional) sphere allows you to build the path of the author's work on the project, avoiding mistakes and disappointments.
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Universal Laws of Composition (Artificial and Natural Form) on the Example of the V.G. Shukhov Tower

https://doi.org/10.58224/2618-7183-2022-5-5-29-41
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 29-41 p.
Abstract
The authors of the article broadcast information about the study of the compositional activity of engineers in Soviet Russia in the 20s of the XX century. in line with the architectural trend "con-structivism". The study, analysis and fixation in graphic images of masterpieces of volume-spatial composition in the history of engineering, scientific thought is considered by the authors as an isola-tion from an artificially created object – an organism of universal laws and means. The authors believe that the study, analysis and fixation in a schematic graphic material of high-class samples of science, technology, engineering allows you to develop compositional thinking, taste and teaches you to under-stand the course and origins of compositional thought in design. The study of the formal (composi-tional) sphere of the Legacy of the classics of modern and past eras allows you to build the path of the author's work on the project, avoiding mistakes and disappointments.
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RESULTS OF ENDURANCE TESTING OF PREFABRICATED CRANE STRUCTURES

https://doi.org/10.58224/2618-7183-2022-5-4-39-49
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 39-49 p.
Abstract
The purpose of the work is to analyze the results of tests of prefabricated crane beams for endurance during cyclic tests on a specially designed stand. The method of carrying out such tests is given. It indicates the inadmissibility of the operation of steel crane structures with cracks and the importance of research aimed at increasing the endurance and durability of crane beams. It proves the need to develop new crane beams (various profiles) to increase the period of accident-free operation of industrial buildings (using bridge lifting mechanisms with heavy duty) up to 25 years. It is proved that the developed prefabricated crane beam has improved (in comparison with the standard) characteristics.
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TECHNOLOGICAL FEATURES OF THE CONSTRUCTION OF A DEMOUNTABLE FOUNDATION FOR TOWER STRUCTURES

https://doi.org/10.58224/2618-7183-2022-5-3-17-26
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 17-26 p.
Abstract
The paper proposes a new type of modular demountable reinforced concrete foundation for the construction of tower-type structures. Numerical modeling and design features of the manufacture and installation of the foundation, implemented under patent 2633604 “Demountable foundation for support” for a real tower with a height of 30 meters and a power of a 150 kV wind power plant, are given. The reduction of material consumption is achieved due to the formation of a cavity in each typical module and filling it with soil or any inert material. The result of the proposed solution is to increase the bearing capacity of the foundation as a whole, increase the strength and rigidity of its main joints, as well as simplify installation in comparison with traditional approaches to design. Moreover, the foundation modules, where maximum stresses occur, can be made of fibre concrete.
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THE RELIABILITY COEFFICIENT FOR FIBRE CONCRETE MATERIAL

https://doi.org/10.58224/2618-7183-2022-5-2-51-58
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 51-58 p.
Abstract
One of the main parameters of the method for calculating building structures made of concrete and fibre concrete by limiting states is the reliability coefficient for the material, which characterizes the heterogeneity of the physical and mechanical properties of the material. In national and foreign standards, it takes a constant value of 1.3 (obtained on the basis of direct tests), or 1.5 (obtained on the basis of indirect tests and the use of graduated dependencies). The concrete matrix for the formation of the structure of fibre concrete is most often fine-grained concrete with special additives, which has greater uniformity in comparison with heavy concrete, which cannot but affect the reliability of the composite material in question as a whole: the stock coefficients for fibre concrete should be lower than for normal concrete, which has not been reflected in modern standards for design yet. Starting from interval estimates of the average strength value, a new approach to determining the reliability coefficient for the material, differentiated by the 1st and 2nd groups of limit states, is proposed. The results of calculations according to the proposed formulas for previously conducted tests of steel- and glass-fiber concrete images allowed us to conclude: the introduction of fiber into the concrete matrix of the proposed effective composite composition increases the uniformity of the strength properties of the material, which leads to an increase in the reliability of its use in building structures, a decrease in the value of the reliability coefficient (margin) for the material to 1.164...1.235 for central axial compression and up to 1.172...1.272 – for central axial stretching. The obtained actual coefficients in strength calculations will allow to reveal the supplemented reserves of the bearing capacity of structures made of this material up to 22.4%.
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CALCULATION OF HIGH-RISE BUILDINGS UNDER SEISMIC EFFECT OF “CONTROLLING EARTHQUAKE” LEVEL BY NONLINEAR STATIC METHOD ON THE EXAMPLE OF ADYGHE WIND POWER PLANT

https://doi.org/10.34031/2618-7183-2020-3-1-14-20
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 14-20 p.
Abstract
The aim of this work is to test a multi-modal nonlinear static method for seismic impact of the "controlling earthquake" level for high-rise structures on the example of a wind power plant (WWP) with a capacity of 1.5-2.0 mW of the Adyghe WPP using computer modeling in the LIRA 10.10 PC. Additionally, the results were verified in the PC “Ansys”. The main bearing element of the WWP is a tower-pipe with a weak taper, the material of which is high-strength steel S355. The assessment of the structure seismic resistance is performed in physically and geometrically nonlinear settings. At the same time, the Vaughn-Mises strength theory was used for steel. Comparison of the calculation results proves the effectiveness of the multi-modal nonlinear static method. The method under consideration has a number of advantages: tolerance to the initial data in terms of numerical description of the seismic impact, less machine capacity of the calculation in comparison with the direct dynamic method, and the ability to automate the calculation process fully.
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