Introduction. As indicated in the first part of the article published in the Industrial and Civil Engineering journal (No. 12, 2023), the relevance of the work is due to the increased volume of use of longitudinal reinforcement couplings in reinforced concrete structures. The analysis of the domestic and foreign regulatory and technical base has shown that there is an opportunity to optimize coupling connections in terms of arrangement of their spacing. In that work, prototypes were described for conducting experimental studies to assess the effect of various design solutions for the spacing of coupling joints of stretched reinforcement on the strength of normal sections of bent elements. This article analyzes the experimental strength data obtained and offers appropriate recommendations for the design of bent reinforced concrete structures with coupling joints.

Aim. Improvement of the urban planning system in terms of clarifying and supplementing of existing regulatory documents on the design of reinforced concrete structures.

Materials and methods. The research was carried out taking into account modern requirements, as well as the analysis of the results of their own experiments.

Results. The result of the work is an analysis of the experimental data obtained for bent reinforced concrete beams with coupling joints of stretched reinforcement. Based on the analysis, recommendations have been formed to optimize design solutions and clarify the requirements for the input control of couplings.

Conclusions. Considering that, in general, according to the results of the work, a fairly good convergence of experimental and theoretical results has been obtained, it is possible to assume a reduced value of coupling spacing for certain types of load-bearing reinforced concrete structures. The need to tighten the input control of couplings in order to detect defects has also been identified. In addition, the need for further research on this issue was noted.

Introduction. Numerous experimental data from Russian and foreign researchers indicate that the classical plasticity hypotheses do not take into account the different resistance to uniaxial tension and compression, the influence of the spherical tensor. At the same time, experiments show that the ultimate resistance depends on the type of stress state, and hydrostatic pressure increases the strength and plasticity of solids.

Aim. To establish the dependence of the influence of the second component of stresses during biaxial compression of concrete on the parameters of the complete diagrams of deformation of the material σ_bR and ε_bR it is necessary to describe these diagrams, and to construct a closed curve on the plane of the main stresses (concrete strength criterion).

Materials and methods. Based on the experimental materials of foreign and domestic researchers, including the experiments of the authors of the article, methods of mechanics of deformed solids, limit curves and a closed curve on the plane of the main stresses in the form of a chain line forming the smallest area strength surface in the form of a catenoid are proposed.

Results. The article provides an analysis of the known strength criteria from the point of view of their geometric interpretation in the stress space. It is shown that these studies relate mainly to metals and metal structures, and for the design of reinforced concrete and steel-concrete structures in a complex stress state, it is necessary to develop an appropriate criterion for the strength of concrete.

Conclusions. As a result, the proposed limit curves and the surface (material strength criterion) on the plane of main stresses in the form of a catenoid accurately reflect the behavior of concrete under conditions of uniform and uneven flat stress state, and the equation of the surface in the form of a catenoid is a generalization of the equations of limit curves for each of the three types of flat stress state. At the same time, there is no overestimation of strength in the "compression – compression" area in this case.

Introduction. The article discusses the possibilities and prospects of using modified concrete for the foundations of overpass supports.

The aim is to study the effect of various additives on the sulfate resistance of the foundations of bridge supports and overpasses.

Materials and methods. To achieve this goal, tests of reinforced concrete samples were carried out with the introduction of various additives into the concrete mixture. As part of the study, a MasterLife® WP 3760 modifying additive was selected. Using this additive, experiments were conducted with an accelerated assessment of the effect on the sulfate resistance of concrete based on general-purpose Portland cement. In accelerated tests, the sulfate resistance of concretes with the studied additive was performed in comparison with concretes of the same composition prepared on sulfate-resistant and general-purpose Portland cement without additional additives. The water-cement ratio in all tested formulations remained constant.

Results. Samples made of general construction cement with the addition of MasterLife® WP 3760 after performing the specified test cycles in a sulfate medium showed a decrease in compressive strength by 3 % from their initial values. The residual strength of concrete samples with MasterLife® WP 3760 additive was 97 %, which exceeds the resistance of concrete to sulfate-resistant cement, the remaining strength of which is 94 %. The MasterLife® WP 3760 additive is a substance that significantly reduces the permeability of concrete due to "blockage" by particles of the substance or neoplasms of pores and capillaries of concrete, these substances due to physical and chemical processes lead to homologation, a decrease in the permeability of concrete, and, as a result, an increase in frost resistance and corrosion resistance.

Conclusion. As a result of the action of the MasterLife® WP 3760 additive, the corrosion resistance of concretes and mortars increases, including resistance to sulfate aggression, by reducing water permeability. Thus, it becomes possible to eliminate cracks in concrete with an opening width of up to 0.4 mm and extend the durability of concrete.

Introduction. This article is devoted to a major Russian scientist, Doctor of Technical Sciences, Professor V.I. Murashev, certain periods of his biography and scientific activity. Based on archival data and special technical literature, it is concluded that Professor Murashev has done a lot for the development of construction science, including the production and introduction of heat-resistant reinforced concrete structures into the metallurgical industry.

Researcher V.I. Murashev for the first time proposed a model for calculating the deformation of reinforced concrete elements with cracks, which made it possible to avoid mistakes in construction.

Aim. Conducting a study of the fruitful scientific activity of Professor V.I. Murashev in the field of reinforced concrete theory, clarifying the history of his creation of temperature-resistant reinforced concrete structures, supplementing the scientific biography of the scientist with new facts based on the study of newly discovered data.

Materials and methods. The author, having studied archival materials on an urgent topic, using retrospective, historical, tipological and comparative research methods, showed certain aspects of the scientific activity of Doctor of Technical Sciences, Professor V.I. Murashev, determining the degree of his active participation in the development of the theory of reinforced concrete, specifying the most significant achievements of the researcher in construction science.

Results. The article presents the first comprehensive study of the scientific activity of Professor V.I. Murashev in the field of concrete and reinforced concrete, analyzes the newly discovered biographical data of the scientist in the period 1904–1959.

Conclusions. The database of research sources has been expanded, new archival documents and materials have been introduced into scientific circulation, confirming the originality of the versatile personality of Professor V.I. Murashev, his outstanding achievements in construction science in the period 1929–1959.

Introduction. Existing cement mortars and fine-grained cement concretes have the same composition, however, according to State Standard, these materials are tested using different methods for evaluating physical and mechanical properties that are not in harmonious accordance with each other. This disagreement in the evaluation of properties confuses the regulatory authorities, which receive data that contradict each other. The introduction describes the appearance of discrepancies in the assessment of the properties of fine-grained cement concrete and cement mortar. A change in the concepts of definitions between the original classification and the modern one is presented.

Aim. Finding the transition coefficients when testing for three-point and four-point bending of samples of mortars and fine-grained cement concrete, taking into account the geometric dimensions of the samples.

Materials and methods. Preparation of cement concrete samples of various classes of materials conforming to State Standard requirements, description of differences in methods for determining three-point and four-point bending, calculation and manufacture of additional installations taking into account the geometric dimensions of the samples, conducting bending tests according to standard methods and using manufactured installations preserving the proportion of values taking into account the scale of the sample, as well as calculation of transition coefficients for each class.

Results. The results of the study showed that the transition coefficients have a significant impact on the processing of the results and the assessment of the strength characteristics of mortars and fine-grained cement concretes and may affect the accuracy of the data obtained.

Conclusions. The study provides a better understanding of the mechanical properties of mortars and cement concretes during bending, which can be useful in the design, construction of structures and quality control.