Introduction. The article examines the use of concrete filled steel tube (CFST) structures in hydraulic engineering and compares various structural options in terms of their stress-strain state and load-bearing capacity.

Aim. The main goal of the work is to analyze the application of concrete-filled steel tubes and various approaches to their design, as well as to compare the stress-strain states of different structural solutions.

Materials and methods. The calculations of reinforced concrete structures were performed using the finite element method with nonlinear models in ANSYS software.

Results. The calculation results showed that for monolithic concrete pipes (without reinforcement), the load-bearing capacity was 56.28 kNm; for reinforced concrete pipes, the load-bearing capacity was 416.60 kNm; for the metal pipe, it was 639.07 kNm; for the concrete-filled steel pipe (tubular concrete), the load-bearing capacity increased to 768.76 kNm; and for reinforced concrete-filled steel pipe, the highest load-bearing capacity was 1085.50 kNm.

Conclusions. The calculation results and comparative analysis show that reinforced tubular concrete is the most effective in terms of load-bearing capacity, although it has a higher cost. At the same time, reinforced concrete and metal pipes offer a more economical option but with lower load-bearing capacity. The choice of material depends on the specific project requirements, including loads, cost, and operating conditions.

Introduction. The calculation of the crack opening width is one of the requirements for the operational reliability of reinforced concrete structures. Cracks in reinforced concrete elements occur both under operating loads and during the initial period of strength gain due to the low tensile strength of concrete and the nature of its operation in general. The increasing speed of construction requires taking into account the thermally stressed state of not only massive, but also conventional structures at an early age of concrete, including calculating the crack opening width at the strength gain stage to ensure the design and operational characteristics of structures and assess the possibility of the loading of the structures whose concrete has not yet reached its operational characteristics.

Aim. The study is aimed at analyzing the need to take into account the features of concrete at an early age (the ratio of strength and modulus of deformation differs from the design age) when calculating the crack opening width.

Materials and methods. The paper analyzes the calculation methods laid down in the regulatory documents. Calculations of crack opening widths for reinforced concrete sections with different percentages of reinforcement have been performed. A comparison of the calculation methods and the obtained values of the crack opening width according to various regulatory documents for concrete in the early stages of hardening was performed, as well as an assessment of the effect of changes in the modulus of elasticity on the cracking process. The analysis was performed taking into account both the standard modulus of elasticity of concrete (28 days) and its reduced value on day 7. Experimental research data was used to verify the results.

Results. It was found that a decrease in the modulus of elasticity of concrete in the early stages of hardening (up to 24 %) leads to an increase in the estimated crack width (up to 11 %) with identical strength.

Conclusions. The results of the study emphasize the need to take into account the changes in the modulus of elasticity of concrete in the early stages of hardening when designing the structures. This will make it possible to more accurately predict the crack opening width, including temperature and shrinkage, and will increase the reliability of reinforced concrete structures during operation.

Introduction. The paper shows the reinforcement tension technology, at the ends of which metal reinforcement segments with shape memory are attached, and also shows technologies comparable to the proposed one. Examples of the use of such technologies in the restoration of reinforced concrete products and in the stretching of reinforcement on concrete are shown.

Aim. To simplify and reduce the cost of restoration work to restore worn-out reinforced concrete structures.

Materials and methods. Patent searches for foreign patents in this area have been conducted, as well as scientific articles from the last 5 years have been studied.

Results. A patent application has been filed and the application of this technology in practice has been substantiated.

Conclusions. This technology is easily feasible in practice and can reduce the cost of restoration work.

Introduction. Based on the experimental studies of the frost resistance of concrete according to the accelerated third method of State Standard 10060-2012 (with Change No. 1) with various methods of samples thawing, the coefficients of transition (K) from the grade of concrete frost resistance determined during thawing under conditions of incomplete immersion of sample containers in a solution of 5 % sodium chloride or when blowing sample containers with warm air, to the grade of concrete determined by the standard method of thawing samples in a bath with a solution of 5 % sodium chloride. The calculation method of the thermally stressed state of concrete has shown that a change in the methodology for concrete testing for the frost resistance, including the method of thawing samples after freezing, can lead to an unreliable assessment of the quality of concrete.

Aim. The numerical calculation of the thermally stressed state of the tested cube samples was performed in order to identify the features of various methods of concrete samples thawing after freezing and to refine the developed transition coefficients for assigning a grade of concrete for frost resistance.

Materials and methods. A numerical calculation of the process of concrete samples freezing and thawing during the frost resistance test using the accelerated third method according to State Standard 10060-2012 (with Change No. 1) in the ATENA software package has been performed. Based on the results of calculating the theoretical temperature values, the temperature differences between the core and the surface of the cubes were determined and the maximum tensile stresses on their surface were determined at the time of the greatest temperature differences.

Results. Numerical calculation of the thermally stressed state of the tested samples during freezing and various thawing modes when determining the frost resistance of concrete using the accelerated third method confirmed the results of experimental laboratory work and showed that the thawing mode when sample containers are not fully immersed in the solution differs qualitatively from the other thawing methods considered and is the most "rigid" due to the possibility of formation of surface cracks on the concrete surface of the samples during the testing process.

Conclusions. The experience of applying numerical calculations of the thermally stressed state of the tested samples has shown that, as experimental data accumulate, they can be used to predict the frost resistance of concrete.

Introduction. The results of studies of high-strength self-compacting lightweight concretes based on a Portland cement binder with an organo-mineral modifier of the MB type and three different types of light aggregates (sand and gravel/crushed stone) are presented, the results of which can be used to calculate and design light-weight reinforced concrete structures of buildings, as well as to make changes and expand the boundaries of the parametric range of light concrete from B40 to B70 in SP 63.13330.2018.

Aim. Assessment of the influence of technological factors on the strength and deformation characteristics of high-strength self-sealing lightweight concrete of classes B40–B70 grades of medium density D1600–D2000 from self-sealing mixtures.

Materials and methods. For the preparation of high-strength self-sealing lightweight concretes, materials were used: Portland cement CEM I 42,5; organo-mineral modifier MB10–50C; micro filler – ground limestone; natural quartz sand; light porous aggregates – artificial expanded clay sand and gravel and natural tuff sand and crushed stone from two deposits. The tests of concrete mixtures and concretes were carried out using standardized and special techniques.

Results. The strength (cubic and prismatic compressive strength) and deformation (initial modulus of elasticity, Poisson's ratio and maximum relative compression deformations) characteristics are determined and stress diagrams (σ – ɛ) of six high-strength self-sealing lightweight concretes of compressive strength classes from B41 to B73 with an average density grade from D1600 to D2000 are constructed. The impact of cement consumption, the type of light porous aggregates (sand and gravel/crushed stone) and the replacement of light expanded clay sand with natural sand from dense rocks on the physical and technical characteristics of light concrete has been assessed.

Conclusions. The use of various types of light porous aggregates of artificial (ex-panded clay sand and gravel) and natural (tuff sand and crushed stone) origin, as well as fine aggregate from dense rocks (natural quartz sand), together with a Portland cement binder with the addition of an organo-mineral modifier of the MB type, makes it possible to obtain high-strength self-sealing lightweight concretes of grades B40–B70 according to medium density D1600–D2000 with strength and deformation characteristics, significantly exceeding the maximum normative values for lightweight concrete of class B40 grade with an average density of D2000 according to SP 63.13330.2018.

Introduction. In two parts of the article, the conceptual and methodological issues arising in the calculations of reinforced concrete structures using the limit state method with a nonlinear deformation model (NDM) according to SP 63.13330.2018 are investigated. The first part is devoted to the formulation of the problem and the development of the conceptual framework.

Aim. To improve the concepts and terms about the laws and diagrams of concrete deformation under compression and tension in terms of their normalization in calculations using the limit state method.

Methods: formal logic (analysis, synthesis, induction, deduction), methods of probability theory and mathematical statistics, the method of limit states.

Results. It is shown that the regulatory framework for calculations using the limit state method based on NDM contains contradictory and ambiguously understood terms, and some very important concepts about the normalization of the mechanical properties of concrete are missing. In this part of the article, it is proposed to fill in these gaps with new concepts introduced by the author and eliminate existing contradictions and inaccuracies.

Conclusions. It is proposed to exclude the ambiguous terms "state diagram", "working diagram" and "diagrammatic method" from the normative and scientific circulation in calc ulations of structures according to NDM. In SP 63.13330.2018, the section "Terms and definitions" should be supplemented with currently completely missing terms and definitions related to NDM calculations, which is possible, among other things, on the basis of the 12 new concepts introduced by the author on the laws and diagrams of concrete deformation under compression and tension with strict mathematical content, which ensure the completeness, integrity and interconnectedness of the normalization of characteristics. physical and mechanical properties of concrete. The differences in concepts are related to the assignment of its fixed probability p∈[0.004;0.5] to the left-hand percentile of the normal distribution at a constant confidence level α = 0.95 to the left boundary of the confidence interval for estimating this percentile based on the t-distribution.

Introduction. Modern construction processes are characterized by high complexity of facilities, strict requirements for safety and reliability, as well as dynamic changes in the construction technology market. In these circumstances, ensuring product quality control becomes a key success factor. Traditional control methods often require significant labor and financial investments, which stimulates the transition to automated digital technologies. Software packages such as BIM systems and specialized solutions for statistical data processing, combined with machine-readable standards (for example, Industry Foundation Classes – IFC), can significantly improve the objectivity and efficiency of quality control. One of the promising tools is the StatBIM software package, which allows for long-term quantitative assessment of product quality, optimizing the use of human and technical resources.

Methods. The research includes: the implementation of StatBIM to automate data collection and analysis (strength, elongation of reinforcement according to State Standard 34028-2016); the use of machine-readable standards for integration with BIM systems and regulatory frameworks (State Standard R 57309-2016, ISO 16739-1); statistical methods – Shapiro – Wilk, Anderson – Darling tests to verify the normality of distribution, impact analysis rounding (up to 0.5 % according to State Standard 12004-81) for variance, average value and availability of characteristics; development of XML templates to formalize the requirements of regulatory documents.

Results. The implementation of the StatBIM software package allows: to reduce the time for compliance with standards checking by 40 % due to automatic data reconciliation; to identify distortions in statistical parameters due to rounding (reducing the accuracy of the average by 7 %, underestimating the variance

Introduction. The article is devoted to the analysis of the depth of digitalization in the Russian construction industry, which is one of the key sectors of the economy. In the context of the decree of the Government of the Russian Federation on the strategy for the development of the construction industry and housing and communal services, the importance of three areas of transformation is emphasized: administrative, digital and professional. Special attention is paid to digital transformation as the main vector of innovative development, contributing to increasing transparency of procedures in construction.

Aim. Identifying the current level of digitalization of the largest construction sector, searching for growth and efforts applying points in accordance with the Wilfredo Pareto (80/20) principle to ensure digital transformation in the largest but opaque sector of one of the most inert sectors of the economy.

Materials and methods. The author of the study applied a comprehensive methodological approach to analyze the level of digitalization in the Russian construction industry. The main research materials and methods include: analysis of the regulatory framework; comparative analysis; qualitative research methods; quantitative research methods; case studies.

Results. The study shows that the construction industry is highly conservative, and innovations are being implemented faster in the segment of apartment buildings, while individual housing remains at the initial level of digital transformation. Key digital technologies such as electronic document management, electronic signature, cloud systems, dynamic pricing and digital design are considered. The analysis shows that leading development companies are significantly ahead of other organizations in digitalization, while individual housing construction has low rates of digital solutions implementation. 95 % of interactions in urban planning activities are still carried out on paper or in non-editable electronic format.

Conclusions. Based on the conducted research, the article highlights the main directions of digitalization of the individual housing construction sector for 2025, including the development of electronic services, the expansion of the use of BIM technologies, and online design. It is emphasized that significant market fragmentation and low digital maturity of contractors are the main obstacles to the digital transformation of the construction industry in Russia.