Introduction. This paper is dedicated to the development of methods for approximating the thermophysical properties of concrete when solving a nonlinear heat conduction problem. The research is relevant in the context of assessing the fire resistance of building structures and enhancing their safety during fires. The goal of the work is to create universal models that describe the dependence of the thermal conductivity coefficient and specific heat capacity on temperature, which will improve the accuracy of temperature field calculations.

Materials and methods. Experimental data from numerous sources, as well as known standards (e.g., Eurocode 2), were used for analysis. The study employs the method of least squares (MLS) for constructing regressions and approximations. Various types of concrete — from lightweight to heavyweight — and their behaviour when heated to high temperatures were considered. Special attention was given to the influence of porosity, aggregate composition, and moisture content on the material’s thermophysical characteristics.

Results. New approximation formulas for the thermal conductivity coefficient of concrete as a function of density and temperature have been obtained. It has been shown that this dependence can be successfully described by a universal exponential model. A linear approximation for specific heat capacity was proposed, demonstrating good agreement with experimental data. It was established that effective heat capacity increases within certain temperature ranges due to endothermic processes such as cement stone dehydration and limestone decarbonization. The results were confirmed by comparison with existing models and regulations.

Conclusions. The approximation models developed in this work allow for more accurate predictions of concrete behaviour under high-temperature exposure. This has significant practical importance for designing fire-resistant structures, especially in nuclear energy and other sectors where safety plays a crucial role. The findings can be used to improve existing engineering approaches and develop new standards. Future research is planned to consider additional factors, such as mass transfer and changes in material structure during heating.

Introduction. The increasingly large-scale use of compressed concrete tube elements in construction practice requires the development of methods for calculating their strength, taking into account the main features of their force resistance. The current design standards of a number of countries offer empirical formulas that ensure good accuracy in calculating axially compressed concrete pipe structures, but incorrectly take into account the distribution of forces between the concrete core and the steel pipe. This paper proposes a method that allows for a reliable assessment of the stress state of concrete and pipe.

Materials and methods. The strength of short centrally compressed CTE can be determined using the method of limiting forces. The accuracy of calculations according to the proposed method depends on the correct determination of the coefficients of the material. Currently, heavy concrete, which has a dense structure, is usually used for pipe-concrete columns. For such concretes, it is proposed to take the values that are obtained after processing the results of experiments conducted under volumetric compression with a constant lateral pressure. To establish these values, a statistical analysis of the results of 232 experiments with short centrally compressed CTE made of heavy concretes of medium and high strength was performed. For each experiment, coefficient values were selected corresponding to the best match between theoretical and experimental destructive loads.

Results. The methodology of the current standards does not allow to take into account the features of the concrete core in compressed CTE concretes of various types. In the proposed methodology, this issue is solved by appropriate selection of material coefficients. If there is a sufficient amount of experimentation with concrete CTE of a specific type, it is not difficult to find the values of the corresponding coefficients.

Conclusions. The developed method for calculating the strength of short centrally compressed solid waste takes into account the main features of the force resistance of a tube-concrete structure and allows us to determine the distribution of forces between the concrete core and the steel pipe.

Introduction. In recent years, a number of experimental and a significant number of numerical studies have been conducted to study the resistance mechanisms of reinforced concrete building frames both under design loads and under emergency and special emergency impacts. The relevance of such studies is determined by both the need to assess the deformation and
destruction of such structural systems as a whole and by a fragmentary study of frame and wall units containing both pure bending zones and transverse bending zones in the presence and absence of longitudinal forces. The stress-strain state and the coordinates of the points of formation of spatial cracks in the structures of such fragments remain poorly understood, together with the unexplored effects that arise when the continuity of reinforced concrete is violated.

Materials and methods. When developing the volume of experimental studies, special attention was paid to such modelling of frame and wall nodes that would not distort the stress-strain state of the studied zones with local application of load, would simplify the study of mating nodes (statically determinate fragments of nodes) to the maximum and at the same time allow for the evaluation of the redistribution of forces in statically indeterminate systems taking into account the flexibility of nodes and the real picture of crack formation.

Results. The justification of the adopted design solutions of experimental reinforced concrete structures of nodes was completed and a programme and methodology for conducting research on the considered types of nodal connections of frame systems was developed, which allows for the development of a test scheme for the experimental identification of the features of the actual operation of the specified type of structures.

Conclusions. A programme and methodology of experimental research were developed to study the characteristics of crack formation, deformation and destruction of reinforced concrete frame structures, taking into account the different nature of their stress-strain state. Particular attention is paid to determining rotation angles, assessing the deformability and flexibility of nodes, as well as deflections, patterns of formation, development and opening of cracks, as well as deformation of concrete in complex stressed areas of reinforced concrete structures.

Introduction. A simple approach is proposed to determine the dangerous weakening of the cross-section of metal chimneys, which inevitably occurs due to the aggressive action of flue gases. Considering that, according to some estimates provided on the Internet, about 107,000 chimneys are in operation in Russia, this task seems to be quite relevant.

Materials and methods. The object of the study was a real chimney, operated in Moscow for more than 20 years, consisting of six cylindrical shells. As a result of corrosion wear, the cross-sectional areas of the shells decreased to varying degrees, as a result of which there was a danger of loss of stability of at least one of the shells. The stability of a cylindrical shell subjected to the combined action of a bending moment and a compressive longitudinal force was investigated based on the approaches described in the scientific and technical literature. Since the actual thickness of the shell was included in the calculation, its corrosion wear is already taken into account.

Results. As a result of the calculations, a simple formula was obtained that determines the conditional critical thickness of the cross-section of the most weakened shell. This weakening of the section requires engineering or management decisions to ensure further safe operation of the pipe. It is noted that the solution obtained is applicable at relatively early stages of chimney operation. As pipe deformations develop, due not only to the effect of the operating load, but also for other reasons, the pipe stretches go into a state of fluidity. The study of the stress-strain state of the “pipe trunk – extension” system under these conditions can be a continuation of the present work.

Conclusions. The identification of a conditional critical thickness during a routine inspection of the pipe, established by the relevant regulatory documents, does not mean that the pipe must be decommissioned or reinforced. In this case, according to the wall thicknesses determined during the examination, the calculation should be carried out according to the methodology described in this article, the actual values of the bending moment of the longitudinal force in dangerous sections should be calculated, and the stability of the pipe should be checked again.

Introduction. The calculation and design of bending elements taking into account shear (spalling) are urgent tasks in the design of building structures made of wood. The variant of application of the deformation approach to calculate the strength of wooden elements in transverse bending taking into account shear, based on the use of wood deformation diagrams in compression and tension taking into account nonlinear work, is considered.

Materials and methods. The verification of the proposed strength calculation approach was carried out on the basis of our own experimental studies of wooden elements during transverse bending. The criterion for the destruction of an element is the maximum value of the internal force at which the equilibrium conditions of the system of resolving equations are fulfilled, or non-compliance with shear strength conditions in cross-sections along the length of the shear site of the structure, including taking into account the nonlinear work of wood during compression.

Results. The proposed deformation approach makes it possible to obtain the distribution of shear forces in the area of possible shear of the beam fibres at any stage of loading. An analysis of the results of experimental and theoretical studies indicates the possibility of using the proposed approach to test the strength of wooden structures when bending, taking into account shear. Schemes of wood destruction during shear were experimentally established, which consist in shifting the fibres not along the plane in the neutral zone, but along the annual rings of wood. The proposed destruction criterion makes it possible to take into account the possible displacement of wood during transverse bending.

Conclusions. Based on the research, it was concluded that special attention should be paid to the actual shear strength of wood when calculating bent wooden elements, taking into account shear, which in real structures depends on the shear site, taking into account the location of the growth rings in the cross-section of the structure.

Introduction. The possibility of intensifying the foaming process of thermal power plant (TPP) slag waste by introducing a mixture of fluxes consisting of sodium tetraborate (Na2B4O7) and sodium fluoride (NaF) was studied. The relevance of the study is due to the need for efficient recycling of industrial waste and the production of building materials with improved characteristics based on them. The scientific novelty of the work lies in the study of the combined effect of these fluxes on the foaming processes and the formation of the porous structure of the material. The purpose of the study is to optimize the composition of the fluxing mixture to reduce the melting point and improve the quality of porous silicate materials.

Materials and methods. The methods of X-ray phase analysis (XRD), infrared spectroscopy (FTIR), microscopic analysis and experimental determination of the density of specimens were used.

Results. A study of changes in the temperature modes of sintering and foaming with the combined introduction of Na2B4O7 and NaF mixtures was performed, as well as their effect on the structural and phase characteristics of the materials. It was shown that sodium tetraborate promotes uniform distribution of pores and formation of amorphous glass phase. Fluoride causes intensive melting of the structure at elevated temperatures, as well as recrystallization of the melt with formation of albite crystals. The optimal ratio of fluxes was revealed, providing minimum density, stable porous structure and formation of glass-crystalline framework, which contributes to increased strength.

Conclusions. The obtained results demonstrate the prospects of the method of recycling slag waste of thermal power plants for obtaining porous building materials using the “self-foaming” technology. Further research can be aimed at optimizing fluxing mixtures and studying the methods of activating ash and slag waste to improve the technological characteristics of the resulting products.

Introduction. The soils at the base of tank foundations are subject to loading and unloading cycles during tank filling and emptying. The construction of such constructions is often carried out in areas with overwatered clay soils. The purpose of the study is to investigate the change in vertical deformations of water-saturated clays under the influence of “loading – unloading” cycles. This will make it possible to identify the values of additional settlements of water-saturated clay subgrade under loading and unloading cycles.

Materials and methods. A series of laboratory tests was performed in an odometer with cycles of loading and unloading with specimens of firm, soft-firm and very soft clays. The values of mechanical parameters of the studied clays obtained during laboratory tests were used in numerical calculations of the settlement of the base of a vertical steel tank in the PLAXIS 2D software package.

Results. The influence of clay consistency on the value of settlement under cyclic loading of samples in a compression device was studied. The ratio of plastic and elastic deformations was determined for clays of firm, soft-firm and very soft consistency. Additional settlement of clays with firm, soft-firm and very soft consistency caused by cyclic loading and unloading (within the first 10 cycles) amounted to 10 % of the total soil settlement. The results of numerical experiments showed that the additional settlement of the tank base at 20 cycles of loading and unloading amounted to 2.4–4.1 % of the total settlement.

Conclusions. Laboratory and numerical studies have shown that loading and unloading cycles of water-saturated clays lead to the development of additional settlement. The amount of additional settlement depends on the number of cycles and the consistency of the clay. During the whole period of the tank operation the number of filling and emptying cycles can be more than 2000, therefore, additional soil deformations in the foundation base should be expected.

Introduction. This paper examines the current challenges and features of using the modern model of organizational management of innovative activities of organizations in the region in the context of the onset of the Industry 5.0 period. A comparative analysis of the applied basic management models of organizational and production processes of companies is carried out. The key aspects of using a modern (network-centric) management model are considered. A brief description of the effectiveness of its use for innovative companies in the region is given. The relevance of the research is related to the presence of organizational and technological challenges of managing high-tech projects in the region. The subject of the research is organizational and production management models of knowledge-intensive companies. The scientific novelty lies in the formation of a modern conceptual model for managing innovation and high-tech production of technology companies in the region. The practical significance of the research work carried out lies in the transfer of its mechanism to the management system for managing innovative processes of companies.

Materials and methods. General research methods (abstraction, generalization, synthesis), comparative analysis, study of primary sources (deconstruction method), historical and genetic method.

Results. During the scientific research, 3 main organizational and production models of enterprise innovation management in regional economic systems were selected: 1) functional; 2) design-oriented and matrix; 3) modern or network-centric model. The conditions of use of each of them are determined depending on many factors: how the production organization is built; what is the focus of the business model; what is the scale of production; what is the priority of the main activity: is the release of innovative products; an exception; how many and which departments are involved in the development and implementation of new technological developments.

Conclusions. The described basic management models have their own distinctive features of conducting production and organizational activities. Their choice depends on the specific needs of the business. The use of a network-centric organizational and production model for managing high-tech projects in the region meets the current challenges of Industry 5.0. The key features of the network-centric model are the complete digital integration of all links in value chains, the organization of a smart virtual space and the on-line production of high-tech products.

Introduction. Digitalization processes intensify competition for investments, tourists and human resources among places. Hence, searching for effective digital tools, designed to promote places, is increasingly relevant. Despite the growing interest in digital marketing, scientific research into its use for place promotion purposes remains fragmentary. The mission of this study is to determine the role, the potential and limitations of digital marketing in creating a positive image of a place and making it more attractive.

Materials and methods. An integrated approach and general research methods were employed to study marketing digitalization processes for place promotion purposes. They included analysis and study of literature, promotion strategies, and digital marketing cases used in particular places. The article also clusters digital marketing tools.

Results. The study identified the main digital marketing tools used to promote places, as well as characteristic features of digital marketing tools employed. Successful place promotion strategies were systematized and typical digital promotion problems were identified.

Conclusions. Digital marketing is the most important tool used to boost the visibility and attractiveness of places. Places lose the competition for tourists, investors and new residents without a strong presence in the digital environment. Successful promotion requires a comprehensive approach; one communication channel (for example, a website or social networks) is not enough: a system of actions is needed, and it should be consolidated by a single idea of a local brand. A local brand must be clear and comprehensible to target audiences. Inconsistent promotion without a clearly formulated image leads to unclear perception places.

Introduction. The pace and direction of development of the construction sector should correspond to the country’s strategic development priorities and ensure the achievement of results established by state strategic planning documents. The article analyzes the current state and prospects of development of the Russian construction industry in the context of the country’s strategic development priorities, identifies the main growth drivers and factors of slowing down the construction industry. The purpose of the paper is to assess the ability of the construction industry to meet the needs of the economy and solve strategic development tasks of the country.

Materials and methods. The research is based on the analysis of strategic planning documents, macroeconomic parameters and the current state of the industry. The main methods used are: analysis of regulatory and methodological documents of strategic planning; analysis of statistical data; comparative analysis; analysis of the implementation and management experience of state programmes and projects; generalization and systematization of the studied information.

Results. The Russian construction sector is showing steady growth: the volume of construction work has increased by 31 per-
cent over the past five years, the national projects “Housing and Urban Environment”, “Safe High-quality Roads” are being successfully implemented, and the groundwork for the long-term progressive development of the region has been formed. At the same time, the record levels of commissioning achieved in housing construction are accompanied by a trend towards a decrease in the average area and room capacity of apartments; significant differentiation in the commissioning of both residential and non-residential buildings in the regional context remains; the volume of construction in progress is increasing, and there is a tendency to reduce capital productivity.

Conclusions. Identification and comprehensive analysis of both external and internal factors that determine the dynamics of construction and shape trends in this area will improve the quality of strategic planning and develop adequate measures to respond to emerging problems. The integration of such measures into state projects and programmes in the construction sector will minimize the negative impact of factors and will contribute to the achievement of national development goals of the country.

Introduction. This study examines the role of the mentoring system in Russian construction organizations, which is becoming especially relevant against the background of current trends in the labour market, where there is a shortage of personnel in this area. The purpose of the work is to analyze existing mentoring practices, identify factors influencing the formation and implementation of a mentoring system in construction companies of various sizes and specific activities, at the stage of transition to regulatory framework of mentors.

Materials and methods. The research is based on the analysis of materials from scientific publications and periodicals, regulatory legal acts related to the formation and functioning of the mentoring system, data on the labour market, the results of a survey conducted among masters working in the construction industry, and Internet resources.

Results. In the course of the work, key factors contributing to the successful introduction of mentoring were identified, including legislative changes and the specifics of the organizational structure of companies. The main results show that mentoring is actively used in many construction organizations, but its forms and content vary depending on the size of the company. In small organizations, less formalized approaches prevail, while in large companies there is a variety of methods and clearer legal framework.

Conclusions. The paper highlights the need to create a systematic approach to mentoring as a way to increase the adaptation of new specialists and reduce staff turnover, as well as recommendations on organizational and educational initiatives to improve the quality of mentoring in the construction sector.

Introduction. The aim of the paper is to develop a scenario-oriented approach to the design of construction projects in integrated territorial development projects.

Materials and methods. The scenario-oriented approach to designing construction projects in complex development of the territory (CDT) projects will be implemented through three key areas: integrated development of residential development areas; integrated development of non-residential development; integrated development of undeveloped areas. The basis for developing the CDT Project software module was the regulatory documentation in force in the Russian Federation.

Results. The software module “Project CDT” was developed for calculating the parameters of objects and the cost of projects according to three main scenarios, which takes into account regional cost coefficients, standards for building density, and regulatory requirements for social infrastructure. The resulting solution is saved in a detailed report in *.xlsx format. The developed software solution is flexible and can be adapted to any requirements and changes in regulatory documents.

Conclusions. The application of the presented approach will reduce the time for developing CDT projects considering the characteristics of the developed territory, and the proposed software module can be adapted to new regulatory requirements if necessary. At the same time, the traditional approach considers CDT objects as isolated elements, which violates the system engineering principles of emergence and hierarchy, which leads to the need to develop new approaches to assess the autonomy of construction objects in CDT projects. The development of a methodology for assessing autonomy will transfer the design of CDT to a fundamentally new level, in which the transition from isolated objects to synergetic complexes with dynamic modeling of their life cycle will be carried out. Further research by the authors will be devoted to this issue.