Introduction. Beams are widely used in the construction industry as load-bearing structures of bridges, overpasses, coverings, slabs, stairs, equipment platforms, etc. In order to fully utilize the bearing capacity of such structures and to reduce the rate of material consumption, beams of variable cross-section along the length can be used. During operation, such structural elements are subjected to various types of vibrations, which determines the relevance of studying various aspects of vibrational motion.

Aim. To apply numerical methods for studying the influence of rotational inertial forces in the presence of viscous frictional forces on free vibrations of variable-section beams. This area of research presents interest, since the calculations are directly related to the determination of frequencies and forms of natural vibrations of structures.

Materials and methods. Free vibrations were described by a homogeneous partial differential equation of hyperbolic type. The methods of variable separation and finite differences were used. A discrete domain in the form of a set of uniform grid nodes and a homogeneous system of algebraic equations were introduced. The system of equations in the matrix-vector form was used.

Results. The spectra of natural frequencies, damping coefficients, and eigenforms of beam vibrations are determined. It is shown that the coefficient matrix has a banded and pentadiagonal form. The matrix elements are functions of the characteristic index. The damping coefficient and the frequency of free vibrations are determined from a system of two nonlinear equations. The solution of the system of equations is found using the method of coordinate descent. An example of calculation of a welded I-beam is considered. Five elements of the spectra of damping coefficients and natural frequencies are calculated.

Conclusions. State-of-the-art MATLAB solvers allows numerical and graphical methods to be combined. In the solved examples, the advantages of these methods were successfully applied to determine the eigenvalues of matrices and eigenfunctions. The high validity and accuracy of the results obtained confirm the simplicity and versatility of the methodology for determining the characteristics of free vibrations of beams of variable cross-section.

Introduction. Prediction of the durability of flame-retardant coatings of steel engineering structures and preservation of their performance during operation remain important research directions. There is a lack of normative documents in the field of fire protection, regulating the process of testing of flame-retardant coatings during operation, as well as determination of their durability (service life).

Aim. To develop test methods for determining the resistance of flame-retardant coatings of steel engineering structures exposed to climatic factors, preservation of their fireproof and anti-corrosion properties during operation.

Materials and methods. Test specimens included 600 x 600 x 5 mm plates made of 08kp and 08ps sheet steel according to State Standard 16523-97 and State Standard 9045-93 with a flame-retardant agent applied on the front side.

Results. Methods for testing thin-layer intumescent and structural flame-retardant coatings during operation are proposed. The methodology of accelerated climatic testing of specimens coated with thin-layer intumescent flame-retardant coatings (flame-retardant paints) corresponds to State Standard 9.401-2018. These coatings are inherently high-solid paint materials. A new methodology, sequence, and modes of testing are developed for structural flame-retardant coatings. The subsequent assessment of fireproof properties of coatings and their preservation is carried out by the methods of fire protection efficiency according to State Standard R 53295-99 and the methods of thermal analysis. These methods imply comparison of the characteristics of the initial flame-retardant coating and those obtained after sample aging. The preservation of fireproof properties by thin-layer intumescent and structural coatings is additionally evaluated by the intumescence coefficient and the change in thermal conductivity, respectively.

Conclusions. Test methods for flame-retardant coatings of steel engineering structures during operation are developed. Threshold levels of changes in their properties are established. After accelerated climatic tests, fire protection efficiency should not decrease by no more than 20 %. For structural fire protection, an increase in thermal conductivity by no more than 5 % is permitted. For thin-layer coatings, the arithmetic mean value of the intumescence coefficient should not decrease by no more than 30 % of the initial value.

Implications. The developed methods were used in the preparation of a draft national standard of the Russian Federation “Steel engineering structures with fireproof coatings. Test methods for anticorrosion properties and resistance to climatic factors during operation” to ensure regulatory fire safety requirements for these structures.

Introduction. Questions of mathematical modeling of the dynamic problem in the form of a generalized system with one degree of freedom are discussed. Such systems include high-rise tower-type structures. Seismic stability of unique tower-type objects represents a relevant research problem.

Aim. To determine the stress-strain state of a studied object under the action of external factors in the form of an earthquake accelerogram.

Materials and methods. The methods of structural mechanics, dynamics of structures, and numerical simulation were used. The Lagrange equation was used as a basis for obtaining the motion equation of a generalized system with distributed parameters. The research methodology also included mathematical modeling of the considered systems, their numerical analysis, comparison of the obtained results with literature data.

Results. A mathematical model was developed to investigate the stress-strain state of engineering structures under various external, including seismic, effects. The differential equation of the generalized system is solved directly using the method of successive approximations and the Duhamel integral at each time step. The developed algorithm was used to compile a software application in the FORTRAN language followed by obtaining the kinematic and static data of the investigated object. Using the example of a tower-type structure, free vibrations from the action of an instantaneous impulse were investigated. The results from a given earthquake accelerogram are presented.

Conclusions. The results obtained on the free vibrations of the object under study agree well with those obtained by numerical simulation. The results obtained by numerical differentiation are effectively identical with those obtained by numerical integration, under the action of various effects. The validity of the results is confirmed by comparing the results obtained by the two methods. The developed software applications can be used for monitoring the state of unique tower-type objects.

Introduction. The article presents a methodological approach to justifying measures designed to ensure the required fire resistance of structures enclosing NPP premises with the use of CFD (computational fluid dynamics) fire modeling. Approaches to justifying fire safety are considered using the fuel storage facility of an NPP standby diesel power plant as an example.

Aim. To develop and analyze the methodological approach to justifying measures designed to ensure the required fire resistance of structures enclosing NPP premises with the use of CFD fire modeling.

Materials and methods. The purpose and application scope of various methods for modeling fire dynamics was analyzed. Fire modeling used to justify measures for ensuring the required fire resistance of enclosing structures was considered using the fuel storage facility of an NPP standby diesel power plant as an example.

Results. The performed analysis of different methods for modeling fire dynamics shows the possibility of using different fire simulation methods in the analysis of the fire hazard of buildings and facilities. The most dangerous fire development scenarios were modeled and the obtained results were analyzed on the example of a specific typical NPP facility in the NPP emergency power supply system. The redundancy requirements for these systems were taken into account to ensure tolerance to system failures in case of process failures and external effects on these systems.

Conclusion. Since the CFD method is the most universal of the existing deterministic methods, it can be widely used to determine/revise the requirements for fire resistance of load-bearing and enclosing structures at NPP premises. It is possible to apply CFD-based fire modeling for the fire hazard of various buildings and facilities. This model is particularly effective in justifying the sufficiency of fire resistance requirements established for structures to prevent the spread of fire beyond the fire zone within the estimated burnout time of the entire fire load The obtained regularities can be used in the development/revision of regulatory documents on fire safety at operating NPPs and NPPs under construction.

Introduction. The article addresses the issues of ensuring the performance reliability of warm roofs in terms of condensation moisture accumulating in their structures, which causes leaks on the upper floors of buildings. Such problems are often revealed when buildings are inspected during repair and reconstruction works. Leaks in the ceilings of buildings with warm roofs were detected in dry, sunny weather with significant heating of the roof covering due to solar radiation.

Aim. To examine the effect of the insolation heating of a roof covering on the formation of condensate in the warm roof of a building in summer, taking into account its design solution.

Materials and methods. Materials are presented on inspection of buildings in the Moscow region for repair and reconstruction needs; they reveal the problem of leak formation in the warm roofs of buildings on dry, sunny summer days. The process of moisture transfer through the exterior covering was analyzed through analytical calculations using the roof design solution in the considered structure as an example.

Results. The calculation of moisture transfer yielded vapor transmission resistance, conventional true and maximum partial pressures of water vapor, as well as temperatures at the layer boundaries in the studied structures. Changes in these parameters across the thickness of structures were revealed via a graphical method, which showed where the dew point indicating possible condensation in the covering is formed. For a comparative analysis, moisture transfer was calculated for a similar design in which mineral wool insulation was replaced by extruded polystyrene.

Conclusions. 1. The calculations of moisture transfer in the examined covering designs confirmed the formation of condensate due to the insolation heating of the roof in summer. 2. The choice of a covering design solution in the design of buildings should be based on accurate heat and moisture calculations taking into account climatic conditions in the construction area, including for the summer season.

Introduction. Soil nails are widely used to reinforce landslide slopes and ground-retaining structures in many countries, including Russia. The interaction of soil nails with the soil base is of high interest to both engineers and researchers. The method of increasing the stability of landslide slopes with soil nails has proved to be versatile and cost-effective. However, the process of designing soil nails is usually carried out using empirical and semi-empirical methods that may ignore a number of important factors.

Aim. To determine the most optimal angle of soil nail inclination, as well as to analyze the characteristics of soil movement of a landslide slope along a potential sliding surface and their influence on the bearing capacity of the soil nail and its strength characteristics.

Materials and methods. A review of scientific publications on the influence of load parameters during landslide slope reinforcement with soil nails based on self-drilling hollow steel bar on their bearing capacity and strength properties was carried out. The review sample included 11 publications most relevant to the topic under study. Calculations were carried out using the PLAXIS 2D software environment.

Results. The conducted calculations and literature review allowed the optimal angle of soil nail inclination in the slope to be established, which corresponds to a value ranging from 0° to 5° to the horizon. The study also showed that the development of shear stresses along the soil nail in time exhibits a non-uniform nature. Therefore, the assumption of a constant value of shear stresses along the entire length of the nail or anchor root can lead to an overestimation of the soil bearing capacity.

Conclusions. The obtained results have confirmed the relevance of further research into the influence of load parameters during the reinforcement of landslide slopes using soil nails.

Introduction. Slope reinforcement with dowels is the most economical and environmentally friendly method of their stabilization. However, the lack of theoretically substantiated schemes for optimal placement of dowels in groups, confirmed by tests in various conditions, leads to inefficient, often excessive use of the material in the arrangement of engineering protection.

Aim. To determine the most effective arrangement of dowels in groups with regard to the overall stability of the reinformed soil mass. To assess quantitatively the stability depending on the spacing and shape of dowels in the group.

Materials and methods. A review of international and Russian literature on the problem of assessing the influence of geometric parameters of dowel and anchor groups was carried out. According to the results of the review, primary calculations with the use of numerical simulation in the PLAXIS 3D software package was carried out.

Results. The available publications mainly analyze configurations of screw anchor groups, paying insufficient attention the use of dowels of cylindrical cross-section. This fact substantiates further research in this field. The conducted numerical simulation allowed the slope stability provided by five dowel group configurations to be compared. The calculation results show that the slope stability depends on the configuration and the number of dowels in the group. The difference between the stability factors for the polygonal and triangular three-row configuration was 0.072 %, with the polygonal configuration requiring three dowels less. Selection of optimal dowel placement contributes to increased landslide control efficiency and reduced costs.

Conclusions. The relevance and importance of studying the effect of dowel group configuration on slope stability, emphasizing the need for more in-depth and comprehensive research in this area.

Aim. To review the history of concrete technology over the past 30 years and to analyze current trends in the field.

Reality. New concepts and terms that manifest the level of modern science in the field of concrete technology are given. It is shown that the use of complex organomineral modifiers produced on an industrial scale, which are characterized by unique compositions, forms, and processability, allowed Russia to organize promptly mass production of concrete with high performance properties in the amount of about 5 million m³. Examples of construction of unique structures from new modified concretes are presented. The list of such structures includes high-rise buildings, sports facilities, bridges, overpasses, tunnels, etc.

Prospects. Priority tasks for further development of concrete technology in Russia have been formulated. Among them are the development and improvement of physical and technical characteristics of concretes; extended use of large-tonnage technogenic wastes in production of concrete mixtures; updating and development of new normative documents for calculation, design, and erection of modern structures with high operational reliability, durability, and aesthetic properties.

Introduction. The article examines the possibility of using steel reinforcement with instances of corrosion and determines the maximum degree of corrosion damage in reinforcing bars (rebars). Although long-term studies show that corroded reinforcement can be used in the manufacture of reinforced concrete structures, some studies and regulatory documents provide different conditions for the use of such rebars, as well as establishing different corrosion thresholds (thickness of the rust layer on the rebar surface).

Aim. To determine the maximum thickness of the rust layer on the surface of corrugated rebars, at which the physicomechanical characteristics of reinforcement are preserved and the capability for composite action with concrete is not hampered; to determine the degree of corrosion damage in rebars at which its use in reinforced concrete is permissible in order to revise the existing regulatory documents on the protection of structures against corrosion.

Materials and methods. The experimental studies were conducted on rebar specimens of two classes (A500 and A800) exhibiting different degrees of corrosion damage (rust layer thickness of 0, 150, 250, and 300 μm). In order to determine the composite action with concrete, B15 and B20 concrete was used. The physicomechanical characteristics of rebars with different rust layer thicknesses were determined on rebar specimens having a diameter of 12 mm and length of 400 mm according to the procedure specified in State Standard 12004-81. The reinforcing steel resistance to corrosion cracking was determined on rebar specimens having a diameter of 12 mm and a length of 400 mm as per the procedure given in State Standard 31383-2008. The passivating effect of concrete on steel reinforcement was determined on concrete specimens — 70 × 70 × 140 mm prisms, with rebars having a diameter of 12 mm and a length of 120 mm in the center — according to the procedure given in State Standard 31383-2008. The bond between rebars and concrete was determined on concrete specimens-cubes (150 mm on edge), with rebars having a diameter of 12 mm and a length of 500 mm in the center — using the procedure specified in State Standard 31938-2012.

Results. The study yielded experimental data on the physicomechanical characteristics of rebars exhibiting different degrees of corrosion damage; on the resistance of reinforcing steel to corrosion cracking; data on the passivating effect of concrete of two classes on steel rebars exhibiting different degrees of corrosion damage; data on the bond between rebars corroded to various degrees and concrete of two classes.

Conclusions. As part of the work, an experimental research program was developed and implemented, which involved the production and testing of rebar specimens of two classes exhibiting four degrees of corrosion damage with the use of concrete of two classes and. The experimental study results were used to determine the effect of corrosion damage of varying degree in rebars on the characteristics of reinforced concrete. The presence of a rust layer on the rebar surface of up to 150 mm in thickness was found not to degrade its physicomechanical characteristics, not to decrease its resistance to corrosion cracking, and not to reduce its composite action with concrete. Any further increase in the thickness of the rust layer on rebar surface reduces these characteristics, except for the bond to concrete. No dependence of rebar-concrete bond stress on the rust layer thickness was observed.

Introduction. Based on archival materials, the article follows a little-known fact of the Great Patriotic War 1941–1945, namely, the scientific discovery by the specialists of the Central Research Institute (TsNIPS), related to the creation of the formulation for the TsNIPS-2 construction adhesive. With its help, in a difficult period for the country, the industrial production of new construction materials was established and Red Army gunsmiths, located on the front line, quickly restored small arms that went out of action in battles with the enemy.

Aim. To introduce into a scientific discourse the materials of archival sources on the history of creating a TsNIPS-2 new construction material, as well as on the individual research results of its inventor – a senior researcher, Cand. Sci. (Engineering) Maria N. Plungyanskaya, who worked for a long period in the TsNIPS Laboratory of Timber Structures.

Materials and methods. Archival materials on the current topic were used in the preparation of the publication. Due to them, as well as with the help of retrospective, historical-typological and comparative research methods, the author traced certain aspects of the complex path of creating a new adhesive by clarifying its composition, order of preparation and industrial application.

Results. The article studies and shows the individual stages of creating the TsNIPS adhesive formula, which ensured (due to cold-dry setting) the large-volume industrial production of high quality construction plywood of various thicknesses for the construction industry, as well as other timber structures that replaced the scarce metal. The procedure and rules for the practical use of the TsNIPS-2 adhesive by gunsmiths beyond the limits of stationary conditions (“in a trench”) for the successful restoration of wooden parts in rifles and assault rifles (butt, forearm, etc.), as well as the prompt return of thousands of weapons to the units are described.

Conclusions. The content of the article will serve as a vivid illustration in the scientific and educational context about the traditions and activities of scientific schools, presented by the institutes of JSC Research Center of Construction, their contribution to the research field on the creation of new construction materials for increasing the power of the country. The research work of the Institute’s scientists was of a great practical importance, offering the construction industry new types of light industrial collapsible structures with a high transportability, their numerous achievements were effectively used at the front to achieve the Great Victory. In the period of 1930–1940, the construction, widely developed in the country, required, on the one hand, high-quality design solutions and, on the other hand, the simplicity and economy of their implementation. In these conditions, adhesive and laminated plywood structures were of a particular importance, ensuring the industrialization of the wooden construction part production and the cost-effectiveness of using timber in construction. The important properties of the TsNIPs-2 adhesive, obtained by the researcher M.N. Plungyanskaya, including water resistance and durability, as well as simplicity and ease of its handling, made it possible to use the material in industry for assembling the hulls of wooden ships, producing laminated structures, parts of cars, and oil pipelines, made of veneer or thin plywood, as well as in combat conditions for the manufacture and repair of small arms, etc., thereby bringing a significant economic effect and expanding the possibilities of its use in the domestic industry.