Introduction. The present paper considers the issues of work planning for fire protection of steel structures, including the correct selection of primer coating in order to avoid potential problems, to save time and budget, as well as to ensure long-term durability of the structures due to the applied fire protection coating. The compatibility of materials appears to be essential when creating projects and coating technology to maximize the effectiveness of fire-proof materials.

Aim. To establish the relevant requirements for the scope and sequence of work in assessing the compatibility of fire-proof compositions with the applied primer of steel structures.

Materials and methods. The compatibility of flame retardants with primers was assessed using certified and verified laboratory equipment. The paper describes a modern laboratory facility for testing.

Results. The results of testing compatibility of flame retardants with primers are presented. The coating system should be evaluated for the defects, its criticality in the subsequent operation, the degree of coating interlayer adhesion, and the ability of the coating to resist adverse environmental effects. Following the obtained information, recommendations are given on the compatibility of certain coating materials.

Conclusion. The study demonstrated the significance of material  compatibility when creating projects and coating application technology to ensure maximum effectiveness of flame retardants and to tackle the crucial task — providing long-term fire resistance of structures.

Introduction. The study considers modern strategies for ensuring the reliability of building structures in Russian and foreign regulations, including probabilistic, risk-informed and semi-probabilistic criteria of reliability assessment, at all stages of the life cycle of the structure. The advantages and disadvantages of prescriptive and parametric approaches are analyzed and ways of their further improvement are suggested.

Aim. To clarify the terminology of parametric regulation in construction, to analyze the existing differences in its interpretation, and to develop an innovative strategy for further development of Russian regulation based on a comparative analysis of domestic and foreign approaches to reliability assessment.

Materials and methods. The methodology involved studying the structure of Russian and foreign regulatory documents in the field of reliability and performing their comparative analysis. The study considered the main approaches to technical regulation in the construction industry.

Results. The analysis outlined the criteria underlying the fastest introduction of innovations and ensuring the safety of technical solutions. The study demonstrated the difference between the meaning of the term “parametric regulation” in Russian strategy and its foreign interpretation. The regulation standards of the Russian Federation are based mainly on a semi-probabilistic approach and specification of partial reliability factors, i.e. individual parameters of strength and loads, while in the foreign standards, notably in ISO 2394:2016 and Eurocodes, the emphasis is shifted to qualitative and probabilistic criteria for assessing reliability. However, all social, economic and performance criteria should be observed only after all requirements for the reliability and safety of people have been met. Thus, both Russian and foreign approaches to regulation demonstrate no fundamental contradictions. The approaches are gradually moving towards convergence while maintaining continuity in the development of the regulatory framework.

Conclusions. The principles of ensuring the reliability of the designed buildings and structures in Russian, international and foreign regulation standards are quite close and are based on the limit state method with a reasonable combination of mandatory and recommended parameters. The main criterion consists in ensuring the safety of human life. Under contemporary conditions, traditional semi-probabilistic approaches to regulation should be accompanied by mechanisms for rapid introduction of innovations and new technologies in construction. In terms of reliability, these mechanisms involve additional probabilistic reliability criteria and risk assessment methods. The reliability criteria will contribute in choosing the optimal design and technological solutions for the construction of unique buildings and structures, higher criticality structures, as well as in assessing existing structures during their life cycle.

Introduction. The authors develop the results of their previously published study in order to build up a nonlinear dissipative theory of concrete compressive strength. The present paper explores possibilities to improve the theory of calculation of concrete and reinforced concrete structures in the light of the accumulated knowledge.

Aim. To introduce an approach to developing a nonlinear dissipative theory of concrete compressive strength in the absence of regulatory documents for loading modes, using instead the standard classification of loads.

Results. The authors refer to the non-linear hereditary creep theory as the most accurate but time-consuming, and keeping its positive properties, reduce its equation of state to the equation of ageless concrete with its simplicity in application. In addition, the equation of state of concrete is solved in elementary functions and closed form in practically important cases.

The overwhelming majority of published scientific data on the behavior of creep curves in the area of reliable performance of reinforced concrete structures indicates smoothness and continuity of the curves. Considering that, the data obtained in short-term tests can be extended to the whole time interval, thus providing possibility for express analyses of the strain properties of concrete.

The study estimated the reversibility of creep strain and found out dissipativity of elastic strain. The authors established a nonlinear relation between strain and constant stress and introduced an approach to developing a nonlinear dissipative theory of concrete compressive strength in the absence of regulatory documents for loading modes, using instead the standard classification of loads.

Conclusions. The considered experimental data were recognized to provide qualitative information due to their apparent deficit. In order to obtain quantitative evaluation, the experiments should be reproduced a sufficient number of times.

Introduction. The paper presents the methods of reinforcing brick-and-stone structures, as well as monitoring of their strain capacity during the reconstruction of the Grand Sports Arena of Luzhniki Olympic Complex. The authors paid special attention to the methods for ensuring the preservation of front wall made of ceramic hollow stones.

Aim. To ensure the reliability and stability of the wall of the Grand Sports Arena during the stadium reconstruction, in particular during the dismantling of the framework and stands.

Materials and methods. The authors calculated the strain capacity (vertical deviation) of the framework of the stands at its dismantling stage and the wall stability, taking into account the framework fastening with rolled steel braces. The wall section taken for calculation at the first stage of dismantling stands consisted of several spans of 6 meters each. An extreme wind action was considered as the main stress factor that has the most severe impact on the front wall strain.

Results. The calculations showed that the wind load on the system “front wall + 1 span of the stand framework” increases tensile and compressive stresses in the load-bearing elements by no more than 5–7% compared to the system “front wall + 2 spans of the stand framework”. Based on the calculations performed, only one span of the stand framework adjacent to the front wall was decided to retain. Monitoring of the structures strain confirmed the reliability and efficiency of the adopted solutions to strengthen the retained structures.

Conclusion. Due to R&D support for the design and reconstruction of the Luzhniki Grand Sports Arena, complex issues arising in the process of reconstruction were efficiently solved. The principles of the Arena reconstruction can be applied to other similar facilities.

Introduction. The acoustic emission (AE) method is successfully used for diagnostics and monitoring in various industries including oil and gas, nuclear, aerospace as well as in welding processes and structural corrosion. However, inspection of reinforced concrete structures seldom involves the AE method. The main reason behind is the lack of regulatory documents and specific control procedures.

State Standard R 59938-2021 “Concretes. Acoustic emission testing method” was issued in 2021. Over the past few years, new data on effective application of the acoustic emission method for non-destructive testing and technical diagnostics of the building structures have been obtained. The studies were carried out on specimens and fragments of structures (reinforced concrete beams, concrete samples in the form of slabs, wall panels, etc.) in NIIZHB named after A.A. Gvozdev. The studies were conducted on the structures under construction at Kursk NPP-2.

Aim. To present the results of the recently developed methods of technical diagnostics and non-destructive AE testing of concrete and reinforced concrete structures.

Materials and methods. The investigations were carried out on concrete and reinforced concrete specimens made of both normal (B15–B40) and high-strength (B60–B100) concrete. A number of beams were made of fiber concrete. Structures were tested in the power unit. AE monitoring of concrete hardening involved concrete mixtures made of heavy, fine-grained, cement concrete with mineral and chemical additives. Concrete hardening was investigated remotely, with online data transmission.

Results. Based on the results of the conducted study, the technologies for acoustic emission monitoring and technical diagnostics of the structures under construction and in operation have been developed.

Conclusions. The given acoustic emission technologies can be used for monitoring and technical diagnostics of structures under construction and in operation. The implementation of technologies in construction will lead to the increase in safety and reliability of building structures due to the introduction of acoustic emission monitoring.

Introduction. The paper presents the process of renovating the roof over the Grand Sports Arena (GSA) of the Luzhniki Stadium from its construction to the present day. It demonstrates the modifications in the roof over the GSA stands, including three reconstructions of the stadium, which were carried out for various reasons during the 65-year history of the stadium.

Aim. To describe the process and peculiarities of erecting the roof over the arena stands and creating a stadium that meets the requirements of the International Football Federation (FIFA) for stadiums hosting the opening and final matches of the FIFA World Cup.

Materials and methods. The study involved methods for creating a unique large-span steel roof of a dome type with the largest unsupported span (310 m) for structures of this class. The paper describes the process of designing and testing a large-size model and a specially made model in a wind tunnel to determine the snow and wind loads. The process of erecting the roof, assembling the outer support contour, and lifting it on the columns is shown in detail. The process of assembling the inner contour is described. Its perimeter accounts for about 600 m, and its weight is 4500 tf. After assembling, the inner contour was lifted to the design level at approximately 50 m within three days. After that, curved beams were installed between the outer support and inner contours with ring trusses in between. A translucent roof made of polycarbonate panels was installed on the dome frame for the first time in the construction practice of Russia. This was the second reconstruction of the roof. The first one was arranged for the 1980 Summer Olympics in Moscow. The third reconstruction of the roof was carried out to meet the strict requirements of FIFA. The reconstruction involved dismantling old stands and building new ones. The roof over the stands became 17 meters closer to the field, and its area was increased to protect the spectators from atmospheric precipitation. Measures were taken to ensure the bearing capacity of the existing large-span roof during the stadium renovation.

Results. The reconstruction of the Grand Sports Arena of the Luzhniki Stadium was developed designed and implemented. The reconstructed arena was recognized by UEFA (Union of European Football Associations) as one of the best stadiums in the world and received “Elite” qualification.

Conclusion. The principles of reconstruction of a large-capacity stadium on the example of the renovated Grand Sports Arena of the Luzhniki Stadium can be used to meet the requirements of FIFA in other arenas with stands for at least 80,000 spectators.

Introduction. The paper describes distortions of geometry in buildings and structures under construction as well as those already commissioned, which increase the risk of an emergency. The paper also shows the reasons for controlling the geometry for its compliance with design form and stability, as well as possible impact of deviations in the design geometry on adjacent buildings and structures.

Aim: to analyze and describe the application of geodetic methods for preventing emergencies in the construction and operation of buildings and structures.

Materials and methods. The paper presents methods and techniques for measuring the deformations of buildings using modern robotic tacheometers, inclinometers, satellite equipment, as well as hydrostatic leveling, in order to obtain reliable and valid parameters of the deformed state of building structures under both static and dynamic effects on the building or structure.

Results. The paper explains the operating principles of measuring systems using automatic geodetic monitoring systems. The authors describe the process of determining displacements and deflections during the erection of large-span shells of unique buildings. These include the steel framed dome of the Luzhniki Stadium in Moscow, Russia, which has the largest unsupported span for structures of this class (310 m), large-span transformed shell of the Gazprom Arena Stadium in Saint Petersburg, and large-span shell of the Kazan Arena Stadium in Kazan, Russia. Deflections and displacements of the reference points of the steel pyramid were determined for the Opening Ceremony at the Kazan Arena Stadium. The paper also presents the methods for determining the parameters of deformations during the construction of the Rhythmic Gymnastics Center in Luzhniki, metro lines in Moscow, and Kashirskaya–Karacharovo section of the Moscow ring railroad. Measurement methods have been developed and implemented for all these facilities.

Conclusion. The above measurement methods are successfully used to determine horizontal displacements and deflections for monitoring the deformations of buildings and structures, which increases their reliability and safety during construction and operation.

Introduction. Frost resistance of concrete is one of the most challenging problems in concrete studies. Particularly important is the issue of methods of testing concrete for frost resistance. The existing standard methods require more detailed regulation of the test process in order to improve the reliability of the results.

Aim. To analyze the regulatory procedures of testing concrete for frost resistance with a view to make suggestions for improving standards.

Materials and methods. The analysis involved Russian and foreign standards and publications on methods of testing concrete for frost resistance.

Results. The authors analyzed the methods of testing concrete for frost resistance, included in Russian and some foreign standards. The quality of determining the frost resistance of concrete can be improved by controlling the temperature while freezing and thawing, in particular, by assessing the temperature in the concrete of the test samples. Controlling the air temperature in the freezer should be recognized as insufficient. The criteria for the state of concrete samples during and after cyclic freezing and thawing should be further verified. It is necessary to continue full-scale testing of concrete under severe climatic conditions, taking into account the real conditions of freezing and thawing of concrete in structures, and comparing the results of laboratory and full-scale tests, including satellite samples.

Conclusion. The analysis revealed the necessity to continue the research on clarifying the test methodology and criteria for assessing the state of concrete samples after freezing and thawing cycles. It is advisable to recreate devices for determining the dynamic modulus of elasticity of samples in freeze-thaw testing, to resume long-term full-scale tests of concrete under severe climatic conditions, and to develop a manual for creating frost-resistant concrete, taking into account the current level of concrete technology. Elimination of the existing drawbacks of the methodology will improve the reliability of test results.

Introduction. At present, in Tajikistan, buildings and structures are designed and constructed on the basis of passive methods of ensuring seismic resistance, which ultimately leads to an increase in stiffness and weight of structures and, accordingly, in seismic load. The present paper analyses seismic isolation of buildings provided by friction pendulum bearings. The dynamic model of the object under study is represented as a system consisting of a superstructure, substructure and seismic isolation.

Aim. To contribute to the development of methods for analysis and evaluation of seismic isolation and earthquake protection of buildings and structures in order to justify the conditions for their effective application in earthquake-resistant construction on the territory of the Republic of Tajikistan.

Materials and methods. The authors used methods of structural mechanics, structural dynamics, and numerical simulation. The research methodology involves mathematical modeling of the systems under consideration, numerical analysis, comparison of the obtained results with the available data. Experimental investigation was carried out on a building fragment model and a vibration platform.

Results. The authors developed a mathematical model for investigating the stress-strain state of a building with friction pendulum bearings subjected to various external influences, including seismic ones. The differential equation system using successive approximations is transformed into a system of algebraic equations, which is solved at each time step. On the basis of the created algorithm, the authors developed a computer program in Fortran and obtained the numerical results of the dynamic calculation for a multistory building with friction pendulum bearings. The results from the action of an instantaneous impulse are obtained on the example of a 10-story frame building.

Conclusions. The results show that the application of seismic isolation in the form of friction pendulum bearings leads to a significant reduction of internal forces in the support part, as well as to a reduction of velocity and acceleration in the upper part of the building compared to the model without seismic isolation bearings. At the same time, the deflections of both the lower and upper parts of the investigated object slightly increase.

Introduction. Development of computational methods for nonlinear systems possesses a significant potential, considering that linear theory sometimes fails to accurately describe the properties of dynamic systems, and the linear approximation gives only a very rough idea of real processes for a number of cases.

Aim. Calculating linear systems and deriving the resulting equations for nonlinear systems involves impulse response and transfer functions of linear “generating” systems of differential equations. Such an approach in comparison with the traditional method of the so-called normal forms enables the calculation algorithm to be simplified considerably, avoiding several stages and presenting the solution by means of the normal mode method for linear systems directly with respect to the generalized coordinates.

Materials and methods. The paper presents a method and an algorithm developed for the calculation of nonlinear systems with a finite number of degrees of freedom under arbitrary dynamic loading and material nonlinearity. Systems of nonlinear differential equations were reduced to nonlinear integral equations of the second kind, considered as resulting equations. The solution was developed in time steps, the value of which, among other things, determines the accuracy of the solution and the nature of the computational algorithm.

Results. The paper presents main computational dependencies in a generalized form, convenient for numerical simulation. The author provides solutions for a nonlinear system with one degree of freedom and a cubic reactiondisplacement relation, as well as for a system with one and two degrees of freedom with a viscous damper. In both cases, the developed solution contains all properties of nonlinear systems, including the jump (transition) from the upper ascending branch to the lower, stable one, and the associated excitation of free oscillations.

Conclusions. According to the calculations, the occurrence of nonlinear effects in oscillating systems makes positive impact on their behavior, in resonant modes in particular.