Introduction. At present, the overall production of light two- and three-layer wall panels and coatings having metal claddings and efficient insulation is continuously increasing in Russia. Especially relevant is the use of sandwich panels, since industrial and administrative buildings can be quickly erected, thereby significantly reducing their payback period. Regulatory documents regulating the production processes of panels were mainly developed in the 1970s and 1980s. However, over the past 40–50 years, much has changed in the technology of panel production, including the development of advanced materials for panel layers, new structural joints, and approaches to assessing the safety of panels. New federal standards for panel constructions and testing methods were developed in order to account for the changes in the intervening period.

Aim. In this work, changes that occurred in the production of laminated panels are addressed, including changes in technical requirements for panel design solutions, butt joints, panel materials, methods of selecting and testing insulation and panels, and safety and environmental protection, in order to inform the manufacturers and consumers on the use of new documents in the production and application of panels.

Materials and methods. When developing new regulatory documents (GOST R), the existing documents and results of panel testing at the TSNIISK named after V.A. Koucherenko were analyzed, along with the identification of new materials and technical solutions on the basis of the technical materials of manufacturing plants.

Results. The work established current technical requirements for panel design solutions, butt joints, panel materials, methods of selecting and testing insulation and panels, and safety and environmental protection. The following new provisions are given in the developed standards: the scope of application and classification of indicators are expanded, more efficient butt joints for panels are recommended, the consumption of insulation material is reduced, and new methods of testing insulation materials are proposed.

Conclusions. The implementation of the developed GOST R will optimize the manufacturing process of two- and three-layer panels having efficient insulation, along with reducing the labor intensity of their production.

Introduction. The article presents the results of testing a developed methodology for assessing the effect of geometric deviations on the stress-strain state of the metal structures of an overbridge at the facility of «Tailings Thickener 1», located at the Natalka Mining Processing Plant. A brief review of previously performed studies for recording deviations of metal structures is provided, along with confirming the relevance of the problems solved in the article and the study in general. It was substantiated that it is necessary to adjust the previously developed project on the overbridge of a thickener (OT); the applicability of the developed methodology was demonstrated.

Aim. In the article, the methodology for determining the stress-strain state of frame metal structures was tested in the light of deviations, using the example of an OT.

Materials and methods. The following materials and methods were used:

– the finite element method implemented in SCAD 11.5 was applied in the numerical study of the state of the (OT) having deviations;

– the theory of dimensional chains and the method of geometric modeling implemented in the authoring software entitled the «Dimensional analysis of rod structures» Computational Complex were used to determine the values of geometric deviations.

Results. The results presented in the article allowed for timely substantiation of the amendments of the documentation and an increase in the reliability and economic efficiency of the OT, as well as the entire facility. During research:

– possible geometric deviations of the OT were forecasted, along with plotting the limiting values of possible geometric deviations of nodes in three directions (X, Y, Z);

– effect of possible geometric deviations on the stress-strain state of the OT metal structures was included in its verification calculations, which substantiated the necessity of adjusting the project and optimizing previously made decisions;

– values of permanent and temporary loads were reduced, which allowed the possible emergency situations at the facility to be avoided.

Conclusions. The developed methodology for determining the stress-strain state of frame metal structures was validated on the example of an overbridge of a thickener, taking into account the accumulation of geometric deviations during its manufacture and installation.

Introduction. Wood, being an affordable and renewable material characterized by high strength characteristics, is used in construction for both residential and non-residential buildings, as well as various structures. The strength and durability of buildings based on wooden structures largely depend on the strength and reliability of joints between wooden elements. At present, various types of nodal joints used in wooden structures all exhibit certain advantages and disadvantages, calling for an improvement and development of new types of joints having high strength and manufacturability.

Aim. In this work, the behavior of an improved joint of wooden structures using insert steel washers was investigated, along with the development of their manufacturing technology and methodology for studying.

Materials and methods. The investigation of the joint involves manufacturing a series of samples and conducting an experiment in order to determine the load to failure and ultimate strain.

Results. The manufacturing method of a joint and the experimental procedure were developed; values of load to failure and deformation were determined experimentally, with the deformation curves being plotted. It was revealed that the threaded connection of an insert steel washer and a rod leads to a decrease in the bearing capacity of the joint due to the thrust occurring in the adhesive line. In addition, it was established that the parameters of the steel washers affect the joint behavior.

Conclusion. Experimental studies of the joint showed that the threaded connection between the rod and the insert steel washers fails to increase the bearing capacity and stiffness of the joint due to the early failure of an adhesive line and the separation of the washers from a wooden element. However, using additional joints that accept the thrust in the connection can solve this problem. It is necessary to conduct additional research in order to assess the feasibility of using such a connection.

Introduction. The mechanism of the formation of snow deposits on the shell of the Luzhniki GSA and their redistribution in winter were established on the basis of the data obtained during the monitoring of the snow load for over 20 years.

Aim. In this article, the mechanism of the formation of snow deposits and their distribution on the shell of the Luzhniki GSA were determined, along with the numerical values of the form factor μ characterizing the transition from the ground snow load to the snow load on the shell.

Materials and methods. The measurements of the load and density of snow deposits on the shell of the Luzhniki GSA were carried out from 1998 to 2019. The obtained results were compared with the parallel measurements of ground snow load (GSL) in Luzhniki. In addition, the snow load, as well as statistical data analysis on the maximum annual values of the GSL, were analyzed using the hydrometeorological data of decadic snow surveys in Moscow, performed by the V.A. Mikhelson Meteorological Observatory following the dates of field measurements. The graphs of the repeatability of wind directions for the month preceding the observation dates were plotted.

Results. The maximum values of the form factor μ for each section of the shell were obtained. The areas characterized by increased snow deposition on the shell during various periods of snow accumulation andthe dependence of their formation on wind speeds and directions in winter were revealed. Graphs depicting the distribution of snow load on the surface by observation years were plotted. It was established that the values of snow loads on the GSA shell during the observation period generally lay within the design values, except for local zones near the internal contour during the installation of the canopy.

Conclusion. It was shown that the formation, accumulation, and redistribution of snow deposits on the shell comprise a complex and uneven process, varying from winter to winter. When selecting the analytical models of snow loads for calculating unique load-bearing structures, it is necessary to account for the most unfavorable wind flow directions, at which an uneven snow deposition pattern occurs, as well as the physical properties of the shell and field observations.

Introduction. The analytical calculation of reinforced concrete waffle slabs calls for the determination of the components of total load on joists, depending on the dimensions of spans and the rigidity of central joists. In the case of slabs having rectangular coffers of various orthogonal rigidity, this theory leads to results differing significantly from those obtained by the finite element method. The waffle slab comprises a ribbed slab, characterized by cylindrical or relative beam stiffness.

Aim. This article discusses the accuracy of the calculated span bending moments in the joists of straight reinforced concrete waffle slabs using the span dimensions and relative stiffness of joists in analytical formulas.

Materials and methods. The work was carried out by comparing the bending moments for joists in the central zones of straight waffle slabs obtained analytically and using the SCAD software by the finite-element method. Square or rectangular in plan, 13 slabs having different aspect ratios of waffle were considered. A T-beam and girder construction were used in the computer model.

Results. The maximum deviations of the bending moments obtained by the analytical calculation from the computer-aided method amount to: -0.6% for a square slab having square coffers, from -2.8 to +2.5% for a square slab having rectangular coffers, from -6.2 to +2.0% at a span ratio of L_max/L_min ≤ 1.5 for a rectangular slab having rectangular coffers, and from -7.3 to +4.8% for those having square coffers. For rectangular slabs having any coffers at a span ratio of L_max/L_min ≥ 1.75, a computer-aided calculation revealed that the plot of bending moments in the long-side direction deviates from parabola.

Conclusions. The use of the span dimensions and relative stiffness of joists in the analytical formulas for calculating straight hinge-supported reinforced concrete waffle slabs allows the values of bending moments to be obtained that are in agreement with those obtained by the finite element method.

Introduction. Current regulatory documents in the field of concrete and reinforced concrete are based mainly on research results obtained in the past century.

Aim. This article addresses the approaches to improve the theory of calculation of concrete and reinforced concrete structures, in the light of the accumulated knowledge.

Materials and methods. Since concrete structures belong to non-conservative systems, it is inaccurate to determine the forces arising in them using standard methods of structural mechanics. To achieve this goal, the deformation and relaxation problems for an axially compressed concrete fiber were solved following the A.A. Gvozdev and K.Z. Galustov’s two-component theory of creep, where deformations are categorized on the basis of reversibility.

Results. Historical background was provided. Proposed by the authors of this article is a solution to the deformation and relaxation problems for the elementary part of a concrete structure for the case of axial compression, since such an event is impossible. In this regard, it was suggested that estimating the loss of stability by Euler is also incorrect. It was observed that the achieved maximum load-bearing capacity of the construction is equivalent to zero resistibility, with a progressive collapse occurring. For further research, it was proposed to use the hypothesis of a straight normal, assuming that this law is valid in the absence of tangential stresses in the studied sections of the structure.

Conclusions. To improve the theory of calculation of concrete and reinforced concrete structures, it is necessary to revise drastically the existing approach to scientific research.

Introduction. The evaluation of structure performance on the basis of experimental studies of full-size facade samples exhibits significant advantages over computational models, allowing the deformation scheme in real conditions to be visualized, while taking into account the installation failures of the actual materials.

Aim. In this work, the strength characteristics of structures for subsequent use in the calculation and theoretical substantiation of design technical solutions were determined.

Materials and methods. The article presents the results of laboratory tests under construction conditions of high-strength brick facing installed on the facades of buildings using metal substructures. Studying life-size facing structures in laboratory conditions using direct destructive methods allowed the strength limits to be determined when constructing niches, along with confirming the necessity to account for chases in thin-layer brickwork.

Results. By using characteristic dependencies plotted while processing the obtained data, the structure performance under load was determined, along with the nature of sample destruction and the maximum displacements, at which a loss of the adhesion strength between bricks and mortar in the brickwork joint occurs.

Conclusion. Conducting full-scale experimental studies is essential due to the lack of regulatory and technical documents for the design of facing structures for facades considered in the article, as well as the necessity to obtain initial data for calculating the load-bearing capacity of combined facing structures. The test results will be used for assessing the load-bearing capacity of thin-layer brickwork under combined action with metal guides as a part of composite facade structures.

Introduction. Cross-laminated timber (CLT) has started to win a market in Russia. Humidity plays an important role in ensuring the operational reliability of buildings based on timber structures. The lack of comprehensive studies on the influence of varying temperature and humidity actions, including atmospheric ones, hinders the development of CLT.

Aim. In this work, the influence of atmospheric actions on various types of CLT building structures was determined in order to amend the requirements in SP 64.13330.2017 for the design and protection of CLT structures.

Materials and methods. Samples of CLT wall panels and floor slabs manufactured as per the current regulatory documents were used as an object of research. Field tests were developed in order to determine the influence of atmospheric actions on the strength and elastic characteristics of CLT panels.

Results. Atmospheric actions have an adverse effect on the strength and elastic characteristics of CLT panels. The decrease in the strength and elastic characteristics varies for the samples of floor slabs and wall panels.

Conclusion. It is proposed that several recommendations given based on the experimental results on the resistance CLT to atmospheric actions are to be included in SP 64.13330.2017 for the design, manufacture, and construction of buildings using CLT structures.

Introduction. Russian manufacturers currently produce screw-threaded reinforcing bars (rebars) and couplers to join them. However, the application of such reinforcement in the construction industry is hindered by a high compliance in screw couplings.

Aim: to assess the compliance of coupling joints reinforced with adhesives.

Materials and methods. The study used Av500P screw-threaded rebars, couplers, as well as adhesive compounds containing a cement binder and epoxy resin. The compounds were injected into the coupling cavity by means of hand pumps, followed by their natural hardening. The tests were conducted using universal testing machines.

Results. In terms of strength, yield, and delaminatability, the compounds were found to meet the required stress-strain properties of couplers. Recommendations for assembling joints are provided.

Conclusions. The conducted studies show that Av500P screw-threaded rebars can be joined by means of couplers in construction.

Introduction. The main provisions for the development of a system for monitoring the stress-strain state (SSS) of the shell covering the Gazprom Arena stadium are described. This shell characterized by an elevated consequence level under Federal Law 384-FZ belongs to a CS-3 class as per GOST 27752 «Safety of structures in buildings and civil engineering works». According to these documents, a stress-strain state monitoring system should be installed in such a building, functioning for the entire life of the structure.

Aim. In this work, an SSS monitoring system was developed and installed in order to determine the parameters of the stress-strain state under continuous control of the unique shell operated at the Gazprom Arena stadium.

Materials and methods. The method of determining the parameters of the stress state, including the snow load over the stadium surface, as well as the strain state, was described. The parameters of the strain state were defined using an automated system installed for the first time in construction practice on a unique long-span shell. The process of installing and configuring an automated system of monitoring the strain state was described.

Results. A stress-strain state monitoring system was developed that allows continuous monitoring of the unique long-span transformable shell operated at the Gazprom Arena stadium in St. Petersburg. Examples of a graphical deformation scheme were obtained as a result of processing the parameters of the strain state.

Conclusions. The development of the most sophisticated stadium in the world having a transformable unique large-span shell and a football field resulted in a sports complex that meets FIFA’s strict requirements for arenas of the World Cup. The system of monitoring the stress-strain state allowed the semi-final and several group matches of the 2018 FIFA World Cup in Russia, as well as eight matches of the European Championship in 2021, to be successfully and safely held. The stadium was ready to host the Champions League Final. Scientific and technical support, including SSS monitoring, ensured the following: monitoring the stress level in the metal elements of a unique long-span shell; determining the movements of its elements; plotting a deformation scheme of the structure; preventing possible emergency situations that occurred and may further occur during the operation of the unique structure.

Introduction. This article discusses methods and means of controlling the diameter and position of reinforcement and the thickness of the concrete protective layer, along with the contemporary techniques and devices for diagnostic and non-destructive testing of concrete. A comparative analysis of the applicability of contemporary devices was carried out.

Aim. In this work, magnetic non-destructive testing was used to assess the thickness of the concrete protective layer, along with establishing the location of the upper row of rod reinforcement and embedded parts. Based on analyzing the interaction between the electromagnetic field of the sensor and the electromagnetic field of eddy currents induced by the source coil of the sensor in rebar, this method allows the diameter of the latter to be approximately estimated at an unknown protective layer.

Materials and methods. As an example, the thickness of the concrete protective layer of enclosing structures (walls, floors) at power unit № 1 at the Kalinin Nuclear Power Plant (NPP) was measured using the POISK-2.6 device.

Results. The analysis of design and as-built drawings for buildings and structures of the main facility of power unit № 1 at the Kalinin NPP was carried out. The state of passive fire protection equipment at the power unit (fire doors, cable penetration seals, and ventilation fire dampers) was evaluated. The actual thickness of the concrete protective layer and the location of the reinforcement of concrete elements at the facilities of the Kalinin NPP power unit were measured as per GOST 22904-93 using electromagnetic NDT. The applicability of the magnetic NDT for determining the thickness of the concrete protective layer was shown during the inspection of building structures.

Conclusions. During the inspection of the facilities, it was established that the average thicknesses of the concrete protective layer, including the thickness of the reinforcement, range from 38 to 85 mm, with the diameter of the reinforcement of 12–20 mm. During the measurements, the applicability of the method was shown; it was also confirmed that the examined structures exhibit fire endurance of at least 90 minutes, which meets the requirements of regulatory documents.

Introduction. The article discusses the improved repair technologies of pipeline material saturated with hydrogen sulfide, which should replace conventional repair methods that ignore operational features in a hydrogen sulfide environment.

The aim of this work is to develop a technology for repairing pipelines operated in a hydrogen sulfide environment by manual arc welding using a consumable electrode.

Materials and methods. Full-scale experiments were carried out to achieve the goals. A section of an industrial pipeline was selected as a test sample, whose service life in a hydrogen sulfide environment at the hydrocracking unit of an oil refinery equals about 10 years. Degassing, i.e., the removal of diffusion atomic hydrogen from the metal in the repairing area, was carried out using electric heating devices. The surfacing of the pipe edges using a layer of austenitic or ferritic metal was carried out by manual arc welding.

Results. The developed technology for repairing pipelines operated in a hydrogen sulfide environment by manual arc welding using a consumable electrode involves degassing and surfacing the edges with metal having the same composition as the parent material. Here, the positive effect of surfacing lies in the fine distribution of non-metallic inclusions in the remolten metal and a favorable change in their shape and chemical composition.

Conclusions. The efficiency of the repair technology of industrial pipelines using welding is achieved by taking into account the properties of a transported product and its influence on the welding process. When developing the welding technology of industrial pipelines operated in the hydrogen sulfide environment, such basic measures as preliminary degassing of pipe metal, preliminary surfacing, and heat treatment of pipe edges are substantiated.

Introduction. The article discusses the results of testing slip-critical high-strength bolts whose contact surfaces are treated using copper slag having a fraction of 0.5–2.5 mm (this processing method was used directly on the construction site for the installation of roof steel structures covering a concert hall). An additional assessment of the bearing capacity of the samples was carried out factoring in local damage to the friction surfaces detected around bolt holes during installation.

Aim. In this work, the actual friction coefficient μ of friction joints was determined when processing contact surfaces using a copper slag of a fraction of 0.5–2.5 mm in order to confirm the design friction coefficient of μ = 0.42.

Materials and methods. The manufacturing and testing of samples of friction joints were carried out following company standard 006-97 «High-strength bolts in steel structures of bridges». Each sample comprised a stack of three steel C355 plates having a thickness of 16, 25, and 16 mm (GOST 27772-2015), tightened using a high-strength bolt M27 (10.9) (GOST 52644). The control tests of three groups of samples where contact surfaces were treated differently were carried out: № 1 – factory, № 2 – treatment using copper slag of a fraction of 0.5–2.5 mm, № 3 – treatment using copper slag of a fraction of 0.5–2.5 mm, with an artificial defect created around the bolt hole.

Results. On the basis of the obtained test results, it was concluded whether the further treatment of the surface of friction joints using copper slag can be employed directly on the construction site.

Conclusions. The treatment of friction surfaces using a copper slag of a fraction of 0.5–2.5 mm offered a friction coefficient μ at or above that of the design value (0.42) (in these specific conditions, even including the identified local defects modeled during testing). Although such treatment remains unregulated by regulatory documents, it is gaining great popularity. Therefore, it is necessary to carry out additional research on the use of copper slag (including various fractions) in order to substantiate the introduction of this method in regulatory documents.

Introduction. Many years of experience in examining corrosion conditions show the dangerous adverse effects of chloride media on reinforced concrete structures.

Although a large number of domestic and foreign publications have been devoted to the aggressive action of chloride salts on reinforcing steel, protection against chloride corrosion remains a relevant issue.

Aim. In this work, the state of this problem, along with the methods for determining the chloride content in concrete, was assessed in order to propose the means to increase its protective action in aggressive chloride media.

Materials and methods. This article discusses the following issues:

– maximum permissible chloride content in concrete;

– binding of chlorides by components in the matrix, the role of the mineral composition of cement;

– critical evaluation of methods for determining the chloride content in concrete;

– reduction of the diffusion permeability of chlorides in concrete as a method of corrosion protection.

Results. The article presents the data on moisture tests of reinforced concrete prepared using Portland cement having various contents of alite, belite, and tricalcium aluminate, as well as CaCl₂ additive.

Indicated were the challenges of identifying aggressive free chlorides in the matrix. The need to develop a standard method for determining free chlorides in concrete was discussed. Until such a standard is developed, the chloride aggressiveness to steel in concrete can be assessed by the electrochemical method. It was shown that concretes of extremely low diffusion permeability obtained using advanced complex additives that reduce the water demand of concrete mixtures and change the charge of the matrix surface can be used as a protection measure against chloride corrosion.

Presented are the results of determining the potentials of steel in concrete by electrochemical method, chlorides in concrete by colorimetric method, and diffusion permeability of chlorides in concrete.

Conclusion. The corrosion activity of chlorides against reinforcing steel depends on a large number of factors, including the total chloride content and the amount of free, physically, and chemically bound chlorides.

Since chloride binding depends on a large number of technological factors, it is recommended to perform electrochemical tests of reinforcing steel in concrete as per GOST 31383 to assess the hazard level of chlorides introduced into concrete with initial materials; a decision on the protective measures for reinforcing steel in chloride environments should be made on the basis of the obtained results.