Introduction. The operating standards for the design of concrete structures with composite reinforcement SP 295.1325800.2017 do not consider the work of compressed reinforcement when calculating eccentrically compressed elements. The previous studies proposed a method for calculating the strength of normal cross-sections of eccentrically compressed elements. Though this method has shown a reasonably high agreement with the experimental data, it has also indicated some underestimation of the load-bearing capacity of such elements. In this paper, a further analysis of the developed method is performed and suggestions for its refinement are formulated in order to identify additional reserves of strength of concrete elements reinforced with composite reinforcement.

Aim. To refine the method for designing the strength of normal cross-sections of eccentrically compressed concrete elements with composite reinforcement, to compare the refined method with experimental and theoretical data, as well as to assess its reliability.

Materials and methods. Theoretical studies are based on the results of the tests that included the experimental examination of concrete samples reinforced with composite reinforcement under the action of eccentrically applied static compressive load consisting of four series of specimens with a total of 12 specimens.

Results. The suggestions were formulated for specifying the value of the height of the compressed zone, as well as the value of tensile stresses in composite reinforcement for designing the strength of normal cross-sections of eccentrically compressed concrete elements with composite reinforcement.

Conclusions. Based on the analysis of experimental data, a refined methodology for designing the strength of normal cross-sections of eccentrically compressed concrete elements reinforced with composite reinforcement is proposed. In addition, the assessment of the proposed refined method is carried out, which proved to have the required level of reliability, while providing the best convergence with the experimental data.

Introduction. Modern wooden structures are mostly connected by mechanical working joints. To increase the reliability of nodal joints, various kinds of washers can be pressed, inserted, or glued into the wood of the elements, thus ensuring the transmission of forces from one element to another. Joints on glued washers can transfer significant forces on a relatively small area of mutual contact, which is due to their high loadbearing capacity. Thus, the gluing of steel washers in places of increased stress concentration during force transfer ensures a significant redistribution of buckling/cracking stresses over a larger area of the connected parts. However, steel washers are highly corrosive, so additional measures are required to protect metal parts from corrosion or to replace the material with the composites. The results of full-scale tests of the samples with glued-in plastic washers are used to consider the ways of increasing the strength and deformation characteristics of the plastic washer material by applying additive technologies.

Aim. To increase the load-bearing capacity of the wooden structure joints by increasing the strength and deformation characteristics of the glued washer material.

Materials and methods. A method for full-scale tests of wooden specimens with glued fiberglass washers is presented. The wooden elements are made of second grade pine, while the washers are of REC Formax and REC Friction plastics. The test was performed in compression along the fibers, with control of vertical shear deformations. The methods of increasing the strength and deformation characteristics of plastic washers by using additive technologies are considered.

Results. Using the data of full-scale tests the diagrams of sample deformations on glued plastic washers are drawn, the obtained results are analyzed. The sufficiently high plasticity of washer materials is established. The ways for increasing the strength and deformation characteristics of plastic washers, particularly by reinforcing the plastic washers is suggested.

Conclusions. In order to increase the load-bearing capacity of the joints on the glued fiberglass washers, the reinforcement of plastic using additive CFC printing technologies and the use of different reinforcing fiber materials is adopted.

Introduction. The warranty or predicted service life of the flame retardant coatings, depending on the service conditions, is a crucial parameter in ensuring fire safety. Service life, or durability, can be defined as the ability of the flame retardant coating to resist external influences, i.e., to remain unchanged and retain its efficiency under climatic and various adverse factors. Since full-scale testing of the coatings’ durability is time consuming, accelerated testing methods are relevant.

Aim. To test methods for determining the resistance to climatic factors during aging in an open industrial atmosphere (HL1 (cold), UHL1 (moderate and cold macroclimatic regions) according to State Standard 15150-69). In addition, to test the efficiency of coatings of steel building structures under operation on the example of a modern fire retardant coating.

Materials and methods. The samples of the flame retardant coating were cyclically aged for 5, 15, and 25 years according to method 6 of State Standard 9.401-2018. The resistance to climatic factors and preservation of flame retardant characteristics during operation was evaluated according to State Standards R 53293-99 and R 53295-2009. The plates made of 08kp and 08ps steel sheets according to State Standards 16523-97 and 9045-93 in the size of 600 × 600 × 5 mm with a flame retardant applied to it from the front side as an anticorrosive primer “DEKOPOKS-FAST” with a dry layer thickness of 80 microns, weather-resistant flame retardant paint “DEKOTHERM-KHROM-R” with a dry layer thickness of 870 microns and finish coating with two-component polyurethane primer-enamel “DEKOPUR-FLEX” with a dry layer thickness of 50 microns.

Results. The flame retardant efficiency was found to decrease slightly with increasing number of artificial aging cycles and amount to 12 % downward from the control sample at 224 cycles (25 years).

Conclusions. The predicted service life of the investigated coating system in open industrial atmosphere (HL1, UHL1) with preservation of the flame retardant efficiency if all requirements of the technological process of obtaining the coating are met is not less than 25 years.

Introduction. The corrosion of concrete and reinforced concrete structures of buildings and facilities in biologically aggressive environments is considered and protective measures are indicated. All the presented materials are resulted from long-term surveys of numerous reinforced concrete structures of buildings and structures for various purposes along with full-scale corrosion tests of concrete samples in biologically aggressive corrosive environments.

Aim. To summarize the results of the performed work on the corrosion and protection of reinforced concrete in biologically aggressive environments.

Materials and methods. The reinforced concrete of structures and concrete samples prepared with means of protection against particular aggressive environments were studied, after they had been in biologically aggressive environments for a long period of time. The main research method is the study of concrete condition after prolonged exposure to aggressive environments.

Results. From the results of the study are outlined the methods of concrete protection from the following exposures: plant roots on the floor slabs of reinforced concrete drinking water tanks; animal life products on the floors of livestock facilities; stone-borers on marine facilities; thionic bacteria on water disposal and treatment facilities; mold fungi on industrial and residential premises.

Conclusion. Reinforced concrete structures in biologically aggressive environments should be protected through studying their peculiarities, corrosion mechanisms, as well as analyzing the condition of structures under prolonged exposure to biological environments.

Introduction. Provided by severe climatic conditions in the Russian Federation, seasonal soil freezing and emerging cryogenic processes cause frost heaving that negatively affect foundations and buried structures. As the magnitude of frost heaving forces significantly depends on the soil freezing depth, the assessment of soil freezing depth becomes very relevant.

Aim. Calculation and estimation of the depth of seasonal soil freezing by engineering and numerical methods.

Materials and methods. Calculations of soil freezing depth were performed for two sites composed of sandy loam and loam. Engineering calculations were performed according to four methods set forth in the normative documents, namely Recommendations on Thermal Engineering Calculations and Pipeline Laying in Areas with Deep Seasonal Soil Freezing, Handbook on Construction on Permafrost Soils, Recommendations on Accounting and Prevention of Deformations and Forces of Soil Frost Heaving, Recommendations on Forecasting the Thermal State of Permafrost Soils. Numerical calculations were performed in the Frost 3D and Borey 3D software systems. The experimental sites are located in the Tymovsky district of Sakhalin Oblast, where the Sakhalin-2 pipeline was laid.

Results. The engineering methods for calculating the required depth of soil freezing give overestimated results when using a large range of climatic and soil parameters: air temperature, snow cover height and density, wind speed, convective heat transfer coefficients, total solar radiation, surface albedo, maximum elasticity of water vapor, etc. At the same time, the use of Stephan’s formula with a limited set of input parameters gives results close in values. The numerical methods showed close results among themselves, though 32–47 % more than the results of engineering calculations at bare ground surface.

Conclusions. Research on the dynamics of soil freezing depth in field conditions is suggested to be carried out and compared with the results of engineering and numerical calculations to improve these methods.

Introduction. In recent years, important connections between the regulatory documents on masonry structures, which were based on a system established many years ago, have been destroyed.

Aim. To identify the key issues and to outline approaches to their solution. This primarily concerns the inconsistency of State Standards on brick and mortar testing methods, as well as codes of practice for the design of masonry structures.

Results. It is shown that the strength of brick and mortar are conditional values, which depend largely on the methods of their testing, shape and size of specimens, exposure conditions prior to testing. In SP 15.13330.2012 “Masonry and reinforced masonry structures”, which is an updated version of SNiP II-22-81*, the design resistance of masonry brick and mortar grades were assigned according to the results of tests in accordance with the State Standards in force at that time. In order to restore connections with State Standards, revisions concerning the design resistance of masonry structures were introduced in SP 15.13330. This was a compromise solution. An optimal solution would be to complement the State Standard for plastic molding bricks with transition coefficients from the strength of polished bricks to the strength of bricks with a mortar-levelled surface. The types of specimens in the State Standard for masonry testing in the form of walls are borrowed from European norms. Testing walls along with columns without taking the scale factor into account leads to incorrect results.

Conclusions. Violation of the connections between State Standards for material testing methods and codes of practice for design occurs largely due to lobbying by material manufacturers, who seek to achieve the greatest benefit for themselves. Sometimes there is an unreasonable desire to interfere in the process of developing codes of practice. On the other hand, the development of high-quality regulatory documents is impossible without the involvement of a broader professional community, taking the interests of all parties into account. However, the balance of interests must not translate into the reduction of reliability of buildings and structures under construction.

Introduction. In recent years, much attention has been paid to the issues of reducing labor costs and increasing the reliability of test results of masonry ceramic wall products (brick, stone, and blocks). It is noted that when determining the masonry strength limit, the levelling of brick support surfaces is performed with mortar. However, when levelling the support surfaces by grinding, the masonry strength limit is artificially overestimated by at least one grade. In order to increase the reliability of erected buildings and structures, Note 1 to Table 6.1 of SP 15.13330.2020 “Masonry and reinforced masonry structures” gives an indication of the need to introduce appropriate correction factors in determining the strength of masonry. In the previous version of the SP, the values of reduction factors were adopted without appropriate justifications.

Aim. To justify reduction of design compression resistance of masonry made of ceramic soft-mud brick (when determining its compressive strength with grinding of supporting surfaces) in order to increase the reliability of erected buildings and structures.

Materials and methods. Comparison of normative and calculated values of the strength of masonry made of ceramic soft-mud brick on conventional mortar according to the norms of the Russian Federation, as well as Britain and Germany, on the basis of which the European norms have been developed.

Results. The conducted comparison of British, German, and Russian norms showed that the calculated values of masonry strength given in the norms of European countries are lower than those in the norms of the Russian Federation due to higher safety factors.

Conclusions. The decrease in the design compressive strength of masonry made of ceramic soft-mud brick by 10 % (when grinding the supporting surfaces to determine the compressive strength) is recognized as reasonable.

Introduction. Structural reinforcement of brick and stone masonry by grouting materials under pressure is an efficient approach to restoring the masonry integrity, and, in some cases, improving its bearing capacity. This paper presents the results of research studies into the strength of a masonry structure reinforced by methyl methacrylate injection. This research is part of a larger project, which was launched in 2004 and continues to date. Due to the high penetrating ability of methyl methacrylate, reinforcement of masonry structures with small crack opening seems highly promising.

Aim. Evaluation of the effectiveness of methyl methacrylate injection for masonry reinforcement.

Materials and methods. The experimental studies were carried out in two stages. At the first stage, masonry specimens manufactured in the form of columns were subjected to compression tests. At the second stage, methyl methacrylate was injected under pressure into the specimens with formed cracks. The as-reinforced specimens were tested again in order to evaluate their strength increase factor.

Results. The distribution of methyl methacrylate throughout masonry when injected under pressure, as well as through individual brick and mortar specimens without pressure, was studied. It is shown that the technology of masonry reinforcement by methyl methacrylate differs significantly from that of concrete consolidaton, where higher pressures contribute to its more even distribution over the concrete body.

Conclusions. Injection of methyl methacrylate into masonry with multiple load cracks can increase its loadbearing capacity by at least 1.2 times.

The results of research were used in the development of normative documents on reinforcement of masonry structures.

Introduction. Special requirements for the calculation of masonry walls using large ceramic blocks with the void content up to 57 %, including under the action of concentrated loads (buckling) are given in SP 15.13330.2020. In particular, Table 7.5 of this SP gives the coefficients for determining the calculated values of masonry under buckling. However, the results of Russian and foreign studies show that the masonry made of blocks with the void content more than 50 % requires clarification of the coefficient values for determining the calculated resistance of masonry buckling. The results of experimental studies conducted at Research Institute of Building Constructions named after V.A. Koucherenko to determine the masonry strength under buckling for clarifying the calculated coefficients presented in SP 15.13330.2020 are given.

Aim. To develop a methodology and specify the transition coefficients for determining the calculated values of the strength of large ceramic block masonry under buckling on the basis of the results of Russian and foreign experimental studies.

Materials and methods. Experimental studies have been carried out to examine the stress-strain state of large ceramic blocks and masonry walls with their use under the action of concentrated loads applied according to the schemes that can be most accurately realized in laboratory conditions, particularly schemes a and e given in paragraph 7.14 of SP 15.13330.2020.

Conclusions. The results of these studies have shown that the buckling strength of large ceramic blocks masonry depends on several factors, including the magnitude of normal and tangential stresses in vertical sections between the compressed zone and the unloaded section of the masonry. In addition, the shell effect in the presence of horizontal joints has a great influence.

Introduction. Stone masonry is a structurally heterogeneous (composite) material; therefore, a number of its physical and mechanical characteristics are orthotropic, including the coefficient of linear thermal expansion. The article analyses the coefficient of linear thermal expansion of stone masonry under the conditions of its operation in different temperature and climatic conditions, including different humidity.

Aim. To obtain the dependence of the coefficient of linear thermal expansion on masonry humidity at freezing temperatures by comparing the results of studies of wet masonry samples.

Materials and methods. The study is based on the data of M.A. Mury published in his work "Temperature deformations of wet brickwork" and some of his previously unpublished data. Regression analysis was used to perform the research.

Results. There were obtained graphical and mathematical dependences of the coefficient of thermal expansion of masonry in the form of piecewise linear functions at freezing temperatures, with account of material humidity.

Conclusions. The presented dependences can be used in calculations of the stress-strain state of masonry structures with the use of modern program complexes. Published data on the coefficient of linear thermal expansion of masonry show a wide range of their values, which indicates fragmentary research based on the use of ceramic stones from a single manufacturer. Therefore, large-scale research with systematization of the results with a logically justified maximum number of varying parameters of masonry should be carried out, with subsequent amendments to the norms of design and construction of masonry structures based on the results of the research.

Introduction. The outer layer of exterior walls is the facing masonry, experiencing a complex stress-strain state when taking its own weight, climatic loads, and exposures (wind pressure, humidity, and air temperature). An analysis of available research results, as well as the requirements of regulatory documents showed that no consideration is given to the temperature deformations of wet masonry when freezing. In this regard, the studies were conducted to assess the impact of this effect on the stress-strain state of the facing masonry.

Aim. To obtain a universal dependence of the temperature block length of the facing masonry, including its freezing.

Materials and methods. The study is applied to the facing masonry (facing layer) of multilayer exterior walls of buildings, modeled in the LIRA-CAD software package, which implements the finite element method in the form of displacement method. The research results of the work of M.A. Mury "Temperature deformations of wet brickwork" (2008) are used here.

Results. An empirical dependence of the temperature block length of the facing masonry for exterior multilayer walls is obtained based on the analysis of the thermal stress state of the masonry resulting from numerical calculation. A logically justified structural solution of the facing masonry unit with antifriction interface with the floor slab is proposed.

Conclusions. According to the results, the length of the masonry temperature block is not only affected by the temperature difference and the stiffness of the supporting structure, but also by the humidity conditions of its operation. When the humidity of the masonry increases from 6 to 12 %, the design length of the temperature block significantly decreases. The lengths of temperature blocks, set according to existing methods (including methods of design standards), have an overestimated value, and thus the durability of facing masonry is essentially reduced, or even destructed in a number of cases.