Introduction. At present, composite materials are widely used in building structures and their components. The relevance of the work is determined by the buckling study of a shell structure made of a carbon fiber reinforced polymer. Despite the available experience in creating geometric models of finite element grids and studying the buckling of shell structures, the task of analyzing the mechanical behavior of shell layers remains insufficiently investigated. Therefore, research into the effects caused by polymer layering variations on a buckling mode appears to be urgent for regulating the layering process at various angle combinations due to a lack of sufficient data.

Aim. The study was aimed at identifying a layering pattern, under which maximum and minimum critical forces operate.

Materials and methods. The object of the study involves a cylindrical shell with a radius of 300 mm, a height of 600 mm, and a wall thickness of 1.56 mm made of eight variously-oriented carbon fiber layers impregnated with epoxy resin. The design modeling was performed using the finite element method. The cylindrical shell walls were modeled in terms of Laminate type flat elements, taking into account the composite layers. At the lower end, the cylinder was rigidly fixed and 100 kN axial compressive force was applied to the upper end of the cylinder. Using a software package, the variants of buckling modes were obtained for further analysis.

Results. The data, describing the buckling of a cylindrical shell, including the critical load coefficient at the first buckling mode were obtained by the finite element method. In addition, the dependence of a critical force on layering patterns was determined. Depending on the critical force value and the buckling mode, the most and least favorable patterns of layering in a package of a composite material were selected.

Conclusions. The orientation of layers in a composite material package affects the buckling mode and the value of critical force. An optimal selection of the layer orientation increases the critical force value by 2.25 times based on the information about the conditions of structural loading and fastening. 

Introduction. The main approaches to long-term creep tests of concrete regulated by GOST 24544-2020, valid in the Russian Federation, as well as foreign ISO, ASTM, and EN standards, are analyzed.

Aim. In this work, fundamental differences in conducting tests following Russian and foreign standards are determined. These efforts are essential and urgent, since, in order to use test results obtained abroad in Russia, it is necessary to harmonize test methods and initial test parameters (samples, measuring and test equipment, etc.).

Materials and methods. The article reviews testing procedures, controlled parameters, and processing of result; part 1 of the article covered the application, testing and measuring equipment, manufacturing process, sample parameters and fittings, and test preparation.

Results. ISO, ASTM, and EN are comparable; however, they differ greatly from GOST 24544 in some respects, in particular, regarding the sample parameters and the methods of their installation in the testing equipment.

Conclusion. Further harmonization of GOST 24544 with the aforementioned foreign standards is necessary. 

Introduction. The heat emission of concrete during its hardening in adiabatic conditions is typically determined according to the GOST 24316 State Satndard. This method is quite limited in research possibilities, since under the conditions of constantly increasing temperature, it appears impossible to adequately assess the influence of various components or hardening conditions on the processes occurring during the concrete hardening. The assessment of the heat emission during the isothermal hardening allows much more information about the hardening process of the studied material to be obtained. The direct determination of the concrete heat emission during hardening in isothermal conditions appears to be extremely difficult in technical aspect.

Aim. The study is aimed at developing a method for determining the heat emission of the concrete in isothermal conditions.

Materials and methods. The GOST 31108-2016 TsEM I 52.5N portland cement, quartz sand, crushed gabbrodiabase, and the GOST 23732-2011 mixing water were used in the study. The strength of concrete samples was determined in accordance with the GOST 10180-2012 State Standard. The TAM Air (TA Instruments) isothermal calorimeter was used for calorimetric studies.

Results. As a result of the performed studies, a method for determining the concrete heat emission in isothermal conditions was developed on the basis of assessment of the heat emission during the hardening of model mixtures reflecting the composition of the studied concrete. The optimal particle size of the sand and crushed stone fractions for model mixtures comprises 0.16–0.315 mm. The heat emission during the isothermal hardening of 10 model mixtures reflecting the composition of the studied concrete grades was determined. The strength class of 10 concrete compositions differing in cement content was established. The dependence of the heat emitted by model mixtures on the strength classes of the studied concrete compositions was determined. The heat emission of model mixtures during the isothermal hardening was established to be directly dependent on the strength of the studied concrete compositions.

Conclusions. The determination of the amount of heat emitted by model mixtures reflecting the composition of concrete mixtures during the isothermal hardening represents a useful cost-effective test significantly accelerating and facilitating the process of control and design of concrete compositions. 

Introduction. Construction enterprises can adversely affect the environment during the extraction of natural raw materials, as well as during the reconstruction, overhaul, and demolition of buildings. The manufacturing of construction materials, the actual erection, and maintenance of various buildings and structures comprise highly material- and energy-intensive processes characterized by waste generation, which need to be disposed. In developed countries, recycling wastes as a commercial commodity represents the preferable way of recovering concrete, reinforced concrete, and masonry (brick) waste. In this regard, the disposal of construction waste (including waste from sand-lime brick and brickwork) is becoming increasingly important.

Aim. In this work, the grain-size distribution, strength, and bulk density of recycled crushed aggregate from crushed sand-lime bricks (open stone mix) and brickwork (containing mortar) were determined and compared, and the prospects of its use as aggregates in the production of general-purpose concrete were identified.

Materials and methods. Recycled crushed aggregate from crushed sand-lime bricks (open stone mix) and brickwork (containing mortar) was used for the studies. The recycled crushed aggregate was tested as per GOST 8269.0-97, its characteristics were evaluated as per GOST 8267-93.

Results. This work shows the correlation between the bulk density, grain-size distribution, and crushing capacity of recycled crushed aggregate produced by crushing fragments of brickwork (containing mortar) and sand-lime bricks (open stone mix).

Conclusions. It is shown that recycled crushed aggregate obtained by crushing fragments of brickwork (containing mortar) and sand-lime bricks (open stone mix) are suitable (along with crushed stone from sedimentary and metamorphic rocks) for use as a coarse aggregate in the production of general-purpose concrete. It is shown that it is necessary to carry out comprehensive experimental work in order to develop a new GOST, which will improve the recycling of sand-lime bricks, as well as structures and products based on them following the end of their operation lifetime, and allow high-quality ready-to-use construction material to be obtained. 

Introduction. The technology of connecting precast reinforced concrete piles using pile joints is a promissing method in construction. According to some previous studies, the use of Leimet ABB+ pile joints provides for a significant reduction in material and labor intensity, as well as the time required for connecting the piles under sufficiently high strength and durability. Currently, the application of this technology is limited due to the insufficient knowledge of mechanical characteristics of pin connections. This article presents the results of strength tests of Leimet ABB+ pile joints for recast reinforced concrete piles.

Aim. Experimental testing of the strength parameters of Leimet ABB+ pile joints under compression, tensile, transverse shear, and bending.

Methods and materials. Experiments were performed using test samples represented by two fragments of recast reinforced concrete piles of the 1.011.1-10 standard, which were joined by a 4-lock Leimet ABB+ 400 pile joint. Loading tests of the samples were carried out in accordance with the GOST 8829-2018.

Results. The qualitative and quantitative destruction parameters of the test samples were obtained. The destruction of all the test samples occurred along the concrete body of piles with no signs of destruction of the metal pin connection. In addition, no signs of concrete indents in the area of the pin connection were observed.

Conclusions. Leimet ABB+ 400 pile joints were concluded to be of the uniform strength to the concrete pile body under the considered conditions. The test results of the pile joint strength are applicable when developing design projects. 

Introduction. A sustainable system of risk management in construction is in great demand for both consumers and suppliers of construction products. As one of the main elements of such a system, probability calculations of loader-bearing structures provide a necessary level of reliability and optimality of construction solutions. At the same time, the transition towards risk-oriented design, including the assessment and management of risks, implies the presence of sufficient statistic data, along with the methods of data collection and probability modeling. This study is focused on the issues concerned with collecting data for probability calculations.

Aim. To propose suggestions for improving the national regulatory framework as related to probability calculations of reinforced concrete structures and collecting the necessary data.

Materials and methods. The main objectives of the study were to investigate and analyze Russian and foreign experience in the field of risk assessment and management in terms of building structures and facilities based on probability calculations. In order to achieve these objectives, an analysis of existing Russian and international documents was carried out. In the course of the study, national regulatory legal acts and standardization documents including codes of rules and GOSTs were considered. In addition, some national regulatory technical documents, which were not included in the lists of both obligatory and non-obligatory applications, were analyzed, as well as other specialized regulatory technical documents. An analysis of foreign regulatory technical documents was conducted, including those regulating the initial data characteristics to perform probability calculations (loads, materials, and calculation models). In general, the methodology for analyzing regulatory technical documents involved a detailed study of the selected documents, an analysis of their positions concerning the issue under consideration, as well as an assessment of the completeness and sufficiency of the positions of the documents concerning the methods for determining the initial data characteristics for probability calculations of reinforced concrete structures regarding loads, materials and calculation models.

Conclusions. On the basis of the conducted analysis, specific subject areas for research works are formulated focusing on the development of probability calculations of reinforced concrete structures. A system of regulatory documents is proposed enabling an optimal risk-oriented design of reinforced concrete structures to be implemented. 

Introduction. The method of determining concrete strength based on steel stud driving into concrete by firing has been used since the 1960s. At present, several institutions promote this method as an alternative to direct nondestructive testing methods (pullout test and shear angles) and propose to introduce it into the current standard GOST 22690-2015. Its availability and low cost compared to those of the existing standard methods are mentioned to substantiate this proposal.

Aim. In this work, domestic and foreign studies and normative documents regulating the considered test method are analyzed, and its standardization and the volume of additional research are evaluated.

Materials and methods. Theses from the mid-20th century to the present, normative documents (ASTM C803-02, BS 1881-207, DIN EN 14488-2), and instructions (Z-WP-534. Windsor Probe System, Driving method Hilti DX 450-SCT) were reviewed.

Results. Significant limitations for the application and the factors having the most profound influence on the accuracy of the method were identified: hardness, type, and fineness of the filler, variation of firing charge power, and indenter parameters (driven stud). These factors have no influence on the control methods recommended by the existing standards. Foreign standards stipulate the application of this test method as an indirect technique, requiring adjustments based on the testing results of standard samples or test cores extracted from structures; however, no data on its accuracy is provided.

Conclusion. Given the revealed limitations, it is premature to standardize the method. Further research is recommended. The statement about the significant availability and cheapness of the reviewed method relative to the standard regulated methods is unsubstantiated. 

Introduction. The article presents a technology of erecting of high-rise building's frame structures made of B60-B100 classes high-strength concretes. This technology includes a complex of processes and considers a number of special features, the most significant of which are connected with the specific character of high-strength concretes and concreting climatic conditions.

Aim. To determine the main requirements for the technology of concreting and parameters of curing the monolithic structures of high-rise buildings made of B60-B100 classes high-strength concretes, including at winter periods, at the various stages of their erection.

Methods and materials. Studies were carried out on the effect of hardening temperature variations from +5 to +50 °С on the hardening kinetics of B60, B80, and B100 classes concretes. Based on the 15-year experience of the “Moscow-City” construction, the mix proportions of high-strength concretes were optimized, as well as the main technological parameters of concreting and curing the frame structures located at an altitude of up to 370 m were analyzed and summarized.

Results. The mix proportions of B60-B100 classes concretes of high-workability and self-compacting mixtures with a cement consumption of 350–480 kg/m3 was optimized using standard materials and MB-type organomineral modifiers. The performed study revealed a regularity between the strength and the temperature-temporal parameter of concrete curing, which is applicable for a preliminary assessment of strength characteristics in high-strength concrete structures on the basis of their temperature measurement results. A systematic approach to concrete curing and the maintenance of building structures as a whole with the vertical division of a high-rise building into four temperature zones led to a reducing the probability of thermal cracks appearance.

Conclusions. According to the results of the study, the proposed complex of technological solutions concerning compositions and properties of concrete mixtures and concretes, the technology of concreting, as well as the methods of heating and curing the concrete of structures at the various stages of their erection ensures thermal resistance to cracks at the early stage of concrete hardening, as well as the high quality and assigned rates of construction. 

Introduction. The analysis of analytical and computer-assisted calculations of waffle slabs shows that, depending on the established finite-element model and structure geometry, the forces in beams can vary significantly. As a rule, the analytical model is used as a reference when comparing bending moments. Examples available in the literature show that regardless of the slab geometry, the stiffness of individual central orthogonal beams or conditionally selected beams is used in the calculations when determining structural loads.

Aim. In this work, the accuracy of resulting forces in the beams of straight waffle slabs was assessed using the stiffness of individual beams in the analytical calculation.

Materials and methods. The work was carried out by comparing the bending moments obtained analytically and in the SCAD software by the finite-element method for beams having various stiffnesses in the central zones of straight waffle slabs. 12.0 × 12.0 m slabs square in plan having different aspect ratios of waffle were considered, as well as slabs having square 1.5 × 1.5 m waffles and different aspect ratios of spans. A T-beam-and-girder construction was used in the computer model.

Results. The values of bending moments of slabs square in plan having square caissons calculated analytically and using the computer-assisted finite-element method coincide, being a particular case. The bending moments calculated analytically and using the finite-element method for rectangular slabs or slabs having rectangular caissons differ. As the ratio of the span or caisson sides increases, these deviations increase.

Conclusions. In the general calculation, using the stiffnesses of individual central orthogonal beams or conditionally selected beams for the analytical determination of forces in the beams of straight waffle slabs leads to erroneous results. 

Introduction. The current standards for the design of concrete and reinforced concrete structures provide no methods for calculating the strength of the oblique sections in bending elements of various cross-sectional shape under the action of transverse forces. This prompts the designers to use simplifications in calculation of such elements, which, in some cases, may lead to excessive consumption of transverse reinforcement or the strength underestimation.

Aim. The performed study was aimed at assessing the reliability of a new method for calculating the strength of oblique sections in bending reinforced concrete structures with a non-rectangular cross-sectional shape.

Materials and methods. The reliability assessment of a new procedure for calculating oblique sections of a various cross-sectional shape was performed by the comparison between the calculated and experimental values of the transverse force received by the oblique section of reinforced concrete elements with various cross-sectional shape. The study considers the oblique bending tests of the samples with an annular, circular, and square cross-sectional shape, as well as T-shaped samples with a crossbar both in a stretched and compressed zone. The reliability assessment was performed using generally accepted methods of statistical analysis.

Results. The distributions of ratios of the experimental and calculated values of the destructive transverse force for various-section test samples were obtained to be close to normal ones. According to the results of the reliability assessment, the proposed procedure of calculating the strength of oblique sections in elements with various cross-sectional shape was established to be comparable with the procedure accepted in the SP 63.13330.2018 Rules and Regulations for calculating rectangular cross-section elements in terms of the accuracy and reliability indices.

Conclusions. The proposed procedure of calculating the strength of oblique sections in elements with various cross-sectional shape was determined to be comparable with the procedure accepted in the SP 63.13330.2018 Rules and Regulations for calculating rectangular cross-section elements in terms of the accuracy and reliability indices. 

Introduction. According to experimental data, at a certain design, the strength of eccentrically compressed elements increases due to the work of a composite polymer reinforcement located in a compressed cross-sectional area. However, dependences for calculating the strength of eccentrically compressed elements, represented in acting regulations for the design of concrete structures with a composite polymer reinforcement, appear to be inapplicable for calculating the reinforcement compression stress and, therefore, require refinement.

Aim. To develop a methodology for calculating the strength of eccentrically compressed concrete elements with a composite polymer reinforcement, considering the work of the latter in a compressed cross-sectional area.

Materials and methods. Considering the work of a reinforcement in the compressed cross-sectional area, the methodology of calculating the strength of eccentrically compressed elements was developed taking into account the positions of current design standards and verified by the data of experimental studies performed by domestic and foreign researchers.

Results. The results of methodology reliability tests were obtained using the experimental data of test samples with a carbon, glass, and basalt-plastic reinforcement of various profile types. During the calculation of eccentrically compressed elements using the proposed dependencies for calculating the height of an element compressed cross-sectional area, the accuracy and reliability were established to be comparable with those calculated according to dependencies adopted in current regulations for the design of concrete structures with a composite polymer reinforcement.

Conclusions. The proposed dependencies for calculating the height of a compressed cross-sectional area provide the sufficient accuracy of strength calculations for eccentrically compressed concrete elements both with and without taking into account the compression work of a composite polymer reinforcement. 

Introduction. At present, various approaches to standardization in construction are used that are often in poor agreement. This hinders international cooperation and collaborative planning, design, and construction of facilities. The harmonization of construction standards has been long overdue.

Aim. In this work, international standards were monitored and compared with Russian analogs in order to develop an approach to their harmonization.

Materials and methods. The European and American standards of the International Organization for Standardization (ISO) were selected for further comparison with the Russian analogs. A random monitoring, analysis, and comparison of ISO standards and Russian regulatory-technical base were carried out for its timely update, the elimination of emerging redundancies and contradictions, and the improvement of the harmonization of Russian and international standards in construction in the scope of ISO/TC 71 “Concrete, reinforced concrete, pre-stressed reinforced concrete.”

Results. The analysis of 14 international ISO standards allowed the documents to be classified into three groups for further work and steps toward their possible harmonization with the Russian national standards and toward the development of analogous national standards to be outlined.

Conclusions. Based on the monitoring results, it is recommended to classify ISO standards into three groups: 1. ISO standards of lesser relevance to national standardization due to a complete or, in some cases, more comprehensive regulatory base. 2. ISO standards where the standardization parameters differ from Russian standards or where the subject of standardization is reflected in several associated standards. Such standards should be harmonized with international standards. 3. ISO standards having no national analogs. Therefore, it is recommended to harmonize the Russian standards related to the second group and, in the absence of Russian analogs, develop national standards equivalent to those of the third group. 

Introduction. Reinforced concrete structures affected by various aggressive environments operate under off-center compression. Fiber-reinforced polymer (FRP) rebars replacing steel reinforcement in these structures are capable of increasing their durability and decreasing operating costs. However, the use of FRP rebars is limited by insufficient previous research into the methods of designing such constructions. The majority of international regulatory technical documents concerning the design of concrete structures reinforced with FRP rebars indicate the necessity of detailed studies into the stress-strain state of these structures under compression.

Aim. To study the effect of longitude and shear reinforcement on load-bearing characteristic of stressed concrete samples reinforced with longitudinal glass fiber-reinforced polymer (GFRP) rebars.

Materials and methods. The study was carried out using a concrete prism sample with different parameters of longitudinal and shear reinforcement. Five types of GFRP rebars differing in mechanical properties, as well as anchorage were considered. Shear reinforcement of the samples was performed with metal clamps at different pitches. The sample testing was fulfilled using centric compression with static load.

Results. The strength values of compressed concrete samples reinforced with GFRP rebars were obtained. An increase of up to 19 % in the strength of compressed concrete samples reinforced with GFRP rebars was found in comparison with non-reinforced samples.

Conclusions. The strength of compressed concrete elements increases when reinforced with glass fiber-reinforced polymer rebars. The degree of increase in the strength of such elements depends on the number of longitudinal reinforcements, as well as shear reinforcement pitch. The effect of the type of anchorage of GFRP rebars along with the values of its compression resistance on the strength of compressed concrete elements have not been established. 

Introduction. The development of the Arctic Region and oil and gas fields in the North Atlantic Ocean leads to an increase in the production of high-strength concrete structures. Thus, it is becoming increasingly vital to make such low-permeability concretes more freeze-thaw resistant.

Aim. To conduct experimental studies for obtaining reliable data required to develop a standardized approach to the normalization of freeze-thaw / frost-salt resistance parameters characterizing high-strength concretes.

Materials and methods. The study was performed using concretes of eight compositions (B60–B100 compressive strength grades). The freeze-thaw/frost-salt resistance of high-strength concretes was determined using the third rapid method involving the saturation, freezing, and thawing of samples in a 5 % sodium chloride solution, as well as assessment of freeze-thaw resistance in terms of strength, mass variation, and the dynamic modulus of elasticity. A variety of methods for increasing the water saturation of highstrength concrete were examined in order to expedite the testing process of high-strength concrete for freeze-thaw resistance.

Results. The studies into the freeze-thaw/frost-salt resistance of high-strength B60-B100 concretes revealed their high freeze-thaw resistance. Following 37 freeze-thaw cycles, the lower confidence limit for the strength of test samples was higher than that of control samples multiplied by a coefficient of 0.9. The frost-resistance grade of these concretes is above F2 300. No critical decrease in the dynamic modulus of elasticity is observed, which indicates a significant freeze-thaw/frost-salt resistance of all tested highstrength concrete compositions.

Conclusions. The freeze-thaw resistance studies of high-strength concretes carried out at NIIZHB named after A.A. Gvozdev yielded experimental data required to subsequently develop a standardized approach to the normalization of freeze-thaw/frost-salt resistance parameters characterizing high-strength concretes.

Introduction. With the introduction of a new national standard GOST 32703–2014 “Automobile roads of general use. Crushed stone and gravel from rocks. Technical requirements”, mining companies producing crushed stone from dense rocks faced the problem of ensuring the production output in compliance with two significantly different standards, both regulating the properties of crushed stone. The complexity of a balanced approach to production planning and stock reserve maintenance determines the need to assess the possibility of using crushed stone produced according to GOST 32703 when producing construction works, concrete mixes, and concrete for general civil construction.

Aim: to define the prospects of using crushed stone produced according to GOST 32703 when producing concrete for general civil construction.

Materials and methods. Crushed stone produced according to GOST 8267 and GOST 32703 from solid rocks of various origin—granite, gabbro-diabase, and dense limestone—was used as coarse aggregates for concrete production. Comparative tests of concrete mixes prepared from crushed stone from one deposit but classified in accordance with two different standards were performed. The main quality parameters of concrete mixes were determined by testing methods according to GOST 10181, while the mechanic al and physical properties of concrete mixes were determined by testing methods according to GOST 10180.

Results. The study showed a certain compatibility of the quality properties of concrete mixes and the mechanical and physical properties of concrete filled with crushed stone, which is classified according to different standards but having the same content of lamellar and needle-shaped particles.

Conclusions. Recommendations are formulated on the prospects of using crushed stone produced according to GOST 32703 when producing concrete for general civil construction. The key issues concerned with simultaneous application of two different standards are indicated. 

In this article, the meaning and purpose of the second part of the postgraduate course entitled History and Philosophy of Technology were briefly described.

What is technology? How one can define its nature and historical purpose? Is technology always beneficial? What constitutes the reality of technical objects, and to what limits does it extend? What is the importance of technology for humankind, and how does it affect every aspect of human life? These and many other questions related to technology, the history of its development, and its increasing influence on the human life sphere are of practical, as well as theoretical and even epistemological, importance. A scientific discipline, the philosophy of technology, which emerged in the second half of the 19th century, seeks answers to these questions.

The article addresses the problems that reveal how and on what basis the philosophy of technology emerged, why engineers were at the origin of its development, and what are the main goals and tasks of this philosophical discipline.