Introduction. The increasing use of a variety of modern architectural forms of public buildings of mass use entails the search for appropriate design solutions that should ensure safety, serviceability, as well as the durability of load-bearing structural systems and their elements.

Aim. Using the example of the designed and already under construction exhibition pavilion “Atomic Energy” on the territory of JSC “VDNH”, one of the possible solutions for the coupling of large-span roof system with a structural system of monolithic reinforced concrete is shown.

This coupling option includes the supporting parts of the steel cantilever trusses of the roof embedded in monolithic pylons and bracing members. The calculations and detailing carried out showed that the new coupling solution meets the requirements of the current standards for load-bearing capacity, rigidity and crack resistance.

Materials and methods. By means of numerical modeling using various computational complexes, analysis of experimental data of full-scale models and their comparison with modeling data, the initial data for the construction of the main load-bearing structures were obtained.

Results. As a result of the applied integrated approach, the initial data for the construction of the main loadbearing structures with atypical cross-sectional parameters were obtained and verified.

Conclusions. During the design of the load-bearing frame, the system of coupling of large-span steel trusses of the cantilever type with monolithic reinforced concrete structures of the “Atomic Energy” pavilion on the territory of JSC “VDNH” was improved.

Introduction. High-strength concrete has high mechanical strength and a number of other advantages, but is prone to explosive destruction during rapid high-temperature heating (in case of fire), which leads to a decrease in the cross-sections of reinforced concrete structures and premature occurrence of the fire resistance limit by loss of bearing capacity (R). The results of studies on the fire resistance of structures made of high-strength concrete are not available in the construction regulatory framework. The calculation method for assessing the fire resistance of structures made of high-strength concrete with fire testing has not been worked out too.

Aim. Experimental study of fire resistance of reinforced concrete slab structures made of high-strength concrete of B60 and B100 classes, taking into account the influence of the process of explosive destruction of highstrength concrete in case of fire.

Materials and methods. Concrete samples and full-scale slabs made of high-strength concrete with the addition of microsilica of B60 and B100 classes were subject to research. Full-scale solid-section slabs made of highstrength concrete of B60–B100 classes with steel reinforcement of A500C class were subject to fire tests. Based on the results of fire tests, the limits of fire resistance of full-scale slabs of high-strength concrete and the specifics of explosive destruction of high-strength concrete in a fire were determined.

Results. The article presents the results of experimental studies and fire tests of the fire resistance of slab structures made of high-strength concrete.

Conclusions. The effectiveness of research is determined by the development of a computational method for assessing fire resistance for structures made of highstrength concrete during design. Based on the results of the work, the need for further studies of the fire resistance of different types of structures made of high-strength concrete, with variations of high-strength concrete classes and types, depending on their material and quantitative composition, was revealed.

Introduction. The article is based on the results of monitoring the regulatory framework of international standards in the field of ISO/TC 71 “Concrete, reinforced concrete, prestressed reinforced concrete”. Monitoring and analysis of newly developed and updated international standards is done to identify gaps in the domestic regulatory framework, to find duplicate or contradict regulatory documents, to establish relationships with regulatory documents related to adjacent areas, to monitor and analyze existing regulatory technical documents for the sufficiency of requirements in the field of the committee’s activities, to prepare proposals for the development of mandatory construction norms.

The aim is to analyze and compare the international and Russian regulatory and technical base for its timely updating and elimination of emerging duplications and contradictions, to increase the level of harmonization of Russian and international norms and standards in the field of construction of buildings and structures, from the point of view of introducing progressive domestic developments into the regulatory framework, to develop proposals for amendments to regulatory technical documents and development of new regulatory documents in this area.

Materials and methods. International ISO standards were selected as the material, and European and American standards were compared with their Russian counterparts for further analysis.

Results. The article provides selective monitoring, analysis and comparison of ISO standards and the Russian regulatory and technical framework for its timely updating and elimination of duplications and contradictions, increasing the level of harmonization of Russian and international norms and standards in the field of construction of buildings and structures ISO/TC 71 “Concrete, reinforced concrete, prestressed reinforced concrete”. Nine international ISO standards have been analyzed with a view to possible harmonization with Russian national standards.

Conclusions. Based on the results of monitoring:

1. 9 ISO/TC 71 standards “Concrete, reinforced concrete, prestressed reinforced concrete” are considered. The systematization of the current ISO standards related to the field of activity of ISO/TC 71 “Concrete, reinforced concrete, prestressed reinforced concrete” has been carried out.

2. The closest analogues of normative technical and methodological documents in the national standardization system for the analyzed ISO standards are identified and analyzed.

3. Proposals have been prepared for the development of new and updating previously approved codes of rules, building codes and regulations.

Introduction. The description of the main results of the research work carried out in JSC Research Center of Construction on the topic “Development of methods for monitoring and predicting the strength of concrete at an early age by acoustic emission method” is given.

Aim. The aim of the work is to obtain experimental data for the development of methods for monitoring and predicting the strength of concrete at an early age by acoustic emission.

Materials and methods. The research was carried out on concrete mixtures made of heavy and fine-grained concrete with mineral and chemical additives. In the process of concrete hardening the acoustic emission method was used. Acoustic emission monitoring was carried out continuously for several days.

Results. According to the results of the study, the most informative parameters of acoustic emission data that correlate with the strength of concrete have been identified. Automated algorithms for concrete strength monitoring have been developed. Based on the results of measuring the propagation velocity of acoustic waves and the decrease in the attenuation coefficient of acoustic signals, as well as the output of these values to the plateau, the periods of completion of setting of concrete mixtures are determined. During the experiments optimal frequency characteristics of acoustic emission sensors were determined.

Conclusions. The results of the research allow us to introduce into the practice of construction a new approach for monitoring the strength properties of concrete during its hardening using the acoustic emission method. Proposed approach can be carried out remotely, without the presence of an operator. The advantages of this approach also include its use in hard-to-reach places where the use of other testing methods is difficult.

Introduction. One of the most important reserves for saving material and energy resources in the construction industry is the re-involvement of recycling concrete materials (products of disposal of substandard concrete, reinforced concrete structures and products), in particular, highly dispersed powders with the prospect of their use as a mineral additive for the production of mortars for general construction purposes, in the production field. The implementation of this approach will practically ensure the introduction of the most important principle of waste-free technological processes (in the production of prefabricated and monolithic concrete, reinforced concrete structures and products) and create conditions for solving important economic and environmental problems.

Aim. The aim of the work were the determining of the main physical and mechanical characteristics, comparative analysis of the mortar on Portland cement, as well as mortars with the replacement of a part of Portland cement (by 10, 15 and 25 %) with a recycling (concrete) fine powder with a specific surface area of 4500 cm²/g.

Materials and methods. For the research, the following components were used: recycling (concrete) fine powder with a specific surface area of 4500 cm²/g, construction sand with a size modulus Mk = 2.31 (according to GOST 8736-2014), portland cement with CEMII/V-W 42.5N (according to GOST 31108-2020) slag, chemical additive “CENTRIPOR TFM 411R”.

The selection of mortar compositions was carried out according to SP 82-101-98. Tests of mortar mixtures and mortars were carried out according to GOST R 58767-2019. Compliance with the compressive strength of mortars with the grade was determined in accordance with GOST R 58766-2019.

Results. As a result of the work carried out, it is shown that fine-dispersed recycling concrete powder with a specific surface area of 4500 cm²/g can be used as a mineral additive (filler) for the production of mortars on a par with additives currently used in the construction industry of the country.

Conclusions. The possibility of using fine-dispersed recycling concrete powder with a specific surface area of 4500 cm²/g as a mineral additive (filler) for the  roduction
of mortars on a par with additives currently used in the construction industry of the country. It has been shown that when 10 % of cement is replaced with recycled (secondary) fine powder with a specific surface area of 4500 cm²/g, the strength of building mortars of the M100–M150 grades increases and its structure improves.