Introduction. The core-suspended system was first used in the construction of high-rise buildings in the 1960s. This system was developed with the aim of rational use of urban space in conditions of dense buildings. It has become widespread around the world. In addition to their architectural advantages, core-suspended buildings have a number of important design features such as the increased flexibility of their load-bearing elements. This can be used to reduce the forces that occur in structures under various dynamic influences. At the same time, the construction and exploitation of buildings of the core-suspended type have technical difficulties. An emergency failure of critical load-bearing elements, such as suspensions or walls of the core of rigidity, in buildings of this type can lead to an avalanche-like collapse of other structures. Special attention should be paid to ensuring the resistance of trunk-suspended buildings to progressive collapse.

Aim. To analyze the susceptibility of a multi-storey suspended building to progressive collapse.

Materials and methods. In the LIRA software package, numerical modeling of a building with a core-suspended load-bearing system was carried out when the accidental failure of most critical load-bearing elements was occured. This allowed an analysis of the building's resistance to progressive collapse.

Results. Data on the stress-strain state of load-bearing elements during local structural failure have been obtained.

Conclusions. The core-suspended building is not susceptible to progressive collapse. This is confirmed by data on the behavior of the building in calculations corresponding to various local structural failures.

Introduction. Guncrete structures are mainly used as columns. In the columns of buildings, guncrete structures operate on central or off-center compression with small eccentricities. Guncrete structures have a number of indisputable advantages over steel and reinforced concrete structures. The guncrete seismic isolating support in the building is operated by central compression. Under seismic impact the support deviates from its vertical position, and the longitudinal axis of the support does not coincide with the vertical line of force from permanent and temporary loads. In this case, there is a complex stressed state, the so-called "oblique" or "diagonal" compression. With diagonal compression, plastic deformations develop under lower loads than with central compression. The manufacture of the reinforcement frame and the assembly of guncrete structures caused considerable difficulties. Therefore, it was decided not to install reinforcement in the central part of the sample, that greatly simplifies the manufacturing technology. In this regard, there was a need for an experimental study of the operation of a guncrete structure under diagonal compression to static and low-cycle loads.

Aim. Conducting of the experimental studies of guncrete structures with diagonal compression for static and low-cycle loads without a reinforcing frame in the middle part of the element.

Materials and methods. Experimental studies were carried out by testing prototypes of guncrete structures, without reinforcement in the central part for central, diagonal compression and under low-cycle load.

Results. Experimental data on the operation of guncrete elements under central, diagonal compression and low-cycle load without a reinforcing frame in the middle part of the element have been obtained.

Conclusions. The load-bearing capacity of guncrete structures during diagonal compression in the elastic stage is less than during central compression. The elastic operation of guncrete structures under low-cycle load practically does not differ from the operation of the element under monotonous loading.

Introduction. The article discusses the types of channeling agents, their application and advantages, as well as ways to improve and technology of application. The differences between channeling agents working together with concrete, the advantages of channeling agents extracted from concrete compared to non-recoverable ones, reusable and single-use channeling agents, as well as their structures made of combustible materials and made of shape-memory metals and screw channeling agents are shown.

Aim. The study of the most promising, in our opinion, channelizers.

Materials and methods. A patent search was conducted for the latest proposals on this topic, initial studies and comparative analyses of the application of the proposed channelizers were conducted.

Results. The results obtained made it possible to recommend new technologies for the use of channeling agents.

Conclusions. Work on the application of new technologies for the use of channel formers should be continued in more equipped laboratories and that technologies should be recommended for use.

REVIEW of the textbook for universities "Reinforced concrete structures" in two parts (authors – E.N. Kodysh, N.N. Trekin, V.S. Fedorov, I.A. Terekhov)

Introduction. The existing regulatory requirements for vibrated reinforced concrete support posts for overhead power lines (overhead lines) of 0.4–10 kV are analyzed. It is noted that the required frost resistance and waterproofness of concrete are insufficient and inadequate, as well as the crack resistance of reinforced concrete pillars exposed to changing seasonal operating conditions and aggressive environmental influences.

Aim. The obtaining of optimal compositions and requirements for concrete mixtures for the manufacture of racks of the SV type. At the same time, the practical implementation of this goal will become the basis for the development of proposals for updating of existing regulatory documents in order to create uniform requirements for Rosseti Group of Companies and increase control over the products supplied by precast concrete plants.

Materials and methods. The results of research aimed at the analysis of the possibility of using of the new materials in the manufacture of reinforced concrete products that enhance their performance and strength qualities, and at the same time improve the quality of concrete mixtures using domestic additives without significant increase of the cost of support posts such as SV 95 and SV 110.

Results. According to the results of the above studies, the composition of the concrete mixture has been obtained, with the help of which it is possible to increase the operational and strength qualities of racks of the SV type, and, as a result, to increase their service life to the level of 50 years or more. The obtained research results will be taken into account when developing Technical Specifications for the production of racks of the SV type.

Conclusions. Based on the obtained indicators of the optimal composition of the concrete mix, the specialists of Rosseti Scientific and Technical Center JSC developed design documentation for the pillars of SV 95-3,5, SV 110-5 and SV 110-7 for the purposes of manufacturing and conducting mechanical tests of prototypes of the pillars.

Introduction. The quality of rolled reinforcement is a key factor in the reliability of reinforced concrete structures in conditions of increasing number of floors and complexity of construction projects. Modern Russian standards (State Standard 34028-2016, State Standard R 52544-2006) require strict statistical control of the mechanical properties of rolled products, including temporary resistance, yield strength and relative elongation. The relevance of the study is due to the need to improve the accuracy of sampling methods in order to minimize the risks of an unreliable quality assessment.

Aim. Development of a methodology for selective quality control of rebar products based on statistical analysis, including verification of the normality of data distribution, elimination of outliers and assessment of compliance with the requirements of standards.

Materials and methods. The study is based on the analysis of test data for rebar rolled products of class A600 (State Standard 34028-2016). The Shapiro–Wilk, Pearson (χ²), and Kolmogorov–Smirnov criteria were applied to verify the normality of the distribution. Outliers were identified by the Charlier method (α = 0.05). Software tools were used to calculate statistical indicators (mean, RMSD, skewness, excess) and visualization (histograms, Q–Q graphs).

Results. It was found that the presence of outliers distorts the distribution of key parameters. For the ratio of temporary resistance to yield strength, the exclusion of emissions allowed the normality of the distribution to be restored (p > 0.05 according to two criteria), whereas for the relative elongation δ_max, their effect turned out to be insignificant. Automated analysis has confirmed that the use of confidence intervals (95 %) and State Standard 34028-2016 methods increases the reliability of quality assessment.

Conclusions. Eliminating of outliers is a critical step to ensure the normality of data distribution. The combined use of agreement criteria increases the reliability of statistical conclusions. Automation of the methodology based on specialized software reduces the monitoring time and minimizes the human factor. Regular sampling is necessary to ensure that products meet the requirements of the standards and reduce risks in construction.

Introduction. In world practice, self-compacting concrete is increasingly used, which has high workability without additional (vibration) efforts. Straining concrete is also known, which is capable of increasing in volume during hardening, and under conditions of limited expansion deformations, it can self-strain, creating its own internal stress state, which neutralizes the manifestation of shrinkage.

Aim. Determination of the abradability of concrete made from a dry, self-sealing, straining concrete mixture.

Materials and methods. Dry self-sealing straining concrete mixes were used. The determination of abradability was carried out according to State Standard 13087-81 using an abrasion circle.

Results. The results showed that the abrasion grade G1 (low) corresponds to the majority of samples, which indicates the high hardness of the material.

Conclusions. The high hardness of the material leads to low abradability, which makes it suitable for use in highload structures. Further investigation of the effect of various additives on the properties of self-sealing concretes is necessary.