Introduction. SP 63.13330.2018 provides two approaches to calculating the strength of normal cross-sections of reinforced concrete structures: the nonlinear deformation model NDM (general approach) and the method of ultimate forces UFM for simple elements of rectangular, T-shaped and I-shaped sections with reinforcement located at the edges of the element. As far as the authors are aware, no detailed studies have been conducted to compare the results obtained with both approaches.

Aim. Conduct researchе to compare the results obtained in the calculations for NDM and UFM, identify the differences, establish their physical cause, evaluate the economic aspects of the problem, and make the necessary recommendations.

Materials and methods. Calculations were carried out according to the program "OM SNiP Reinforced Concrete". Studies were performed for three types of structures. The first type included four cross sections of elements under two stress states: bending (T-shaped and rectangular), off-center compression (rectangular and annular). The second type of structures included beams tested at the NIIZHB named after A.A. Gvozdev. The third type is lintels according to State Standard 948-84. In all types of structures, under the action of the same forces, reinforcement was selected according to NDM and UFM.

Results. It turned out that the compressed zone of concrete in UFM participates in the resistance of cross sections to acting forces much more effectively than in NDM. This can lead to a significant difference in reinforcement. In one of the cases, the steel consumption in the calculations for UFM turned out to be 78 % less than for NDM. 

Conclusions. For the considered structures, the calculation of the strength of normal cross sections by UFM turned out to be more effective than by NDM. At the same time, all the necessary regulatory requirements are met. Further research is needed to amend the existing regulations.

Introduction. For 35 years since the introduction of State Standard 6665-91, the regulatory framework for the design and production of reinforced concrete products has been significantly changed and supplemented. In this regard, an updated interstate standard for concrete and reinforced concrete side stones has been developed, taking into account changes in the regulatory literature.

Aim. Familiarization of specialists in the design and production of concrete and reinforced concrete side stones with the updated State Standard 6665-91 in connection with the updating of the regulatory framework.

Materials and methods. The information about the updated interstate standard State Standard 6665 "Concrete and reinforced concrete side stones. Technical conditions", which provides rules and requirements for the design, testing and manufacturing technology of concrete and reinforced concrete side stones.

Results. As a result of the revision of the standard, stricter requirements for concrete have been established, the choice of reinforcement classes for reinforcing side stones has been expanded, which can significantly increase their durability.

Conclusions. Updating the requirements for acceptance rules and control methods allows to improve the quality of factory production of precast concrete and reinforced concrete side stones.

Introduction. Currently, loop overlapping joints of reinforcing bars are used in reinforced concrete structures. These types of working rebar connections are most widely used in NPP structures for the construction of slabs and walls made of monolithic reinforced concrete. Loop joints in these structures are used to connect adjacent three-dimensional reinforced blocks that are assembled in advance and installed in the design position before concreting. This type of connection leads to an increase in the manufacturability of construction and installation works, as it significantly reduces labor costs on the construction site when installing reinforcement frames.

The relevance of the development of the standard is due to the fact that the current regulatory framework did not contain detailed instructions on the design requirements for such connections. The absence of these provisions led to significant difficulties in the design of such structures, which led to excessive material and time costs.

The aim of the work is to improve the system of urban planning activities in terms of clarifying and supplementing existing regulatory documents on the design of reinforced concrete structures.

Materials and methods. The development of the standard was carried out taking into account modern requirements, as well as an analysis of the results of recent scientific research. Additionally, the practical domestic experience of using loop joints in the construction of nuclear power facilities was analyzed.

Results. The result of the work is the State Standard R 70447-2022 standard, the provisions of which include new calculation methods, as well as clarifications of existing calculation and design methods, and updated requirements. The draft standard passed public discussions, as well as the necessary expertise and was put into effect.

Conclusions. The standard State Standard R 70447-2022 "Reinforced concrete structures with loop joints of reinforcement for nuclear power facilities" has been developed, the provisions of which will allow developing reliable structural solutions for such structures, including achieving a certain economic effect. At the same time, certain areas for improving the provisions of this standard are noted.

Introduction. The article discusses the innovative structural system of SPMF (prefabricated monolithic spatial frame) in terms of its practical implementation at enterprises producing precast reinforced concrete structures. In particular, we mean low-capacity plants located in the regions and not having a developed technological base. The introduction of SPMF at these enterprises will allow to organize the production of products for the construction of social and cultural facilities, as well as residential buildings in conventional and seismically active areas. The structural system consists of H-shaped frames arranged orthogonally to each other and interconnected in height by monolithic inserts, and horizontally by ties. The floors are prefabricated from solid reinforced concrete slabs, connected to each other through embedded parts by welding. It is possible to use multi-hollow flooring. Enclosing structures made of small-piece elements or hinged panels on a frame with effective insulation.

H-shaped frames are located on a grid of axes of 6 × 3 m or 6 × 6 m – in the case of multi-hollow flooring. The frame is manufactured in a horizontal position. The size of the molds in length does not exceed 3,000 mm, one half-frame is made in the mold. The dimensions of the half-frame are 2,000 × 3,000 mm. The half-frames have rebar outlets in the crossbar part for subsequent enlargement assembly. The consolidation assembly can be carried out at the factory or on the construction site during the installation process. Products are transported in a horizontal position by flatbed trailers.

For low-rise buildings, seismic protection is provided using the "sliding foundation" technology.

Materials and methods. On the basis of a given architectural and planning solution of a residential 4-storey building located in the Prokopyevsk area, for the concrete plant of LLC Promkombinat in Kaltan, Novokuznetsk region, at the "concept" stage, the layout schemes of frames, floor slabs, as well as the main technical solutions of nodal connections were developed, the calculation of the building was carried out.

The range of products for the construction of the aboveground part of the house consists of 10 positions: half-frame – 2 units; floor slabs – 2 units; stiffness diaphragms – 2 units; staircases – 2 units; staircases – 2 units.

The foundation for the building is provided from monolithic concrete with an active seismic isolation device in the form of a sliding belt, which is arranged under the pillars of H-shaped frames. A pair of fluoroplast F-4 – steel is considered as a sliding element.

Results. A practical example of the implementation of an innovative frame system of SPMF at a specific enterprise is given.

Conclusions. During the development work on the adaptation of the SPMF frame system at the precast concrete plant, technical solutions were obtained for a 4-storey residential building located in an area with seismic activity of 8 points. The main load-bearing elements of the H-shaped frame and the ceiling are made in horizontal forms available at the enterprise. The dimensions of the products do not exceed those established for transportation by flatbed vehicles. The introduction of this system at the enterprise makes it possible to establish the production of residential buildings in the region, as well as social and cultural facilities.

Introduction. In conditions of negative temperatures or in the absence of the possibility to optimize the composition of concrete during the period of strength gain of concrete monolithic reinforced concrete structures, the formation of thermal cracks is possible, the repair of which requires significant additional costs that are not provided before the start of work.

The aim of the work is to reduce the cost of repairing these manufacturing defects in the form of pre-operational temperature-shrinkage cracks.

Materials and methods. Cost reduction was achieved by assigning several options for concrete care, calculating the thermally stressed state of structures for each of the assigned options and choosing the optimal option for concrete care, providing minimal tensile stresses leading to the appearance of temperature-shrinkage cracks in structures, with the least amount, width of opening and depth of crack propagation.

The calculation was carried out using modern calculation programs according to the methodology used in the NIIZHB named after A.A. Gvozdev, JSC Research Center of Construction.

The features of the construction conditions were: concreting at a negative ambient temperature, the use of a concrete mixture with a cement consumption of 440 kg/m³; concreting the structure with sections 2.25–5.05 m high with an interval of 12 days between divisions; ensuring heat exchange of the structure with the environment in the initial period of 2–3 days after concreting and regulating the cooling rate of the structure using thermal insulation materials.

Results. According to the results of the work, it was possible to practically eliminate the appearance of the defects in question and the cost of repairing cracks.

Conclusions. The cost of work and repairs turned out to be about 10 times less than the estimated cost of repairing cracks that usually occur in similar structures and construction conditions.

In the Arctic, in the area of the Kislaya Bay of the Barents Sea, the first Russian tidal power plant, the Kislogubskaya TPP named after L.B., has been successfully operating since December 1968. Bernstein. In the world practice of hydropower, this is the only experience in constructing a facility using the floating method, which radically (by a third) reduced the cost estimate and accelerated the construction period (by half). The PES is recognized as an outstanding structure of the twentieth century, a durable large reinforced concrete facility located in difficult arctic climatic conditions.

Researchers talk about the monument of domestic science and technology, the history of its creation, and the scientific research carried out on its basis: Candidate of Technical Sciences Igor Nikolaevich Usachev - one of the founders of the Russian scientific and engineering school of tidal energy and floating structures, co-author of the creation of a pioneer tidal power station in Russia; Doctor of Technical Sciences Nikolai Konstantinovich Rosenthal, an authoritative researcher of the quantitative theory of corrosion processes under the influence of various aggressive environments on concrete with a forecast of the durability of structures.