The research concerns the strength and deformability of threaded and crimped mechanical couplings of fittings used in Russia, the technology of their implementation and the quality of the result obtained.

An analysis of the research results found that after cyclic loads according to GOST 34227-2017 of categories S1 and S2, the strength of threaded cylindrical couplings made using Rollcon technology decreases by 2-12% compared with the strength of the connected fittings. Considering this, in order to meet the strength requirements, it is necessary that the temporary resistance of the reinforcement rods connected in this way be higher by more than 10%. For the A500 reinforcement class, σ_в≥ 660 Mpa should be taken. It is necessary to provide measures to prevent the destruction of the coupling joint by tearing the ends of the rods from the couplings with a thread cut, which is possible by increasing the length of the couplings, changing the type of thread, its geometric characteristics, the quality of cutting or knurling, additional processing to increase the strength of the metal of this section of the rods, etc. Cases of abnormal malleability of threaded cylindrical couplings as in static, as well as with cyclic loading of categories S1 and S2. To eliminate this disadvantage, additional research is needed to assess the factors influencing it (type and quality of the thread, its dimensions, length, production technology, etc.). Cases of abnormal malleability of threaded cylindrical couplings as in static, as well as with cyclic loading of categories S1 and S2.

To eliminate this disadvantage, additional research is needed to assess the factors influencing it (type and quality of the thread, its dimensions, length, production technology, etc.).

The main, difficult-to-correct and controlled disadvantage of crimped reinforcement joints is that their strength and deformability largely depend on the quality of work on crimping couplings at a construction site. In addition, you should also pay attention to the purpose of the dimensions, the selected material of the couplings and the technology of work during their manufacture. The experimentally revealed destruction of the pressed joint from the uniaxially directed wedging force of the "European" reinforcement with a two-sided arrangement of transverse ribs once again confirms the expediency of the preferred use of the recommended joint venture 14.13330.2018 (revision 2) in the earthquake-resistant construction of new fittings with four-row conventional and screw profile types of class A500sp and Av500P, having two times less uniaxially directed wedging effort.

Proposals for design in seismic areas:

1.      All mechanical connections proposed by the design documentation for construction in seismic areas must meet the requirements for cyclic loading of categories S1 and S2 without fail;

2.      The destruction of mechanical joints of all kinds must occur outside the joint, along the base metal;

3.      If the conditions of clauses 1 and 2 are met, as well as clauses 6.7.2; 6.7.3; 6.7.12 of SP 14.13330.2018 (change No. 2), the value of the residual deformation of the mechanical joint after loading to a stress in the connected valve equal to 0.6σ_т(0.2) can be increased to 0.3 mm;

4.      Crimping joints of fittings with a four-row profile Au500SP can be produced without monitoring the requirements of categories S1 and S2.

During individual construction in seismic areas, the designer often has to solve problems that violate certain requirements of regulatory documentation on the configuration and number of storeys of the building, architectural and planning solutions of its internal and underground space. In this case, it is necessary to develop special technical conditions (STC) with compensating measures for these deviations, ensuring high seismic resistance of construction objects. The article considers the possibility of using the technology of plastic deformation of the bearing structural elements of the building to ensure the seismic resistance of the object, and also offers a method for assessing the degree of plastic work of the structure.

As a result of the release of GOST 34028-2016 «Reinforcing bars for reinforced concrete structures» the manufacturability of new kinds of reinforcing bars, taking into account the needs of different areas of construction were increased. The materials of the present study prove the ability of reinforcement with a multi-row (six-row and screw four-row) arrangement of transverse ribs on its surface to maintain adhesion with concrete even at the stage of exceeding the limit values of deformation. This factor, as well as high endurance at cyclic dynamic effects, possibility of connection using couplings of four-row screw reinforcing bars and anchoring it with nuts, expands the possibilities of using the new valves not only in earthquake engineering, but also in nuclear power, transport and other types of construction. The new reinforcing bars of domestic production are able to gain a leading position not only in the domestic but also in foreign construction markets.

Introduction. The article considers the influence of the design solution of the reinforcement of periodic profile on the strength and deformability of adhesion to concrete.

Aim. Description of design solutions for new types of multi-row profiles, the results of their research and prospects for mass application in construction.

Materials and methods. The effectiveness of reinforcement in reinforced concrete depends on the mechanical properties of the material of the rods, the adhesion and interaction of their surface with concrete at all stages of loading, characterized by the design of a periodic profile. The methodology and equipment of the Research Institute of Concrete and Reinforced Concrete named after A.A. Gvozdev were used to conduct the research.

Results. According to the results of foreign and domestic studies, it has been established that it is impossible to completely eliminate the existing disadvantages of the "ring" and double-row "crescent" profiles, due to the peculiarities of their design solutions, and improvement is futile.

Due to the preservation of adhesion strength with concrete in the extreme stage of deformation (after reaching the yield point), as a result of low spacer, new types of reinforcement provide increased construction safety, especially under extreme external influences (seismic, explosions, impacts, etc.).

The four-row profile of reinforcement, when synchronizing rolling rolls, forms a two-way screw thread on the surface of the rods and can successfully compete with foreign GEWI-Stahl screw rods.

Conclusions. Replacing rods with a two-row European crescent profile with rods with a four-row profile of domestic design will reduce the consumption of reinforcement in reinforced concrete structures by 10–25 %, ensure increased construction safety and save lives, especially in earthquake-prone areas of development, increase the competitiveness of Russian rebar products in foreign construction markets, and ensure substitution of foreign screw rods.

With an annual production of 10 million tons of rebar, only a 10 % reduction in its consumption in reinforced concrete will have an effect, due to saving metal, energy resources for its production, transport and technological costs, production of additional products, at least 100 billion rubles.