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.