Introduction. Different approaches are used to study the structure and properties of structural steels. The properties of steels are determined using traditional methods (physical methods, field tests, X-ray analysis, microscopy, etc.). Structure studies are also carried out using traditional methods based on Euclid's integer geometry. A similar approximation of structural elements by Euclid's figures leads to a decrease in the accuracy of forecast models due to the complex shape of its elements. The reason for this is the fractality (fine dimensionality) of most elements of the material structure. The paper proposes an approach based on a combination of expert and fractal assessments when creating a forecast model for the quality of construction steel. Materials and methods. Construction steel 20 in the mode of factory delivery was studied. The steel had a ferrite-pearlite structure. Mechanical tests and determination of chemical composition were carried out in accordance with the existing regulatory documents (DSTU 7809). The content of pearlite in steel ranged from 10 to 18 %, depending on the amount of carbon. Ferrite occupied the entire other part of the area of the slide examined under the Neophot-2 optical microscope. The results of the experiment. Expert assessment was used to predict mechanical indicators of strength with the aim of reducing material and time costs for conducting field tests with metal samples. The effect of the ferrite-pearlite structure on the mechanical characteristics of strength was investigated by comparing the fractal evaluations of the structure with the indicators of mechanical tests. It has been established that an increase in the fractal dimension of pearlite has a positive effect on the growth of strength indicators of steel 20. A similar effect is, in a certain way, associated with the change in the shape of pearlite grains in the process of changing the amount of carbon in steel within the limits of regulatory documents. Conclusions. For structural steel 20, models for assessing its mechanical characteristics were obtained using the fractal dimensions of structural elements and expert assessments. Coefficients of pairwise correlation of regression equations are recorded in the range of 0.65...0.85. The obtained results can be used to forecast strength indicators of steel, which is especially relevant when assessing its residual resource during operation.
Introduction. In reinforced concrete structures, the ends of reinforcing bars are anchored in the concrete by launching the reinforcement beyond the considered section for the length of the force transfer zone from the reinforcement to the concrete as well as by using anchoring devices. If the required design length of the reinforcement cannot be ensured, special measures to anchor the reinforcement bars are applied [1, p. 5.36]. One of these measures is to install special anchoring devices in the form of plates at the ends of the longitudinal bars. When anchoring devices in the form of plates, special attention is paid to the welding type of the plate with the bar, which should prevent the bar from being pulled out when longitudinal forces from external load are applied. Materials and methodology. The material to be investigated was reinforcing bars of class A500C with diameters of 25 and 32 mm, connected at the ends to metal plates by means of contact welding. Holes with a diameter equal to the diameter of the reinforcement were drilled in the metal plates. The bars were inserted into the holes flush with the surface of the plates and welded to the plates by one and double sided welding. A total of two bars were used per welded joint. The strength of welded connection of reinforcing bars with plates was determined on the tensile testing machine HMS-100 by applying maximum tensile force to reinforcing bars. The fracture pattern of each reinforcing bar to plate joint was noted. The results of the experiment. As a result of the experiment, it was found that the destruction of the connection between the two reinforcing bars of 25 mm and 32 mm diameter and the metal plate during one-sided welding occurred by destroying the welding connection and pulling the bars out of the plate. When the bars were joined on both sides, there was no pulling out of the plate. In this case, one 25-mm-diameter bar joint is out of service due to bar breakage in the area of contact with the weld and the other is due to the exhaustion of its physical yield strength. The destruction of the 32mm diameter bars and metal plate joint in the two-sided welding process was due to the rupture of one bar in the area of its contact with the weld and the cracking of the other bar's contact with the weld. Conclusions. As a result of the experiment, it was found that the strength values of the welded connection between reinforcing bars 25 mm and 32 mm in diameter and a metal plate at bilateral welding were 1,33−1,36 times higher than those at one-sided welding.
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