One of the methods of restoring the operational qualities of reinforced concrete bent elements is to strengthen their compressed zone. This reinforcement is performed by placing a concrete overlay, usually of a different grade of concrete than the existing element. In existing research publications, reinforcement of reinforced concrete structures with various materials was considered. A comparison of the reinforcement of experimentally tested different beams was made: unreinforced, reinforced with a layer of steel fiber concrete, polymer concrete, reinforced polymer concrete, fine-grained concrete and reinforcement, and others. Compared to unreinforced samples, all reinforcement methods significantly increased the load-bearing capacity. For beams reinforced with a layer of reinforced steel fiber concrete and polymer concrete, the bearing capacity increased by approximately 1.4 times. And in beams reinforced with a layer of reinforced fine-grained concrete, the indicator of the increase in bearing capacity is slightly less - about 1.18. In the work, a numerical and theoretical study of the position of the zero line in reinforced concrete beams made of concrete of different classes in the stretched and compressed parts of the cross section is performed. According to the task, namely the optimization of the geometric parameters of the location of concrete of different classes according to the height of the sections of bent reinforced concrete structures, the results of the calculation of the stress-strain state of reinforced concrete single-span beams with a rectangular cross-section of size b×h=100×150 mm were simulated and analyzed. The length of the beams was 1200 mm. The upper compressed part of the beams was modeled from C20/25 class concrete, and the lower stretched part - from C12/15 class concrete. The beam was reinforced with two reinforcing rods Ø12 mm of periodic profile class A400C in the stretched zone. Structural reinforcement of the beam frame was not taken into account during modeling. From the obtained studies, it can be seen that bi-concrete beams, in comparison with concrete beams, withstand more load. Therefore, the cross-section of the reinforced concrete beam decreases and its estimated cost decreases. The different ratio of stretched and compressed concrete to the height of the cross-section of bi-concrete beams has different effects on the overall load-bearing capacity of the beams. In the perspective of further developments in this direction, it is necessary to obtain optimal ratios of the concrete strength of the stretched and compressed zones at different ratios of their thickness.

Bi-concrete reinforced beams, bending, numerical study

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