TO DETERMINE THE BEARING CAPACITY OF BI-CONCRETE REINFORCED BEAMS OF RECTANGULAR CROSS-SECTION

As is known, the tensile concrete is not considered in calculating the overall load-bearing capacity of reinforced concrete structures; it only increases their weight and, consequently, the manufacturing costs. Therefore, replacing the tensile concrete in such structures with a less expensive material, such as lower-grade concrete or concrete with porous aggregates, is a relevant issue. The purpose of this work is to develop recommendations for calculating the load-bearing capacity and determining the deformations of two-layer reinforced concrete flexural elements with higher-grade concrete in the compressed zone. To achieve this, two advanced methods are used, based on the classical model of the stress-strain state of a composite beam and the equilibrium of normal sections using the limit state method. When applying the classical model of the stress-strain state of a multilayer beam in bending to calculate bi-concrete reinforced beams with a rectangular cross-section and higher-grade concrete in the compressed zone, the cross-section of the beam is divided into three rectangular layers – higher-grade concrete in the compressed zone, lower-grade concrete in the tensile zone, and longitudinal working reinforcement in the tensile zone. For convenience, the coordinates of the extreme points of each layer should be determined relative to the lowest point of the cross-section. A comparison was made to assess the convergence of the theoretical, numerical, and experimental results obtained. The study involved five types of bi-concrete beams with rectangular cross-sections of 100×150 mm and a working length of 1200 mm, each with varying height ratios of different concrete classes. The upper compressed portion of the beams was made from class C20/25 concrete, while the lower tensioned portion utilized class C12/15 concrete. The working reinforcement consisted of two Ø12 A400C reinforcement bars.