Experimental and theoretical research on the stressstain state of reinforced concrete beams strengthened with external bars

Today, the majority of long-maintained construction objects of the Ukrainian building complex require upgrading and reconstruction. Therefore, the choice of an effective and convenient strengthening method is an important scientific and engineering problem. The paper presents a new structure for strengthening reinforced concrete bending elements. The new regulating system includes external flexible steel bars and rigid levers. The specific feature of the work of this system is the unloading of the beam's compressed zone, compression of it bottom fiber and placement of a pliable support in the middle of beam span, which results in efficient redistribution of stresses in the beam, significant increase in its carrying capacity and reduction in deformability, in contrast to a traditional strutted system that increases the negative impact of external load. In addition, the system effectively works under asymmetrical loads. The authors propose a design scheme for reinforced concrete beams of rectangular cross-section, strengthened with this system with external bars. The article reveals a computation method based on the building codes in force, which takes into account the work of the external strengthening system. The computation method is realized due to the specially designed computer programs. The stress-strain state of the beam's cross-sections is determined considering the full ? σ-ε? diagram and specified discrete linear diagram of steel work. Besides this, the method of experimental research and testing of concrete beams, strengthened by the proposed system, and regular beams is presented in the paper. We also improved the power stand for testing such beams. During the testing, strain state of the beam's dangerous cross-sections and deformations of external bars were determined. The results of theoretical calculations of strengthened beams' carrying capacity were compared with experimental research. The discrepancy is within permissible limits, indicating the reliability of experimental and theoretical studies, while a significant increase in carrying capacity and reduction in the beam's deformability confirms the expediency of this proposed strengthening system. Along with this, strengthened beams showed a decrease in the residual deformation, which indicated their more elastic work under load.