A PROCEDURE FOR THE CALCULATION OF THE STRESS-STRAIN STATE OF REINFORCED CONCRETE BEAMS WITH EXTERNAL STRENGTHENING

Abstract

The choice of an effective and convenient strengthening method is an important scientific and engineering problem. The paper presents a new structure for strengthening one-span reinforced concrete beams of rectangular cross-section. The new regulating system includes external flexible steel bars and rollers. The specific feature of the work of this system is the unloading of the beam’s compressed zone, 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 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 using specially designed computer programs. The stress-strain state of the beam’s cross-sections is determined considering the full «σ-ε» diagram and a specified discrete linear diagram of steel work. The study proposes a method of calculation of such strengthened beams by the example of strengthened beam БП-VI (without rigid levers). The technique takes into account the loss of tension because of friction under contact of external wire with rollers. The procedure considers the true concrete and steel diagrams and the deformation model of the work of the structure under load. For the БП-VI series of reinforced beams the calculated bending moment was 15.508 kNm, and the corresponding experimental bending moment was 15.523 kNm. For this series of beams the discrepancy was insignificant, which confirms the adequacy of the calculation model БП-VI. 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 the strengthening system proposed.