Test Research Of Simply Supported Beams Strengthened By External Prestressing

The study was carried out to further investigate the simply supported reinforced concrete beam strengthened by external prestressing through experiment and theory analysis.In this paper, according to experimental data and analyzes the characteristic of strengthened beams, some curves was provided. Such as load-deflection, load-stress curves of tendon and reinforced bar, load-stain curves of concrete. based on experiment curves and phenomenon, this thesis put up the following contrast between beams strengthened by external prestressing and reinforced beams: Stress and strain in section, stress of external tendons and reinforced bars, the failure of the beam .The experimental research showed that the strengthening method of external prestressing was a positive strengthening method of which improved the utmost bearing capacity, strengthening effect was very perfect. Besides the use of higher effective prestressing force led to a higher ultimate strength. After strengthened , the structure gave satisfactory service load behavior: the ability to resist deformation clearly improved, the rigidity distinctly enhanced, ductility at ultimate was perfect.At the base of the testing research, this thesis study the strengthened beams structure behavior and theory, deduced the relation between stress increment of external tendon and deflection and comer, provided calculation formula. Also the thesis study bearing-load performance of strengthened beam, analyzed the stress in section and deflection. Moreover, according to the strain geometry relation and accounting for second-order effects utmost bearing capacity is made out.This thesis studied the strengthening mechanism of strengthened method by external prestressing. the strengthening mechanism is effective prestressing force and tendon stress increment had effective effect to bearing load. Theoretical calculation based on this concept was found to be in very good agreement with the experimental results. Moreover, this thesis analyzed the degree of prestress of strengthened beam, with a view to establishing a rational different degree of prestress under different conclusion.