Study on Stress Increment of Externally Strengthened Prestressed Box Beams

Abstract

With different original status including crack, controlled stretching stress and reinforcement ratio, five reinforced concrete box beams strengthened with external prestressed tendons were designed. The stress increment of external tendons was studied by indoor test and Finite Element Method analysis. The study shows that the less the controlled stretching stress is, the more rapidly the prestressed stress increment increases. There is no clear difference between the beam with original crack and without crack. In the test, the measured ultimate stress of external prestressed tendon agrees with the calculated result based on deflection method, and the stress in serviceability stage agees with the result based on structural mechanics method. In Finite Element model, the change of effective prestress, concrete strength, the area and depth of external tendons will result in a little change of stress in serviceability stage, but obvious change in ultimate status. the change of tendons lateral distance to the web results in litlle change of stress in the whole loading stage , no matter it is inside or outside the box at cross section.