Application of Measuring Concrete Compactness Using Supersonic in Bridge Bearing Capacity Appraisal

Abstract

Aiming at the phenomenon of small size and concrete incompactness in the densely packed reinforcement in the web plate, the top plate and between the prestressed reinforcement, the concrete compactness coefficient was put forward based on the strength measurement principle using ultrasonic-rebound method. On the basis of probability theory, two kinds of methods were proposed to calculate the compactness of the whole bridge. The compactness was calculated and the concrete distribution regularity was analyzed through the ultrasonic-rebound test of four pieces of post tensioned prestressed beams with variable section. In addition, the influence of concrete compactness on cracking load and ultimate capacity was analyzed through the bending static test. The formulas were given to calculate cracking load and ultimate capacity of prestressed beam with I type section taking compactness into consideration. The results show that size and distributed reinforcing bar can influence the concrete compactness which presents normal distribution approximately. The attribute method of compactness super limit and low limit which takes equalizing value as the center with 95% guaranteed rate can show concrete compactness better. It is more practical to consider concrete compactness in calculating the resisting capacity.