Method for Testing the Tension of Vertical Prestressing Bars in Webs of Concrete Box Girder Bridges

Abstract

Vertical prestress is widely used in the webs of large-span concrete box girder bridges but has lost efficacy since it was first applied. To solve this widespread problem, a dynamic model for the exposed segment of the vertical prestress system is built to help detect effective tension retained in the bar. Results of laboratory experiments show that the flexural rigidity of the exposed segment in the anchorage zone increases as effective tension gets larger. Both approximate and exact solutions of the dynamic model are proposed to identify the flexural rigidity. On this basis, some field experiments have been conducted to fit the flexural rigidity-tension relationship curves, which can be used to identify the effective tension indirectly when the inherent frequency of the exposed segment is obtained. The aforementioned principle is easy to implement and can be used to find a practical quantitative testing method to detect the effective tension retained in vertical prestressing bars. Thus, it will be significant to ensuring construction quality and preventing the webs of concrete box girder bridges from cracking.