Application of differential fiber Bragg grating displacement cell in bridge crack monitoring

Abstract

During the construction and service period of concrete bridges, the cracks often influence the quality of the project even the safety of the structure. An effective and long-term crack monitoring of concrete bridges with the appropriate choice of displacement sensors is imperative under the situation. The differential fiber bragg grating displacement cell is based on the composite structure which consisted of pulling spring and cantilever. It has realized differential measure of normal FBG displacement sensor and has solved the serious problem of temperature disturbance. The differential fiber bragg grating displacement cell has the advantages of high accuracy, anti-interference, long distance transmitting and good durability etc. In this paper, the differential fiber bragg grating displacement cells were applied to monitor the cracks of web slabs during the tension process of external prestressed tendons when the continuous prestressed concrete box girder bridges and continuous concrete rigid frame bridges were maintained and reinforced. A group of typical cracks of web slabs was selected respectively in the continuous prestressed concrete box girder bridge and the continuous concrete rigid frame bridge. And a group of three sensors were installed across the three cracks. The external prestressed tendons had been tensioned by four grades. Then the widths of these cracks were recorded in accordance with the four tension grades of the external prestressed tendons: before tension, 10% tension, 80% tension, 100% tension. The results of the differential FBG displacement cells used during the process of tension of external prestressed tendons show that the cracks monitoring data are accurate and in accordance with the cracks changing rule.