Encapsulation techniques for FBGs and smart monitoring for bridges with FBG sensors

Optical fiber sensors, especially fiber Bragg grating (FBG) sensors, have been the focus for structural health monitoring due to their distinguishing advantages: electro-magnetic resistance, small size, resistance to corrosion, multiplexing a large number of sensors along a single fiber, etc. In this paper, firstly, due to the fragility of bare FBG, 2 novel encapsulation techniques for bare FBGs strain sensors are put forward and their sensing properties are studied. Secondly, the techniques of FBG sensors installation have been explored, and 15 FBG strain and 3 FBG temperature sensors have been successfully installed in 2 prestressed box girders during the construction of Heilongjiang Hulan River Bridge. The box girder's deformation, under prestress tension and dead load during construction, has been monitored by the FBG sensors. The deformation and temperature of the bridge in service have been also monitored by the installed FBG sensors. The fact that the FBG sensors have withstood the ordeal for more than 2 years proves that their durability and stability satisfies the need of bridge's health monitoring. Finally, the bridges under construction, such as Heida Niutoushan Bridge and Songhua River Bridge, which have been installed FBG sensors, are also biefly introduced.