Improvement And Applied Study On Embedded Fiber Fabry-Perot Stain Sensor

Civil infrastructures play a very important role in people's daily life, and health monitoring of them becomes a hot research point. As a new strain sensor, Fiber Optic Fabry-Perot (FF-P) strain sensor was gradually accepted in strain monitoring of these structures. However, when installing in practical concrete structures, a metal shell is necessary to protect bared FF-P interferometer from breaking. Affected by the shell, the measuring accuracy of the FF-P sensing probe (with a metal shell) is quite different from a bared one, so calibration is needed. In addition, the imperfect installing technique is another important reason which restricts the application of FF-P sensor heavily. Therefore, the applied research on embedded FF-P strain sensor has significant practical value. The main points of this thesis are as follows:(1) In the first part of the thesis, the domestic and oversea research status of FF-P sensors and its application to health monitoring of civil structures was briefly stated. The principle of FF-P sensors was also introduced, and research missions of this thesis were then put forward.(2) The embedded FF-P sensor and its calibrating system were introduced in detail. Lots of calibrating experiments on embedded sensors were carried out, and the error reasons of the calibrating system were analyzed. According to these experiments, structural defects of the existed embedded FF-P sensor (Type GYQ-Ⅲ-B) were pointed out. To address these problems, a new and reasonable shell was designed.(3) A model concrete pier was made and three improved FF-P sensors were embedded in it. After pouring, the pier had been monitored for about 3 months, and a lot of original strain data was collected. The monitoring experiment and data demonstrated the feasibility of the new protecting shell.(4) The research result was adopted in the health monitor project of Caiyuanba Yangtze River Bridge soon. It takes about one year to install 40 improved FF-P sensors in its piers (P17 and P18) successively, and many interesting data were obtained by these sensors. In that year, more than 10 sensors were damaged because its pigtail fiber was broken, and extra sensors were fixed to replace them. To protect the pigtail fiber, a new embedding method based on armored fiber cable was put forwarded.