2. Key Lab of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin, Heilongjiang 150001, China
Overview: In this paper, two fiber reinforced polymer/plastic (FRP) encapsulated fiber Bragg grating (FBG) sensors are installed on the two sides of the angle steel beam, which are used to measure the displacement and direction of the diagonal steel beam, so as to realize the health inspection of the angle steel structure. Compared with the traditional angle sensors, fiber Bragg grating is chosen as the sensor in this paper for its excellent characteristics of small volume, light weight, anti-electromagnetic interference, good electrical insulation and stable performance in harsh environment. The FBG is protected by FRP encapsulation to ensure that the sensor can work steadily in the severe working environment of the angle steel. Besides, according to the shape of the angle steel beam, the sensor installation fixture is designed to facilitate changing the installation position of the sensor on the angle steel beam. The influence of the installation of the sensor and the sensor fixture on the angle steel beam is analyzed by the finite element method. It is found that the fixture installation has no effect on the strain distribution on the surface of the angle steel beam, Based on these, the transfer relationship between sensor strain and displacement of angle beam are carefully analyzed on the different sensor installation positions of the angle beam. The sensitivity and errors of sensor are analyzed at each side of position 0, 1, 2 and gets the result that the sensor can achieve maximum sensitivity and minimum errors when being installed at position 2 on any surfaces or at any installation positions on surface 3 or 4. Finally, sensor mounted on surface 3 is chosen for experimental verification. The experimental results are in agreement with the simulation results. At the same time, it can be seen that the displacement and direction of the diagonal steel beams can be measured by the sensor installed at the position 2 on the surface 3. In this paper, optimization design of the installation positions of the FRP fiber Bragg grating sensor on the different surfaces of the angle steel beam are discussed and the experimental verification is carried out the experimental. To achieve the health monitoring by using optical fiber sensors on the structures composed by angle steel, such as bridges, electric towers and cranes, and so on, a basic research is provided.