Based On Fiber Bragg Grating Strain Sensors Measuring Bolt

As one of an important component forms of strengthen structure, anchor rod was widely used in high slope works of road, railways, water conservancies, mines and other sites. The prestress anchor was lead a pressure on its own structure before undertake the outside stress. After the anchor rod have installed, the states of anchor rod is affected by the weather of geotechnical and the relaxation deformation of surrounding rock will change along with the time pass by. The relaxation deformation descends after anchor rod's stress was locked.In order to avoid the accident, the state of the anchor rod should be surveyed chronically. Traditional electric measuring ways were widely used for axial force. evaluate anchorage performance via mearsuring. But this kind of method is susceptible to electromagnetic interference. Which is limited the signal transmission distance shortly.In this paper, via fiber Bragg grating as the sensing element, The stress sensing characteristic of fiber Bragg grating is analyzed theoretically. Analysis and experimental research.In the experiment choosed the structure of spooked and tube stress structure as the strain sensor, and the anchor rod which yield strength is 335MPa, length is 490 mm, diameter is 25/16 mm, and sectional area is 290 mm2. Which was adopted to testing axial force of anchor head and anchor tendor.The results of theory and experiments are as follows:(1)At the anchor head, surveyed the whole force of the anchor rod by the Spoke-and-wheel structure. The stress of anchor caused the shear deformation of spokes, and the deformation arise the wavelength-shift of fiber Bragg grating, and in this way the mathematical sense model for the wavelength-shift of fiber Bragg grating and pressure is built.(2)At the anchor tendor, surveyed the axial force by the fiber Bragg grating strain sensor which is based on the structure of tube stress structure, and the sensor is welted onto the surface of anchor along the axial direction through its two pins. The deformation caused by the axial stress changed the distance between the two pins, and so arise the wavelength-shift of fiber Bragg grating. In this way, the mathematical sense model for the wavelength-shift of fiber Bragg grating and pull is built.(3)The stretch and press experiments results indicated that, the sensitivity of stretch is 0.7 pm/kN, the sensitivity of press of spoke structure fiber Bragg grating 1 is 74 pm/kN, fiber Bragg grating 2 is 151 pm/kN.