| Due to the influence of underground mined-out areas in coal mines,buildings around the mining area are prone to disasters such as uneven settlement and cracks.Therefore,it is of great significance to monitor the long-term structural health of buildings around the mining area.Fiber Bragg grating sensors are widely used in structural health monitoring because of their high sensitivity and strong anti-electromagnetic interference ability.In this paper,combined with the needs of monitoring the uneven settlement of buildings around the mining area,a double fiber Bragg grating static level is developed to monitor the uneven settlement of structures.The specific work accomplished is as follows:(1)This paper summarizes the research status of fiber Bragg grating sensing field and structural settlement monitoring technology at home and abroad,analyzes the feasibility of using fiber Bragg grating sensor for uneven settlement monitoring,and puts forward the design method of static level based on fiber Bragg grating according to the current engineering needs.(2)Based on fiber Bragg grating sensing theory,connector principle and equal strength beam theory,a fiber Bragg grating static level based on equal strength beam is developed.Considering the deformation of the beam with equal strength,the sensing principle of the double fiber Bragg grating static level is derived,and the linear functional relationship between the sum of the two fiber Bragg grating wavelength changes and the settlement changes is obtained.The double fiber Bragg grating static level can eliminate the errors caused by temperature changes and liquid surface height changes by itself.(3)The structure of double fiber Bragg grating static level is designed.The sensor structure includes: cylindrical container,connecting rod,cylindrical float,equal strength cantilever beam,fiber Bragg grating and bottom support.The sensor has the advantages of convenient disassembly and reassembly,preventing liquid leakage,strong anti-electromagnetic interference ability and being able to transmit data remotely.The calibration test of double fiber Bragg grating static level is carried out,and its sensitivity and static characteristic indexes are calculated according to the calibration test results.(4)The high precision fiber Bragg grating static level based on spring structure is designed.The sensing principle of the high-precision double fiber Bragg grating static level is derived,and the linear functional relationship between the sum of the wavelength changes of the two fiber Bragg gratings and the settlement changes is obtained.The high-precision double fiber Bragg grating static level can eliminate the errors caused by temperature changes and liquid surface height changes by itself.(5)Design the structure of the high-precision double fiber Bragg grating static level.The components include: cylindrical container,connecting rod,cylindrical float,spring,pulley,PE line,fiber Bragg grating and bottom support.The calibration test of high precision double fiber Bragg grating static level is carried out,and its sensitivity is calculated from the calibration results and its static characteristics are analyzed.High-precision double fiber Bragg grating static level keeps the advantages of double fiber Bragg grating static level and significantly improves the accuracy.(6)The double fiber Bragg grating static level is applied to the field monitoring of a building to monitor the uneven settlement between two pillars,and the clamping fiber Bragg grating strain sensor and fiber Bragg grating temperature sensor are used to monitor the changes of strain and temperature,so as to comprehensively evaluate the building. |
