Research On The Line-shape Measurement Of Bridge Based On Tri-axis Fiber Optic Gyro

Bridges are critical links of transportation networks.Bridge health monitoring and safe operation evaluation are getting more and more attention.Line-shape of bridge is an important factor to evaluate the bridge health status,and it can reflect the changes of internal force.The traditional line-shape measurement of the bridges were completed by the total station,level,global position system(GPS)and so on.However,these measurement methods can only obtain limited discrete points.Wuhan University of Technology has implemented a novel measurement technique based on single fiber optic gyro(FOG)for continuous line-shape of long span bridge.This measurement is continuous and high efficient with high precision.However,it can only apply to the straight-line structure bridges,and will cause large error for the curved bridge.In the thesis,we propose a continuous line-shape measurement based on the tri-axis FOG(TFOG),which can expand the measuring range to large-span curved bridge and retain the advantages of single-axis FOG.In the thesis,a novel measurement method of bridge based on TFOG is studied,the main work is as follows:(1)Principle and core devices of line-shape measurement based on TFOG are studied.Parameter update method(i.e.attitude,position and velocity)for coarse and fine initial alignment are conducted.(2)In order to decrease the zero bias error and random error in the line-shape measurement,the static Allan variance analysis is used to process the static output data of the FOG.The static random error models of the TFOG are built and the dynamic Allan variance analysis is applied in dynamic data process.To improve the measurement accuracy of line-shape measurement method of bridge,the Kalman filter is constructed to filter the noise of the output signal.The experimental results show that the filter can reduce the influence of noise,and increase the measurement accuracy.(3)Experiments are designed to demonstrate the performance of the TFOG system.Based on the results of the horizontal position measured by high precision GPS and the altitude measured by level,the TFOG system is used to detect the preset road surface in different measurement distance,path,road conditions and carrier platforms.When there are only two correction points,the maximum relative errors of 120 m,210 m and 300 m straight section are 2.96 cm,2.43 cm and 5.10 cm respectively.When the curve section are 210 m and 600 m,the altitude maximum errors are 3.8 cm and 25 cm respectively.The measurement will have higher accuracy when we are taking further efforts by optimizing algorithm,and can be conveniently used to measure bridge deformation for bridge health monitoring.(4)The factors which effect measurement accuracy are analyzed,such as the heading angle,the road surface roughness,and the auxiliary correction points.Additionally,the adoption of the soft tyre wheel which has a certain damping effect can also improve the measurement accuracy.