Research On The Key Technology And Application Of Bridge Structure Curve Detection Based On Fiber Optic Inertial Sensing

Bridges are critical links within transportation networks.Bridge performance and deterioration have been of great concern to owners and maintenance engineers for many years.Therefore,more and more novel designs and complicated structural components for long-span and modern bridges structures have been employed.The requirements for Structural Health Monitoring system have been highly improved.Several different types of transducers can be used to measure the deflection,including netsuke,dial indicator,level gauge,electronic total station,Global Positioning System(GPS),and photogrammetric techniques.However,most of the traditional methods(netsuke,dial indicator,level gauge,electronic total station,GPS)require point-by-point personnel handling or the access to measurement location on bridges.As a result,the traffic of the bridge will be interrupted normally for the setup of these transducers.In addition,the installation of these transducers is time-consuming.It is impossible to perform efficient measurements for a huge amount of bridges.A new method based on fiber optic inertial sensor for bridge structural curve deflection measuring was proposed in 2011 by National Engineering Laboratory for Fiber Optic Sensing Technology,Wuhan University of Technology.The feasibility of this method has been proved in theory and practice.A series of improvements are required to enhance the reliability and absolute accuracy of the system for engineering applications.This thesis will focus on a series of methods to put this technology forward to the field applications.The main works of this thesis will be listed as following:Firstly,a new algorithm is discussed theoretically to improve the accuracy of the FOG-based deflection measuring method.Based on the analysis of the basic principle of the fiber optic gyroscope used in line detection,the paper discusses the influence of the vehicle length induced error and proposes a new algorithm based on the secant line to reduce error.A secant line between the front and back wheels of the vehicle is built for the new algorithm to replace the previous approximation in which the vehicle is regarded as a point.The deviation improvements of the new algorithm are discussed thoroughly.The algorithm is able to measure the accurate trajectory,especially for the curve with a curvature comparable with the vehicle length.The zero bias error and random divergence error of the fiber optic gyro used in bridge structure detection are suppressed and reduced.In this paper,two calibration method,the start/end-point and fixed-point calibration,are used to reduce the errors of gyro error effects on measurement.The experimental results show that the above methods can correct effectively the inherent errors during the measuring process,and improve the absolute accuracy of the final results.Data manipulation and processing methods are used to overcome the influence of the external vibration interference caused by roughness and bumps on the road pavement to the linear detection system.In this paper,a wavelet algorithm is designed for de-noising of FOG data and to pick up the singularities.At the same time,the pseudo random signal is used to reconstruct the singular data segment,so as to ensure the authenticity,continuity and integrity of the curve measuring.This paper discusses the reliability of the system by investigating the measurement on tiny deformation and the performance with the vertical vibration by using a scale model of long-span bridge.The system is used to detect the static loading experiment of bridge model step by step,and compared with the test data of dial indicator.The experimental results show that the system has good repeatability,with a scale of millimeter.It can accurately locate the maximum deflection in the span and the angular velocity of the insensitive vertical direction.Several examples in field have been presented for both the new bridges and existing bridges.Generally,the system can provide the whole continuous curve of existing or new long-span bridges.On one side,the data will contribute to the disease diagnosis and health monitoring of existing bridge,with the capability to locate accurately the maximum deflection.On the other side,the system is applied to measure the geometric alignment of the new bridge under various load test.The results show that the measurement accuracy of the system can reach centimeter level.For the existing bridges,the location of the maximum deflection will be diagnosed.For new bridge,the comparing between the deformation of the main beam before and after load test can provide the essential information for the health status evaluation of bridges.