Study On Non-contact Monitoring Technology For Bridge Dynamic Deflection Based On Optical Fiber Ultrasonic Sensor

Bridge deflection as an important parameter to most intuitively reflect the force conditions of bridge structure,to evaluate bridge health and to analysis bridge potential problems,the deflection monitoring becomes particularly important for bridge monitoring and health assessment.Due to the limitations of the existing deflection monitoring technologies and the challenge of long-term real-time online monitoring for bridge deflection,breaking through the limitations of the existing measurement methods and developing a new type of bridge deflection monitoring technology is very valuable both for academia and engineering application.This paper firstly analyzes the significance of bridge deflection monitoring and the existing monitoring technologies for bridge deflection,through detailed analysis of principles and its advantages and disadvantages of the existing monitoring technologies,the limitations and difficulties of bridge deflection monitoring are summarized.Based on this,optical fiber ultrasonic sensor system based on multimode interference is proposed to be used for non-contact monitoring for bridge dynamic deflection This paper makes a further study on the structural design and optimization of the optical fiber sensor,the principle of static displacement sensor system,designing and establishment of static displacement sensor system,the static displacement sensing experiments,the optimization of static displacement sensor system,the development of double balanced microwave dynamic phase module,the mechanism of dynamic displacement sensor system,designing and establishment of dynamic displacement sensor system,the dynamic displacement sensing experiments,signal filter processing and the simulation experiments of bridge deflection monitoring.The main research contents include:1.The paper analyzes comprehensively principles of the existing monitoring technologies for bridge deflection.Based on the analysis of application ranges and limitations of the existing monitoring technologies,the difficulties of bridge deflection monitoring are summarized.2.The paper studies comprehensively the generating mechanism and physical characteristics of ultrasonic,analyzes the principle of ultrasonic ranging technologies,and summarizes the application and existing problems of ultrasonic ranging technology.3.The SMS optical fiber sensor based on multimode interference and the mechanism of ultrasonic detection are studied.Based on finite element analysis of sensor diaphragm initial stress,the feasibility of improving response sensitivity of the optical fiber sensor through imposing initial stress on diaphragm is theoretically analysed.Based on this,the structure of C type optical fiber sensor whose diaphragm prestressed can be adjustable is firstly proposed and designed,and the optical fiber sensing system based on C type sensor is established.Based on ultrasonic detection experiments,it has been confirmed that response sensitivity and response intensity on 25 kHz ultrasonic of optical fiber sensor can be effectively increased by increasing initial stress on sensor diaphragm.4.An optical fiber ultrasonic static displacement sensor system is designed and established,and non-contact static displacement detection experiments are carried out,the results show that the largest error of single measurement is 0.1137 mm,maximum relative error is 5.685%,these prove that the sensing system can achieve high precision monitoring for static displacement.The optical fiber sensor system is researched to optimize by conducting temperature compensation.Environment temperature is monitored simultaneously to modify the ultrasonic velocity in the period of static displacement detection experiment,the results show that it has decreased the error of the sensing system,and its largest error of single measurement is 0.0908 mm,compared with the result of experiments without temperature correction,the measurement error after temperature correction was reduced by 1.145%.5.Phase reference based double balanced microwave dynamic phase module is developed,and it can be used for anlyzing real-time phase difference between two input signals,thus real-time demodulating and detecting for dynamic displacement can be realized.Based on this,an optical fiber ultrasonic dynamic displacement sensor system is firstly designed.By means of non-contact dynamic displacement detection experiments in the effect of impact loads and simple harmonic loads,the feasibility of applying the sensing system to detect dynamic displacement under various vibration forms is verified.Among them,the experiment results in the effect of impact loads show that the dynamic displacement resolution of the sensing system can reach 0.1 mm,its maximum measurement error is 0.15 mm;Based on the dynamic displacement detection experiments in the effect of simple harmonic loads,it has been comformed that the sensing system can realize the high precision non-contact detecting for dynamic displacement under a variety of vibration frequency.6.By studying the general regularity and characteristics of bridge deflection deformation after construction,the bridge deflection deformation in different stages are built under laboratory conditions to simulate the actual bridge deflection development,the results prove that the optical fiber ultrasonic sensor system based on multimode interference can realize the non-contact monitoring for static and dynamic deflection of bridge,these provide the reliable theory basis and technical support for the static and dynamic deflection monitoring in the actual bridge.