The Thin Rod Fiber Bragg Grating Vibration Sensor And Its Application In Cable Force Monitoring

Cable force is an important parameter for measuring the safety status of bridge structure.It is of great sense to prepare high-performance and high-stability vibration sensors for cable force monitoring.Due to the advantages of small size,good repeatability and corrosion resistance,strong anti-electromagnetic interference resistance,Fiber Bragg grating(FBG)vibration sensor overcomes the limitations of traditional vibration sensors and has become an important component for cable force monitoring.At present,the FBG sensor has many problems,such as complex structure,complicated installation,small contact range with the cable body or difficult to fully close contact with the cable due to shape design,which leads to poor follow-up of vibration deformation and unsatisfactory measurement accuracy when the load is small.Therefore,a thin-rod fiber grating vibration sensor is developed.Through theoretical analysis and indoor steel strand cable force monitoring test,it is proved that the sensor is feasible for cable force monitoring.Finally,the engineering applicability of the thin-rod fiber grating vibration sensor is verified.The main research contents are:(1)Design of a thin-rod fiber grating vibration sensor.The working principle of the sensor is introduced,that is,the vibration frequency of the structure can be obtained by measuring the strain change of the surface structure material.According to the key points of making sensors,the sensor is designed.Two kinds of elastic materials,steel strand center wire and carbon fiber reinforced polymer(CFRP)bars,with a length of 300 mm,are used to package the fiber bragg grating directly to make the thin-rod fiber bragg grating vibration sensors finally.(2)Experimental studies on the thin-rod fiber bragg grating vibration sensor.The OP-V50 fiber grating acceleration sensor is used to measure the cable force of the steel strand at the same time,which verifies the feasibility of the thin rod fiber grating vibration sensor for cable force measurement.On this basis,three groups of tests were carried out,according to the three main factors affecting the test accuracy of the sensor:the cross-sectional area,the elastic modulus and the wrapping method of the sensor.The experimental results show that the measurement accuracy decreases with the increase of the cross-sectional area of the sensor;compared with the use of carbon fiber reinforcement as the matrix material,the measurement accuracy can be improved by using the steel strand center wire to make a thin-rod fiber bragg grating vibration sensor;when the cable force is small,the effect of measuring the cable force of the steel strand is basically the same by using four hoops fixing sensors or pading both ends of the sensor and fixing the sensor with two hoops;when the cable tension is large,the measurement accuracy can be improved by pading both ends of the sensor and fixing the sensor with two hoops.(3)Engineering adaptability verification of thin-rod fiber bragg grating vibration sensor.The thin-rod fiber bragg grating vibration sensor is applied to Xiangsizhou Bridge,and the cable force of stay cables is monitored.The measurement accuracy is about 5 %,which is within a reasonable range.It indicates that the sensor can be used to measure the cable force in the actual bridge with high measurement accuracy,and it is an ideal device for long-term safety monitoring of bridge cable structure.