Research On Strain Monitoring Of Distributed Optical Fiber Sensor In Super Large Bridge

In recent years,China’s transportation industry has become more and more developed,and the number of bridges has increased rapidly each year.Among them,the growth rate of the number of super large bridges is particularly prominent.The problem that follows is the safety monitoring of super large bridges.The traditional small and medium bridge monitoring The means can no longer meet the needs of current bridge structure monitoring.Therefore,it is of great significance to realize the health monitoring of these super large bridges.Distributed optical fiber monitoring technology can realize continuous monitoring in a wide range and long distance space.Compared with traditional The monitoring method has obvious advantages and can realize continuous and long-distance monitoring of super-large bridges.In this paper,in response to the problems encountered in the application of distributed optical fiber sensing technology to super-large bridge monitoring,the bridge frequency shift strain correlation is proposed.The bridge corrosion simulation experiment,the bridge stay cable force monitoring simulation experiment and the optical fiber monitoring simulation experiment of the bridge body affected by tidal surge provide theoretical basis.The main research contents are as follows:First,the basic principles of distributed optical fiber sensing technology are introduced,three distributed optical fiber sensing technologies are briefly described,the relationship between Brillouin dispersion radio frequency shift and strain and temperature is derived,and the Brillouin optical time domain reflection is discussed.The basic principle of the technology puts forward the relationship between frequency shift and strain of bridge.Secondly,according to the bridge concrete structure part,the stayed cable part and the bridge cap part,the bridge concrete corrosion monitoring model,the stay cable force monitoring model and the bridge cap monitoring model affected by tidal surge were made respectively.In the bridge concrete corrosion monitoring simulation experiment,combined with the accelerated corrosion test,with the Brillouin optical time domain reflection technology as the core,real-time monitoring of the bridge body deformation state affected by the corrosion products in the accelerated corrosion environment;In the force monitoring simulation experiment,the cable force simulation test of the stay cable optical fiber monitoring is carried out.In the experiment,the weight is added to make the model produce a larger amount of deformation,so as to observe the Brillouin fiber frequency shift;when the tidal surge affects the bridge In the simulation test of the impact monitoring of the platform,the impact of the deformation of the bridge body is monitored in real time by simulating the tidal surge of the seawater in the test.Finally,the test data analysis is carried out.The results show that although the bridge concrete corrosion monitoring simulation experiment has accelerated the test process through the accelerated corrosion test,the final analysis shows that the corrosion deformation variables in the natural environment are similar,and the Brillouin optical time domain reflectometry technology can work well.Monitor the corrosion of the bridge concrete structure with high accuracy;in the cable force monitoring simulation test,the cable force is obtained by monitoring the change in the frequency shift of the optical fiber.The monitoring accuracy is high.It is observed that the frequency shift of the Brillouin optical fiber and the tension curve are Linear relationship,draw the fitting curve of Brillouin fiber frequency shift-stay cable force,and propose the relationship between Brillouin fiber frequency shift-stay cable force;in the simulation test of the impact of tidal surge on the bridge platform,it is very good The deformation of the bridge body affected by tidal surging is monitored.The greater the flow velocity,the greater the deformation of the bridge body,the greater the frequency shift of the Brillouin fiber,and the higher the water surface,the more obvious the influence of the water pressure on the bridge body.The greater the pressure deformation generated.