Research On Bridge Monitoring Based On Distributed Brillouin Optical Fiber Sensing

As an important transportation infrastructure,bridges have an irreplaceable and important role in industrial production and people’s lives.However,due to the continuous loading of vehicles,they are subject to strain,which makes the bridge prone to deformation,breakage,and even collapse,posing a serious threat to people’s lives and property safety.Therefore,effective monitoring of its structural health is of great significance.Distributed Brillouin optical fiber sensing can realize long-distance spatial continuous measurement.It has unparalleled advantages of traditional point sensing technology,and can be used for distributed temperature and strain measurement of large building structures.Aiming at the technical bottleneck problem that the measurement distance and spatial resolution cannot be considered in the current bridge structure health monitoring,this paper takes distributed Brillouin optical fiber sensing as the core and Tongling Yangtze River Bridge as the research object,and conducts distributed strain measurement research.The specific research contents are as follows:First,the basic theory of distributed Brillouin optical fiber sensing is introduced,the sensing mechanism of Brillouin scattering is explained,and the relationship between Brillouin frequency shift and strain or temperature is derived;Brillouin optical time is discussed The research direction of Brillouin optical time domain analysis(BOTDA)in high spatial resolution,ultra-long distance and ultra-fast measurement.Second,the tensile strain and temperature characteristics of bare fiber,tight-sleeved fiber and loose-sheathed fiber were tested respectively,and the strain coefficient and temperature coefficient of Brillouin frequency shift were obtained.Based on the experimental results,the strain and temperature characteristics of the optical fibers with different packaging structures are analyzed,and their durability,measurement range,and mechanical strength are compared to discuss their scope of application,which provides a theoretical basis for the selection of sensing optical fibers.Finally,the differential pulse pair Brillouin optical time domain analysis technology is applied to the structural health monitoring of long-span suspension bridges,and the Tongling Yangtze River Bridge is used as the research object to achieve a strain distribution of 1000 m on the whole bridge with a spatial resolution of 5 cm Type measurement.Using the proposed slotted adhesive cloth,we tried to lay out the continuous sensing optical fiber for the full bridge,and changed the strain situation of the bridge by designing a series of different vehicle load forms,and measured the full bridge’s strain under various load conditions strain distribution and analysis of the measurement results.In addition,the measurement error and temperature error compensation of the system are discussed.