Research On Structural Health Monitoring Based On BOTDA Distributed Fiber-optic Sensor

Bridges, tunnels, dams, urban lifeline and other major civil engineering structuresoften exist in physical space in form of large network systems, and are made up of adiverse group of clusters of engineering structures. Structures have a strong correlationwith each other on the operation function, structure safety. Complex serviceenvironment, higher construction costs, random occurrence of damage, significanttime-varying damage effects and other features, makes major engineering structurehealth monitoring more and more attractive to researchers. Looking for distributedmonitoring sensor with high accuracy, high resolution and good stability to meet projectneeds, is the important way to improve the efficiency of structural healthmonitoring.Brillouin fiber sensor (Brillouin Optical Time Domain Analysis Techniques,referred to as BOTDA) has a natural advantage in monitor field, regarding as distributedstrain and temperature monitoring tool simultaneously.This paper develops its systematic study on distributed Brillouin fiber strain andtemperature sensing characteristics, influencing factors of monitoring signals, structuralcracks and fiber-optic sensor network monitoring and other issues. The main contentsinclude:First, we introduce the building and demodulation principle of Brillouin opticalfiber sensing test system, study the paste Brillouin fiber strain transfer efficiency withJ39glue, uniform changes signal value selecting method. We also discuss the mutualcoupling relationship between strain and temperature compensation.Secondly, through a large number of comparative tests, we summarize theinfluential factors for BOTDA monitoring signals, focusing on the spatial resolution,spatial sampling interval, and average number of sampling. Through geometric analysiswe also discusses the monitor method with BOTDA for cracks (including crack width,crack length, fracture trend).In addition, the influence of layout of fiber winding on themonitoring sensitivity is also studied in theory.Finally, Brillouin optical fiber is applied in model tests. The white tight fiber ispasted in compressive and tensile reinforcement of the simply-supported beam as wellas vertical surface of the RC-beam to verify that the fiber can effectively feel the tensionand compression strain of concrete beams in the complex environment and monitor therandom cracks through an optical fiber sensor network arranged in advance. In addition,FRP-wrapped Brillouin fiber and fiber grating strings are embedded in simulativeconcrete tunnel model which will be under explosion impact load, succeed to monitortunnel structure model residual strain and damage accumulation under differentdropping heights of heavy hammer.The tests proved that encapsulated with FRP Brillouin optical fiber is intelligent to be able to effectively monitor the deformation ofthe structure..Its flexible installation, the high survival rate makes it suitable for theconstruction of civil engineering environment and structural monitoring.