Research On Corrosion Performance And Evaluation Methods Of High-strength Steel Wire Based On Fiber Bragg Grating Sensors

Corrosion of stay cables,which are vital load-bearing components of cable-stayed bridges,is inevitable during their operational lifespan.To ensure the structural safety of the bridges,monitoring the corrosion of stay cables becomes crucial.Traditional corrosion monitoring devices,based on electrical components,fail to meet the long-term monitoring requirements due to poor durability,low measurement accuracy,and limited stability.In this study,a method is proposed to monitor the corrosion level of highstrength steel wires within stay cables by implanting Fiber Bragg Grating(FBG)corrosion sensors.The corrosion degree of the high-strength steel wires is reflected by the wavelength shift of the FBG corrosion sensors.This method offers real-time monitoring,durability,and high accuracy.With the application background of corrosion monitoring of galvanized highstrength steel wires within parallel wire stay cables of cable-stayed bridges,the research employs theoretical derivation,numerical simulation,experimental study,and statistical analysis.The main content and conclusions of the research are as follows:(1)Two types of FBG corrosion sensors for monitoring the corrosion of internal steel wires within stay cables are designed.The theoretical formulas for calculating the mass corrosion rate of steel wires using the wavelength shift of the sensors are derived based on the assumption of uniform corrosion.Through parameter analysis and numerical simulation,reasonable design parameters for the sensors are determined.The coefficients of the theoretical formulas of the FBG corrosion sensors are fitted based on accelerated corrosion test results.The study indicates that the maximum mass corrosion rate detectable by the wound-type FBG corrosion sensor is 3.55%,while for the tension-type FBG corrosion sensor,it is 5.47%.Both types of FBG sensors exhibit a highly linear relationship between wavelength shift and mass corrosion rate.The wavelength shift trends of both sensors can to some extent reflect the corrosion condition of high-strength steel wires.(2)Three-dimensional laser scanning technology is employed to reconstruct the corroded high-strength steel wires.Combined with digital image technology,automatic measurements of geometric parameters such as residual cross-sectional area and pit dimensions are achieved.Tensile tests are conducted to determine the mechanical characteristic parameters of the steel wires,including nominal ultimate strength,nominal yield strength,elastic modulus,and elongation at break.The relationship between geometric parameters,mechanical characteristic parameters of corroded high-strength steel wires,and the corrosion degree and grading is established.Additionally,the range between wavelength shift of FBG corrosion sensors and the corrosion grading of highstrength steel wires is determined.The study reveals that with an increase in corrosion degree,the non-uniformity of residual cross-sectional area along the axial direction,maximum corrosion depth,major axis length of pits,and minor axis length of pits show an increasing trend,while the minimum cross-sectional area decreases.The lengths of major and minor axes of the pits both follow a logarithmic normal distribution.Nominal ultimate strength,nominal yield strength,and elongation at break exhibit a decreasing trend,while the elastic modulus remains largely unchanged.(3)FBG corrosion sensors are embedded during the production process of replacing stay cables in a cable-stayed bridge.After more than 100 days of monitoring,the sensors have operated well,laying a solid foundation for the subsequent application of FBG corrosion sensors.