Study On Methodlogy For Damage Identification Of Anchoring Steel Strand Based On Ultrasonic Guided Wave

Steel strand damage of anchorage zone has been the important factor affecting the safety of the cable-stayed bridge structure,using the NDT technology to identify damage is the key to maintaining bridge for normal use.Being a new NDT technology,ultrasonic guided wave has advantages of a long detection distance,high efficiency and testing speed.This article focuses on the corrosion,broken wires and other typical damage of steel strand in anchorage zone,with piezoelectric ultrasonic guided wave,through theory,simulation,algorithm and test research,to extract the time-frequency characteristics of damage echo as the indicators of detection.It has a great value of steel strand damage detection.The main contributions are:1)At first,the theory of ultrasonic guided wave testing and the acoustoelastic effect of strand structure were introduced as the basic.Dispersion characteristics of guided wave in straight and helical rod structure were theoretically analyzed.From the propagation characteristics of ultrasonic guided wave in strand structure,the low longitudinal L(0,1)mode guided wave was determined to be suitable for testing.2)Secondly,simulation analysis of ultrasonic guided wave testing on steel strand was carried out by the finite element software.The typical damage,helical structure and anchoring entity models were established by ANSYS.Six different excite-receive patterns and different incentive parameters are simulated to study the influence on testing effect.The time-frequency analysis methods were used to extract characteristics of guided wave signal,obtained from different damage types and sizes.The influence of helical structure,contact effect and anchoraging entities on ultrasonic guided wave testing effect were also studied in this paper.3)Based on wavelet transform theory and the characters of testing signal energy,a judgment index,called wavelet packet energy rate,was put forward to judge the steel strand structure with damage or not.To improve the traditional algorithm,a double-sensor damage identification algorithm,combining the cross-correlation analysis and the complex wavelet transform,was designed.With this algorithm,the positioning and quantitative analysis of typical steel strand damages in anchorage zone could be realized.4)Finally,on the basis of theoretical research and numerical simulation,the experiment platform of ultrasonic guided wave testing was established.Tension test and contact test were designed,to research the influence of structure stress and contact effect on ultrasonic guided wave testing.By damage test,the judging index was determined,the double-sensors location algorithm was proved,and the quantitative curves of typical damage size was obtained.Through the above research,the ultrasonic guided wave testing effect of anchoring steel strand in cable-stayed bridge was verified.The research of piezoelectric ultrasonic guided wave testing laid a certain foundation for the field of steel strand test application.