The Study Of Ultrasonic Testing For Concrete-Filled Steel Tube

Ultrasonic testing technology (UTT) has been widely applied in the defects detection of Concrete-filled Steel Tube (CST), showing a great advantage of qualitative identification. Of the UTT, qualitative detection techniques most used include travel time method, frequency method, amplitude method, and comprehensive parametric method. Although these methods can be qualitatively described defects, both of the following drawbacks are almost impossible to avoid. One is the possible false and omitted judgments due to single parameter, and the second is the increasing workloads of additional equipments and higher-level staff accompanied by the multiple parameters. Besides, the post-data processing would be complicated, and interpretation of results are not intuitive.In the research of quantitative detection, ultrasonic geometry path is often employed to calculate the range of defects. The method appears quite accurately; however its feasibility is heavily constrained owning to the problem of selecting pivotal sensing positions. To address these problems aforementioned, a corresponding investigation was implemented, and the main content of this thesis was follows:(1) The ultrasonic velocity and strength of concrete of C50were recorded for various age of concrete, so that relationships of ultrasonic velocity versus strength and age of concrete were obtained simultaneously, which provide a useful guide for ultrasonic testing of CST in Dalian.(2)The ultrasound CT imaging technique was introduced in this paper, based on which the quantitative detection of I-type defect (the cavity, debris, and uncompacted areas existing in the core concrete) is investigated thoroughly. On the basis of MATLAB language, the SIRT algorithm and the shortest path ray-tracing algorithm have been realized, and accordingly the method proposed in the paper was verified by numerical simulation, as well as the physical experiment. It is found that ultrasound CT imaging technology is applicable to the quantitative detection for I-type defect in steel concrete, and imaging results are very sensitive to the size and location of defects.(3)For the â…¡-type defect (separation or poor adhesion between the steel tube and the concrete), the Chromatogram of Ultrasonic Travel Time Distribution (CUTTD) was proposed firstly to quantify the damage. Based on the ultrasonic wave travel time from the physical experiment, the CUTTD was achieved by the effective interpolation of MATLAB. The study showed that the method of CUTTD satisfies the requirements of quantitative detection by virtue of accuracy, visualization and high-efficiency. (4)In the bearing capacity test of CST within the predefined defects, the bearing capacity decreases badly as the defects become larger, while the II-type defect has a greater impact on the bearing capacity than the I-type.This study has achieved its desired purpose, seeking to employ the simplest method with minimal acoustic parameters to quantify internal defects of CST, so as to make the process of detection visualization and high-efficiency. However, the accuracy of ultrasonic CT imaging program needs to be improved further, and more attention should be paid on the algorithm of optimization and program acceleration.