Experimental study of quantitative detection of cavity defect in concrete filled steel tube structure using ultrasonic

摘要

According to the actuality that there was no mature technology to quantificationally detect the void in the concrete filled steel tube structure, the article based on a concrete filled steel tube arch bridge developed the ultrasonic detecting technology, which was feasible in technology and economy, through interior full-scale model test to quantificationally detect the void in concrete filled steel tube structure in lab. Two aspects of the research result had been obtained as follows: (1) According as the empty tube model test and the theory of ultrasonic propagation, the actual path that the ultrasonic propagated along the arc-length in the steel pipe wall had been proposed firstly, which the wave propagated into the steel pipe at the incident angle of a relative to the tangent of the ektexine of the steel pipe and traveled by multiple reflections between the inner and the ektexine of the steel pipe wall. The calculational formula of propagation time was t_s = l/2v_s cosα, and l was the arc-length of the steel pipe, v_s was the velocity of ultrasonic in steel pipe, a was the angle of incidence. On this basis, The calculational formula of the total transit time that the ultrasonic diffracted the single cavity defect and the calculational formula of the maximum thickness hmax about quantitative detecting of the single cavity defect had been proposed. (2) Four full-scale models of concrete filled steel tube had been built in lab, the diameter of tubes were 700mm and some controlled defect had been made in them. Quantitative detecting defect had been investigated in ten cross sections. The maximum absolute error was 1.5mm between the test value and the true value. The absolute error of four cross sections were over 1.0mm and remanent sections' were not more than 0.7mm, thereinto, five sections' were not more than 0.4mm.