Detection of deep and shallow defects in Concrete Filled Steel Tube Using Impact-Echo Method

Abstract

Abstract Concrete Filled Steel Tube (CFST) is widely used in construction due to its good bearing performance, low cost and excellent structural seismic performance. Quality problems such as voids and debonding are often encounters in the process of pouring CFST. They significantly reduce the bearing capacity and ductility of specimens, and adversely affect the restraining effect of concrete. Such internal hidden defects cannot be visually identified. However, Non-destructive Testing Technique (NDT) is required. This paper employed the Impact Echo (IE) method to determine the location of defects in various types of concrete structures. Since the IE method was developed in the 1980s and used to test concrete structures, there have been little researches on defect detection in CFST. Therefore, this paper studies the square CFST specimens with defects located at different depths which are tested using the IE method. The Fast Fourier Transform (FFT) was employed to detect the location of defects by analyzing waveform and frequency spectrum. In addition, the CFST finite element model under more working conditions has been established, including internal defects of different depths and widths. The analysis of frequency distribution provides more details about the depth and location of the defects. A time-frequency analysis using Wavelet Transform was introduced in this study to assess the reliability of the IE method. According to the models carried out in this work it is demonstrated that IE method has been able to detect defects in Concrete Filled Steel Tube.