Improved stack imaging of spectral amplitude based on the impact echo method for identification of defects in grout-filled lap connection
Abstract
In this paper, we designed defects considering different sizes, burial depths and arrangement modes in the grout-filled lap connection specimens to carry out impact echo test. Different signal processing methods, including Fast Fourier Transform (FFT), Wavelet Transform (WT), and improved Stack Imaging of spectral amplitude based on the Impact Echo (SIBIE), were used to analyze the data. The results show that the improved SIBIE method can efficiently increase the accuracy of multi-media interface defect imaging by filtering the original echo signal and smoothing the spectrum. The superposition of multiple sets of data can eliminate the adverse effects of abnormal samples.
Section snippets
Instruction
The grout-filled lap connection, as shown in Fig. 1, has become one of the important technologies for the construction of prefabricated concrete structures due to its excellent prefabricated component connection ability [1]. However, the incorrect operations in the actual grouting project and the unqualified fluidity of the grout easily lead to poor grout density, resulting in voids. In this case, the grouting material cannot provide effective radial restraint and adhesion, and steel bars
Experimental program
In order to study the defects of grout-filled lap joints, 16 kinds of working conditions were designed to carry out impact echo test before collecting the echo signals and analyzing the defect characteristics.
1 Frequency domain analysis
The corresponding spectrum diagram can be obtained by FFT transform of the time-history signal. The theoretical reflection frequency of the layered structure can be calculated by equation (1). Due to the small thickness of the pipes and the small diameter of the steel bars, the calculation results of the two are very close, so the influence can be ignored and simplified by equation (2).Where, β is the geometric coefficient of the section and the rectangular section β
1 Basic principle
SIBIE procedure is a post-processing technique for impact echo data, and it is also an imaging technique for the detected waveform in the frequency domain [25]. Firstly, the distance from the center of each unit to the impact point and the acquisition point is calculated respectively, and then the frequency value corresponding to the unit is calculated by the following equation (3) [26], [27]. As shown in Fig. 11, the cross-section of the specimen to be tested is divided into several square
Conclusions
For the sake of accurately detecting the quality of the grouting in Grout-filled lap connection of prefabricated concrete structures, impact-echo test was carried out towards multiple defect conditions in this research. In addition to the conventional FFT and WT methods, an improved SIBIE method is proposed and applied to the impact echo signal processing. The following conclusions can be drawn:
(1)
The impact echo method can identify the internal grouting defects of the metal bellows at the
CRediT authorship contribution statement
Fei Yao: Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing. Jinchao Chu: Formal analysis, Software, Visualization, Writing – original draft, Writing – review & editing. Xingqi Lu: Data curation, Formal analysis, Investigation, Software.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the Fundamental Research Funds for the Central University of China (Grant No. B200202086) and the National Natural Science Foundation of China (Grant No. 51408188)