# Study on Impact-Echo Response of Concrete Column near the Edge
###### Abstract  
The impact-echo method is a superior method for detecting the health of concrete structures, but it has the disadvantage of significant errors when identifying structural boundaries. In order to overcome this limitation, this paper proposes a calculation method using a cross-sectional vibration mode in combination with the impact-echo method to detect concrete columns. The variation of the predominant frequency in the mid-column region and the critical boundary is studied. The influence of the edge on the detection results is analyzed. The differences in eigenvalues under different cross-section vibration modes are revealed. A quantitative method for evaluating concrete health using the impact-echo method is further established. Through field tests and finite element simulation calculations, it was verified that the eigenvalues in the fixed mode are very consistent with the predominant frequency measured near the edge region. This makes up for the defect of inaccurate measurements when the impact-echo method is used to detect the edge area of concrete members. The impact-echo method can be better used for the non-destructive testing of concrete members.  
impact-echo; finite element simulation; dominant frequency; column edge Article Study on Impact-Echo Response of Concrete Column near the Edge  
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causes various durability problems by reducing the stiffness of concrete. In addition, they can cause certain defects or delaminations in concrete members. These factors affect the accuracy of the impact-echo method. Therefore, when designing the test, it is necessary to supervise the site to ensure that the test components meet the required standards during the pouring process and eliminate the possibility of internal defects [10]. [PERSON] analyzed a series of high-order vibration modes of thin-walled beams. Analyzing high-order vibration modes in these structures requires more accurate and precise methods. The overall vibration modes related to the deformation of rigid sections, such as bending and torsion, can be detected through classical and shear refinement theories [11; 12]. [PERSON], proposed that in practice, vibration sensors (such as displacement sensors, accelerometers, and microphones) are located near the tapping point to measure the dynamic response of the object. The measured transient time signal reveals the maximum (peaks) of certain frequencies dominated by non-propagating waves (or resonance modes) via Fourier transform (amplitude spectrum). The interpretation of non-propagating waves is an important process in IE data analysis. The fundamental thickness stretch mode normally dominates the spectral response of a plate if there are no near-surface defects, such as cracking, debonding, and honeycombs, in the concrete [13]. In the process of test and simulation detection, the predominant frequency detected in the middle of the column is the eigenvalue of the fundamental thickness stretch mode of the column.  
When the impact-echo method is used to detect the concrete columns, the predominant frequency within a specific range from the edge has a low-frequency offset. In this paper, the two-dimensional cross-section of the concrete column is simulated using the finite element method to determine whether the predominant frequency under the influence of boundary conditions was related to the eigenvalue change of the cross-section vibration mode [14; 15; 16; 17; 18; 19]. By analyzing the signals collected at the boundary of the concrete column, it was found that the decrease in the dominant frequency was related to the torsional deformation of the column. Currently, the sensor does not identify the thickness frequency of the concrete column but the eigenvalue under the fixed mode.