Research On The Impact-Echo Response Of Concrete Members Near Fixed Boundaries

The impact-echo method has been widely used in the non-destructive testing of concrete structures.It is based on the stress wave theory and judges the internal conditions of the structure by analyzing the echo signals received by the sensor.When the research group used the impact-echo method to detect defects in concrete structures,it was found that when the excitation ball and the sensor are near the fixed boundary of the concrete member,the high-frequency offset phenomenon occurs when the excellent frequency value collected by the sensor is relatively far away from the boundary area.In order to explore this specific influence,this paper based on the impact-echo method and stress wave theory,using numerical simulation analysis and field test research methods to analyze the echo response of concrete members near a fixed boundary,the main work of the paper is as follows :1.Summarize and analyze the propagation characteristics of stress waves in continuous elastic media,and use ABAQUS finite element software to establish finite element models of concrete members with plate thicknesses of 120 mm,160mm,200 mm,240mm,and 280 mm,respectively.Through analysis of simulation results,when the component model is loaded at different distances from the fixed boundary,the stress wave will generate an echo signal with a stable frequency;for concrete members with different plate thicknesses,certain distances near the fixed boundary must be high frequency shifts occur in the area.2.By analyzing the amplitude corresponding to the excellent frequency value of the simulation results,the analytical amplitude corresponding to the low frequency gradually decreases as the distance between the signal acquisition point and the excitation point increases,and the analytical amplitude corresponding to the high frequency increases with the signal acquisition point distance The fixed boundary distance increases and gradually decreases;by analyzing the change of the excellent frequency value,the high-frequency offset area of concrete members with different slab thicknesses is determined.With the increase of the thickness of the concrete member,The influence coefficient of the fixed boundary on the excellent frequency value shows a decreasing trend.3.Simulate under the condition of containing steel bars,when the spacing between the steel bars is kept constant,the change in the diameter of the steel bars and the position of the steel bars will not change much compared to those without the steel bars.Therefore,the simulation and the effect of steel bars can be ignored during the actual measurement;through the analysis of the numerical simulation results of the five kinds of plate thickness concrete members,the shape influence coefficient of the impact-echo calculation formula is revised.4.The field test of 160 mm,200mm and 240 mm concrete wall panels was carried out using an impact-echo instrument.The test results show that for 160 mm and 200 mm thick concrete wall panels,the high frequency deviation phenomenon occurs within 5cm from the fixed boundary for 240 mm thick concrete wall panels,high frequency shift occurs within 6cm.Comparing the test results with the simulation results,the excellent frequencies of the two are relatively close,and the area of the measured frequency deviation is consistent with the results of the numerical simulation.Figure [40] table [28] reference [55]...