CN111664818A - Impact echo method for detecting concrete thickness - Google Patents
Impact echo method for detecting concrete thickness Download PDFInfo
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- CN111664818A CN111664818A CN201910172134.4A CN201910172134A CN111664818A CN 111664818 A CN111664818 A CN 111664818A CN 201910172134 A CN201910172134 A CN 201910172134A CN 111664818 A CN111664818 A CN 111664818A
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
- G01B17/02—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring thickness
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Abstract
The invention discloses an impact echo method for detecting the thickness of concrete, which applies mechanical impact on the surface of the concrete to be detected to generate instantaneous stress waves, and utilizes longitudinal waves in the stress waves to carry out nondestructive detection on the concrete; stress waves generated by mechanical impact are transmitted into a concrete structure and are reflected, transmitted or diffracted when encountering an interface with discontinuous medium wave impedance; when the reflected echo reaches the surface of the structure, the reflected echo can be reflected into the structure again, so that the repeated reciprocating reflection can excite the local transient resonance of the structure, and the waveform has periodic characteristics; the frequency spectrum of the signal shows a frequency peak value corresponding to the thickness of the structure or the depth of the defect, and the thickness and the internal quality condition of the tested concrete structure can be identified by performing spectrum analysis on the echo signal obtained by testing. The invention detects the thickness of the concrete by the impact echo method, compares the influence of different impact sources on the impact echo signal, and improves the detection efficiency of the impact echo method.
Description
Technical Field
The invention belongs to the technical field of mechanical detection, relates to detection of structure thickness, and particularly relates to an impact echo method for detecting concrete thickness.
Background
With the continuous development of science and technology, various detection methods are emerging continuously. The impulse echo method is a nondestructive testing technology based on stress waves developed in the middle of the 80's of the 20 th century. As an emerging nondestructive testing technology, the method can be used for testing the thickness of a single-layer structure with only a single testing surface. Compared with the traditional ultrasonic device, the device has the problem of insufficient energy when used for detecting the thickness of concrete.
Researchers at home and abroad are always studying to detect the structure thickness based on the impact echo method. Medin et al studied impulse echo method with mutual power density improvement; lin et al apply EMD decomposition to the signal analysis of the impulse echo method, improving the interpretation of the signal; wang et al use the impulse echo method for detecting the thickness of a refractory wall of a high temperature furnace, but the corresponding thickness frequency cannot be effectively obtained in the frequency spectrum, so that the calculation becomes difficult; on the basis of analyzing the current blast furnace lining detection technology, HONG, LEE and the like introduce the basic principle and the test characteristics of an impact echo method, and the method is applied to estimate the thickness of a concrete structure by a blast furnace lining method and an ultrasonic pulse velocity method, and the effects of the method and the ultrasonic pulse velocity method are compared, so that the effect of the impact echo method is verified to be better. As is known from the relevant documents of the impulse echo method, the impulse source has a significant influence on the quality of the echo signal, and the detection efficiency of the impulse echo method in the related art is not high.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides the impact echo method for detecting the thickness of the concrete.
Therefore, the invention adopts the following technical scheme:
an impact echo method for detecting the thickness of concrete features that the mechanical impact is applied to the surface of concrete to generate instantaneous stress waves, and the longitudinal waves in the stress waves are used to perform nondestructive test on the concrete.
Preferably, the stress wave generated by the mechanical impact propagates into the concrete structure and undergoes reflection transmission or diffraction when encountering interfaces of discontinuity of medium wave impedance including the structure bottom surface boundary or internal defect; when the reflected echo reaches the surface of the structure, the reflected echo can be reflected into the structure again, so that the repeated reciprocating reflection can excite the local transient resonance of the structure, and the waveform has periodic characteristics; the frequency spectrum of the signal shows a frequency peak value corresponding to the thickness of the structure or the depth of the defect, and the thickness and the internal quality condition of the tested concrete structure can be identified by performing spectrum analysis on the echo signal obtained by testing.
Preferably, these reflections constitute a time curve, the duration of which is only a few milliseconds; digitizing the recorded time signal, and converting the time domain into the frequency domain through Fourier transform; the dominant frequency, which is formed as a result of multiple reflections of the stress wave inside the structure, appears as a peak in the frequency spectrum.
Preferably, the mechanical impact is performed with a small steel ball strike, and the input pulse function is approximated as a half-sine curve, the width and corresponding contact time of which depends on the size of the impact source used.
Preferably, for steel balls acting on concrete, the contact time with the structure surface is expressed as a linear function of the diameter of the steel ball, and the expression is: t is tc0.0043D, wherein D is the diameter of the steel ball and the unit is m; t is tcIs the contact time of the steel ball with the surface of the structure, and is expressed in s.
Preferably, the maximum frequency of the impact source is defined as: f. ofmax＝1.25/tcWherein t iscThe contact time of the steel ball with the surface of the structure.
Preferably, the thickness or defect depth of the concrete structure is solved by the following formula:
wherein: t is the thickness of the concrete, and the unit is mm; v. ofcIn m/s, is the propagation velocity of longitudinal waves in the concrete structure, f is the frequency of the defect depth or the thickness of the concrete structure, corresponding to the peak frequency in the spectrogram, in Hz, and β is the structure shape factor.
Preferably, for concrete slabs, wall structures, β is taken to be 0.96; for concrete square beam, column structures, β is 0.87.
Compared with the prior art, the invention has the beneficial effects that:
(1) the impact echo method is used for detecting the thickness of the concrete, the influence of different impact sources on an impact echo signal is compared, and the detection efficiency of the impact echo method is improved.
(2) Simple calculation, convenient use and better detection effect.
(3) The applicability is wide, and the method can be applied to detection of other structures.
Drawings
Fig. 1 is a schematic diagram of an impact echo method for detecting concrete thickness according to the present invention.
Fig. 2 is a time domain diagram of an echo signal provided by an embodiment of the invention.
Fig. 3 is a signal spectrum diagram provided by an embodiment of the invention.
FIG. 4 is a graph of the echo signal spectrum of a 5mm impact source striking a 100mm concrete slab provided by an embodiment of the present invention.
FIG. 5 is a graph of the echo signal spectrum of an 11mm impact source striking a 100mm concrete slab provided by an embodiment of the present invention.
FIG. 6 is a graph of the echo signal spectrum of a 5mm impact source striking a 200mm concrete slab in accordance with an embodiment of the present invention.
FIG. 7 is a graph of the echo signal spectrum of a 7mm impact source striking a 200mm concrete slab in accordance with an embodiment of the present invention.
FIG. 8 is a graph of the echo signal spectrum of an 11mm impact source striking a 200mm concrete slab in accordance with an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and specific embodiments, which are provided for illustration only and are not to be construed as limiting the invention.
The invention discloses an impact echo method for detecting the thickness of concrete, which applies mechanical impact on the surface of the concrete to be detected to generate instantaneous stress waves and utilizes longitudinal waves in the stress waves to carry out nondestructive detection on the concrete.
Stress waves generated by mechanical impact are transmitted into the concrete structure and are reflected, transmitted or diffracted when encountering the interface with discontinuous medium wave impedance, including the bottom surface boundary or the internal defect of the structure; when the reflected echo reaches the surface of the structure, the reflected echo can be reflected into the structure again, so that the repeated reciprocating reflection can excite the local transient resonance of the structure, and the waveform has periodic characteristics; the frequency spectrum of the signal shows a frequency peak value corresponding to the thickness of the structure or the depth of the defect, and the thickness and the internal quality condition of the tested concrete structure can be identified by performing spectrum analysis on the echo signal obtained by testing.
These reflections constitute a time curve, only a few milliseconds in duration; digitizing the recorded time signal, and converting the time domain into the frequency domain through Fourier transform; the dominant frequency, which is formed as a result of multiple reflections of the stress wave inside the structure, appears as a peak in the frequency spectrum.
The mechanical impact is performed by using a small steel ball, the input pulse function is approximate to a half-sine curve, and the width and the corresponding contact time of the input pulse function depend on the size of an impact source used.
For steel balls acting on concrete, the contact time with the structure surface is expressed as a linear function of the diameter of the steel ball, and the expression is as follows:
tc＝0.0043D (1)
wherein D is the diameter of the steel ball and the unit is m; t is tcIs the contact time of the steel ball with the surface of the structure, and is expressed in s.
The maximum frequency of the impact source is defined as:
fmax＝1.25/tc(2)
wherein t iscThe contact time of the steel ball with the surface of the structure.
The thickness or the defect depth of the concrete structure is solved by adopting the following formula:
wherein: t being concreteThickness in mm; v. ofcIn m/s, is the propagation velocity of longitudinal waves in the concrete structure, f is the frequency of the defect depth or the thickness of the concrete structure, corresponding to the peak frequency in the spectrogram, in Hz, and β is the structure shape factor.
For concrete slabs and wall structures, beta is 0.96; for concrete square beam, column structures, β is 0.87.
The principle of an impact echo method for detecting the thickness of concrete is shown in FIG. 1, wherein t1、t2Respectively corresponding to the time of occurrence of the peak, f1、f2Respectively corresponding to the peak frequencies.
Examples
The problem of measuring concrete thickness using ABAQUS software for analysis and simulation of impact echo in terms of geometric dimensions (1000 × 1000 × T) mm3Two concrete geometric models were created, where T is its thickness, set at 100mm and 200mm, respectively. The concrete parameters were set as in table 1.
TABLE 1 concrete model parameters
From the above parameters, the velocity of the longitudinal wave can be obtained by the calculation formula of the longitudinal wave, and the value thereof is 4206 m/s. The theoretical thickness frequencies of the two thicknesses can be calculated by formula 3 to be 20199Hz and 10094Hz respectively.
As can be seen from the formula 1, the contact time of the steel balls with different sizes and the concrete is different, and the frequency components of the excitation are also different. To investigate the impact of the impact source on impact echo detection, here half cycle sinusoidal loads for different contact times were set, simulating different sizes of pellets striking the concrete slab. A total of three impact sources with different contact times were set, with the maximum frequency and centroid frequency of the excitation, as shown in table 2.
TABLE 2 impact sources' relevant parameters
And carrying out time sequencing on signals collected by a sensor arranged near the surface of the structure to obtain a time domain diagram of the impact echo signal. And carrying out Fourier transform on the time domain signal to obtain a spectrogram of the impact echo signal. The peak frequency in the spectrogram is the frequency f in equation 3. FIG. 2 is a time domain plot of the shock echo signal obtained by striking a 100mm thick concrete slab with a steel ball 7mm in diameter; fig. 3 shows a spectrum diagram of the signal. As can be seen from fig. 3, the peak frequency of the spectrum is 19840Hz, which corresponds to the thickness frequency of the concrete. The thickness of the concrete slab obtained by substituting into equation 3 was calculated to be 101.75mm, and compared with the actual thickness of 100mm, the error of the detection was 1.75%.
Three impact sources of different sizes are provided, which act on two concrete slabs of different thicknesses. Fig. 4-5 are frequency spectra of signals obtained after steel balls with diameters of 5mm and 11mm strike a 100mm concrete slab, respectively.
From the signal frequency spectra shown in fig. 4-5, the peak frequency is 35710Hz, and the thickness of the concrete slab can be calculated to be 56.53mm by substituting the peak frequency into equation 3. The error of detection is 43.46% compared to the real thickness of 100 mm.
Signal spectra were obtained by tapping a 200mm concrete slab with 5mm, 7mm and 11mm steel balls as shown in figures 6-8, respectively.
From the signal frequency spectrums shown in fig. 6-7, the peak frequency is 35160Hz, and the thickness of the concrete slab can be calculated to be 57.42mm by substituting the peak frequency into equation 3; the error of detection is 71.29% compared to the actual thickness of 200 mm. The signal spectrum diagram shown in fig. 8 has a peak frequency of 9766Hz, and the thickness of the concrete slab is 206.72mm by substituting the peak frequency into equation 3; the error of detection is 3.36% compared to the real thickness of 200 mm.
The results of the numerical simulation were compared as shown in table 3. After comparison, when a concrete plate with the thickness of 100mm is knocked by a steel ball with the thickness of 7mm, the calculated thickness is compared with the real thickness, the error is minimum, and the detection effect is optimal. When the steel balls with the thickness of 5mm and 11mm are used for knocking, the calculated thickness is larger than the real thickness, and the error is larger. When a concrete slab with the thickness of 200mm is knocked by an impact source with the thickness of 11mm, the error of the calculated thickness is minimum compared with the real thickness, and the detection effect is optimal. When the steel balls with the thickness of 5mm and 7mm are used for knocking, the calculated thickness is larger than the real thickness, and the error is larger.
Table 3 comparison of numerical simulation results
Comparing these three impact sources (see table 2) it was found that the centroid frequency of the 7mm impact source is closest to the theoretical thickness frequency of the 100mm concrete slab; the centroid frequency of the 11mm impact source is closest to the theoretical thickness frequency of the 200mm concrete slab. The detection errors of the two are within 5 percent, so that the thickness detection effect is best when the centroid frequency of the seismic source is close to the theoretical thickness frequency of the structure.
The above description is only exemplary of the present invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and scope of the present invention should be included in the present invention.
Claims (8)
1. An impact echo method for detecting the thickness of concrete is characterized in that: applying mechanical impact on the surface of the concrete to be detected to generate instantaneous stress waves, and performing nondestructive testing on the concrete by utilizing longitudinal waves in the stress waves.
2. The impact echo method for detecting the thickness of concrete according to claim 1, wherein: stress waves generated by mechanical impact are transmitted into the concrete structure and are reflected, transmitted or diffracted when encountering the interface with discontinuous medium wave impedance, including the bottom surface boundary or the internal defect of the structure; when the reflected echo reaches the surface of the structure, the reflected echo can be reflected into the structure again, so that the repeated reciprocating reflection can excite the local transient resonance of the structure, and the waveform has periodic characteristics; the frequency spectrum of the signal shows a frequency peak value corresponding to the thickness of the structure or the depth of the defect, and the thickness and the internal quality condition of the tested concrete structure can be identified by performing spectrum analysis on the echo signal obtained by testing.
3. The impact echo method for detecting the thickness of concrete according to claim 2, wherein: these reflections constitute a time curve, only a few milliseconds in duration; digitizing the recorded time signal, and converting the time domain into the frequency domain through Fourier transform; the dominant frequency, which is formed as a result of multiple reflections of the stress wave inside the structure, appears as a peak in the frequency spectrum.
4. A shock echo method for detecting concrete thickness according to any one of claims 1 to 3, characterized in that: the mechanical impact is performed by using a small steel ball, the input pulse function is approximate to a half-sine curve, and the width and the corresponding contact time of the input pulse function depend on the size of an impact source used.
5. The impact echo method for detecting the thickness of concrete according to claim 4, wherein: for steel balls acting on concrete, the contact time with the structure surface is expressed as a linear function of the diameter of the steel ball, and the expression is as follows: t is tc0.0043D, wherein D is the diameter of the steel ball and the unit is m; t is tcIs the contact time of the steel ball with the surface of the structure, and is expressed in s.
6. The impact echo method for detecting the thickness of concrete according to claim 5, wherein: the maximum frequency of the impact source is defined as: f. ofmax＝1.25/tcWherein t iscThe contact time of the steel ball with the surface of the structure.
7. The impact echo method for detecting the thickness of concrete according to claim 6, wherein: the thickness or the defect depth of the concrete structure is solved by adopting the following formula:
wherein: t is the thickness of the concrete, and the unit is mm; v. ofcIn m/s, is the propagation velocity of longitudinal waves in the concrete structure, f is the frequency of the defect depth or the thickness of the concrete structure, corresponding to the peak frequency in the spectrogram, in Hz, and β is the structure shape factor.
8. The impact echo method for detecting the thickness of concrete according to claim 7, wherein: for concrete slabs and wall structures, beta is 0.96; for concrete square beam, column structures, β is 0.87.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112666255A (en) * | 2020-12-15 | 2021-04-16 | 中国矿业大学 | Rapid detection system and method for shallow layering of concrete bridge deck |
| CN113064166A (en) * | 2021-03-22 | 2021-07-02 | 石家庄铁道大学 | Method and device for detecting thickness of thin layer defect of multilayer concrete structure and terminal |
| CN115467378A (en) * | 2022-08-16 | 2022-12-13 | 江苏鸿基节能新技术股份有限公司 | Portable foundation engineering intelligence wireless detection equipment |
| CN117630174A (en) * | 2024-01-25 | 2024-03-01 | 中国铁路设计集团有限公司 | Plate-type concrete multichannel-multi-degree-of-freedom pulse wave nondestructive testing method |
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2019
- 2019-03-07 CN CN201910172134.4A patent/CN111664818A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112666255A (en) * | 2020-12-15 | 2021-04-16 | 中国矿业大学 | Rapid detection system and method for shallow layering of concrete bridge deck |
| CN113064166A (en) * | 2021-03-22 | 2021-07-02 | 石家庄铁道大学 | Method and device for detecting thickness of thin layer defect of multilayer concrete structure and terminal |
| CN113064166B (en) * | 2021-03-22 | 2023-01-06 | 石家庄铁道大学 | Method and device for detecting thickness of thin layer defect of multilayer concrete structure and terminal |
| CN115467378A (en) * | 2022-08-16 | 2022-12-13 | 江苏鸿基节能新技术股份有限公司 | Portable foundation engineering intelligence wireless detection equipment |
| CN115467378B (en) * | 2022-08-16 | 2024-01-30 | 江苏鸿基节能新技术股份有限公司 | Portable foundation engineering intelligence wireless detection equipment |
| CN117630174A (en) * | 2024-01-25 | 2024-03-01 | 中国铁路设计集团有限公司 | Plate-type concrete multichannel-multi-degree-of-freedom pulse wave nondestructive testing method |
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