KR20090116525A - Nondestructive testing method of concrete structures using stress wave techniques - Google Patents

Abstract

PURPOSE: A non-destructive inspection method for a concrete structure is provided to improve accuracy of inspection on crack of the concrete structure by removing an error resulting from attachment of a sensor. CONSTITUTION: A non-destructive inspection method for a concrete structure comprises steps of: generating stress wave in the concrete structure using a transducer(S10), measuring the stress wave generated by the concrete structure(S20), interpreting the measured stress wave in a frequency domain(S30), removing an error according to the attachment of the transducer to estimate the transfer speed and energy of the stress wave(S40), and evaluating the concrete structure based on the transfer speed and energy of the stress wave(S50).

Description

Non-destructive testing method for concrete structures using stress waves {NONDESTRUCTIVE TESTING METHOD OF CONCRETE STRUCTURES USING STRESS WAVE TECHNIQUES}

The present invention relates to a non-destructive testing method, and more particularly, to a non-destructive testing method of a concrete structure using a stress wave that can evaluate the stiffness and damage to the concrete structure using the stress wave transmission speed and energy.

In general, concrete has excellent durability and heat resistance compared to other materials and can easily construct a structure having an arbitrary shape in the field. It is also widely used in special structures.

However, compared with other structures, concrete structures have a higher self load and are more prone to cracking, which may cause collapse.

Cracks in concrete appear before and after the hardening of concrete for various reasons. When the cracks can be observed from the surface, the internal structure of the concrete is already damaged due to micro cracks.

If cracks occur in concrete, the strength of the concrete will not meet expectations, and the cracks will gradually grow and corrode due to changes in ambient temperature and humidity, and penetration of chemicals such as salt water, causing a great problem for the safety of concrete.

On the other hand, the strength of concrete changes over time and this change depends on the surrounding climatic conditions, the use environment, and the concrete mixing conditions. In particular, in case of an external shock such as fire or earthquake, the strength of concrete drops significantly.

Therefore, a method of measuring the strength of concrete has been devised, and the most reliable method of measuring strength is the compressive strength test of the core taken from the structure.

Since the compressive strength test causes damage to the structure, in most cases, the compressive strength test is performed on a specimen prepared during pouring, and as few cores as possible are taken for existing structures.

If it is difficult to extract the core from the concrete structure, there is a problem that it is difficult to inspect the concrete structure. Therefore, there is a need for improvement.

The present invention has been made to improve the above problems, to provide a non-destructive testing method of a concrete structure using a stress wave to inspect the concrete structure using the stress wave transmission rate and the stress wave energy transfer characteristics. The purpose is.

In order to achieve the above object, the present invention comprises the steps of generating a stress wave in the concrete structure using a transducer; Measuring the stress wave generated in the concrete structure using the transducer; Analyzing in the frequency domain using the measured stress wave; Removing an error due to attachment of the transducer to calculate a transfer rate and a transfer energy of the stress wave; And it provides a non-destructive inspection method of the concrete structure using the stress wave, characterized in that it comprises the step of evaluating the concrete structure through the transfer rate and the transfer energy of the stress wave.

The step of measuring the stress wave is characterized in that the ultrasonic transmission method, the transducer is attached to both sides of the concrete structure, characterized in that facing each other.

Measuring the stress wave is an ultrasonic reflection inspection method, the transducers are characterized in that each attached to one side of the concrete structure spaced apart.

In order to achieve the above object, the present invention comprises the steps of generating a stress wave in the concrete structure using a stress wave generator; Measuring the stress wave generated in the concrete structure using a sensor; Analyzing in the frequency domain using the measured stress wave; Removing an error due to the attachment of the sensor to calculate the transfer rate and the transfer energy of the stress wave; And it provides a non-destructive inspection method of the concrete structure using the stress wave, characterized in that it comprises the step of evaluating the concrete structure through the transfer rate and the transfer energy of the stress wave.

Measuring the stress wave uses a surface wave flaw detection method, the sensor is characterized in that each attached to one side of the concrete structure spaced apart.

The step of analyzing the frequency is characterized by using a Fourier transform or a wavelet transform.

The evaluation step is characterized by using a regression equation.

As described above, the non-destructive inspection method of the concrete structure using the stress wave according to the present invention has an effect of checking whether the concrete is damaged by using the transfer rate and energy of the stress wave.

In particular, the non-destructive inspection method of the concrete structure using the stress wave according to the present invention has the effect of improving the inspection accuracy for the crack of the concrete by removing the error due to the attachment of the sensor.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of a non-destructive inspection method of a concrete structure using a stress wave according to the present invention.

In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of description.

In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to a user's or operator's intention or custom.

Therefore, the definitions of these terms should be made based on the contents throughout the specification.

1 is a flow chart illustrating a non-destructive inspection method of a concrete structure using a stress wave according to an embodiment of the present invention.

Referring to Figure 1, for the non-destructive testing of the concrete structure, the stress wave is first generated in the concrete structure to be examined (S10). At this time, the stress wave generator or the transducer generates the stress wave in the concrete structure. These stress wave generators or transducers can be hammers or toy guns that can impact concrete structures. On the other hand, such a stress wave generator or transducer may be a device for passing ultrasonic waves through the concrete structure as a medium.

The stress wave can be classified into a surface wave and a volume wave, the surface wave includes a love wave and a Rayleigh wave, and the volume wave includes a longitudinal wave and a transverse wave.

When the stress wave is generated in the concrete structure, the sensor or transducer mounted on the concrete structure measures the stress wave (S20).

And the analyzer associated with the sensor or the transducer is analyzed in the frequency domain using the measured stress wave (S30). In this case, Fourier transform or Wavelet transform is used to analyze in the frequency domain. Since this conversion method is a known technique, a detailed description thereof will be omitted.

Analysis in the frequency domain derives the transfer rate and transfer energy of the stress wave. However, as sensors or transducers are mounted or coupled to concrete structures, errors occur in the rate of transfer of stress waves or the value of energy delivered.

Therefore, the analyzer removes the error due to the attachment of the sensor or transducer from the value derived by analyzing the frequency (S40), and then evaluates the concrete structure to be inspected (S50).

At this time, the evaluation of the concrete structure using a regression equation, and other various databases can be used.

Here, the transfer rate of the stress wave enables evaluation of the rigidity of the concrete structure, and the transfer energy of the stress wave enables evaluation of damages such as voids and cracks of the concrete structure.

First, the evaluation method of the concrete structure through the stress wave transmission rate is as follows.

)와 횡파의 속도(

)는 각각 식(1)과 식(2)과 같다.The velocity of stress waves in infinitely large media is determined by the density of the media and the modulus of elasticity.

) And the velocity of the shear wave (

Are the same as in Equation (1) and (2), respectively.

식(2)

Formula (1)

Formula (2)

는 매질의 밀도,

는 탄성계수,

는 포아송비 이다.here,

Is the density of the medium,

Is the modulus of elasticity,

Is Poisson's ratio.

)는 다음의 식(3)과 같다.Also, the rate of Rayleigh waves propagating on the surface of the

) Is as shown in the following equation (3).

Formula (3)

Therefore, by measuring the velocity of the stress wave, the elastic modulus and Poisson's ratio of the test object can be obtained.

And the evaluation method of the concrete structure through the transfer energy of the stress wave is as follows.

The transfer energy of the stress wave is determined by the attenuation of the concrete member. Factors that reduce the transfer energy can be classified into geometric spreading, intrinsic attenuation, and scattering by damage.

Since the energy transmission function of the stress wave decreases as the damage of the concrete structure is increased, the damage degree can be evaluated by measuring the transmission function. However, in order to calculate the attenuation due to damage purely in the transmission function, a process of normalizing the transmission function when there is no damage as shown in Equation (4) is additionally required.

Formula (4)

는 응력파를 이용하여 측정된 주파수 응답함수로써,

는 주파수 응답함수의 진폭, 여기서는 전달된 에너지량인 투과함수를 의미한다.here,

Is the frequency response function measured using the stress wave,

Is the amplitude of the frequency response function, here the transmission function, which is the amount of energy delivered.

는 측정된 투과함수와 손상이 없을 때 전달된 에너지량인

의 비율이다. Thus delivery rate

Is the measured transmission function and the amount of energy delivered in the absence of damage

Ratio.

For reference, the energy transfer rate of surface waves decreases as surface-breaking cracks deepen, such as concrete cracks.

In other words, the energy transfer rate of the surface wave has a value of 1.0 when there is no crack and a value of 0 when there is a crack penetrating the medium.

Using this principle, the crack depth of the inspection object can be estimated by measuring the transmission coefficient of the stress wave.

Therefore, the amplitude of the frequency response function measured by the self-compensated frequency response function technique means the energy transmitted to the stress wave, and is greatly affected by the frequency and damage.

FIG. 2 is a schematic diagram for using ultrasonic transmission flaw detection according to an embodiment of the present invention, and FIG. 3 is a schematic diagram for using ultrasonic reflection flaw detection according to an embodiment of the present invention, and FIG. 4. Is a schematic diagram for using a surface wave flaw detection method according to an embodiment of the present invention.

Referring to FIG. 2, in the ultrasonic penetrating method, the transducers 21 are mounted on one side and the other side of the concrete structure 20, respectively. The transducer 21 is mounted to the concrete structure 20 to face each other using the concrete structure 20 as a medium.

The transducer 21 generates stress waves in the concrete structure 20, measures such stress waves, and transmits measurement information to the analyzer 22.

Therefore, when the stress wave is generated in the transducer 21 mounted on one side of the concrete structure 20, the stress wave passes through the concrete structure 20 as a medium to move to the other side of the concrete structure 20, the concrete The transducer 21 mounted on the other side of the structure 20 measures the stress wave.

Similarly, when a stress wave is generated in the transducer 21 mounted on the other side of the concrete structure 20, the stress wave passes through the concrete structure 20 which is a medium and moves to one side of the concrete structure 20, and the concrete The transducer 21 mounted on one side of the structure 20 measures the stress wave.

Referring to FIG. 3, in the ultrasonic reflection flaw detection method, a pair of transducers 31 are mounted on one side of the concrete structure 30. These transducers 31 are located at a distance from each other.

The transducer 31 generates stress waves in the concrete structure 30, measures such stress waves, and transmits measurement information to the analyzer 32.

Therefore, when a stress wave is generated in any one of the pair of transducers 31 mounted on one side of the concrete structure 30, the stress wave is reflected from the concrete structure 30 as a medium, and the transducer 31 The other measures the reflected stress wave.

Similarly, when a stress wave is generated in the other of the pair of transducers 31 mounted on one side of the concrete structure 30, the stress wave is reflected from the concrete structure 30 which is a medium, and the transducer 31 One of them measures the reflected stress wave.

Referring to FIG. 4, the surface wave flaw detection method is installed so that a pair of sensors 41 are spaced apart from one side of the concrete structure 40, and each sensor 41 transmits measurement information to the analyzer 42. The stress wave generator 43 generates stress waves at both ends of the concrete structure 40.

When the stress wave generator 43 is close to any one of the pair of sensors 41 to generate a stress wave, the other sensor 41 of the sensor 41 measures the stress wave.

Similarly, when the stress wave generator 43 approaches the other of the pair of sensors 41 to generate the stress wave, the sensor 41 of any one of the sensors 41 measures the stress wave.

In this case, the transducers 21 and 31 in FIG. 2 and FIG. 3 generate longitudinal or transverse waves of high frequency, and the stress wave generator 43 in FIG. 4 generates surface waves of low frequency.

2 to 4, a stress wave waveform called a (t) measured by either one of the pair of transducers 21 and 31 or the sensor 41 is a concrete structure 20, 30, or 40 as a medium. Through, it is measured by b (t) in the other transducer 21, 31 or sensor 41. In the opposite direction, the c (t) waveform is measured as d (t) through the concrete structures 20, 30 and 40.

5A and 5B illustrate waveforms according to an embodiment of the present invention. 5A and 5B show stress wave waveforms in the time domain, and solid black lines and solid red lines are waveforms measured by two sensors, respectively. Since the stress wave is measured in both directions, in FIG. 5A, the a (t) waveform (black) is changed into the b (t) waveform (red) through the medium, and in FIG. 5B, the c (t) waveform (red) is inversely d. (t) The waveform is changed to black.

Such a waveform needs to be transformed into a frequency domain (frequency axis) using a Fourier transform, a wavelet transform, or the like.

In the frequency domain, stress waves are expressed in amplitude and phase according to frequency. In general, the frequency domain signals are represented by imaginary numbers, and the measured stress wave waveforms are represented by A (f), B (f), C (f), and D (f), respectively.

On the other hand, for an ideal signal without noise, the energy transfer rate through the medium can be simply calculated as B (f) / A (f) or D (f) / C (f).

However, in the actual measurement, the energy value is distorted due to the variation due to the mounting or coupling of the sensor. FIG. 6 is a diagram illustrating a functional relationship of energy according to an embodiment of the present invention.

Referring to Figure 6, H (f) represents the frequency response function of the concrete structure, X (f) and Y (f) refers to the stress wave measured by both sensors. In addition, U (f) and V (f) are response functions according to the sensor's own characteristics and mounting / coupling characteristics, and M (f) and N (f) are noises generated during measurement at both sensors.

Therefore, through the self-compensated frequency response function technique, the frequency response function can be obtained from the actual measured waveform expressed by the following equation.

First, in the forward (forward) is the same as the formula (5) and (6).

식(6)

Formula (5)

Formula (6)

In the case of backward, the equations (7) and (8) are the same.

식(8)

Formula (7)

Formula (8)

On the other hand, the frequency response function in each direction is represented by equations (9) and (10).

Formula (9)

Formula (10)

In order to remove noise based on such an equation, equations (11) and (12) are applied to measure and sum signals several times in each direction.

Formula (11)

Formula (12)

Finally, adding the bidirectional function gives the frequency response function of the final concrete structure as shown in Eq. (13).

Formula (13)

On the other hand, Figure 7 is a diagram showing the amplitude of the frequency response function according to an embodiment of the present invention, Figure 8 is a diagram correcting the Figure 7.

Referring to FIG. 7, the amplitude of the frequency response function is different depending on the strength and the method (mounting / coupling) attached to each concrete structure.

8, the forward and reverse graphs of FIG. 7 may be corrected with each other to obtain a final energy transfer rate. Here, if the transmission rate excluding the spherical divergence is 1, there is no damage to the concrete structure, it can be seen that the damage is less than 1.

Since the energy transfer rate of the stress wave is particularly sensitive to damages such as cracks in concrete, it is possible to evaluate damages such as excessive voids and cracks in concrete. In addition, the transfer rate of the stress wave can be evaluated for the stiffness of the concrete.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art to which the art belongs can make various modifications and other equivalent embodiments therefrom. Will understand.

Therefore, the true technical protection scope of the present invention will be defined by the claims below.

1 is a flow chart illustrating a non-destructive inspection method of a concrete structure using a stress wave according to an embodiment of the present invention.

Figure 2 is a schematic diagram for using the ultrasonic permeation scanning method according to an embodiment of the present invention.

3 is a schematic diagram for using the ultrasonic reflection scanning method according to an embodiment of the present invention.

4 is a schematic diagram for using a surface wave flaw detection method according to an embodiment of the present invention.

5A and 5B illustrate waveforms according to an embodiment of the present invention.

6 is a diagram illustrating a functional relationship of energy according to an embodiment of the present invention.

7 is a graph showing the amplitude of the frequency response function according to an embodiment of the present invention.

FIG. 8 is a graph of FIG. 7 corrected. FIG.

* Description of the symbols for the main parts of the drawings *

20,30,40: concrete structure 21,31: transducer

22,32,42 Analyzer 41: Sensor

43: stress wave generator

Claims (10)

Generating a stress wave in the concrete structure using the transducer; Measuring the stress wave generated in the concrete structure using the transducer; Analyzing in the frequency domain using the measured stress wave; Removing an error due to attachment of the transducer to calculate a transfer rate and a transfer energy of the stress wave; And Non-destructive testing method of a concrete structure using a stress wave, characterized in that it comprises the step of evaluating the concrete structure through the transfer rate and the transfer energy of the stress wave. The method of claim 1, The step of measuring the stress wave is non-destructive inspection method of the concrete structure using the stress wave, characterized in that using the ultrasonic transmission method. The method of claim 2, The transducer is attached to both sides of the concrete structure, each non-destructive inspection method of a concrete structure using a stress wave, characterized in that facing each other. The method of claim 1, The step of measuring the stress wave is non-destructive inspection method of a concrete structure using a stress wave, characterized in that using the ultrasonic reflection method. The method of claim 4, wherein The transducer is a non-destructive testing method of a concrete structure using a stress wave, characterized in that attached to each spaced apart from one side of the concrete structure. Generating a stress wave in the concrete structure using a stress wave generator; Measuring the stress wave generated in the concrete structure using a sensor; Analyzing in the frequency domain using the measured stress wave; Removing an error due to the attachment of the sensor to calculate the transfer rate and the transfer energy of the stress wave; And Non-destructive testing method of a concrete structure using a stress wave, characterized in that it comprises the step of evaluating the concrete structure through the transfer rate and the transfer energy of the stress wave. The method of claim 6, Measuring the stress wave is a non-destructive inspection method of a concrete structure using a stress wave, characterized in that using the surface wave flaw detection method. The method of claim 7, wherein The sensor is a non-destructive testing method of a concrete structure using a stress wave, characterized in that attached to each spaced apart from each side of the concrete structure. The method according to claim 1 or 6, The step of analyzing the frequency is a non-destructive inspection method of a concrete structure using a stress wave, characterized in that using the Fourier transform or wavelet transform. The method according to claim 1 or 6, The evaluation step is a non-destructive testing method of a concrete structure using a stress wave, characterized in that using a regression analysis.

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