JP2001337077A - Device for non-destructively inspecting exfoliation in concrete structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for non-destructively inspecting exfoliation in a concrete structure capable of highly accurately detecting exfoliation which occurs in the concrete structure including aggregate such as shingle and reinforcing bars in a short time through the use of ultrasonic waves. SOLUTION: The method for non-destructively inspecting exfoliation in a concrete structure comprises a first process to provide an impact force for the surface of the concrete structure 11 through the use of an impact force generating means 13 to generate standing waves between the surface of the concrete structure 11 and exfoliation, a second process to detect the elastic oscillations of the concrete structure 11 due to the generated standing waves by an ultrasonic probe 14 mounted on the surface of the concrete structure 11, and a third process to obtain the location of the exfoliation in the concrete structure 11 through the use of a general-purpose frequency analyzing method or a maximum likelihood method to take a predetermined number of standing waves as a state variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive inspection method for detecting peeling occurring in a concrete structure.

[0002]

2. Description of the Related Art Conventionally, as a nondestructive inspection method of peeling occurring in a concrete structure, a skilled inspector gives an impact to the concrete structure with a hammer, and an abnormality is generated by a reaction force or sound at that time. A so-called hammering sound inspection method of detecting and diagnosing is often adopted. However, this hammering test has the drawback that the accuracy of peeling detection is said to be about 60%, which is not only low in reliability but also that subjective factors are strongly reflected in the diagnosis and individual differences are large. Therefore, X-ray method, electromagnetic wave method, infrared method,
Development of various inspection methods such as an ultrasonic method has been attempted.

[0003] However, the X-ray method requires complicated handling of equipment used for inspection and involves the risk of exposure to X-rays, so that only qualified persons can use the equipment and the inspection becomes expensive. In the electromagnetic wave method, when a reinforcing bar is present inside, it is often impossible to detect a peeled portion. Furthermore, in the infrared method, since the presence or absence of peeling is determined based on the temperature difference between the front and rear of the peeling, in the case where there is no sunshine and the temperature difference due to the peeling hardly occurs in the inspection object such as inside a tunnel, etc. This makes it difficult to detect peeling. Therefore, in order to generate a temperature difference, it is conceivable to heat the surface of the test object with a burner or the like, but heating results in fatigue damage to the test object, and is not a recommended method. .

[0004] The ultrasonic method is a method for determining the presence or absence of peeling and measuring the position based on the propagation time when the ultrasonic wave reciprocates between the surface of the concrete structure and the peeling. Since multiple reflections occur on the surface and these reflected waves overlap each other, it is difficult to measure the round-trip propagation time from the surface to the separation using the first reflected wave from the separation.
Actually, since the transmission signal is further superimposed on the superimposed reflected wave, the situation becomes more serious, and it is practically impossible to measure the round trip propagation time from the surface to the separation. However, the ultrasonic method is harmless to the human body and easy to handle, and is difficult to discard as a medium for a nondestructive inspection system. For this reason, it can be assumed that the inspection object is a uniform continuum that does not include aggregates such as pebbles and reinforcing bars, and when it is assumed that an ultrasonic sensor is used, the physical characteristics of the ultrasonic sensor should be considered. Creates a predicted waveform of the received signal waveform from peeling, etc., and performs pattern matching between this and the actual received signal waveform to measure the reciprocating propagation time from the surface to the peeling, thereby determining the presence or absence of peeling A multi-reflection wave model method has been developed to determine the separation position.

[0005]

However, when aggregate is present as in a normal concrete structure and the ultrasonic wavelength of an ultrasonic sensor available for inspection is not so long as compared with the size of the aggregate, The ultrasonic waves are strongly affected by the aggregate when propagating, and the ultrasonic waves transmitted from the ultrasonic sensor collide with the aggregate existing in the middle and propagate while repeating scattering. Accordingly, since the received signal received by the ultrasonic sensor includes the contribution of scattering by the aggregate, a multiple reflected wave model that is established between the separation and the surface can be applied to the received signal. Therefore, it is necessary to develop a different measurement method for diagnosing peeling. Furthermore, due to the sudden decrease in the number of skilled inspectors in recent years, or the sudden increase in the number of objects to be diagnosed from the viewpoint of extending the life of existing buildings, highly accurate diagnosis can be performed in a short time even by unskilled inspectors. There is a need for a diagnostic method that can be performed. The present invention has been made in view of such circumstances, and concrete capable of detecting peeling occurring in a concrete structure including aggregates such as pebbles and reinforcing bars in a short time and with high accuracy using ultrasonic waves. An object of the present invention is to provide a non-destructive inspection method for peeling of a structure.

[0006]

According to the present invention, there is provided a non-destructive inspection method for peeling of a concrete structure according to the present invention. A non-destructive inspection method, wherein a first step of generating a standing wave between the surface of the concrete structure and the separation by applying an impact force to the surface of the concrete structure using an impact force generating means, A second step of detecting the generated standing wave by an ultrasonic probe attached to the surface of the concrete structure, and a frequency analysis of a received signal obtained by the ultrasonic probe to the concrete structure. And a third step of determining the position of the peeling of.

[0007] When, for example, a repetitive impact force is applied to the surface of the concrete structure by the impact force generating means, the repetitive impact force is triggered and a large number of standing waves are generated between the surface of the concrete structure and the separation. . The generated standing wave is a fundamental mode standing wave uniquely determined by the propagation speed of sound waves in the concrete structure and the position of separation (distance from the surface to the separation, that is, the depth), and an integral multiple of the fundamental mode. And a number of higher-order mode standing waves having the following modes. Therefore, when the frequency of the generated standing wave is determined, the position of the separation of the concrete structure can be determined using this frequency.

[0008] In the nondestructive inspection method for delamination of a concrete structure according to the present invention, in the third step, the frequency of a theoretical standing wave is determined by a general-purpose frequency analysis method for the received signal. The position of the peeling of the concrete structure can be obtained by making the above equation.
When, for example, a repeated impact force is applied to the surface of the concrete structure, a standing wave as shown in FIG. 6 is generated between the separation and the surface. At this time, the angular frequency ω of the j-th mode standing wave
Since there is a relationship of ω _j = 2πf _j between _j and the frequency f _j , if the propagation speed of the sound wave in the concrete structure is V, and the depth of separation in the concrete structure is L, Equation (1) holds between the frequency f _{j of} the j-th mode standing wave, the propagation velocity V of the sound wave in the concrete structure, and the separation depth L in the concrete structure. .

[0009]

(Equation 1)

Since the frequency of the standing wave corresponds to the frequency giving the peak of the frequency spectrum obtained by the frequency analysis, the standing wave generated in the concrete structure is detected by the ultrasonic probe attached to the surface, and this is detected. When the frequency analysis of the obtained received signal is performed, the frequency f _{j of} each standing wave is obtained.
Can be obtained directly. When calculating the frequency f _j ,
It is desirable to employ the maximum entropy method in which the frequency resolution does not easily deteriorate even when the number of data points is small.
Now, assuming that the frequency giving the peak of the frequency spectrum by the maximum entropy method is M _j (j = 1, 2,..., M), the peeling depth in the concrete structure is (2)
The value of L minimizes the expression.

[0011]

(Equation 2)

The standing wave generated in a concrete structure is generated not only between the surface and the separation but also between the surface and the bottom surface if there is no separation. However, if the data at the time of design, etc. are examined in advance, it is easy to distinguish between a standing wave generated between the surface and the separation or a standing wave generated between the surface and the bottom. Is obtained.

[0013] In the nondestructive inspection method for delamination of a concrete structure according to the present invention, in the third step, a predetermined number of standing waves is selected as a state variable, and a sum of the predetermined number of standing waves is calculated. By matching the received signal with the maximum likelihood, the position at which the concrete structure is separated can be determined. The higher the frequency component (higher-order mode standing wave) of the standing wave generated between the separation and the surface in the concrete structure, the more severely the attenuation, so the ultrasonic probe detects it in a short time interval. Vibration z of concrete structures
(T) can be approximated by equation (3), which is a linear combination of standing waves from the fundamental mode (first mode) to the fourth mode.

[0014]

(Equation 3)

Here, ω_j Stands for the peeling depth L
The angular frequency of the j-th mode of the wave, ω _j = J2πV /
(2L) (i = 1, 2, 3, 4). What
Contact, t is time, a_j , B_j In the j-mode standing wave
The magnitude of the contribution of each component is shown. Also, in equation (4)
X representing elastic vibration due to standing wave of each mode represented_j 
(T) satisfies the differential equation of equation (5).

[0016]

(Equation 4)

[0017]

(Equation 5)

Here, x (t) = (x ₁ (t), dx ₁
(T) / dt, x ₂ (t), dx ₂ (t) / dt, x ₃
(T), dx ₃ (t) / dt, x ₄ (t), dx ₄
When a state vector of (t) / dt) ^T is introduced, a state equation relating to the elastic vibration of the standing wave up to the fourth mode is as shown in equation (6).

[0019]

(Equation 6)

Here, w (t) = (0, w ₁ (t),
0, w ₂ (t), 0, w ₃ (t), 0, w ₄ (t)) ^T
Is the transition noise, w _j (t) (j = 1, 2, 3, 4)
Are white Gaussian noises independent of each other with a mean value of 0 and a variance of σ ² . By taking such transition noise into account, it is possible to compensate for slight attenuation of elastic vibration in a short time interval. On the other hand, if the noise generated in the ultrasonic probe and the standing waves of all higher-order modes higher than the fifth mode are regarded as noise, the observation equation given by the ultrasonic probe is expressed by the following equation (7). Become like

[0021]

(Equation 7)

Here, H = (1,0,1,0,1,0,
1, 0), and y _k and v _k indicate the observation value and the observation noise at the sampling time kΔT (ΔT is the sampling period), respectively. At this time, if Expression (6) is discretized in accordance with the observation sampling time, Expression (8) is obtained.

[0023]

(Equation 8)

Here, x _k and w _k represent the state vector and the transition noise vector at the sampling time kΔT, respectively, as shown in equation (9). Note that F
Is a transition matrix defined by equation (10). Where I
₈ is an 8 × 8 unit matrix.

[0025]

(Equation 9)

[0026]

(Equation 10)

At this time, w _k is white Gaussian noise having an average value of 0, and the covariance matrix W of w _k is given by equation (11). Here, Σ is the covariance matrix of the transition noise w (t) Σ = E
[W (t) w (t) ^T ], and Σ = diag ｛0, σ
² , 0, σ ² , 0, σ ² , 0, σ ² }. Note that d
iag representing the ^{{0, σ 2, 0,} σ 2, 0, σ 2, 0, σ 2} is a diagonal matrix for the arguments as elements.

[0028]

[Equation 11]

The observation noise is obtained by adding the standing waves of the fifth mode or higher and the noise generated in the ultrasonic probe. The observation waves obtained by linearly combining the standing waves of many modes are statistically white. It has properties close to Gaussian noise. Therefore, the fourth standing wave
Estimation of the state vector x _k related to the sound pressure variations up mode (elastic vibration) can be carried out by the Kalman filter shown in equation (12). Note that R indicates the variance of the observation noise v _k . However, the Kalman filter cannot be applied directly because the depth L of the separation in the concrete structure and the variance R of the observation noise v _k are unknown. Therefore, these two parameters are represented as θ = (L, R) ^T, and the Kalman filter is applied by giving various candidates to θ.

[0030]

(Equation 12)

Here, when estimating the optimum value of θ, the observation predicted value using the state vector x _k relating to the sound pressure fluctuation (elastic vibration) of the standing wave up to the fourth mode is a true observation value (received value). When the value of θ is determined so as to match the wave signal), the value of θ = (L, R) ^T at that time is the optimum parameter.
Therefore, the peeling depth L in the concrete structure is (1
3) It results in obtaining the maximum value of the likelihood function shown in the equation. Here, p (y _k / θ, Y ^k−1 ) is the observation information Y ^k−1
= {Y _j ; 0 ≦ j ≦ k−1} and observation y _k under θ
Is the conditional probability density function of.

[0032]

(Equation 13)

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a block diagram of an inspection apparatus applied to a nondestructive inspection method for peeling of a concrete structure according to the first and second embodiments of the present invention, and FIG. 2 applies the same nondestructive inspection method. Explanatory drawing of the shape of the inspection object,
FIG. 3 is an explanatory diagram of a received signal waveform detected by the inspection device applied to the nondestructive inspection method, and FIG. 4 is a maximum entropy method of a received signal waveform detected by the inspection device applied to the nondestructive inspection method. FIG. 5 is an explanatory diagram of a frequency spectrum obtained by the frequency analysis according to FIG. 5, and FIG. 5 is an explanatory diagram of contour lines of the likelihood function when the depth of separation is determined by maximizing the likelihood function.

As shown in FIG. 1, the first and second embodiments of the present invention
The inspection apparatus 10 applied to the concrete structure non-destructive inspection method according to the embodiment transmits a ultrasonic pulse based on a signal from an ultrasonic oscillator 12 to the surface of the concrete structure 11 and transmits the ultrasonic pulse to the concrete structure. An ultrasonic oscillator 13 which is an example of an impact force generating means for generating a standing wave in the object 11, and an ultrasonic probe 14 which detects elastic vibration of the concrete structure 11 due to the standing wave and converts the elastic vibration into an electric signal.
And an amplifier 15 that amplifies the electric signal output from the ultrasonic probe 14 and a computer 16 that performs A / D conversion on the signal amplified by the amplifier 15 to perform signal processing. Hereinafter, these will be described in detail.

As shown in FIG. 2, the concrete structure 1
1 is, for example, an aggregate made of pebbles having a diameter of about 10 mm,
Sand, cement, and water were blended at the same blending ratio as ordinary concrete materials, and were manufactured with a length of 242 mm and a width of 110 mm.
It is a plate having a thickness of 0 mm and a thickness of 184 mm. The ultrasonic oscillator 12 is used in nondestructive inspection such as ultrasonic flaw detection and measurement of the propagation speed of a sound wave in a material, and transmits a large number of pulse voltages in a short time, for example, at intervals of 5 to 30 ms. A sound wave oscillator is available. The ultrasonic transmitter 13 and the ultrasonic probe 14 have a well-known structure using a piezoelectric element. The ultrasonic transmitter 13 converts voltage fluctuation into mechanical vibration (shock), The probe 14 converts mechanical vibration (elastic vibration) into voltage fluctuation. Note that the response range of the ultrasonic transmitter 13 and the ultrasonic probe 14 may be in principle any frequency band.

The amplifier 15 amplifies the minute electric signal output from the ultrasonic probe 14 to an electric signal of a predetermined size which can be easily processed. The computer 16 is composed of, for example, a personal computer, and converts the input signal to A
It has an AD converter for D-conversion, a first operation unit, a second operation unit, and a display unit for processing the AD-converted signal. The first calculating means is for determining the position of the separation in the concrete structure using a general-purpose frequency analysis method, and the second calculating means is a maximum likelihood method using a predetermined number of standing waves as a state variable. The position of the peeling in the concrete structure is obtained by the display means, the display means, such as detection data such as input signals,
It displays a frequency spectrum, a contour line of a likelihood function, and a calculation result of a separation position and the like. In practice, either one of the first and second calculation means may be used. If both means are used together, the reliability can be further increased.

Next, the first embodiment of the present invention using the inspection apparatus 10 will be described.
A nondestructive inspection method for delamination of a concrete structure according to the embodiment will be described. In addition, since it was difficult to provide peeling in the concrete structure 11, the effectiveness of the present invention was confirmed by detecting the position of the bottom surface of the concrete structure 11, that is, measuring the thickness instead of peeling.

As shown in FIG. 2, the concrete structure 1
An ultrasonic transmitter 13 and an ultrasonic probe 14 on the surface of
For example, by attaching mechanical grease as a contact medium, an ultrasonic oscillator 12 is used to
A pulse voltage is applied at intervals of s, an ultrasonic pulse is generated and transmitted into the concrete structure 11, and a standing wave is generated between the surface and the bottom surface of the concrete structure 11. The elastic vibration of the concrete structure 11 formed by the standing wave generated at this time is detected by the ultrasonic probe 14, converted into an electric signal, and input to the amplifier 15. The electric signal amplified by the amplifier 15 so as to be easily processed by the signal is input to the computer 16. FIG. 3 shows the result of displaying the electric signal input to the computer 16, that is, the waveform of the received signal (the relationship between time and amplitude) detected by the inspection device 10 using the display means. As shown in FIG. 3, in a region of about 70 μs or less after receiving the wave, the influence of the multiple reflection wave and the surface wave between the surface of the ultrasonic probe 14 and the surface of the concrete structure 11 strongly appears. I have. These effects disappear,
Time period when the received signal is considered to be settled, for example, about 80
It can be seen that even after μs, multiple reflected waves cannot be read due to scattering of aggregate.

The received signal is settled, for example, 7
The frequency analysis processing contained in the first calculation means was applied to the signal in the portion of 3.0 to 193.0 μs (region D ₂ ), and the frequency spectrum was obtained by the maximum entropy method. FIG. 4 shows the result of displaying the obtained frequency spectrum (the relationship between frequency and amplitude) using the display means.
The numbers in FIG. 4 indicate the frequency at which each peak is given. Using these peak frequencies and obtaining the thickness that minimizes the expression (3) using the propagation speed of sound waves in the concrete structure 3 of 3500 m / s, the thickness is 187.3 mm, which makes it possible to measure the thickness with extremely high accuracy. (Measurement error rate 1.8%).

Next, the second embodiment of the present invention using the inspection apparatus 10 will be described.
A nondestructive inspection method for delamination of a concrete structure according to the embodiment will be described. Also in the second embodiment, the effectiveness of the present invention was confirmed by detecting the position of the bottom surface of the concrete structure 11, that is, measuring the thickness instead of peeling. Here, the second embodiment is different from the first embodiment.
As compared with the embodiment, only the calculation contents of the first and second calculation means applied to the electric signal input to the computer 16, that is, the received signal waveform detected by the inspection device 10, are different. Only the calculation contents of the second calculation means and the display contents of the display means associated therewith will be described.

The sound pressure fluctuation (elastic vibration) generated in the concrete structure 11 is approximated by the first-order combination of the standing waves of the first to fourth modes, and all the higher-order standing waves of the fifth mode or higher are observed. Regarded as noise. Therefore, if the received signal is used as it is, a large signal appears near the center frequency 400 kHz of the ultrasonic probe 14, and the observation noise increases,
Measurement accuracy deteriorates. For this reason, the received signal is stored in the second calculating means, for example, when the cutoff frequency is 5
A low-pass Butterworth filter process of about 0 kHz was performed to remove a frequency component near the center frequency of the ultrasonic probe 14. Next, the maximum likelihood method was applied to the received signal subjected to the low-pass Butterworth filter processing, and the position of the separation was determined by maximizing the likelihood function.

In the maximization of the likelihood function, a method of calculating contour lines of the likelihood function that can be visualized to determine the position of peeling (here, the thickness of the concrete structure 11) was adopted. FIG. 5 shows contour lines of the likelihood function when the likelihood function is projected on the L-lnV plane. Here, L indicates the thickness of the concrete structure, V indicates the propagation speed of the sound wave, and ln indicates the natural logarithm. As shown in FIG. 5, the contour lines are almost parallel to the lnV axis (vertical axis), indicating that the likelihood function is not affected by V. For example, if the value of lnV is -6.5,
The value of L that maximizes the contour at this time is 186 mm. In FIG. 5, the interval between contour lines is roughly drawn, but if it is drawn densely, the optimum value of L that maximizes the contour line is 186 mm for any value of InV. This value is
The value is very close to the actual thickness of 184 mm (measurement error rate 1.09%).

The embodiment of the present invention has been described above.
The present invention is not limited to this embodiment,
For example, the impact force was applied to the surface of a concrete structure by using an ultrasonic oscillator and an ultrasonic oscillator capable of obtaining a multi-pulse impact as an impact force generating means, but repeated mechanical impacts caused by a hammer, an air knocker, etc. It can also be applied to the surface of a concrete structure. Therefore, the applicability of the concrete structure as a non-destructive inspection method for delamination is expanded. In addition, an ultrasonic transmitter for transmitting multiple pulse impacts to the surface of the concrete structure and an ultrasonic probe for receiving to detect elastic vibration of the concrete structure were used. A two element ultrasonic probe can also be used. This makes it possible to easily generate and detect standing waves even for a concrete structure having a complex surface. In addition, by inspecting while moving the ultrasonic probe at an appropriate interval on the surface of the concrete structure, it is possible to accurately grasp the depth and extent of the delamination. be able to.

Although the maximum entropy method is used for frequency analysis of a received signal obtained by the ultrasonic probe, a fast Fourier transform method may be used. Further, when the position of the separation is determined by maximizing the likelihood function, a method based on visualization using contour lines of the likelihood function is employed. However, the position of the separation is automatically searched using the Powell method (optimization method). A method can also be adopted. In this method, the position of peeling can be automatically determined in a short time.

[0045]

According to the nondestructive inspection method for concrete structure peeling according to the first to third aspects, the concrete structure surface is separated from the concrete structure surface by applying an impact force to the surface of the concrete structure by using an impact force generating means. A first step of generating a standing wave during the second step, a second step of detecting the generated standing wave by an ultrasonic probe attached to the surface of the concrete structure, and a step obtained by the ultrasonic probe Since the method includes the third step of determining the position of the peeling of the concrete structure by analyzing the frequency of the received signal, the detection of the peeling occurring in the concrete structure containing aggregates such as pebbles and reinforcing bars using ultrasonic waves. And the depth of separation can be measured with high accuracy.

In particular, in the nondestructive inspection method for concrete structure delamination according to the second aspect, in the third step, the frequency of the theoretical standing wave is obtained from the received signal by a general-purpose frequency analysis method. To determine the location of concrete structure delamination by matching the peak frequency
In the nondestructive inspection method for concrete structure separation, a predetermined number of standing waves is selected as a state variable in a third step, and a sum of the predetermined number of standing waves is received. The maximum likelihood is used to determine the position of delamination of a concrete structure, so it is possible to detect the delamination occurring in a concrete structure and measure the depth of the delamination in a short time and with high accuracy. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inspection apparatus applied to a concrete structure non-destructive inspection method according to first and second embodiments of the present invention.

FIG. 2 is an explanatory diagram of a shape of an inspection object to which the nondestructive inspection method is applied.

FIG. 3 is an explanatory diagram of a received signal waveform detected by an inspection device applied to the nondestructive inspection method.

FIG. 4 is an explanatory diagram of a frequency spectrum obtained by frequency analysis of a received signal waveform detected by an inspection device applied to the nondestructive inspection method.

FIG. 5 is an explanatory diagram of contour lines of the likelihood function when the peeling position is determined by maximizing the likelihood function.

FIG. 6 is an explanatory diagram of a state of a standing wave generated between a separation and a surface in a concrete structure.

[Explanation of symbols]

10: inspection apparatus, 11: concrete structure, 12: ultrasonic oscillator, 13: ultrasonic transmitter (impact force generating means),
14: ultrasonic probe, 15: amplifier, 16: computer

Claims (3)

[Claims] 1. A non-destructive inspection method for peeling of a concrete structure when a peel exists between a surface and a bottom surface of the concrete structure, wherein the surface of the concrete structure is subjected to impact by using an impact force generating means. A first step of applying a force to generate a standing wave between the surface of the concrete structure and the separation, and detecting the generated standing wave by an ultrasonic probe attached to the surface of the concrete structure. A second step;
A third step of analyzing the frequency of the received signal obtained by the ultrasonic probe to determine the position of the concrete structure peeling, the method comprising the steps of: 2. The non-destructive inspection method for delamination of a concrete structure according to claim 1, wherein in the third step, a frequency of a theoretical standing wave is determined by a general-purpose frequency analysis method with respect to the received signal. A non-destructive inspection method for peeling of a concrete structure, wherein the position of the peeling of the concrete structure is obtained by making the peak frequency coincide with the obtained peak frequency. 3. The nondestructive inspection method of a concrete structure according to claim 1, wherein a predetermined number of standing waves is selected as a state variable in the third step. A non-destructive inspection method for concrete structure separation, wherein the sum is matched with the received signal with maximum likelihood to determine the position of separation of the concrete structure.