JP2001311724A - Concrete soundness determination method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concrete soundness determination method capable of determining accurately the soundness of concrete even if anybody uses it, miniaturizing a device, and removing the restriction of a place where it can be used. SOLUTION: In this concrete soundness determination method, the concrete surface is hammered by a hammering means to generate vibration, and a hammering sound (vibration) propagated in the concrete is collected as aerial vibration by a microphone arranged on the position separated from the hammering position and converted into an electric signal, and the signal is analyzed to thereby determine the soundness of the concrete. The method is characterized by executing hammering by using a hammer having the known change with time of a hammering input value, and analyzing the known quantity of the hammering input and the hammering sound (vibration) propagated in the concrete, to thereby determine the concrete soundness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for judging the degree of soundness of concrete, and more particularly, to non-destructive inspection of the presence of cracks and voids occurring inside a concrete structure such as a tunnel. And a method and apparatus used to make the determination.

[0002]

2. Description of the Related Art Conventionally, the soundness of concrete has been determined by a method in which an inspector listens to the hammering sound of a hammer hitting himself and determines the presence of cracks or voids.

Japanese Patent Publication No. 4-10987 discloses an apparatus in which hammering is performed by a machine and the sound of the hammering is collected by a microphone. In this device, the impact sound is a system in which the vibration of the impact portion generated by the impact of the hammer is sampled through the air vibration (sound), and propagates at a fixed distance from the hammer impact portion through the inside of the concrete. It does not pick up the propagation vibration deformed by the condition (1).

[0004] Japanese Patent No. 3009543 discloses a method of judging the soundness of concrete by hitting the concrete surface and analyzing the hitting sound by an analysis unit, wherein a sound receiving means is arranged at a position distant from the hitting point. Have been
The sound receiving means includes a microphone that collects a striking sound (vibration) propagated through the concrete as air vibration, and a microphone in which the sound receiving direction is open, and is a substantially hemispherical hood member. The sound-absorbing member is constituted by a sound-absorbing member and the sound-absorbing sound transmitted through the concrete itself is sampled as air vibration by the sound-receiving means in which the sound-insulating member is close to or close to the concrete surface, and is analyzed by the analysis unit. A method for judging the soundness of concrete, and an apparatus for judging the soundness of concrete by hitting the surface of the concrete and analyzing the sound of the striking sound; A sound receiving means arranged at a position distant from the apparatus, and an analyzing unit for analyzing the collected propagation impact sound, wherein the sound receiving means is Propagation was striking sound through the door (vibration)
Concrete sound characterized by being provided with a microphone that collects air as air vibration, and a sound insulation member that is provided with the microphone and that has an open sound receiving direction and is formed of a substantially hemispherical hood member. Degree judgment device,
Is disclosed.

[0005]

The classical method of judging the soundness of concrete by directly hearing the hammer hitting sound hit by oneself with the ear has been performed up to now, but this method has been used. Judgment requires skill, and
There is also a problem that the determination accuracy varies, and that the determination takes a long time.

In the apparatus described in Japanese Patent Publication No. 4-10987 described above, in which the hammering is mechanically performed and the vibration of the hitting part is sampled by a microphone as air vibration, the vibration of the inspection object generated in the hitting part is disclosed. The detection result is likely to vary when the surface condition of the impacted part such as the adhesion of dirt or the presence of aggregates in the vicinity, and it is necessary to perform multiple impact inspections at the same location. There is a problem in the point.

[0007] The method and apparatus for judging the soundness of concrete disclosed in the above-mentioned Japanese Patent No. 3009543 overcomes the disadvantages of the various methods and apparatuses described above.
Further research has shown that there is room for improvement as follows. That is, in this method or apparatus, as a hammer for hitting, (A) a general hammer used for percussion, (B) a hammer having a spherical head described in Japanese Patent Publication No. 4-10987, and (C). The use of a hammer that mechanically strikes, rather than manually, so as to obtain a substantially constant impact energy is disclosed. According to research,
In the hits by the hammer of (A) and (B), the restriction by the hitting position can be avoided. However, since there is a difference in the strength of the hammer, the hitting energy is not constant, and the correlation with the output hitting sound is unclear. It was found that the judgment results tended to vary.

Further, it has been found that the hammer of (C) requires a large-scale device and cannot respond to a demand for downsizing, and its use is restricted depending on the hitting position.

As is apparent from the above, the present invention is to improve the impacting means used in the concrete soundness judging method and apparatus disclosed in Japanese Patent No. 3009543 from the above viewpoint. As an issue.

[0010]

The present invention for solving the above problems has the following constitution. 1. The concrete surface is struck by a striking means to generate vibration, and a microphone arranged at a position distant from the striking position collects striking sound (vibration) transmitted through the concrete as air vibration and converts it into an electric signal. In a method of judging the soundness of concrete by analyzing this signal, a hit is performed using a hammer having a known time change of a hit input value, and a known amount of the hit input and a hitting sound propagated through the concrete ( A concrete soundness determination method characterized in that the soundness of concrete is determined by analyzing vibration. 2. The analysis based on the known amount of impact input and the impact sound (vibration) propagated through the concrete yields the ratio of the maximum impact amplitude to the maximum impact amplitude (amplitude ratio) and the effective value of the impact input value and the impact sound output value. One of the ratio of the effective value (effective value ratio), the center of gravity of the transfer function between the frequency spectrum of the striking input and the frequency spectrum of the striking sound (frequency centroid), or a combination thereof is used as a parameter. The concrete soundness determination method according to the above item 1, wherein 3. The concrete surface is struck by a striking means to generate vibration, and a microphone arranged at a position distant from the striking position collects striking sound (vibration) transmitted through the concrete as air vibration and converts it into an electric signal. An apparatus for judging the soundness of concrete by analyzing this signal, wherein a hammer having a known time change of a hitting input value is used as a hitting means. 4. 4. The concrete soundness judging device according to the item 3, wherein the striking means is an impulse hammer having a built-in accelerometer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of an apparatus for performing a concrete soundness determining method according to the present invention, whereby the soundness of concrete is determined as follows.

Concrete structure 1 to be judged
In a state where the microphone 20 with the hood 21 is arranged on the surface 0, the striking means 30 strikes the surface of the concrete structure 10 which is at an arbitrary distance from the position where the microphone 20 is arranged. The vibration generated by this impact propagates inside the concrete and is transmitted to the position of the microphone 20 to vibrate the air on the upper surface. This air vibration is picked up by the microphone 20 as sound, converted into an electric signal, and input to the personal computer 40 through the cable 22. In the personal computer 40, an operation unit for performing various operations (analysis) according to a calculation formula described later, a recording unit,
A display unit and the like are provided.

As described above, the microphone 20 does not directly pick up the air vibration (sound) generated directly around the microphone 20 by the impact, but generates the air vibration (sound) generated at the position of the microphone 20 by the vibration propagated in the concrete. Sound). For this reason,
The hood 21 preferably surrounds and is sound-insulated so as not to pick up air vibrations (sound) or ambient noise directly generated by the impact.

One of the features of the present invention resides in that an impulse hammer incorporating an accelerometer is used as the striking means 30. By using an impulse hammer, not only can the entire device be miniaturized, but also it is possible to perform hammering with human power, and the amplitude ratio between the impulse hammer input value and the hitting sound output value, the effective value ratio The center of gravity of the transfer function (frequency center of gravity) can be obtained, whereby the impact energy becomes a known amount, and the frequency characteristic of the impact input becomes clear, so that the state inside the concrete structure can be determined more accurately. It becomes possible.

Available impulse hammers include:
Any hammer having a configuration capable of outputting a striking force with a voltage or the like can be used as long as the size (striking force) of the hammer can be changed depending on the target structure.

The next feature of the present invention resides in that an analysis using a hitting input value and a hitting sound output value is performed. In particular,
A: By using the ratio (amplitude ratio) of the maximum impact sound output amplitude to the maximum impact input amplitude as a parameter, it is possible to more accurately determine a location where large amplitude vibration is likely to occur. B: By using the ratio of the effective value of the striking input value and the effective value of the striking sound output value (effective value ratio) as a parameter, it is possible to more accurately determine a portion where large reverberation vibration is likely to occur. C: Transmission of the frequency spectrum of the striking input and the frequency spectrum of the striking sound The frequency characteristics of structures and members can be evaluated by calculating the center (frequency center of gravity) of Rongguan. The details will be described later.

For the purpose of understanding the present invention, vibration, propagation of vibration and sound in the impact inspection will be described.

The sound that can be felt by human ears is usually 20 Hz
Air vibration at a frequency of ２０20 kHz. This air vibration is sensed as a sound when the eardrum vibrates, but the tapping method in the concrete soundness determination which is the target of the present invention is based on the air generated when the surface of the concrete structure to be measured is hit. Vibration is to be measured by acoustic equipment. The impact sound generated by the impact has a very strong correlation with the surface vibration of the structure, whereby various characteristics such as the physical property value, shape, and presence or absence of a defect of the target structure can be grasped.

It should be noted that not all of the sounds produced when hit are important. In order to explain the reason, if the impact sound generated when a hit object (hammer or the like) collides with the hit object (concrete structure) is considered in some detail, the hitting sound is greatly increased as follows. Can be divided into two.

The sound generated by the deformation of the contact surface due to the contact between the hit object and the hit object The sound generated from each part of the hit object and the hit object by the propagation of the elastic wave generated by the deformation, as shown in FIG. The sound generated by the contact of the above-mentioned struck object indicates the local properties of the struck object,
The sound produced by the propagation of
This is considered to indicate the average properties of the entire object such as the natural frequency of the member excited by the elastic wave.

Considering that concrete is composed of heterogeneous materials such as mortar and coarse aggregate, the locally generated sound is considered to have a greater variation. It is considered that the sound radiated from each part of the structure is more appropriate than the sound caused by the propagated vibration. Conversely, it is considered desirable not to collect other sounds as much as possible.

Basic characteristics representing a transient sound such as an impact sound include vibration, frequency, attenuation, phase, and the like. Considering long structures such as concrete structures, it is difficult to analyze a huge amount of measurement results individually, and the boundary conditions are often not clear. It is often difficult to perform analysis using vibration theory or the like. Therefore, it is considered effective to replace the obtained striking sound with a simple parameter and evaluate the area distribution and time change of the parameter. Therefore, of the above characteristics, focusing on the amplitude, frequency, and attenuation, three parameters of an amplitude ratio, an effective value ratio, and a frequency center of gravity as described below are considered. In this method, the impact is performed manually, but an impulse hammer with a built-in accelerometer is used as described above.

This is because the impact energy for each impact is measured, and the impact energy is removed to obtain a parameter.

First, according to FIG. 3, the amplitude ratio (Am / A
i) will be described. This is a parameter indicating the magnitude of vibration, which is a value obtained by dividing the maximum impact sound amplitude value (Am) by the maximum impulse hammer force amplitude value (Ai). In addition, the impulse hammer needs to be converted into physical quantity by multiplying the applied value or acceleration, and the impact sound by the sound pressure and the calibration coefficient, respectively.
The amplitude ratio and the following effective value ratio should be indicated by the output sound pressure per unit impact force (unit: Pa / N), etc., but the values shown in FIG. 3 are compared with the voltage output values from the measuring device. It has become

The effective value ratio (Rm / Ri) will be described with reference to FIG. The effective value (Rm) of the impact sound over a certain period of time
It is a parameter indicating the magnitude of vibration and the magnitude of damping, divided by the impulse hammer applied effective value. The calculation of the effective value is based on the following equation (2.1).

[0026]

(Equation 1)

Here, R: effective value, a: amplitude, t ₁ ,
t ₂ : Start time and end time for calculating the effective value.

The frequency center of gravity (F) will be described with reference to FIG.

Center of gravity (F) of frequency spectrum in measurement range
Is a parameter indicating the tone level. Here, the center of gravity of the transfer function between the frequency spectrum of the input impulse hammer and the frequency spectrum of the impact sound is determined. The transfer function indicates a frequency characteristic of an intermediate medium between input and output, and here indicates a frequency characteristic of lining concrete (+ air layer between concrete and microphone).

The calculation of the frequency center of gravity is based on the following equation (2.2).

[0031]

(Equation 2)

Here, F: frequency center of gravity, A: frequency amplitude, and f: frequency.

Next, the relationship between the impact sound parameter and the defect of the lining concrete will be described. Factors that change three parameters of the impact sound such as amplitude ratio, effective value ratio, and frequency center of gravity are considered in relation to various states of the tunnel lining concrete. It is clear that the actual tunnel lining has a complicated structure with various internal and rear states, but for simplicity, the free vibration in a one-mass system model will be considered as an example. Impact force P in one-mass system model
Can be expressed by the following equation 2.3.

[0034]

(Equation 3)

Where M: mass, C: damping coefficient, K: spring constant, u: displacement,

[0036]

(Equation 4)

Is shown. (1) Relationship between Amplitude Ratio and Defect Since it is considered that the amplitude of the impact sound is strongly related to the acceleration of the surface of the concrete structure, the equation (2.3) is modified to obtain the following equation (2.4) ) Is the mass of the mass

[0038]

(Equation 5)

It can be seen that acceleration has a large effect on acceleration. Defects and deterioration phenomena related to the mass of the hit point as the state of the structure include: a. Places that are about to peel off from the overall structure, b. There may be places where member dimensions are insufficient compared to others. Therefore, if there is a portion where the amplitude ratio is larger than other portions at a position where the structure is determined to have a constant shape, it is considered that there is a high possibility that the above-described defect exists.

(2) Relationship between effective value ratio and defect The effective value is determined as an index of the wave attenuation characteristic as described above. If the damping coefficient C is zero in the equation (2.3), the struck structure continues to vibrate forever. But
Actually, viscous damping due to contact with air, etc., hysteresis damping due to internal heat generation during repeated vibration, friction damping that causes friction in the oscillating system, part of energy during vibration Is dissipated.
In particular, focusing on the dissipation decay, considering defects and deterioration phenomena related to the damping characteristic near the impact point, a. Where there are cavities or low-density material that reflects elastic waves where there is to be solid; b. Conversely, places where water, earth and sand, etc. are filled in places that should be hollow, c. A place surrounded by cracks, etc. can be considered. Although it depends on the use and shape of the structure, it is generally considered that there is a high possibility that a defect is present in a place where the damping is small and the vibration continues.

(3) Relationship between frequency centroid and defect In a one-mass system model, the natural frequency f of the model is calculated by the following equation (2.5).

[0042]

(Equation 6)

Therefore, the lower the spring constant K, the lower the frequency. Considering defects and deterioration phenomena related to the spring constant in a structure, a. Where a decrease in the elastic modulus of concrete is observed, b. Places where the member thickness is smaller than others or where the second moment of area is small due to cross-sectional defects, etc .; c. It is considered that there is a place where the rigidity is reduced due to a crack or the like, and it is considered that there is a high possibility that a defect exists in a place where the frequency center of gravity is on the low frequency side.

[0044]

According to the present invention, the soundness of concrete can be determined with high accuracy no matter who uses it.
Since the device can be miniaturized, there are no restrictions on where it can be used, and the problems described above are solved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an apparatus according to the present invention.

FIG. 2 is a conceptual diagram showing a striking sound.

FIG. 3 is an explanatory diagram of an amplitude ratio.

FIG. 4 is an explanatory diagram of an effective value ratio;

FIG. 5 is an explanatory diagram of a frequency center of gravity.

[Explanation of symbols]

 Reference Signs List 10-Concrete structure 20-Microphone 21-Hood 22-Cable 30-Striking means 40-PC

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G047 AA10 BA04 BC03 BC04 CA03 EA15 GG28 2G061 AA13 BA03 CA08 EA06 EA07 EA08 EA09 EC02

Claims (4)

[Claims] An impact is generated by striking a concrete surface with a striking means to generate vibration, and a striking sound (vibration) propagated through the concrete is collected as air vibration by a microphone disposed at a position distant from the striking position. In a method of determining the soundness of concrete by converting the signal into a signal and analyzing the signal, a hit is performed using a hammer having a known time change of the hit input value, and the hit amount and the known amount of the hit input and the concrete are compared. A concrete soundness judging method, characterized by judging the soundness of concrete by analyzing the transmitted impact sound (vibration). 2. An analysis based on a known amount of a percussion input and a percussion sound (vibration) propagating in concrete, the ratio of the percussion output maximum amplitude to the percussion input maximum amplitude (amplitude ratio), the effective value of the percussion input value and Ratio of the effective value of the impact sound output value (effective value ratio),
2. The concrete soundness according to claim 1, wherein any one of a center of gravity (frequency center of gravity) of a transfer function between a frequency spectrum of the impact input and a frequency spectrum of the impact sound or a combination thereof is used as a parameter. Degree judgment method. The surface of the concrete is struck by a striking means to generate vibrations, and a striking sound (vibration) propagated through the concrete is sampled as air vibrations by a microphone arranged at a position distant from the striking position to generate electricity. In a device for converting the signal into a signal and analyzing the signal to determine the soundness of the concrete, a hammer having a known time change of a hitting input value is used as a hitting means, wherein the concrete soundness determining device is used. . 4. The concrete soundness judging device according to claim 3, wherein the striking means is an impulse hammer having a built-in accelerometer.