JP2008267897A - Method for measuring cracks in harmful depth of concrete surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly and accurately detect critical cracks. <P>SOLUTION: An oscillating means 1 and a receiver are placed on the surface of concrete W with cracks C1 and C2 therebetween. The oscillating means 1 on one side transmits an oscillating wave and the receiver on the other side receives the oscillating wave coming through the concrete W to measure cracks of critical depths on the surface of the concrete. With the reference depth of a critical crack represented by d (equal to the coating thickness of the concrete) and the propagation speed of the oscillating wave in the concrete represented by V, the oscillating means transmits an oscillating wave of the following frequency f on one side of the area that contains the cracks. f ≈ V/4d The degree of attenuation in the amplitude of the incoming oscillating wave is measured on the other side of the area containing the cracks. With this, whether the cracks are deeper than the reference depth d or not is evaluated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for measuring a crack having a harmful depth (for example, a depth reaching a reinforcing bar) among cracks generated on a concrete surface.

  The depth of cracks generated on the concrete surface is one of the important indicators of the soundness of concrete structures. If the depth of cracks on the concrete surface can be determined, the strength of the concrete structure can be determined more accurately. Can be estimated.

Conventionally, as a method of nondestructively inspecting the crack depth, (1) the propagation distance from the oscillation means to the receiving means is measured from the velocity and propagation time of the vibration wave traveling through the concrete, and the geometrical distance of the propagation distance is measured. A method of estimating the crack depth from the relationship is known (for example, see Patent Document 1). In addition, (2) a diffraction angle method using a change in the phase of a vibration wave, (3) a method using attenuation of a surface wave (for example, see Patent Document 2), and the like are also known.
JP-A-8-54378 (FIG. 3) JP 2001-12933 A

  However, in both methods (1) and (2), attention is paid to the initial component of the longitudinal wave that has propagated, and as shown in FIG. 3, an oscillator is generated for each of the cracks C1 and C2 on the surface of the concrete W. Since the depths of the cracks C1 and C2 are measured by arranging 1 and the geophone 2 and performing multipoint measurement, there is a problem that a considerable time is required for the measurement.

  The method (3) can be applied to steel, but in the case of concrete, which is a composite raw material for cement and aggregate, there are many causes of wave attenuation other than cracks. There was a problem with accuracy.

  In view of the above circumstances, an object of the present invention is to provide a crack measuring method capable of detecting a harmful crack quickly and accurately even if a concrete surface has a plurality of cracks.

According to the first aspect of the present invention, a vibration wave is oscillated on one side sandwiching a crack on the concrete surface, and the vibration wave propagating through the concrete is received on the other side to crack a harmful depth of the concrete surface. Wherein the reference is d for the harmful depth of the crack, and the transmission speed of the vibration wave on the concrete surface is V, and the vibration wave of the next frequency f on one side of the crack. While oscillating
f ≒ V / 4d
By measuring the degree of attenuation of the amplitude of the vibration wave received on the other side across the crack, it is evaluated whether the crack is deeper than the reference d or lower than the reference d. And

  The invention of claim 2 is characterized in that, in claim 1, the reference d for the harmful depth of cracks is the cover thickness of the concrete with respect to the reinforcing bars inside the concrete.

  According to a third aspect of the present invention, in the first or second aspect, the amplitude of the vibration wave is detected by a vibrometer on one side and the other side sandwiching the crack, and the vibration wave is detected based on both detection values. It is characterized by measuring the degree of amplitude attenuation.

The invention of claim 4 provides a vibration wave to a concrete surface having cracks, and also scans the entire concrete surface with a vibrometer and receives the vibration waves, thereby detecting the position, width and length of the cracks on the concrete surface. When the first step of acquiring the information of the above and the reference of the harmful depth of the crack is d and the transmission speed of the vibration wave used on the concrete surface is V, the vibration wave of the next frequency f is applied to the concrete surface. As well as
f ≒ V / 4d
A second step of detecting the position of a crack having a depth greater than or equal to the reference d by measuring the degree of attenuation of the vibration wave propagating beyond the crack by scanning the concrete surface with a vibrometer; And based on the information acquired in the first step, the position of the crack on the concrete surface is visually displayed, and on the display, the crack of the depth of the reference d or more measured in the second step And a third step of visually displaying the positions so that the positions can be distinguished from each other.

  According to the first aspect of the present invention, the depth of the crack on the concrete surface is not estimated from the arrival time of the initial wave and the change in phase, but the amplitude of the wave is attenuated when a vibration wave having a specific frequency is applied. By paying attention to this, it is possible to make a quick and accurate measurement because it is estimated whether the crack has a harmful depth.

  According to the invention of claim 2, in order to estimate whether or not the crack is deep enough to reach the reinforcing bar embedded in the concrete, if it is known that the crack has not reached the reinforcing bar, there is a risk of corrosion of the reinforcing bar. It can be determined that there is no need for immediate repair.

  According to the invention of claim 3, since the degree of attenuation of the vibration wave is measured with the vibrometer, it is possible to make a quick measurement without contact.

  According to the invention of claim 4, since not only the information on the crack position and its width and length but also the position of only the harmful crack can be estimated, the measures after the measurement can be efficiently performed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1A is a diagram showing an implementation status of a measurement method according to an embodiment of the present invention, FIG. 1B is a characteristic diagram showing a propagation status of vibration waves when a crack does not reach a harmful depth, and FIG. It is a characteristic view which shows the propagation condition of a vibration wave when a crack reaches a harmful depth.

  In FIG. 1A, two cracks C1 and C2 are generated on the surface of the concrete W to be measured, and the oscillating means 1 is arranged on one surface sandwiching them. Then, the oscillation means 1 oscillates a vibration wave having a specific frequency f (described later) on one side of the surface of the concrete W with the cracks C1 and C2 interposed therebetween, and on one side and the other side of the cracks C1 and C2. At points A and B, the amplitude of the vibration wave is detected by the laser Doppler vibrometers 11 and 12, and the degree of attenuation of the vibration wave amplitude is measured based on both detection values. When the laser Doppler vibrometers 11 and 12 are used, non-contact and quick measurement is possible.

  Here, as shown in (c), the harmful cracks to be measured are those in which the depth of cracks C1 and C2 is equal to or greater than the cover thickness d of the concrete W and reaches the rebar 10 inside the concrete. Point to. This is because when it reaches the reinforcing bar 10, moisture penetrates and the reinforcing bar 10 is corroded.

Therefore, the reference for the harmful depth of cracking is a value d equal to the concrete cover thickness, and the frequency f of the vibration wave applied by the oscillation means 1 is
f ≒ V / 4d
And That is, a vibration wave having a wavelength λ≈4d is applied to the concrete W.
However, V is the speed of the vibration wave transmitted on the surface of the concrete W. As the speed V, a known value is used or an actually measured value is used.

As a basis for specifying the frequency (wavelength) as described above, the following phenomenon is used.
That is, if the crack depth is d,
It is a phenomenon that it is easy to attenuate when the wavelength λ is 4d or less.

  When the specific frequency f is oscillated as described above, as shown in FIG. 1B, when the depths of the cracks C1 and C2 are shallow, the attenuation is reduced, but the depths of the cracks C1 and C2 are small. When it is deep enough to reach the reinforcing bar 10, a phenomenon in which the attenuation is remarkably increased is observed. Accordingly, by measuring the degree of attenuation of the amplitude of the vibration wave received on the other side across the cracks C1 and C2, the cracks C1 and C2 are deeper than the reference d, that is, deep enough to reach the reinforcing bar 10. It can be judged whether it is true.

  Thus, according to the measurement method of the present embodiment, the depth of the cracks C1 and C2 on the surface of the concrete W is not estimated from the arrival time or phase change of the initial wave, but the vibration of the specific frequency f. Focusing on the attenuation of the wave amplitude when a wave is applied, it is possible to make a quick and accurate measurement to estimate whether the crack has a harmful depth (that is, a crack that reaches the reinforcing bar 10). It becomes. If it is known that the cracks C1 and C2 have not reached the reinforcing bar 10, it can be determined that there is no need for immediate repair because there is no concern about the corrosion of the reinforcing bar.

Next, another embodiment of the present invention will be described with reference to FIG.
The measurement method of this embodiment is to visualize and display the position where harmful cracks exist on a display or the like.

  In this measurement method, first, as a first step, as shown in the flowchart of FIG. 2A and the situation explanatory diagram of FIG. 2B, the vibration wave from the oscillating means 1 is applied to the surface of the concrete W having cracks C1 and C2. In addition, the laser Doppler vibrometers 11 and 12 measure vibrations at various points. At that time, the laser Doppler vibrometer 12 receives vibration waves while scanning the entire concrete surface, thereby acquiring information on the positions, widths, and lengths of the cracks C1, C2 on the surface of the concrete W.

Next, as a second step, when the reference for the harmful depth of cracking is d (concrete cover thickness) and the transmission speed of the vibration wave to be used on the concrete W surface is V, the surface of the concrete W is oscillated by the oscillation means 1. Is given a vibration wave of the following frequency f,
f ≒ V / 4d
By scanning the surface of the concrete W with the laser Doppler vibrometer 12, the degree of attenuation of the vibration wave propagating beyond the cracks C1 and C2 is measured, and the position of the crack having a depth greater than the reference d is determined. To detect.

  And as shown in (c) as a 3rd process, based on the information acquired at the 1st process, while displaying the position of crack C1, C2 on the concrete surface visually, on the display, the above-mentioned The positions of cracks having a depth greater than or equal to the reference d measured in two steps are displayed so as to be distinguishable from each other.

Thus, since not only the information on the crack positions C1 and C2 and the width and length but also the position of only the harmful crack is displayed, it is possible to efficiently deal with after the measurement.
In the present invention, not only the non-contact type laser Doppler vibrometer but also other types of vibrometers such as a contact type vibrometer can be used.

It is explanatory drawing of the measuring method of embodiment of this invention, (a) is a figure which shows the implementation condition of a measuring method, (b) is a characteristic figure which shows the propagation condition of a vibration wave when a crack does not reach a harmful depth (C) is a characteristic view which shows the propagation state of a vibration wave when a crack reaches a harmful depth. It is explanatory drawing of the measuring method of other embodiment of this invention, (a) is a flowchart which shows a process, (b) is a figure which shows the implementation condition of a measuring method, (c) shows the display of the measurement result on a display. FIG. It is explanatory drawing of the conventional measuring method.

Explanation of symbols

W Concrete C1, C2 Crack 1 Oscillation means 11, 12 Laser Doppler vibrometer (vibrometer)

Claims (4)

A method of measuring a crack of harmful depth on a concrete surface by oscillating a vibration wave on one side across a crack on the concrete surface and receiving the vibration wave propagating inside the concrete on the other side. ,
When the reference of the harmful depth of the crack is d and the transmission speed of the vibration wave on the concrete surface is V, a vibration wave having the next frequency f is oscillated on one side of the crack,
f ≒ V / 4d
By measuring the degree of attenuation of the amplitude of the vibration wave received on the other side across the crack, it is evaluated whether the crack is deeper than the reference d or lower than the reference d. Method for measuring cracks in harmful depth of concrete surface.   2. The method for measuring cracks of harmful depth on a concrete surface according to claim 1, wherein the reference d for the harmful depth of cracks is the cover thickness of the concrete with respect to the reinforcing bars inside the concrete.   The amplitude of the vibration wave is detected by a vibrometer on one side and the other side across the crack, and the degree of attenuation of the amplitude of the vibration wave is measured based on both detection values. Item 3. A method for measuring cracks of harmful depth on a concrete surface according to Item 1 or 2. A vibration wave is applied to a concrete surface having cracks, and the entire concrete surface is scanned by a vibrometer and the vibration waves are received, thereby obtaining information on the position, width, and length of cracks on the concrete surface. Process,
When the criterion of the harmful depth of the crack is d and the transmission speed of the vibration wave to be used on the concrete surface is V, a vibration wave having the following frequency f is given to the concrete surface,
f ≒ V / 4d
A second step of detecting the position of a crack having a depth greater than or equal to the reference d by measuring the degree of attenuation of the vibration wave propagating beyond the crack by scanning the concrete surface with a vibrometer; When,
Based on the information acquired in the first step, the position of the crack on the concrete surface is visually displayed, and on the display, the position of the crack having a depth greater than the reference d measured in the second step is displayed. A third step for visual display so that it can be distinguished from the others;
A method for measuring cracks of harmful depth on a concrete surface, characterized by comprising:

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