JP2011027586A - Crack depth measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crack depth measurement method for correctly measuring a crack depth formed from a surface of a hardened cement object to the inside. <P>SOLUTION: In the crack depth measurement method, the crack depth is calculated by the first formula: d=-α×λ×InF. In the first formula, the d is the crack depth (mm), and the λ is a primary wavelength (mm). The F is an amplitude ratio obtained by dividing the second minimum negative amplitude fluctuated toward the negative side right after a surface wave is initiated among the second surface waves propagated on a surface of the hardened cement object and detected in a second sensor 13 by the first minimum negative amplitude fluctuated toward the negative side right after the surface wave is initiated among the first surface waves propagated on the surface of the hardened cement object and detected in a first sensor 12, and the α is a constant (0.381) calculated from an approximate expression: y=αe<SP>bx</SP>derived from a correlation diagram for indicating the (F) along a vertical axis, and a ratio of the crack depth (d)/the primary wavelength (λ) along a horizontal axis. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a crack depth measuring method for measuring the depth of a crack generated in a hardened cement material.

  Based on the detected surface wave, the hammer hits a striking position that is a predetermined distance away from the crack position generated in the concrete structure with a steel ball hammer and detects the surface wave propagating through the concrete structure using an acceleration sensor. There is a crack depth measurement method for measuring the crack depth (see Patent Document 1). In this measurement method, the crack depth is calculated by the formula: H = C1 · λ · In (x) + C2. Here, (H) is the crack depth from the surface of the concrete structure, (λ) is the wavelength of the surface wave, (x) is the amplitude ratio, and (C1) and (C2) are theoretical or test constants. The amplitude ratio (x) is a value obtained by dividing the signal amplitude (corrected) detected by each sensor after cracking by the signal amplitude (corrected) detected by each sensor before cracking.

JP 2001-12933 A

  The crack depth measurement method disclosed in Patent Document 1 detects a surface wave among elastic waves propagating through a concrete structure, and measures the crack depth based on the surface wave. It is not clear whether to use surface waves at the time. The surface wave itself decays with the passage of time, and since the reflected wave and diffraction wave are included in the surface wave with the passage of time, the wavelength and waveform of each surface wave differ depending on the detection time of the surface wave, When these different surface waves are employed, different crack depths are measured, and the accurate crack depth may not be measured.

  The objective of this invention is providing the crack depth measuring method which can measure correctly the crack depth formed toward the inside from the surface of the cement hardened | cured material.

  The premise of the present invention for solving the above-mentioned problem is that the hardened cement is formed by striking a striking position separated by a predetermined dimension from a crack position formed from the surface of the hardened cement material toward the inside with a steel ball hammer having a predetermined diameter. This is a crack depth measurement method that generates an elastic wave in an object and detects the elastic wave propagating through the hardened cement material, and measures the crack depth of the hardened cement material based on the detected elastic wave.

  The first feature of the present invention based on the above premise is that the crack depth measuring method is installed at a first installation position between the crack position and the striking position, and propagates from the striking position to the surface of the hardened cement material. A first sensor that detects a wave and a second surface that is installed at a second installation position on the opposite side of the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor for detecting waves,

によって算出され、 Crack depth is formula 1

Calculated by

In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor by propagating on the surface of the hardened cement material, The minimum second minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave is the minus side of the first surface wave detected by the first sensor after propagating through the surface of the hardened cement material. Is the amplitude ratio divided by the minimum first minus-side amplitude, and α is a correlation indicating (F) on the vertical axis and the ratio of crack depth (d) / major wavelength (λ) on the horizontal axis. An approximate expression: y = αe ^bx is derived from the figure, and is a constant (0.381) calculated from the approximate expression.

  The second feature of the present invention based on the above premise is that the crack depth measuring method is installed at a first installation position between the crack position and the striking position, and propagates from the striking position to the surface of the hardened cement material. A first sensor that detects a wave and a second surface that is installed at a second installation position on the opposite side of the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor for detecting waves,

によって算出され、 Crack depth is formula 1

Calculated by

In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor by propagating on the surface of the hardened cement material, The maximum second plus side amplitude that first swung to the plus side after the initial motion of the surface wave is the first of the first surface waves that are detected by the first sensor by propagating through the surface of the cemented material, and after the first motion of the surface wave. Amplitude ratio divided by the maximum first plus side amplitude swung to the plus side, α indicates (F) on the vertical axis, and ratio of crack depth (d) / major wavelength (λ) on the horizontal axis The approximate expression: y = αe ^bx is derived from the correlation diagram, and is a constant (0.398) calculated from the approximate expression.

  The third feature of the present invention based on the above premise is that the crack depth measurement method is installed at a first installation position between the crack position and the striking position, and propagates from the striking position to the surface of the hardened cement material. A first sensor that detects a wave and a second surface that is installed at a second installation position on the opposite side of the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor for detecting waves,

によって算出され、 Crack depth is formula 1

Calculated by

In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor by propagating on the surface of the hardened cement material, The second absolute value of the minimum second minus side amplitude that swung to the minus side immediately after the surface wave initial motion and the maximum second plus side amplitude that swung to the plus side first after the surface wave first motion Among the first surface waves propagated and detected by the first sensor, the minimum first minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave and the first maximum that has swung to the plus side first after the initial motion of the surface wave Amplitude ratio divided by the first absolute value with respect to the plus side amplitude, α is a correlation indicating (F) on the vertical axis and the ratio of crack depth (d) / major wavelength (λ) on the horizontal axis. approximate expression Figures: leads to y = .alpha.e ^bx, a constant calculated from the approximate formula (0.394) In the Rukoto.

によって算出され、第２式において、ｃが、鋼球ハンマーの直径によって異なる表面波の平均伝搬速度（ｍ／ｓｅｃ）、ｆ_ｃが、重心周波数（ｋＨｚ）であり、 As an example of the present invention having the first to third features, (λ) is the second formula

Is calculated by the second equation, c is the average propagation velocity of the surface waves varies depending on the diameter of the steel ball hammer (m / sec), _{f c} is the center of gravity frequencies (kHz),

によって算出され、第３式において、Ｘ（ｆ_ｋ）が、周波数（ｆ_ｋ）における振幅値、Ｎが、サンプリング数である。 (F _c ) is the third formula

In the third equation, X (f _k ) is the amplitude value at the frequency (f _k ), and N is the number of samplings.

As another example of the present invention having the first to third features, in the crack depth measurement method, calculations from the first expression to the third expression are performed using a computer, and the computer is changed to the third expression. A center-of-gravity frequency calculating unit for determining a center-of-gravity frequency (f _c ) based on the above, a main wavelength calculating unit for calculating a main wavelength (λ) based on the second equation, and a crack depth (d) based on the first equation. And a calculation result storage means for storing the calculated center-of-gravity frequency (f _c ), principal wavelength (λ), and crack depth (d).

  As another example of the present invention having the first to third features, in the crack depth measurement method, the striking position, the first installation position, and the second installation position are arranged in a substantially straight line, and the first from the striking position. The separation dimension to the setting position, the separation dimension from the first setting position to the crack position, and the separation dimension from the crack position to the second installation position are the same, and these separation dimensions are in the range of 90 to 110 mm.

  As another example of the present invention having the first to third features, in the crack depth measurement method, the surface wave detection interval of the first and second sensors is in the range of 1 to 5 μsec, and the first and second The surface wave detection time of the sensor is in the range of 0.01 to 0.03 seconds.

  According to the crack depth measuring method of the present invention having the first feature, the surface of the second surface wave detected by the second sensor as the amplitude ratio (F) in the first equation for calculating the crack depth. Divide the minimum second minus side amplitude that has swung to the minus side immediately after the initial wave motion by the minimum first minus side amplitude that has swung to the minus side immediately after the initial surface wave of the first surface wave detected by the first sensor. Therefore, the surface wave for deriving the amplitude ratio (F) does not include an extra wave such as a reflected wave or a diffraction wave. In this crack depth measurement method, only one type of surface wave that shook to the minus side immediately after the initial motion of the surface wave was used to measure the crack depth, so that various surface waves and other waves were mixed. The measurement error of the crack depth due to the use of the surface wave can be prevented, and the accurate depth of the crack formed from the surface of the hardened cement product to the inside can be measured.

  According to the crack depth measuring method of the present invention having the second feature, the surface of the second surface wave detected by the second sensor as the amplitude ratio (F) in the first equation for calculating the crack depth. The maximum second plus side amplitude that first swung to the plus side after the first wave motion is the maximum first plus side amplitude that has swung to the plus side first after the surface wave first motion among the first surface waves detected by the first sensor. Therefore, the reflected wave and the diffracted wave are not included in the surface wave for deriving the amplitude ratio (F). This crack depth measurement method uses only one type of surface wave that first swung to the positive side after the initial motion of the surface wave to measure the crack depth, so that various surface waves and other waves are mixed. The measurement error of the crack depth due to the use of the surface wave can be prevented, and the accurate depth of the crack formed from the surface of the hardened cement product to the inside can be measured.

  According to the crack depth measuring method of the present invention having the third feature, the surface of the second surface wave detected by the second sensor as the amplitude ratio (F) in the first equation for calculating the crack depth. A first absolute value detected by the first sensor is a second absolute value of the minimum second minus side amplitude that has swung to the minus side immediately after the initial wave motion and the maximum second plus side amplitude that has swung to the plus side first after the initial motion of the surface wave. Divide by the first absolute value of the minimum first minus side amplitude that swings to the minus side immediately after the initial surface wave of one surface wave and the maximum first plus side amplitude that swings to the plus side first after the surface wave initial motion. Therefore, the reflected wave and the diffracted wave are not included in the surface wave for deriving the amplitude ratio (F). In this crack depth measurement method, the absolute value of the surface wave that shook to the negative side immediately after the initial motion of the surface wave and the surface wave that first shook to the positive side after the initial motion of the surface wave should be used to measure the crack depth. Therefore, it is possible to prevent crack depth measurement errors due to the use of surface waves mixed with multiple types of surface waves and other waves. Accurate depth can be measured.

The crack depth measurement method for calculating the principal wavelength (λ) by the second equation and calculating the center-of-gravity frequency (f _c ) by the third equation is most affected by using the third equation among the detected elastic waves. The frequency (centroid frequency) of a certain elastic wave component can be obtained, and the principal wavelength is obtained using the center of gravity frequency, so the elastic wave component does not contain other unnecessary components, and the elastic wave component It is possible to prevent crack depth measurement errors due to the inclusion of other unnecessary components in the crack, and to measure the exact depth of cracks formed from the surface of the hardened cement product to the inside.

The crack depth measurement method in which the calculations according to the first to third formulas are performed using a computer, the main wavelength of the elastic waves detected by the first and second sensors by causing the computer to perform each calculation. (Λ) and the center-of-gravity frequency (f _c ) of the most influential elastic wave component can be accurately calculated. Further, based on the calculated main wavelength (λ) and center-of-gravity frequency (f _c ), The exact depth of the crack formed from the surface toward the inside can be calculated.

  The striking position, the first installation position, and the second installation position are arranged in a substantially straight line, the separation dimension from the striking position to the first setting position, the separation dimension from the first setting position to the crack position, and the second installation from the crack position. In the crack depth measurement method in which the separation distance to the position is the same, if the positions are separated by different dimensions, the consistency of the surface waves detected by the first and second sensors cannot be taken. By aligning the first installation position, the crack position, and the second installation position in a straight line at equal intervals, the consistency of the surface waves detected by the first and second sensors can be taken, and the detection is performed by these sensors. The detection error of the surface wave can be prevented, and the accurate depth of the crack formed from the surface of the hardened cement product to the inside can be measured.

  The crack depth measurement method in which the surface wave detection interval of the first and second sensors is 1 to 5 μsec, and the surface wave detection time of the first and second sensors is 0.01 to 0.03 seconds. By setting the interval within the above range, an accurate waveform of the surface wave detected by the first and second sensors can be drawn, and based on the waveform of the surface wave, from the surface of the hardened cement material to the inside. The exact depth of the formed crack can be measured. In addition, by setting the surface wave detection time within the above range, it is possible to confirm that the detected waveform is a stack of excess energy components due to phenomena such as reflection and diffraction. The amplitude can be accurately identified, and only the surface wave can be detected without the surface wave to be detected being affected by an extra wave such as a reflected wave or a diffraction wave.

The schematic block diagram of the crack depth measurement system shown as an example. The top view of the concrete structure for a test shown as an example. The top view of the concrete structure for a test shown as an example. The side view of the concrete structure for a test. The figure which shows the mixing | blending of the concrete structure for a test. The perspective view of the steel ball hammer shown as an example. The figure which shows an example of the waveform detected in the healthy part and the crack position of a different depth. The figure which shows an example of the detection waveform of the elastic wave generated with the steel ball hammer of diameter 15mm. The figure showing the gravity center frequency and main wavelength by the steel ball hammer of a different diameter. The figure which shows the correlation of amplitude ratio (F) calculated by the 1st case, and d / λ. The figure which shows the correlation of the amplitude ratio (F) calculated by the 2nd case, and d / λ. The figure which shows the correlation of amplitude ratio (F) calculated by the 3rd case, and d / λ. The figure which shows an example of an initial screen. The figure which shows an example of a calculation formula selection screen. The figure which shows an example of a measurement start screen. The figure which shows an example of a measurement result screen.

  The details of the crack depth measuring method according to the present invention will be described with reference to FIG. 1 which is a schematic configuration diagram of a crack depth measuring system 11 shown as an example. A crack depth measurement system 11 that executes a crack depth measurement method includes a first sensor 12 and a second sensor 12 that are installed in the vicinity of a crack position that is formed from the surface of the hardened cement product to the inside thereof, and these sensors. The computer 14 calculates the crack depth (d) (see FIG. 4) of the hardened cement based on the surface waves detected by the numerals 12 and 13. The hardened cement includes concrete structures (including structures made of mortar) such as dams, tunnels, and walls made of concrete.

  The hardened cement product is deteriorated by the influence of a load, drying shrinkage, temperature change, reinforcing bar corrosion, and the like, and cracks may be generated at arbitrary locations. The cracks generated in the hardened cement material greatly reduce the function of the hardened cement material depending on its width and depth, occurrence location, crack distribution, and the like. Repair is required to restore the function of the hardened cement, but it is necessary to measure the crack depth before repair. The crack depth measurement method executed by the system 11 is a steel ball hammer 17 (see FIG. 6) having a predetermined diameter at a striking position 18A (see FIGS. 2 and 3) spaced a predetermined dimension from a crack position generated in a hardened cement material. The crack depth (d) is measured on the basis of the detected surface wave while detecting the surface wave (Rayleigh wave) propagating through the cement hardened material. To do.

  2 and 3 are top views of the test concrete structures 15 and 16 shown as examples, and FIG. 4 is a side view of the test concrete structures 15 and 16. FIG. 5 is a view showing the composition of the test concrete structures 15 and 16, and FIG. 6 is a perspective view of a steel ball hammer 17 shown as an example. As the first and second sensors 12 and 13, acceleration sensors showing flat characteristics up to 30 kHz are used. The first and second sensors 12 and 13 are placed opposite to the surfaces of the concrete structures 15 and 16 with the crack position 20 in between. These sensors 12 and 13 are connected to a computer 14 via an interface. The first sensor 12 is installed at a first installation position 19 that is separated from the crack position 20 by a predetermined dimension. The second sensor 13 is installed at a second installation position 21 that is opposite to the first installation position 19 across the crack position 20 and that is separated from the crack position 20 by a predetermined dimension.

  As shown in FIGS. 2 to 4, the impact position 18 </ b> A, the first installation position 19 where the first sensor 12 is installed, the crack position 20, the second installation position 21 where the second sensor 13 is installed, and the impact position 18 </ b> B are substantially as shown in FIGS. It is aligned on a straight line. In addition, the separation dimension from the striking position 18A to the first setting position 19, the separation dimension from the first setting position 19 to the crack position 20, the separation dimension from the crack position 20 to the second installation position 21, and the second installation position 21. The separation dimension L1 to the striking position 18B is the same, and the positions 18A, 19, 20, 21, 18B are separated at equal intervals. The distance L1 between the positions 18A, 19, 20, 21, 18B is in the range of 90 to 110 mm, preferably 100 mm. When measuring the crack depth L1 generated in an actual concrete structure or mortar structure other than for testing, the striking positions 18A, B and the first and second installation positions 19, 21, the positions 18A, 19, 20, The distance between 21 and 18B is the same as that of the test concrete structures 15 and 16.

  The first sensor 12 detects a first surface wave that propagates from the striking position 18A to the surface of the test concrete structures 15 and 16 (including the actual cement hardened material having cracks), and detects the detected first surface wave. Is output to the computer 14. The second sensor detects the second surface wave that propagates from the striking position 18A through the surface of the concrete structures 15 and 16 for test (including the actual hardened cement material that has cracked) and passes through the cracking position 20. The detected second surface wave is output to the computer 14. The surface wave detection interval of the first and second sensors 12 and 13 is in the range of 1 to 5 μsec, preferably in the range of 1 to 3 μsec, and more preferably 1 μsec. The surface wave detection time of the first and second sensors 12, 13 is in the range of 0.01 to 0.03 seconds, preferably 0.01 seconds.

  The computer 14 has a central processing unit (CPU or MPU) and a memory, and incorporates a large-capacity hard disk. Input devices such as a mouse 22 and a keyboard 23 and output devices such as a display 24 and a printer (not shown) are connected to the computer 14 via an interface. The memory of the computer 14 stores applications for causing the computer 14 to execute various means (various processes).

The hard disk of the computer 14 has a first formula for calculating the crack depth (d), a second formula for calculating the main frequency (λ), a third formula for calculating the center of gravity frequency (f _c ), and steel balls having different diameters. The center-of-gravity frequency and the main wavelength (see FIG. 8) by the hammer 17 are stored. Further, the hard disk stores specific information for specifying the actual hardened cement material having cracks. Specific information includes the name of the hardened cement, the address of the place where the hardened cement exists, an image of the hardened cement, a number indicating the order of cracks to be measured, and the date and time when the cracks were measured. In the specific information, an identifier for individually identifying the hardened cement is set. The first to third formulas are shown below.
(Formula 1)

d: crack depth (mm), λ: dominant wavelength (mm), F: amplitude ratio, α: constant (2nd formula)

c: Average propagation speed of surface wave (m / sec), f _c : Centroid frequency (kHz)
(Formula 3)

X (f _k ): amplitude value at frequency (f _k ), N: number of sampling

  The central processing unit of the computer 14 activates an application from the memory based on control by the operating system, and executes the following means (each process) according to the activated application. The central processing unit of the computer 14 includes first continuous waveform generating means for generating a first continuous waveform (first surface wave) of the surface wave based on the surface wave output from the first sensor 12 at a predetermined sampling interval. And a second continuous waveform creating means for creating a second continuous waveform (second surface wave) of the surface wave based on the surface wave output from the second sensor 13 at a predetermined sampling interval.

The central processing unit of the computer 14 executes continuous waveform storage means for storing the created first and second continuous waveforms in the hard disk. The central processing unit executes a center-of-gravity frequency calculating unit that calculates a center-of-gravity frequency (f _c ) based on the third equation, and executes a main wavelength calculating unit that calculates a main wavelength (λ) based on the second equation. . The central processing unit executes a main wavelength and barycentric frequency storage unit (calculation result storage unit) that stores the calculated barycentric frequency (f _c ) and main wavelength (λ) for each diameter of the steel ball hammer 17 and stores them in the hard disk. To do.

  The central processing unit of the computer 14 has a minimum first minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave (see FIG. 8 for the initial motion of the surface wave) of the stored first continuous waveform (first surface wave). Of the stored second continuous waveform (second surface wave), the minimum first minus-side amplitude extracting means for extracting (refer to FIG. 8 for the minus-side amplitude oscillating to the minus side immediately after the initial motion of the surface wave) is executed. Then, the minimum second minus side amplitude extracting means for extracting the minimum second minus side amplitude swung to the minus side immediately after the initial motion of the surface wave is executed. The central processing unit executes amplitude ratio first calculation means for calculating an amplitude ratio (F) by dividing the extracted minimum second minus side amplitude by the minimum first minus side amplitude, and using the first equation A crack depth first calculating means for calculating the crack depth (d) formed from the surface of the predetermined hardened cement material to the inside is executed. Note that the constant (α) of the first equation used in the crack depth first calculation means is 0.381. The central processing unit sets an identifier for individually identifying the hardened cement in the crack depth (d) calculated by the crack depth first calculation means, and stores the crack depth (d) in the hard disk together with the identifier. A depth storage means (calculation result storage means) is executed, and a crack depth output means for outputting the calculated crack depth (d) together with the specific information of the cement hardened material is executed.

  The central processing unit of the computer 14 is the maximum first plus side that first swings to the plus side after the initial motion of the surface wave (see FIG. 8 for the initial motion of the surface wave) in the stored first continuous waveform (first surface wave). The maximum first plus-side amplitude extracting means for extracting the amplitude (see FIG. 8 for the plus-side amplitude that first swings to the plus side after the initial motion of the surface wave) is executed, and the stored second continuous waveform (second surface wave) Among them, the maximum second plus side amplitude extracting means for extracting the maximum second plus side amplitude first swung to the plus side after the initial motion of the surface wave is executed. The central processing unit executes amplitude ratio second calculating means for calculating the amplitude ratio (F) by dividing the extracted maximum second plus side amplitude by the maximum first plus side amplitude, and using the first equation The crack depth second calculation means for calculating the crack depth (d) formed from the surface of the predetermined cement hardened material toward the inside is executed. The constant (α) of the first equation used in the crack depth second calculating means is 0.398. The central processing unit sets an identifier for individually identifying the hardened cement material in the crack depth (d) calculated by the crack depth second calculating means, and stores the crack depth (d) in the hard disk together with the identifier. A depth storage means (calculation result storage means) is executed, and a crack depth output means for outputting the calculated crack depth (d) together with the specific information of the cement hardened material is executed.

  The central processing unit of the computer 14 extracts the minimum first minus side amplitude extraction that extracts the minimum first minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave from the stored first continuous waveform (first surface wave). A maximum first plus-side amplitude extracting means for extracting the maximum first plus-side amplitude that first swings to the plus side after the initial motion of the surface wave out of the stored first continuous waveform (first surface wave). And executing a minimum second minus-side amplitude extracting means for extracting a minimum second minus-side amplitude that has swung to the minus side immediately after the initial motion of the surface wave from the stored second continuous waveform (second surface wave). The maximum second plus-side amplitude extracting means for extracting the maximum second plus-side amplitude that first swings to the plus side after the initial motion of the surface wave from the stored second continuous waveform (second surface wave) is executed.

  The central processing unit of the computer 14 calculates the first absolute value from the extracted minimum first minus side amplitude and the maximum first plus side amplitude, and extracts the extracted minimum second minus side amplitude and the maximum second plus side amplitude. Then, absolute value calculating means for calculating the second absolute value is executed. The central processing unit executes an amplitude ratio third calculation unit that calculates the amplitude ratio (F) by dividing the second absolute value by the first absolute value, and uses the first formula to calculate the predetermined cement hardened material. A crack depth third calculating means for calculating the crack depth (d) formed from the surface toward the inside is executed. The constant (α) of the first formula used in the crack depth third calculation means is 0.394. The central processing unit sets an identifier for individually identifying the hardened cement in the crack depth (d) calculated by the crack depth third calculation means, and stores the crack depth (d) in the hard disk together with the identifier. A depth storage means (calculation result storage means) is executed, and a crack depth output means for outputting the calculated crack depth (d) together with the specific information of the cement hardened material is executed.

  The amplitude ratio (F) and constant (α) were determined using two regular square columnar test concrete structures 15 and 16 (1000 mm × 1000 mm × 1000 mm) shown in FIGS. Asked. The artificial crack H is formed after placing concrete by placing a plurality of steel plates having a thickness of 0.4 mm and a length of 300 mm in a mold (not shown) at different depths before placing the concrete. The steel plates were made by pulling them out of the concrete before hardening. The depth (d) of the crack H is 11 types from 50 mm to 500 mm.

  One test concrete structure 15 has a healthy part (a part without cracks) for comparison on one side, and (d) = 50 mm, 80 mm, 100 mm, 130 mm, and 150 mm artificial cracks on the other side. I made H. The other test concrete structure 16 produced artificial cracks H of (d) = 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, and 500 mm on each side. The length L2 of the artificial crack H is 300 mm.

As shown in FIG. 5, these test concrete structures 15 and 16 use ordinary Portland as cement, W / C is 53.5%, s / a is 46.8%, and coarse aggregate maximum dimension Is 20 mm. The mix of the test concrete structures 15 and 16 is 181 for water, 338 for cement, 819 for fine aggregate, 959 for coarse aggregate, and 3.38 for admixture per unit amount (kg / m ³ ). is there. A φ100 mm cylindrical specimen of the same composition had an average compressive strength of 29.1 MPa, Young's modulus of 26.4 GPa, and Poisson's ratio of 0.19 at the age of 28.

  The measurement of elastic waves in the concrete structures for testing 15 and 16 was performed in the sensor arrangement shown in FIGS. Specifically, the striking position 18A, the first setting position 19, the crack position 20, the second installation position 21 and the striking position 18B are set on a straight line at equal intervals (100 mm intervals). 1 sensor 12 was installed and a second sensor 13 was installed at the second installation position 21. These positions 18A, 19, 20, 21, 18B are at a distance of 150 mm from the side edge of one side to the other side. The elastic wave was generated by hitting hitting positions 18A and 18B with a steel ball hammer 17. In order to generate elastic waves of various frequencies (wavelengths), a steel ball hammer 17 having a diameter L3 (see FIG. 6) of 5 mm, 8 mm, 11 mm, 15 mm, 25 mm, and 35 mm was used. The crack depth measuring method is detected by the first and second sensors 12 and 13 by hitting positions 18A and 18B, the first installation position 19, the crack position 20 and the second installation position 21 being aligned at equal intervals. Therefore, the surface wave detection errors detected by the sensors 12 and 13 can be prevented.

  The elastic wave generated by hitting the steel ball hammer 17 at the hitting positions 18A and 18B propagates through the test concrete structures 15 and 16 and is detected by the first sensor 12, and further passes through the cracking position 20 to the second. It is detected by the sensor 13. The sampling interval (detection interval) of the sensors 12 and 13 is 5 μsec, and the sampling time (detection time) of the sensors 12 and 13 is 0.02 seconds.

In order to reduce the ambient noise, the elastic waves are detected five times and are superposed (stacked), and the striking position is changed from the striking position 18A to the striking position 18B on the second sensor side. Were further detected 5 times, and polymerization processing (stacking) of these elastic waves was performed (see FIG. 4). The average value (F) of the synthesized wave thus obtained was calculated by the following formula. F _1-2 = a ₂ / a ₁ , F _2-1 = a ₁ / a ₂ , F = √F _1-2 × F _2-1 , where F _1-2 is a steel ball at the hitting position 18A A value obtained by generating an elastic wave by hitting the hammer 17 and dividing the elastic wave (a ₂ ) detected by the second sensor 13 by the elastic wave (a ₁ ) detected by the first sensor 12, F _{2− 1} generates an acoustic wave by striking the steel ball hammer 17 in the striking position 18B, in the detected acoustic wave by the first sensor 12 (a ₁₎ of the detected acoustic waves by a second sensor 13 (a ₂₎ It is the value divided. F is a square root of a value obtained by multiplying F _1-2 and F _2-1 . By averaging the data, the inherent error due to the installation positions of the sensors 12 and 13 was reduced.

  In the crack depth measurement method, an accurate waveform of the surface wave detected by the first and second sensors 12 and 13 can be drawn by setting the surface wave detection interval to 5 μsec. Further, by setting the surface wave detection time to 0.02 seconds, it is possible to detect only the surface wave without being influenced by an extra wave such as a reflected wave or a diffraction wave.

  FIG. 7 is a diagram illustrating an example of waveforms detected at a healthy portion and crack positions at different depths. In FIG. 7, the vertical axis represents the crack depth (d), and the horizontal axis represents the elapsed time (sec). The waveform detected by the second sensor 13 in the healthy part was lower in amplitude (energy) than the waveform detected by the first sensor 12. This is presumably because the waves propagated on the surfaces of the concrete structures 15 and 16 were scattered and the wave energy was attenuated. On the other hand, if there was a crack in the wave propagation path, the amplitude of the waveform detected by the second sensor 13 was further reduced compared to that of the healthy part. Further, the larger the crack depth (d), the smaller the amplitude of the waveform. This is probably because the wave was diffracted and reflected due to the presence of cracks, and the energy of the wave was scattered.

  FIG. 8 is a diagram showing an example of a detection waveform of an elastic wave generated by a steel ball hammer 17 having a diameter L3 of 15 mm, and FIG. 9 shows a center-of-gravity frequency and a main wavelength by the steel ball hammer 17 having a different diameter L3. FIG. In FIG. 8, the vertical axis represents amplitude (v) and the horizontal axis represents elapsed time (sec). As shown in FIG. 8, the initial motion amplitude of the surface wave significantly increases after the initial motion amplitude of the P wave (longitudinal wave). The average surface wave velocity was 2247 m / sec.

The center-of-gravity frequency (f _c ) of the elastic wave is calculated from the frequency spectrum obtained by the fast Fourier transform (FFT) according to the third equation. The center-of-gravity frequency (f _c ) is calculated by the computer 14 based on the third equation (center-of-gravity frequency calculating means). The main wavelength (λ) of the surface wave was calculated according to the second equation using the average velocity and the centroid frequency. The main wavelength (λ) of the surface wave is calculated by the computer 14 based on the second equation (main wavelength calculating means). The center-of-gravity frequency and main wavelength (calculation result) divided for each of the various steel ball hammers in FIG. 9 are stored in the hard disk of the computer 14 (calculation result storage means). The crack depth measurement method can determine the frequency (center of gravity frequency) of the elastic wave component having the most influence from the detected elastic waves using the third equation, and uses the center of gravity frequency (f _c ). Thus, since the main wavelength (λ) is obtained, other unnecessary components are not included in the elastic wave component.

  As shown in FIG. 9, the center of gravity frequency of the hammer 17 having a diameter L3 of 5 mm is 18.08 (kHz), the main wavelength is 124 (mm), and the center of gravity frequency of the hammer 17 having a diameter L3 of 8 mm is 11.56 (kHz). In the hammer 17 having a main wavelength of 194 (mm) and a diameter L3 of 11 mm, the center of gravity frequency is 10.74 (kHz), and in the hammer 17 having a main wavelength of 209 (mm) and a diameter L3 of 15 mm, the center of gravity frequency is 9.48 ( The center of gravity frequency is 6.49 (kHz) for the hammer 17 having a major wavelength of 237 (mm) and a diameter L3 of 25 mm, and the center of gravity frequency is 4.4 for the hammer 17 having a major wavelength of 346 (mm) and a diameter L3 of 35 mm. The main wavelength was 19 (kHz) and 537 (mm).

  The amplitude ratio (F) of the surface wave was calculated based on the following three cases so that the crack depth (d) could be measured using the attenuation characteristic of the surface wave. The first case is the minimum second negative wave that has propagated on the surface of the test concrete structures 15 and 16 and has swung to the negative side immediately after the initial motion of the surface wave among the second surface waves detected by the second sensor 13. Among the first surface waves detected by the first sensor 12 by propagating the side amplitude on the surfaces of the test concrete structures 15, 16, the minimum first minus side amplitude swung to the minus side immediately after the initial motion of the surface wave The amplitude ratio (F) was calculated by dividing by.

  In the second case, the second surface wave that propagates through the surfaces of the test concrete structures 15 and 16 and is detected by the second sensor 13 is the maximum second wave that first swings to the plus side after the initial motion of the surface wave. Among the first surface waves detected by the first sensor 12 by propagating on the surface of the test concrete structures 15 and 16 with the positive side amplitude, the maximum first plus that first swung to the positive side after the initial motion of the surface wave The amplitude ratio (F) was calculated by dividing by the side amplitude.

  The third case is the minimum second negative wave that has propagated through the surfaces of the test concrete structures 15 and 16 and detected on the second sensor 13 and has swung to the negative side immediately after the initial surface wave motion. The second absolute value (minimum second minus side amplitude x square root of the maximum second plus side amplitude value) of the side amplitude and the maximum second plus side amplitude that first swung to the plus side after the initial motion of the surface wave is for testing. Of the first surface waves that are propagated through the surfaces of the concrete structures 15 and 16 and detected by the first sensor 13, the minimum first minus side amplitude and the first surface wave initial motion that have swung to the minus side immediately after the surface wave initial motion First, the amplitude ratio (F) was calculated by dividing by the first absolute value (minimum first minus side amplitude × maximum first plus side amplitude square root value) with the maximum first plus side amplitude swung to the plus side first. .

  FIG. 10 is a diagram showing a correlation between the amplitude ratio (F) calculated by the first case and d / λ, and FIG. 11 is a graph showing the correlation between the amplitude ratio (F) calculated by the second case and d / λ. It is a figure which shows correlation with. FIG. 12 is a diagram showing the correlation between the amplitude ratio (F) calculated by the third case and d / λ. In these drawings, the vertical axis indicates the amplitude ratio (F), and the horizontal axis indicates the ratio of crack depth (d) / main wavelength (λ). From the diagram showing these correlations, the first equation for obtaining the crack depth (d) can be derived.

The constant (α) in the first case was calculated from an approximate expression y = αe ^bx derived from the correlation diagram of FIG. The constant (α) in the first case was 0.381. Therefore, the first equation derived by the first case is d = −0.381 · λ · InF, and is stored in the hard disk of the computer 14. In the correlation in FIG. 10, y = e− ^2.6265x and R ² = 0.7743.

The constant (α) in the second case was calculated from the approximate expression obtained by deriving an approximate expression: y = αe ^bx from the diagram showing the correlation in FIG. The constant (α) in the second case was 0.398. Therefore, the first equation derived by the second case is d = −0.398 · λ · InF, and is stored in the hard disk of the computer 14. In the correlation shown in FIG. 11, y = e ^−2.5121x and R ² = 0.7231.

The constant (α) in the third case was calculated from an approximate expression y = αe ^bx derived from the correlation diagram of FIG. The constant (α) in the third case was 0.394. Therefore, the first equation derived by the third case is d = −0.394 · λ · InF, and is stored in the 14 hard disks of the computer. In the correlation shown in FIG. 12, y = e ^−2.5394x and R ² = 0.8767.

  FIG. 13 is a diagram illustrating an example of an initial screen displayed on the display 24, and FIG. 14 is a diagram illustrating an example of a calculation formula selection screen displayed on the display 24. FIG. 15 is a diagram illustrating an example of a measurement start screen displayed on the display 24, and FIG. 16 is a diagram illustrating an example of a measurement result screen displayed on the display 24. In these drawings, numerical values and data are not specifically displayed in the input area and the display area. Also, the first and second sensors 12 and 13 are installed in the state shown in FIGS. 2 to 4 on the surface of the actual hardened cement material where cracks have occurred, and are already in a state where the surface wave can be detected (power ON). Suppose that

  When the computer 14 is activated, an initial screen is displayed on the display 24 connected thereto. On the initial screen, as shown in FIG. 13, a sensor sampling interval setting input area 30, a sensor sampling time setting input area 31, a hammer diameter input area 32, and a cemented material specific information input area are displayed. Button and end button are displayed. In the specific information input area, a name input area 33, an address input area 34, an image input area 35, a number input area 36, and a date / time input area 37 are displayed.

  For example, 5 (μsec) is input to the sensor sampling interval setting input area 30, and 0.02 (second) is input to the sensor sampling time setting input area 31, for example. The sampling interval and sampling time can also be selected from a pull-down list displayed in the sampling interval setting input area 30 and the sampling time setting input area 31. A hammer diameter is input to the hammer diameter input area 32. The hammer diameter can also be selected from a pull-down list displayed in the hammer diameter input area 32.

  Next, for example, a dam name or a tunnel name is input in the name input area 33, and the address of the dam or tunnel is input in the address input area 34. A check mark is placed in either the input check box or the non-input check box in the image input area 35, a number indicating the measurement order is input in the number input area 36, and a measurement date and time is input in the date input area 37. When the measurement order and the measurement date / time are not input, the computer 14 automatically sets the measurement order and the measurement date / time. When the clear button is pressed, the entered numerical values and data are cleared and the numerical values and data are input again. Press the exit button to exit the system. When a check mark is entered in the input check box in the image input area 35, although not shown, an image capture screen is displayed on the display 24, and a cracked image taken with a digital camera is input based on the instructions on the screen. To do.

  When the execution button is pressed after each numerical value or each data is input to these input areas, the computer 14 generates a predetermined identifier, sets the generated identifier in the input numerical value or data, and then sets the numerical value or data. Is stored on the hard disk together with the identifier. Next, the computer 14 displays a calculation formula selection screen on the display 24. On the calculation formula selection screen, as shown in FIG. 14, a formula display area 38 for displaying the first formula derived in the first case, and a formula for displaying the first formula derived in the second case. A display area 39, an expression display area 40 for displaying the first expression derived in the third case, check boxes corresponding to the expression display areas 38 to 40 are displayed, and an execution button, a clear button, and a cancel button are displayed. Is done. When a chuck mark is put in any of these check boxes and the execution button is pressed, the computer 14 sets an identifier for the selected calculation formula, and stores the calculation formula together with the identifier in the hard disk.

  After storing the calculation formula, the computer 14 displays a measurement start screen on the display 24. On the measurement start screen, as shown in FIG. 15, the sampling interval set in the sampling interval display area 41, the sampling time set in the sampling time display area 42, the hammer diameter in the hammer diameter display area 43, and the calculation formula display area 44 The selected calculation formula, the name input in the name display area 45, the address input in the address display area 46, the image input in the image display area 47, the number in the number display area 48, and the date and time in the date display area 49 are displayed. In addition, a start button, a return button, and an end button are displayed. The numerical values and data displayed in the display areas 41 to 49 are confirmed. If there is a change in the numerical values or data, the return button is pressed to return to the initial screen and input each numerical value or each data again. If there are no changes to the values or data, press the start button. When the start button is pressed, the computer 14 outputs a surface wave detection command to the first and second sensors 12 and 13.

  When the hardened cement hitting position 18A is hit with the steel ball hammer 17, the elastic wave generated from the hitting position 18A propagates through the hardened cement. The surface wave generated from the striking position 18A propagates on the surface of the hardened cement material. The first sensor 12 installed at the first installation position 19 detects a surface wave that has propagated from the striking position 18A and reached the first installation position 19 at a sampling interval and a sampling time. The second sensor 13 installed at the second installation position 21 propagates from the striking position 18A, passes through the crack position 20, and detects the surface wave that reaches the second installation position 21 at a sampling interval and a sampling time. The first and second sensors 12 and 13 output the detected surface waves to the computer 14 in time series. The computer 14 creates a first continuous waveform (first surface wave) of the surface wave based on the surface wave outputted from the first sensor 12 (first continuous waveform creating means), and outputs it from the second sensor 13. Based on the surface wave thus generated, a second continuous waveform (second surface wave) of the surface wave is created (second continuous waveform creating means). The computer 14 stores the created first and second continuous waveforms in the hard disk (continuous waveform storage means).

  When the first formula derived in the first case is selected on the calculation formula selection screen, the computer 14 sets the first continuous waveform (first surface wave) stored to the minus side immediately after the initial motion of the surface wave. The minimum first minus-side amplitude that has been shaken is extracted (minimum first minus-side amplitude extracting means), and the minimum second that has swung to the minus side immediately after the initial motion of the surface wave is stored among the stored second continuous waveforms (second surface waves). 2. Extract the minus side amplitude (minimum second minus side amplitude extracting means). The computer 14 extracts the main wavelength (λ) corresponding to the input hammer diameter from the hard disk.

  The computer 14 calculates the amplitude ratio (F) by dividing the extracted minimum second minus side amplitude by the minimum first minus side amplitude (amplitude ratio first calculating means), and the amplitude ratio (F) and the main wavelength ( λ) is applied to the first formula (d = −0.381 · λ · InF) derived in the first case, and the crack depth (d) of the hardened cement material is calculated based on the first formula. Calculate (crack depth first calculation means). The computer 14 sets an identifier for the crack depth (d) calculated by the crack depth first calculation means, and stores the crack depth (d) in the hard disk together with the identifier (crack depth storage means). Further, the computer 14 displays the crack depth (d) on the display 24 together with the specific information of the cement hardened material (crack depth output means).

  In the measurement result screen displayed on the display 24, as shown in FIG. 16, the sampling interval set in the sampling interval display area 50, the sampling time set in the sampling time display area 51, the hammer diameter in the hammer diameter display area 52, The center of gravity frequency is displayed in the center of gravity frequency display area 53, the main wavelength is displayed in the main wavelength display area 54, the first expression derived by the first case in the calculation formula display area 55, and the crack depth measured in the crack depth display area 56 (d ) Is displayed. Further, the name input in the name display area 57, the address input in the address display area 58, the image input in the image display area 59, the number in the number display area 60, and the date in the date display area 61 are displayed. A screen button and an end button are displayed. When the print button is pressed, the computer 14 outputs the specific information and crack depth (d) of the hardened cement displayed on the measurement result screen in a predetermined format via the printer (crack depth output means).

  The crack depth measurement method using the first equation derived by the first case is detected by the second sensor 13 as the amplitude ratio (F) in the first equation for calculating the crack depth (d). Of the second surface waves, the minimum second minus side amplitude that has swung to the minus side immediately after the first wave of the surface wave is swung to the minus side immediately after the first wave of the surface wave of the first surface wave detected by the first sensor 12. Further, since the ratio divided by the minimum first minus side amplitude is adopted, the surface wave for deriving the amplitude ratio (F) does not include an extra wave such as a reflected wave or a diffraction wave. This crack depth measurement method uses only one type of surface wave that sways to the minus side immediately after the initial motion of the surface wave to measure the crack depth (d), so that various surface waves and other waves can be detected. Measurement error of crack depth (d) due to use of mixed surface wave can be prevented, and accurate depth of crack formed from the surface of the hardened cement product to the inside can be measured. .

  When the first formula derived in the second case is selected on the calculation formula selection screen, the computer 14 first stores the first continuous waveform (first surface wave) on the plus side after the initial motion of the surface wave. The maximum first plus-side amplitude swung to the maximum is extracted (maximum first plus-side amplitude extracting means), and among the stored second continuous waveforms (second surface waves), the first first swing to the plus side after the initial motion of the surface wave The maximum second plus side amplitude extracting means is extracted (maximum second plus side amplitude extracting means extracting means). The computer 14 extracts the main wavelength (λ) corresponding to the input hammer diameter from the hard disk.

  The computer 14 calculates the amplitude ratio (F) by dividing the extracted maximum second plus side amplitude by the maximum first plus side amplitude (amplitude ratio second calculating means), and the amplitude ratio (F) and the main wavelength ( λ) is applied to the first equation (d = −0.398 · λ · InF) derived in the second case, and the crack depth (d) of the hardened cement material is calculated based on the first equation. Calculate (crack depth second calculation means). The computer 14 sets an identifier for the crack depth (d) calculated by the crack depth second calculating means, and stores the crack depth (d) in the hard disk together with the identifier (crack depth storage means). Further, when there is an instruction to output the calculated crack depth (d), the computer 14 displays the crack depth (d) on the display 24 together with the specific information of the cement hardened material, or outputs it via a printer ( Crack depth output means). The measurement result screen displayed on the display 24 uses FIG. 16 and its description is omitted.

  The crack depth measurement method using the first equation derived from the second case is detected by the second sensor 13 as the amplitude ratio (F) in the first equation for calculating the crack depth (d). Of the second surface waves, the maximum second plus side amplitude that first swung to the plus side after the first wave of the first surface wave is detected. Since the ratio divided by the maximum first plus side amplitude swayed is used, the reflected wave and the diffracted wave are not included in the surface wave for deriving the amplitude ratio (F). This crack depth measurement method uses only one type of surface wave that first swung to the positive side after the initial motion of the surface wave to measure the crack depth (d). It is possible to prevent cracking depth (d) measurement errors due to the use of surface waves mixed with, and to measure the exact depth of cracks formed from the surface of the hardened cement product to the inside. it can.

  When the first formula derived in the third case is selected on the calculation formula selection screen, the computer 14 sets the first continuous waveform (first surface wave) stored to the minus side immediately after the initial motion of the surface wave. The minimum first minus-side amplitude that has been shaken is extracted (minimum first minus-side amplitude extracting means), and among the stored first continuous waveforms (first surface waves), the maximum that first swings to the plus side after the initial motion of the surface wave While extracting the first plus side amplitude (maximum first plus side amplitude extracting means), among the stored second continuous waveforms (second surface waves), the minimum second minus that has swung to the minus side immediately after the initial motion of the surface wave The side amplitude is extracted (minimum second minus side amplitude extracting means), and the maximum second plus side amplitude that first swings to the plus side after the initial motion of the surface wave is stored in the stored second continuous waveform (second surface wave). Extract (maximum second plus side Width extraction means). The computer 14 extracts the main wavelength (λ) corresponding to the input hammer diameter from the hard disk.

  The computer 14 calculates the first absolute value from the extracted minimum first minus side amplitude and the maximum first plus side amplitude, and calculates the first absolute value from the extracted minimum second minus side amplitude and the maximum second plus side amplitude. A second absolute value is calculated (absolute value calculating means). Next, the computer 14 calculates the amplitude ratio (F) by dividing the second absolute value by the first absolute value (amplitude ratio third calculation means), and the amplitude ratio (F), the main wavelength (λ), and the like. Is applied to the first formula (d = −0.394 · λ · InF) derived in the third case, and the crack depth (d) of the hardened cement is calculated based on the first formula ( Crack depth second calculation means).

  The computer 14 sets an identifier for the crack depth (d) calculated by the crack depth third calculation means, and stores the crack depth (d) in the hard disk together with the identifier (crack depth storage means). Further, when there is an instruction to output the calculated crack depth (d), the computer 14 displays the crack depth (d) on the display 24 together with the specific information of the cement hardened material, or outputs it via a printer ( Crack depth output means). The measurement result screen displayed on the display 24 uses FIG. 16 and its description is omitted.

  The crack depth measurement method using the first equation derived by the third case is detected by the second sensor 13 as the amplitude ratio (F) in the first equation for calculating the crack depth (d). Of the second surface wave, the second absolute value of the minimum second minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave and the maximum second plus side amplitude that has swung to the plus side first after the surface wave initial motion is obtained. Of the first surface waves detected by the first sensor 12, the minimum first minus side amplitude that has swung to the minus side immediately after the initial motion of the surface wave, and the maximum first plus side that has swung to the plus side first after the surface wave initial motion. Since the ratio divided by the first absolute value with respect to the amplitude is employed, the reflected wave and the diffracted wave are not included in the surface wave for deriving the amplitude ratio (F). This crack depth measurement method is used to measure the crack depth (d) by calculating the absolute value of the surface wave that shook to the minus side immediately after the initial motion of the surface wave and the surface wave that first shook to the plus side after the initial motion of the surface wave. This will prevent the measurement error of crack depth (d) due to the use of various surface waves and surface waves mixed with other waves. It is possible to measure the exact depth of the crack formed.

DESCRIPTION OF SYMBOLS 11 Crack depth measurement system 12 1st sensor 13 2nd sensor 14 Computer 15 Concrete structure for a test (hardened cement material)
16 Concrete structure for testing (hardened cement)
17 Steel ball hammer 18A Hitting position 18B Hitting position 19 First installation position 20 Cracking position 21 Second installation position L1 Separation dimension L2 Diameter

Claims (7)

An impact wave separated by a predetermined distance from the crack position formed on the hardened cement material is hit by a steel ball hammer having a predetermined diameter to generate an elastic wave in the hardened cement material, and the elastic wave is detected from the hardened cement material However, in the crack depth measurement method for measuring the crack depth based on the detected elastic wave,
The crack depth measuring method is a first sensor that is installed at a first installation position between the crack position and the striking position and detects a first surface wave propagating from the striking position to the surface of the hardened cement material. And a second surface wave that is installed at a second installation position opposite to the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor to detect,
The crack depth is the first formula

Calculated by
In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor as it propagates through the surface of the hardened cement material. Among the first surface waves detected by the first sensor by propagating through the surface of the hardened cement material with the minimum second minus side amplitude that has swung to the minus side immediately after the surface wave initial movement. Is the amplitude ratio divided by the minimum first minus-side amplitude that oscillates to the minus side immediately after ## EQU2 ## where α represents the above-mentioned (F) on the ordinate, and the crack depth (d) / principal wavelength (λ) on the abscissa. A crack depth measurement method, wherein an approximate expression: y = αe ^bx is derived from a correlation diagram showing the ratio of the above, and is a constant (0.381) calculated from the approximate expression. An impact wave separated by a predetermined distance from a crack position formed in the hardened cement product is hit by a steel ball hammer having a predetermined diameter to generate an elastic wave in the hardened cement product, and the elastic wave is detected from the hardened cement product However, in the crack depth measurement method for measuring the crack depth based on the detected elastic wave,
The crack depth measuring method is a first sensor that is installed at a first installation position between the crack position and the striking position and detects a first surface wave propagating from the striking position to the surface of the hardened cement material. And a second surface wave that is installed at a second installation position opposite to the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor to detect,
The crack depth is the first formula

Calculated by
In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor as it propagates through the surface of the hardened cement material. Of the first surface waves detected by the first sensor by propagating through the surface of the hardened cement material, the maximum second plus side amplitude that first swung to the plus side after the initial motion of the surface wave is detected. It is an amplitude ratio divided by the maximum first plus side amplitude first swung to the plus side after the initial movement, and α represents the above (F) on the vertical axis, and the crack depth (d) / main wavelength ( An approximate expression: y = αe ^bx is derived from a correlation diagram showing the ratio of λ), and the crack depth measurement method is a constant (0.398) calculated from the approximate expression. An impact wave separated by a predetermined distance from the crack position formed on the hardened cement material is hit by a steel ball hammer having a predetermined diameter to generate an elastic wave in the hardened cement material, and the elastic wave is detected from the hardened cement material However, in the crack depth measurement method for measuring the crack depth based on the detected elastic wave,
The crack depth measuring method is a first sensor that is installed at a first installation position between the crack position and the striking position and detects a first surface wave propagating from the striking position to the surface of the hardened cement material. And a second surface wave that is installed at a second installation position opposite to the first installation position across the crack position, propagates through the surface of the hardened cement material from the striking position, and passes through the crack position. Using a second sensor to detect,
The crack depth is the first formula

Calculated by
In the first equation, d is the crack depth (mm), λ is the main wavelength (mm), and F is the second surface wave detected by the second sensor as it propagates through the surface of the hardened cement material. Among the above, the second absolute value of the minimum second minus side amplitude that swings to the minus side immediately after the initial motion of the surface wave and the maximum second plus side amplitude that swings to the plus side first after the initial motion of the surface wave is the cement hardening Of the first surface waves that propagate through the surface of the object and are detected by the first sensor, the minimum first minus-side amplitude that has swung to the minus side immediately after the initial motion of the surface wave and the first to the plus side after the initial motion of the surface wave The amplitude ratio divided by the first absolute value of the maximum first plus side amplitude that has swung, and α represents the above (F) on the vertical axis, and the crack depth (d) / principal wavelength (λ) on the horizontal axis. approximate expression from the correlation diagram showing the ratio: it leads to y = .alpha.e ^bx, calculated from the approximate expression Crack depth measuring method which is a constant (0.394). Said (λ) is the second formula

Calculated by, in the second equation, c is the average propagation velocity of the surface waves varies depending on the diameter of the steel ball hammer (m / sec), _{f c} is the center of gravity frequencies (kHz),
Said (f _c ) is the third formula

The crack depth measurement method according to any one of claims 1 to 3, wherein X (f _k ) is an amplitude value at a frequency (f _k ) and N is a sampling number in the third equation. . In the crack depth measurement method, calculation according to the first to third formulas is performed using a computer, and the computer calculates a centroid frequency (f _c ) based on the third formula. A main wavelength calculating means for calculating a main wavelength (λ) based on the second formula, a crack depth calculating means for calculating a crack depth (d) based on the first formula, and a calculated center-of-gravity frequency. The crack depth measuring method according to claim 4, wherein calculation result storage means for storing (f _c ), dominant wavelength (λ), and crack depth (d) is executed.   In the crack depth measurement method, the striking position, the first setting position, and the second setting position are arranged on a substantially straight line, and a separation dimension from the striking position to the first setting position and the first setting position. The separation dimension from the crack position to the crack position and the separation dimension from the crack position to the second installation position are the same, and the separation dimension is in the range of 90 to 110 mm. Crack depth measurement method.   In the crack depth measurement method, the surface wave detection interval of the first and second sensors is in the range of 1 to 5 μsec, and the surface wave detection time of the first and second sensors is 0.01 to 0.03 seconds. The crack depth measuring method according to any one of claims 1 to 6, wherein the crack depth is in the range.

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