JP2018119845A - Survey method of internal defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply also to a thick structure other than a tabular object; and to detect accurately an internal defect.SOLUTION: Surface vibration generated when inputting an elastic wave into the surface of a structure is received, and the received wave is subjected to Hilbert transformation to calculate an instantaneous phase, and a momentary phase difference which is a variation per unit time of the instantaneous phase is calculated, and a time from the input time of the elastic wave until generation of a change in the instantaneous phase is obtained. Then, the position of an internal defect is estimated from a reciprocation distance to the internal defect D obtained by multiplying the time by a propagation velocity of the elastic wave inside the structure.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an internal defect search method for inspecting internal defects such as cavities, cracks, jumpers, and delaminations existing in a structure such as a concrete structure in a nondestructive manner.

  Conventionally, as the prestressed concrete by the post-tension method, after the concrete has hardened, after inserting the PC steel material such as a steel wire or a steel bar into the sheath embedded in advance, after introducing the tension to the PC steel material, There is known a PC structure in which prestress is introduced by injecting grout into a space between the PC steel material in the sheath.

  The grout is used to fill a space between the PC steel material in the sheath and the like for the purpose of preventing corrosion of the PC steel material and integrating the member concrete and the PC steel material. Therefore, when a cavity is generated in the sheath due to insufficient filling of grout, the penetration or penetration of water or chloride causes corrosion or breakage of the PC steel material, which significantly changes the PC structure and increases the safety of the structure. There is a risk that it cannot be secured.

  As a method for nondestructively exploring concrete defects such as cavities in the sheath, an X-ray transmission method in which X-rays are irradiated from the surface of an object (such as Patent Document 1 below), a surface of a concrete structure The ultrasonic wave is incident on the surface of the concrete structure, the propagating ultrasonic wave is received by the surface of the concrete structure, and the shock wave is input into the concrete by an ultrasonic method (such as Patent Document 2 below) that analyzes the received wave. In addition, a shock elastic wave method (such as Patent Document 3 below) that receives and analyzes surface vibrations by a sensor is known.

JP 2001-208705 A JP 2000-2692 A JP 2011-185892 A

  However, the X-ray transmission method can be applied only to a relatively thin plate-like structure having a thickness of about 50 cm or less, and X-rays do not pass through a structure thicker than this. There was a problem. In addition, when a plurality of internal defects exist at a position overlapping with the transmission direction, there is a problem that an accurate position cannot be searched.

  In the ultrasonic method, since the incident wave has a high frequency region, the detectable depth is limited to a region shallower than 20 cm. In addition, if a higher frequency incident wave is used to improve the resolution, scattering will occur in aggregates, bubbles, reinforcing bars, sheaths, etc. in the concrete, and the reflected waves from the unfilled part in the sheath can be accurately captured. There was a problem of becoming difficult.

  On the other hand, the shock elastic wave method is a technique for a plate-like structure on the premise that the input elastic wave is reflected on the opposing surface and is subjected to multiple reflection in the thickness direction of the structure. There is a problem that it cannot be applied to a structure other than a plate shape, for example, a cross-sectional shape such as a T-girder flange.

  Accordingly, a main object of the present invention is to provide a method for searching for an internal defect that can be applied to a structure having a thickness other than a plate shape and can detect an internal defect with high accuracy.

  In order to solve the above-mentioned problem, the present invention according to claim 1 receives vibration of the surface when an elastic wave is input to the surface of the structure, calculates the instantaneous phase by converting the received wave into a Hilbert transform, and After calculating the instantaneous phase difference, which is the amount of change in the instantaneous phase per unit time, and obtaining the time from when the elastic wave is input until the instantaneous phase difference changes, the elastic wave inside the structure is There is provided an internal defect search method characterized by estimating the position of an internal defect from a round trip distance to the internal defect obtained by multiplying the propagation velocity.

  The invention of claim 1 utilizes the fact that a wave propagating on the surface of the structure and a reflected wave reflected by an internal defect interfere with each other by inputting an elastic wave to the surface of the structure. It is a non-destructive exploration method that estimates the position of internal defects.

  In the case of a structure with internal defects, the received wave measured on the surface when the elastic wave is input to the surface of the structure is the wave propagating on the surface due to the input elastic wave, Is reflected by the internal defect and reflected waves that have reached the surface overlapped. In this exploration method, the instantaneous phase is calculated by Hilbert transform of the received wave, and the instantaneous phase difference, which is the amount of change of the instantaneous phase per unit time, is calculated to change to the instantaneous phase difference from the time of elastic wave input. By determining the time until the wave propagating on the surface interferes with the reflected wave, and by multiplying this time by the propagation velocity of the elastic wave inside the structure, the round trip to the internal defect is obtained. The position of the internal defect is estimated from the distance.

  In this exploration method, the position of the internal defect is estimated by utilizing the mutual interference between the wave propagating on the surface accompanying the input wave and the reflected wave reflected by the internal defect, so a structure having a cross section other than a plate shape It can be applied to a structure having a large thickness.

  In addition, even when there are a plurality of internal defects, by capturing the reflected waves reflected by each internal defect, the position of each internal defect can be accurately grasped, and the internal defect can be detected with high accuracy.

  The present invention according to claim 2, wherein vibrations are received at a plurality of positions at intervals along a straight line passing through an elastic wave input position, and the internal defect obtained from each received wave is shown in a sectional view of the structure. 2. An internal defect position is estimated from a position where an elliptical arc-shaped defect position assumption curve having a reciprocation distance equal to the reciprocation distance up to is drawn, and a position of the internal defect is estimated from a position where the plurality of defect position assumption curves intersect or approach each other. An exploration method is provided.

  In the invention described in claim 2, in order to detect the position of the internal defect with higher accuracy, vibration is received at a plurality of positions, and the position obtained from each received wave is combined to estimate the position of the internal defect. ing. Specifically, by measuring vibration at a plurality of positions at intervals along a straight line passing through the elastic wave input position, it is possible to simultaneously measure the received waves at a plurality of positions by inputting the elastic wave once. become. In addition, since it is not certain which path the reflected wave has actually reflected from only one received wave, in the present invention, the received wave is changed to one received wave from the propagation characteristics of the elastic wave inside the structure. On the other hand, possible internal defect positions are indicated by elliptic arc-shaped lines called defect position estimation curves. And the position where the several defect position estimation curve drawn with respect to each received wave cross | intersects or adjoins is estimated as a position of an internal defect.

  According to a third aspect of the present invention, there is provided the internal defect search method according to any one of the first and second aspects, wherein the input elastic wave includes a specific frequency component having a frequency between 10 kHz and 25 kHz. .

  In the third aspect of the invention, the frequency of the input elastic wave includes a specific frequency component between 10 kHz and 25 kHz. By using a high-frequency wave as the input elastic wave, the influence of diffraction as if the elastic wave overcame the obstacle is reduced, but the influence of scattering due to aggregates and minute voids inside the concrete is increased. In addition, in an elastic wave having a frequency with a wide bandwidth, the wave has dispersibility due to the difference in diffraction and scattering frequency characteristics, making it difficult to search for internal defects using phase information. In order to reduce the influence of such diffraction and scattering, an elastic wave having a narrow bandwidth is input.

As the present invention according to claim 4, after the concrete is hardened, the structure is inserted into a sheath embedded in advance, and after introducing tension into the PC steel material, It is a PC structure by a post tension system formed by injecting grout into a gap with the PC steel material,
The search method of the internal defect in any one of Claims 1-3 in which the said search method is used for confirming the filling state of the said grout.

  In the invention described in claim 4 above, it is shown that it is particularly preferable to use the present exploration method for confirming the grout filling state in a post-tension type PC structure.

  As described above, according to the present invention, the present invention can be applied to a structure having a cross-sectional shape other than a plate shape such as a T-girder flange or a structure having a large thickness, and an internal defect can be detected with high accuracy.

It is a block diagram for enforcing the internal defect search method according to the present invention. It is a two-dimensional schematic diagram showing the propagation state of elastic waves. It is an example of an output waveform when there is no internal defect. It is an example of an output waveform when there is an internal defect. It is an example of a surface wave and a reflected wave when there is an internal defect. It is a graph which shows the relationship between the real part and imaginary part by Hilbert transform. It is an example of the result of having calculated the instantaneous phase and the instantaneous phase difference when there is no internal defect and when there is. 1 is a side view showing a striking device 1. It is a block diagram for enforcing the internal defect search method according to a modification. 3 is a side view showing a multichannel elastic wave sensor 7. FIG. It is a figure which shows the drawing point of a defect position assumption curve. The T-girder flange used in the experiment is shown, (A) is a sectional view, and (B) is a side view. It is sectional drawing which shows the condition of the internal defect D used for experiment. It is a graph which shows an experimental result. It is sectional drawing of the structure which shows a defect position assumption curve.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the internal defect D exploration method according to the present invention receives surface vibration when an elastic wave is input to the surface of a structure, and calculates the instantaneous phase by converting the received wave into a Hilbert transform. And calculating an instantaneous phase difference that is a change amount per unit time of the instantaneous phase, obtaining a time from when an elastic wave is input until the instantaneous phase difference is changed, and The position of the internal defect D is estimated from the reciprocating distance to the internal defect D obtained by multiplying the propagation speed of the elastic wave in FIG.

  In this exploration method, when an elastic wave is input to the surface of the structure, the wave propagates through the surface of the structure due to the input elastic wave and the internal defect D is propagated. Focusing on the fact that the reflected waves that have reflected the internal defect D and arrived at the surface interfere with each other on the surface of the structure, find the time when the phase change occurred by the Hilbert transform of the received wave Thus, the position of the internal defect D is to be estimated.

Hereinafter, the principle of this exploration method will be described in detail.
As shown in FIG. 1, when elastic waves are input to the surface of the structure, the vibration of the structure surface at the measurement position separated from the input position by a predetermined distance (50 mm) in the plane direction is free from internal defects. , A vertical distortion due to the Poisson's ratio of the P wave (longitudinal wave, see FIG. 2) having the fastest propagation speed is observed after a predetermined time from the input of the elastic wave, and then the R wave (surface wave ( Rayleigh wave), see FIG. 2). In FIG. 3, a wave propagating on the superposed surface of both is shown as a −sin wave.

  On the other hand, as shown in FIG. 1, when an internal defect D (a cubic cavity having a cross section of 20 × 20 mm) exists at a predetermined position (depth: 100 mm) inside the structure, the vibration of the structure surface at the measurement position is As shown in FIG. 4, the waveform is different from that in the case of no internal defect in FIG. This is because, as shown in FIG. 5, the P wave propagating inside the structure is reflected by the internal defect D after the wave propagating on the surface, and the reflected wave reaching the surface is superimposed. Is.

  The elastic wave generated inside the structure by the input of the elastic wave has a phase component in which the first wave displaces the measurement surface downward, and its frequency basically depends on the input elastic wave and Match the frequency. When an elastic wave propagating inside the structure collides with an internal defect D such as a cavity, a reflected wave is generated. The reflected wave has a phase component in which the first wave has a downward direction, and has the same wave as the input elastic wave. When this reflected wave reaches the surface of the structure, wave interference occurs between the wave propagating on the surface and the reflected wave, resulting in a waveform different from the situation of only the wave propagating on the surface.

  In this way, if the vibration of the surface of the structure is received, the received wave is analyzed, and the time when the reflected wave overlaps the wave propagating on the surface can be obtained, the reflected wave is generated from the propagation speed of the elastic wave. The position can be estimated.

  Next, a method for analyzing the received wave will be described. In this exploration method, first, the instantaneous phase is calculated by Hilbert transform of the received wave. In the Hilbert transform, after passing through a frequency filter that passes only the positive frequency region in the complex Fourier transform, a time axis waveform is obtained by inverse Fourier transform, and the amplitude and phase can be separated and discriminated. (See the following formula and FIG. 6).

x (t) = xr (t) + i × xi (t)
xr (t) = A (t) cosθ (t), xi (t) = A (t) sinθ (t)
Amplitude A (t) = (xr (t) ² + xi (t) ² ) ^1/2
Phase θ (t) = tan ⁻¹ (xi (t) / xr (t))
Specific examples of the observation results when there is no internal defect D and when there is no internal defect D are shown in FIG. 7A to 7C show the case where there is no internal defect, and FIGS. 7D to 7F show the case where there is an internal defect. 7 (A) and (D) are measured vibration waveforms on the surface of the structure, and FIGS. 7 (B) and (E) are instantaneous phases obtained by Hilbert transform of the received waves. FIGS. F) is an instantaneous phase difference obtained by calculating a change amount of the instantaneous phase per unit time. The vertical axes in FIGS. 7A and 7D are amplitudes expressed as a ratio when the maximum amplitude of the input waveform is 1.

  When there is no internal defect, when the measured vibration waveform is a sine wave with a constant amplitude as shown in FIG. 7 (A), the instantaneous phase obtained by Hilbert transform is as shown in FIG. 7 (B). As shown in the figure, a sawtooth waveform is formed which is proportional to the time and whose folding interval is substantially constant. The instantaneous phase having such a sawtooth waveform reflects a state in which the phase is represented by −π / 2 to π / 2 and is turned back when the phase is exceeded. Next, since the instantaneous phase difference is obtained from the amount of change in the instantaneous phase per unit time, as shown in FIG. 7C, the instantaneous phase difference changes with time. It becomes almost constant value. Incidentally, there is a portion where a sudden change in the instantaneous phase difference occurs corresponding to a sudden change caused by turning back when the phase angle makes one revolution in the instantaneous phase, but this may be ignored in this analysis. is there.

  On the other hand, when there is an internal defect D, a reflected wave reflected by the internal defect is added (interfered) to the received wave at a predetermined time, so that the measured vibration is shown in FIG. The waveform is a waveform whose amplitude and phase are disturbed, and the instantaneous phase obtained by converting the waveform into a Hilbert transform forms a sawtooth waveform having different folding intervals as shown in FIG. Further, as shown in FIG. 7F, the instantaneous phase difference changes at the time when the reflected wave reaches the surface of the structure.

  In this way, the Hilbert transform of the received wave is used to calculate the instantaneous phase, and by calculating the instantaneous phase difference that is the amount of change of the instantaneous phase per unit time, the wave propagating on the surface and the reflected wave are easily separated. Since the time at which the instantaneous phase difference changes due to mutual interference is obtained, the time from when the elastic wave is input until the instantaneous phase difference changes is multiplied by the propagation velocity of the longitudinal elastic wave inside the structure. The round trip distance to the internal defect D can be obtained. Furthermore, the position of the internal defect D can be estimated from the reciprocating distance to the internal defect D.

  Specifically, in the example shown in FIG. 7 (F), the time until the instantaneous phase difference changes is about 0.05 ms, which is multiplied by the longitudinal elastic wave propagation velocity 4000 m / s in the case of concrete. The value of the reciprocating distance from the surface of the structure to the internal defect is 200 mm. By dividing this by 2, it can be estimated that there is an internal defect at a depth of about 100 mm. This is consistent with the above-described actual machine test model.

  The point in time when the instantaneous phase difference changes can be determined based on the following concept. The change in instantaneous phase difference occurs when the wave propagation velocity changes or when another wave having a different phase component is superimposed. When waves having the same phase component are superimposed, the phase does not change but the amplitude changes. When attention is paid only to the phase, such superposition of waves of the same phase component cannot be detected, but this problem can be dealt with by performing measurement at a plurality of points. In a signal in a narrow frequency band, there is no factor that causes a phase change other than the arrival of an external signal. When noise is mixed, the phase changes randomly, and the instantaneous phase difference cannot be obtained in the first place. Therefore, when the instantaneous phase difference can be detected as the analysis target signal, it is not necessary to consider the influence of noise, and only the presence of the external signal needs to be considered. Further, after the external signal is superimposed, the phase changes uniformly. In this case, this uniform change cannot be detected by a differential operation such as an instantaneous phase difference. Therefore, it is possible to assume the time when the instantaneous phase difference changes as the arrival of the external signal, that is, the arrival time of the reflected wave from the internal defect. At this time, the variation amount of the instantaneous phase difference is a function of the ratio between the intensity of the input elastic wave and the intensity of the reflected wave, and therefore, a certain threshold (for example, ± 5 of the average value of the instantaneous phase difference over the entire measurement time) Within ± 5% or within ± 5% of the moving average value of instantaneous phase difference within a certain time from the measurement time), and if there is a change exceeding that value, it can be determined that an external signal has arrived It becomes possible.

  As described above, in this exploration method, the internal defect distance is estimated using the mutual interference between the wave propagating on the surface accompanying the input wave and the reflected wave reflected by the internal defect. It can be applied not only to a plate-like structure but also to a thick structure. Therefore, the present invention can be applied to a structure having a complicated sectional shape such as a T-girder flange.

  In addition, even when there are a plurality of internal defects, by capturing the reflected waves reflected by each internal defect, the position of each internal defect can be accurately grasped, and the internal defect can be detected with high accuracy.

  In this exploration method, the input elastic wave preferably includes a specific frequency component having a frequency between 10 kHz and 25 kHz. By inputting an elastic wave having a narrow bandwidth in the high frequency region, there is no influence of diffraction or scattering, and the internal defect can be reliably detected by detecting the phase. By using an input elastic wave having a high frequency of 10 kHz to 25 kHz, the influence of diffraction as if the elastic wave overcame the obstacle is reduced, but the influence of scattering by aggregates and minute voids inside the concrete is reduced. Will increase. In addition, when an elastic wave having a frequency with a wide bandwidth is input, dispersibility occurs in the wave due to the difference in the frequency characteristics of diffraction and scattering, making it difficult to search for internal defects using phase information. For this reason, in this exploration method, as described above, the influence of diffraction and scattering is reduced by using an elastic wave having a narrow bandwidth in the high frequency region as an input wave. Here, the input elastic wave “includes a specific frequency component” means not only a case of a single frequency component that can be regarded as a sine wave, but also a narrow bandwidth (for example, the power level of the peak value is halved). It is a concept including a frequency component having a bandwidth having a frequency of ± 10% or less, preferably 5% or less with respect to the peak frequency.

  The generated elastic wave may be generated by impulse excitation that strikes the structure or may be generated by tone burst excitation having a constant steady amplitude portion. In the generation of the elastic wave, it is particularly preferable to use a striking device (Japanese Patent Application No. 2016-13955) used in the shock elastic wave method previously filed by the present inventors. As shown in FIG. 8, this striking device 1 is a steel rod having a predetermined length manufactured with a constant cross-sectional area over its entire length, and a tip surface 2a that collides with an inspection object has a spherical crown shape. The upper end surface 2b is composed of a plunger 2 having a planar shape and a steel ball 3 having a predetermined diameter that collides with the upper end surface 2b of the plunger 2.

  In the hitting device 1, the test object is not directly hit by the steel ball, but the test object is hit by the steel ball 3 having a predetermined diameter via the plunger 2 (one-dimensional bar) having the above-described structural condition. To give elastic waves. By using such indirect impact, the impact force is generated when the steel ball 3 collides with the plunger upper end surface 2b, and the object to be inspected via the distal end surface 2a of the plunger 2 that is in contact with the object to be inspected. Is transmitted to the object. Since these are materials (steel) having a stable elastic coefficient, the contact time between the steel ball 3 and the plunger 2 is always constant, and a wave having a constant frequency can be given stably.

  In addition, since it is known that a specific frequency that resonates with the length of the steel rod is generated in the plunger 2 having a specified length (multiple reflection theory of elastic wave), the frequency caused by the impact and the resonance of the plunger 2 By matching the frequency within a certain range, an elastic wave having a resonance frequency corresponding to the plunger length is generated in the plunger, and this can be transmitted to the inspection object. .

  Therefore, when the plunger 2 of the same material is hit with the steel ball 3 having the same diameter and the same mass while sequentially moving the inspection object point, an elastic wave having a constant frequency is stably applied to the inspection object. It becomes possible.

  As shown in FIG. 1, the elastic wave measuring means is configured such that a response elastic wave of a structure is placed on the same plane as the elastic wave input surface and at a predetermined distance from the elastic wave input position. An elastic wave sensor 4 to be measured, a waveform recording device 5, and an evaluation device 6 connected to the waveform recording device 5 are configured.

  The elastic wave sensor 4 measures a response elastic wave of a wave applied to the structure by the impact device 1 in a state where the elastic wave sensor 4 is in contact with the surface of the structure. As this elastic wave sensor 4, an acceleration sensor, a vibration sensor, etc. can be used, for example. The vibration receiving direction of the elastic wave sensor 4 is not particularly limited, but is preferably the elastic wave input direction (vertical direction (vertical direction) with respect to the measurement surface).

  The vibration measured by the elastic wave sensor 4 is analog / digital converted by an A / D converter (not shown) and then input to the waveform recording device 5.

  The waveform recording device 5 is a device for recording an electrical signal of a wave measured by the elastic wave sensor 4. The waveform recording device 5 includes a server for storing electrical signals, a storage such as a hard disk, a recording medium such as a CD and a DVD, a memory, and the like. The waveform recording device 5 can receive signals from the elastic wave sensor 4 and store them in time series.

  The said evaluation apparatus 6 is comprised by electronic devices, such as PC (personal computer), a smart phone, a tablet-type terminal, and a wearable terminal, for example. The evaluation device 6 analyzes the waveform stored in the waveform recording device 5. This evaluation device 6 calculates an instantaneous phase and an instantaneous phase difference that is a change amount per unit time by, for example, performing a Hilbert transform on the recorded waveform. Also, by applying FFT (Fast Fourier Transform), the waveform data on the time axis is converted into spectrum data on the frequency axis. Further, the evaluation device 6 may determine the presence or absence of an internal defect in a structure such as concrete through the presence or absence of a change in the instantaneous phase difference. The time until the change occurs may be obtained so that the position of the internal defect can be calculated.

  The evaluation device 6 can display each data via a display unit including a display (not shown). Further, the evaluation device 6 can record each of these data in the storage, display these data on the display unit based on an instruction from the user, or write these data in the portable memory. The user can take out the portable memory from the evaluation device 6 and carry it freely. Furthermore, the evaluation device 6 can transfer these data to other electronic devices via the public communication network.

  As shown in FIG. 1, the elastic wave sensor 4 may be provided in only one place, or as shown in FIG. 9, a plurality of the elastic wave sensors 4 spaced along a straight line passing through the elastic wave input position. By installing at the position, the measurement may be performed simultaneously at the plurality of positions with respect to one input of the elastic wave.

  In the case of measuring with a plurality of elastic wave sensors 4, 4..., It is preferable to use a multichannel elastic wave sensor 7 as shown in FIG. The multi-channel type acoustic wave sensor 7 includes a plurality of acoustic wave sensors 4, 4... And a holder 8 that holds the plurality of acoustic wave sensors 4, 4. ing. In using the multi-channel elastic wave sensor 7, the holder 8 is grasped by hand and the tips of the elastic wave sensors 4, 4 ... are pressed against the measurement surface, or the tips of the elastic wave sensors 4, 4 ... are used. Is fixed to the measurement surface. The number of elastic wave sensors 4 is preferably about 4 to 10. The interval between the adjacent elastic wave sensors 4 and 4 may be constant or different. As this space | interval, about 10-100 mm, especially about 10-50 mm are preferable.

  The method of estimating the position of the internal defect D when measured by a plurality of elastic wave sensors 4... Is a cross section of a structure cut along a straight line where the elastic wave sensors 4. In the figure, an elliptical arc-like defect position assumption curve 9a having a round trip distance equivalent to the round trip distance to the internal defect D obtained by each elastic wave sensor 4a is drawn, and a plurality of the defect position assumption curves 9a, 9b. Alternatively, the position of the internal defect D can be estimated from the adjacent position. The defect position assumption curves 9a, 9b,... Indicate that the distance from the elastic wave input position to the measurement position through the structure reaches the measurement position until the instantaneous phase difference changes. It is an elliptical arc-shaped curve centered on two points of the elastic wave input position and measurement position, which are drawn so as to have a round-trip distance to the internal defect obtained by multiplying the wave propagation speed. The round trip distance to the internal defect obtained from the measurement results of the acoustic wave sensors 4a, 4b,... Indicates that the internal defect exists on the defect position assumption curves 9a, 9b,. Therefore, the position of the internal defect can be estimated more precisely by measuring vibration using the plurality of elastic wave sensors 4a, 4b. It is also possible to estimate the size of the internal defect from the range where the plurality of defect position assumption curves 9a, 9b.

  The position where the plurality of defect position assumption curves intersect is a position where the plurality of defect position assumption curves intersect or overlap each other in the region where the elastic wave sensor is disposed from the elastic wave input position. In addition, a position where a plurality of defect position assumption curves are close to each other is a region closest to the elastic wave input position where the elastic wave sensor is disposed, but the plurality of defect position assumption curves do not overlap. It is a position. If an appropriate number of elastic wave sensors are used and an appropriate number of measurements are repeated, the reliability of the measurement data is improved, and a portion where a plurality of defect position assumption curves intersect in principle appears.

  As internal defects of structures targeted by this exploration method, it is possible to broadly target defects that occur inside concrete structures such as cavities, cracks, jumpers, and delaminations.

  In particular, as the structure, after the concrete has hardened, the PC steel material is inserted into a sheath embedded in advance, and after introducing tension into the PC steel material, a gap with the PC steel material in the sheath In the case of a post-tension type PC structure in which grout is injected into the target, it is preferable to use this exploration method to check the filling state of the grout.

  Grouting is filled in the PC steel sheath tube in PC structures such as bridges, viaducts, buildings, etc., but if such a grout filling failure occurs in the PC steel sheath tube, it is caused by this. There is a possibility that PC steel may be corroded or broken. Therefore, it is very important to investigate the degree of grout filling in the sheath tube of PC steel by the shock elastic wave method.

  By using this exploration method as a method for exploring internal defects in PC structures, it is possible to accurately confirm the lack of grout filling and to take appropriate measures such as refilling unfilled parts. Become.

  As shown in FIG. 12, an experiment was performed to estimate a defect position by the present exploration method using a T-girder flange, which is a PC structure by a post-tension method.

  In the experiment, as shown in FIGS. 12 and 13, a T-girder flange in which a plurality of sheaths are embedded in the longitudinal direction is used, and there are two unfilled portions (cavities) in which the sheath is not filled with grout. did.

  The elastic wave to be input was a shock elastic wave generated using the impact device 1 shown in FIG. The multi-channel elastic wave sensor 7 was installed at a plurality of positions spaced apart from the input position, and the response (velocity) when the impact elastic wave was input by the impact device 1 was measured.

  FIG. 14 shows the result of calculating the output waveform and its instantaneous phase difference. In the output waveform, the unit of the vertical axis is speed (m / s), but the value is not a physical value but a value that is in a certain proportional relationship with the physical value. Further, FIG. 15 is a diagram in which a defect position assumption curve is drawn from the time when the instantaneous phase difference change occurs. From FIG. 15, although the internal defect at a position where the depth from the input surface is about 250 mm can be estimated, the internal defect at a position where the depth is shallow (depth of about 80 mm) could not be detected. FIG. 15 shows FIG. 14 rotated 90 degrees so that the elastic wave input surface is the upper surface.

  The reason why the above-mentioned internal defect at a position where the depth is shallow cannot be detected is probably because a stable wave including a specific frequency component between 10 kHz and 25 kHz was not obtained as an input wave in this experiment. It is. An input wave in a high frequency band is required to detect an internal defect in a shallow portion, but in this experiment, the band component is 10 kHz or less. It is also considered effective to perform a filtering process that measures the frequency component of the input elastic wave and removes the other frequency components. Furthermore, it seems that one of the causes is that the signal processing of the initial motion part of the input wave is not stable. For this reason, it is considered that a stable input with a narrow frequency range is necessary.

  Further, in this example, in FIG. 15, the plurality of defect position assumption curves did not intersect at the position of the internal defect, but this is considered to be caused by the fact that the number of measurement is small and the number of defect position assumption curves is insufficient. Therefore, if a sufficient number of measurements are performed, it is considered that a plurality of defect position assumption curves intersect at the position of the internal defect.

  DESCRIPTION OF SYMBOLS 1 ... Blow device, 2 ... Plunger, 3 ... Steel ball, 4 ... Elastic wave sensor, 5 ... Waveform recording device, 6 ... Evaluation apparatus, 7 ... Multichannel type elastic wave sensor, 8 ... Holder, 9 ... Defect position Assumed curve, D ... Internal defect

Claims (4)

  The vibration of the surface when an elastic wave is input to the surface of the structure is received, the received wave is Hilbert transformed to calculate the instantaneous phase, and the instantaneous phase difference that is the amount of change of the instantaneous phase per unit time is calculated Then, after obtaining the time from when the elastic wave is input until the instantaneous phase difference is changed, the internal defect is determined from the round trip distance to the internal defect obtained by multiplying the time by the propagation speed of the elastic wave inside the structure. A method for searching for an internal defect, characterized by estimating a position of a defect.   Vibration is received at a plurality of positions at intervals along a straight line passing through the input position of the elastic wave, and the cross-sectional distance of the structure is equal to the round-trip distance to the internal defect obtained from each received wave. 2. An internal defect search method according to claim 1, wherein a defect position assumption curve having an elliptic arc shape is drawn, and the position of the internal defect is estimated from a position where the plurality of defect position assumption curves intersect or approach each other.   The method for searching for internal defects according to claim 1, wherein the input elastic wave includes a specific frequency component having a frequency between 10 kHz and 25 kHz. After the concrete has hardened, the structure is inserted with a PC steel material in a sheath embedded in advance, and after introducing tension into the PC steel material, a grout is formed in a gap with the PC steel material in the sheath. Is a PC structure with a post-tension method,
The search method of the internal defect in any one of Claims 1-3 in which the said search method is used for confirming the filling state of the said grout.

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