JP2013130452A - Nondestructive inspection method and nondestructive inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nondestructive inspection method and a nondestructive inspection device capable of detecting a break of a reinforcing-bar inside of concrete even if covering of concrete is superficial.SOLUTION: According to a nondestructive inspection method for detecting whether a reinforcing-bar 2 is broken or not by magnetizing the reinforcing-bar 2 in a concrete body 1 from a surface 1A by means of a magnet 5 and then measuring a magnetic flux density on the surface 1A of that concrete body 1, the magnet 5 is moved from right above the reinforcing-bar 2 along a length direction of the reinforcing-bar 2, the reinforcing-bar 2 is magnetized along the length direction and thereafter, the reinforcing-bar 2 is magnetized again along the length direction by moving the magnet 5 at a surface position of the concrete body 1 on a neighboring reinforcing-bar 2 along the length direction of the reinforcing bar 2A. A magnetic sensor is then moved along the length direction of the reinforcing-bar 2 on the surface of the concrete body 1, and a magnetic flux density on the surface 1A of the concrete body 1 is measured, thereby detecting whether or not the reinforcing-bar 2 is broken.

Description

  The present invention relates to a nondestructive inspection method and a nondestructive inspection device for detecting the presence or absence of breakage of a reinforcing bar provided in a concrete body such as a pier.

  Conventionally, a nondestructive inspection method for detecting defects of reinforcing bars in concrete has been known (see Patent Document 1).

  Such a non-destructive inspection method is a method in which a permanent magnet is moved along the surface of the concrete along the longitudinal direction of the reinforcing bar embedded in the concrete, thereby magnetizing the reinforcing bar along the longitudinal direction and leaking the vertical magnetic flux from the surface of the concrete. The presence / absence of breakage of the reinforcing bars is determined from the distribution of density components.

Japanese Patent No. 3734822

  However, in such a non-destructive inspection method, in order not to be affected by residual magnetism, it is necessary to give the rebar a large magnetization close to the saturation magnetization, and use a permanent magnet with a strong magnetic force. Yes. For this reason, when the concrete cover is shallow, the permanent magnet will be too close to the reinforcing bar, and in such a case, the magnetic flux in the direction opposite to the desired longitudinal direction will increase due to the influence of the permanent magnet. There is a problem in that a uniform magnetic flux is not generated along the longitudinal direction in the reinforcing bar, and it is difficult to detect a break.

  An object of the present invention is to provide a nondestructive inspection method and a nondestructive inspection apparatus capable of reliably detecting the breakage of reinforcing bars in concrete even when the concrete cover is shallow.

The invention of claim 1 is a nondestructive inspection method for detecting the presence or absence of breakage of the reinforcing bar by magnetizing a reinforcing bar provided in the concrete body with a magnet and then measuring the magnetic flux density on the surface of the concrete body. There,
Moving the magnet on the surface of the concrete body along the longitudinal direction of the reinforcing bar to magnetize the reinforcing bar along the longitudinal direction;
After that, the rebar is magnetized along the longitudinal direction again by moving the magnet along the longitudinal direction of the rebar at a position away from the position where the rebar is magnetized,
Thereafter, the presence or absence of breakage of the reinforcing bars is detected by measuring the magnetic flux density on the surface of the concrete body.

  According to this invention, even if the concrete cover is shallow, the breakage of the reinforcing bars in the concrete can be reliably detected.

It is the block diagram which showed the structure of the nondestructive inspection apparatus which concerns on this invention. It is explanatory drawing which showed the positional relationship of the reinforcing bar embed | buried in a concrete body, and the magnet which magnetizes this reinforcing bar from right above. FIG. 3 is a plan view of FIG. 2. It is explanatory drawing which showed the magnetic force line in the middle of magnetizing a reinforcing bar from right above. It is explanatory drawing which showed the magnetic field line after magnetizing a reinforcing bar from right above. It is the graph which showed the relationship between the magnetic flux density of the perpendicular direction of the surface of a concrete body, and the position when there is a fracture in a reinforcing bar. It is the graph which showed the relationship between the magnetic flux density of the perpendicular direction of the surface of a concrete body when there is no fracture in a reinforcing bar, and its position. It is explanatory drawing which shows the state which magnetizes the reinforcing bar examined from the position right above the adjacent reinforcing bar after magnetizing the reinforcing bar from right above. FIG. 8 is a plan view of FIG. 7. It is explanatory drawing which showed the magnetic force line in the state of the magnetization shown in FIG. 7 when there exists a fracture | rupture in a reinforcing bar. FIG. 10 is a plan view of FIG. 9. It is the top view which showed the magnetic force line when not performing magnetizing when there is no fracture in a reinforcing bar. It is the top view which showed the line of magnetic force when performing magnetism when there is no fracture in a reinforcing bar. It is explanatory drawing which showed the method of magnetization of the reinforcing bar when the position of the reinforcing bar is not known. FIG. 14 is a plan view of FIG. 13. It is explanatory drawing which showed the measuring method when the position of a reinforcing bar is not known. It is explanatory drawing which showed the method to scan and inspect the magnetic detection part to the longitudinal direction of a reinforcing bar. It is explanatory drawing which showed the other scanning method of the magnetic detection part. It is the block diagram which showed the structure of the nondestructive inspection apparatus of 2nd Example. It is the block diagram which showed the structure of the nondestructive inspection apparatus of 3rd Example. It is explanatory drawing which showed the method of the other example of the magnetization of a reinforcing bar. It is a top view of FIG.

  Hereinafter, an embodiment as an embodiment of a nondestructive inspection method and a nondestructive inspection apparatus according to the present invention will be described with reference to the drawings.

[First embodiment]
In FIG. 1, 1 is a concrete body, and a plurality of main reinforcing bars (rebars) 2 are arranged in parallel in the concrete body 1.
[Non-destructive inspection method]
As shown in FIGS. 2 and 3, the magnet 5 is placed at a position P1 on the surface 1A of the concrete body 1 just above the reinforcing bar 2 to be inspected. The magnet 5 is a permanent magnet made of a rare earth metal such as Nd, but may be an electromagnet. Further, one end (left end in FIG. 3) of the magnet 5 is an S pole, and the other end (right end) is an N pole.

  For example, the magnet 5 is moved from the left side to the right side in FIG. 3 along the rebar 2 to magnetize the rebar 2 along the longitudinal direction. That is, the reinforcing bar 2 is magnetized along the longitudinal direction before and after the position where the reinforcing bar 2 breaks. In this case, the direction of the magnetic pole may be opposite to the above.

  For example, as shown in FIG. 4, when the magnet 5 is positioned in the middle of the reinforcing bar 2, if the separation distance between the magnet 5 and the reinforcing bar 2 is small, a position close to the magnet 5 in the reinforcing bar 2 (see FIG. 4). 4 on the right side), a magnetic flux E1 is generated in the left direction, and at a position far from the magnet 5 (on the left side in FIG. 4), the direction is opposite to the direction of the magnetic flux E1 due to the influence of the magnet 5 having a strong magnetic force. A magnetic flux E2 (| E1 |> | E2 |) in the right direction is generated. For this reason, after magnetization (after removal of the magnet 5), as shown in FIG. 5, a leftward magnetic flux E1 'is generated in the right portion of the reinforcing bar 2, but a leftward magnetic flux E3 smaller than the magnetic flux E1' in the left portion. Occurs.

  When the magnetic flux density in the vertical direction of the surface 1A of the concrete body 1 is measured in this state, graphs G1 and G2 shown in FIGS. 6 and 6A are obtained. This graph G1 is a graph when the reinforcing bar 2 has a fracture H, and the graph G2 is a graph when the reinforcing bar 2 does not have a fracture H. In addition, both graph G1, G2 shows the case where the thickness of the covering of the concrete body 1 covering the reinforcing bar 2 is 100 mm.

  As can be seen from the graph G1 in FIG. 6, peaks Pa1 and Pa2 occur on both sides of the fracture H, but even when the reinforcing bar 2 does not have the fracture H, the peaks Pb1 and Pb2 are likely to appear as shown in the graph G2 in FIG. 6A. Occurs. For this reason, the presence or absence of the fracture H of the reinforcing bar 2 may not be clearly determined. This is because magnetic flux E <b> 2 (see FIG. 4) is generated when the reinforcing bar 2 is magnetized by the magnet 5.

  In order to eliminate the generation of the magnetic flux E2, as shown in FIG. 7 and FIG. 8, at a position P2 on the surface 1A of the concrete body 1 just above the reinforcing bar 2A arranged next to the reinforcing bar 2 to be inspected. Place the magnet 5. Then, the magnet 5 is moved in the right direction from the left position shown in FIG. 8, and the rebar 2 is magnetized (magnetized) again along the longitudinal direction. In this case, the direction of the magnetic pole of the magnet 5 is the same as that in FIG.

  When the magnet 5 is located in the middle of the reinforcing bar 2A, the separation distance between the magnet 5 and the reinforcing bar 2 is large, so that magnetic fluxes E4 and E5 (E1> in the same direction are placed in the reinforcing bar 2 as shown in FIG. E4, E5) occurs. That is, even if the covering of the concrete body 1 of the reinforcing bar 2 is shallow, a magnetic flux having a substantially uniform size can be generated in the longitudinal direction of the reinforcing bar 2.

  For this reason, after the rebar 2A is magnetized (after the magnet 5 is removed), if there is no break H in the rebar 2, a magnetic field at equal intervals is generated as shown in FIG. 12. In addition, when the magnetic field is not performed, the lines of magnetic force as shown in FIG. 11 are generated.

  When the reinforcing bar 2 has a fracture H, a closed curve J of a magnetic field surrounding the fracture H is formed as shown in FIG. When the magnetic flux density in the vertical direction of the surface 1A of the concrete body 1 is measured in this state, a graph G3 shown in FIG. 6 is obtained.

  As can be seen from this graph G3, the slope of the graph G3 is greatly increased in the portion of the break H.

  When there is no break H in the reinforcing bar 2, a magnetic flux density graph G4 when the reinforcing bar 2 is magnetized again as shown in FIGS. 7 and 8 after the reinforcing bar 2 is magnetized as shown in FIGS. Shown in 6A.

  As described above, when the reinforcing bar 2 has no break H as shown in FIG. 6A, the slope of the graph G4 is substantially constant, and clearly differs from the graph G3 of FIG. For this reason, even if the concrete cover is shallow, it is possible to reliably detect the fracture H of the reinforcing bar 2 in the concrete body 1.

Reference numeral 20 shown in FIG. 1 is a nondestructive inspection device that detects a break H of the main reinforcing bar 2.
[Non-destructive inspection equipment]
The nondestructive inspection device 20 includes a magnetic detection unit 11 having a magnetic sensor 10 that detects magnetism in the Z direction (a direction orthogonal to the surface 1A of the concrete body 1), and a detection signal detected by the magnetic sensor 10 to detect the concrete body 1. The magnetic flux density in the direction perpendicular to the surface 1A is calculated and calculated, the calculation unit 21 generates a graph of the calculated magnetic flux density, the display unit 22 displays the magnetic flux density graph generated by the calculation unit 21, and the magnetic A distance sensor 30 for obtaining the moving distance of the detection unit 11 and a memory 23 for storing the magnetic flux density obtained by the calculation unit 21 and the distance obtained by the distance sensor 30 are provided. The distance sensor 30 is incorporated in the magnetic detection unit 11.

The magnetic sensor 10 is a highly sensitive, for example, MI sensor, fluxgate sensor, Hall element, superconducting quantum interference element, or the like.
[Measuring method]
Next, an inspection method for inspecting the breakage of the reinforcing bars using the nondestructive inspection apparatus 20 will be described.

  When the position of the reinforcing bar 2 is known, first, as shown in FIGS. 2 and 3, the magnet 5 is placed on the upper surface position P1 of the concrete body 1 just above the reinforcing bar 2 to be inspected. The rebar 2 is moved along the longitudinal direction, and the rebar 2 is magnetized in a state close to saturation magnetization along the longitudinal direction. This magnetization close to the saturation magnetization eliminates the influence of the residual magnetic field of the rebar 2 before the inspection.

  Next, as shown in FIGS. 7 and 8, a magnet 5 is placed on the upper surface position P2 of the concrete body 1 immediately above the reinforcing bar 2A adjacent to the reinforcing bar 2 to be inspected, and the magnet 5 is placed in the same manner as described above. The rebar 2 is moved along the longitudinal direction of 2A, and the rebar 2 is magnetized (magnetized) along the longitudinal direction.

  After this magnetization, as shown in FIG. 1, the magnetic detection unit 11 of the nondestructive inspection apparatus 20 is moved along the rebar 2 on the surface 1 </ b> A of the concrete body 1.

  By the movement of the magnetic detection unit 11, the movement position in the X direction of the surface 1 </ b> A of the concrete body 1 is obtained by the distance sensor 30. Further, the magnetic flux detected at each position (magnetic flux density orthogonal to the surface 1A: magnetic flux density in the Z direction) is obtained by the calculation unit 21 by the magnetism detected by the magnetic sensor 10.

  The memory 23 stores the movement position obtained by the distance sensor 30 and the magnetic flux density obtained by the calculation unit 21 corresponding to the movement position.

  The display unit 22 displays the graph G3 shown in FIG. 6 or the graph G4 shown in FIG. 6A based on the magnetic flux density and the movement position stored in the memory 23.

  This graph is generated by the calculation unit 21 based on the data stored in the memory 23 and displayed on the display unit 22. The calculation unit 21 has a function of a graph generation unit that generates a graph from the calculated magnetic flux density and the movement position obtained by the distance sensor 30.

  If the graph G3 shown in FIG. 6 is displayed on the display unit 22, it can be determined that the reinforcing bar 2 has a fracture H, and if the graph G4 in FIG. 6A is displayed, the reinforcing bar 2 has no fracture H. Judgment can be made.

  In the above embodiment, after magnetizing the reinforcing bar 2 along the longitudinal direction, the magnet 5 is placed on the upper surface position P2 of the concrete body 1 immediately above the reinforcing bar 2A adjacent to the reinforcing bar 2, and this magnet 5 is placed in the longitudinal direction of the reinforcing bar 2A. The reinforcing bar 2 is magnetized along the longitudinal direction by moving it along the direction. For example, after the reinforcing bar 2 is magnetized along the longitudinal direction, the concrete body 1 directly above the reinforcing bar 2 as shown in FIG. It may be placed at a position away from the upper surface position P1 by a predetermined distance and moved from this position along the longitudinal direction of the reinforcing bar 2 shown in FIG. 21 to magnetize the reinforcing bar 2 in the longitudinal direction again.

That is, when the rebar 2 is magnetized for the second time, any position may be used as long as the rebar 2 can be magnetized along the longitudinal direction from a position where the rebar 2 is separated from the rebar 2 by a predetermined distance and does not cause saturation magnetization. . That is, the position may be a position separated from the upper surface position P1 by a predetermined distance.
[Measurement method when the position of the reinforcing bar is unknown]
Next, a measurement method when the position of the reinforcing bar 2 is not known will be described.

  As shown in FIGS. 13 and 14, a magnet 5 is placed at the position (solid line position) of the surface 1 </ b> A of the concrete body 1 that is the end of the inspection range, and the magnet 5 is moved along the longitudinal direction of the reinforcing bar 2. The rebar 2 is magnetized along the longitudinal direction. Next, the magnet 5 is placed at a position (two-dot chain line position) that is a predetermined distance away from the position of the solid line, and similarly, the magnet 5 is moved along the longitudinal direction of the reinforcing bar 2 to magnetize the reinforcing bar 2 along the longitudinal direction. Let By repeatedly performing these magnetizing operations, when the magnet 5 is positioned in the vicinity of the reinforcing bar 2 (dash-dotted line position), the reinforcing bar 2 can be magnetized in a state close to saturation magnetization. When positioned, the rebar 2 can be magnetized (magnetized) as shown in FIG.

  Then, the magnetic detection unit 11 of the nondestructive inspection apparatus 20 is placed at the end of the inspection range as shown in FIG. 15, and the magnetic detection unit 11 is moved along the longitudinal direction of the reinforcing bar 2 to measure the magnetic flux density. Go. Thereafter, the magnetic detector 11 is positioned at the chain line position in FIG. 15 and is moved along the longitudinal direction of the reinforcing bar 2 to measure the magnetic flux density.

  By shifting the position of the magnetic detection unit 11 to the right in FIG. 15 each time these measurements are repeated, the magnetic detection unit 11 can be positioned in the vicinity of the reinforcing bar 2. The magnetic flux density can be measured as shown in graphs G3 and G4 of 6A. For this reason, even if the covering of the concrete 1 is shallow, the fracture H of the reinforcing bar 2 can be reliably detected.

  In any of the above-described embodiments, the magnetic detection unit 11 is moved in the longitudinal direction of the reinforcing bar 2 to measure the magnetic flux density. However, as shown in FIG. The magnetic flux density at each position is measured by scanning the section 11, and graphs G3 and G4 (see FIGS. 6 and 6A) of the magnetic flux density along the longitudinal direction of the reinforcing bar 2 are obtained from the measurement results at the respective positions. The break H may be detected.

Further, the magnetic detection unit 11 may scan in the arrow direction shown in FIG.
[Second Embodiment]
FIG. 18 shows a configuration of a nondestructive inspection apparatus 200 according to the second embodiment. The nondestructive inspection apparatus 200 determines whether or not the gradient of the graph is greater than or equal to a preset threshold value from the differentiation circuit 201 for differentiating the graph stored in the memory 23 and the differential value obtained by the differentiation circuit 201. In addition, an inclination determination circuit 202 that detects a break H of the reinforcing bar 2 and a display unit 203 that displays a determination result of the inclination determination circuit 202 and a graph stored in the memory 23 are provided.
[Operation]
Next, the operation of the nondestructive inspection apparatus 200 will be described.

  When the position of the reinforcing bar 2 is known, the magnet 5 is placed at a position P1 directly above the reinforcing bar 2 to be inspected as shown in FIGS. Then, the reinforcing bar 2 is magnetized along the longitudinal direction, and thereafter, as shown in FIGS. 7 and 8, the magnet 5 is placed on the upper surface position P2 of the concrete body 1 just above the reinforcing bar 2A, and the reinforcing bar 2 is magnetized.

  Next, the magnetic detection unit 11 of the nondestructive inspection apparatus 200 is moved on the surface 1 </ b> A of the concrete body 1 along the reinforcing bar 2. As a result of this movement, the memory 23 stores the movement position obtained by the distance sensor 30 and the magnetic flux density obtained by the calculation unit 21 corresponding to this movement position, as in the first embodiment. Further, the calculation unit 21 creates the graph shown in FIG. 11 or 12 based on the data stored in the memory 23 and stores it in the memory 23.

  The differentiation circuit 201 differentiates the graph stored in the memory 23 and obtains the slope of the graph at each position from the differentiation value obtained by the differentiation circuit 201. When there is no break H in the reinforcing bar 2, the inclination is almost constant as shown in the graph G4 in FIG. 6A. However, when the reinforcing bar 2 has the break H, as shown in the graph G3 in FIG. The inclination of the graph G3 greatly increases in the plus direction at the 0 mm position).

  The inclination determination circuit 202 detects the inclination in the positive direction as compared with the threshold value, and when detecting an inclination greater than a predetermined value in the positive direction, determines that there is a break H and displays it on the display unit 203.

  When the position of the reinforcing bar 2 is not known, as shown in FIGS. 13 and 14, the reinforcing bar 2 is magnetized, and the magnetic detection unit 11 is moved as shown in FIG. 15 to measure the magnetic flux density.

Also, the magnetic detection unit 11 is scanned as shown in FIG. 16 or 17 to obtain the magnetic flux density at each position, and graphs G3 and G4 of the magnetic flux density with respect to the longitudinal direction of the reinforcing bar 2 are obtained. You may determine the presence or absence of the fracture | rupture H of the reinforcing bar 2 by calculating | requiring the inclination of a density change. Even when the position of the reinforcing bar 2 is known, the presence or absence of the fracture H of the reinforcing bar 2 may be similarly determined.
[Third embodiment]
FIG. 19 shows a configuration of a nondestructive inspection apparatus 300 according to the third embodiment. The nondestructive inspection apparatus 300 includes a magnetic detection unit 310 having a pair of magnetic sensors 10A and 10B spaced apart from each other by Δx, a difference circuit 301 for determining a difference ΔBz in magnetic flux density detected by the pair of magnetic sensors 10A and 10B, An inclination determination circuit 302 that determines whether or not the difference ΔBz obtained by the difference circuit 301 is equal to or greater than a threshold value, and a display unit 22 that displays that the reinforcing bar 2 has a fracture H when the obtained difference ΔBz is equal to or greater than the threshold value. It has.

  Since the pair of magnetic sensors 10A and 10B are separated by a certain distance Δx, the difference between the magnetic flux densities Bz1 and Bz2 detected by the magnetic sensors 10A and 10B indicates the inclination of the change in the magnetic flux density with respect to the longitudinal direction of the reinforcing bar 2. Will show.

  In the measurement method, first, the reinforcing bar 2 is magnetized in the same manner as in the first embodiment. Thereafter, the magnetic sensor 10 </ b> A, 10 </ b> B is moved along the longitudinal direction of the reinforcing bar 2 to move the magnetic detection unit 310 on the surface of the concrete body 1.

  Changes in the magnetic flux density at each position on the surface of the concrete body 1 are measured by the movement of the magnetic detection unit 310. When the change exceeds a threshold value, it is indicated on the display unit 22 that the rebar 2 has a fracture H. Is displayed.

  According to the nondestructive inspection apparatus 300 of the third embodiment, if the magnetic sensors 10A and 10B are arranged along the longitudinal direction of the reinforcing bar 2, the magnetic detection unit 310 can be used in a direction other than the longitudinal direction of the reinforcing bar 2 or a direction orthogonal thereto. Since it may be moved so as to draw an oblique direction or a circle, the inspection of breakage becomes very easy.

  In the above embodiments, the method for detecting the breakage of the rebar 2 extending in a straight line has been described. However, the above-described magnetic shunting method can also be used for detecting the breakage of the bent portion of the rebar that bends at the corner of the concrete body. (The method for detecting the breakage of the bent portion is described in Japanese Patent Application No. 2008-330287, and is omitted here).

  For example, the reinforcing bars may be magnetized by magnets from one surface and the other surface of the corners of the concrete body, and thereafter, magnetizing may be performed on each surface as described above.

  The present invention is not limited to the above-described embodiments, and design changes and additions are permitted without departing from the spirit of the invention according to each claim of the claims.

1 Concrete body 1A Surface 2 Reinforcing bar (reinforcing object)
2A Reinforcing bar (reinforcing bar next to the diagnosis object)
5 Magnet

Claims (3)

A non-destructive inspection method for detecting the presence or absence of breakage of the reinforcing bar by magnetizing a reinforcing bar provided in the concrete body with a magnet and then measuring the magnetic flux density on the surface of the concrete body,
Moving the magnet on the surface of the concrete body along the longitudinal direction of the reinforcing bar to magnetize the reinforcing bar along the longitudinal direction;
After that, the rebar is magnetized along the longitudinal direction again by moving the magnet along the longitudinal direction of the rebar at a position away from the position where the rebar is magnetized,
Then, the presence or absence of the fracture | rupture of the said reinforcing bar is detected by measuring the magnetic flux density of the surface of the said concrete body, The nondestructive inspection method characterized by the above-mentioned. The first rebar is magnetized from directly above the rebar,
The nondestructive inspection method according to claim 1, wherein the subsequent magnetization is performed from a position directly above a reinforcing bar arranged next to the reinforcing bar. A magnetic sensor that moves on the surface of the concrete body after magnetizing the reinforcing bar by the method according to claim 1 or 2,
An arithmetic means for obtaining the magnetic flux density in the vertical direction of the surface of the concrete body from the detection signal detected by the magnetic sensor;
A break determination means for obtaining a change in the magnetic flux density in the longitudinal direction of the reinforcing bar from the magnetic flux density obtained by the calculating means, and determining whether or not the reinforcing bar is broken based on the degree of the change; Nondestructive inspection equipment.