JP6546075B2 - Detection method - Google Patents

Description

  The present invention relates to a detection method.

  The reinforced concrete structure is a composite structure of compressive-strength concrete and tensile-strength reinforcement, and the reinforcement is protected by concrete. However, when a crack occurs in the concrete of the reinforced concrete structure, the corrosion of the reinforcing steel proceeds due to the neutralization of the concrete, and the stress is concentrated locally on the reinforcing steel due to the decrease in the strength of the concrete itself. It may lead to a decrease in life. Therefore, in the maintenance of reinforced concrete structures, early detection of cracks in concrete is required.

  Conventionally, cracks have been detected visually by using a sensor that changes color due to cracking or performing image processing on a concrete surface with a digital camera (see Non-Patent Documents 1 and 2). However, when using a sensor, crack detection was dependent on the inspection interval of the sensor. In addition, when using a digital camera, there are problems in that the imaging range is limited and the cost of data storage and image processing. Therefore, instead of visual crack detection, a technology has been proposed in which a strain gauge is attached to a position where occurrence of a crack in concrete is predicted, and a change in strain is monitored to detect the crack.

Ishikawa Yuji, 4 others, "Automatic Measurement of Width and Length of Concrete Crack Using Digital Camera Image", 60th Annual Conference of the Japan Society of Civil Engineers, September 2005, pp. 203-204 Kaneko, Y., et al., "Cracking Inspection Technique for Concrete Structures Using Digital Camera Images", NTT Technical Journal, December 2011, p. 21-24

  However, when a strain gauge is used, the range in which a crack can be detected is limited to the range of the application position of the strain gauge. On the other hand, the measured value of strain by the strain gauge is output as a ratio to the gauge length. That is, for example, when the width of the generated crack is 0.1 mm, the measured value of displacement by a strain gauge of 1 mm in gauge length is 10%, and the measured value of displacement by a strain gauge of 60 mm in gauge length is about 0. It will be 1%. Therefore, as the size of the strain gauge is increased, the crack detection sensitivity decreases.

  In addition, since the variation in strain to be measured includes variation over time due to expansion and contraction of the surface of the concrete due to thermal expansion and wind pressure of concrete as well as variation due to occurrence of crack, variation in strain due to occurrence of crack is It was difficult to identify.

  The present invention has been made in view of the above, and it is an object of the present invention to easily and accurately detect a wide range of cracks occurring in concrete on the surface of a reinforced concrete structure.

To solve the above problems and to achieve the object, the detection method of the present invention uses a strain gauge installed at a plurality of locations on the line take concrete tensile stress on the surface of the reinforced concrete of each strain gauge A measuring step of measuring the strain at the installation position, and a judging step of judging that a crack is generated when the behavior of any change in the measured strain at a plurality of points is different. I assume.

  According to the present invention, detection of a wide range of cracks occurring in concrete on the surface of a reinforced concrete structure can be easily and accurately performed.

FIG. 1 is a flowchart illustrating a detection processing procedure according to an embodiment of the present invention. FIG. 2 is a schematic view illustrating the strain gauge according to the present embodiment. FIG. 3 is an explanatory view for explaining a detection range of strain due to the occurrence of a crack of the strain gauge of the present embodiment. FIG. 4 is an explanatory view for explaining the behavior of the change in strain due to a crack according to the present embodiment. FIG. 5 is a figure which illustrates the behavior of the change of the distortion by one strain gauge of this embodiment. FIG. 6 is a figure which illustrates the behavior of the change of the distortion by two strain gauges of this embodiment. FIG. 7 is an explanatory view for explaining an outline of this embodiment. FIG. 8 is a diagram illustrating the results of the load-loading test of the present embodiment. FIG. 9 is a diagram illustrating the results of the load-loading test of the present embodiment.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited by this embodiment. Further, in the description of the drawings, the same portions are denoted by the same reference numerals.

  First, an outline of a detection method according to the present embodiment will be described. The detection method of the present embodiment includes a measurement step and a determination step. In the measurement process, the displacement of the installation position of each displacement measurement meter is measured using the displacement measurement meters installed at a plurality of points on the straight line where the tensile stress of the concrete on the surface of the reinforced concrete structure is applied. In the determination step, it is determined that a crack has occurred if the behavior of any change among the measured displacements at a plurality of locations is different. Each step will be described in detail below with reference to FIG. In the present embodiment, a strain gauge is applied as a displacement measurement meter. That is, a strain gauge is attached to the surface of the reinforced concrete structure, and the strain at the attachment position is measured.

[Measurement process]
In the measurement process, strain gauges for measuring strain are attached to a plurality of locations on a straight line where tensile stress of concrete on the surface of the reinforced concrete structure is applied, and the strain at the application position of each strain gauge is measured (step S1). As the application position of the strain gauges, the load application direction assumed for the reinforced concrete structure is predicted, and two or more places on the straight line to which the tensile stress of the surface concrete is applied are determined. The strain gauges may be attached to three or more places.

  Here, the strain gauge used is not particularly limited, and may be any of a foil strain gauge, a linear strain gauge, a semiconductor strain gauge, and the like. In the present embodiment, a foil strain gauge is applied. In this strain gauge 1, as illustrated in FIG. 2, metal foils laid out in a zigzag shape in a range of a predetermined gauge length are attached on the base of a thin insulator, and changes in electrical resistance due to deformation are measured. Convert to strain.

  As described above, the measured value of strain by the strain gauge 1 is output at a ratio to the gauge length. That is, for example, when the width of the generated crack is 0.1 mm, the measured value of displacement by a strain gauge of 1 mm in gauge length is 10%, and the measured value of displacement by a strain gauge of 60 mm in gauge length is about 0. It will be 1%. Therefore, as the gauge length or size of the strain gauge 1 increases, the crack detection sensitivity decreases.

  In addition, the detection range of the strain due to the crack of the strain gauge 1 is limited to immediately below and near the sticking position of the strain gauge 1 when the strain gauge 1 is attached to the concrete 2 to be measured as illustrated in FIG. Be done. Therefore, the position away from the application position of the strain gauge 1 is out of the detection range of the strain due to the crack.

[Determination process]
In the determination step, it is determined that a crack has occurred if the behavior of any change among the measured strains at a plurality of points is different. In this distortion determination step, for example, an arithmetic unit realized using a CPU (Central Processing Unit) or the like that executes a processing program stored in the memory receives the distortion input measured in the processing of step S1. Accept and execute.

  Here, first, with reference to FIG. 4, the relationship between the position at which a crack is generated and the behavior of fluctuation or change in strain measured by the strain gauge 1 will be described. As illustrated in FIG. 4A, it is assumed that the concrete 2 is stretched in a state in which the strain gauge 1 is attached to the surface of the concrete 2. In this case, as illustrated in FIG. 4B, if a crack is generated immediately below the application position of the strain gauge 1, the crack expands and the measured strain increases. On the other hand, as illustrated in FIG. 4C, if a crack is generated in the vicinity other than immediately below the strain gauge 1, the generated crack expands, and the concrete 2 shrinks immediately below the strain gauge 1, and the measurement is performed. Strain is reduced.

  FIG. 5 is a diagram illustrating the behavior of the change in strain when a crack occurs immediately below one strain gauge 1 as illustrated in FIG. 4 (b). In this case, as shown by the white arrows in the region between the broken lines in FIG. However, when there is only one strain gauge 1, it is difficult to determine whether the sudden increase in strain is due to the generation of a crack or whether it is successive due to thermal expansion, wind pressure or the like.

  On the other hand, FIG. 6 is a diagram illustrating the behavior of change in strain due to two strain gauges 1. FIG. 6 exemplifies the behavior of the change in strain when a crack is generated immediately below one strain gauge 1 and in the vicinity other than immediately below the other strain gauge 1. That is, in the strain gauge 1 in which the crack is generated immediately below, as shown by the white arrow a in FIG. On the other hand, in the strain gauge 1 where a crack has occurred other than immediately below, as shown by the white arrow b in FIG. Thus, if a crack occurs immediately below and in the vicinity of the plurality of strain gauges 1, different strain change behavior is shown in the same region.

  In the case of continuous strain fluctuation due to thermal expansion or temporary wind pressure etc., all strain of the entire reinforced concrete structure exhibits almost uniform behavior. On the other hand, in the strain fluctuation due to the occurrence of a crack, as described above, the increase and decrease are locally reversed between the strains at a plurality of points. Therefore, when the behavior of any change in the strain at a plurality of points is different, it is clearly detected that a crack has occurred.

  Therefore, in the determination step of the present embodiment, if all the behaviors of changes in strain measured at the processing in step S1 are the same (step S2, Yes), it is determined that no crack has occurred (step S2) S3), the determination process ends.

  On the other hand, when the behavior of the change in strain at any one of a plurality of places is different (Step S2, No), it is determined that a crack is generated (Step S4). In this case, if the measured value of strain at one of the strain gauges 1 is rapidly increasing (Yes at step S5), it is determined that a crack has occurred immediately below the application position of the strain gauge 1 (step S6) ). In addition, it is determined that a crack has occurred in the vicinity other than immediately below the attachment position of another strain gauge 1 in which the measured value of strain has not increased rapidly (Step S5, No → Step S7). Thus, the series of determination processing ends.

  As described above, according to the detection method of the present embodiment, the attachment positions of the strain gauges 1 using the strain gauges 1 attached to a plurality of locations on the straight line where the tensile stress of the concrete 2 on the surface of the reinforced concrete structure is applied. Strain is measured. In addition, it is determined that a crack is generated when the behavior of any change among the measured strains at a plurality of points is different.

  As a result, even when stress is concentrated in a wide range that can not be measured with one strain gauge 1 and occurrence of a crack is predicted, tensile stress is applied on a straight line without increasing the size of the strain gauge 1 and reducing sensitivity. Cracks can be easily detected simply by attaching a plurality of strain gauges 1. In addition, it is possible to detect a crack with high accuracy by detecting the fluctuation of strain due to the occurrence of a crack, as distinguished from the fluctuation of strain over time due to thermal expansion, wind pressure or the like. As described above, according to the detection process of the present embodiment, it is possible to easily and accurately detect a wide range of cracks generated in the concrete 2 on the surface of the reinforced concrete structure.

[Example]
In the present embodiment, as illustrated in FIG. 7, a strain gauge having a gauge length of 60 mm is applied to the concrete 2 on the surface of a concrete pole (CP) which is a reinforced concrete structure having a hollow inside formed by the reinforcing bars 3 and the concrete 2. 1 was affixed. That is, as shown by arrow A in FIG. 7, when a load-loading test was performed in which a load is applied in the horizontal direction near the end of the upper portion of CP, the adhesive was stuck at two or more places on the straight line where tensile stress occurs. Specifically, two strain gauges 1 of a strain gauge 11 at a position of 6000 mm from the end of the CP surface and a strain gauge 12 of a position of 6200 mm were attached at an interval of 200 mm around the ground part. In addition, the sticking position of the strain gauge 1 is not limited to the vicinity of the ground portion, and may be, for example, in the vicinity of an assumed mounting position of a cable or a branch line.

  As a result of the load test, generation of a crack with a width of about 0.1 mm was visually confirmed around a load of 2.0 kN. The visually confirmed cracks are directly under the application position of the strain gauge 12 at a position 6200 mm from the end of the CP, and in the vicinity several tens of mm away from the application position of the strain gauge 11 at a position 6000 mm from the end of the CP. Occurred at

  FIG. 8 and FIG. 9 are diagrams showing the results of the loading test. FIG. 8 is a diagram illustrating the relationship between strain and load in the strain gauge 12 at a position of 6200 mm from the end. Moreover, FIG. 9 is a figure which illustrates the relationship of the distortion and load in the strain gauge 11 of the position of 6000 mm from an end. The straight line indicated by the broken line in FIGS. 8 and 9 is a regression line showing the relationship between the strain and the applied load when no crack occurs in the CP. This regression line is derived by extending a straight part indicating the relationship between the strain and the applied load in the range of the applied load where the CP does not crack in the initial stage of the applied load test. The load load range in which the CP does not crack is, for example, about half the design load of the CP.

  In FIG. 8, it was confirmed that the strain increased sharply and deviated to the positive side, that is, the upper side from the regression line due to the extension of the crack generated immediately below the application position of the strain gauge 12. In FIG. 8, the deviation of the strain from the regression line starts at around 1 kN. From this, although the crack generated immediately below the application position of the strain gauge 12 was visually confirmed when a load of about 2 kN was applied, it was generated when a load of about 1 kN was already applied. I understand.

  On the other hand, in FIG. 9, the straining position of the strain gauge 11 contracts due to the extension of the crack generated near the sticking position of the strain gauge 11, and the strain decreases, and the negative side from the regression line, that is, the lower side confirmed.

  Although the embodiments to which the invention made by the inventors of the present invention has been applied have been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to the embodiments. That is, other embodiments, examples, operation techniques and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

1 strain gauge 2 concrete 3 rebar

Claims (3)

Measuring the strain at the installation position of each strain gauge using strain gauges installed at multiple points on a straight line where tensile stress is applied to the concrete on the surface of the reinforced concrete structure;
A determination step of determining that a crack is generated if the behavior of any change among the plurality of measured strains is different;
A detection method characterized in that In the determination step, when it is determined that a crack is generated, a crack is generated immediately below the installation position of the strain gauge in which the measured strain is further increased in the region where the change behavior is different. The detection method according to claim 1, wherein it is determined that In the determination step, when it is determined that a crack is generated, a crack is further generated in the vicinity of the installation position of the strain gauge in which the strain measured in the region where the change behavior is different is reduced. The detection method according to claim 2, characterized in that:

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