JP7611870B2 - Inspection device and method for internal reinforcing bars in reinforced concrete structures - Google Patents

Description

The present invention relates to an inspection device and method for the internal reinforcing bars of reinforced concrete structures.

To prevent reinforced concrete pillars from breaking, regular visual inspections are conducted. Visual inspections of reinforced concrete pillars do not adequately grasp the condition of the internal rebar, so efforts are underway to develop methods for non-destructively inspecting the broken parts of the internal rebar in reinforced concrete pillars. For example, Patent Document 1 discloses an inspection method for determining whether or not the internal rebar is broken by magnetizing the internal rebar of a reinforced concrete pillar from the outside and measuring the minute amount of magnetic flux leaking from the broken parts of the internal rebar.

JP 2006-177747 A

The inspection method of Patent Document 1 has the problem that if equipment such as overhead line fittings, electric wires, and machinery is attached to a reinforced concrete pole, the internal rebar cannot be magnetized and it is not possible to determine whether or not the internal rebar is broken. For this reason, it is necessary to remove various equipment from the reinforced concrete pole before magnetizing the internal rebar, which makes the inspection work take a lot of time. This problem is not limited to determining whether or not the internal rebar is broken in a reinforced concrete pole, but also exists when determining whether or not the internal rebar is broken in other reinforced concrete structures.

The present invention was made based on this background, and aims to provide an inspection device and an inspection method that can determine whether or not there are any breaks in the internal rebars, even in reinforced concrete structures with equipment attached.

In order to achieve the above object, an inspection device according to the present invention comprises:
An inspection device for detecting the presence or absence of fractures in internal reinforcing bars in a reinforced concrete structure,
a thermometer for measuring a change over time in the temperature distribution on the surface of the reinforced concrete structure due to a thermoelastic effect ;
a calculation device that generates data relating to a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the change over time in temperature distribution measured by the thermometer; and
Equipped with.

The present invention provides an inspection device and an inspection method that can determine whether or not there are any breaks in the internal rebars, even in reinforced concrete structures with equipment attached.

1 is a schematic diagram showing a configuration of an inspection device according to a first embodiment of the present invention; 1 is a block diagram showing a hardware configuration of a calculation device according to a first embodiment of the present invention; FIG. 1A is a diagram showing an example of a data table stored in a temperature video memory unit according to embodiment 1 of the present invention, and FIG. 1B is a diagram showing an example of a data table stored in a stress fluctuation image memory unit according to embodiment 1 of the present invention. 5 is a diagram showing a procedure in which the calculation device according to the first embodiment of the present invention calculates a temperature difference for each pixel of a temperature image. 3 is a flowchart showing a flow of an inspection method according to the first embodiment of the present invention. 4 is a flowchart showing a flow of a calculation process according to the first embodiment of the present invention. FIG. 11 is a schematic diagram showing a configuration of an inspection device according to a second embodiment of the present invention. 10A is a perspective view showing the configuration of a wind-type coil according to a second embodiment of the present invention, and FIG. 10B is a perspective view showing the configuration of a spot-type coil according to the second embodiment of the present invention. 10 is a flowchart showing the flow of an inspection method according to a second embodiment of the present invention. FIG. 2 is a cross-sectional view showing a test piece of a reinforced concrete column in Example 1. 4A and 4B are photographs taken from above and from the side, respectively, of the state of the bending test in Example 1. 4A and 4B are diagrams showing stress variation images of a test specimen of a reinforced concrete column in Example 1. 1A and 1B are diagrams showing temperature change images and stress fluctuation images of a test specimen of a reinforced concrete column to which a mounting bracket is attached in Example 1. 13A and 13B are diagrams showing the state in which a wind coil and a spot coil are set on a test piece of a reinforced concrete column in Example 2. 1A is a diagram showing a temperature image of a test piece of a reinforced concrete column in Example 2, and FIG. 1B is a diagram showing a temperature image of a test piece of a reinforced concrete column to which a mounting bracket in Example 2 is attached.

The inspection device and inspection method according to the embodiment of the present invention will be described in detail below with reference to the drawings. In each drawing, the same or equivalent parts are given the same reference numerals.

(Embodiment 1)
An inspection device and an inspection method according to a first embodiment will be described with reference to Figures 1 to 6. In the first embodiment, a method for detecting a breakage point of an internal rebar in a reinforced concrete column (hereinafter abbreviated as "CP") will be described when an unbalanced load occurs at the breakage point of the internal rebar and the internal stress is constantly fluctuating. The inspection device and the inspection method according to the first embodiment are useful when the internal rebar in the middle part of the CP breaks and an unbalanced load occurs at the breakage point due to stress concentration.

In the inspection method according to the first embodiment, a thermoelastic stress measurement technique is used to determine whether or not there is a fracture in the internal rebar of a CP in a state of stress fluctuation. Specifically, an infrared camera is first used to measure the temperature distribution on the surface of a CP in a state of stress generation. The temperature distribution on the CP surface reflects the temperature distribution of the internal rebar due to heat transfer. Next, a stress fluctuation image is generated that shows the distribution of stress fluctuations in the CP based on the change over time in the measured temperature distribution on the CP surface.

If the generated stress fluctuation image shows an area with a large stress fluctuation compared to the surrounding area, the area with the large stress fluctuation is determined to be the location of the fracture of the internal rebar. This is because in a healthy CP, the load is applied evenly to the internal rebar and concrete, and no areas of stress concentration occur, whereas in a CP where the internal rebar is fractured, the fractured internal rebar cannot withstand the tensile load, and the load is concentrated on the internal rebar that receives the compressive load on the opposite side.

The mechanism of thermoelastic stress measurement technology, which is the premise of the inspection method according to the first embodiment, will be described below. It is widely known that adiabatic expansion of gas reduces the temperature, and adiabatic compression of gas increases the temperature, but a similar phenomenon occurs when stress is applied to a solid. The phenomenon in which temperature change occurs due to elastic deformation of a solid is called the "thermoelastic effect." The relationship between the amount of change ΔT in the temperature of the measurement object in the thermoelastic effect and the fluctuation width Δσ of the sum of the principal stresses of the measurement object is expressed by the following formula.
ΔT=-K*T*Δσ…(1)

The principal stress is the stress acting on the principal stress surface of the measurement object. The principal stress surface is the surface of the measurement object where the shear stress is zero and the normal stress is maximum or minimum. In addition, T in formula (1) is the absolute temperature of the measurement object at the time of measurement, and K is the thermoelastic coefficient. The thermoelastic coefficient K is a unique value set for each material of the measurement object, and for example, in the case of CP, K = 4.0 x ^10-6 MPa ^-1 .

In thermoelastic stress measurement technology, an infrared camera is used to measure the minute temperature change ΔT when a stress fluctuation occurs in the measurement object, and the measured temperature change ΔT is substituted into formula (1) to convert it into the fluctuation width Δσ of the sum of principal stresses. The reason that an infrared camera is used to measure the temperature of the measurement object is that the temperature of the measurement object is measured without contact, thereby not disturbing the temperature field of the measurement object.
This is how thermoelastic stress measurement technology works.

Next, the configuration of the inspection device 1 according to the first embodiment will be described with reference to FIG. 1. The inspection device 1 includes an infrared camera 2 that captures a temperature image (thermography) that is an image showing the temperature distribution on the surface of the CP to be measured, and a calculation device 100 that generates a stress fluctuation image that is an image showing the stress fluctuation of the CP based on the temperature image captured by the infrared camera 2. The calculation device 100 is, for example, a general-purpose computer. The infrared camera 2 and the calculation device 100 are connected to be able to communicate with each other via a wired or wireless communication line.

The infrared camera 2 is an example of a thermometer that measures the temperature distribution on the CP surface. The temperature image captured by the infrared camera 2 is, for example, a video (temperature video) showing the change in temperature distribution on the CP surface. The temperature video is a chronological arrangement of frames showing the temperature distribution on the CP surface acquired at a constant sampling period. The stress fluctuation image is an image that expresses the distribution of stress fluctuations on the CP using a color distribution.

The infrared camera 2 detects infrared energy emitted from the measurement object and converts it into a signal indicating the intensity of the infrared energy. The converted signal is then processed to generate a temperature image in which the temperature distribution of the measurement object is visualized by a color distribution. The infrared camera 2 preferably has a highly accurate temperature resolution, and the temperature resolution is, for example, 0.02 K or less. This is because the temperature change of a solid is extremely minute, and in order to improve the accuracy of the converted value of the stress variation, it is necessary for the infrared camera 2 to have a highly accurate temperature resolution. The infrared camera 2 may be supported by, for example, a tripod.
The inspection device 1 has the above configuration.

Next, the hardware configuration of the arithmetic device 100 according to the first embodiment will be described with reference to FIG. 2. The arithmetic device 100 includes an operation unit 110, a display unit 120, a communication unit 130, a storage unit 140, and a control unit 150. The units of the arithmetic device 100 are connected to each other via an internal bus (not shown).

The operation unit 110 receives instructions from the user and supplies operation signals corresponding to the received operations to the control unit 150. The operation unit 110 includes, for example, a mouse and a keyboard.

The display unit 120 is equipped with a display drive circuit and displays various images to the user based on data supplied from the control unit 150.

The communication unit 130 is a communication interface that allows the computing device 100 to communicate with external devices. The communication unit 130 communicates with external devices via a communication network such as the Internet and an input/output terminal. The input/output terminal is, for example, a Universal Serial Bus (USB).

The storage unit 140 includes, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, and a hard disk. The storage unit 140 stores the programs executed by the control unit 150 and various data, for example, the formula (1) and the value of the thermoelastic coefficient K for each material. The storage unit 140 also temporarily stores various information and functions as a work memory for the control unit 150 to execute processing. Furthermore, the storage unit 140 includes a temperature video storage unit 141 and a stress variation image storage unit 142.

As shown in FIG. 3(a), the temperature video storage unit 141 stores the temperature video captured by the infrared camera 2 in association with the CP identification number and the capture position. The CP identification number is a unique identification number assigned to each CP. The capture position is expressed, for example, by the axial position (height) z1, z2, ... of the CP and the angle r1, r2, ... around the CP axis.

As shown in FIG. 3(b), the stress variation image storage unit 142 stores the stress variation image generated by the calculation device 100 based on the temperature change image in association with the CP identification number and the shooting position.

Returning to FIG. 2, the control unit 150 includes a processor and controls each part of the arithmetic device 100. The processor is, for example, a CPU (Central Processing Unit). The control unit 150 executes the program stored in the storage unit 140 to perform the arithmetic processing of FIG. 6. Functionally, the control unit 150 includes an acquisition unit 151, a temperature difference calculation unit 152, a stress variation image generation unit 153, and an output unit 154.

The acquisition unit 151 acquires a temperature video showing the temperature distribution on the CP surface captured by the infrared camera 2, and stores the video in the temperature video storage unit 141 in association with the CP identification information and the capture position. The acquisition of data by the acquisition unit 151 includes reading out data stored in the storage unit 140.

The temperature difference calculation unit 152 calculates the temperature difference for each pixel of the temperature video based on the temperature video acquired by the acquisition unit 151. Specifically, a certain number of analysis points of frames are extracted from the temperature video acquired by the acquisition unit 151, and the difference between the maximum and minimum temperature values for each pixel is calculated from the collection of extracted frames. The number of analysis points is the number of frames to be extracted, for example, 250 frames. As shown in FIG. 4, the extraction of frames is performed at a certain analysis step from the first frame, and the temperature differences ΔT1, ΔT2, ΔT3, ΔT4, ... are calculated one after another from the collection of extracted frames. The analysis step is the position at which the extraction of frames starts, and may be, for example, every 150 steps from the first frame. The temperature difference calculation unit 152 may generate a temperature change image showing the change in temperature distribution on the CP surface by expressing the calculated value of the temperature difference for each pixel as a color distribution.

The stress variation image generating unit 153 generates a stress variation image showing the stress variation of the CP based on the calculated temperature difference value showing the temperature change of the CP surface for each pixel calculated by the temperature difference calculating unit 152, and stores it in the stress variation image storage unit 142 in association with the CP identification information and the shooting position. Specifically, the calculated temperature difference value ΔT is substituted into formula (1) for each pixel of the temperature variation image, and converted into a converted value Δσ of the stress variation. Next, the converted value of the stress variation for each pixel is expressed as a color distribution to generate a stress variation image showing the stress variation of the CP. Note that the generation of the stress variation image includes the generation of data (image data) related to the stress variation image and the generation of a latent image of the stress variation image.

The output unit 154 outputs to the outside the data of the stress variation image converted by the stress variation image generating unit 153. For example, the stress variation image may be displayed on the display unit 120.
The above is the hardware configuration of the arithmetic device 100.

Next, referring to FIG. 5, the flow of the inspection method performed by the user using the inspection device 1 according to the first embodiment will be described. First, the infrared camera 2 is set up facing the CP (step S11). Specifically, a tripod is attached to the infrared camera 2, and the tripod is set on the ground so that the infrared camera 2 faces the CP.

Next, a temperature video showing the temperature distribution on the CP surface is captured using the infrared camera 2 installed in step S11 (step S12). The frame rate and capture time of the temperature video are preset by the user. To grasp the temperature change on the CP surface, it is preferable to capture images of, for example, 2000 frames or more.

Next, based on the temperature video captured by the infrared camera 2 in step S12, the calculation device 100 is caused to execute the calculation process shown in FIG. 6, thereby causing the display unit 120 of the calculation device 100 to display a stress variation image of the CP (step S13).

Next, based on the stress variation image obtained in step S13, the presence or absence of a fractured portion of the CP internal rebar is determined (step S14). Specifically, in a portion where the internal rebar is not fractured, there is almost no stress variation, whereas in a portion where the internal rebar is fractured, the load remains unbalanced, causing a large stress variation. Therefore, the user can observe the color distribution of the CP stress variation image and determine whether there is a portion where the color distribution is significantly different from the surrounding area, thereby determining the fractured portion of the internal rebar.
The above is the flow of the inspection method.

(Calculation processing)
Next, a flow of the calculation process executed by the calculation device 100 according to the first embodiment will be described with reference to Fig. 6. The calculation process starts when an instruction from a user is received after a temperature video of the CP surface is captured by the infrared camera 2.

First, the acquisition unit 151 acquires a temperature video that captures the temperature distribution on the CP surface (step S21).

Next, the temperature difference calculation unit 152 calculates the temperature difference indicating the temperature change of the CP surface for each pixel based on the temperature video acquired in the processing of step S21 (step S22). Specifically, a certain number of frames are extracted from the temperature video acquired in the processing of step S21, and the difference between the maximum and minimum temperature values for each pixel is calculated from the collection of extracted frames.

Next, the stress variation image generating unit 153 generates a stress variation image showing the stress variation of the CP based on the calculated temperature difference showing the temperature change of the CP surface for each pixel calculated in the processing of step S22 (step S23). Specifically, the calculated temperature difference value ΔT for each pixel of the temperature image is substituted into formula (1) and converted into a conversion value Δσ of the stress variation.

Next, the output unit 154 causes the display unit 120 to display the stress variation image obtained in the processing of step S23 (step S24), and ends the processing.
The above is the flow of the calculation process.

As described above, the inspection device 1 according to the first embodiment includes an infrared camera 2 that measures the change over time in the temperature distribution on the surface of the CP, and a calculation device 100 that generates a stress variation image showing the stress variation of the CP based on the change over time in the temperature distribution measured by the infrared camera 2. Therefore, it is possible to determine the presence or absence of fractures in the internal rebar even in areas where equipment is installed in the CP, and as a result, the degree of deterioration of the CP can be determined quickly and accurately. This reduces the costs required for maintenance management of the CP and the burden of inspection on workers.

(Embodiment 2)
An inspection device and an inspection method according to the second embodiment will be described with reference to Figures 7 to 9. In the first embodiment, the temperature of the CP surface in a stressed state is measured, but in the second embodiment, the temperature of the CP surface is measured after the internal rebar of the CP in a stationary state is heated by an induction coil. The inspection device and inspection method according to the second embodiment can also be applied to cases where no unbalanced load due to stress concentration is occurring. The following mainly describes the differences between the two.

The configuration of the inspection device 1 according to the second embodiment will be described with reference to FIG. 7. The inspection device 1 includes an induction heating coil 3 that heats the internal rebar of the CP from the outside, and an infrared camera 2 that measures the temperature distribution on the surface of the CP after the internal rebar is heated by the induction heating coil 3.

The infrared camera 2 is equipped with a monitor that displays a temperature image showing the temperature distribution on the CP surface. The temperature image captured by the infrared camera 2 may be a still image showing the temperature distribution on the CP surface, or a temperature video showing the change in the temperature distribution on the CP surface.

The induction heating coil 3 is an example of a heating means for externally heating the internal rebar of a CP. The induction heating coil 3 utilizes the principle of electromagnetic induction to heat the internal rebar without coming into contact with it. The principle of electromagnetic induction is that when an alternating current is passed through the coil's conductor, a fluctuating magnetic field is generated around it, and when metal is placed in this magnetic field, an induced current flows due to electromagnetic induction, and this induced current generates Joule heat in the metal.

The induction heating coil 3 may be a wound coil 3A as shown in FIG. 8(a), a spot coil 3B as shown in FIG. 8(b), or another type. The wound coil 3A heats the internal rebar while wound around the CP. The spot coil 3B is made of a water-cooled spiral coil, and is suitable for pinpoint heating of cracked areas.

Next, referring to FIG. 9, the flow of the inspection method performed by the user using the inspection device 1 according to the second embodiment will be described. First, the infrared camera 2 and the induction heating coil 3 are placed on the CP (step S31). Specifically, a tripod is attached to the infrared camera 2, and the tripod is placed on the ground so that the infrared camera 2 faces the CP. The induction heating coil 3 may be wrapped around the surface of the CP or placed in the vicinity of the surface.

Next, the internal rebar of the CP is heated by the induction heating coil 3 installed in step S31 (step S32). Specifically, a fluctuating magnetic field is generated in the vicinity of the induction heating coil 3 by supplying a high frequency wave to the induction heating coil 3, and an eddy current is generated in the internal rebar, thereby generating Joule heat in the internal rebar.

Next, the infrared camera 2 installed in step S31 is used to capture a temperature image showing the temperature distribution on the surface of the CP where the internal rebar has been heated in step S32 (step S33). The temperature image may be either a still image or a video image.

Next, the temperature image obtained in step S33 is displayed on the monitor (step S34), and the presence or absence of a fractured portion of the CP internal rebar is determined based on the temperature image displayed on the monitor (step S35), and the process is terminated. Specifically, in the portion where the internal rebar is not fractured, the CP surface also heats up due to the heat generated by the internal rebar, whereas in the portion where the internal rebar is fractured, the CP surface does not heat up as a result of no induction heating of the internal rebar. Therefore, the user can determine the presence or absence of a fractured portion of the internal rebar by observing the color distribution of the temperature image. Note that even if equipment is attached to the CP, the heat generated by the equipment does not affect the temperature distribution of the CP over a wide area, so the presence or absence of a fractured portion of the internal rebar can be determined except for the portion overlapping with the equipment.
The above is the flow of the inspection method according to the second embodiment.

The inspection device 1 according to the second embodiment includes, in addition to the infrared camera 2 and the calculation device 100, an induction heating coil 3 that is installed next to the CP and heats the internal rebar of the reinforced concrete structure from the outside. Therefore, even if no stress fluctuation occurs in the internal rebar, the presence or absence of a fracture can be determined by using the induction heating coil 3. Also, unlike the inspection device 1 according to the first embodiment, there is no need to analyze temperature images, so the presence or absence of a fracture in the internal rebar can be determined quickly on-site.

The present invention is not limited to the above embodiment, and the following modifications are also possible.

(Modification)
In the above embodiment, there is one infrared camera 2, but the present invention is not limited to this. For example, two or more infrared cameras 2 may be provided in order to quickly capture an image of the entire CP.

In the above embodiment, an infrared camera 2 is used as a thermometer, but the present invention is not limited to this. For example, a non-contact thermometer other than the infrared camera 2 may be used.

In the above embodiment, the infrared camera 2 captures a temperature image showing the temperature distribution on the CP surface, but the present invention is not limited to this. If data showing the temperature distribution on the CP surface can be obtained, it is not necessary to capture a temperature image, and the data showing the temperature distribution on the CP surface may be treated as numerical data corresponding to pixel positions.

In the above-mentioned first embodiment, the calculation device 100 generates a stress variation image, and the user determines whether or not there is a fracture in the internal rebar by referring to the stress variation image displayed on the display unit 120 of the calculation device 100, but the present invention is not limited to this. For example, the control unit 150 of the calculation device 100 may detect whether or not there is a fracture in the internal rebar based on the stress variation image.

Specifically, the converted value of the stress variation for each pixel in the stress variation image is compared with a preset stress variation threshold, and if a pixel exists where the converted value of the stress variation is equal to or greater than the stress variation threshold, it is determined that the internal rebar is broken at the location corresponding to that pixel. At this time, it is not necessary to display the stress variation image on the display unit 120 of the computing device 100, and it is sufficient to simply compare the converted value of the stress variation at each pixel of the stress variation image with the stress variation threshold and display the comparison result.

In the above-mentioned second embodiment, the monitor of the infrared camera 2 displays a temperature image, and the user determines whether or not there is a fracture in the internal rebar by referring to the temperature image displayed on the monitor of the infrared camera 2, but the present invention is not limited to this. For example, the calculation device 100 may be communicatively connected to the infrared camera 2, and the control unit 150 of the calculation device 100 may detect whether or not there is a fracture in the internal rebar based on the temperature image captured by the infrared camera 2.

Specifically, the area corresponding to the internal rebar is recognized in the temperature image, the measured temperature value is compared with a preset temperature threshold for each pixel in the recognized area, and if there is a pixel whose measured temperature value is equal to or lower than the temperature threshold, it is determined that the internal rebar is broken at the location corresponding to that pixel. At this time, it is not necessary to display the temperature image on the display unit 120 of the computing device 100, and it is sufficient to simply compare the measured temperature value at each pixel of the temperature image with the temperature threshold and display the comparison result.

In the above-mentioned second embodiment, one induction heating coil 3 is applied to the CP, but the present invention is not limited to this. The number of induction heating coils 3 for the CP is arbitrary, and for example, there may be two or more in order to heat a wide area of the internal rebar.

In the above-mentioned first embodiment, various data are stored in the storage unit 140 of the computing device 100, but the present invention is not limited to this. For example, all or part of the various data may be stored in an external control device or computer via a communication network.

In the above-mentioned first embodiment, the arithmetic device 100 operates based on the programs stored in the storage unit 140, but the present invention is not limited to this. For example, the functional configuration realized by the programs may be realized by hardware.

In the above embodiment 1, the calculation device 100 is, for example, a general-purpose computer, but the present invention is not limited to this. For example, the calculation device 100 may be realized by a computer provided on a cloud.

In the above-mentioned first embodiment, the processing executed by the computing device 100 is realized by a device having the above-mentioned physical configuration executing a program stored in the memory unit 140, but the present invention may also be realized as a program or as a storage medium on which the program is recorded.

In addition, a program for executing the above-mentioned processing operations may be stored and distributed on a non-transitory computer-readable recording medium such as a flexible disk, a CD-ROM (Compact Disk Read-Only Memory), a DVD (Digital Versatile Disk), or an MO (Magneto-Optical Disk), and the program may be installed on a computer to configure a device that executes the above-mentioned processing operations.

In the above embodiment, the inspection object is a reinforced concrete pillar, which is an example of a long reinforced concrete structure, but the present invention is not limited to this. Other reinforced concrete structures, such as bridge decks, bridge piers, and building beams, girders, and columns, may also be inspected.

The above embodiments are examples, and the present invention is not limited to these, and various embodiments are possible without departing from the spirit of the invention described in the claims. The components described in each embodiment and variant can be freely combined. Furthermore, inventions equivalent to the inventions described in the claims are also included in the present invention.

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to these examples.

Example 1
In Example 1, bending stress was artificially generated in the middle of the CP sample, and it was verified whether or not the presence or absence of fractures in the internal rebar could be determined using the method according to the first embodiment.

First, as shown in Figure 10, a radial cut was made in the middle of a CP with 12 internal rebars, and 4 internal rebars were cut to create a CP sample (fractured sample). Next, bending deformation was applied to the CP sample so that a tensile load was applied to the fractured parts of the internal rebars, and the surface (compressed surface) of the CP sample on the side where the compressive load was applied was photographed with an infrared camera for about 20 seconds (about 2000 frames). Specifically, as shown in Figure 11(a), a bending test was performed using a bending test device according to JIS (Japanese Industrial Standards) A 5373. At this time, with the middle part of the CP fixed with a wire as shown in Figure 11(b), the end of the CP was pulled so that a tensile load was applied to the fractured parts of the internal rebars. The load on the fractured sample was in the range of 2.5 kN to 3 kN.

Next, a stress fluctuation image was generated based on the temperature video of the compression surface of the CP sample captured by infrared camera 2. Specifically, the measured temperature difference for each pixel obtained from the temperature video was converted into a corresponding stress fluctuation value using equation (1). Then, it was confirmed whether the fracture location of the internal rebar could be detected based on the stress fluctuation image. For comparison, a similar experiment was also conducted on a sound sample in which the rebar was not cut. The loading load on the sound sample was 7 kN (the standard fracture value for CP).

As a result, in the healthy specimen, as shown in Figure 12 (a), the stress was dispersed overall, and there were no areas of stress concentration. On the other hand, in the fractured specimen, as shown in Figure 12 (b), it was confirmed that there were areas of stress concentration, i.e. fractured areas of the internal rebar, even in the load range of 2.5 kN to 3 kN.

Next, we verified whether it was possible to identify the fractured location of the internal rebar even when overhead wiring fittings were attached to the middle part of the CP. All other experimental conditions were the same as when overhead wiring fittings were not attached. As a result, as shown in the stress fluctuation image in Figure 13, it was confirmed that there were stress concentration points in the internal rebar even when overhead wiring fittings were attached to the middle part of the CP.

Example 2
In Example 2, a CP sample was heated from the outside, and it was verified whether or not the presence or absence of fractures in the internal rebar could be determined using the method according to the second embodiment.

First, a CP test specimen was taken from the middle of the CP of an actual facility where part of the internal rebar had broken. Next, as shown in Figures 14(a) and (b), the surface of the CP test specimen was photographed with an infrared camera 2 while the internal rebar of the taken CP test specimen was heated, and an attempt was made to determine the location of the break in the internal rebar based on the temperature image obtained by the infrared camera 2. Note that a wind-type coil 3A and a spot-type coil 3B were used as the induction heating coils 3 used to heat the internal rebar. Hereinafter, the method using the wind-type coil will be referred to as the "wind method" and the method using the spot-type coil will be referred to as the "spot method."

As a result, as shown in the temperature image in Figure 15 (a), in both the wind method and the spot method, the temperature difference between the fractured part of the internal rebar and the surrounding area became noticeable as a result of the internal rebar generating heat, and the two could be clearly distinguished.

Next, we verified whether it was possible to identify the location of the fractured internal rebar even when overhead wire fittings were attached to the middle of the CP. All other experimental conditions were the same as when overhead wire fittings were not attached. As a result, as shown in the temperature images in Figure 15 (b), in both the wind method and the spot method, a significant temperature difference was observed between the fractured location of the internal rebar and other locations, except for the location where the overhead wire fittings were attached, making it possible to clearly distinguish between the two.

1 Inspection device 2 Infrared camera 3 Induction heating coil 100 Calculation device 150 Control unit 152 Temperature difference calculation unit 153 Stress variation image generation unit

Claims (10)

An inspection device for detecting the presence or absence of fractures in internal reinforcing bars in a reinforced concrete structure,
a thermometer for measuring a change over time in the temperature distribution on the surface of the reinforced concrete structure due to a thermoelastic effect ;
a calculation device that generates data relating to a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the change over time in temperature distribution measured by the thermometer; and
An inspection device comprising: the thermometer is an infrared camera that generates a temperature image showing the temperature distribution on the surface of the reinforced concrete structure;
The computing device generates data on a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the temperature image generated by the infrared camera.
2. The inspection device according to claim 1. The thermal resolution of the infrared camera is 0.02 K or less.
3. The inspection device according to claim 2. The computing device includes:
Calculating a temperature difference indicating a temperature change on the surface of the reinforced concrete structure for each pixel of the temperature image based on the temperature image generated by the infrared camera;
generating data relating to a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the temperature difference calculated for each pixel of the temperature image;
4. The inspection device according to claim 2 or 3. The arithmetic device causes the generated stress variation image to be displayed on a display unit.
The inspection device according to any one of claims 1 to 3. An inspection device for detecting the presence or absence of fractures in internal reinforcing bars in a reinforced concrete structure,
an infrared camera for generating a temperature image showing the temperature distribution on the surface of the reinforced concrete structure;
a calculation device that calculates a temperature difference indicating a temperature change on the surface of the reinforced concrete structure for each pixel of the temperature image based on the temperature image generated by the infrared camera, and generates data relating to a stress fluctuation image indicating stress fluctuations of the reinforced concrete structure based on the temperature difference calculated for each pixel of the temperature image;
Equipped with
The infrared camera generates a temperature video showing a change in temperature distribution on a surface of the reinforced concrete structure;
The arithmetic device extracts frames of a certain number of analysis points from a first frame in the temperature video generated by the infrared camera at regular intervals, and calculates a temperature difference for each pixel from the collection of extracted frames, the difference between a maximum temperature value and a minimum temperature value .
Inspection equipment. An inspection method for detecting the presence or absence of fractures in internal reinforcing bars in a reinforced concrete structure, comprising:
a measuring step of measuring a change over time in the temperature distribution on the surface of the reinforced concrete structure due to a thermoelastic effect ;
a generating step of generating data relating to a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the change over time in the temperature distribution measured in the measuring step;
The inspection method includes: The stress fluctuation image generated in the generating step is further displayed on a display unit.
The inspection method according to claim 7. The reinforced concrete structure is a reinforced concrete column.
The inspection method according to claim 7 or 8. An inspection method for detecting the presence or absence of fractures in internal reinforcing bars in a reinforced concrete structure, comprising:
generating a temperature image showing a temperature distribution on a surface of the reinforced concrete structure;
A step of calculating a temperature difference indicating a temperature change on the surface of the reinforced concrete structure for each pixel of the temperature image based on the temperature image generated in the step of generating the temperature image;
and generating data relating to a stress fluctuation image showing stress fluctuations in the reinforced concrete structure based on the temperature difference calculated for each pixel of the temperature image in the step of calculating the temperature difference,
In the step of generating a temperature image, a temperature video showing a change in temperature distribution on a surface of the reinforced concrete structure is generated,
In the step of calculating the temperature difference, frames having a certain number of analysis points are extracted from the first frame in the generated temperature video at regular intervals, and a difference between a maximum temperature value and a minimum temperature value is calculated for each pixel from the collection of extracted frames as a temperature difference.
Testing method.

Images