JP7629825B2 - Stress monitoring sensor, sensor positioning member, and stress monitoring method - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. July 20, 2021, 2021 Annual Meeting of the Architectural Institute of Japan (Tokai), Academic Lecture Abstracts, pages 157-158, Architectural Institute of Japan

The present invention relates to a stress monitoring sensor, a sensor positioning member, and a stress monitoring method for inside a concrete structure.

In concrete structures such as RC (Reinforced Concrete) and SRC (Steel Reinforced Concrete), the occurrence of cracks significantly reduces the structural performance of the concrete structure and leads to the spalling of the covering concrete. This can result in damage to third parties. Therefore, detecting damage to concrete, including the occurrence of cracks, is extremely important for the maintenance and management of concrete structures. Concrete cracks can be caused by rebar corrosion, drying shrinkage, temperature stress, or external forces. In particular, when external forces such as earthquakes or subsidence are applied, strain occurs in each part. Under such circumstances, it is extremely important to monitor the strain that occurs in each part of the concrete structure.

Concrete generally has an elastic range and will shrink or expand. However, when a concrete structure is subjected to a large external force that exceeds its elastic limit, such as an earthquake or subsidence, causing cracks, the strain generated in each part of the concrete structure will not return to normal, and large residual strain will result. When large residual strain occurs in a concrete structure in this way, it means that the concrete structure has been damaged.

When damage occurs to a concrete structure, cracks often appear on the surface, but in cases where there is a finishing material, such as in buildings, it is difficult to confirm with the naked eye. Also, when cracks occur inside a concrete structure, there are many parts of the structure that cannot be confirmed with the naked eye.

As a method for measuring strain inside a concrete structure, a method for measuring stress inside the concrete structure using an optical fiber sensor is known (see Patent Document 1). In the invention described in Patent Document 1, the detection units of multiple optical fiber sensors are provided so that they pass through a specific point and extend in non-parallel directions, and multi-directional strain inside the concrete structure is measured.

In addition, the invention described in Patent Document 1 makes it possible to install the optical fiber sensor in a straight line by installing a fixing member such as a thread or wire inside a mold and fixing the optical fiber sensor covered with a protective tube to the fixing member using an adhesive or the like.

JP 2020-56768 A

However, in the invention described in Patent Document 1, it is difficult to know where to install the detection unit, and installing the optical fiber sensor may be a burden for the worker. This problem is particularly pronounced when measuring strain in multiple directions. Therefore, there is a demand for technology that makes it easy to install the sensor in a straight line in the desired direction, even when measuring strain in multiple directions.

The present invention was made in consideration of these circumstances, and aims to provide a stress monitoring sensor, a sensor positioning member, and a stress monitoring method for inside a concrete structure that can be easily installed in a straight line in a desired direction, even when measuring strain in multiple directions.

(1) In order to achieve the above object, the present invention employs the following means. That is, the stress monitoring sensor of the present invention is a stress monitoring sensor that monitors stress inside a concrete structure, and is characterized by comprising a plurality of optical fiber sensors in which a detection unit that detects strain is provided on an optical fiber cable that transmits an optical signal, or a single optical fiber sensor in which a plurality of detection units that detect strain are provided, a support member that supports the optical fiber sensors, and a positioning unit that is provided on the support member and restricts the positions of the detection units so that the plurality of detection units intersect with each other at a specific point and extend in non-parallel directions.

In this way, the optical fiber sensor is provided with a support member that supports the optical fiber sensor, and a positioning unit that is provided on the support member and restricts the positions of the detection units so that the multiple detection units intersect with each other at a specific point and extend in non-parallel directions, making it easy to install the sensor in a straight line in the desired direction even when measuring strain in multiple directions.

(2) In addition, in the stress monitoring sensor of the present invention, the multiple detection sections include a first detection section and a second detection section, and the first detection section and the second detection section are orthogonal to each other.

In this way, since the first and second detection units are perpendicular to each other, it is possible to measure strain in two perpendicular directions. Furthermore, by installing the stress monitoring sensor inside the concrete structure so that the extension directions of the first and second detection units are parallel to the surface of the concrete structure, it is possible to easily grasp the direction and magnitude of strain inside the concrete structure.

(3) In the stress monitoring sensor of the present invention, the multiple detection units are installed in at least three non-parallel directions passing through a specific point. In this way, since the multiple detection units are installed in at least three non-parallel directions passing through a specific point, it is possible to calculate the principal stress inside the concrete structure.

(4) In the stress monitoring sensor of the present invention, the plurality of detection sections include a first, a second, and a third detection section, and the first, second, and third detection sections are arranged so as to be perpendicular to each other.

In this way, the first, second, and third detectors are arranged perpendicular to each other, so that the strain inside the concrete structure can be measured three-dimensionally, enabling the calculation of the three-dimensional distribution of strain within the concrete structure.

(5) In the stress monitoring sensor of the present invention, the multiple detection sections include a first, a second, and a third detection section, the first detection section and the second detection section are arranged to intersect, and the third detection section is arranged to extend between the first detection section and the second detection section on the plane where the first detection section and the second detection section intersect.

In this way, the first and second detection units are arranged to intersect, and the third detection unit is arranged to extend between the first and second detection units on the plane where the first and second detection units intersect. Therefore, compared to a case where three detection units are not arranged on the same plane, the magnitude and direction of the strain on the plane on which the first, second, and third detection units are arranged can be grasped more accurately.

(6) The stress monitoring sensor of the present invention is characterized in that it further comprises a covering portion that covers the optical fiber sensor so as to surround the detection portion. In this way, since it further comprises a covering portion that covers the optical fiber sensor so as to surround the detection portion, the position of the detection portion positioned by the sensor positioning member can be fixed by the covering portion before pouring concrete. This makes it even easier to install the sensor in a straight line in the desired direction, even when measuring strain in multiple directions.

(7) In the stress monitoring sensor of the present invention, the coating portion is a first coating portion, and the sensor is further characterized by including a second coating portion that coats at least the optical fiber cable excluding the detection portion.

In this way, since the stress monitoring sensor is provided with not only the first covering portion but also the second covering portion that covers the optical fiber cable, damage to the stress monitoring sensor can be suppressed when the stress monitoring sensor is embedded in a concrete structure. As a result, the handleability of the stress monitoring sensor is improved. In addition, since the second covering portion is provided on at least the portion excluding the detection portion, strain can be detected by the detection portion.

(8) The sensor positioning member of the present invention is a sensor positioning member that holds a plurality of optical fiber sensors provided with detection units that detect strain on an optical fiber cable that transmits an optical signal, or a single optical fiber sensor provided with a plurality of detection units that detect strain, and is characterized in that it comprises a support member that supports the optical fiber sensors, a fixing member that fixes the position of the support member, and a positioning unit that is provided on the support member and limits the position of the detection units so that the plurality of detection units intersect with each other at a specific point and extend in non-parallel directions.

In this way, the optical fiber sensor is provided with a support member that supports the optical fiber sensor, a fixing member that fixes the position of the support member, and a positioning unit that is provided on the support member and limits the position of the detection units so that the multiple detection units intersect with each other at a specific point and extend in non-parallel directions, making it easy to install the detection units of the optical fiber sensor in a desired position. This makes it possible to install the detection units in a linear manner in a desired direction even when measuring strain in multiple directions.

(9) In the sensor positioning member of the present invention, the plurality of detection sections include a first detection section and a second detection section, and the positioning section is provided so that the first detection section and the second detection section are perpendicular to each other.

In this way, since the positioning unit is provided so as to be perpendicular to the first and second detection units, it becomes easy to accurately position the detection units at a position that allows for measurement of strain in two perpendicular directions. In addition, by providing the stress monitoring sensor within the concrete structure so that the extension directions of the first and second detection units are parallel to the surface of the concrete structure, it is possible to easily grasp the direction and magnitude of strain within the concrete structure.

(10) The sensor positioning member of the present invention is characterized in that the positioning parts are provided so that the multiple detection parts are installed in at least three non-parallel directions passing through a specific point.

In this way, positioning units are provided so that multiple detection units are installed in at least three non-parallel directions passing through a specific point, making it easy to accurately position the detection units at positions that allow calculation of the principal stress inside the concrete structure.

(11) In the sensor positioning member of the present invention, the plurality of detection sections include a first, a second, and a third detection section, and the positioning section is provided so that the first, second, and third detection sections are mutually orthogonal.

In this way, the positioning unit is provided so that the first, second, and third detection units are mutually perpendicular, so that the strain inside the concrete structure can be measured three-dimensionally, and it becomes easy to accurately position the detection units at positions where the three-dimensional strain distribution in the concrete structure can be calculated.

(12) In the sensor positioning member of the present invention, the plurality of detection sections include a first, second and third detection section, and the positioning section is provided such that the first detection section and the second detection section intersect, and the third detection section extends between the first detection section and the second detection section on a plane where the first detection section and the second detection section intersect.

In this way, the first and second detectors are arranged to intersect, and it is easy to arrange the third detector to extend between the first and second detectors on the plane where the first and second detectors intersect. Therefore, the magnitude and direction of strain on the plane on which the first, second, and third detectors are arranged can be grasped more accurately than when three detectors are not arranged on the same plane.

(13) In the sensor positioning member of the present invention, the fixing member is further characterized by having an insertion portion through which the optical fiber cable can be inserted. In this way, since the fixing member further has an insertion portion through which the cable can be inserted, the optical fiber cables can be bundled by the insertion portion, particularly when multiple optical fiber sensors are held, and thus the handleability of the stress monitoring sensor is improved.

(14) The sensor positioning member of the present invention is characterized in that the support member and the fixing member are separable. In this way, since the support member and the fixing member are separable, the fixing member can be removed and the sensor can be embedded in a concrete structure. In particular, when the optical fiber sensor is embedded in a concrete structure after the position is fixed using a cement-based material, the cement-based material used for fixing and the concrete that constitutes the concrete structure are integrated, so that the strength of the concrete structure is not affected.

(15) The stress monitoring method of the present invention is a stress monitoring method for monitoring stress inside a concrete structure using a plurality of optical fiber sensors in which a detector for detecting strain is provided on an optical fiber cable that transmits an optical signal, or a single optical fiber sensor in which a plurality of detectors for detecting strain is provided, and is characterized by including at least the following steps: a sensor positioning step of positioning the optical fiber sensor by restricting the position of the detector using a sensor positioning member that includes a support member that supports the optical fiber sensor, a fixing member that fixes the position of the support member, and a positioning part that is provided on the support member and restricts the position of the detector so that the plurality of detectors intersect with each other at a specific point and extend in non-parallel directions; a step of embedding the positioned optical fiber sensor in the concrete structure; a step of measuring the strain of the embedded optical fiber sensor; and a step of estimating the stress generated in the concrete structure based on the characteristics of the change over time of the measured strain.

In this way, the method includes a sensor positioning step of positioning the optical fiber sensor by using a positioning member to restrict the positions of the multiple detection parts so that they intersect with each other at a specific point and extend in non-parallel directions, making it easy to install the sensor in a straight line in the desired direction even when measuring strain in multiple directions.

(16) The stress monitoring method of the present invention is characterized by further including a step of covering the optical fiber sensor with a covering portion so as to surround the detection portion, and a step of removing the fixing member from the covered optical fiber sensor.

In this way, the method further includes a step of covering the optical fiber sensor so as to surround the detection unit with the covering portion in order to embed the optical fiber sensor. Therefore, the position of the detection unit, which has been positioned by the sensor positioning member, can be fixed by the covering portion before the concrete is poured. This makes it even easier to install the sensor in a straight line in the desired direction, even when measuring strain in multiple directions.

In addition, the method further includes a step of removing the fixing member from the coated optical fiber sensor, so that when the sensor is embedded in a concrete structure, the amount of concrete that constitutes the concrete structure increases by the amount of the fixing member that is removed, thereby improving the strength of the concrete structure.

(17) The stress monitoring method of the present invention is characterized in that, in the sensor positioning step, the optical fiber sensor is installed in the positioning section so that the loss value of the optical fiber sensor is equal to or greater than a predetermined threshold value.

In this way, the optical fiber sensor is held in the sensor positioning member so that the loss value of the optical fiber sensor is equal to or greater than a predetermined threshold value, making it possible to maintain a loss value sufficient for monitoring.

In this way, the present invention makes it easy to install the device in a straight line in the desired direction, even when measuring strain in multiple directions. This makes it possible to more accurately grasp the direction and magnitude of strain inside a concrete structure, and also more accurately grasp damage conditions such as cracks inside the concrete structure.

1 is a schematic diagram showing a state in which a first and second detection unit are perpendicular to each other on an XY plane and a third detection unit extends between them. FIG. FIG. 2 is a front view of the schematic diagram shown in FIG. 1, with the XY plane taken as the front. 10 is a schematic diagram showing a state in which the first, second and third detection units are perpendicular to each other; FIG. FIG. 13 is a schematic diagram showing the state of rosette wiring when the intersection is located at an end portion. 10 is a schematic diagram showing six detection units crossing each other. FIG. This is a cross-sectional view taken along the line BB in the schematic diagram shown in FIG. 5A. FIG. 2 is a perspective view of a sensor positioning member according to the embodiment. FIG. 2 is a perspective view of a formwork forming member in the present embodiment. 13 is a diagram showing a state in which the sensor positioning member and the formwork forming member are fitted together. FIG. 3A and 3B are diagrams illustrating a schematic configuration of a support member in the present embodiment. 13A and 13B are diagrams showing a schematic configuration of a modified example of the support member. 13A and 13B are diagrams showing a schematic configuration of a modified example of the support member. 13A and 13B are schematic diagrams showing a schematic configuration of a modified example of the sensor positioning member. 11 is a perspective side view of the sensor positioning member shown in FIG. 10. 13A and 13B are schematic diagrams showing a schematic configuration of a modified example of the sensor positioning member. 1 is a schematic diagram showing a schematic configuration of a stress monitoring sensor in an embodiment of the present invention. 1 is a diagram showing a configuration of an optical fiber sensor according to an embodiment of the present invention; 1 is a diagram showing a schematic diagram of a stress monitoring sensor according to an embodiment of the present invention installed in a concrete structure. 1 is a flowchart showing a stress monitoring method according to an embodiment of the present invention. FIG. 13 is a diagram showing the positions at which strain gauges are installed as a comparative example. 1 is a graph showing the results of a load test performed on a strain gauge. 13 is a graph showing the results of a load test performed on a rosette-wired stress monitoring sensor. 13 is a graph showing the results of a load test performed on a three-axis wired stress monitoring sensor.

[Location for installing the detection unit]
In this specification, the optical fiber sensor 10 includes a detection unit 3 that detects strain in an optical fiber cable 9 that transmits an optical signal. A plurality of optical fiber sensors 10 each provided with a single detection unit 3 may be used, or a single optical fiber sensor 10 including a plurality of detection units 3 may be used. First, the positions at which the plurality of detection units 3 included in one or a plurality of optical fiber sensors 10 are installed according to the present invention will be described. The plurality of detection units 3 in the present invention are installed so as to intersect with each other at a specific point and extend in non-parallel directions. In other words, the plurality of detection units 3 are installed so that two or more detection units 3 intersect with each other at a specific point and extend in different directions.

Figure 1 shows the first and second detection units crossing each other at right angles, with the third detection unit extending between them. Figure 2 is a front view of the XY plane of Figure 1, seen from the z-axis direction. Figure 3 shows the first detection unit, second detection unit, and third detection unit crossing each other at right angles. Note that Figures 1 to 3 only show the detection unit 3, and the optical fiber cable 9 is omitted.

In FIG. 1, the first detection unit 3A and the second detection unit 3B are perpendicular to each other at the intersection I on the XY plane in a three-dimensional orthogonal coordinate system with the apex of a rectangular parallelepiped as the origin. As shown in FIG. 2, the third detection unit 3C extends so that the distance from the first detection unit 3A is equal to the distance from the second detection unit 3B. With this configuration, the detection unit 3A can evaluate the strain in the X-axis direction, and the detection unit 3B can evaluate the strain in the Y-axis direction, and the principal stress can also be properly evaluated. In this specification, the arrangement of the detection units 3 as shown in FIG. 1 is also called "rosette wiring". Note that the intersection angle of each detection unit 3 is not limited to the above example. If three detection units 3 extending on the same plane are arranged so as to intersect at a specific point, at least the principal stress can be properly evaluated.

When three detectors 3 are installed as shown in Figure 1, the magnitude and direction of strain on the plane on which the first, second, and third detectors are installed can be grasped more accurately than when three detectors 3 are not installed on the same plane. In addition, because the first detector 3A and the second detector 3B are perpendicular to each other, it becomes easier to calculate the principal stress inside the concrete structure.

In FIG. 3, in a three-dimensional orthogonal coordinate system similar to that in FIG. 1, the first detection unit 3A is parallel to the x-axis, the second detection unit 3B is parallel to the y-axis, and the third detection unit 3C is parallel to the z-axis, and they are mutually orthogonal at a specific point, i.e., intersection point I. In this specification, the arrangement of the detection units 3 as shown in FIG. 1 is also referred to as "triaxial wiring."

In this way, since the first, second, and third detection units are arranged so as to be perpendicular to one another, it is possible to measure the strain inside the concrete structure three-dimensionally, and it is possible to calculate the three-dimensional distribution of strain in the concrete structure 100. In addition, since the first, second, and third detection units are perpendicular to one another, it is easy to calculate the distribution of strain.

In Figures 1 and 3, intersection I is located near the center of detection unit 3, but intersection I may be located at the end of detection unit 3 as shown in Figure 4. As long as detection units 3 at least intersect, local strain near intersection I can be detected by multiple detection units 3 regardless of the position of intersection I. Note that when intersection I is located near the center of detection unit 3, the detection range centered on intersection I becomes approximately equal in three directions, making it possible to detect more localized strain. For this reason, it is preferable that intersection I be located near the center of detection unit 3.

In addition, the number of detection units 3 passing through intersection I may be two, but it is preferable that there are three or more. Since there are three or more detection units 3 passing through intersection I, the principal stress inside the concrete structure 100 can be calculated.

Furthermore, it is preferable that among the multiple detection units 3, there is at least one pair of detection units 3 that are perpendicular to each other at the intersection I. Because there are detection units 3 that are perpendicular to each other at the intersection I, it is possible to easily grasp the strain inside the concrete structure 100.

In addition, in FIG. 1, three detectors 3 are arranged to extend on the XY plane, but the three detectors 3 only need to be located on the same plane, and their positions in the Z-axis direction are not important, and they may be located on the far side of the page, or on the YZ or XZ plane. Detectors 3 may also be provided on multiple surfaces. In this case, there may be a surface on which there are fewer detectors 3 passing through intersection I than on other surfaces, so that the directions of strain detected by the detectors 3 do not overlap.

In addition, six detection units 3 may be used. FIG. 5A is a diagram showing six detection units 3 intersecting at intersection I. In a three-dimensional orthogonal coordinate system with intersection I as the center, three detection units 3 extend so as to intersect at intersection I in each of three planes that intersect at intersection I, similar to rosette wiring.

Figure 5B is a cross-sectional view in the XY plane. Note that detection units 3D-F that do not extend parallel to the XY plane are omitted. As shown in Figure 5B, in the XY plane, the first detection unit 3A and the second detection unit 3B intersect at an intersection I, and the third detection unit 3C extends so that the distance to the first detection unit 3A is equal to the distance to the second detection unit 3B.

Similar to the XY plane, in the YZ plane, the first detection unit 3A and the fourth detection unit 3D are perpendicular to each other at intersection I, and the fifth detection unit 3E extends so that the distance to the first detection unit 3A is equal to the distance to the fourth detection unit 3D. In the ZA plane, the second detection unit 3B and the fourth detection unit 3D are perpendicular to each other at intersection I, and the sixth detection unit 3F extends so that the distance to the second detection unit 3B is equal to the distance to the fourth detection unit 3D.

As described above, the multiple detectors 3 in the present invention are installed so that they intersect with each other at a specific point and extend in non-parallel directions, making it possible to detect strain in multiple directions.

[Configuration of sensor positioning member]
The sensor positioning member, the stress monitoring sensor, and the stress monitoring method according to this embodiment will be described below in order.

Figure 6A is a perspective view showing the configuration of a first formwork forming member. Figure 6B is a perspective view showing the configuration of a second formwork forming member. Figure 7 is a diagram showing a pair of a first formwork forming member and a second formwork forming member assembled together. Figure 8 is a schematic diagram showing a support member according to this embodiment.

The sensor positioning member 200 positions the optical fiber sensor 10 so that the multiple detection units 3 intersect each other at a specific intersection I and extend in non-parallel directions. In the sensor positioning member 200 including the first formwork forming member 21 shown in FIG. 6A, the first detection unit 3A and the second detection unit 3B are perpendicular to each other, and the third detection unit 3C extends between the first detection unit 3A and the second detection unit 3B on the plane where the first detection unit 3A and the second detection unit 3B are perpendicular to each other. That is, the multiple detection units 3 are positioned as shown in FIG. 1. The intersection angle of each detection unit 3 is not particularly limited, and it is sufficient that the three detection units 3 extending in the same plane can be positioned so as to intersect at a specific point.

The sensor positioning member 200 includes a first formwork forming member 21 shown in FIG. 6A and a second formwork forming member 25 shown in FIG. 6B. The first formwork forming member 21 and the second formwork forming member 25 are each formed from three plate members 205. The first formwork forming member 21 has a mating recess 22, and the second formwork forming member 25 has a mating protrusion 26. The first formwork forming member 21 and the second formwork forming member 25 form a cubic formwork as shown in FIG. 7 by mating the mating recess 22 and the mating protrusion 26.

It is also preferable that the first form-forming member 21 and the second form-forming member 25 have a cutout portion 42. The cutout portion 42 forms an inlet 201 through which the material for forming the first covering portion 11 can be poured when the form is formed. The inlet 201 need only be capable of pouring in the material, and is not limited to the shape of the cutout portion 42. A through hole may be formed in the plate member 205 that forms the form-forming member, and the through hole may serve as the inlet 201.

The first formwork forming member 21 includes a support member 30 and a fixing member 40. The support member 30 is a member that supports the optical fiber sensor 10, and the fixing member 40 is a member that fixes the position of the support member 30.

The support member 30 supports the optical fiber sensor 10 at two or more points, making it easy to install the detection unit 3 in a straight line. That is, the optical fiber sensor 10 is installed so that the detection unit 3 is located between two or more parts supported by the support member 30. The support member 30 is, for example, a rod-shaped member as shown in FIG. 8, but may have any shape as long as it can support the optical fiber sensor 10, and may be composed of one or more members.

The support member 30 also includes a positioning portion 31 that positions the detection portion 3 and limits the position of the detection portion 3. Therefore, by holding the optical fiber sensor 10 in the positioning portion 31, the position of the detection portion 3 is prevented from shifting, making it easier to install the optical fiber sensor 10.

From the viewpoint of positioning the optical fiber sensor 10, the positioning portion 31 is preferably a through hole as shown in FIG. 7. Furthermore, the positioning portion 31 may be a concave or convex portion as shown in FIGS. 9 and 10 as long as it is capable of holding the optical fiber sensor 10. Furthermore, multiple positioning portions 31 may be provided on one support member 30 in accordance with the positions where the detection portion 3 is to be installed.

The fixing member 40 is coupled to the multiple support members 30 and fixes the positions of the support members 30. In the first formwork forming member 21 shown in FIG. 6A, of the three plate members 205, two plate members 205 are fixing members 40, and two support members 30 are fixed to each plate member. The sensor positioning member 200 needs to determine the positions of the multiple detection units 3 three-dimensionally, but by fixing the support members 30 to the fixing members 40, it becomes easy to determine the positions of the multiple detection units 3 three-dimensionally. This makes it easy to install the multiple detection units 3 that measure strain in multiple directions in a straight line in the desired direction.

The first formwork forming member 21 preferably includes an insertion portion 41. The insertion portion 41 is a portion through which the optical fiber sensor 10 is inserted, and may be formed, for example, by providing an insertion hole near the outer periphery of the fixing member 40. The insertion portion 41 may also be a recess or a notch formed in the outer periphery of the fixing member 40 so as to form an insertion hole when the formwork is formed. When the sensor positioning member 200 holds multiple optical fiber sensors 10, the optical fiber sensors 10 are grouped together at the insertion portion 41, thereby improving the handleability of the stress monitoring sensor 1.

The sensor positioning member 200 may be formed from any material and by any method, but is preferably integrally molded using a 3D printer or the like. In this case, it is preferable that the support member 30 and the fixing member 40 are made of a resin that is strong enough to be separated by hand. If the cross-sectional area of the support member 30 is small, it can be easily separated by hand using a resin that is typically used in 3D printers. On the other hand, the support member 30 and the fixing member 40 may be formed separately, or may be configured to be connectable and separable via a connection portion.

The sensor positioning member 200 may be not only cubic, but also rectangular, polygonal, spherical, columnar, etc. When the sensor positioning member 200 is cubic, it is preferable that the length of one side is 5 cm or less. Since the length of one side is 5 cm or less, it becomes easy to install in the dense rebar area of a typical concrete structure 100, and the effect of installing the stress monitoring sensor 1 on the strength of the concrete structure 100 can be reduced.

The sensor positioning member 200 may be formed so that three detection units 3 are mutually orthogonal, as shown in Figs. 11 and 12. Figs. 11 and 12 show a first formwork forming member 21 that positions a plurality of detection units 3 so that the three detection units 3 are mutually orthogonal, as shown in Fig. 3, and is produced to be paired with the second formwork forming member 25 shown in Fig. 6B. In the first formwork forming member 21 shown in Figs. 11 and 12, all three plate members 205 that form the first formwork forming member 21 are fixing members 40, and two support members 30 are fixed to each plate member 205.

The sensor positioning member 200 may also be formed so that six detection units 3 intersect at intersection I, as shown in FIG. 13. FIG. 13 shows a first formwork forming member 21 that positions a plurality of detection units 3 so that six detection units 3 intersect at intersection I, as shown in FIG. 5A. FIG. 13 shows a state in which one optical fiber sensor 10 is held, and the fitting recess 22, insertion portion 41, and cutout portion 42 are omitted.

In the first formwork forming member 21 shown in FIG. 13, similar to FIGS. 11 and 12, all three plate members 205 forming the first formwork forming member 21 are fixed members 40, and two support members 30 are fixed to each plate member 205. On the other hand, the number of positioning portions 31 provided on one support member 30 differs from that of the first formwork forming member 21 shown in FIGS. 11 and 12. In the first formwork forming member 21 shown in FIGS. 11 and 12, one positioning portion 31 is provided for each support member 30, but in the first formwork forming member 21 shown in FIG. 13, two positioning portions 31 are provided for each support member 30.

Although the above describes a case where the support member 30 is formed only on the first formwork forming member 21, it is sufficient that the support member 30 is formed on at least one of the first formwork forming member 21 and the second formwork forming member 25.

The sensor positioning member 200 may be only a support member 30 and a fixing member 40 as long as it can hold the detection unit 3 at the desired position. In other words, it is not necessary to provide a plate member 205 other than the fixing member 40 that forms the formwork, and the second formwork forming member 25 may not be provided. However, since it is difficult to form the first covering portion 11 described below, it is preferable to form the formwork using the plate member 205.

(Structure of stress monitoring sensor)
Fig. 14 is a diagram showing a schematic configuration of a stress monitoring sensor according to this embodiment. Fig. 15 is a diagram showing a schematic configuration of an optical fiber sensor 10. In Fig. 14, the detection unit 3 of the stress monitoring sensor is hatched. Note that in this embodiment, a case will be described in which the optical fiber sensor 10, which is an FBG sensor, is used.

The stress monitoring sensor 1 has detection units 3 that are installed so as to intersect with each other at an intersection I and extend in non-parallel directions, and measures strain in multiple directions. The stress monitoring sensor 1 includes one or more optical fiber sensors 10 and a support member 30.

As described above, the support member 30 is a member that supports the optical fiber sensor 10. The stress monitoring sensor 1 may further include a member that constitutes the sensor positioning member 200 in addition to the support member 30.

The stress monitoring sensor 1 may also have a coating that protects the optical fiber sensor 10. For example, the stress monitoring sensor 1 may have a first coating 11 that covers the periphery of the detection unit 3 of the optical fiber sensor 10, and a second coating 12 that covers the optical fiber cable 9.

The first covering portion 11 is made of a cement-based material or resin. The cement-based material or resin constituting the first covering portion 11 may be a material having a strength equal to or greater than that of the concrete used in the concrete structure in which the stress monitoring sensor 1 is installed. Furthermore, when a cement-based material is used for the first covering portion 11, it is more preferable to use a mortar with low shrinkage or no shrinkage in order to prevent the first covering portion 11 from cracking and allowing deterioration factors such as moisture and salt to penetrate.

It is preferable that the first covering portion 11 has a thickness sufficient to cover the detection portion 3. For example, if the detection portion 3 is 10 mm, it is preferable that the thickness of the first covering portion 11 is also greater than 10 mm, and depending on the thickness of the detection portion 3, it is preferable that the first covering portion 11 has a thickness equal to or greater than the thickness of the detection portion 3 so that the detection portion 3 is not exposed.

More preferably, the first covering portion 11 is provided to form a rectangular, polygonal, spherical or columnar shape so as to cover the multiple detecting portions 3 that intersect with each other at the intersection I. In particular, when formed in a rectangular shape, by providing the detecting portions 3 so as to be parallel to the surface of the first covering portion 11, it becomes easier to install the detecting portions 3 at the desired positions of the concrete structure 100, even if the positions of the detecting portions 3 are not visible from the outside due to the first covering portion 11.

When the first covering portion 11 is cubic, it is preferable that the length of each side is 5 cm or less. If the length of each side is 5 cm or less, it becomes easy to install the sensor in the densely packed reinforcing bar portion of a typical concrete structure 100, and the effect of the installation of the stress monitoring sensor 1 on the strength of the concrete structure 100 can be reduced. However, the length of each side is not particularly limited, and it may be any length that allows it to be placed between the reinforcing bars, and may be, for example, greater than 5 cm depending on the density of the reinforcing bars of the concrete structure 100.

As shown in FIG. 15, the second covering portion 12 preferably protects the optical fiber cable 9 at least in a portion excluding the detection portion 3. More preferably, the optical fiber cable 9 is protected at least in a portion excluding the portion held by the sensor positioning member 200, which makes it easier to install the optical fiber sensor 10 since the optical fiber sensor 10 protected by the second covering portion 12 tends to be difficult to bend. The second covering portion 12 is, for example, a cylindrical protective tube through which the optical fiber cable 9 can be inserted, but may also be formed by coating the surface of the optical fiber cable 9.

Materials for the second covering portion 12 include, but are not limited to, fluororesin, PEEK (polyether ether ketone) resin, TPEE (thermoplastic polyether ester elastomer, Hytrel), highly heat-resistant and flexible elastomer resin, PI (polyimide) resin, PU (polyurethane) resin, etc. In addition, it is preferable that the inner diameter of the second covering portion 12 is 0.3 to 0.5 mm and the outer diameter is 1 mm or less.

[Example of installation of stress monitoring sensors in concrete structures]
Fig. 16 is a diagram showing a stress monitoring sensor embedded inside a concrete structure 100. The concrete structure 100 has reinforcing bars 101 in the horizontal and vertical directions. The optical fiber sensor is preferably installed in a main structural part of the structure, such as a pillar or beam. Fig. 16 is a diagram showing a case where the stress monitoring sensor is composed of three optical fiber sensors. In Fig. 16, the multiple detection units 3 and the first covering unit 11 are shown diagrammatically, and the support member 30 is omitted.

The stress monitoring sensor 1 is connected to a measuring instrument 80. The measuring instrument 80 is connected to each optical fiber sensor 10 of the stress monitoring sensor 1, and measures the strain detected by the detection unit 3. The measuring instrument 80 only needs to be able to measure the strain caused by the optical fiber sensor, and when performing vibration monitoring during an earthquake, it is preferable for the measuring frequency to be 100 Hz or higher, and more preferably 1 kHz or higher.

By carrying out a load test on the sensor in advance and determining the relationship between the stress and the strain of the optical fiber sensor, it is possible to grasp the stress at that location. In addition, when checking for the presence or absence of damage, it is possible to determine whether damage has occurred from the residual strain by monitoring the strain.

Furthermore, as shown in FIG. 16, the stress monitoring sensor 1 may be configured so that one stress monitoring sensor 1 can measure strain at multiple locations inside the concrete structure 100. That is, the optical fiber cable 9 may extend from both ends of the detection unit 3. In this case, one sensor positioning member 200 may have two or more insertion portions 41.

[Stress monitoring method]
Next, a stress monitoring method according to this embodiment will be described with reference to a flowchart shown in FIG.

First, the optical fiber sensor 10 is positioned by restricting the position of the detection units 3 using the sensor positioning member 200 described above so that the multiple detection units 3 intersect with each other at the intersection I and extend in non-parallel directions (step S1). At this time, the detection units 3 are positioned so that they are located between two or more positioning units 31. This allows the detection units 3 to be installed in a straight line.

When installing the optical fiber sensor 10 in the sensor positioning member 200, it is preferable to install the optical fiber sensor 10 so that the loss value of the propagating light is equal to or greater than a predetermined threshold. That is, the optical fiber sensor 10 is installed while confirming that the loss value of the optical fiber sensor 10 is equal to or greater than a predetermined threshold. The predetermined threshold is a loss value that is sufficient for monitoring stress. For example, when multiple optical fiber cables 9 are inserted into the insertion portion 41, bending occurs in each optical fiber cable. However, by installing each optical fiber cable 9 while confirming that the loss value of the optical fiber sensor 10 is equal to or greater than a predetermined threshold, it is possible to obtain strain even within the range of the minimum bending radius. Note that there is a possibility that errors may occur in the loss value depending on the type of measuring equipment, etc., so when determining the predetermined threshold, it is preferable to prototype multiple stress monitoring sensors 1 with different loss values before producing the stress monitoring sensor 1, and to determine the predetermined threshold.

The stress monitoring sensor 1 may be made up of one or more optical fiber sensors 10, but it is preferable to use multiple optical fiber sensors 10 in order to make the loss value of the optical fiber sensor 10 equal to or greater than a predetermined threshold value. When a single optical fiber sensor 10 having multiple detection units 3 is held by the sensor positioning member 200, the sensor positioning member 200 may be made larger to the extent that it can be installed on the concrete structure 100 in order to suppress bending.

Next, the first covering portion 11 is formed so as to surround the detection portion 3 (step S2). The first covering portion 11 is formed by filling the material of the first covering portion 11 through the inlet 201. The second covering portion 12 may be formed at the same time as the formation of the first covering portion (step S2), but is preferably formed before the installation of the optical fiber sensor (step S1).

Next, after the first covering portion 11 is formed, the fixing member 40 is removed (step S3). The fixing member 40 can be removed by hand, or a tool such as a cutter or nippers may be used as an aid to process the surface. By removing the fixing member 40, the first covering portion 11 made of a cement-based material and the concrete that constitutes the concrete structure are integrated, so there is no effect on the strength of the concrete structure 100.

Next, a stress monitoring sensor is embedded inside the concrete structure to be stress monitored (step S4). The stress monitoring sensor 1 is installed inside the formwork that forms the concrete structure 100, and is embedded inside the concrete structure 100 by pouring concrete in that state.

Next, the strain of the embedded stress monitoring sensor is measured (step S5). The strain detected by the detection unit 3 is measured by a measuring instrument 80 connected to the stress monitoring sensor.

Next, the principal stress is calculated from the measured strain (step S6). When there are three or more detection units that intersect at intersection point I and extend on the same plane, the magnitude and direction of the principal stress can be calculated from the measured strain.

[Example]
Next, the performance of the stress monitoring sensor according to this embodiment was verified. The stress monitoring sensor 1 used in this example was a stress monitoring sensor fabricated based on steps S1 to S3 in the stress monitoring method described above. Moreover, a stress monitoring sensor fabricated using the sensor positioning member shown in FIG. 6A was designated as Example 1, and a stress monitoring sensor fabricated using the sensor positioning member shown in FIG. 11 was designated as Example 2. In Examples 1 and 2, the first covering portion 11 was fabricated to form a cube with each side measuring 4 cm. Moreover, a strain gauge was used as a comparative example.

Table 1 shows the mix proportions of the concrete constituting the first covering portion according to the embodiment. As shown in Table 1, "W" is "tap water (density 1 g/cm3)". In addition, "PM-A" is "Ductal Premix A", which is a cement of Ductal (registered trademark, manufactured by Pacific Cement Corporation), and "PM-B" is "Ductal Premix B", which is a fine aggregate of Ductal (registered trademark, manufactured by Pacific Cement Corporation). Ductal (registered trademark, manufactured by Pacific Cement Corporation) is an ultra-high strength fiber reinforced concrete, but it was used as a high flow and high strength cement material without mixing in fibers.

In the comparative example, strain gauges were attached to the surface of the first cubic covering part with sides measuring 4 cm, in the positions shown in FIG. 18. That is, the first strain gauge 500A and the second strain gauge 500B intersect at right angles at intersection I, and the third strain gauge 500C was installed so that the distance to the first strain gauge 500A was equal to the distance to the second strain gauge 500B. After attaching the strain gauges to the first covering part, a load test of the sensor was performed using a pressure tester. FIG. 19 shows the results of the comparative example.

In Examples 1 and 2, after forming the first covering portion 11 and removing the fixing member, a load test of the sensor was performed using a pressure tester. Figures 20 and 21 are graphs showing the results of the load test performed using the pressure tester, with Figure 20 showing the results of Example 1 and Figure 21 showing the results of Example 2.

In the comparative example, the horizontal strain measured when the largest load was applied was 24μ, and the vertical strain was -176μ. In Example 1, the horizontal strain measured when the largest load was applied was 27μ, and the vertical strain was -176μ. In Example 2, the horizontal strain measured when the largest load was applied was 43μ, and the vertical strain was -254μ.

In both examples, when the relationship between the longitudinal strain and the lateral strain in the elastic region was confirmed, the lateral strain was about 1/6 of the longitudinal strain. Since the relationship between the longitudinal strain and the lateral strain of the strain gauge attached to the surface of the first covering portion was also about 1/6, it was confirmed that the stress monitoring sensor could accurately obtain strain.

From the above, it has been confirmed that the stress monitoring sensor of the present invention can be easily installed in a straight line in the desired direction, even when measuring strain in multiple directions, and that the measured strain has the same level of accuracy as a strain gauge.

1 Stress monitoring sensor 3 Detection section 3A First detection section 3B Second detection section 3C Third detection section 9 Optical fiber cable 10 Optical fiber sensor 11 First covering section 12 Second covering section 21 First formwork forming member 22 Fitting recess 25 Second formwork forming member 26 Fitting protrusion 30 Support member 31 Positioning section 40 Fixing member 41 Insertion section 42 Notch section 80 Measuring instrument 100 Concrete structure 101 Reinforcing bar 200 Sensor positioning member 201 Insertion port 205 Plate member 500A First strain gauge 500B Second strain gauge 500C Third strain gauge I Intersection

Claims (17)

A stress monitoring sensor for monitoring stress inside a concrete structure, comprising:
a plurality of optical fiber sensors each having a detection unit for detecting strain provided on an optical fiber cable for transmitting an optical signal, or a single optical fiber sensor each having a plurality of detection units for detecting strain;
a support member for supporting the optical fiber sensor;
A stress monitoring sensor characterized by comprising a positioning portion provided on the support member and limiting the positions of the detection portions so that the multiple detection portions intersect with each other at a specific point and extend in non-parallel directions. The plurality of detection units include a first detection unit and a second detection unit,
2. The stress monitoring sensor according to claim 1, wherein the first detection portion and the second detection portion are perpendicular to each other. The stress monitoring sensor according to claim 1 or 2, characterized in that the multiple detection units are installed in at least three non-parallel directions passing through a specific point. the plurality of detectors include a first detector, a second detector, and a third detector;
4. The stress monitoring sensor according to claim 1, wherein the first, second and third detection portions are provided so as to be perpendicular to each other. the plurality of detectors include a first detector, a second detector, and a third detector;
The first detection portion and the second detection portion are provided so as to intersect with each other,
A stress monitoring sensor as described in any one of claims 1 to 3, characterized in that the third detection portion is arranged to extend between the first detection portion and the second detection portion on a plane where the first detection portion and the second detection portion intersect. The stress monitoring sensor according to any one of claims 1 to 5, further comprising a covering section that covers the optical fiber sensor so as to surround the detection section. the covering portion is a first covering portion,
7. The stress monitoring sensor according to claim 6, further comprising a second covering portion that covers at least the optical fiber cable excluding the detection portion. A sensor positioning member for holding a plurality of optical fiber sensors each having a detection unit for detecting strain in an optical fiber cable for transmitting an optical signal, or a single optical fiber sensor each having a plurality of detection units for detecting strain,
a support member for supporting the optical fiber sensor;
A fixing member that fixes the position of the support member;
A sensor positioning member comprising: a positioning portion provided on the support member, which limits the positions of the detection portions so that the detection portions intersect with each other at a specific point and extend in non-parallel directions. The plurality of detection units include a first detection unit and a second detection unit,
9. The sensor positioning member according to claim 8, wherein the positioning portion is provided so that the first detection portion and the second detection portion are perpendicular to each other. The sensor positioning member according to claim 8 or 9, characterized in that the positioning parts are provided so that the multiple detection parts are installed in at least three non-parallel directions passing through a specific point. the plurality of detectors include a first detector, a second detector, and a third detector;
11. The sensor positioning member according to claim 8, wherein the positioning portion is provided so that the first, second and third detection portions are perpendicular to each other. the plurality of detectors include a first detector, a second detector, and a third detector;
The first detection portion and the second detection portion intersect with each other,
The sensor positioning member according to any one of claims 8 to 10, characterized in that the positioning portion is provided so that the third detection portion extends between the first detection portion and the second detection portion on a plane where the first detection portion and the second detection portion intersect. The sensor positioning member according to any one of claims 8 to 12, characterized in that the fixing member further comprises an insertion portion through which the optical fiber cable can be inserted. The sensor positioning member according to any one of claims 8 to 13, characterized in that the support member and the fixing member are separable. A stress monitoring method for monitoring stress inside a concrete structure using a plurality of optical fiber sensors each having a detection unit for detecting strain provided on an optical fiber cable for transmitting an optical signal, or a single optical fiber sensor each having a plurality of detection units for detecting strain, comprising:
a sensor positioning step of positioning the optical fiber sensor by restricting the positions of the detection units so that the multiple detection units intersect with each other at a specific point and extend in non-parallel directions, using a sensor positioning member including a support member that supports the optical fiber sensor, a fixing member that fixes the position of the support member, and a positioning unit that is provided on the support member and restricts the positions of the detection units so that the multiple detection units intersect with each other at a specific point and extend in non-parallel directions;
embedding the positioned optical fiber sensor in the concrete structure;
measuring the strain of the embedded optical fiber sensor;
and estimating the stress generated in the concrete structure based on characteristics of the change in the measured strain over time. covering the optical fiber sensor with a covering portion so as to surround the detection portion;
The method of claim 15 further comprising the step of: removing the fastener from the coated fiber optic sensor. In the sensor positioning step,
17. The stress monitoring method according to claim 15, wherein the optical fiber sensor is installed on the positioning part so that a loss value of the optical fiber sensor is equal to or greater than a predetermined threshold value.

Images