Stress monitoring sensor, sensor positioning member, and stress monitoring method

Abstract

To facilitate linear installation in a desired direction even when multi-directional distortions are measured.SOLUTION: A stress monitoring sensor for monitoring a stress inside a concrete structure includes: a plurality of optical fiber sensors having a detection part for detecting distortion provided in an optical fiber cable for transmitting an optical signal or a single optical fiber sensor having a plurality of detection parts for detecting distortion; a support member for supporting the optical fiber sensor; and a positioning part which is provided on the support member, and restricts the position of the detection part so that the plurality of detection parts cross each other at one specific point and extend in a non-parallel direction.SELECTED DRAWING: Figure 6A

Description

[Technical Field]

[0001] The present invention relates to a sensor for monitoring stress inside a concrete structure, a sensor positioning member, and a method for monitoring stress inside a concrete structure. [Background technology]

[0002] The occurrence of cracks in concrete structures, such as RC (Reinforced Concrete) and SRC (Steel Reinforced Concrete), significantly reduces the structural performance of the concrete structure and can lead to spalling of the cover concrete. This can result in damage to third parties. Therefore, detecting concrete damage, including crack occurrence, 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 ground subsidence are applied, strain occurs in each part of the concrete structure. Under these circumstances, it is extremely important to monitor the strain that occurs in each part of the concrete structure.

[0003] Concrete generally has an elastic range and shrinks or expands. However, when a concrete structure is subjected to a large external force that exceeds its elastic limit, such as an earthquake or subsidence, cracks occur, and the strain generated in each part of the concrete structure does not return to its original state, resulting in large residual strain. When large residual strain occurs in a concrete structure like this, it means that the concrete structure has been damaged.

[0004] When damage occurs to a concrete structure, cracks often appear on the surface, but this is difficult to confirm visually, for example, in buildings where there are finishing materials. Also, when cracks occur inside a concrete structure, there are many areas of the concrete structure that cannot be confirmed visually.

[0005] One known method for measuring strain inside a concrete structure is to measure stress inside the concrete structure using an optical fiber sensor (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 strain in multiple directions inside the concrete structure is measured.

[0006] Furthermore, in the invention described in Patent Document 1, a fixing member such as a thread or wire is placed inside a formwork, and an optical fiber sensor covered with a protective tube is fixed to the fixing member using an adhesive or the like, thereby making it possible to install the optical fiber sensor in a straight line. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-56768 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the invention described in Patent Document 1, it is difficult to know where to install the detection unit, which can make installation of the optical fiber sensor a burden for the worker. This problem is particularly pronounced when measuring strain in multiple directions. Therefore, there is a need for a technology that makes it easy to install the sensor linearly in a desired direction, even when measuring strain in multiple directions.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a stress monitoring sensor, a sensor positioning member, and a stress monitoring method for use inside concrete structures that can be easily installed in a straight line in a desired direction, even when measuring strain in multiple directions. [Means for solving the problem]

[0010] (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 for monitoring stress inside a concrete structure, and is characterized by comprising: a plurality of optical fiber sensors in which detecting units for detecting strain are provided on an optical fiber cable that transmits an optical signal, or a single optical fiber sensor in which a plurality of detecting units for detecting 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 detecting units so that the plurality of detecting units intersect with each other at a specific point and extend in directions that are not parallel to each other.

[0011] In this way, the optical fiber sensor is provided with a support member that supports the optical fiber sensor, and a positioning section that is provided on the support member and restricts the positions of the detection sections so that the multiple detection sections 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.

[0012] (2) Furthermore, in the stress monitoring sensor of the present invention, the plurality of detection sections include a first detection section and a second detection section, and the first detection section and the second detection section are perpendicular to each other.

[0013] In this way, the first and second detection units are perpendicular to each other, making it 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.

[0014] (3) In the stress monitoring sensor of the present invention, the plurality of detectors are arranged in at least three non-parallel directions passing through a specific point. In this way, the plurality of detectors are arranged in at least three non-parallel directions passing through a specific point, so that the principal stress inside the concrete structure can be calculated.

[0015] (4) In the stress monitoring sensor of the present invention, the plurality of detection units include first, second, and third detection units, and the first, second, and third detection units are arranged so as to be perpendicular to each other.

[0016] In this way, since the first, second, and third detection units are arranged perpendicular to each other, it is possible to measure strain inside the concrete structure in three dimensions, making it possible to calculate the three-dimensional distribution of strain within the concrete structure.

[0017] (5) In the stress monitoring sensor of the present invention, the plurality of detection sections include first, second, and third detection sections, the first detection section and the second detection section are arranged so as to intersect, and the third detection section is arranged so as 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.

[0018] In this way, the first and second detectors are arranged to intersect, and the third detector is arranged 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 where the first, second, and third detectors are arranged can be more accurately determined than in a case where three detectors are not arranged on the same plane.

[0019] (6) The stress monitoring sensor of the present invention is characterized by further comprising a covering portion that covers the optical fiber sensor so as to surround the detection portion. Since the covering portion that covers the optical fiber sensor so as to surround the detection portion is further provided, the position of the detection portion, which has been positioned by the sensor positioning member, can be fixed by the covering portion before concrete is poured. This makes it easier to install the sensor linearly in a desired direction, even when measuring strain in multiple directions.

[0020] (7) In the stress monitoring sensor of the present invention, the covering portion is a first covering portion, and the stress monitoring sensor further includes a second covering portion that covers the optical fiber cable excluding at least the detection portion.

[0021] In this way, since the stress monitoring sensor is provided with not only the first coating but also the second coating that coats 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. Furthermore, since the second coating is provided on at least the part excluding the detection part, strain can be detected by the detection part.

[0022] (8) The sensor positioning member of the present invention is a sensor positioning member for holding a plurality of optical fiber sensors each having a detection unit for detecting strain on an optical fiber cable that transmits an optical signal, or a single optical fiber sensor each having a plurality of detection units for detecting strain, and is characterized by comprising: a support member for supporting the optical fiber sensors; a fixing member for fixing the position of the support member; and a positioning unit provided on the support member for restricting the position of the detection units so that the plurality of detection units intersect with each other at a specific point and extend in directions that are not parallel to each other.

[0023] In this way, the optical fiber sensor includes a support member that supports the optical fiber sensor, a fixing member that fixes the position of the support member, and a positioning member that is provided on the support member and restricts the positions of the multiple detecting units so that they intersect with each other at a specific point and extend in non-parallel directions, making it easy to install the detecting units of the optical fiber sensor in desired positions, thereby enabling them to be installed linearly in the desired direction even when measuring strain in multiple directions.

[0024] (9) In the sensor positioning member of the present invention, the plurality of detection portions include a first detection portion and a second detection portion, and the positioning portion is arranged so that the first detection portion and the second detection portion are perpendicular to each other.

[0025] 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 in a position that enables measurement of strain in two perpendicular directions. Furthermore, 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 becomes easy to grasp the direction and magnitude of strain within the concrete structure.

[0026] (10) In the sensor positioning member of the present invention, the positioning parts are provided so that the plurality of detecting parts are arranged in at least three directions that are not parallel to each other and pass through a specific point.

[0027] 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 where the principal stress inside the concrete structure can be calculated.

[0028] (11) In the sensor positioning member of the present invention, the plurality of detection units include first, second, and third detection units, and the positioning unit is arranged so that the first, second, and third detection units are perpendicular to each other.

[0029] In this way, the positioning units are provided so that the first, second, and third detection units are perpendicular to each other, making it possible to measure strain inside the concrete structure in three dimensions and making it easy to accurately position the detection units at positions where the three-dimensional strain distribution within the concrete structure can be calculated.

[0030] (12) In the sensor positioning member of the present invention, the plurality of detection sections include first, second, and third detection sections, and the positioning section is provided so 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.

[0031] 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 where the first, second, and third detectors are arranged can be more accurately determined compared to when three detectors are not arranged on the same plane.

[0032] (13) In the sensor positioning member of the present invention, the fixing member further comprises an insertion portion through which the optical fiber cable can be inserted. In this way, since the fixing member further comprises an insertion portion through which the cable can be inserted, the optical fiber cables can be bundled by the insertion portion, particularly when holding multiple optical fiber sensors, thereby improving the handleability of the stress monitoring sensor.

[0033] (14) The sensor positioning member of the present invention is characterized in that the support member and the fixing member are separable. Since the support member and the fixing member are separable, the sensor positioning member can be embedded in a concrete structure with the fixing member removed. In particular, when the optical fiber sensor is embedded in a concrete structure after its 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.

[0034] (15) A 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, each having a detector for detecting strain attached to an optical fiber cable that transmits an optical signal, or a single optical fiber sensor having a plurality of detectors for detecting strain, characterized by including at least the following steps: a sensor positioning step of positioning the optical fiber sensors by restricting the positions of the detectors so that the plurality of detectors intersect with each other at a specific point and extend in non-parallel directions, using a sensor positioning member that includes a support member that supports the optical fiber sensors, a fixing member that fixes the position of the support member, and a positioning part that is attached to the support member and restricts the positions of the detectors so that the plurality of detectors intersect with each other at a specific point and extend in non-parallel directions; a step of burying the positioned optical fiber sensors in the concrete structure; a step of measuring the strain of the buried optical fiber sensors; and a step of estimating the stress generated in the concrete structure based on the characteristics of the change in the measured strain over time.

[0035] 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 units 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.

[0036] (16) The stress monitoring method of the present invention is characterized by further comprising the steps of covering the optical fiber sensor with a covering portion so as to surround the detection portion, and removing the fixing member from the covered optical fiber sensor.

[0037] In this way, since the method for burying the optical fiber sensor further includes a step of covering the optical fiber sensor so as to surround the detection unit with the covering unit, the position of the detection unit positioned by the sensor positioning member can be fixed by the covering unit before pouring concrete. This makes it easier to install the sensor linearly in the desired direction even when measuring strain in multiple directions.

[0038] Furthermore, since the method further includes a step of removing the fixing member from the coated optical fiber sensor, when the sensor is embedded in a concrete structure, the amount of concrete that makes up the concrete structure increases by the amount of the fixing member removed, thereby improving the strength of the concrete structure.

[0039] (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 a loss value of the optical fiber sensor is equal to or greater than a predetermined threshold value.

[0040] In this way, the optical fiber sensor is held by 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. [Effects of the Invention]

[0041] In this way, the present invention makes it easy to install the device linearly 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 the state of damage, such as cracks, inside the concrete structure. [Brief explanation of the drawings]

[0042] [Figure 1] 10 is a schematic diagram showing a state in which the first and second detection units are orthogonal to each other on the XY plane and the third detection unit extends between them. FIG. [Figure 2]FIG. 2 is a front view of the schematic diagram shown in FIG. 1, with the XY plane as the front. [Figure 3] 10 is a schematic diagram showing a state in which the first, second, and third detection units are orthogonal to each other. FIG. [Figure 4] FIG. 10 is a schematic diagram showing the state of rosette wiring when the intersection is located at an end portion. [Figure 5A] FIG. 10 is a schematic diagram showing six detecting units crossing each other. [Figure 5B] 5B is a cross-sectional view of the schematic diagram shown in FIG. 5A. [Figure 6A] FIG. 2 is a perspective view of a sensor positioning member according to the embodiment. [Figure 6B] FIG. 2 is a perspective view of a formwork forming member in the present embodiment. [Figure 7] 10 is a diagram showing a state in which the sensor positioning member and the form forming member are fitted together. FIG. [Figure 8] 3A and 3B are diagrams illustrating a schematic configuration of a support member according to the present embodiment. [Figure 9] 10A and 10B are diagrams showing a schematic configuration of a modified example of the support member. [Figure 10] 10A and 10B are diagrams showing a schematic configuration of a modified example of the support member. [Figure 11] 10A and 10B are schematic diagrams showing the general configuration of a modified example of the sensor positioning member. [Figure 12] 11 is a perspective side view of the sensor positioning member shown in FIG. 10. FIG. [Figure 13] 10A and 10B are schematic diagrams showing the general configuration of a modified example of the sensor positioning member. [Figure 14] 1 is a schematic diagram showing a schematic configuration of a stress monitoring sensor according to an embodiment of the present invention; [Figure 15] 1 is a diagram illustrating a configuration of an optical fiber sensor according to an embodiment of the present invention. [Figure 16] 1 is a diagram showing a schematic view of a stress monitoring sensor according to an embodiment of the present invention installed in a concrete structure. [Figure 17] 1 is a flowchart illustrating a stress monitoring method according to the present embodiment. [Figure 18]FIG. 10 is a diagram showing the positions at which strain gauges are installed as a comparative example. [Figure 19] 10 is a graph showing the results of a load test performed on a strain gauge. [Figure 20] 10 is a graph showing the results of a load test performed on a rosette-wired stress monitoring sensor. [Figure 21] 10 is a graph showing the results of a load test performed on a triaxially wired stress monitoring sensor. DETAILED DESCRIPTION OF THE INVENTION

[0043] [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 locations 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 according to the present invention are installed so that they intersect with each other at a specific point and extend in directions that are not parallel to each other. 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.

[0044] Fig. 1 shows a state in which the first and second detection units are orthogonal to each other and the third detection unit extends between them. Fig. 2 is a front view of the XY plane of Fig. 1 as seen from the z-axis direction. Fig. 3 shows a state in which the first detection unit, second detection unit, and third detection unit are orthogonal to each other. Note that Figs. 1 to 3 only show the detection unit 3, and the optical fiber cable 9 is omitted.

[0045] In FIG. 1, a first detector 3A and a second detector 3B intersect at an intersection I on the XY plane of a three-dimensional Cartesian coordinate system with the vertex of a rectangular parallelepiped as the origin. As shown in FIG. 2, a third detector 3C extends so that the distance between the first detector 3A and the second detector 3B is equal. This configuration allows the detector 3A to evaluate strain in the X-axis direction, the detector 3B to evaluate strain in the Y-axis direction, and the principal stress to be properly evaluated. In this specification, the arrangement of the detectors 3 as shown in FIG. 1 is also referred to as "rosette wiring." The intersecting angle of each detector 3 is not limited to the example described above. Arranging three detectors 3 extending in the same plane so that they intersect at a specific point allows proper evaluation of at least the principal stress.

[0046] When three detectors 3 are installed as shown in Figure 1, the magnitude and direction of strain on the plane where 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.

[0047] 3, in a three-dimensional Cartesian coordinate system similar to that of 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 perpendicular to each other at a specific point, which is the 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."

[0048] In this way, the first, second, and third detection units are arranged so as to be orthogonal to one another, so that strain inside the concrete structure can be measured three-dimensionally, enabling calculation of the three-dimensional strain distribution in the concrete structure 100. Furthermore, because the first, second, and third detection units are orthogonal to one another, calculation of the strain distribution becomes easy.

[0049] 1 and 3, intersection I is located near the center of detection unit 3, but as shown in FIG. 4, intersection I may also be located at the end of detection unit 3. 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.

[0050] Furthermore, the number of detectors 3 passing through the intersection I may be two, but preferably three or more. Since there are three or more detectors 3 passing through the intersection I, the principal stress inside the concrete structure 100 can be calculated.

[0051] Furthermore, it is preferable that, among the multiple detection units 3, there is at least one pair of detection units 3 that are orthogonal to each other at the intersection I. Because there are detection units 3 that are orthogonal to each other at the intersection I, it is possible to easily grasp the strain inside the concrete structure 100.

[0052] 1, three detectors 3 are provided extending on the XY plane, but the three detectors 3 may be located on the same plane, and their positions in the Z-axis direction are not particularly important; 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 fewer detectors 3 pass through intersection I than on other surfaces, so that the strain directions detected by the detectors 3 do not overlap.

[0053] Additionally, the number of detection units 3 may be six. 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 right angles at intersection I, similar to rosette wiring.

[0054] 5B is a cross-sectional view in the XY plane. Note that detection units 3D to 3F that do not extend parallel to the XY plane are omitted. As shown in FIG. 5B, in the XY plane, the first detection unit 3A and the second detection unit 3B intersect at right angles at an intersection I, and 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.

[0055] As in the XY plane, in the YZ plane, the first detection unit 3A and the fourth detection unit 3D intersect at right angles at the intersection I, and the fifth detection unit 3E extends so that the distance from the first detection unit 3A is equal to the distance from the fourth detection unit 3D. In the ZA plane, the second detection unit 3B and the fourth detection unit 3D intersect at right angles at the intersection I, and the sixth detection unit 3F extends so that the distance from the second detection unit 3B is equal to the distance from the fourth detection unit 3D.

[0056] As described above, the plurality of detectors 3 in the present invention are arranged so as to intersect with each other at a specific point and extend in non-parallel directions, thereby making it possible to detect strain in multiple directions.

[0057] [Configuration of sensor positioning member] The sensor positioning member, stress monitoring sensor, and stress monitoring method of this embodiment will be described below in order.

[0058] Fig. 6A is a perspective view showing the configuration of a first form-frame forming member. Fig. 6B is a perspective view showing the configuration of a second form-frame forming member. Fig. 7 is a view showing a pair of a first form-frame forming member and a second form-frame forming member assembled together. Fig. 8 is a schematic view showing a support member according to this embodiment.

[0059] The sensor positioning member 200 positions the optical fiber sensor 10 so that the multiple detecting units 3 intersect with each other at a specific intersection point I and extend in non-parallel directions. The sensor positioning member 200 including the first formwork forming member 21 shown in FIG. 6A is configured to position each detecting unit 3 so that the first detecting unit 3A and the second detecting unit 3B are orthogonal to each other, and the third detecting unit 3C extends between the first detecting unit 3A and the second detecting unit 3B on the plane where the first detecting unit 3A and the second detecting unit 3B intersect at right angles. That is, the multiple detecting units 3 are positioned as shown in FIG. 1. The intersecting angle of each detecting unit 3 is not particularly limited, as long as the three detecting units 3 extending in the same plane can be positioned so as to intersect at a specific point.

[0060] The sensor positioning member 200 includes a first form-frame forming member 21 shown in FIG. 6A and a second form-frame forming member 25 shown in FIG. 6B. The first form-frame forming member 21 and the second form-frame forming member 25 are each formed from three plate members 205. The first form-frame forming member 21 has a mating recess 22, and the second form-frame forming member 25 has a mating protrusion 26. The first form-frame forming member 21 and the second form-frame forming member 25 form a cubic form as shown in FIG. 7 by mating the mating recess 22 and the mating protrusion 26.

[0061] 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 introduced when the form is formed. The inlet 201 need only be able to introduce the material, and is not limited to the form of the cutout portion 42. A through hole may be formed in a plate member 205 that forms the form-forming member, and the through hole may serve as the inlet 201.

[0062] 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.

[0063] The support member 30 supports the optical fiber sensor 10 at two or more locations, thereby 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 locations 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.

[0064] 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.

[0065] 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 recess or protrusion as shown in Figs. 9 and 10 as long as it is capable of holding the optical fiber sensor 10. Furthermore, a plurality of positioning portions 31 may be provided on one support member 30 in accordance with the positions where the detection unit 3 is to be installed.

[0066] The fixing members 40 are coupled to the multiple support members 30 and fix the positions of the support members 30. In the first formwork forming member 21 shown in FIG. 6A, two of the three plate members 205 are fixing members 40, and two support members 30 are fixed to each of the plate members 205. The sensor positioning member 200 is required to determine the positions of the multiple detection units 3 three-dimensionally, and fixing the support members 30 to the fixing members 40 makes it 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.

[0067] Moreover, the first form 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 notch formed in the outer periphery of the fixing member 40 so as to form an insertion hole when the form is formed. When the sensor positioning member 200 holds multiple optical fiber sensors 10, grouping the optical fiber sensors 10 at the insertion portion 41 improves the handleability of the stress monitoring sensor 1.

[0068] Furthermore, the sensor positioning member 200 may be formed using any material and any method, but is preferably integrally molded using a 3D printer or the like. In this case, the support member 30 and the fixing member 40 are preferably made of a resin 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 typically used in 3D printers. Alternatively, the support member 30 and the fixing member 40 may be formed separately, or may be configured to be connectable and separable via a connecting portion.

[0069] Furthermore, 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 the sensor positioning member 200 in an overcrowded rebar section of a typical concrete structure 100, and the impact of installing the stress monitoring sensor 1 on the strength of the concrete structure 100 can be reduced.

[0070] The sensor positioning member 200 may be formed so that three detecting units 3 are orthogonal to one another, as shown in Figures 11 and 12. Figures 11 and 12 show a first form-forming member 21 that positions multiple detecting units 3 so that the three detecting units 3 are orthogonal to one another, as shown in Figure 3, and is fabricated to be paired with the second form-forming member 25 shown in Figure 6B. In the first form-forming member 21 shown in Figures 11 and 12, all three plate members 205 that form the first form-forming member 21 are fixing members 40, and two support members 30 are fixed to each plate member 205.

[0071] Furthermore, the sensor positioning member 200 may be formed so that six detecting units 3 intersect at an intersection I, as shown in Fig. 13. Fig. 13 shows a first form forming member 21 that positions a plurality of detecting units 3 so that the six detecting units 3 intersect at an intersection I, as shown in Fig. 5A. Fig. 13 shows a state in which one optical fiber sensor 10 is held, and the mating recess 22, insertion portion 41, and notch portion 42 are omitted.

[0072] 11 and 12, the first form-forming member 21 shown in Fig. 13 has three plate members 205 that form the first form-forming member 21, all of which are fixed members 40, and two support members 30 are fixed to each plate member 205. On the other hand, the first form-forming member 21 shown in Fig. 11 and 12 differs from the first form-forming member 21 shown in Fig. 11 and 12 in the number of positioning portions 31 provided on each support member 30. In the first form-forming member 21 shown in Fig. 11 and 12, one positioning portion 31 is provided for each support member 30, but in the first form-forming member 21 shown in Fig. 13, two positioning portions 31 are provided for each support member 30.

[0073] In the above, the case where the support member 30 is formed only on the first form-frame forming member 21 has been described, but it is sufficient that the support member 30 is formed on at least one of the first form-frame forming member 21 and the second form-frame forming member 25.

[0074] Furthermore, the sensor positioning member 200 may consist of only the support member 30 and the fixing member 40 as long as it can hold the detection unit 3 at a desired position. In other words, the plate member 205 other than the fixing member 40 that forms the formwork may not be provided, and the second formwork forming member 25 may not be provided. However, since it is difficult to form the first covering unit 11 described below, a form in which the formwork is formed by the plate member 205 is preferred.

[0075] (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 this embodiment will describe a case where the optical fiber sensor 10 is an FBG sensor.

[0076] 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.

[0077] 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.

[0078] The stress monitoring sensor 1 may also have a covering portion that protects the optical fiber sensor 10. For example, the stress monitoring sensor 1 may have a first covering portion 11 that covers the periphery of the detection portion 3 of the optical fiber sensor 10, and a second covering portion 12 that covers the optical fiber cable 9.

[0079] The first covering portion 11 is made of a cement-based material or resin. The cement-based material or resin that makes up the first covering portion 11 may be a material that has 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 low-shrinkage or non-shrinkage mortar to prevent cracks in the first covering portion 11 and the infiltration of deterioration factors such as moisture and salt.

[0080] It is preferable that first covering portion 11 has a thickness sufficient to cover detection portion 3. For example, if detection portion 3 is 10 mm, it is preferable that the thickness of first covering portion 11 is also greater than 10 mm, and depending on the thickness of detection portion 3, it is preferable that first covering portion 11 has a thickness approximately equal to or greater than the thickness of detection portion 3 so that detection portion 3 is not exposed.

[0081] Furthermore, it is more preferable that the first covering portion 11 is provided so as 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 the first covering portion 11 is 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 desired positions on 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.

[0082] 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 stress monitoring sensor 1 in an overcrowded rebar area of ​​a typical concrete structure 100, and it is possible to reduce the effect of the installation of the stress monitoring sensor 1 on the strength of the concrete structure 100. However, the length of each side is not particularly limited, and may be any length that allows placement between the rebars. For example, it may be longer than 5 cm depending on the degree of overcrowding of the rebars in the concrete structure 100.

[0083] 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, and the optical fiber sensor 10 protected by the second covering portion 12 is less likely to bend, which makes it easier to install the optical fiber sensor 10. 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.

[0084] Examples of materials for 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. Preferably, second covering portion 12 has an inner diameter of 0.3 to 0.5 mm and an outer diameter of 1 mm or less.

[0085] [Example of installation of stress monitoring sensors on 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 arranged horizontally and vertically. 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 schematically, and the support member 30 is omitted.

[0086] 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 using the optical fiber sensor, and when monitoring vibrations during an earthquake, it is preferable that the measurement frequency be 100 Hz or higher, and more preferably 1 kHz or higher.

[0087] A load test was conducted on the sensor in advance to determine the relationship between stress and strain on the optical fiber sensor. By doing so, it is possible to grasp the stress at that location. In this case, it is possible to monitor the strain and determine whether damage has occurred due to residual strain. Cut.

[0088] 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, optical fiber cables 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.

[0089] [Stress monitoring method] Next, the stress monitoring method according to this embodiment will be described with reference to a flowchart shown in FIG.

[0090] First, the optical fiber sensor 10 is positioned by using the above-described sensor positioning member 200 to restrict the positions of the detecting units 3 so that the multiple detecting units 3 intersect with each other at the intersection I and extend in non-parallel directions (step S1). At this time, the detecting units 3 are positioned so that they are located between two or more positioning units 31. This allows the detecting units 3 to be installed linearly.

[0091] Furthermore, when installing the optical fiber sensor 10 in the sensor positioning member 200, it is preferable to install it so that the loss value of the propagating light of the optical fiber sensor 10 is equal to or greater than a predetermined threshold. That is, the optical fiber sensor 10 is installed while confirming that its loss value is equal to or greater than the predetermined threshold. The predetermined threshold is a loss value sufficient for monitoring stress. For example, when multiple optical fiber cables 9 are inserted into the insertion portion 41, each optical fiber cable will bend. 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 the predetermined threshold, strain can be obtained even within the minimum bending radius. Note that, because errors in the loss value may occur depending on the type of measuring instrument, when determining the predetermined threshold, it is preferable to prototype multiple stress monitoring sensors 1 with different loss values ​​before fabricating the stress monitoring sensor 1, and to determine the predetermined threshold.

[0092] The stress monitoring sensor 1 may comprise one or more optical fiber sensors 10, but it is preferable that the stress monitoring sensor 1 be comprised of 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. When one 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 within the range that allows it to be installed on the concrete structure 100 in order to suppress bending.

[0093] 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 simultaneously with the formation of the first covering portion (step S2), but is preferably formed before the installation of the optical fiber sensor (step S1).

[0094] 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 tools such as cutters 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.

[0095] 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 as concrete is poured in that state.

[0096] Next, the strain of the embedded stress monitoring sensor is measured (step S5).The strain detected by the detection unit 3 is measured by the measuring instrument 80 connected to the stress monitoring sensor.

[0097] Next, the principal stress is calculated from the measured strain (step S6). When there are three or more detectors that intersect at intersection I and extend on the same plane, the magnitude and direction of the principal stress can be calculated from the measured strain.

[0098] [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 according to steps S1 to S3 of the stress monitoring method described above. Example 1 was a stress monitoring sensor fabricated using the sensor positioning member shown in FIG. 6A, and Example 2 was a stress monitoring sensor fabricated using the sensor positioning member shown in FIG. 11. In Examples 1 and 2, the first covering portion 11 was fabricated to form a cube with sides measuring 4 cm. A strain gauge was used as a comparative example.

[0099] Table 1 shows the mix proportions of the concrete constituting the first covering portion according to the example. As shown in Table 1, "W" is tap water (density 1 g / cm3). Furthermore, "PM-A" is Ductal Premix A, which is cement from Ductal (registered trademark, manufactured by Taiheiyo Cement Corporation), and "PM-B" is Ductal Premix B, which is fine aggregate from Ductal (registered trademark, manufactured by Taiheiyo Cement Corporation). Ductal (registered trademark, manufactured by Taiheiyo Cement Corporation) is an ultra-high-strength fiber-reinforced concrete, but this was used as a highly fluid, high-strength cement-based material without incorporating fibers. [Table 1]

[0100] In the comparative example, strain gauges were attached to the surface of a cubic first covering with sides measuring 4 cm, in positions as shown in FIG. 18. That is, first strain gauge 500A and second strain gauge 500B were perpendicular to each other at intersection I, and third strain gauge 500C was installed so that the distance between it and first strain gauge 500A was equal to the distance between it and second strain gauge 500B. After attaching the strain gauges to the first covering, a load test of the sensor was performed using a pressure tester. FIG. 19 shows the results of the comparative example.

[0101] In Examples 1 and 2, after forming the first covering portion 11 and removing the fixing member, a load test of the sensor was carried out using a pressure tester. Figures 20 and 21 are graphs showing the results of the load test carried out using the pressure tester, with Figure 20 showing the results of Example 1 and Figure 21 showing the results of Example 2.

[0102] In the comparative example, the horizontal strain measured when the largest load was applied was 24 μm, and the vertical strain was −176 μm. In Example 1, the horizontal strain measured when the largest load was applied was 27 μm, and the vertical strain was −176 μm. In Example 2, the horizontal strain measured when the largest load was applied was 43 μm, and the vertical strain was −254 μm.

[0103] In both examples, when the relationship between longitudinal strain and lateral strain in the elastic region was confirmed, the lateral strain was about 1 / 6 of the longitudinal strain. Since the relationship between the lateral strain and the longitudinal strain of the strain gauge attached to the surface of the first covering part was also about 1 / 6, it was confirmed that the stress monitoring sensor could accurately obtain strain.

[0104] 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 accuracy as that of a strain gauge. [Explanation of symbols]

[0105] 1. Stress monitoring sensor 3. Detection unit 3A First detection unit 3B Second detection unit 3C Third detection unit 9. Fiber Optic Cable 10 Optical fiber sensor 11 First covering part 12 Second covering part 21 First formwork forming member 22. Joint recess 25 Second formwork forming member 26 Engagement convex part 30 Support member 31 Positioning part 40 Fixing member 41 Insertion part 42 Notch 80 Measuring Instruments 100 Concrete Structures 101 Reinforced concrete 200 Sensor positioning member 201 Inlet 205 Plate members 500A First Strain Gauge 500B Secondary Strain Gauge 500C Third Strain Gauge I intersection

Claims

1. 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.

2. 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.

3. 3. The stress monitoring sensor according to claim 1, wherein the plurality of detection sections are disposed in at least three directions that are not parallel to each other and pass through a specific point.

4. 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.

5. 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.

6. 6. The stress monitoring sensor according to claim 1, further comprising a covering portion that covers the optical fiber sensor so as to surround the detection portion.

7. 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.

8. A sensor positioning member for holding a plurality of optical fiber sensors each having a detection unit for detecting strain 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 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.

9. 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.

10. 10. The sensor positioning member according to claim 8, wherein the positioning portion is provided so that the plurality of detection portions are disposed in at least three directions that are not parallel to each other and pass through a specific point.

11. 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.

12. 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.

13. 13. The sensor positioning member according to claim 8, wherein the fixing member further comprises an insertion portion through which the optical fiber cable can be inserted.

14. 14. The sensor positioning member according to claim 8, wherein the supporting member and the fixing member are separable.

15. 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.

16. 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.

17. 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.

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