Measuring device and method for installing the measuring device

Abstract

To provide a measurement device that can measure the load on a concrete member with a compact structure using an optical fiber, and a method for setting the measurement device.SOLUTION: A measurement device 1 includes: a load conversion unit 20 set in a measurement target concrete member, the load conversion unit converting a load along an axial direction D1 from a concrete member around the measurement target concrete member to a displacement along a radial direction D2; an optical fiber cable 30 wound along a side surface 24b of the load conversion unit 20 in which a displacement occurs; and a load operation unit for measuring a strain of the optical fiber cable 30 and acquiring a load on the basis of the measured strain of the optical fiber cable 30 and the conversion characteristics of converting the load on the load conversion unit 20 to a displacement.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a measurement device and a method for installing the measurement device. [Background technology]

[0002] Conventionally, an optical fiber sensor described in Patent Document 1 is known as a measuring device for measuring strain occurring in a concrete member. This optical fiber sensor includes an optical fiber, a conversion section that converts stress into strain in the optical fiber, and a detection section that detects changes in backscattered light from the optical fiber associated with strain. The conversion section is made of an elastic body and is linear. The optical fiber follows the deformation caused by the action of stress on the elastic body, and strain occurs in the optical fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-38794 A Summary of the Invention [Problem to be solved by the invention]

[0004] By the way, there have been attempts to acquire the load acting on a concrete member by attaching an optical fiber to an elastic member using an optical fiber for measuring strain buried in the concrete member. In measuring strain with an optical fiber, due to the characteristics of the measurement, it is necessary to average the strain (measurement value) at a plurality of positions on the optical fiber. Therefore, it is necessary to install the optical fiber in consideration of the inspection length (spatial resolution), which is the distance between the plurality of positions. When the elastic member is linear as in the conventional technology, the total length of the elastic member becomes long in order to secure the required number of measurement points, and there is a risk that it may be difficult to arrange it on the concrete member. In addition, if the inspection length is extremely shortened without changing the total length of the elastic member to increase the number of measurement points per distance, this may lead to an excessive number of measurement points per distance in other parts of the optical fiber, and the overall amount of data may become enormous.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a measuring device capable of measuring a load applied to a concrete member using optical fibers with a compact configuration, and a method for installing the measuring device. [Means for solving the problem]

[0006] One aspect of the present invention is a measurement device that measures a load applied to a concrete member, and includes a load conversion unit that is installed inside the concrete member to be measured and converts a load along a first direction from the surrounding concrete members into a displacement along a second direction intersecting the first direction, an optical fiber wound along a displacement surface of the load conversion unit where displacement occurs, and a load calculation unit that measures strain in the optical fiber and obtains a load based on the measured strain in the optical fiber and the load-to-displacement conversion characteristics of the load conversion unit.

[0007] In this measuring device, when a load from the surrounding concrete members along a first direction is applied to a load converter installed inside a concrete member to be measured, the displacement surface of the load converter is displaced along a second direction. Since an optical fiber is wound around the displacement surface of the load converter, when the displacement surface of the load converter is displaced, a strain is generated in the optical fiber. Here, by using the characteristics of the load converter that converts a load along the first direction into a displacement along the second direction, it is possible to obtain the load along the first direction from the displacement of the displacement surface. The displacement of the displacement surface can be obtained based on the strain of the measured optical fiber. In addition, since the optical fiber is wound around the displacement surface, the dimension of the load converter in the first direction to ensure the same number of measurement points can be shorter than in a linear arrangement where the optical fiber is not wound. Therefore, according to the measuring device, it is possible to measure the load applied to the concrete member using an optical fiber with a compact configuration.

[0008] In one embodiment, the load conversion unit includes a columnar elastic member having a bottom surface that receives the load along the first direction and a side surface that is a displacement surface, and the load calculation unit may calculate the load based on the elastic coefficient and Poisson's ratio of the elastic member as the conversion characteristic of the load conversion unit. In this case, if the elastic coefficient and Poisson's ratio of the elastic member are known, the load received at the bottom surface can be easily obtained from the displacement of the side surface by using such conversion characteristic.

[0009] In one embodiment, the load conversion unit includes a plurality of elastic members and a plate member sandwiched between adjacent elastic members, and the elastic members and the plate members may be alternately stacked along the first direction. In this case, for example, under the condition that the dimension of the entire load conversion unit along the first direction is the same, the dimension of each elastic member along the first direction is smaller in a configuration in which a plurality of elastic members and a plate member are alternately stacked along the first direction than in a case in which the load conversion unit is composed of a single elastic member. This reduces the displacement of the side surface of each elastic member, thereby suppressing the variation in the magnitude of the displacement of the side surface along the first direction.

[0010] In one embodiment, the measurement device may further include a buffer member provided to cover the displacement surface and the optical fiber. In this case, since the buffer member covers the displacement surface and the optical fiber, the displacement of the displacement surface and the optical fiber is permitted by the thickness of the buffer member. Therefore, it is possible to suppress the influence of the displacement of the displacement surface and the optical fiber on the measurement of the load due to the obstruction of the displacement of the displacement surface and the optical fiber.

[0011] In one embodiment, the load conversion unit may include a tensile load receiver that receives a load in a direction away from the load conversion unit. In this case, the load in the direction away from the load conversion unit is transmitted to the load conversion unit as a tensile load by the tensile load receiver. This makes it possible to measure the tensile load applied to the concrete member using an optical fiber.

[0012] Another aspect of the present invention may be a method for installing a measuring device that measures a load applied to a concrete member, comprising the steps of preparing the measuring device and pouring concrete so as to embed the measuring device in a state in which a load along a first direction is applied in advance. In this case, since the measuring device is embedded in a state in which a load along the first direction is applied in advance, the tensile load applied to the concrete member can be suitably measured. Effect of the Invention

[0013] According to the present invention, the load applied to a concrete member can be measured with a compact configuration using optical fibers. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram showing a measurement device according to an embodiment. [Diagram 2] FIG. 2 is a schematic configuration diagram showing a main part of the measuring device of FIG. [Diagram 3] 3A is a cross-sectional view of the vicinity of the surface of the elastic member of Fig. 2. (b) is a cross-sectional view of the vicinity of the surface of an elastic member of a modified example. [Figure 4] FIG. 2 is a diagram for explaining winding specifications of an optical fiber. [Diagram 5]3 is a diagram for explaining conversion from a load to a displacement by the elastic member in FIG. 2. [Figure 6] FIG. 13 is a schematic diagram showing a modified example of the measuring device. [Figure 7] 7A is a cross-sectional view illustrating an example of the inside of the measurement device of Fig. 6. (b) is a cross-sectional view illustrating another example of the inside of the measurement device of Fig. 6. [Figure 8] FIG. 13 is a diagram illustrating an example of a method for installing a measuring device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of a measuring device according to the present invention will be described in detail with reference to the drawings. In the description, the same elements or elements having the same functions may be designated by the same reference numerals, and duplicated descriptions will be omitted.

[0016] 1 is a schematic diagram showing a measuring device according to an embodiment. The measuring device 1 is a device that measures a load applied to a concrete structure (concrete member) S. Examples of the concrete structure S include structures such as tunnel lining concrete (tunnel circumferential direction), PC box girders, and dam concrete.

[0017] The measurement device 1 comprises a stress suppression container 10 embedded in a concrete structure S, a load conversion unit 20 provided inside the stress suppression container 10, a linear optical fiber cable (optical fiber) 30 extending from the stress suppression container 10, and a load calculation unit 40 provided at the end of the optical fiber cable 30. Note that to make the drawing easier to understand, hatching corresponding to the concrete structure S has been omitted in Fig. 1.

[0018] The stress suppression container 10 is a container that houses the load converter 20 and a part of the optical fiber cable 30. The stress suppression container 10 is placed at a location in the concrete structure S where load measurement is required. The stress suppression container 10 may be provided at a plurality of locations in the concrete structure S. The stress suppression container 10 suppresses the transmission of stress from the external concrete S1 to the internal concrete S2. The stress suppression container 10 is made of a hard material such as resin or metal. The stress suppression container 10 may be in the shape of a cylinder or the like, or may be in the shape of a box with a lid. The dimensions of the stress suppression container 10 are not particularly limited, but as an example, the length of the stress suppression container 10 in the axial direction D1 (first direction) may be about 200 mm.

[0019] Concrete S2 similar to the surrounding (external) concrete S1 is poured inside the stress suppression container 10. The concrete S2 is made of the same material and is of the same age as the external concrete S1. A buffer material (not shown) is attached to the inner wall surface of the stress suppression container 10 to suppress the transmission of stress from the external concrete S1 to the internal concrete S2. The buffer material may be, for example, filter paper, a porous sheet, a wire mesh, and felt layered from the inside to the outside in this order. This provides a so-called separation between the external concrete S1 and the internal concrete S2, suppressing the transmission of stress in a direction intersecting the axial direction of the stress suppression container 10.

[0020] The load conversion unit 20 is installed inside the concrete S2 inside the stress suppression container 10 that is the measurement target. The load conversion unit 20 is arranged so that its axial direction is along the axial direction D1 so that the load from the concrete S2 acts on one end face 21 and the other end face 22. An anchor 23 may be provided on one end face 21 of the load conversion unit 20. The anchor 23 functions as a tensile load receiving part that receives a load from the internal concrete S2 in a direction away from the load conversion unit 20. Note that the tensile load receiving part may be a flange including a portion that protrudes in a direction intersecting the axial direction of the stress suppression container 10 instead of the anchor 23. The detailed configuration of the load conversion unit 20 will be described later.

[0021] At both ends of the stress suppression container 10, for example, a through-hole is provided through which the optical fiber cable 30 is inserted. The optical fiber cable 30 is drawn into one side of the stress suppression container 10 and attached in a spiral shape to the load conversion unit 20 (described in detail later), and is drawn out from the other side of the stress suppression container 10. The optical fiber cable 30 extending from both ends of the stress suppression container 10 is arranged so as to follow, for example, structural reinforcing bars (not shown) inside the concrete structure S.

[0022] The optical fiber cable 30 extending from both ends of the stress suppression container 10 is connected to a load calculation unit 40 outside the concrete structure S. The load calculation unit 40 measures the strain of the optical fiber cable 30. The optical fiber cable 30 inside the stress suppression container 10 is used to measure the load applied to the concrete S2. The load calculation unit 40 obtains the load from the internal concrete S2 based on the measured strain of the optical fiber cable 30 (particularly the strain of the optical fiber cable 30 along the load conversion unit 20) and the conversion characteristics of the load conversion unit 20 described below. The optical fiber cable 30 outside the stress suppression container 10 can be used to measure the total strain acting on the concrete S1. In other words, a single optical fiber cable 30 can measure the load and the total strain of the concrete inside the concrete structure S.

[0023] The load calculation unit 40 includes a measuring instrument and an analyzing device. The measuring instrument inputs measuring light K1 into the optical fiber cable 30, receives backscattered light K2 returning from each measuring position in the longitudinal direction of the optical fiber cable 30, and transmits information on the intensity, wavelength, etc. of the received backscattered light K2 to an analyzing device (not shown). The above-mentioned scattered light includes Rayleigh scattered light, Brillouin scattered light, etc. Examples of the measuring instrument that can be used include an OTDR (Optical Time Domain Reflectometer) that uses Rayleigh scattered light, and a BOTDR (Brillouin Optical Time Domain Reflectometer) that uses Brillouin scattered light.

[0024] The analysis device is a computer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls the analysis device based on a control program stored in the ROM. The RAM functions as a work memory when the CPU executes the control program stored in the ROM. In the analysis device, the intensity and wavelength of the backscattered light K2 at each measurement position in the longitudinal direction of the optical fiber cable 30 are analyzed based on the principle that the intensity and wavelength of the backscattered light K2 depend on the strain applied to the optical fiber cable 30. By this analysis, the strain at each measurement position in the longitudinal direction of the optical fiber cable 30 is obtained, and as a result, the longitudinal strain distribution applied to the optical fiber cable 30 is obtained.

[0025] Fig. 2 is a schematic diagram showing the main parts of the measuring device of Fig. 1. As shown in Fig. 2, the load converter 20 has an elastic member 24, a buffer member 25 surrounding the elastic member 24, and a cover member 26 surrounding the buffer member 25.

[0026] The load conversion section 20 is connected to the surrounding concrete S 2 The elastic member 24 converts a load acting along the axial direction D1 from the concrete S2 into a displacement along the radial direction D2 of the load conversion unit 20. The radial direction D2 is a second direction intersecting the axial direction D1. The elastic member 24 has a function of converting such a load acting along the axial direction D1 into a displacement along the radial direction D2. The elastic member 24 is columnar and has a bottom surface 24a and a side surface 24b. The bottom surface 24a receives a load acting along the axial direction D1 (first direction) of the stress suppression container 10. The side surface 24b is a displacement surface that displaces along the radial direction D2 in response to the load acting along the axial direction D1. The bottom surface 24a may be provided with a load-receiving member (not shown) for receiving a load acting along the axial direction D1 from the concrete S2 and transmitting the load to the bottom surface 24a.

[0027] The elastic member 24 is made of a material whose elastic modulus and Poisson's ratio are known (for example, proportional relationship) and whose change over time is sufficiently small. The elastic member 24 is preferably made of a material whose Poisson's ratio is relatively large, for example, rubber. When the elastic member 24 is made of rubber, for example, the Young's modulus is 0.1 to 10 kN / mm 2 , and the Poisson's ratio may be about 0.5. The elastic member 24 may have known changes over time, such as creep and shrinkage. In other words, the elastic coefficient and Poisson's ratio of the elastic member 24 are characteristics of the load conversion unit 20 that converts a load along the axial direction D1 into a displacement along the radial direction D2. The material of the elastic member 24 may be, in addition to rubber, a metal material or a resin material, for example.

[0028] In the elastic member 24, the optical fiber cable 30 is wound around along the side surface 24b of the elastic member 24. Fig. 3 is a cross-sectional view of the surface vicinity of the elastic member of Fig. 2. As shown in Fig. 3(a), the optical fiber cable 30 may be adhered to the side surface 24b of the elastic member 24. Alternatively, as shown in Fig. 3(b), the optical fiber cable 30 may be adhered to the bottom of a groove formed in the side surface 24b of the elastic member 24.

[0029] Fig. 4 is a diagram for explaining the winding specifications of the optical fiber. In Fig. 4, R is the radius of the wound portion of the optical fiber cable 30, θ is the angle of the optical fiber cable 30 with respect to the radial direction D2 in a side view of the wound portion of the optical fiber cable 30, and H is the length of one turn of the wound portion of the optical fiber cable 30 in the axial direction D1.

[0030] The optical fiber cable 30 is wound in a spiral shape so as to form a cylindrical outer diameter as a whole. The diameter (2R) of the wound portion of the optical fiber cable 30 can be, for example, about 40 mm to 50 mm, assuming that the minimum bending radius of the optical fiber cable 30 is 20 mm. The total length in the axial direction D1 of the wound portion of the optical fiber cable 30 (length multiplied by the number of turns of H) is determined taking into consideration the number of measurement points of the optical fiber cable 30 in the load conversion unit 20, and can be, for example, about 50 mm. θ is set according to the above-mentioned R and H, and is, for example, 10°.

[0031] For example, if the spatial resolution is 10 cm and the data acquisition interval is 5 cm, the effective measurement points for such parameters are about 15 plots. -6 ) and the Young's modulus is 10000N / mm 2 If so, the measurement sensitivity when converting the strain to axial direction D1 is 0.058N / mm 2 The measurement sensitivity when the strain is converted to the radial direction D2 is 0.020N / mm 2 In this way, by installing the optical fiber cable 30 in a spiral shape on the elastic member 24, even if the length of the axial direction D1 of the elastic member 24 is short compared to the length of the optical fiber cable 30 required to measure the load, for example, it is possible to set a number of significant measurement points.

[0032] Returning to FIG. 2, the side surface 24b of the elastic member 24 is covered with the buffer member 25. The buffer member 25 covers the optical fiber cable 30 wound around the side surface 24b. In other words, the buffer member 25 is provided so as to cover the displacement surface and the optical fiber cable 30. The buffer member 25 has a dimension in the axial direction D1 that is approximately the same as that of the elastic member 24, for example. The thickness of the buffer member 25 in the radial direction D2 is a dimension that does not restrain the deformation according to the Poisson's ratio of the elastic member 24. The buffer member 25 also functions as a member that protects and fixes the optical fiber cable 30. The buffer member 25 is made of a material that is softer than the load conversion unit 20. As an example, the buffer member 25 can be made of a sponge.

[0033] The side surface of the buffer member 25 is surrounded by a cover member 26. The cover member 26 is a member for maintaining the external shape of the load conversion section 20. The cover member 26 is, for example, a cylindrical member, and has a dimension in the axial direction D1 that is approximately the same as that of the elastic member 24. The outside diameter of the cover member 26 may be an outside diameter that allows it to be housed inside the stress suppression container 10. The cover member 26 is made of a material harder than the buffer member 25. For example, a polyvinyl chloride pipe or the like can be used as the cover member 26.

[0034] FIG. 5 is a diagram for explaining the conversion of load to displacement by the elastic member of FIG. 2. As shown in FIG. 5, when a load along the axial direction D1 acts on the bottom surface 24a of the load conversion unit 20 from the concrete S2, the side surface 24b expands in the radial direction D2. As a result, the shape of the elastic member 24 is generally bale-shaped. Since the buffer member 25 is interposed between the elastic member 24 and the cover member 26, the side surface 24b can expand in the radial direction D2 without being restrained by the surrounding concrete S2 and the cover member 26. As a result, the side surface 24b is displaced in the radial direction D2 in accordance with the relationship between the elastic coefficient and the Poisson's ratio, and the optical fiber cable 30 is pushed out along the radial direction D2. A strain is generated in the optical fiber cable 30 according to the load along the axial direction D1 that the bottom surface 24a receives.

[0035] Here, the concrete S2 inside the stress suppression container 10 is separated from the surrounding concrete S1 by the stress suppression container 10, so that the bottom surface 24a receives a load along the axial direction D1 with the effect of stress from the surrounding concrete S1 being reduced. The strain measured in the optical fiber cable 30 substantially corresponds only to the load along the axial direction D1 in the concrete S2. Therefore, the load calculation unit 40 calculates the load along the axial direction D1 received by the bottom surface 24a from the strain of the optical fiber cable 30 wound around the load conversion unit 20, which is a partial section of the optical fiber cable 30 installed over the entire concrete structure S, via the elastic coefficient and Poisson's ratio of the elastic member 24 (the conversion characteristic of the load conversion unit 20).

[0036] As described above, in the measurement device 1 according to the present embodiment, when a load along the axial direction D1 (first direction) of the stress suppression container 10 is applied from the surrounding concrete S2 to the load conversion unit 20 installed inside the concrete S2 to be measured, the side surface 24b, which is the displacement surface of the load conversion unit 20, is displaced along the radial direction D2 (second direction) of the load conversion unit 20. Since the optical fiber cable 30 is wound around the side surface 24b of the load conversion unit 20, when the side surface 24b of the load conversion unit 20 is displaced, a strain is generated in the optical fiber cable 30. Here, by using the characteristic of the load conversion unit 20 that converts the load along the axial direction D1 into a displacement along the second direction, it is possible to obtain the load along the axial direction D1 from the displacement of the side surface 24b. This displacement of the side surface 24b can be obtained based on the measured strain of the optical fiber cable 30. Furthermore, since the optical fiber cable 30 is wound around the side surface 24b, the dimension of the load conversion unit 20 in the axial direction D1 to ensure the same number of measurement points can be shorter than in a linear arrangement in which the optical fiber cable 30 is not wound. In other words, the required measurement length due to spatial resolution is apparently shortened. Therefore, according to the measurement device 1, it is possible to measure the load applied to the concrete S2 using the optical fiber cable 30 with a compact configuration.

[0037] In addition, by using the optical fiber cable 30 for measuring strain buried in the concrete structure S as the optical fiber for measuring the load, so-called continuous measurement including the load can be achieved by measuring the strain using the optical fiber cable 30. Also, since there is no need to prepare a conventional load cell type load meter in addition to the optical fiber cable 30 for measuring the strain, the load (stress) acting on the concrete S2 can be easily measured. Also, compared to the case where an optical fiber is attached to a long elastic member, the member for measuring the load is smaller, so there are fewer restrictions on the placement inside the concrete S2.

[0038] In the measurement device 1, the load conversion unit 20 includes a columnar elastic member 24 having a bottom surface 24a and a side surface 24b that receive a load along the axial direction D1. The load calculation unit 40 calculates the load based on the elastic coefficient and Poisson's ratio of the elastic member 24 as the conversion characteristics of the load conversion unit 20. As a result, when the elastic coefficient and Poisson's ratio of the elastic member 24 are known and, for example, have a proportional relationship, the load received by the bottom surface 24a can be easily obtained from the displacement of the side surface 24b by using such conversion characteristics.

[0039] The measurement device 1 further includes a buffer member 25 provided to cover the side surface 24b and the optical fiber cable 30. As a result, the buffer member 25 covers the side surface 24b and the optical fiber cable 30, and thus displacement of the side surface 24b and the optical fiber cable 30 is permitted by an amount equivalent to the thickness of the buffer member 25. This makes it possible to suppress the displacement of the side surface 24b and the optical fiber cable 30 from being hindered and affecting the measurement of the load.

[0040] In the measurement device 1, the load conversion unit 20 includes an anchor 23 that receives a load in a direction away from the load conversion unit 20. The load in the direction away from the load conversion unit 20 is transmitted to the load conversion unit 20 as a tensile load by the anchor 23. This makes it possible to measure the tensile load applied to the concrete S2 using the optical fiber cable 30.

[0041] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and may be modified within the scope of the gist described in each claim.

[0042] The configuration of the load conversion unit 20 is not limited to the above example. For example, the load conversion unit 20A may be configured as shown in FIG. 6. FIG. 6 is a schematic diagram showing a modified example of the measuring device. The load conversion unit 20A includes a plurality of elastic members 27 and a plate member 28 sandwiched between adjacent elastic members 27. The elastic members 27 and the plate members 28 are alternately stacked along the axial direction D1, and configured like a so-called laminated rubber bearing. For example, the dimension of the plurality of elastic members 27 and the plate member 28 of the entire load conversion unit 20A along the axial direction D1 is set to be equal to the entire length of the elastic member 24, and the elastic members 27 are arranged on both ends of the load conversion unit 20A.

[0043] The elastic member 27 and the plate member 28 are, for example, bonded to each other. Therefore, at the joint surface between the elastic member 27 and the plate member 28, the elastic member 27 is not displaced in the radial direction D2 relative to the plate member 28. The elastic member 27 is made of a material having a higher Poisson's ratio than the plate member 28, for example, a rubber cylindrical material. The plate member 28 is made of a material having a lower Poisson's ratio than the elastic member 27, for example, a disk-shaped steel plate.

[0044] According to such a configuration in which a plurality of elastic members 27 and plate members 28 are alternately stacked along the axial direction D1, the main detection site of the load in the axial direction D1 is divided among the plurality of elastic members 27, and thus the dimension along the axial direction D1 of each elastic member 27 is smaller than when the load conversion unit 20 is composed of one elastic member 24. Also, when the bottom surface 27a of the elastic member 27 receives a load in the axial direction D1, the side surface 27b of the elastic member 27 is displaced in the radial direction D2, and the load in the axial direction D1 is distributed to the plurality of elastic members 27. Therefore, for one elastic member 27, the lateral bulge of the bale shape of the elastic member 27 is smaller than the lateral bulge of the bale shape of the elastic member 24, so the magnitude of the displacement of the side surface 27b in the radial direction D2 based on the joint surface between the elastic member 27 and the plate member 28 is smaller than the magnitude of the displacement of the side surface 24b in the radial direction D2 based on the bottom surface 24a of the elastic member 24 in the above embodiment. In other words, it is possible to suppress the magnitude of the displacement of the side surface 27b from varying along the axial direction D1. As a result, the magnitude of the strain of the optical fiber cable 30 caused by the displacement of the side surface 27b is leveled along the axial direction D1, and the variation in the strain value at multiple measurement points of the optical fiber cable 30 can be suppressed.

[0045] In addition to or instead of bonding the elastic member 27 to the plate member 28, a member for suppressing the relative movement between the elastic member 27 and the plate member 28 may be provided. FIG. 7(a) is a cross-sectional view illustrating an example of the inside of the measurement device of FIG. 6. FIG. 7(b) is a cross-sectional view illustrating another example of the inside of the measurement device of FIG. 6. In the example of FIG. 7(a), a protrusion 28a protruding toward the elastic member 27 is provided at the center of each plate member 28. The relative movement between the elastic member 27 and the plate member 28 is suppressed by each protrusion 28a. In the example of FIG. 7(b), a rod 29 is provided penetrating the center of the elastic member 27 and the plate member 28. The rod 29 also suppresses the relative movement between the elastic member 27 and the plate member 28.

[0046] The load conversion unit 20 in the above embodiment is capable of measuring the tensile load in the direction away from the load conversion unit 20 as the load from the internal concrete S2. Hereinafter, a method of installing the measuring device 1 that is more suitable for measuring the tensile load will be described.

[0047] The method for installing the measuring device 1 includes a step of preparing the measuring device 1 and a step of pouring concrete S2 so as to bury the measuring device 1 in a state where a load along the axial direction D1 is applied in advance. The state where a load along the axial direction D1 is applied in advance means a state (initial state) in which the side surface 24b is displaced in advance along the radial direction D2 (due to the Poisson effect) in response to the load along the axial direction D1, and a strain corresponding to the displacement of the side surface 24b is also generated in the optical fiber cable 30. In order to apply a load along the axial direction D1 in advance, for example, as shown in FIG. 8, a pressurizing device 50 that applies a compressive load to the measuring device 1 may be used before pouring the concrete S2 so as to bury the measuring device 1. In this case, the direction in which the pressurizing device 50 applies the compressive load corresponds to the axial direction D1. The measuring device 1 is placed at a planned installation position in a state where the pressurizing device 50 applies a compressive load, and then concrete S2 is poured, so that the measuring device 1 is embedded in the concrete S2. This makes it possible to suitably measure the tensile load applied to the concrete S2.

[0048] Other modified examples will be described. In the above embodiment and modified examples, the load conversion part 20 (i.e., the elastic member 24, the buffer member 25, and the cover member 26) is generally cylindrical, but is not limited to this. It may be another columnar shape or another shape (for example, a cone shape).

[0049] In the above embodiment, the load conversion unit 20 converts the load along the axial direction D1 into a displacement along the radial direction D2 using the elastic member 24, which is a rubber cylindrical member, but is not limited thereto. In other words, as long as the load along the first direction from the surrounding concrete members is converted into a displacement along the second direction intersecting the first direction and the load-to-displacement conversion characteristic of the load conversion unit is known, a load conversion unit of another configuration can be adopted. As an example of such a load conversion unit, the load conversion unit may be configured to include a member that is provided so as to be displaceable along the first direction upon receiving a load along the first direction from the surrounding concrete members, and a conversion mechanism that mechanically converts the displacement of the member along the first direction into a displacement along the second direction intersecting the first direction. The conversion mechanism may include a mechanism that operates with a predetermined conversion characteristic using, for example, a cam or the like. In this case, for example, a spiral spring or the like with a known spring constant is used, and the load applied to the concrete S2 can be measured based on the amount of deformation by configuring the deformation (displacement along the second direction) via the operation of the cam to be proportional to the load along the first direction.

[0050] In the above embodiment, the side surface 24b of the elastic member 24 is covered with the buffer member 25, but a part of the side surface 24b may be covered. In short, it is sufficient if the configuration does not restrict the deformation of the elastic member 24 according to the Poisson's ratio, and it may be a gap retaining member that maintains a gap between the side surface 24b and the cover member 26 in the range of the side surface 24b where the optical fiber cable 30 is not provided. The buffer member 25 may be omitted.

[0051] In the above embodiment, a cushioning material is provided on the inner wall surface of the stress suppression container 10, but this is not essential. Also, although the stress suppression container 10 is used, this is not essential, and the stress suppression container 10 may be omitted.

[0052] In the above embodiment, the load calculation unit 40 calculates the load based on the elastic coefficient and Poisson's ratio of the elastic member 24 as the conversion characteristics of the load conversion unit 20, but the elastic coefficient and Poisson's ratio are not essential. For example, the load calculation unit 40 may calculate the load using a coefficient set in advance by performing calibration as the conversion characteristics of the load conversion unit 20. In this case, the elastic coefficient and Poisson's ratio of the elastic member 24 do not need to be known. [Explanation of symbols]

[0053] 1...measuring device, 20, 20A...load conversion section, 24, 27...elastic member, 24a, 27a...bottom surface, 24b, 27b...side surface, 25...buffer member, 28...plate member, 30...optical fiber cable (optical fiber), 40...load calculation section, D1...axial direction (first direction), D2...radial direction (second direction), S...concrete structure (concrete member), S2...concrete (concrete member).

Claims

1. A measuring device for measuring a load applied to a concrete member, A load conversion unit is installed inside the concrete member to be measured and converts a load from the surrounding concrete members along a first direction into a displacement along a second direction intersecting the first direction; an optical fiber wound around a displacement surface of the load conversion unit where the displacement occurs; a load calculation unit that measures a strain of the optical fiber and obtains the load based on the measured strain of the optical fiber and a conversion characteristic from the load to the displacement of the load conversion unit, the load conversion unit includes a plurality of columnar elastic members each having a bottom surface that receives a load along the first direction and a side surface that is the displacement surface, and a plate member sandwiched between adjacent ones of the elastic members, A measuring device in which a protrusion that protrudes toward the elastic member is provided on each of the plate members as a member that suppresses relative movement between the elastic member and the plate member, or a rod that penetrates the elastic member and the plate member is provided.

2. A measuring device as described in Claim 1, wherein the elastic member and the plate member are stacked alternately along the first direction.

3. The measuring device according to claim 1 , further comprising a buffer member provided to cover the displacement surface and the optical fiber.

4. 4. The measurement device according to claim 1, wherein the load converter includes a tensile load receiver that receives the load in a direction away from the load converter.

5. A measuring device described in any one of claims 1 to 4, wherein the load calculation unit calculates the load based on the elastic coefficient and Poisson's ratio of the elastic member as conversion characteristics of the load conversion unit.

6. A method for installing a measuring device that measures a load applied to a concrete member, comprising the steps of: Providing a measurement device according to claim 4; pouring concrete to bury the measurement device while applying a load along the first direction in advance.

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