Optical fiber cable installation structure

Abstract

To provide an optical fiber cable installation structure that suppresses breaking and peeling of an optical fiber cable.SOLUTION: An optical fiber cable installation structure 1 is so constructed as to install an optical fiber cable 5 for measuring strain of a reinforcing bar 3 on the reinforcing bar 3, and comprises an adhesion layer 11 for bonding the optical fiber cable 5 to a flat part 7 of the reinforcing bar 3, a cover member 13 which covers the optical fiber cable 5 and adhesion layer 11, and an adhesion layer 12 for bonding the cover member 13 to the flat part 7, wherein the cover member 13 and adhesion layer 12 are not in contact with the optical fiber cable 5 and adhesion layer 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical fiber cable installation structure. [Background technology]

[0002] Conventionally, it is known that a strain distribution or temperature distribution of an object is measured by adhering an optical fiber cable to the object and detecting backscattered light generated by irradiating a pulsed light into the optical fiber (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-131024 A Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of strain measurement using an optical fiber cable, if the optical fiber cable breaks or peels off from the object, it becomes impossible to perform the desired strain measurement. Here, in order to suppress breakage of the optical fiber cable, it is preferable to increase the diameter of the optical fiber cable and the thickness of the adhesive layer to improve the mechanical strength of the optical fiber cable and the adhesive layer. On the other hand, the stiffness of the portion where the optical fiber cable and the adhesive layer are combined increases as the diameter of the optical fiber cable increases and the adhesive layer becomes thicker. This increases the shear shear force generated at the interface between the object and the adhesive layer when strain occurs in the object. This makes it easier for the adhesive layer to peel off from the object, that is, the optical fiber cable to peel off from the object. In this way, it is difficult to simultaneously suppress breakage and peeling of the optical fiber cable. Therefore, an object of the present invention is to provide an optical fiber cable installation structure that suppresses breakage and peeling of the optical fiber cable. [Means for solving the problem]

[0005] The gist of the present invention lies in the following [1] to [4].

[0006] [1] An optical fiber cable installation structure for installing an optical fiber cable in a target member for measuring strain of the target member, comprising: a first adhesive layer for adhering the optical fiber cable to a surface of the target member; a cover member for covering the optical fiber cable and the first adhesive layer; and a second adhesive layer for adhering the cover member to the surface of the target member, wherein the cover member and the second adhesive layer are not in contact with the optical fiber cable and the first adhesive layer.

[0007] [2] The optical fiber cable installation structure described in [1], further comprising a filling layer that fills the space between the surface of the target component and the cover member so as to embed the optical fiber cable and the first adhesive layer, the filling layer having a smaller elastic modulus than the first adhesive layer.

[0008] [3] An optical fiber cable installation structure for installing an optical fiber cable in a target component for measuring strain of the target component, comprising: an adhesive layer for adhering the optical fiber cable to a surface of the target component; and a covering member made of a material having a smaller elastic modulus than the adhesive layer, attached to the surface of the target component, and covering the optical fiber cable and the adhesive layer.

[0009] [4] The optical fiber cable installation structure according to any one of [1] to [3], wherein the target member is a reinforcing bar in a reinforced concrete structure. Effect of the Invention

[0010] According to the present invention, it is possible to provide an optical fiber cable installation structure that suppresses breakage and peeling of the optical fiber cable. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1(a) is an exploded perspective view showing an optical fiber cable installation structure of a first embodiment, and FIG. 1(b) is a cross-sectional view of the optical fiber cable installation structure. [Diagram 2] FIG. 1(a) is a cross-sectional view showing an optical fiber cable installation structure according to a second embodiment, and FIG. 1(b) is a cross-sectional view showing an optical fiber cable installation structure according to a third embodiment. [Diagram 3] FIG. 1 is a diagram showing the results of a tensile test conducted by the present inventors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment) Hereinafter, a first embodiment of the optical fiber cable installation structure according to the present invention will be described in detail with reference to the drawings. Fig. 1(a) is an exploded perspective view showing an optical fiber cable installation structure 1 of this embodiment, and Fig. 1(b) is a cross-sectional view of the optical fiber cable installation structure 1. The optical fiber cable installation structure 1 shown in Fig. 1 has an optical fiber cable 5 for strain measurement bonded and integrated with a reinforcing bar 3. The optical fiber cable 5 is, for example, an optical fiber core wire with a diameter of 0.9 mm.

[0013] A flat portion 7, which forms a flat surface as part of the circumferential surface of the reinforcing bar 3, exists over the entire length of the reinforcing bar 3. An optical fiber cable 5 extending in the longitudinal direction of the reinforcing bar 3 is bonded to the flat portion 7 so as to be integrated with the reinforcing bar 3 over the entire area to be measured for strain. The reinforcing bar 3 to which the optical fiber cable 5 is bonded is embedded in concrete 103 as a reinforcing bar for a reinforced concrete structure 100. For example, the reinforcing bar 3 in this embodiment is a commercially available threaded reinforcing bar, and the flat portion of the threaded reinforcing bar is used as the flat portion 7. In the following, the term "longitudinal direction" simply refers to the longitudinal direction of the flat portion 7 (the longitudinal direction of the reinforcing bar 3), and the term "width direction" simply refers to the width direction of the flat portion 7.

[0014] An end of the optical fiber cable 5 is pulled out to the outside of the reinforced concrete structure 100 and connected to a strain measuring instrument (not shown) such as an OTDR (Optical Time Domain Reflectometer) or a BOTDR (Brillouin Optical Time Domain Reflectometer). When pulsed light is incident from this strain measuring instrument to the optical fiber of the optical fiber cable 5, scattered light from each portion in the longitudinal direction of the optical fiber returns to the strain measuring instrument. By analyzing this scattered light with the strain measuring instrument, it is possible to know the strain at each portion in the longitudinal direction of the optical fiber cable 5, and therefore the strain at each portion in the longitudinal direction of the reinforcing bar 3 to which the optical fiber cable 5 is integrally bonded.

[0015] As shown enlarged in Figure 1(b), the optical fiber cable installation structure 1 comprises an optical fiber cable 5, an adhesive layer 11 (first adhesive layer) that adheres the optical fiber cable 5 to the flat portion 7, a cover member 13 that covers the optical fiber cable 5 and the adhesive layer 11, and an adhesive layer 12 (second adhesive layer) that adheres the cover member 13 to the flat portion 7.

[0016] In the process of adhering the optical fiber cable 5 to the flat portion 7, for example, the optical fiber cable 5 is temporarily fixed on the flat portion 7, and an adhesive is applied to the flat portion 7 from above the optical fiber cable 5 in a width that protrudes on both sides of the optical fiber cable 5. The adhesive hardens to form an adhesive layer 11, and the optical fiber cable 5 and the adhesive layer 11 are integrally adhered to the reinforcing bar 3. It is preferable that the adhesive is applied relatively thinly, and the adhesive layer 11 is formed relatively thin.

[0017] The cover member 13 is a member that extends over substantially the entire longitudinal direction of the reinforcing bar 3, and the cross-sectional shape of the cover member 13 forms an arc that bulges outward from the flat portion 7. The portions corresponding to both ends of the arc are respectively adhered to the flat portion 7, thereby fixing the cover member 13 to the flat portion 7. The cover member 13 is a member made of a hard material, and may be made of, for example, metal or resin (for example, polyvinyl chloride resin). A space 15 with a semicircular cross section is formed between the cover member 13 and the flat portion 7, and the optical fiber cable 5 and adhesive layer 11 described above are present in the space 15.

[0018] In the step of adhering the cover member 13 to the flat portion 7, for example, an adhesive is applied to two positions sandwiching the optical fiber cable 5 and the adhesive layer 11 already present on the flat portion 7 in the width direction. Here, the adhesive is applied with a gap in the width direction between the adhesive layer 11 and the cover member 13 so as not to come into contact with the adhesive layer 11. Then, the cover member 13 is placed on the flat portion 7, and both ends of the cover member 13 are adhered to the flat portion 7 by the applied adhesive. The adhesive is cured to form the adhesive layer 12. For example, the same adhesive as that for forming the adhesive layer 11 is used as the adhesive for forming the adhesive layer 12. Such an adhesive step for adhering the cover member 13 may be performed after the adhesive layer 11 for the optical fiber cable 5 is completely cured.

[0019] The cover member 13 is not in contact with the optical fiber cable 5, and is also not in contact with the adhesive layer 11. Moreover, the adhesive layer 12 is also not in contact with the optical fiber cable 5, and is also not in contact with the adhesive layer 11. As described above, the cover member 13 is a hard member, and the elastic modulus of the cover member 13 is smaller than the elastic modulus of the reinforcing bar 3, and larger than the elastic modulus of the adhesive layer 11 and the adhesive layer 12. Moreover, the elastic modulus of the adhesive layer 11 and the adhesive layer 12 is larger than the elastic modulus of the optical fiber cable 5. That is, the elastic modulus of each of the above-mentioned parts is greatest in the order of the reinforcing bar 3, the cover member 13, the adhesive layer 11 and the adhesive layer 12, and the optical fiber cable 5.

[0020] The effects of the optical fiber cable installation structure 1 as described above will be described. In constructing the reinforced concrete structure 100, the concrete 103 of the reinforced concrete structure 100 is poured so as to embed the reinforcing bar 3 in a state where the optical fiber cable 5 is installed in the reinforcing bar 3. The concrete 103 is in contact with the outer surface of the cover member 13. When pouring the concrete, for example, an external force may be applied to the reinforcing bar 3 when a worker comes into contact with the reinforcing bar 3 or when a vibrator for compaction comes into contact with the reinforcing bar 3. In contrast, in the optical fiber cable installation structure 1, the optical fiber cable 5 is covered with the hard cover member 13, and the cover member 13 and the optical fiber cable 5 are not in contact with each other and there is a gap between them. Therefore, the force applied to the optical fiber cable 5 due to the above-mentioned external force is kept small, and as a result, breakage of the optical fiber cable 5 due to the external force is suppressed.

[0021] As described above, since the optical fiber cable 5 is covered with the cover member 13, there is little need to thicken the adhesive layer 11 to protect the optical fiber cable 5, and the adhesive layer 11 can be made thin. In other words, the thickness of the adhesive layer 11 is sufficient as long as it can integrate the optical fiber cable 5 with the reinforcing bar 3. There is also little need to thicken the optical fiber cable 5, and for example, an optical fiber cable thinner than the optical fiber core wire with a diameter of 0.9 mm as described above can be used. In this way, the rigidity of the portion where the optical fiber cable 5 and the adhesive layer 11 are combined can be kept low, and the shear force generated at the interface between the reinforcing bar 3 and the adhesive layer 11 when the reinforcing bar 3 is distorted can be kept low.

[0022] Moreover, the cover member 13 is a member having a relatively large elastic modulus. Therefore, if the combined portion of the optical fiber cable 5, the adhesive layer 11, the adhesive layer 12, and the cover member 13 behaves as an integral unit, the rigidity of the integral unit is relatively high. As a result, when the reinforcing bar 3 is distorted, the shear force generated at the interface between the reinforcing bar 3 and the integral unit is relatively large, and the integral unit is likely to peel off from the reinforcing bar 3. That is, the optical fiber cable 5 is likely to peel off from the reinforcing bar 3. In contrast, in the optical fiber cable installation structure 1, the cover member 13 is not in contact with the optical fiber cable 5 and is not in contact with the adhesive layer 11. Moreover, the adhesive layer 12 is not in contact with the optical fiber cable 5 and is not in contact with the adhesive layer 11. Therefore, the optical fiber cable 5 and adhesive layer 11 behave separately from the cover member 13 and adhesive layer 12, and as a result, as mentioned above, the shear force generated at the interface between the reinforcing bar 3 and the adhesive layer 11 when strain occurs in the reinforcing bar 3 is kept small.

[0023] As described above, the shear force occurring at the interface between the reinforcing bar 3 and the adhesive layer 11 when strain occurs in the reinforcing bar 3 is kept small. Therefore, when strain occurs in the reinforcing bar 3, the adhesive layer 11 is unlikely to peel off from the reinforcing bar 3, i.e., the optical fiber cable 5 is unlikely to peel off from the reinforcing bar 3. As a result, it may be possible to measure large strains of tens of thousands of μ that may occur after the yielding of the reinforcing bar 3, for example. As described above, according to the optical fiber cable installation structure 1, breakage and peeling of the optical fiber cable 5 can be suppressed.

[0024] Second embodiment Next, a second embodiment of the optical fiber cable installation structure will be described. Fig. 2(a) is a cross-sectional view of an optical fiber cable installation structure 51 of this embodiment. As shown in the figure, the optical fiber cable installation structure 51 includes a filling layer 17 in addition to the optical fiber cable installation structure 1 of the first embodiment. Since the optical fiber cable installation structure 51 is otherwise similar to the optical fiber cable installation structure 1, the same reference numerals are used for the same or equivalent components, and duplicated explanations will be omitted.

[0025] The filling layer 17 fills the space 15 surrounded by the flat portion 7 of the reinforcing bar 3 and the cover member 13. For example, a material with a small elastic modulus, such as silicone resin, is used as the material of the filling layer 17. The elastic modulus of the filling layer 17 is smaller than that of the adhesive layer 11 and smaller than that of the optical fiber cable 5. In the process of forming the filling layer 17, for example, after the cover member 13 is bonded to the flat portion 7, a fluid filling material is injected into the space 15. Alternatively, the filling material may be filled into the space 15 so that the cover member 13 is bonded to the flat portion 7 from a state in which the filling material is charged inside the cover member 13. The filling layer 17 is formed by hardening the filling material. The optical fiber cable 5 and the adhesive layer 11 in the space 15 are embedded in the filling layer 17.

[0026] According to such an optical fiber cable installation structure 51, the filling layer 17 absorbs the impact force applied to the reinforcing bar 3 during concrete pouring, and thus protects the optical fiber cable 5 from external forces together with the cover member 13, and prevents the optical fiber cable 5 from breaking. The filling layer 17 is interposed between the optical fiber cable 5 and the adhesive layer 11 and the cover member 13 and the adhesive layer 12, but the elastic modulus of the filling layer 17 is relatively small. Therefore, the action of the optical fiber cable 5 and the adhesive layer 11 acting as one unit together with the cover member 13, etc. is suppressed to a small extent. Therefore, the possibility that the optical fiber cable 5 will peel off from the reinforcing bar 3 is not extremely increased due to the presence of the filling layer 17. In addition, since the filling layer 17 blocks the space 15, the possibility that the space 15 will become a water path and cause corrosion of the reinforcing bar 3 in the reinforced concrete structure 100 is reduced.

[0027] Third embodiment Next, a third embodiment of the optical fiber cable installation structure will be described. Fig. 2(b) is a cross-sectional view of an optical fiber cable installation structure 61 of this embodiment. As shown in the figure, the optical fiber cable installation structure 61 includes a protective tape 19 (coating member) instead of the cover member 13 of the optical fiber cable installation structure 1 of the first embodiment. Since the optical fiber cable installation structure 61 is otherwise similar to the optical fiber cable installation structure 1, the same reference numerals are used for the same or equivalent components, and duplicated explanations will be omitted.

[0028] The protective tape 19 is a strip-shaped member that extends over substantially the entire longitudinal direction of the reinforcing bar 3 and has an adhesive surface on one side. The protective tape 19 is attached to the flat portion 7 with the adhesive surface facing the flat portion 7 so as to cover the optical fiber cable 5 and the adhesive layer 11. There may be a gap between the protective tape 19 and the optical fiber cable 5, or there may be a gap between the protective tape 19 and the adhesive layer 11. The elastic modulus of the protective tape 19 is smaller than that of the adhesive layer 11 and smaller than that of the optical fiber cable 5. The step of attaching the protective tape 19 to the flat portion 7 may be performed after the adhesive layer 11 for the optical fiber cable 5 has completely hardened.

[0029] According to such an optical fiber cable installation structure 61, the concrete 103 of the reinforced concrete structure 100 is poured so as to embed the reinforcing bar 3, and the concrete 103 contacts the outer surface of the protective tape 19. When pouring the concrete, the protective tape 19, which has a relatively small elastic modulus, acts as a cushion to protect the optical fiber cable 5 from external forces, and breakage of the optical fiber cable 5 is suppressed. Even if the protective tape 19 is attached to the optical fiber cable 5 and the adhesive layer 11, the elastic modulus of the protective tape 19 is relatively small. Therefore, even if the optical fiber cable 5 and the adhesive layer 11 behave as an integral part together with the protective tape 19, the rigidity of the integral part is not extremely increased compared to the rigidity of the optical fiber cable 5 and the adhesive layer 11. Therefore, the possibility that the optical fiber cable 5 will peel off from the reinforcing bar 3 is not extremely increased due to the presence of the protective tape 19.

[0030] 3 shows the results of a tensile test of rebar conducted by the present inventors for the optical fiber cable installation structure 61. An optical fiber cable was installed in the rebar of this test sample using the optical fiber cable installation structure 61, and a strain gauge was installed at a position 550 mm from the bottom end of the rebar. In the tensile test, the strain of the rebar measured by the strain gauge and the strain of the rebar measured by the optical fiber cable were approximately 11,500 μ, which was almost the same. This test confirmed that the optical fiber cable installation structure 61 can measure large strains of rebar of approximately 10,000 μ, and can also be used to measure strains that may occur after the yielding of the rebar, for example.

[0031] The present invention can be implemented in various forms including the above-described embodiment and various modifications and improvements based on the knowledge of those skilled in the art. In addition, it is possible to configure modified examples by utilizing the technical matters described in the above-described embodiment. The configurations of each embodiment may be used in appropriate combination. [Explanation of symbols]

[0032] 1, 51, 61...optical fiber cable installation structure, 3...reinforcing bar (target member), 7...flat portion, 5...optical fiber cable, 11...adhesive layer (first adhesive layer), 12...adhesive layer (second adhesive layer), 13...cover member, 15...space, 17...filling layer, 19...protective tape (covering member), 100...reinforced concrete structure.

Claims

1. An optical fiber cable installation structure for installing an optical fiber cable for measuring a strain of a target member in the target member, a first adhesive layer that adheres the optical fiber cable to a surface of the target member; a cover member covering the optical fiber cable and the first adhesive layer; a second adhesive layer that adheres the cover member to the surface of the target member; An optical fiber cable installation structure, wherein the cover member and the second adhesive layer are not in contact with the optical fiber cable and the first adhesive layer.

2. a filling layer that fills a space between the surface of the target member and the cover member so as to embed the optical fiber cable and the first adhesive layer; The optical fiber cable installation structure according to claim 1 , wherein the filling layer has a smaller elastic modulus than the first adhesive layer.

3. An optical fiber cable installation structure for installing an optical fiber cable for measuring a strain of a target member in the target member, an adhesive layer that adheres the optical fiber cable to a surface of the target member; An optical fiber cable installation structure comprising: a covering member made of a material having a smaller elastic modulus than the adhesive layer, attached to the surface of the target component, and covering the optical fiber cable and the adhesive layer.

4. 4. The optical fiber cable installation structure according to claim 1, wherein the target member is a reinforcing bar in a reinforced concrete structure.

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