Optical fiber laying structure and method for repairing optical fiber laying structure

Abstract

This invention provides an optical fiber laying structure and a method for repairing an optical fiber laying structure that reduce the risk caused by optical fiber breakage. [Solution] The optical fiber laying structure 10 for laying an optical fiber cable 11 in a box culvert 1 comprises a plurality of internal passage sections 13, which are sections in which the optical fiber cable 11 passes inside the side wall 7 of the box culvert 1, and a plurality of external passage sections 15, which are sections between the internal passage sections 13 and in which the optical fiber cable 11 passes outside the side wall 7 of the box culvert 1.

Description

Technical Field

[0001] The present invention relates to an optical fiber laying structure and a method for repairing an optical fiber laying structure.

Background Art

[0002] Conventionally, there is known a technique for measuring the strain distribution and temperature distribution of a concrete skeleton by injecting laser pulse light into an optical fiber embedded in the concrete skeleton, and observing and analyzing scattered light (for example, see Patent Document 1 below). When constructing this type of concrete skeleton, an optical fiber cable is pre-wired in a concrete formwork, and concrete is poured, so that the optical fiber cable and the concrete skeleton are integrated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, because optical fiber cables are thin, easily broken, and susceptible to contact, they are prone to breakage due to contact with reinforcing bars during rebar assembly within formwork, exposure to concrete pouring pressure (including contact with concrete aggregates) during concrete pouring, or contact with vibrators during compaction. If an optical fiber cable breaks at a point in the concrete structure, measurement becomes impossible from the perspective of the measuring device beyond the point of breakage. For example, if the break occurs close to the measuring device, a large portion of the measurement target section becomes unmeasurable. Furthermore, if an optical fiber cable breaks within the formwork during concrete pouring, repair is virtually impossible, and even if repair is attempted during the assembly of reinforcing bars and formwork, significant rework may be required depending on the location of the break. Thus, while optical fiber measurement methods can measure strain and temperature distributedly along the entire length of the optical fiber, they carry a high risk of optical fiber breakage. In view of this problem, the present invention aims to provide an optical fiber laying structure and a method for repairing an optical fiber laying structure that reduces the risk of optical fiber breakage. [Means for solving the problem]

[0005] The gist of this invention is as follows: [1] to [6] and

[11] to

[16] .

[0006] [1] An optical fiber laying structure for laying optical fibers in a building structure, comprising: a plurality of internal passage sections, which are sections in which the optical fibers pass through the inside of the building structure; and a plurality of external passage sections, which are sections between the internal passage sections, in which the optical fibers pass through the outside of the building structure.

[0007] [2] The optical fiber laying structure according to [1], wherein the frame includes a unit optical fiber that forms part of the optical fiber and has a plurality of unit frame sections connected in the laying direction of the optical fiber, the unit optical fiber is embedded inside the unit frame section at a position corresponding to the internal passage section and both ends are pulled out to the outside of the unit frame section from a position corresponding to the boundary between the internal passage section and the external passage section, and at least a part of the external passage section has an optical fiber connection section that connects the ends of the unit optical fibers of adjacent unit frame sections.

[0008] [3] The optical fiber laying structure according to [2], wherein the other part of the external passing section has skip connection sections that connect the ends of the unit optical fibers of the unit structural sections that are arranged with other unit structural sections sandwiched between them.

[0009] [4] An optical fiber laying structure according to any one of [1] to [3], comprising an optical fiber protection section that protects the optical fiber at the boundary between the internal passage section and the external passage section.

[0010] [5] An optical fiber laying structure according to any one of [1] to [3], comprising a box-out section provided at the boundary between the internal passage section and the external passage section for drawing the optical fiber from the inside of the structure to the outside of the structure.

[0011] [6] A method for repairing the optical fiber laying structure described in [2] when a break occurs in the optical fiber, comprising: separating the unit optical fiber including the break in two external passing sections sandwiching the break between the optical fibers; and connecting the separated portions of the optical fibers from which the unit optical fiber has been separated via a new bypass optical fiber.

[0012]

[11] An optical fiber laying structure in which optical fibers are laid on the building structure, The optical fiber has multiple internal passage sections, which are sections through which it passes inside the body, The optical fiber comprises a plurality of external passing sections, which are sections in which the optical fiber passes outside the body, The internal passage section and the external passage section are alternately located along the extending direction of the optical fiber. The interior of the frame is the part inside the outer surface of the frame, in which the optical fiber is embedded in the concrete of the frame. The exterior of the frame is the portion outside the outer surface of the frame in which the optical fiber is not embedded in the concrete of the frame. Optical fiber laying structure.

[0013]

[12] The frame has a plurality of unit frame sections connected in series, The optical fiber is configured by connecting multiple unit optical fibers in series. The aforementioned internal passage section is the section in which the unit optical fiber is embedded in the concrete of the unit structural body. The aforementioned external passage section is a section that spans the connecting sections between the aforementioned unit structural parts. The aforementioned external passage section contains connection points between the unit optical fibers. The optical fiber laying structure described in

[11] .

[0014]

[13] A portion of the external passing section spans multiple connecting sections. The optical fiber laying structure described in

[12] .

[0015]

[14] An optical fiber laying structure according to any one of

[11] to

[13] , comprising an optical fiber protection section that protects the optical fiber at the boundary between the internal passage section and the external passage section.

[0016]

[15] An optical fiber laying structure according to any one of

[11] to

[13] , comprising a box-out section provided at the boundary between the internal passage section and the external passage section for drawing the optical fiber from the inside of the structure to the outside of the structure.

[0017] 〔16〕 A repair method for an optical fiber installation structure for repairing the optical fiber installation structure according to〔12〕 or〔13〕 when a disconnection point occurs in the optical fiber, the method comprising: separating the unit optical fiber including the disconnection point from the optical fiber in two of the external passing sections that sandwich the disconnection point therebetween; connecting the separated portions of the optical fiber from which the unit optical fiber has been separated via a new detour optical fiber. Effects of the Invention

[0018] According to the present invention, it is possible to provide an optical fiber installation structure and a repair method for the optical fiber installation structure that reduce the risk caused by optical fiber disconnection. Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view showing an example of a box culvert to which the optical fiber installation structure according to the embodiment is applied. [Figure 2] It is a front view schematically showing the state of the side wall of the box culvert as viewed from the inner side of the box culvert. [Figure 3] (a) is a cutaway perspective view of the side wall showing the vicinity of the optical fiber lead-out portion. (b) is a cross-sectional view showing the vicinity of the box body of the optical fiber lead-out portion, and (c) is a IIIc-IIIc cross-sectional view of the box body. [Figure 4] (a) is a diagram showing the optical fiber installation structure in which a disconnection has occurred, and (b) is a diagram showing the optical fiber installation structure after repair. [Figure 5] (a) is a cutaway perspective view of the side wall showing the vicinity of an optical fiber lead-out portion according to a modification. (b) is a cross-sectional view of the side wall showing the vicinity of an optical fiber lead-out portion according to another modification. [Figure 6] (a) is a cutaway perspective view of the side wall showing an optical fiber installation structure according to a modification. (b) is a cutaway perspective view of the side wall showing an optical fiber installation structure according to another modification. [Figure 7]This is a cross-sectional perspective view of a side wall showing another modified optical fiber laying structure. [Modes for carrying out the invention]

[0020] Hereinafter, embodiments of the optical fiber laying structure and the repair method for the optical fiber laying structure according to the present invention will be described in detail with reference to the drawings. Components that are identical or equivalent to each other are denoted by the same reference numerals in the drawings, and redundant descriptions are omitted.

[0021] The optical fiber laying structure of this embodiment can be applied to various concrete structures such as box culverts, bridge piers, girders, and caissons. In the following description, an optical fiber laying structure for laying optical fiber cables 11 in a box culvert 1 shown in Figure 1 will be described as an example. The box culvert 1 is constructed in units of 3 (unit structural parts) and consists of a plurality of unit blocks 3 connected in the longitudinal direction of the box culvert 1 (direction of arrow A in the figure). In the optical fiber laying structure of this embodiment, optical fiber cables 11 are laid over almost the entire length in the longitudinal direction of the box culvert 1.

[0022] As shown in Figure 1, the optical fiber cable 11 is located at the bottom of one side wall 7 of the box culvert 1. Here, the optical fiber cable 11 may be, for example, an optical fiber core with a diameter of 0.9 mm, or it may be an optical fiber cable in the narrow sense that includes multiple bundled optical fiber cores.

[0023] A measuring device 5 is connected to the end of the optical fiber cable 11 laid in the box culvert 1. This measuring device 5 incidents laser pulse light onto the optical fiber strands of the optical fiber cable 11 and receives scattered light returning from various positions along the longitudinal direction of the optical fiber strands. Based on the principle that the intensity and wavelength of the scattered light depend on the strain and temperature changes applied to the optical fiber strands, the measuring device acquires the strain and temperature at each position along the longitudinal direction of the optical fiber cable 11, and consequently acquires the longitudinal strain distribution and temperature distribution in the box culvert 1.

[0024] Figure 2 is a schematic front view showing the side wall 7 of the box culvert 1, on which the optical fiber cable 11 is laid, as seen from inside the box culvert 1. The longitudinal direction A of the box culvert 1 corresponds to the left-right direction in Figure 2. In the following explanation, terms such as "right side / left side" and "rightward / leftward" will be used in reference to the left-right direction in Figure 2.

[0025] The optical fiber laying structure 10 in the box culvert 1 comprises a plurality of internal passage sections 13 through which the optical fiber cable 11 passes inside the side wall 7, and a plurality of external passage sections 15 between the internal passage sections 13 through which the optical fiber cable 11 passes outside the side wall 7. The internal passage sections 13 and external passage sections 15 are arranged alternately in the longitudinal direction of the box culvert 1.

[0026] The internal passage section 13 is a section in which the optical fiber cable 11 is embedded within the side wall 7 and integrated with the side wall 7. One internal passage section 13 is set in each unit block 3 of the box culvert 1. The optical fiber cable 11 of the external passage section 15 is brought out to the outside of the side wall 7 through the side wall surface 7a and exists within the hollow part of the box culvert 1. The optical fiber cable 11 of the external passage section 15 may be protected by being attached to the side wall surface 7a with adhesive, or by being covered with a protective tube such as a flexible stainless steel tube or a designated box.

[0027] A unit optical fiber cable 21, which forms part of the optical fiber cable 11, is installed on the side wall 7 of each unit block 3. Optical fiber extraction sections 23 are provided at the right and left ends of the side wall 7 of each unit block 3, respectively, for drawing the unit optical fiber cable 21 from the inside to the outside of the side wall 7. Most of the unit optical fiber cable 21 is embedded inside the side wall 7, and both ends 27, 27 of this unit optical fiber cable 21 are drawn out from the side wall surface 7a side to the outside of the side wall 7 through the optical fiber extraction sections 23, and are located in the hollow part of the box culvert 1. The ends 27 of the unit optical fiber cable 21 of adjacent unit blocks 3 are connected by an optical fiber connection section 25. At the optical fiber connection section 25, the ends of the unit optical fiber cable 21 are connected by fusion splicing or connector connection.

[0028] The section between the left and right optical fiber extraction sections 23 in one unit block 3 corresponds to the internal passage section 13. The section between the rightmost optical fiber extraction section 23 in one unit block 3 and the leftmost optical fiber extraction section 23 in the adjacent unit block 3 corresponds to the external passage section 15, which includes the optical fiber connection section 25. An optical fiber extraction section 23 is located at the boundary between the internal passage section 13 and the external passage section 15. The optical fiber cable 11 is composed of multiple unit optical fiber cables 21 connected in series via the optical fiber connection section 25.

[0029] In this box culvert 1 construction method, a new unit block 3 is constructed adjacent to an existing unit block 3, and the end 27 of the unit optical fiber cable 21 of the new unit block 3 is connected to the end 27 of the unit optical fiber cable 21 of the existing unit block 3 to form an optical fiber connection section 25, and this procedure is repeated. The optical fiber extraction section 23 is preferably located in a position that is easily accessible to workers from inside the box culvert 1 in order to improve the workability of connecting the unit optical fiber cables 21 to each other.

[0030] Next, the details of the optical fiber extraction section 23 will be described. Figure 3(a) is a broken perspective view of the side wall 7 showing the vicinity of the optical fiber extraction section 23. Figure 3(b) is a side view showing the vicinity of the box body 24 of the optical fiber extraction section 23, and Figure 3(c) is a cross-sectional view of the box body 24 taken along the line IIIc-IIIc. As shown in the figures, the optical fiber extraction section 23 is formed as a box-out section including a box body 24 embedded in the side wall 7. The box body 24 is a hollow box structure that is roughly rectangular in shape, for example, about 10 cm × 10 cm × 2 cm in size, through which a unit optical fiber cable 21 passes. Since such a box-out section results in a cross-sectional defect in the side wall 7, it is preferable that the optical fiber extraction section 23 be installed in a part of the side wall 7 that has little impact on the structural load-bearing capacity and deformation resistance (for example, near the neutral axis).

[0031] When constructing a unit block 3 (Figure 2) having two optical fiber extraction sections 23, 23, the above-mentioned box bodies 24, 24 are installed in the concrete formwork at positions corresponding to the optical fiber extraction sections 23, 23. Furthermore, the unit optical fiber cable 21 is installed in the planned embedding position within the side wall 7. The ends 27, 27 of the unit optical fiber cable 21 are then installed so that they pass through the inside of the box bodies 24, 24, and then penetrate the concrete formwork and are pulled out to the outside of the concrete formwork. Concrete is poured into the concrete formwork to embed the box bodies 24, 24 and the unit optical fiber cable 21 installed in this manner.

[0032] Since the box body 24 is embedded in the concrete and a portion of it is exposed on the concrete surface, it is preferable that the material of the box body 24 is a material with excellent alkali resistance and weather resistance. From this viewpoint, for example, ASA resin (Acrylate Sthrene Acrylonitrile) is used as the material of the box body 24. Also, since concrete shrinks due to self-shrinkage and drying shrinkage, it is preferable that the surface material of the part of the box body 24 that is embedded in the concrete is an expandable material (for example, urethane) that can absorb the deformation of the concrete. Furthermore, it is preferable that the corners of the box body 24 are chamfered so that the shrinkage of the concrete is restrained by the box body 24 and cracking is less likely to occur. In addition, in order to correct any twisting of the optical fiber cable 11 that may occur inside the box body 24 before concrete pouring, it is preferable that the side walls of the box body 24 be detachable covers 24e (Figure 3(c)).

[0033] Next, the structure of the box body 24 will be described. The box body 24 is equipped with a cable entry port 24a located inside the side wall 7 for drawing in the unit optical fiber cable 21 from inside the side wall 7, and a cable exit port 24b located so as to be exposed on the side wall surface 7a for drawing the unit optical fiber cable 21 to the outside of the side wall 7. Inside the box body 24, a circular cable passage space 24c is formed between the cable entry port 24a and the cable exit port 24b for passing the unit optical fiber cable 21. Within the cable passage space 24c, a circular cable winding section 24d is formed, which has a smaller diameter than the cable passage space 24c. The cable winding section 24d is positioned eccentrically with respect to the cable passage space 24c towards the cable entry port 24a and cable exit port 24b side.

[0034] In the optical fiber extraction section 23, the end 27 of the unit optical fiber cable 21 inside the side wall 7 is drawn into the box body 24 through the cable entry port 24a, wound 360° in a loop around the cable winding section 24d, passes through the cable passage space 24c, and is pulled out to the outside of the side wall 7 through the cable exit port 24b. This extraction section extends to the optical fiber connection section 25, where it is connected to the end 27 of another unit optical fiber cable 21.

[0035] By pulling the end 27 of the unit optical fiber cable 21 from the cable outlet 24b, the end 27 can be pulled out of the box body 24 until the loop of the unit optical fiber cable 21 in the cable passage space 24c becomes smaller and wraps around the cable winding section 24d. Conversely, by pushing this end 27 in from the cable outlet 24b, the loop of the unit optical fiber cable 21 in the cable passage space 24c becomes larger and the end 27 can be pushed into the box body 24 until it fully expands within the cable passage space 24c. Therefore, the length of the end 27 pulled out from the side wall 7 can be adjusted, and the excess length of the unit optical fiber cable 21 can be accommodated inside the box body 24. For example, the end 27 of the unit optical fiber cable 21 can be pulled out to the required length for the work, connection processing (e.g., fusion splicing) can be performed at the optical fiber connection section 25, and after the connection processing, the excess length can be pushed back into the box body 24.

[0036] Furthermore, within the cable passage space 24c, the radius of curvature of the bending of the unit optical fiber cable 21 is not smaller than the radius of the cable winding section 24d. Therefore, by appropriately setting the radius of the cable winding section 24d, damage to the unit optical fiber cable 21 due to bending at a small radius of curvature can be avoided. In addition, the cable outlet 24b has a trumpet shape that widens towards the outside of the side wall 7. Therefore, the possibility of the unit optical fiber cable 21 bending and being damaged at the edge of the cable outlet 24b is reduced. Furthermore, by forming the cable outlet 24b with an elastic material with low rigidity, the possibility of damage to the unit optical fiber cable 21 at the cable outlet 24b is further reduced.

[0037] Furthermore, the cable entry port 24a is provided with an optical fiber protection section 29 to protect the unit optical fiber cable 21. In the optical fiber protection section 29, for example, the unit optical fiber cable 21 is inserted through a flexible stainless steel pipe inserted into the cable entry port 24a, thereby suppressing breakage of the unit optical fiber cable 21 due to bending. In addition, the gap between the cable entry port 24a and the flexible stainless steel pipe is filled with a sealant (clay, putty, resin, etc.), and the gap between the flexible stainless steel pipe and the unit optical fiber cable 21 at the end of the flexible stainless steel pipe is also filled with the sealant, preventing concrete from entering the inside of the box body 24. Here, an appropriate sealant is used considering the concrete pressure at the location of the cable entry port 24a.

[0038] Next, an embodiment of the repair method for an optical fiber laying structure according to the present invention will be described. The optical fiber cable 11 of this optical fiber laying structure 10 may break, for example, during the assembly of reinforcing bars and formwork or during concrete pouring. Here, as shown in Figure 4(a), the optical fiber cable 11 is laid over unit blocks 3A, 3B, 3C, ... arranged in the longitudinal direction A, and a break point 31 occurs in the portion of the optical fiber cable 11 embedded in unit block 3B. In this case, it becomes impossible to measure the strain distribution and temperature distribution at a position farther away from the break point 31 from the measuring device 5 connected to unit block 3A.

[0039] Therefore, as a repair method for the optical fiber laying structure 10, the optical fiber cable 11 is connected by bypassing the unit block 3B, as shown in Figure 4(b). Specifically, the connection of the optical fiber cable 11 is released at the optical fiber connection section 25B between unit block 3A and unit block 3B, and at the optical fiber connection section 25C between unit block 3B and unit block 3C, and the unit optical fiber cable 21 of unit block 3B is disconnected. Here, if the optical fiber cables 11 are fusion spliced ​​together at the optical fiber connection sections 25B and 25C, it is sufficient to cut the optical fiber cable 11 near the optical fiber connection sections 25B and 25C. If the optical fiber cables 11 are connected together with connectors at the optical fiber connection sections 25B and 25C, it is sufficient to release the connector connections at the optical fiber connection sections 25B and 25C. Then, the connection between these optical fiber connection sections 25B and 25C is made via a newly prepared bypass optical fiber cable 12. These connections may be fusion spliced ​​or with connectors. According to the repaired optical fiber laying structure 10, the optical fiber cable 11 will be connected across unit blocks 3A, 3C, 3D, ... in a manner that bypasses the broken section 31 in unit block 3B.

[0040] Therefore, although it becomes impossible to measure the strain and temperature distribution in unit block 3B, the measurement of strain and temperature distribution in other unit blocks is maintained, and an extreme loss of the measurable range is avoided. In other words, a situation in which the strain and temperature distribution beyond the break point 31, as seen from the measuring device 5, becomes impossible to measure is avoided. Here, the optical fiber connection sections 25B and 25C belong to the external passage section 15, which is the section in which the optical fiber cable 11 passes outside the side wall 7, and are relatively easily accessible from inside the box culvert 1, so the above repair can be carried out relatively easily.

[0041] In the repaired optical fiber laying structure 10, the section connecting unit block 3A and unit block 3C by bypassing unit block 3B corresponds to the external passing section 15 in which the optical fiber cable 11 passes outside the side wall 7. If this external passing section 15 is referred to as "external passing section 15B", then external passing section 15B has skip connection sections (bypass optical fiber cable 12 and optical fiber connection sections 25B, 25C) that connect the ends of the unit optical fiber cables 21 of unit blocks 3A and 3C, which are arranged with unit block 3B in between them.

[0042] Furthermore, the bypass optical fiber cable 12, optical fiber connector 25B, and optical fiber connector 25C in the external passage section 15B may be attached to the side wall surface 7a with adhesive, or protected by being covered with a protective tube such as a flexible stainless steel tube or a predetermined box. Alternatively, the bypass optical fiber cable 12 may be integrally bonded to the side wall surface 7a in a manner that extends in the longitudinal direction A. In this case, the measuring device 5 can acquire the strain distribution and temperature distribution on the side wall surface 7a of the unit block 3B based on the scattered light of the bypass optical fiber cable 12. Alternatively, the side wall surface 7a of the unit block 3B may be cut to form a groove extending in the longitudinal direction A, and the bypass optical fiber cable 12 may be embedded in this groove and integrated with the side wall 7 of the unit block 3B. In this case, the measuring device 5 can acquire the strain distribution and temperature distribution near the side wall surface 7a of the unit block 3B with even higher accuracy based on the scattered light of the bypass optical fiber cable 12.

[0043] Next, the effects of the optical fiber laying structure 10 will be explained. The optical fiber laying structure 10 has intermittent external passage sections 15 in which the optical fiber cable 11 passes outside the side wall 7 of the box culvert 1. If a break 31 occurs in the optical fiber cable 11 in the internal passage section 13, the optical fiber laying structure 10 can be repaired relatively easily to bypass the break 31 by performing a predetermined treatment on the optical fiber cable 11 in the two external passage sections 15, 15 that sandwich the internal passage section 13. Therefore, with such an optical fiber laying structure 10, redundancy can be provided against the risk of a drastic reduction in the measurable range due to a break in the optical fiber cable 11. In other words, the risk due to a break in the optical fiber cable 11 is reduced with the optical fiber laying structure 10.

[0044] Furthermore, according to the optical fiber laying structure 10, a temperature change can be applied to the portion of the optical fiber cable 11 that is exposed to the outside of the side wall 7 in the external passage section 15, and the position of that portion within the measurement range can be determined by detecting the change in the measured value of the measuring device 5 at that time. In addition, a mechanism for applying a temperature change (for example, a heater) may be provided in the optical fiber cable 11 of a predetermined external passage section 15 for such position determination.

[0045] The present invention can be implemented in various forms, including the embodiments described above, by making various changes and improvements based on the knowledge of those skilled in the art. Furthermore, it is possible to construct modified versions of the embodiments by utilizing the technical matters described in the embodiments described above. The configurations of each embodiment may be used in appropriate combinations.

[0046] For example, the open section of the optical fiber extraction section 23 is not limited to the box body 24 (Figure 3) described above, but may include, for example, a handhole-shaped box body 26 as shown in Figure 5(a). The excess length of the unit optical fiber cable 21 can be stored inside the box body 26. If the open section poses a design problem, the box body 26 may be backfilled with concrete or the like after the end 27 of the unit optical fiber cable 21 has been extracted. In this case, it is preferable that the unit optical fiber cable 21 that has been extracted to the outside is protected by a switch box or cover. Furthermore, the excess length of the unit optical fiber cable 21 can be covered with a sheet-like material along the side wall surface 7a to minimize the protrusion of the protective material from the side wall surface 7a. In addition, the configuration of the optical fiber protection section 29 (Figure 3(b)) described above may be applied to the portion where the unit optical fiber cable 21 penetrates the wall of the box body 26.

[0047] Furthermore, the optical fiber extraction section 23 is not limited to a box-shaped section, and may be constructed as shown in Figure 5(b), for example. That is, as shown in Figure 5(b), the concrete formwork 33 of the unit block 3 is provided with a through-hole 35 for inserting the unit optical fiber cable 21, and a flexible stainless steel tube 39 is inserted through the through-hole 35 via a buffer material 37, and the unit optical fiber cable 21 is inserted into the flexible stainless steel tube 39. The flexible stainless steel tube 39 is installed around the unit optical fiber cable 21 over a range of about 10 cm inward from the concrete formwork 33 and about 1 m outward from the concrete formwork 33. When concrete is poured onto the concrete formwork 33 in this state and the concrete formwork 33 is removed, the optical fiber extraction section 23 is constructed. With such an optical fiber extraction section 23 including the flexible stainless steel tube 39, breakage due to bending of the unit optical fiber cable 21 during removal, for example, is suppressed. The flexible stainless steel tube 39 functions as an optical fiber protection section that protects the unit optical fiber cable 21 at the boundary between the internal passage section 13 and the external passage section 15.

[0048] Furthermore, although the above-described embodiment explained an example in which one optical fiber cable 11 is laid on the side wall 7 of the box culvert 1, multiple optical fiber cables 11 may be laid on the side wall 7, for example, as shown in Figure 6(a). In Figure 6(a), a total of two optical fiber cables 11 are laid, one on the upper part and one on the lower part of the side wall 7. Also, when multiple optical fiber cables 11 are laid on the side wall 7, one optical fiber exit section 23 may be shared by multiple optical fiber cables 11, for example, as shown in Figure 6(b).

[0049] Furthermore, although the above-described embodiment described an example in which the optical fiber cable 11 is laid in the longitudinal direction (direction A) of the box culvert 1 in the internal passage section 13, the invention is not limited to this, and the optical fiber cable 11 may extend in any direction in the internal passage section 13. For example, a single optical fiber cable 11 in the internal passage section 13 may have multiple portions extending in different directions from each other. For example, the optical fiber cable 11 in the internal passage section 13 may be laid so as to include a portion extending in the height direction (up and down direction). As a specific example, as shown in Figure 7, by arranging the optical fiber cable 11 in the internal passage section 13 in a meandering manner, both the longitudinal strain distribution and the height direction (up and down direction) strain distribution of the side wall 7 can be measured. In this case, the portion of the optical fiber cable 11 in the internal passage section 13 that extends in the up and down direction may be arranged along the main reinforcement of the side wall 7. [Explanation of Symbols]

[0050] 1...Box culvert (structure), 3,3A~3D...Unit block (unit structure), 10...Optical fiber laying structure, 11...Optical fiber cable (optical fiber), 12...Bypass optical fiber cable (skip connection section), 13...Internal passage section, 15...External passage section, 21...Unit optical fiber cable (unit optical fiber), 24,26...Box body (box opening section), 25...Optical fiber connection section, 25B,25C...Optical fiber connection section (skip connection section, disconnection section), 27...End section, 29...Optical fiber protection section, 31...Break point, 39...Flexible stainless steel tube (optical fiber protection section).

Claims

1. A fiber optic cable laying structure in which fiber optic cables are laid on the building structure, The optical fiber has multiple internal passage sections, which are sections through which it passes inside the body, An optical fiber laying structure comprising a plurality of external passing sections, which are sections between the internal passing sections and in which the optical fiber passes outside the structure.

2. The aforementioned frame includes a unit optical fiber that forms part of the optical fiber and has a plurality of unit frame sections connected in the laying direction of the optical fiber. The aforementioned unit optical fiber is It is embedded inside the unit structure at a position corresponding to the internal passage section, and both ends are pulled out to the outside of the unit structure from a position corresponding to the boundary between the internal passage section and the external passage section. At least a portion of the aforementioned external passage section is The optical fiber laying structure according to claim 1, further comprising an optical fiber connection portion for connecting the ends of the unit optical fibers of adjacent unit structural portions.

3. The other part of the aforementioned external passage section is, The optical fiber laying structure according to claim 2, further comprising a skip connection portion for connecting the ends of the unit optical fibers of the unit structural members arranged with other unit structural members sandwiched between them.

4. The optical fiber laying structure according to any one of claims 1 to 3, further comprising an optical fiber protection section that protects the optical fiber at the boundary between the internal passage section and the external passage section.

5. An optical fiber laying structure according to any one of claims 1 to 3, comprising a box-out section provided at the boundary between the internal passage section and the external passage section for drawing the optical fiber from the inside of the structure to the outside of the structure.

6. A method for repairing the optical fiber laying structure described in claim 2 when a break occurs in the optical fiber, In the two external passage sections that sandwich the aforementioned break point, the unit optical fiber including the break point is separated from the optical fiber. A method for repairing an optical fiber laying structure, comprising connecting the separated portions of the optical fibers, where the unit optical fibers have been separated, via a new bypass optical fiber.

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