Pc steel strand with optical fiber, strain measuring device, and method for manufacturing pc steel strand with optical fiber

Abstract

A PC steel strand with an optical fiber, having: a PC steel strand formed by twisting a plurality of PC steel wires; and an optical fiber fixed to a twist groove by a resin, wherein the twist groove is a groove provided between two adjacent PC steel wires on the outer surface of the PC steel strand, and a coefficient of variation of a distance between a common tangent line of the two adjacent PC steel wires forming the twist groove and a center of the optical fiber is 0.5 or less when measured in ten cross sections perpendicular to a length direction of the PC steel strand.

Description

Technical Field

[0001] This disclosure relates to PC steel strands with optical fibers, strain measuring devices, and methods for manufacturing PC steel strands with optical fibers.

[0002] This application claims priority based on Japanese Application No. 2021-134853, filed on August 20, 2021, and invokes the entire contents of the stated Japanese application. Background Technology

[0003] Patent Document 1 discloses a PC steel stranded wire, characterized by comprising: a PC steel wire assembly having a plurality of stranded PC steel wires; and an optical fiber component having an optical fiber and a resin filler, the optical fiber comprising an optical fiber wire and a coating covering the optical fiber wire, the filler surrounding the optical fiber, the optical fiber component being configured to extend between the adjacent PC steel wires along the adjacent PC steel wires, and in a cross section orthogonal to the length direction of the PC steel wire assembly, the optical fiber component being housed within a region enclosed by the respective surfaces of the adjacent PC steel wires and the common tangent of the adjacent PC steel wires.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-57231 Summary of the Invention

[0007] The disclosed PC steel stranded wire with optical fiber comprises: a PC steel stranded wire formed by stranding multiple PC steel wires; and an optical fiber fixed to a twisted groove by resin, wherein the twisted groove is a groove disposed between two adjacent PC steel wires on the outer surface of the PC steel stranded wire, and the coefficient of variation of the distance between the common tangent of the two adjacent PC steel wires constituting the twisted groove and the center of the optical fiber, measured in ten cross sections perpendicular to the length direction of the PC steel stranded wire, is 0.5 or less. Attached Figure Description

[0008] Figure 1 This is a perspective view of a PC steel stranded cable with optical fiber according to one of the schemes disclosed herein.

[0009] Figure 2 yes Figure 1 A cross-sectional view of a PC steel strand with optical fiber perpendicular to its length direction.

[0010] Figure 3 It is shown in magnification Figure 2 A diagram of the area surrounding the optical fiber.

[0011] Figure 4It is a cross-sectional view of a PC steel strand with optical fiber in the case of corrosion-inhibiting coating, at a plane perpendicular to the length direction.

[0012] Figure 5 This is an explanatory diagram of a scattered light measuring apparatus according to one embodiment of the present disclosure.

[0013] Figure 6 This is an explanatory diagram of a scattered light measuring apparatus according to one embodiment of the present disclosure.

[0014] Figure 7 This is an explanatory diagram of a manufacturing apparatus for PC steel stranded wire with optical fiber. Detailed Implementation

[0015] [The problem this disclosure aims to solve]

[0016] Concrete structures are characterized by weak tensile strength. Therefore, in order to pre-apply compressive force to concrete structures and control the tensile stress when the concrete structure is under load, thereby preventing cracks, tensioning materials such as PC steel strands are used.

[0017] Furthermore, as a tensioning material, for example, a PC steel strand with an optical fiber disclosed in Patent Document 1 can be used to measure the strain distribution of the PC steel strand along its length direction and evaluate the tension force introduced into the PC steel strand.

[0018] After applying uniform tension to the end of a conventional PC steel strand with optical fiber, when using optical fiber to measure the strain distribution, the measured values ​​may sometimes differ depending on the position along the length of the PC steel strand with optical fiber.

[0019] For PC steel stranded wires with optical fibers, depending on the installation location, there is sometimes a need to further improve the accuracy of strain measurement. Therefore, there is a need for a PC steel stranded wire with optical fibers that can suppress the differences in measurement values ​​caused by the position along the length direction of the PC steel stranded wire with optical fibers, and can perform precise strain measurement.

[0020] The purpose of this disclosure is to provide a PC steel stranded wire with optical fiber capable of precise strain measurement.

[0021] [The Effects of This Disclosure]

[0022] According to this disclosure, a PC steel stranded wire with optical fiber can be provided, which is capable of precise strain measurement.

[0023] [Description of embodiments of this disclosure]

[0024] First, embodiments of this disclosure are listed for illustration. In the following description, the same or corresponding elements are labeled with the same reference numerals, and they are not described in the same way repeatedly.

[0025] (1) One aspect of the present disclosure is a PC steel stranded wire with optical fiber, comprising: a PC steel stranded wire, which is formed by stranding multiple PC steel wires together; and an optical fiber, wherein the optical fiber is fixed to a twisted groove by resin, wherein the twisted groove is a groove disposed between two adjacent PC steel wires on the outer surface of the PC steel stranded wire, and the coefficient of variation of the distance between the common tangent of the two adjacent PC steel wires constituting the twisted groove and the center of the optical fiber, measured in ten cross sections perpendicular to the length direction of the PC steel stranded wire, is 0.5 or less.

[0026] By making the coefficient of variation of the fiber-embedded PC steel strand of one embodiment of this disclosure less than 0.5, it means that the unevenness of the distance between the common tangent of two adjacent PC steel wires constituting the twisted groove and the center of the optical fiber in the ten measured cross-sections is suppressed. That is, it means that the unevenness of the position of the optical fiber in the cross-section perpendicular to the length direction of the PC steel strand is suppressed. Therefore, when the strain distribution along the length direction of the fiber-embedded PC steel strand is measured using this fiber-embedded PC steel strand under uniform tension, the difference in the measured strain value caused by the position along this length direction can be suppressed, i.e., the amplitude of variation can be suppressed. Therefore, by using this fiber-embedded PC steel strand, precise strain measurement can be performed.

[0027] It should be noted that the coefficient of variation is a parameter that represents the degree of unevenness of the measured values. It is obtained by dividing the standard deviation of the measured values ​​by the average value of the measured values, and it is a dimensionless number.

[0028] (2) Alternatively, in a cross section perpendicular to the length direction of the PC steel strand, the optical fiber is located in an area enclosed by a straight line parallel to the common tangent and 0.1 mm further inward than the common tangent from the PC steel strand and the surfaces of two adjacent PC steel wires forming the twist groove.

[0029] By placing optical fibers in the aforementioned area, optical fibers can be configured in a manner similar to that of PC steel strands, enabling more precise measurement of the strain of PC steel strands.

[0030] (3) Alternatively, in a cross section perpendicular to the length direction of the PC steel strand, the outer surface of the optical fiber is covered by the resin.

[0031] By coating the outer surface of the optical fiber with resin, the fiber can be securely fixed to the PC steel strand, allowing the fiber to track the expansion and contraction of the PC steel strand with exceptional accuracy. Therefore, the strain state generated in the PC steel strand is reflected in the optical fiber with particularly high precision, enabling the measurement of the PC steel strand's strain using this fiber. Furthermore, coating the outer surface of the optical fiber with resin protects it, preventing damage.

[0032] (4) Alternatively, it may have two or more optical fibers.

[0033] In cases where a PC steel stranded cable with optical fiber has two or more optical fibers, even if one optical fiber is damaged during construction or due to years of deterioration, other optical fibers can be used for strain measurement.

[0034] Furthermore, while it is possible to use optical fibers to measure the strain and temperature of PC steel strands via scattered light, there are also cases where strain and temperature can be measured simultaneously, or where more than two optical fibers are required depending on the method of strain and temperature measurement. Therefore, to accommodate diverse measurement methods, PC steel strands with optical fibers preferably have two or more optical fibers.

[0035] (5) Alternatively, the elongation at break of the resin may be 3.5% or more.

[0036] According to JIS G 3536 (2014), the elongation at break of PC steel strand is 3.5% or more. Therefore, by ensuring that the elongation at break of the resin is also 3.5% or more, it means that even when force is applied to the fiber-reinforced PC steel strand until the PC steel strand and resin break, the resin can deform in accordance with the deformation of the PC steel strand. Thus, by ensuring that the elongation at break of the resin is 3.5% or more, when tension is applied to the fiber-reinforced PC steel strand, the resin easily deforms in accordance with the PC steel strand, improving the durability of the fiber-reinforced PC steel strand.

[0037] (6) Alternatively, it may have a corrosion-inhibiting coating covering the outer surface of the PC steel strand.

[0038] The PC steel strands with optical fibers have a corrosion-inhibiting coating, which protects them from external environmental influences and thus inhibits corrosion.

[0039] (7) One strain measuring device of the present disclosure has: a PC steel strand with optical fiber as described in any one of (1) to (6); and a scattered light measuring device connected to the PC steel strand with optical fiber.

[0040] According to one aspect of the strain measuring apparatus disclosed herein, a PC steel strand with optical fiber is used. Therefore, the variation amplitude of the measured strain value caused by the position along the length direction of the PC steel strand with optical fiber can be suppressed, and the strain can be measured with high precision.

[0041] According to one aspect of the strain measuring apparatus disclosed herein, strain and temperature can be measured using a PC steel strand with optical fiber. Therefore, even when the PC steel strand with optical fiber is buried, making external measurement difficult, strain and temperature can be easily measured. Furthermore, compared to cases where temperature is measured using a thermometer other than a PC steel strand with optical fiber, the strain measurement point is close to the temperature measurement point, thus enabling high-precision temperature-based strain correction.

[0042] Furthermore, the strain measuring device according to one embodiment of this disclosure uses scattered light to measure strain and temperature, which reduces the on-site measurement burden and makes the measurement easy to perform.

[0043] (8) Alternatively, the scattered light measuring device may have an interface for outputting measurement data.

[0044] The light scattering measuring device has an interface that allows it to output measured strain or temperature data, as well as corrected strain data, to an external source. For example, it can be configured to output the aforementioned strain data, etc., to an external information terminal via a network or similar means. With this configuration, strain data, etc., of distant concrete structures can be easily acquired.

[0045] (9) A method for manufacturing a PC steel stranded wire with optical fiber according to one aspect of the present disclosure includes: a configuration step in which an optical fiber is configured in a twisted groove of a PC steel stranded wire formed by multiple PC steel wires twisted together, wherein the twisted groove is a groove configured between two adjacent PC steel wires on the outer surface of the PC steel stranded wire; and a fixing step in which the optical fiber is fixed to the twisted groove with resin, wherein in the configuration step, a tension greater than 0 N and less than or equal to 20 N is applied to the optical fiber.

[0046] By pre-applying a tension greater than 0N to the optical fiber, the supplied optical fiber can be easily aligned, allowing it to be positioned at the desired location within the twisted groove of the PC steel strand. Therefore, uneven positioning of the optical fiber within the twisted groove in multiple cross-sections perpendicular to the length direction of the fiber-bearing PC steel strand can be suppressed. Consequently, when measuring the strain distribution along the length direction of the fiber-bearing PC steel strand under uniform tension, the variation in strain measurement values ​​caused by position along that length direction can be suppressed. In other words, precise strain measurement is possible using this fiber-bearing PC steel strand.

[0047] By applying a tension of less than or equal to 20N to the optical fiber, damage to the optical fiber can be prevented.

[0048] (10) Alternatively, after the configuration step and before the fixing step, there may be a resin supply step that supplies the resin to the twisting groove.

[0049] By supplying resin to the twisted groove after the configuration process and before the fixing process, resin can be supplied over a wide area of ​​the outer surface of the optical fiber. Therefore, the optical fiber can be securely fixed to the PC steel strand, and the optical fiber can follow the expansion and contraction of the PC steel strand with exceptional accuracy. As a result, the state of strain generated in the PC steel strand is reflected in the optical fiber with exceptional accuracy, allowing the optical fiber to be used to measure the strain of the PC steel strand with exceptionally high precision.

[0050] (11) Alternatively, the curing time of the resin may be less than 1 minute.

[0051] By using a resin with a curing time of less than 1 minute, the time from placing the optical fiber in the designated position in the twisted groove until the fiber is fixed by the resin can be shortened. Therefore, optical fiber positional shift during the period until the resin cures can be prevented. As a result, in multiple cross-sections perpendicular to the length direction of the fiber-bearing PC steel strand, the optical fiber can be precisely positioned in the desired position within the twisted groove, such as the initial position when placing the optical fiber in the twisted groove. Therefore, when measuring the strain distribution along the length direction of the fiber-bearing PC steel strand under uniform tension, the variation in the measured strain value caused by the position along that length direction can be particularly suppressed. That is, strain can be measured with particularly high precision.

[0052] (12) Alternatively, the resin may be an ultraviolet-cured resin, and the resin may be irradiated with ultraviolet light during the fixing process.

[0053] UV-curable resins can be cured simply by irradiating them with ultraviolet light. Therefore, compared to methods involving heating, it can suppress the impact on components other than the resin, such as optical fibers. Furthermore, compared to thermosetting resins and two-component mixed resins, UV-curable resins generally have shorter curing times, which can particularly prevent the optical fiber from shifting in the twisted groove during the period until the resin cures.

[0054] [Details of the embodiments of this disclosure]

[0055] Hereinafter, specific examples of an embodiment of the present disclosure (hereinafter referred to as "this embodiment") of a PC steel stranded wire with optical fiber, a strain measuring device, and a method for manufacturing a PC steel stranded wire with optical fiber will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is intended to include all modifications within the meaning and scope equivalent to the claims, as shown in the claims.

[0056] 1. PC steel stranded wire with optical fiber

[0057] use Figures 1-4 An example of the configuration of the PC steel stranded wire with optical fiber in this embodiment will be described.

[0058] Figure 1 This is a perspective view of the PC steel stranded wire with optical fiber in this embodiment. Figure 2 It shows Figure 1 Examples of the configuration of cross sections perpendicular to the length direction of PC steel stranded wires 10 and 11 with optical fibers are shown. Figure 3 yes Figure 2 A magnified view of a portion of the image. Figure 4 This is an illustration of a cross-section perpendicular to the length direction of a PC steel strand with optical fiber and a corrosion-inhibiting coating.

[0059] The PC steel stranded wire with optical fiber in this embodiment may include: a PC steel stranded wire, which is formed by stranding multiple PC steel wires together; and an optical fiber. Furthermore, the optical fiber is fixed to a twisted groove by resin, wherein the twisted groove is a groove disposed between two adjacent PC steel wires on the outer surface of the PC steel stranded wire.

[0060] It should be noted that PC in PC steel strand and PC steel wire refers to prestressed concrete.

[0061] First, the PC steel strand, optical fiber, and resin, which are components of the PC steel strand with optical fiber in this embodiment, will be described.

[0062] (1) Regarding the components of PC steel stranded wire with optical fiber

[0063] (1-1) PC steel strand

[0064] Figure 1 The illustrated PC steel stranded wire 10 with optical fiber has a PC steel stranded wire 11 formed by twisting together multiple PC steel wires 111, which are steel wires. When tension is introduced into the PC steel stranded wire 10 with optical fiber, each PC steel wire 111 bears the tension.

[0065] Figure 1The X-axis is the axis along the length direction of the PC steel strands 10 and 11 with optical fibers. Furthermore, the YZ plane, formed by the Y-axis and Z-axis orthogonal to the X-axis, is a cross-section perpendicular to the length direction of the PC steel strands 10 and 11 with optical fibers.

[0066] The number of PC steel wires 111 constituting the PC steel stranded cable 11 is not particularly limited. The number of PC steel wires 111 constituting the PC steel stranded cable 11 can be selected based on the required performance and usage of the PC steel stranded cable with optical fiber; examples include seven wires, nineteen wires, etc. When the number of PC steel wires 111 is seven, such as... Figure 1 , Figure 2 As shown, the structure of the PC steel strand 11 can be configured as a single-layer twisted structure consisting of six PC steel wires 111B as outer peripheral wires, spirally twisted around a PC steel wire 111A as a central wire. In this case, the PC steel wires 111B as outer peripheral wires are located at the outermost periphery of the PC steel strand 11. Figure 1 , Figure 2 The example shown is of using PC steel wires of the same outer diameter as PC steel wire 111A as the center wire and PC steel wire 111B as the outer circumferential wire, but it is not limited to this method. For example, the outer diameter of PC steel wire 111A as the center wire may be different from the outer diameter of PC steel wire 111B as the outer circumferential wire.

[0067] On the other hand, when there are nineteen PC steel wires, although the diagram is omitted, the structure of the PC steel strand can be set as a two-layer twisted structure, in which the PC steel wires serving as the inner and outer circumferential wires are spirally twisted together to a single PC steel wire serving as the center wire. Representatively, there are two types with different combinations of the number of inner and outer circumferential wires.

[0068] Specifically, there are types consisting of one central wire, nine inner circumferential wires, and nine outer circumferential wires, and types consisting of one central wire, six inner circumferential wires, and twelve outer circumferential wires. In the former type, the central wire and outer circumferential wires can be made of PC steel wires with approximately equal outer diameters, while the inner circumferential wires can be made of PC steel wires with an outer diameter smaller than that of the central wire.

[0069] In the latter type, the center wire and inner circumferential wire can be composed of PC steel wires with approximately equal outer diameters. The outer circumferential wire can be composed of alternating PC steel wires with an outer diameter approximately equal to that of the center wire and PC steel wires with a smaller outer diameter.

[0070] like Figure 2As shown, the PC steel strand 11 has a twisted groove 21, which is a recess formed between two adjacent PC steel wires 111B disposed on the outer surface 11A of the PC steel strand 11, i.e., a groove between the outer peripheral wires. Furthermore, the PC steel strand 11 has an internal void 22, which is a space surrounded by three adjacent PC steel wires 111. These twisted grooves 21 and internal voids 22 have a spiral shape centered on the central axis A, extending along the length direction of the PC steel strand 11.

[0071] like Figure 1 , Figure 2 As shown, when the PC steel strand 11 has a single twisted structure, that is, when the PC steel strand 11 has seven PC steel wires, the gap 22 is formed between the PC steel wire 111A, which is the center wire, and the two PC steel wires 111B, which are the outer peripheral wires.

[0072] When the PC steel strand has a two-layer twisted structure, that is, when the number of PC steel wires is, for example, nineteen, the gaps in the internal structure are formed between the center wire and two inner circumferential wires, between one inner circumferential wire and two outer circumferential wires, and between two inner circumferential wires and one outer circumferential wire.

[0073] (1-2) Optical fiber

[0074] As mentioned above, PC steel stranded wire with optical fiber can have optical fiber.

[0075] Optical fibers can preferably be those having a core and a cladding. Examples of materials for the core and cladding include plastics and quartz glass. Optical fibers can also be constructed using fiber optic cables, such as those with a primary coating around the cladding, a secondary coating around the core, a reinforcing material around the secondary coating, and an outer sheath covering the reinforcing material. Examples of materials for the primary coating include UV-cured resins. Examples of materials for the secondary coating include flame-retardant polyester elastomers. Examples of materials for the reinforcing material include glass fiber, carbon fiber, and aramid fiber. Examples of materials for the outer sheath include flame-retardant polyolefins such as flame-retardant polyethylene, flame-retardant cross-linked polyethylene, and heat-resistant vinyl.

[0076] The type of optical fiber in a PC stranded steel cable with optical fiber is not particularly limited. Preferably, the optical fiber in a PC stranded steel cable with optical fiber is selected from one or more of single-mode optical fiber, multimode optical fiber, and polarization-maintaining optical fiber.

[0077] By using the optical fiber inherent in PC steel stranded wire and utilizing scattered light, the strain and temperature of PC steel stranded wire can be measured. When measuring strain and temperature, Brillouin scattering, Rayleigh scattering, and Raman scattering are preferred as the scattered light source. Therefore, a suitable optical fiber can be selected based on the scattered light used and the required measurement accuracy.

[0078] The fiber-optic PC stranded wire of this embodiment may have only one optical fiber or two or more optical fibers. For example, the optical fibers of the fiber-optic PC stranded wire of this embodiment can be used to measure strain and temperature. Therefore, the fiber-optic PC stranded wire of this embodiment may also have, for example, an optical fiber for strain measurement and an optical fiber for temperature measurement, depending on the measurement application. As the optical fiber for strain measurement and the optical fiber for temperature measurement, appropriate types of optical fibers corresponding to the measurement conditions such as the scattered light used can be used.

[0079] The outer diameter of the optical fiber is not particularly limited. In the PC stranded wire with optical fiber in this embodiment, the optical fiber is disposed within a twisted groove. Therefore, it is preferable to select the outer diameter of the optical fiber in a manner that allows it to be accommodated within the twisted groove. For example, the outer diameter of the optical fiber is preferably 1.5 mm or less, and more preferably 1.0 mm or less.

[0080] By making the outer diameter of the optical fiber less than 1.5mm, the optical fiber can be easily accommodated in the twisted groove of the PC steel strand.

[0081] The lower limit of the outer diameter of the optical fiber is not particularly limited, but the outer diameter is preferably 0.235 mm or more, and more preferably 0.8 mm or more. During the manufacturing process of the PC steel stranded wire with optical fiber, and when the PC steel stranded wire with optical fiber is installed in a structure, heat and external forces are sometimes applied to the optical fiber; therefore, it is preferable that the optical fiber also has excellent durability. By making the outer diameter of the optical fiber 0.235 mm or more, durability can be improved.

[0082] It should be noted that the outer diameter of the aforementioned optical fiber refers to the outer diameter of the entire optical fiber, including the primary coating, secondary coating, and other coatings mentioned above.

[0083] Furthermore, the elongation at break of the optical fiber is preferably 3.5% or more.

[0084] The optical fiber is preferably capable of following the deformation of the PC steel strand. According to JIS G 3536 (2014), the elongation at break of the PC steel strand is 3.5% or more. Therefore, by ensuring that the elongation at break of the optical fiber is also 3.5% or more, it means that even if a force is applied to the PC steel strand with the optical fiber until the PC steel strand and the optical fiber break, the optical fiber can deform in accordance with the deformation of the PC steel strand. Therefore, by ensuring that the elongation at break of the optical fiber is 3.5% or more, when tension is introduced into the PC steel strand with the optical fiber, the optical fiber can easily deform in a way that matches the PC steel strand, thus improving the durability of the PC steel strand with the optical fiber. It should be noted that, in this specification, the elongation at break of the optical fiber and resin can be measured according to JIS G 3536 (2014) based on the conditions of the PC steel strand used in the PC steel strand with the optical fiber.

[0085] Specifically, for example, the elongation at break can be evaluated by performing a tensile test after the PC steel strand with optical fiber is manufactured. When performing a tensile test on the PC steel strand with optical fiber, if the elongation at break of the PC steel strand with optical fiber is 3.5% or more, and if the optical fiber and resin do not break, then these components can also be evaluated as having an elongation at break of 3.5% or more.

[0086] The tensile strength of the optical fiber is preferably above 100 MPa and below 1500 MPa, more preferably above 120 MPa and below 1300 MPa.

[0087] PC steel strands with optical fibers are used, for example, within concrete structures. Tensile force is introduced by pulling the ends of the PC steel strands with optical fibers, applying compressive force to the concrete structure. This controls the tensile stress in the concrete structure under load, thereby preventing cracks. When tension is introduced by pulling the PC steel strands with optical fibers, force is also applied to the optical fibers. Furthermore, if the tensile strength of the optical fiber is 100 MPa or higher, and normal tension is applied to the PC steel strands with optical fibers, fiber breakage can be prevented. However, it is not necessary to excessively increase the tensile strength of the optical fiber; therefore, the tensile strength of the optical fiber is preferably 1500 MPa or less.

[0088] It should be noted that, in this specification, the tensile strength of the optical fiber and resin is calculated as follows: the strength value measured using a tensile testing machine at a tensile speed of 5 mm / min and a support interval of 150 mm is divided by the cross-sectional area of ​​the specimen used for evaluation.

[0089] (1-3) resin

[0090] In the PC steel stranded wire 10 with optical fiber in this embodiment, the optical fiber 12 is fixed to the twisted groove 21 of the PC steel stranded wire 11 by resin 13.

[0091] The inventors of this invention investigated the reasons for differences in the measured strain values ​​caused by the position of the optical fiber in the PC steel strand along its length direction after a uniform tension force was applied to it and the strain distribution was measured using the optical fiber. As a result, it was discovered that the uneven position of the optical fiber in the twisted groove in multiple cross-sections perpendicular to the length direction of the PC steel strand is the cause of these differences in strain measurements.

[0092] In the past, for example, an optical fiber component was made by placing the optical fiber in resin or the like, the optical fiber component was placed in the twisted groove of a PC steel strand, and fixed by an adhesive or the like, thereby producing a PC steel strand with optical fiber.

[0093] However, it is difficult to perfectly match the shape of the fiber optic component with the shape of the twisted groove and maintain that shape until the fiber optic component is fixed in the twisted groove. Therefore, gaps sometimes occur between the fiber optic component and the twisted groove, resulting in instability in the position of the fiber optic component and the optical fiber disposed inside the fiber optic component within the twisted groove.

[0094] Furthermore, since the optical fiber component includes optical fibers and resin, its rigidity is higher compared to the case with only optical fibers. Therefore, it is difficult to arrange and fix the optical fiber component in the twisted groove of the PC steel strand. Considering the difficulty of assembling the optical fiber component into the PC steel strand as described above, the position of the optical fiber component and the optical fiber disposed inside the optical fiber component within the twisted groove is sometimes unstable.

[0095] Therefore, in the PC steel stranded cable with optical fiber in this embodiment, it is preferable to fix the optical fiber to the twist groove of the PC steel stranded cable with resin. That is, in the PC steel stranded cable with optical fiber in this embodiment, it is preferable to directly place the optical fiber in the twist groove and fix it with resin, rather than pre-coating the optical fiber with resin or the like.

[0096] The resin 13 is not particularly limited, but is preferably a resin that cures in a short time so that the position of the optical fiber 12 does not shift after it is positioned in the desired location in the twisted groove 21 of the PC steel strand 11.

[0097] Specifically, for example, the curing time of resin 13 is preferably less than 1 minute, and more preferably less than 50 seconds.

[0098] By using a resin with a curing time of less than 1 minute as resin 13, the time from placing the optical fiber 12 in the predetermined position of the twisted groove 21 until the optical fiber 12 is fixed by the resin can be shortened. Therefore, it is possible to prevent the position of the optical fiber 12 from shifting during the period until the resin 13 cures. As a result, in multiple cross-sections of the PC steel strand with optical fiber perpendicular to the length direction, the optical fiber 12 can be precisely positioned in the desired position within the twisted groove 21, such as the initial position when the optical fiber 12 is placed in the twisted groove 21.

[0099] The lower limit of the curing time of resin 13 is not particularly limited, but the curing time is preferably 0.1 seconds or more, more preferably 0.3 seconds or more. By making the curing time 0.1 seconds or more, for example, clogging of the nozzle or other parts supplying resin 13 can be prevented.

[0100] The curing time mentioned above refers to the time from the start of the curing process under predetermined curing conditions, depending on the type of resin, until the resin is cured. The predetermined curing conditions, depending on the type of resin, refer to heating conditions such as heating temperature for thermosetting resins, and ultraviolet irradiation conditions for ultraviolet-curing resins. Furthermore, resin curing refers to a state where the resin does not adhere to the fingertip when the surface of the resin test piece is lightly touched.

[0101] Resin 13 is not particularly limited; for example, thermosetting resins, UV-curing resins, and two-component mixed resins can be used. Two-component mixed resins refer to resins that begin curing by mixing two liquids.

[0102] In particular, a UV-curable resin is preferably used as resin 13. This is because UV-curable resins can be cured simply by irradiation with ultraviolet light, thus suppressing the impact on components other than the resin 13, such as optical fibers, compared to methods involving heating. Furthermore, UV-curable resins generally have shorter curing times compared to thermosetting resins and two-component mixed resins, which can particularly prevent the optical fiber 12 in the twisted groove 21 from shifting position during the period until the resin 13 has cured.

[0103] Furthermore, the elongation at break of the resin is preferably 3.5% or more.

[0104] The resin is preferably capable of following the deformation of the PC steel strand. According to JIS G 3536 (2014), the elongation at break of the PC steel strand is 3.5% or more. Therefore, by ensuring that the elongation at break of the resin is also 3.5% or more, it means that even if a force is applied to the PC steel strand with optical fiber until the PC steel strand and resin break, the resin can deform in accordance with the deformation of the PC steel strand. Therefore, by ensuring that the elongation at break of the resin is 3.5% or more, when tension is introduced into the PC steel strand with optical fiber, the resin can easily deform in a way that matches the PC steel strand, thereby improving the durability of the PC steel strand with optical fiber.

[0105] The tensile strength of the resin is preferably 100 MPa or more and 300 MPa or less, more preferably 120 MPa or more and 250 MPa or less.

[0106] When used, PC steel strands with optical fibers are installed, for example, within concrete structures. Tensile force is introduced by pulling the ends of the PC steel strands with optical fibers, applying compressive force to the concrete structure. This controls the tensile stress in the concrete structure under load, thereby preventing cracks. When tension is introduced by pulling the PC steel strands with optical fibers, force is also applied to the resin that secures the optical fibers. Furthermore, if the tensile strength of the resin is 100 MPa or higher, and normal tension is applied to the PC steel strands with optical fibers, the resin will not break, allowing the optical fibers to remain securely fixed; therefore, this is preferable. However, it is not necessary to excessively increase the tensile strength of the resin; therefore, a tensile strength of 300 MPa or less is preferably preferred.

[0107] (2) Regarding the structure of PC steel stranded wire with optical fiber

[0108] Next, an example of a preferred structure for a PC steel stranded wire with optical fiber will be described.

[0109] like Figure 2 As shown, in the PC steel strand 10 with optical fiber, in the section perpendicular to the length direction of the PC steel strand 11, that is, in the section perpendicular to the central axis A, the optical fiber 12 can be arranged in the twisted groove 21 of the PC steel strand 11 and fixed by the resin 13 mentioned above.

[0110] By placing the optical fiber 12 in the twisted groove 21 of the PC steel strand 11, the optical fiber 12 can easily follow the expansion and contraction of the PC steel strand 11. Therefore, the state of strain generated in the PC steel strand 11 is reflected in the optical fiber 12, and the optical fiber 12 can be used to measure the strain of the PC steel strand 11 with high precision.

[0111] When fixing the optical fiber 12 with resin 13, the amount of resin 13 is not particularly limited; for example, it can be configured to fix the optical fiber 12 to the PC steel strand 11 to a certain extent. However, it is preferable that, Figure 2 As shown, in a cross-section perpendicular to the length direction of the PC steel strand 11, the outer surface of the optical fiber 12 is covered with resin 13.

[0112] By covering the outer surface of the optical fiber 12 with resin 13, the optical fiber 12 can be firmly fixed to the PC steel strand 11, allowing the optical fiber 12 to follow the expansion and contraction of the PC steel strand 11 with particular accuracy. Therefore, the strain state generated in the PC steel strand 11 is reflected in the optical fiber 12 with particular accuracy, enabling the optical fiber 12 to be used for highly precise measurement of the strain of the PC steel strand 11. Furthermore, covering the outer surface of the optical fiber 12 with resin 13 protects the optical fiber 12, thereby preventing damage to it.

[0113] (2-1) The coefficient of variation of the distance between the common tangent of the two adjacent PC steel wires forming the twisted groove and the center of the optical fiber

[0114] Regarding the PC steel stranded wire with optical fiber in this embodiment, the coefficient of variation of the distance between the common tangent of two adjacent PC steel wires forming the twisted groove and the center of the optical fiber, measured in ten cross-sections perpendicular to the length direction of the PC steel stranded wire, is preferably 0.5 or less. More preferably, the coefficient of variation is 0.4 or less.

[0115] As described above, the inventors of this invention investigated the cause of the following situation: when the strain distribution is measured along the length direction of a PC steel strand with optical fibers to which uniform tension has been introduced, differences appear in the measured strain values ​​depending on their position along this length direction. As a result, it was discovered that the uneven position of the optical fibers arranged in the twisted grooves in multiple cross-sections perpendicular to the length direction of the PC steel strand with optical fibers is the cause of the aforementioned differences in measured values, i.e., the cause of the variation amplitude.

[0116] Here, in Figure 3 shown in the Figure 2 A magnified view of the area surrounding fiber optic cable 12. Figure 3 and Figure 2 Similarly, this is a cross-sectional view of the PC steel strand 10 and PC steel strand 11 with optical fiber at a plane perpendicular to the length direction.

[0117] like Figure 3As shown, in this embodiment, the distance between the common tangent 311 of two adjacent PC steel wires 111B constituting the twisted groove 21 of the PC steel strand 11 and the center 121 of the optical fiber 12 in the fiber-embedded PC steel strand 10 is defined as distance L12. Furthermore, by ensuring that the coefficient of variation of the distance L12 measured in ten cross-sections perpendicular to the length direction of the PC steel strand 11 is 0.5 or less, it means that the non-uniformity of distance L12 among the ten measured cross-sections is suppressed. That is, it means that the non-uniformity of the position of the optical fiber 12 in the cross-sections perpendicular to the length direction of the PC steel strand is suppressed. Therefore, when using this fiber-embedded PC steel strand with uniform tension, if the strain distribution is measured along the length direction of the fiber-embedded PC steel strand, the difference in the measured strain value caused by the position along this length direction can be suppressed, i.e., the variation amplitude can be suppressed. Therefore, by using this fiber-embedded PC steel strand, precise strain measurement can be performed.

[0118] like Figure 3 As shown, the common tangent 311 is a common tangent drawn in the above cross section in such a way that it is at two points of tangency with the two PC steel wires 111B and that the two points of tangency are located on the exposed surface of the PC steel strand 11.

[0119] It should be noted that the coefficient of variation is a parameter that represents the degree of unevenness of the measured values. It is obtained by dividing the standard deviation of the measured values ​​by the average value of the measured values, and it is a dimensionless number.

[0120] The method for selecting the ten cross-sections used to determine the aforementioned distance L12 is not particularly limited, but it is preferable to select the cross-sections such that the distances between the cross-sections being evaluated are equal. Although it also depends on the length of the test piece, it is preferable to select the cross-sections being evaluated in a manner, for example, such that the distance between adjacent cross-sections is 50 cm.

[0121] The lower limit of the aforementioned coefficient of variation is not particularly limited, but the coefficient of variation is preferably 0.05 or higher, and more preferably 0.1 or higher. By making the coefficient of variation 0.05 or higher, the time required for optical fiber alignment can be suppressed when manufacturing PC stranded wire with optical fiber, thereby improving productivity.

[0122] In the case where the PC steel stranded wire with optical fiber in this embodiment has multiple optical fibers, it is preferable that at least one optical fiber satisfies the above-mentioned coefficient of variation, and more preferably that all optical fibers satisfy the above-mentioned coefficient of variation.

[0123] (2-2) Regarding the position of the optical fiber in the twisted groove

[0124] By configuring the optical fiber in a manner that satisfies the aforementioned coefficient of variation, unevenness in the fiber's position along the length of the fiber-bearing PC steel strand can be suppressed. As a result, strain can be measured with high precision using this fiber-bearing PC steel strand.

[0125] However, from the viewpoint of ensuring that the optical fiber follows the expansion and contraction of the PC steel strand, thereby accurately reflecting the state of strain generated in the PC steel strand to the optical fiber, it is preferable that the optical fiber is entirely housed within the twisted groove of the PC steel strand. Particularly more preferably, the optical fiber is positioned near the bottom of the twisted groove of the PC steel strand.

[0126] For example, such as Figure 3 As shown, in the cross-section of the PC steel stranded wire 10 with optical fiber perpendicular to the length direction of the PC steel stranded wire 11, a straight line parallel to the common tangent 311 and 0.1 mm further inward than the common tangent 311 towards the inside of the PC steel stranded wire 11 is designated as straight line 312. Figure 3 As shown, straight line 312 is positioned closer to the center A1 of the PC steel strand 11 than the common tangent 311. Center A1 is the center of the circumcircle C1 of the PC steel strand 11 in a section perpendicular to the length direction of the PC steel strand 11 (refer to...). Figure 2 ).also, Figure 3 The distance L312 between the common tangent 311 and the straight line 312 is 0.1 mm.

[0127] In this case, it is preferable that the optical fiber 12 is located within the region 33 enclosed by the aforementioned straight line 312 and the surfaces 32 of the two adjacent PC steel wires 111B constituting the twisted groove 21. It should be noted that "the optical fiber 12 is located within the region 33" means that, in the aforementioned cross-section being evaluated, the entire optical fiber 12 is located within the region 33.

[0128] The evaluation of the position of the optical fiber 12 in the aforementioned twisted groove 21 is preferably performed in multiple cross sections, for example, preferably in ten cross sections. The ten cross sections are preferably the same ten cross sections used when determining the coefficient of variation of the distance L12 between the common tangent 311 of the two adjacent PC steel wires 111B constituting the twisted groove 21 and the center 121 of the optical fiber 12.

[0129] Furthermore, it is preferable that the optical fiber 12 is located within region 33 in eight or more of the ten cross-sections evaluated, and more preferably in nine or more cross-sections. In particular, it is even more preferable that the optical fiber 12 is located within region 33 in all the cross-sections evaluated.

[0130] By placing the optical fiber 12 within the aforementioned region 33, the optical fiber 12 can be configured in a manner similar to that of the PC steel strand 11, enabling more precise measurement of the strain of the PC steel strand.

[0131] In the case where the PC steel stranded wire with optical fiber in this embodiment has multiple optical fibers, it is preferable that at least one optical fiber is arranged in the above-mentioned region 33, and more preferably all optical fibers are arranged in the above-mentioned region 33.

[0132] (2-3) Regarding the number and configuration of optical fibers

[0133] The number of optical fibers in the PC stranded steel cable 10 with optical fibers in this embodiment is not particularly limited; it may have only one or more optical fibers. However, the PC stranded steel cable 10 with optical fibers in this embodiment preferably has two or more optical fibers.

[0134] This is because: when a PC steel stranded cable with optical fiber has two or more optical fibers, even if one optical fiber is damaged during construction or due to years of deterioration, other optical fibers can still be used for strain measurement.

[0135] Furthermore, while it is possible to use optical fibers to measure the strain and temperature of PC steel strands via scattered light, there are also cases where strain and temperature can be measured simultaneously, or where more than two optical fibers are required depending on the method of strain and temperature measurement. Therefore, to accommodate diverse measurement methods, PC steel strands with optical fibers preferably have two or more optical fibers.

[0136] use Figure 2 An example of a configuration where the PC stranded wire with optical fibers has two or more optical fibers will be described. For example, the PC stranded wire 10 with optical fibers preferably has a pair of optical fibers 12A and 12B at a point-symmetric position with respect to the center A1 of the circumscribed circle C1 of the PC stranded wire 11 in a cross-section perpendicular to the length direction of the PC stranded wire 11. That is, for example, the PC stranded wire 10 with optical fibers preferably has a pair of optical fibers 12A and 12B at both ends of the diameter of the circumscribed circle C1 of the PC stranded wire 11. Specifically, the optical fibers 12A and 12B can be arranged along twisted grooves 21A and 21B, which are point-symmetric positions with respect to the center A1 of the circumscribed circle C1 of the PC stranded wire 11.

[0137] By arranging a pair of optical fibers 12A and 12B at a point-symmetric position with the center A1 of the circumscribed circle C1 of the PC steel strand 11 as the symmetric point, as described above, the optical fibers can be dispersedly arranged within the PC steel strand 10 containing the optical fibers. Therefore, for example, even if optical fiber 12A is damaged, damage to the dispersedly arranged optical fiber 12B can be suppressed.

[0138] It should be noted that when a PC steel stranded cable with optical fiber has multiple optical fibers, the configuration of the optical fibers is not limited to the above method. For example, multiple optical fibers can also be configured in the same twisted groove.

[0139] (3) Regarding corrosion-inhibiting coatings

[0140] The PC steel strand with optical fiber in this embodiment may also have a corrosion-inhibiting coating covering the outer surface of the PC steel strand.

[0141] Figure 4 A cross-sectional view of the PC steel strand 40 with corrosion-inhibiting coating and fiber optic cable, perpendicular to the longitudinal direction of the PC steel strand 11, is shown. It should be noted that the PC steel strand 40 with fiber optic cable can be configured to be the same as the previously described PC steel strand with fiber optic cable, except that it has the corrosion-inhibiting coating 41 and the outer coating 42 described below.

[0142] The fiber-optic PC steel strand 40 with corrosion-inhibiting coating can have a corrosion-inhibiting coating 41 covering the outer surface 11A of the PC steel strand 11.

[0143] The PC steel strand 40 with optical fiber has a corrosion-inhibiting coating 41, which protects the PC steel strand 11 from the influence of the external environment and thus inhibits the corrosion of the PC steel strand 11. The outer surface 41A of the corrosion-inhibiting coating 41 may, for example, have a shape along the outer periphery of the PC steel strand 11, but is not limited to this manner.

[0144] The material (material) of the corrosion-inhibiting coating 41 is not particularly limited; for example, resins or greases with excellent corrosion resistance can be preferred. Examples of such resins include epoxy resin and polyethylene resin. High-density polyethylene resin is particularly preferred as the polyethylene resin. High-density polyethylene resin refers to a material with a density of 0.942 g / cm³. 3 The above is polyethylene resin. The density of the material was determined according to JIS K 6922 (2018).

[0145] It should be noted that a corrosion-inhibiting coating may also be provided in the internal voids 22. When a corrosion-inhibiting coating is provided in the internal voids 22, grease is preferably used as the material for the corrosion-inhibiting coating. The grease may contain, for example, petroleum-based hydrocarbons, thickeners, lubricating oil additives, etc. The grease may also be used as described above to cover the corrosion-inhibiting coating 41 on the outer surface 11A of the PC steel strand 11.

[0146] The PC steel stranded wire 40 with optical fiber can also have an outer coating 42 that further covers the outer surface 41A of the corrosion-inhibiting coating 41. It should be noted that the corrosion-inhibiting coating 41 and the outer coating 42 can also be formed from the same material, but it is preferable to use different materials. This is because the outer coating 42 can primarily function to prevent degradation caused by ultraviolet radiation, but if the corrosion-inhibiting coating 41 is also formed using only the material of the outer coating 42, the cost would likely increase.

[0147] The material (material) covering the outer layer 42 is not particularly limited; for example, polyethylene resin can be listed. High-density polyethylene resin is particularly preferred as the polyethylene resin.

[0148] 2. Strain measurement methods and strain measurement devices

[0149] An example of the configuration of the strain measurement method and strain measurement device of this embodiment will be described.

[0150] (1) Strain Measurement Method

[0151] An example of the configuration of the strain measurement method of this embodiment will be described.

[0152] The strain measurement method of this embodiment is a strain measurement method that uses the fiber-optic PC steel strand disclosed in this invention to measure the strain of the PC steel strand, and may include the following steps.

[0153] Strain measurement procedure: The strain of the PC steel strand is measured by using the optical fiber of the PC steel strand with optical fiber to scatter light.

[0154] Furthermore, the strain measurement method of this embodiment can also use optical fibers to measure temperature and correct the strain measured in the strain measurement process described above.

[0155] In this case, the following steps may also be included.

[0156] Temperature measurement procedure: The temperature is measured by scattering light using the optical fiber in the PC steel stranded wire with optical fiber.

[0157] Calibration process: The temperature measured in the temperature measurement process is used to correct the strain of the PC steel strand measured in the strain measurement process.

[0158] Each process step is explained.

[0159] (Strain measurement procedure)

[0160] In the strain measurement process, the optical fiber of the PC steel stranded wire with optical fiber disclosed herein can be used to measure the strain. It should be noted that in the strain measurement process, the strain at any position along the length direction of the optical fiber and the strain distribution along the length direction of the optical fiber can be measured.

[0161] The scattered light used in the strain measurement process is not particularly limited; for example, one or more of the following can be used: Brillouin scattering, Rayleigh scattering, and Raman scattering.

[0162] The method of strain measurement is not particularly limited. Examples include BOCDA (Brillouin Optical Correlation Domain Analysis), BOTDR (Brillouin Optical Time Domain Reflectometry), FBG (Fiber Bragg Grating), BOTDA (Brillouin Optical Time Domain Analysis), and BOCDR (Brillouin Optical Correlation Domain Reflectometry).

[0163] The number of optical fibers in the PC stranded steel wire with optical fibers used for measurement can be selected according to the measurement method, etc. For example, it is preferable that when the measurement method is set to BOCDA or BOTDA, the number of optical fibers is set to an even number of two or more, and when the measurement method is set to BOTDR, FBG, or BOCDR, the number of optical fibers is set to one or more.

[0164] Then, after connecting the scattered light measuring device corresponding to the measurement method to the optical fiber of the PC steel strand with optical fiber, strain measurement can be performed at any time.

[0165] (Temperature measurement process)

[0166] In the temperature measurement process, the optical fiber of the PC steel stranded wire with optical fiber of this disclosure can be used to measure the temperature. It should be noted that in the temperature measurement process, the temperature at any location along the length of the optical fiber, and the temperature distribution along the length of the optical fiber, can be measured. However, as described below, the temperature measured in the temperature measurement process is used to correct the strain measured in the strain measurement process; therefore, it is preferable to measure the temperature and temperature distribution at a location corresponding to the location where the strain and strain distribution were measured in the strain measurement process.

[0167] The scattered light used in the temperature measurement process is not particularly limited; for example, one or more of the following can be used: Brillouin scattering, Rayleigh scattering, and Raman scattering.

[0168] The method of temperature measurement is not particularly limited; for example, BOCDA, BOTDR, FBG, BOTDA, BOCDR, and ROTDR (Raman Optical Time Domain Reflectometer) can be listed.

[0169] The number of optical fibers in the PC steel stranded wire with optical fibers used for measurement can be selected according to the measurement method, etc. For example, it is preferable that when the measurement method is set to BOCDA or BOTDA, the number of optical fibers is set to an even number of two or more, and when the measurement method is set to BOTDR, FBG, BOCDR, or ROTDR, the number of optical fibers is set to one or more.

[0170] Then, after connecting the scattered light measuring device corresponding to the measurement method to the optical fiber of the PC steel stranded wire with optical fiber, temperature measurement can be performed at any time interval.

[0171] It should be noted that the scattered light is not only affected by the strain generated in the optical fiber corresponding to the strain of the PC steel strand, but is also sometimes affected by the temperature around the optical fiber. Therefore, it is preferable to use different types of scattered light in the strain measurement process and the temperature measurement process.

[0172] For example, preferably, in the strain measurement process, optical fiber is used to measure strain via Brillouin scattering and Rayleigh scattering, and in the temperature measurement process, optical fiber is used to measure temperature via Raman scattering. By using different scattered light in the strain measurement and temperature measurement processes, strain and temperature can be measured with high precision respectively.

[0173] When performing strain measurement and temperature measurement processes, the fiber-optic PC stranded wire disclosed herein can be used, but the fiber-optic PC stranded wire preferably has multiple optical fibers. For example, the fiber-optic PC stranded wire preferably includes optical fibers for strain measurement and optical fibers for temperature measurement as the aforementioned optical fibers.

[0174] This is because by using fiber-optic PC steel stranded wire with fiber optic cables for strain measurement and temperature measurement, strain and temperature can be measured simultaneously, which can improve measurement accuracy and shorten the measurement time.

[0175] Furthermore, the optical fiber used for strain measurement and the optical fiber used for temperature measurement are preferably selected from one or more optical fibers selected from single-mode optical fiber, multimode optical fiber and polarization-maintaining optical fiber, respectively.

[0176] In particular, the optical fibers for strain measurement and temperature measurement are preferably selected from those suitable for the scattered light used in the strain measurement process and the temperature measurement process, respectively.

[0177] For example, when using Brillouin scattering or Rayleigh scattering, single-mode fiber is preferred, while when using Raman scattering, multimode fiber is preferred. This is because single-mode fiber produces particularly sharp peaks when used for measurements with Brillouin or Rayleigh scattering. Furthermore, multimode fiber produces particularly high peak intensities when used for measurements with Raman scattering.

[0178] As described above, for example, in the strain measurement process, Brillouin scattering light or Rayleigh scattering light can be preferably used, therefore it is preferable to use a single-mode fiber for strain measurement. Furthermore, in the temperature measurement process, Raman scattering light can be preferably used, therefore it is preferable to use a multimode fiber for temperature measurement.

[0179] By using the appropriate type of optical fiber according to the scattered light used in each measurement process, the measurement accuracy can be significantly improved.

[0180] (Correction process)

[0181] In the calibration process, the temperature measured in the temperature measurement process can be used to calibrate the strain measured in the strain measurement process.

[0182] In the correction process, the corrected strain can be calculated, for example, according to the following formula (1).

[0183] (Corrected strain (%)) = (Strain (%) measured in the strain measurement process) - (Temperature (°C) measured in the temperature measurement process) × (Temperature coefficient (%) / °C) ... (1)

[0184] It should be noted that the temperature change from the reference temperature can also be used to replace "the temperature measured in the temperature measurement process" in the above formula (1).

[0185] The temperature coefficient can be calculated in advance, for example, using the same fiber-optic PC steel strand used for the measurement, based on the known relationship between temperature and known strain.

[0186] By implementing temperature measurement and calibration processes in addition to strain measurement, the measured strain and strain distribution can be corrected using temperature. Therefore, by implementing temperature measurement and calibration processes, strain can be measured with particularly high precision.

[0187] According to the strain measurement method of this embodiment, the PC steel stranded wire with optical fiber disclosed herein is used, thus, errors can be suppressed and strain can be measured with high precision.

[0188] Furthermore, according to the strain measurement method of this embodiment, strain and temperature can be measured using a PC steel strand with optical fiber. Therefore, even when the PC steel strand with optical fiber is buried and thus difficult to measure from the outside, strain and temperature can be easily measured. Moreover, compared to cases where temperature is measured using a thermometer other than a PC steel strand with optical fiber, the strain measurement point is close to the temperature measurement point, thus enabling high-precision temperature-based strain correction and high-precision strain measurement.

[0189] Furthermore, the strain measurement method according to this embodiment uses scattered light to measure strain and temperature, which reduces the on-site measurement burden and makes the measurement easy to perform.

[0190] (2) Strain measuring device

[0191] Next, an example of the configuration of a strain measuring device that can be preferably used in the above strain measuring method will be described.

[0192] The strain measuring device of this embodiment may have the fiber-optic PC steel strand disclosed herein and a scattered light measuring device connected to the fiber-optic PC steel strand.

[0193] use Figure 5 , Figure 6 A specific configuration example of the scattered light measuring device will be described. It should be noted that, in order to illustrate the connection method with the PC stranded steel cable with optical fiber, in... Figure 5 , Figure 6 The image also shows PC steel strands with optical fibers, configured as strain measurement devices 500 and 600.

[0194] Figure 5 The scattered light measuring device 50 shown is a type of scattered light measuring device that inputs and outputs laser light from both ends of an optical fiber. For example, it can be used when performing measurements via BOCDA or BOTDA.

[0195] Figure 6 The scattered light measuring device 60 shown is a measuring device that inputs and outputs laser light from one end of an optical fiber. For example, it can be used when performing measurements using a BOTDR, FBG, BOCDR, or ROTDR.

[0196] The scattered light measuring devices 50 and 60 include: an optical signal transmitting unit 501 for transmitting optical signals; and an optical signal receiving unit 502 for receiving optical signals from the optical fiber. Furthermore, the scattered light measuring devices 50 and 60 include an analysis unit 503 that analyzes the optical signals received by the optical signal receiving unit 502 and obtains information selected from strain and temperature of the optical fiber. If necessary, the scattered light measuring devices 50 and 60 may also include a display unit 504 that displays the information obtained by the analysis unit 503.

[0197] The optical signal transmitting unit 501 and the optical signal receiving unit 502 can be configured as an integrated measuring device, for example. The analysis unit 503 is, for example, a computing device such as a computer, and the display unit 504 is, for example, a display monitor that displays the calculation results obtained by the computing device. Alternatively, a personal computer or the like, which integrates the analysis unit 503 and the display unit 504, can also be used.

[0198] Regarding the optical fibers 511 and 512 of the PC steel stranded cable 51 with optical fibers connected to the scattered light measuring device 50, the first ends 511A and 512A of each optical fiber are led out from the first end 51A of the PC steel stranded cable with optical fibers. Furthermore, these first ends 511A and 512A are connected to each other. In addition, regarding the optical fibers 511 and 512 of the PC steel stranded cable 51 with optical fibers, the second ends 511B and 512B of each optical fiber are led out from the second end 51B of the PC steel stranded cable 51 with optical fibers and connected to the scattered light measuring device 50.

[0199] Furthermore, regarding the optical fiber 521 of the PC steel stranded cable 52 with optical fiber connected to the scattered light measuring device 60, a first end 521A of the optical fiber 521 is disposed at the first end 52A of the PC steel stranded cable 52 with optical fiber. And, a second end 521B of the optical fiber 521 of the PC steel stranded cable 52 with optical fiber is led out from the second end 52B of the PC steel stranded cable 52 with optical fiber and connected to the scattered light measuring device 60.

[0200] In the scattered light measuring devices 50 and 60, the optical signal transmitting unit 501, the optical signal receiving unit 502, and the optical fibers 511, 512, and 521 are appropriately connected via the optical splitter 506, the coupler 507, etc.

[0201] It should be noted that the strain measuring device of this embodiment may have a scattered light measuring device corresponding to the measurement method used when using scattered light to measure strain and temperature, or it may have both a scattered light measuring device 50 and a scattered light measuring device 60.

[0202] The PC steel stranded wire with optical fiber used in the above-described strain measurement method can also have both a strain measurement optical fiber and a temperature measurement optical fiber. Therefore, the strain measurement device of this embodiment can, for example, have a scattered light measurement device connected to the strain measurement optical fiber and a scattered light measurement device connected to the temperature measurement optical fiber. Furthermore, the strain measurement device of this embodiment can, for example, be configured to have a scattered light measurement device, and the connections of the optical fibers, etc., within or connected to the scattered light measurement device can be changed depending on whether the strain or temperature is being measured.

[0203] Furthermore, in the calibration step of the strain measurement method described above, the temperature measured in the temperature measurement step can be used to correct the strain measured in the strain measurement step. Therefore, the scattered light measuring devices 50 and 60 may also have a calculation unit 505 for performing calculations for this calibration. In the case where the strain measuring device of this embodiment has multiple scattered light measuring devices, multiple scattered light measuring devices may share one calculation unit 505. Alternatively, the calculation unit 505 may be pre-installed in each scattered light measuring device 50 and 60, allowing the information required for calibration to be shared among multiple calculation units 505. It should be noted that the calculation unit 505 may also be installed separately from the scattered light measuring device.

[0204] Furthermore, the scattered light measuring devices 50 and 60 may also have an interface 508, which outputs measurement data such as strain, temperature, and corrected strain data to an external source. The configuration of this interface 508 is not particularly limited; examples include interfaces for LAN (Local Area Network) connections and various interfaces for connecting to recording media. By having an interface, the scattered light measuring device can output measured strain or temperature data, as well as corrected strain data, to an external source. For example, it can be configured to output the aforementioned strain data to an external information terminal via a network or similar means. With this configuration, strain data from distant concrete structures can be easily acquired.

[0205] The strain measuring apparatus of this embodiment described above uses the fiber-optic PC steel strand disclosed herein. Therefore, it can suppress the variation amplitude of the strain measurement value caused by the position along the length direction of the fiber-optic PC steel strand, and can measure the strain with high precision.

[0206] According to the strain measuring device of this embodiment, strain and temperature can be measured using a PC steel strand with optical fiber. Therefore, even when the PC steel strand with optical fiber is buried and thus difficult to measure from the outside, strain and temperature can be easily measured. Furthermore, compared to cases where temperature is measured using a thermometer other than a PC steel strand with optical fiber, the strain measurement point is close to the temperature measurement point, thus enabling high-precision temperature-based strain correction.

[0207] Furthermore, the strain measuring device according to this embodiment uses scattered light to measure strain and temperature, which reduces the on-site measurement burden and makes it easy to perform measurements.

[0208] 3. Manufacturing method of PC steel stranded wire with optical fiber

[0209] Next, the manufacturing method of the PC stranded wire with optical fiber according to this embodiment will be described. The manufacturing method of the PC stranded wire with optical fiber according to this embodiment may include the following configuration step and fixing step.

[0210] In the configuration process, the optical fiber can be configured in the twisted groove of a PC steel strand made of multiple PC steel wires twisted together, wherein the twisted groove is configured between two adjacent PC steel wires on the outer surface of the PC steel strand.

[0211] In the fixing process, the optical fiber can be fixed to the twisted groove using resin.

[0212] Furthermore, during the configuration process, a tension greater than 0 N and less than or equal to 20 N can be applied to the optical fiber.

[0213] use Figure 7 The various steps in the manufacturing method of the fiber-optic PC steel stranded wire of this embodiment will be described.

[0214] Figure 7 This schematically illustrates a manufacturing apparatus 70 for PC stranded wire with optical fiber, illustrating the manufacturing method of PC stranded wire with optical fiber according to this embodiment. Figure 7 In the diagram, the PC steel strand 11 is conveyed from left to right along arrow B1. The method of conveying the PC steel strand 11 is not particularly limited; for example, it can be conveyed by roll-to-roll or by traction using a winch.

[0215] (1) Configuration process

[0216] In the configuration process, as described above, the optical fiber 12 can be configured in the twisted groove 21 of the PC steel strand 11.

[0217] As described above, conventionally, after fabricating an optical fiber component by covering the outer surface of the optical fiber with resin or the like, this optical fiber component is placed in the twist groove 21 of the PC steel strand 11. In contrast, in the method for manufacturing an optical fiber-bearing PC steel strand in this embodiment, the optical fiber 12 is directly placed in the twist groove 21. Compared to the case where an optical fiber component is fabricated, the optical fiber has lower rigidity and therefore superior processability. Thus, compared to the case where an optical fiber component is fabricated, the operability of the placement process can be improved.

[0218] In the configuration process, it is preferable to apply tension to the optical fiber in advance, for example, it is preferable to apply tension greater than 0N and less than or equal to 20N in advance, and more preferably to apply tension greater than 7N and less than 15N in advance.

[0219] By pre-applying a tension greater than 0N to the optical fiber, the supplied optical fiber 12 can be easily aligned, allowing it to be positioned at the desired location in the twisted groove 21 of the PC steel strand 11. Therefore, uneven positioning of the optical fibers in the twisted grooves across multiple cross-sections perpendicular to the length direction of the fiber-bearing PC steel strand can be suppressed. Consequently, when measuring the strain distribution along the length direction of the fiber-bearing PC steel strand under uniform tension, the variation in strain measurement values ​​caused by position along that length direction can be suppressed. In other words, precise strain measurement is possible using this fiber-bearing PC steel strand.

[0220] By applying a tension of less than or equal to 20N to the optical fiber 12, damage to the optical fiber 12 can be prevented.

[0221] The method of applying tension to the optical fiber 12 is not particularly limited; for example, the following methods can be listed: along Figure 7 The middle arrow B2 pulls the spool 71 that supplies the optical fiber 12, that is, it pulls the spool 71 that supplies the optical fiber 12 in the opposite direction to the arrow B1 that supplies the PC steel strand 11. By adjusting the force of the pulling spool 71, the tension applied to the optical fiber 12 can be adjusted.

[0222] Furthermore, before starting the configuration process, the end of the optical fiber 12 can be fixed to the twisted groove 21 of the PC steel strand 11. During the configuration process, the optical fiber 12 and the PC steel strand 11 are moved together along... Figure 7 The middle arrow B1 pulls from left to right in the diagram. Therefore, as a method of applying tension to the optical fiber 12, another method is to adjust the force pulling the PC steel strand 11 and the optical fiber 12 simultaneously.

[0223] Preferably, during the period from when the optical fiber 12 is supplied from the reel in the configuration process until the optical fiber 12 is fixed by the resin in the fixing process, a tension greater than 0 N and less than or equal to 20 N is applied to the optical fiber 12.

[0224] It should be noted that the adjustment is preferably carried out in the following manner: while pulling the PC steel strand 11 along arrow B1, the PC steel strand 11 is rotated along the central axis A, and the twisting groove 21 is always located at the position where the optical fiber 12 is supplied from the reel 71.

[0225] When a PC stranded steel cable with optical fibers has two or more optical fibers, it is preferable to provide multiple spools 71 according to the number of optical fibers, supplying multiple optical fibers simultaneously. In this case, it is preferable to pre-apply the aforementioned tension to each optical fiber. Then, each optical fiber can be positioned in a predetermined twisting groove.

[0226] In the configuration process, a guide path for guiding the optical fiber 12 can be provided between the spool 71 and the PC steel strand 11 on the transport path of the optical fiber 12, so that the optical fiber 12 supplied from the spool 71 can be positioned particularly accurately at the desired position in the twisted groove 21. This guide path can be composed of a guide roller, a guide member with a groove formed for the optical fiber 12 to pass through, etc.

[0227] Furthermore, in the configuration process, the optical fiber 12 can be configured such that after placing it in the twisted groove 21 of the PC steel strand 11, the optical fiber 12 is pressed with an insertion roller or the like, thereby inserting the optical fiber 12 into the desired position within the twisted groove 21. At this time, the resin supply process, described later, can also be performed simultaneously. Regarding the insertion roller, it is preferable that the portion in the cross-section passing through the central axis (rotation axis) of the insertion roller has a curved shape corresponding to the outer shape of the optical fiber 12. Furthermore, regarding the insertion roller, it is preferable that the portion in the cross-section in contact with the twisted groove 21 has a shape corresponding to the twisted groove 21.

[0228] By using the aforementioned insertion rollers to press and insert the optical fiber into the twisted groove, the tension applied to the optical fiber can be stabilized, and the positional accuracy of the optical fiber in the twisted groove 21 can be significantly improved.

[0229] (2) Fixed process

[0230] In the fixing process, the optical fiber can be fixed to the twisted groove using resin. Specifically, for example, the optical fiber can be fixed to the twisted groove by curing the resin.

[0231] The method for curing the resin is not particularly limited and can be selected according to the type of resin. If the resin is a thermosetting resin, it can be cured by heating it in a manner that meets the curing conditions during the setting process. Furthermore, if the resin is an ultraviolet-curing resin, it can be cured by irradiating it with ultraviolet light in a manner that meets the curing conditions during the setting process.

[0232] Therefore, the manufacturing apparatus 70 for PC steel stranded wire with optical fiber can include a resin curing device 73. If the resin is a thermosetting resin, the resin curing device 73 can be a heating device equipped with a heater or the like. Furthermore, if the resin is an ultraviolet-curing resin, the resin curing device 73 can be an ultraviolet irradiation device equipped with an ultraviolet lamp that irradiates ultraviolet light onto the resin or the like.

[0233] (3) Resin supply process

[0234] In the resin supply process, resin is supplied to the twisting groove. The timing of the resin supply process is not particularly limited; for example, the optical fiber can be placed in the twisting groove after the resin has been supplied to it in advance. That is, it can also be performed in the order of resin supply, placement, and fixing.

[0235] Furthermore, resin can be supplied to the twisted groove after the optical fiber is positioned within it. That is, the resin supply process can be performed after the positioning process and before the fixing process, in the order of positioning, resin supply, and fixing. By performing the resin supply process after positioning and before fixing, resin can be supplied to a wide range of the outer surface of the optical fiber. Therefore, the optical fiber can be securely fixed to the PC steel strand, and the optical fiber can follow the expansion and contraction of the PC steel strand with exceptional accuracy. As a result, the strain state generated in the PC steel strand is reflected in the optical fiber with exceptional accuracy, allowing for the measurement of the strain of the PC steel strand with particularly high precision.

[0236] To implement the resin supply process, the manufacturing apparatus 70 for PC stranded wire with optical fiber may also include a resin supply device 72. The configuration of the resin supply device 72 is not particularly limited; for example, an air-type resin supply device that supplies resin by extruding resin from a nozzle using air, or a volumetric resin supply device that supplies resin by metering resin with a screw and conveying it to a nozzle, etc.

[0237] The amount of resin supplied is not particularly limited, but the amount of resin supplied per unit length of the twisting trough is preferably 15 g / m or less, more preferably 10 g / m or less. This is because by keeping the amount of resin supplied at 15 g / m or less, dripping and the like can be prevented.

[0238] The lower limit of the resin supply is not particularly limited, but the resin supply per unit length of twisted groove is preferably more than 1 g / m, more preferably more than 2 g / m, relative to one twisted groove. By supplying resin at more than 1 g / m, the optical fiber can be fixed to the twisted groove with sufficient strength.

[0239] In the resin supply process, resin may be supplied at least to the twisted groove 21 where the optical fiber 12 is disposed, but resin may also be supplied to the twisted groove 21 where no optical fiber is disposed. In addition, for example, resin may be supplied not only to the twisted groove 21, but also to the entire surface of the PC steel strand 11. In this case, the resin supply device 72 may be configured, for example, to allow the PC steel strand to pass through the resin tank containing the resin.

[0240] The resin supply device 72 may also include a resin removal device to remove excess resin in case of oversupply. The resin removal device may be configured as, for example, a device with a scraper or a die, to remove excess resin adhering to the surface of the PC steel strand 11.

[0241] The resin supplied in the resin supply process is not particularly limited. For example, as described in "(1-3) Resin" of PC steel strand with optical fiber, a resin that cures in a short time is preferred so that the position of the optical fiber 12 does not shift after it is placed in the desired position of the twisted groove 21 of the PC steel strand 11.

[0242] Therefore, the curing time of the resin 13 supplied in the resin supply process is preferably 1 minute or less, and more preferably 50 seconds or less.

[0243] By using a resin with a curing time of less than 1 minute as resin 13, the time from placing the optical fiber 12 in the predetermined position of the twisted groove 21 until the optical fiber 12 is fixed by the resin can be shortened. Therefore, positional shift of the optical fiber 12 during the period until the resin 13 cures can be prevented. As a result, in multiple cross-sections of the fiber-bearing PC steel strand perpendicular to its length direction, the optical fiber 12 can be precisely positioned in the desired position within the twisted groove 21, such as the initial position when the optical fiber 12 is placed in the twisted groove. Therefore, when measuring the strain distribution along the length direction of the fiber-bearing PC steel strand under uniform tension using the obtained fiber-bearing PC steel strand, the variation in the measured strain value caused by the position along that length direction can be particularly suppressed. That is, strain can be measured with particularly high precision.

[0244] The lower limit of the curing time of resin 13 is not particularly limited, but the curing time is preferably 0.1 seconds or more, more preferably 0.3 seconds or more. By making the curing time 0.1 seconds or more, for example, clogging of the nozzle or other parts supplying resin 13 can be prevented.

[0245] Resin 13 is not particularly limited; for example, thermosetting resins, UV-curing resins, two-component mixed resins, etc., can be used.

[0246] In particular, a UV-curable resin is preferably used as resin 13. This is because UV-curable resins can be cured simply by irradiation with ultraviolet light, thus suppressing the impact on components other than the resin 13, such as optical fibers, compared to methods involving heating. Furthermore, UV-curable resins generally have shorter curing times compared to thermosetting resins and two-component mixed resins, which can particularly prevent the optical fiber 12 in the twisted groove 21 from shifting position during the period until the resin 13 has cured.

[0247] When using a UV-curable resin as the resin, the resin can be irradiated with UV light during the curing process as described above.

[0248] Regarding the resin, other points have already been explained, so the explanation will be omitted here.

[0249] (4) Corrosion-inhibiting coating formation process and outer coating formation process

[0250] The PC steel stranded wire with optical fiber in this embodiment can also have a corrosion-inhibiting coating as described above. Therefore, the manufacturing method of the PC steel stranded wire with optical fiber in this embodiment can also include the following corrosion-inhibiting coating formation process and outer coating formation process as needed.

[0251] In the corrosion-inhibiting coating formation process, for example, a resin constituting the corrosion-inhibiting coating can be supplied and coated onto the outer surface of the PC steel strand with optical fibers fixed to the surface of the PC steel strand by resin. In the corrosion-inhibiting coating formation process, heating or other processes can be performed as needed to form the corrosion-inhibiting coating on the outer surface of the PC steel strand with optical fibers.

[0252] Furthermore, in the outer coating configuration process, for example, the resin constituting the outer coating 42 can be molded onto the outer periphery of the corrosion-inhibiting coating 41 by extrusion molding to form the outer coating 42.

[0253] Resins suitable for use as corrosion inhibitor coatings and outer coatings have already been described, so their descriptions are omitted here.

[0254] Example

[0255] The following specific embodiments are provided for illustration, but the present invention is not limited to these embodiments.

[0256] (Evaluation Method)

[0257] First, the evaluation method for the fiber-optic PC stranded wires produced in the following experimental examples will be explained.

[0258] (1) The coefficient of variation of the distance between the common tangent of the two PC steel wires forming the twisted groove and the center of the optical fiber

[0259] For the PC steel stranded wire with optical fiber produced in the following experimental example, the distance between the common tangent 311 of the two adjacent PC steel wires 111 constituting the twisted groove 21 and the center 121 of the optical fiber 12 is measured in ten measurement sections perpendicular to the length direction (hereinafter also referred to as "measurement sections for measuring the coefficient of variation").

[0260] like Figure 3 As shown, in the above-mentioned measurement section, the common tangent 311 is drawn out in such a way that the tangent points with the two PC steel wires 111B are two points and the two tangent points are located on the exposed surface of the PC steel strand 11.

[0261] For the fiber-optic PC steel strands produced in each experimental example, a portion will be used in this experiment, and the remainder will be used for the determination of the strain distribution below.

[0262] It should be noted that the above measurement sections were selected with a distance of 50cm between adjacent measurement sections.

[0263] Then, the coefficient of variation was calculated based on the measurements from the ten cross-sections.

[0264] In the following experimental example, a PC stranded wire with optical fibers was manufactured, comprising two optical fibers. Therefore, for each optical fiber, the coefficient of variation of the distance between the common tangent and the center of the optical fiber was determined.

[0265] In the following experimental examples, two optical fibers were fixed to the twisted groove of a PC steel strand under the same conditions. Therefore, in the same experimental examples of PC steel strands with optical fibers, the coefficient of variation was approximately the same. Thus, Table 1 shows the measurement results for the optical fiber with the larger coefficient of variation among the two optical fibers measured in each experimental example.

[0266] (2) Determination of strain distribution

[0267] The strain distribution was measured under tension on a PC steel strand with optical fiber manufactured in the following experimental example. When measuring the strain distribution, a tension of 0.7 times the lower limit of the maximum test force specified in JIS G 3536 (2014) was applied to the PC steel strand with optical fiber.

[0268] Strain is measured through the following process.

[0269] like Figure 6 As shown, the scattered light measuring device 60 is connected to the optical fiber of the PC steel strand with optical fiber manufactured in the following experimental example, and the strain distribution is measured by Brillouin scattered light through a BOTDR (strain measurement process).

[0270] Then, the variation amplitude ratio is calculated according to the following formula (2), which is the difference between the maximum and minimum values ​​in the strain distribution, i.e., the variation amplitude relative to the maximum value.

[0271] (Percentage of variation (%)) = [(Variation range) ÷ (Maximum value)] × 100……(2)

[0272] Furthermore, a score of A is awarded for a variation rate of less than 3%, a score of B for a variation rate greater than 3% but less than 6%, and a score of C for a variation rate greater than 6%. A score of A or B indicates that the variation in strain measurements caused by the position along the length of the fiber-supported PC steel strand can be suppressed. Conversely, a score of C indicates that the variation in strain measurements caused by the position along the length of the fiber-supported PC steel strand is large. The evaluation results are shown in the "Strain Variation Rate" column of Table 1.

[0273] The proportion of strain variation was calculated using the results of the strain distribution, which was determined using optical fibers with the coefficients of variation shown in Table 1.

[0274] (Regarding the experimental example)

[0275] The experimental conditions are described below. Examples 1 to 3 are exemplary cases, and Example 4 is a comparative case.

[0276] [Experimental Example 1]

[0277] Aside from using two spools to supply optical fibers and feeding two optical fibers from those spools, the use of... Figure 7 The same apparatus shown is used to manufacture PC steel stranded wire with optical fibers.

[0278] Regarding the manufactured PC steel stranded wire with optical fiber, the cross-section of the PC steel stranded wire with optical fiber perpendicular to the length direction has... Figure 2 The structure shown has a PC steel strand 11 formed by twisting seven PC steel wires 111 together. It should be noted that the outer diameter of the PC steel strand 11 is 15.2 mm. Furthermore, optical fibers 12A and 12B are respectively disposed in twisted grooves 21A and 21B, which are formed between adjacent PC steel wires 111 serving as outer peripheral wires. It should be noted that single-mode optical fibers with an outer diameter of 0.9 mm and an elongation at break of 3.5% or more are used as optical fibers 12A and 12B.

[0279] In addition, such as Figure 3As shown, optical fibers 12A and 12B are respectively disposed within a region 33 enclosed by a straight line 312 and the surfaces 32 of two adjacent PC steel wires 111 forming a twisted groove. The straight line 312 is parallel to the common tangent 311 of the two adjacent PC steel wires 111, and the distance L312 between the straight line 312 and the common tangent 311 is 0.1 mm.

[0280] When evaluating the position of the optical fibers in the aforementioned twisted grooves, the positions of optical fibers 12A and 12B were observed in ten measurement sections used for measuring the coefficient of variation of the obtained PC steel stranded wire with optical fibers. The results showed that, in all measurement sections used for measuring the coefficient of variation, optical fibers 12A and 12B were positioned within region 33. Similarly, in Experimental Examples 2 and 3 below, the positions of optical fibers 12A and 12B were observed in ten measurement sections used for measuring the coefficient of variation, and the results showed that, in all measurement sections used for measuring the coefficient of variation, optical fibers 12A and 12B were positioned within region 33.

[0281] The above-mentioned PC steel stranded wire with optical fiber is manufactured according to the following process.

[0282] (Configuration process)

[0283] like Figure 7 As shown, the traction is achieved by the PC steel strand 11, which is composed of seven PC steel wires twisted together. Figure 7 The PC steel strand 11 is conveyed from left to right in the figure along arrow B1 at the right end of the strand.

[0284] At this time, the optical fiber 12 supplied from the reel 71 is pre-fixed to the PC steel strand 11. Figure 7 The twisted groove 21 at the right end of the fiber 12, together with the PC steel strand 11, is used to pull and transport the fiber 12 along arrow B1. Adjust the force pulling the PC steel strand 11 and along... Figure 7 The force applied to the spool 71 by the middle arrow B2 is adjusted so that the tension applied to each optical fiber 12 is 3N. This tension is applied to each optical fiber 12 from the time it is supplied from the spool during the configuration process until it is fixed by resin during the fixing process.

[0285] Then, as described above, while conveying the PC steel strand 11 and the optical fiber 12, the position of the optical fiber 12 is aligned with the desired position in the twisted groove 21 of the PC steel strand 11, and the optical fiber is placed in the twisted groove of the PC steel strand.

[0286] (Resin supply process)

[0287] Resin was supplied to the twisted groove 21 of the PC steel strand and the optical fiber 12.

[0288] The resin used has a tensile strength of 200 MPa and an elongation at break of 3.5% or higher. It should be noted that the UV-curable resin used cures within 0.5 seconds when irradiated with UV light using a UV lamp. In other words, the UV-curable resin used has a curing time of 0.5 seconds.

[0289] The resin is supplied using an air-type resin supply device 72.

[0290] At this point, the coating is supplied in such a manner that the coating amount per unit length of twisted groove is 5 g / m relative to one twisted groove.

[0291] (Fixed process)

[0292] The resin curing device 73, equipped with an ultraviolet lamp, irradiates the resin supplied in the resin supply process with ultraviolet light to cure the resin, thereby fixing the optical fiber to the twisted groove of the PC steel strand.

[0293] The cross-section of the fiber-reinforced PC steel stranded wire, perpendicular to the length direction of the PC steel stranded wire, obtained through the above processes, was confirmed, and the result was that it was possible to confirm the cross-section of the fiber-reinforced PC steel stranded wire. Figure 2 The entire outer surface of the optical fiber 12 shown is covered with resin.

[0294] The evaluation results of the obtained fiber-optic PC stranded wires are shown in Table 1. It should be noted that the standard deviation of the fiber-optic PC stranded wires obtained in Experiment 1, when calculating the coefficient of variation shown in Table 1, is 0.095 cm.

[0295] [Experimental Examples 2 and 3]

[0296] Except that the tension applied to each optical fiber was set to 10N (Experimental Example 2) and 20N (Experimental Example 3) during the configuration process, PC steel strands with optical fibers were manufactured under the same conditions as in Experimental Example 1 and evaluated.

[0297] The cross-section of the PC steel strand with optical fiber obtained in Experiment 2 and Experiment 3, perpendicular to the length direction of the PC steel strand, was confirmed, and it was found that the entire outer surface of the optical fiber 12 was covered with resin.

[0298] The evaluation results of the obtained PC steel strands with optical fibers are shown in Table 1.

[0299] [Experiment Example 4]

[0300] Except that no tension was applied to the optical fibers during the configuration process, PC stranded wires with optical fibers were manufactured and evaluated under the same conditions as in Experimental Example 1. That is, the tension applied to each optical fiber was 0N.

[0301] For the obtained PC steel stranded wire with optical fibers, the positions of optical fibers 12A and 12B were observed in ten measurement sections used for coefficient of variation determination. The results showed that, in six measurement sections used for coefficient of variation determination, optical fibers 12A and 12B were located outside region 33.

[0302] The evaluation results of the obtained PC steel strands with optical fibers are shown in Table 1.

[0303] [Table 1]

[0304]

[0305] Based on the results shown in Table 1, it can be confirmed that, compared with the PC steel strand with optical fibers in Example 4, the fiber-bearing PC steel strands of Examples 1 to 3, manufactured by applying a tension greater than 0 N and less than or equal to 20 N to the optical fibers during the configuration process, can suppress the coefficient of variation. That is, it can be confirmed that, compared with the PC steel strand with optical fibers in Example 4, the unevenness in the position of the optical fibers disposed within the twisted grooves in the cross-section perpendicular to the length direction can be suppressed in the fiber-bearing PC steel strands of Examples 1 to 3.

[0306] Furthermore, when the strain distribution was measured along the length of the fiber-optic PC steel strands used in Examples 1 to 3, it was confirmed that the evaluation of the strain variation amplitude ratio was A or B. That is, when the strain distribution was measured along the length of the fiber-optic PC steel strands used in Examples 1 to 3, it was confirmed that the variation amplitude of the strain value caused by the position along that length direction could be suppressed. Therefore, it can be confirmed that precise strain measurement can be performed by using the fiber-optic PC steel strands used in Examples 1 to 3.

[0307] Explanation of reference numerals in the attached figures

[0308] 10, 40, 51, 52: PC steel stranded wire with optical fiber

[0309] 11: PC steel strand

[0310] 11A: Outer surface

[0311] 111, 111A, 111B: PC steel wire

[0312] 12, 12A, 12B, 511, 512, 521: Fiber optic cables

[0313] 121: The center of the optical fiber

[0314] L12: Distance

[0315] 13: Resin

[0316] X: X-axis (length direction)

[0317] Y: Y-axis

[0318] Z: Z-axis

[0319] C1: Circumcircle

[0320] A: Central axis

[0321] A1: Center

[0322] 21, 21A, 21B: Twisted grooves

[0323] 22: Internal gaps

[0324] 311: Common tangent

[0325] 312: Straight line

[0326] L312: Distance

[0327] 32: The surface of two adjacent PC steel wires

[0328] 33: Region

[0329] 41: Corrosion-inhibiting coating

[0330] 41A: Outer surface

[0331] 42: Outer covering

[0332] 50, 60: Scattered light measuring device

[0333] 500, 600: Strain measuring device

[0334] 501: Optical Signal Transmission Unit

[0335] 502: Optical signal receiving unit

[0336] 503: Analysis Department

[0337] 504: Display Section

[0338] 505: Computation Department

[0339] 506: Optical splitter

[0340] 507: Coupler

[0341] 508: Interface

[0342] 51A, 52A: First end

[0343] 51B, 52B: Second end

[0344] 511A, 512A, 521A: First end

[0345] 511B, 512B, 521B: Second end

[0346] 70: Manufacturing apparatus for PC steel stranded wire with optical fiber

[0347] 71: Scroll

[0348] 72: Resin supply device

[0349] 73: Resin curing device

[0350] B1: Arrow

[0351] B2: Arrow.

Claims

1. A PC steel stranded wire with optical fiber, comprising: PC steel strand, composed of multiple PC steel wires twisted together; and optical fiber, The optical fiber is fixed to the twisted groove by resin, wherein... The twisted groove is a groove disposed on the outer surface of the PC steel strand between two adjacent PC steel wires. The coefficient of variation of the distance between the common tangent of two adjacent PC steel wires forming the twisted groove and the center of the optical fiber, measured in ten cross sections perpendicular to the length direction of the PC steel strand, is less than 0.

5.

2. The PC steel stranded wire with optical fiber according to claim 1, wherein, In a cross-section perpendicular to the length direction of the PC steel strand, the optical fiber is located in the area enclosed by a straight line parallel to the common tangent and 0.1 mm further inward than the common tangent from the PC steel strand, and the surfaces of two adjacent PC steel wires forming the twist groove.

3. The PC steel stranded wire with optical fiber according to claim 1 or 2, wherein, In a cross-section perpendicular to the length direction of the PC steel strand, the outer surface of the optical fiber is covered by the resin.

4. The PC steel stranded wire with optical fiber according to claim 1 or 2, wherein, It has two or more of the aforementioned optical fibers.

5. The PC stranded steel wire with optical fiber according to claim 1 or 2, wherein, The resin has an elongation at break of 3.5% or more.

6. The PC stranded steel wire with optical fiber according to claim 1 or 2, wherein, It has a corrosion-inhibiting coating covering the outer surface of the PC steel strand.

7. A strain measuring device, comprising: PC steel stranded wire with optical fiber as described in any one of claims 1 to 6; and The scattered light measuring device is connected to the PC steel stranded wire with optical fiber.

8. The strain measuring device according to claim 7, wherein, The scattered light measuring device has an interface for outputting measurement data.

9. A method for manufacturing PC steel stranded wire with optical fiber, comprising: In the configuration process, the optical fiber is placed in the twisted groove of a PC steel strand made of multiple PC steel wires. The twisted groove is a groove disposed on the outer surface of the PC steel strand between two adjacent PC steel wires; as well as In the fixing process, the optical fiber is fixed to the twisted groove using resin. In the configuration process, a tension greater than 0 N and less than or equal to 20 N is applied to the optical fiber. The coefficient of variation of the distance between the common tangent of two adjacent PC steel wires forming the twisted groove and the center of the optical fiber, measured in ten cross sections perpendicular to the length direction of the PC steel strand, is less than 0.

5.

10. The method for manufacturing PC steel stranded wire with optical fiber according to claim 9, wherein, After the configuration step and before the fixing step, there is a resin supply step that supplies the resin to the twisting groove.

11. The method for manufacturing PC steel stranded wire with optical fiber according to claim 9 or 10, wherein, The curing time of the resin is less than 1 minute.

12. The method for manufacturing PC steel stranded wire with optical fiber according to claim 9 or 10, wherein, The resin is a UV-curable resin. In the fixing process, the resin is irradiated with ultraviolet light.

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