Patent Description:
A PC steel, such as a PC (prestressed concrete) steel stranded cable, has been known as a member (tension member) for reinforcing a concrete structure by transferring compressive force to the concrete structure when the member is embedded inside the concrete structure or disposed outside the concrete structure.

For example, Patent Document <NUM> (<CIT>) discloses a tension member (PC steel stranded cable) including: a hollow body; and a plurality of elemental wires twisted together to surround an outer circumference of the hollow body so as to bear tension force. Inside the hollow body of this tension member (PC steel stranded cable), an optical fiber and a filler material are provided. The optical fiber is used as a strain sensor. The filler material is provided between the hollow body and the optical fiber so as to hold the position of the optical fiber within the hollow body. By storing the optical fiber inside the hollow body, the optical fiber is prevented from being damaged during use of the tension member and strain generated in the tension member is transferred to the optical fiber via the elemental wire, the hollow body, and the filler material.

<CIT> discloses a coated PC steel stranded cable according to the preamble of independent claim <NUM>.

A demand arises in a configuration that ensures transfer of strain using a thinner structure without using the above-described hollow body and filler material while sufficiently protecting the optical fiber. The hollow body and filler material thus provided serve to protect the optical fiber and allow the optical fiber to follow expansion and contraction of the elemental wire. However, since the hollow body and filler material do not substantially serve as a tension member, the inclusion of the hollow body and filler material leads to an increased number of components and an increased diameter of the tension member.

The present invention has been made in view of the above-described circumstances, and has an object to provide a coated PC steel stranded cable that facilitates transfer of strain of an elemental wire and facilitates protection of an optical fiber.

A coated PC steel stranded cable according to the present invention is according to independent claim <NUM>.

The coated PC steel stranded cable described above facilitates transfer of strain of the elemental wire and facilitates protection of the optical fiber.

First, contents of embodiments of the present invention are listed and described.

According to the above-described configuration, the anti-corrosive coating included therein facilitates the elemental wires to behave uniformly as compared with a case where no anti-corrosive coating is provided. Accordingly, precision in measuring strain by an optical fiber is facilitated to be increased. Moreover, since the optical fiber is disposed at a position inwardly of the outer circumferential surface of the outer coating and corresponding to the strand groove, the optical fiber is facilitated to follow expansion and contraction of the stranded cable, whereby strain of each elemental wire is facilitated to be transferred and measured with precision.

When the stranded cable is tensioned if there is no anti-corrosive coating, the elemental wires are biased, with the result that excessive compressive force may act on the optical fiber at the position corresponding to the strand groove. This may lead to decreased precision in measuring strain and damage of the optical fiber. To address this, according to the above configuration, since the anti-corrosive coating is included, the elemental wire upon the stranded cable being tensioned can be suppressed from being biased, thereby facilitating suppression of decreased precision in measuring the strain and suppression of mechanical damage of the optical fiber. Moreover, by disposing the optical fiber at the position corresponding to the strand groove, the optical fiber is readily protected from an external environment by the elemental wires disposed at the both sides of the optical fiber and the elemental wires surrounding the optical fiber. Moreover, the optical fiber is facilitated to be disposed in the envelope circle of the coated PC steel stranded cable, whereby the diameter of the coated PC steel stranded cable is unlikely to be large.

When the optical fiber is disposed between the anti-corrosive coating and the outer coating (boundary portion), the outer coating included therein further facilitates the optical fiber to follow expansion and contraction of the stranded cable. Moreover, corrosion of the stranded cable is facilitated to be suppressed.

According to the above configuration, no conventional hollow body or filler material is included, whereby the number of components can be reduced.

(<NUM>) In a reference example, the optical fiber is fixed by an adhesive agent to the strand groove in a surface of the anti-corrosive coating.

According to the above configuration, the optical fiber is fixed to the strand groove of the anti-corrosive coating using an adhesive agent, whereby the optical fiber is facilitated to follow expansion and contraction of the stranded cable.

(<NUM>) As one embodiment of the coated PC steel stranded cable, the optical fiber is fixed by the anti-corrosive coating without using an adhesive agent.

According to the above configuration, the optical fiber can be fixed by the anti-corrosive coating itself, whereby the adhesive agent can be unnecessary. This eliminates complicatedness related with an operation of applying the adhesive agent. Moreover, as compared with a case where the optical fiber is fixed using the adhesive agent, the optical fiber can be expected to follow expansion and contraction of the stranded cable for a long period of time.

(<NUM>) As one embodiment of the coated PC steel stranded cable in which the optical fiber is fixed by the anti-corrosive coating without using an adhesive agent, the optical fiber has a portion embedded in and incorporated with the anti-corrosive coating.

According to the above configuration, the optical fiber has a portion embedded in and incorporated with the anti-corrosive coating, whereby the optical fiber is facilitated to follow expansion and contraction of the stranded cable. Moreover, the optical fiber can be unlikely to be separated from the anti-corrosive coating, thus facilitating prevention of detachment of the optical fiber.

(<NUM>) As one embodiment of the coated PC steel stranded cable in which the optical fiber is fixed by the anti-corrosive coating without using an adhesive agent, the anti-corrosive coating has a surface provided with a press-fit groove in which a portion of the optical fiber is press-fitted.

According to the above-described configuration, the surface of the anti-corrosive coating is provided with the press-fit groove in which a portion of the optical fiber is press-fitted, whereby the optical fiber is facilitated to follow expansion and contraction of the stranded cable.

(<NUM>) As one embodiment of the coated PC steel stranded cable, the anti-corrosive coating has a surface provided with an irregularity for increasing frictional resistance with the optical fiber and the outer coating. In this case, the irregularity is smaller than an irregularity formed by the strand groove.

According to the above-described configuration, frictional resistance between the optical fiber and the anti-corrosive coating and frictional resistance between the anti-corrosive coating and the outer coating are facilitated to be increased, whereby the optical fiber is facilitated to follow expansion and contraction of the stranded cable.

(<NUM>) In a reference example, the optical fiber is disposed at a triple point surrounded by an outer circumferential elemental wire and an inner circumferential elemental wire or central elemental wire, the outer circumferential elemental wire and the inner circumferential elemental wire or the central elemental wire constituting the stranded cable, the inner circumferential elemental wire or the central elemental wire being adjacent to the outer circumferential elemental wire.

According to the above-described configuration, since the optical fiber is surrounded by the elemental wires, the optical fiber can be protected mechanically. Moreover, the optical fiber is disposed in the space at the triple point, whereby the diameter of the coated PC steel stranded cable is unlikely to be large.

(<NUM>) In a reference example, when the optical fiber is disposed at the triple point, the anti-corrosive coating has a filler portion provided between the elemental wires.

According to the above-described configuration, since the optical fiber can be incorporated with the elemental wire at the triple point by the filler portion, the optical fiber is facilitated to follow expansion and contraction of the stranded cable.

(<NUM>) In a reference example, when the optical fiber is disposed at the triple point, the stranded cable includes the central elemental wire, and a plurality of outer circumferential elemental wires helically twisted around an outer circumference of the central elemental wire, and a space between adjacent outer circumferential elemental wires has a length equal to or more than a diameter of the optical fiber.

According to the above-described configuration, the optical fiber is facilitated to be disposed at the triple point. This is because a space equal to or larger than the diameter of the optical fiber is formed if an interval is widened at one position between the outer circumferential elemental wires and the other intervals therebetween are closed when disposing the optical fiber at the triple point. This length of the space refers to, when a space is formed by widening an interval at one position between the outer circumferential elemental wires and the other intervals therebetween are closed, a length between straight lines circumscribed to each of these outer circumferential elemental wires among straight lines orthogonal to the common circumscribed line of two outer circumferential elemental wires that form the space.

The following describes details of embodiments of the present invention with reference to figures. It should be noted that the present invention is defined by the terms of the claims, rather than this example.

With reference to <FIG> and <FIG>, a coated PC steel stranded cable la according to a first embodiment will be described. Coated PC steel stranded cable la includes: a stranded cable <NUM> having a plurality of steel elemental wires <NUM> twisted together; an anti-corrosive coating <NUM> having an outer circumferential portion <NUM> that coats the outer circumference of stranded cable <NUM>; an outer coating <NUM> that coats the outer circumference of anti-corrosive coating <NUM>; and an optical fiber <NUM>. A main feature of this coated PC steel stranded cable la lies in that optical fiber <NUM> is combined with stranded cable <NUM> by disposing optical fiber <NUM> at a position (inclusive of a strand groove) inwardly of the outer circumferential surface of outer coating <NUM> and corresponding to the strand groove in stranded cable <NUM>. Although described later in detail, by combining optical fiber <NUM> with stranded cable <NUM>, optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM> (elemental wire <NUM>), whereby strain of elemental wire <NUM> can be measured with precision. Hereinafter, each configuration will be described in detail. The same reference characters in the figures represent the same components.

Coated PC steel stranded cable la is embedded inside a concrete structure or is disposed outside the concrete structure so as to reinforce the concrete structure, for example. Specifically, the concrete structure is reinforced by applying tension force to stranded cable <NUM> (elemental wire <NUM>) and transferring the tension force to the concrete structure as compressive force.

Stranded cable <NUM> is formed by twisting the plurality of steel elemental wires <NUM> together. Each elemental wire <NUM> bears tension force. The number of elemental wires <NUM> can be selected appropriately depending on a manner of use of coated PC steel stranded cable la (as an inner cable or an outer cable). Examples of the number of elemental wires <NUM> include <NUM>, <NUM>, and the like.

When the number of elemental wires <NUM> is <NUM>, stranded cable <NUM> has a one-layer stranded structure in which six outer circumferential elemental wires 21o are twisted helically around the outer circumference of one central elemental wire 21c. Outer circumferential elemental wires 21o are located at the outermost circumference of stranded cable <NUM>. Central elemental wire 21c and outer circumferential elemental wire 21o may be constituted of elemental wires having substantially the same diameter (<FIG>). Alternatively, central elemental wire 21c (outer circumferential elemental wire 21o) may be constituted of an elemental wire having a diameter larger (smaller) than the diameter of outer circumferential elemental wire 21o (central elemental wire 21c) (<FIG>; see a modification <NUM>-<NUM> below).

On the other hand, when the number of the elemental wires is <NUM>, the stranded cable has a two-layer stranded structure (not shown) in which inner circumferential elemental wires and outer circumferential elemental wires are helically twisted around one central elemental wire sequentially from the inner side. Representatively, there are two types of stranded cables having different numbers of inner circumferential elemental wires and outer circumferential elemental wires. Specifically, there are the following two types of stranded cables: a stranded cable including one central elemental wire, nine inner circumferential elemental wires, and nine outer circumferential elemental wires; and a stranded cable including one central elemental wire, six inner circumferential elemental wires, and twelve outer circumferential elemental wires. In the former type, the central elemental wire and each outer circumferential elemental wire are constituted of elemental wires having substantially the same diameter, and each inner circumferential elemental wire is constituted of an elemental wire having a diameter smaller than that of the central elemental wire. In the latter type, the central elemental wire and each inner circumferential elemental wire are constituted of elemental wires having substantially the same diameter. The outer circumferential elemental wires are disposed such that elemental wires having the substantially the same diameter as that of the central elemental wire and elemental wires having a smaller diameter are disposed alternately.

A valley formed at a triple point surrounded by three adjacent elemental wires of stranded cable <NUM> or a valley formed between two adjacent elemental wires of outer circumferential elemental wire 21c is a strand groove <NUM> continuous in the longitudinal direction of stranded cable <NUM>. When stranded cable <NUM> has one-layer stranded structure (with <NUM> elemental wires), the space at the triple point is formed between central elemental wire 21c and each of two outer circumferential elemental wires 21o. When the stranded cable has a two-layer stranded structure (with <NUM> elemental wires), the space at the triple point is formed between the central elemental wire and each of two inner circumferential elemental wires, between one inner circumferential elemental wire and each of two outer circumferential elemental wires, and between each of two inner circumferential elemental wires and one outer circumferential elemental wire.

Here, stranded cable <NUM> has a one-layer stranded structure having <NUM> elemental wires <NUM> with central elemental wire 21c and each outer circumferential elemental wire 21o having substantially the same diameter. For stranded cable <NUM>, elemental wires each composed of a known material and having a known size can be used.

Anti-corrosive coating <NUM> suppresses corrosion of stranded cable <NUM> by protecting stranded cable <NUM> from an external environment. Anti-corrosive coating <NUM> has an outer circumferential portion <NUM> that coats the outer circumference of stranded cable <NUM>. Outer circumferential portion <NUM> has a surface along the outer circumferential outline of stranded cable <NUM>, and in the surface, a strand groove <NUM> is formed at a position corresponding to strand groove <NUM> of stranded cable <NUM>.

Anti-corrosive coating <NUM> has a filler portion <NUM> provided between elemental wires <NUM> (triple point). Accordingly, moisture or the like can be suppressed from entering the space in stranded cable <NUM>, thus further facilitating suppression of the corrosion of stranded cable <NUM>. Moreover, when optical fiber <NUM> is disposed at the triple point as in a reference example described later (<FIG>), filler portion <NUM> thus included can fix optical fiber <NUM> and elemental wire <NUM> at the triple point, whereby optical fiber <NUM> is facilitated to follow expansion and contraction of elemental wire <NUM>. Since filler portion <NUM> is included, outer circumferential portion <NUM> and filler portion <NUM> may be continuously formed using the same material. Here, there is provided filler portion <NUM> continuously formed using the same material as that of outer circumferential portion <NUM>.

Examples of the material of anti-corrosive coating <NUM> include a resin excellent in corrosion resistance. Examples of such a resin include an epoxy resin, a polyethylene resin, and the like. Here, anti-corrosive coating <NUM> (outer circumferential portion <NUM> and filler portion <NUM>) is composed of an epoxy resin.

Optical fiber <NUM> is used as a sensor for measuring strain of elemental wire <NUM>. For optical fiber <NUM>, a fiber including a core and a clad can be used suitably. Examples of the materials of the core and the clad include a plastic and quartz glass. For the configuration of optical fiber <NUM>, it is possible to use: an optical fiber elemental wire (not shown) having a primary coating at the outer circumference of the clad; an optical fiber core wire (not shown) further including a secondary coating; an optical fiber cord (not shown) including a reinforcing material at the outer circumference of the secondary coating and an outer sheath that covers the outer circumference of the reinforcing material; and the like. Examples of the material of the primary coating include an ultraviolet curing type resin. Examples of the material of the secondary coating include a flame-retardant polyester elastomer and the like. Examples of the material of the reinforcing material include glass fiber, carbon fiber, aramid fiber, and the like. Examples of the material of the outer sheath include: a flame-retardant polyolefin, such as flame-retardant polyethylene; a flame-retardant cross-linked polyolefin, such as a flame-retardant cross-linked polyethylene; a heat-resistant vinyl; and the like. Here, optical fiber <NUM> is an optical fiber core wire including a primary coating and a secondary coating with each of the core and the clad being composed of quartz glass.

One or a plurality of optical fibers <NUM> may be provided. The number of optical fibers <NUM> can be selected appropriately depending on a method for measuring strain. Examples of the method for measuring strain include: BOCDA (Brillouin Optical Correlation Domain Analysis); BOTDR (Brillouin Optical Time Domain Reflectometry); FBG (Fiber Bragg Grating); and the like. When BOCDA is employed as the measurement method, an even number of optical fibers <NUM> not less than two are employed. When BOTDR or FBG is employed as the measurement method, one or more optical fibers <NUM> are employed. When BOCDA is employed as the measurement method, end portions of two optical fibers <NUM> are drawn from one end side of coated PC steel stranded cable 1a so as to connect the end portions to each other, and the other end portions of the two optical fibers are drawn from the other end side of coated PC steel stranded cable 1a so as to connect to a BOCDA measurement device (not shown). When BOTDR or FBG is employed as the measurement method, one end portion of one optical fiber <NUM> is disposed at the one end side of coated PC steel stranded cable 1a, and the other end portion of optical fiber <NUM> is drawn from the other end side of coated PC steel stranded cable 1a so as to connect to a BOTDR measurement device (not shown) or an FBG measurement device (not shown). In each of the measurement methods, when there are provided optical fibers <NUM> more than necessary for the measurement of strain, an optical fiber <NUM> not used for the measurement of strain can be used as a spare.

Optical fiber <NUM> is disposed at a position inwardly of the outer circumferential surface of outer coating <NUM> and corresponding to the strand groove of stranded cable <NUM>. The expression "optical fiber <NUM> is disposed inwardly of the outer circumferential surface of outer coating <NUM>" encompasses: a case where optical fiber <NUM> is embedded in anti-corrosive coating <NUM>; a case where optical fiber <NUM> is disposed between anti-corrosive coating <NUM> and outer coating <NUM> (boundary portion); and a case where optical fiber <NUM> is embedded in outer coating <NUM>. When optical fiber <NUM> is embedded in outer coating <NUM>, optical fiber <NUM> is representatively disposed at a position near the outer circumference of anti-corrosive coating <NUM>. Examples of the position corresponding to the strand groove include: strand groove <NUM> at the outer side of anti-corrosive coating <NUM> (surface of outer circumferential portion <NUM>); and strand groove <NUM> at the inner side of anti-corrosive coating <NUM>. When a plurality of optical fibers <NUM> (for examples, two) are included, strand grooves <NUM> and <NUM> are provided such that optical fibers <NUM> face each other with central elemental wire 21c being interposed therebetween.

Depending on the position of this optical fiber <NUM>, the coated PC steel stranded cable is configured as: an outer positioning type in which optical fiber <NUM> is provided in strand groove <NUM> at the outer side (surface of outer circumferential portion <NUM>) of anti-corrosive coating <NUM>; and an inner positioning type in which optical fiber <NUM> is provided in strand groove <NUM> at the inner side of anti-corrosive coating <NUM>. For the outer positioning type, there are the following types: a fixing type in which optical fiber <NUM> follows expansion and contraction of stranded cable <NUM> by fixing optical fiber <NUM> to the surface of outer circumferential portion <NUM>; and a non-fixing type in which optical fiber <NUM> follows expansion and contraction of stranded cable <NUM> by frictional resistance between optical fiber <NUM> and anti-corrosive coating <NUM> without fixation. For the fixing type, there are the following types: at least one of below-described configurations (<NUM>) and (<NUM>) in which a fixation member <NUM> is additionally provided independent of anti-corrosive coating <NUM>; and a below-described configuration (<NUM>) or (<NUM>) in which no such an independent fixation member <NUM> is included and anti-corrosive coating <NUM> itself serves to perform the function of fixation member <NUM>. An example of the non-fixing type is to provide an irregularity <NUM> at the surface of anti-corrosive coating <NUM> to increase frictional resistance with optical fiber <NUM>. This irregularity <NUM> is smaller than the irregularity formed by each of strand grooves <NUM>, <NUM>. Examples of the non-fixing type include: a below-described configuration (<NUM>) in which irregularity <NUM> is formed at the surface of anti-corrosive coating <NUM> by a different member independent of anti-corrosive coating <NUM>; and a below-described configuration (<NUM>) in which no such a different member is included and irregularity <NUM> is formed at anti-corrosive coating <NUM> itself. On the other hand, examples of the inner positioning type include below-described configurations (<NUM>) and (<NUM>).

Here, the configurations (<NUM>) and (<NUM>) will be described. The configuration (<NUM>) will be described in a modification <NUM>-<NUM>. The configuration (<NUM>) will be described in a modification <NUM>-<NUM>. The configuration (<NUM>) will be described in a modification <NUM>-<NUM>. The configuration (<NUM>) will be described in a modification <NUM>-<NUM>. The configuration (<NUM>) will be described in a second embodiment and a modification <NUM>-<NUM>. The configuration (<NUM>) will be described in a modification <NUM>-<NUM>.

In the first embodiment, optical fiber <NUM> is disposed at a position corresponding to strand groove <NUM> of the surface of outer circumferential portion <NUM>. Namely, optical fiber <NUM> is disposed at a position substantially corresponding to a boundary portion between anti-corrosive coating <NUM> (outer circumferential portion <NUM>) and outer coating <NUM> (described below). Optical fiber <NUM> is disposed in a helical manner along strand groove <NUM>. When two optical fibers <NUM> are included, these optical fibers <NUM> are provided in strand grooves <NUM> such that optical fibers <NUM> face each other with central elemental wire 21c interposed therebetween (<FIG>).

Fixation member <NUM> fixes optical fiber <NUM> to anti-corrosive coating <NUM> (<FIG>). In <FIG>, for ease of description, outer coating <NUM> (described below) shown in <FIG> is omitted. With this fixation, optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM>, whereby a strain of elemental wire <NUM> can be readily measured with precision. Fixation member <NUM> includes an adhesive agent <NUM>. Adhesive agent <NUM> is applied onto positions at an equal interval along the longitudinal direction of optical fiber <NUM>. For example, adhesive agent <NUM> is applied per pitch of optical fiber <NUM>. Accordingly, optical fiber <NUM> can be fixed to the surface of outer circumferential portion <NUM> to such an extent that optical fiber <NUM> can follow expansion and contraction of stranded cable <NUM> while preventing application of adhesive agent <NUM> from being complicated.

Coated PC steel stranded cable 1a includes outer coating <NUM> that coats the outer circumference of anti-corrosive coating <NUM>. This further facilitates suppression of corrosion of stranded cable <NUM>. This outer coating <NUM> can be expected to have a function as fixation member <NUM> for fixing optical fiber <NUM> to anti-corrosive coating <NUM>. When outer coating <NUM> is sufficiently expected to have the function as fixation member <NUM>, adhesive agent <NUM> described above may be omitted. The outer circumferential surface of outer coating <NUM> is constituted of a cylindrical surface provided with no strand groove. Examples of the material of outer coating <NUM> include a PE resin.

Coated PC steel stranded cable 1a described above can be manufactured by a method for manufacturing a coated PC steel stranded cable, the method including a preparing step, a fixing step, and an extruding step below.

In the preparing step, a coated wire including stranded cable <NUM> and anti-corrosive coating <NUM>, and an optical fiber <NUM> are prepared. The coated wire may be prepared by: preparing a produced coated wire; or forming a coated wire by forming anti-corrosive coating <NUM> onto stranded cable <NUM>. Stranded cable <NUM> can be formed by helically twisting six outer circumferential elemental wires 21o around the outer circumference of central elemental wire 21c.

Anti-corrosive coating <NUM> is formed through a known powder coating. For the powder coating, outer circumferential elemental wires 21o of stranded cable <NUM> are untwisted using a batten plate. A space is formed between untwisted outer circumferential elemental wires 21o, thereby sufficiently supplying a resin to between each outer circumferential elemental wire 21o and central elemental wire 21c. Accordingly, the resin (epoxy resin) of anti-corrosive coating <NUM> can be applied onto the outer circumferences of central elemental wire 21c and outer circumferential elemental wire 21o. These outer circumferential elemental wires 21o are re-twisted around central elemental wire 21c and then the applied resin is cooled. The untwisting and re-twisting allow for formation of filler portion <NUM> without forming a space at a triple point between central elemental wire 21c and each of two outer circumferential elemental wires 21o, and allows for formation of anti-corrosive coating <NUM> by forming outer circumferential portion <NUM> along the helical outer circumferential outline of outer circumferential elemental wire 21o at the outer circumference of outer circumferential elemental wire 21o.

In the fixing step, optical fiber <NUM> is disposed in strand groove <NUM> of anti-corrosive coating <NUM> and is fixed by applying adhesive agent <NUM>. Here, adhesive agent <NUM> is applied per pitch of optical fiber <NUM> (<FIG>).

In the extruding step, a PE resin serving as the resin of outer coating <NUM> on the outer circumference of anti-corrosive coating <NUM> is extrusion-molded into outer coating <NUM>. Accordingly, optical fiber <NUM> is fixed between anti-corrosive coating <NUM> and outer coating <NUM>.

According to coated PC steel stranded cable 1a, the following effects can be exhibited:.

With reference to <FIG>, a coated PC steel stranded cable 1b of a modification <NUM>-<NUM> will be described. Coated PC steel stranded cable 1b is different from coated PC steel stranded cable 1a of the first embodiment in that optical fiber <NUM> is fixed to the surface of anti-corrosive coating <NUM> by anti-corrosive coating <NUM> itself without using an adhesive agent <NUM> (<FIG>) such as the one in the first embodiment, and is the same as coated PC steel stranded cable 1a of the first embodiment in the other points. That is, coated PC steel stranded cable 1b includes stranded cable <NUM>, anti-corrosive coating <NUM>, optical fiber <NUM>, and outer coating <NUM>. The following mainly describes this difference and the same configuration will not be described.

Optical fiber <NUM> has a portion embedded in the surface of outer circumferential portion <NUM> of anti-corrosive coating <NUM> and incorporated with anti-corrosive coating <NUM>. Since they are incorporated with each other in this way, optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM>, whereby the strain of elemental wire <NUM> is readily measured with precision. A remaining portion of optical fiber <NUM> is exposed from the surface of outer circumferential portion <NUM> and is coated with outer coating <NUM>. In the surface of outer circumferential portion <NUM> of anti-corrosive coating <NUM>, a recess <NUM> is formed which is formed by embedding optical fiber <NUM>. This recess <NUM> is helically formed along the helix of optical fiber <NUM>.

Coated PC steel stranded cable 1b is manufactured by disposing optical fiber <NUM> during formation of anti-corrosive coating <NUM> described in the first embodiment. Specifically, outer circumferential elemental wire 21o untwisted once is re-twisted around central elemental wire 21c, optical fiber <NUM> is then pressed against the surface of the resin, and then the resin is cooled. Accordingly, a portion of optical fiber <NUM> is embedded in the surface of outer circumferential portion <NUM> of anti-corrosive coating <NUM>, thereby incorporating it with anti-corrosive coating <NUM>.

With reference to <FIG> and <FIG>, a coated PC steel stranded cable 1c of a modification <NUM>-<NUM> will be described. Coated PC steel stranded cable 1c is different from coated PC steel stranded cable 1b of modification <NUM>-<NUM> in terms of a configuration in which optical fiber <NUM> is fixed to the surface of anti-corrosive coating <NUM> by anti-corrosive coating <NUM> itself. Namely, coated PC steel stranded cable 1c is the same as that of modification <NUM>-<NUM> in terms of no use of adhesive agent and the other configuration. Coated PC steel stranded cable 1c includes stranded cable <NUM>, anti-corrosive coating <NUM>, optical fiber <NUM>, and outer coating <NUM>. Hereinafter, the following mainly describes this difference, and similar configurations will not be described.

In anti-corrosive coating <NUM>, a press-fit groove <NUM> into which optical fiber <NUM> is press-fitted is formed in the surface of outer circumferential portion <NUM>. By press-fitting optical fiber <NUM> in press-fit groove <NUM>, optical fiber <NUM> can be fixed to anti-corrosive coating <NUM>, whereby optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM>.

Press-fit groove <NUM> may be formed across the total length of strand groove <NUM> in the longitudinal direction of strand groove <NUM>, or may be partially formed in the longitudinal direction of strand groove <NUM>. Here, as shown in <FIG>, press-fit groove <NUM> is formed across the total length in the longitudinal direction of strand groove <NUM>. It should be noted that in <FIG>, for ease of description, outer coating <NUM> shown in <FIG> is omitted and optical fiber <NUM> is illustrated to be separated from anti-corrosive coating <NUM> (press-fit groove <NUM>).

Press-fit groove <NUM> has a width substantially the same as or slightly smaller than the diameter of optical fiber <NUM>. Accordingly, optical fiber <NUM> can be facilitated to be press-fitted therein without damaging optical fiber <NUM>. After disposing it in press-fit groove <NUM>, optical fiber <NUM> is unlikely to be detached from press-fit groove <NUM>. The depth of press-fit groove <NUM> can be appropriately selected as long as optical fiber <NUM> is not detached. For example, the depth of press-fit groove <NUM> can be as large as the diameter of optical fiber <NUM>. Press-fit groove <NUM> can be formed by cutting after forming anti-corrosive coating <NUM>.

With reference to <FIG> and <FIG>, a coated PC steel stranded cable 1d of a modification <NUM>-<NUM> will be described. Coated PC steel stranded cable 1d is different from the first embodiment and modifications <NUM>-<NUM> and <NUM>-<NUM> in that optical fiber <NUM> follows expansion and contraction of stranded cable <NUM> by frictional resistance between optical fiber <NUM> and anti-corrosive coating <NUM> without fixing optical fiber <NUM> to anti-corrosive coating <NUM>. The other configurations are the same as those of the first embodiment and modifications <NUM>-<NUM> and <NUM>-<NUM>. The following mainly describes this difference, and similar configurations will not be described. It should be noted that in <FIG>, for ease of description, outer coating <NUM> shown in <FIG> is omitted and optical fiber <NUM> is shown to be separated from anti-corrosive coating <NUM> (strand groove <NUM>).

Coated PC steel stranded cable 1d includes: the same stranded cable <NUM>, anti-corrosive coating <NUM>, and optical fiber <NUM> as those in the first embodiment; solid particles <NUM> for forming irregularity <NUM> for increasing frictional resistance with optical fiber <NUM>; and outer coating <NUM>. Here, solid particles <NUM> are constituted of a member different from that of anti-corrosive coating <NUM>, and has a portion partially exposed from the surface of outer circumferential portion <NUM> of anti-corrosive coating <NUM>, and has a remainder embedded in outer circumferential portion <NUM>. With these solid particles <NUM>, the frictional resistance between optical fiber <NUM> and anti-corrosive coating <NUM> and the frictional resistance between anti-corrosive coating <NUM> and outer coating <NUM> can be increased, whereby optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM>. For solid particles <NUM>, known particles such as sand can be used.

Coated PC steel stranded cable 1d is manufactured by spraying solid particles <NUM> and then cooling the resin in the manufacturing process of coated PC steel stranded cable 1b of modification <NUM>-<NUM> instead of pressing optical fiber <NUM> against the resin applied to stranded cable <NUM>. Then, a portion of solid particles <NUM> is exposed from the epoxy resin surface and a remainder is embedded in the resin. Optical fiber <NUM> is embedded in the material of outer coating <NUM> by: disposing optical fiber <NUM> in contact with the embedded surface of solid particles <NUM>; and extruding the molten resin for outer coating <NUM> at the outer circumferential portion. Then, the resin for outer coating <NUM> is cooled and is accordingly contracted to bring outer coating <NUM> into contact with the surface in which solid particles <NUM> are embedded. The material of outer coating <NUM> is preferably a PE resin as described above.

With reference to <FIG> and <FIG>, a coated PC steel stranded cable 1e of modification <NUM>-<NUM> will be described. Coated PC steel stranded cable 1e is different from modification <NUM>-<NUM> in that irregularity <NUM> for causing optical fiber <NUM> to follow expansion and contraction of stranded cable <NUM> by way of frictional resistance is formed at anti-corrosive coating <NUM> itself, and is the same as that of modification <NUM>-<NUM> in the other point. Namely, coated PC steel stranded cable 1e includes stranded cable <NUM>, anti-corrosive coating <NUM>, optical fiber <NUM>, and outer coating <NUM>. The following mainly describes this difference, and similar configurations will not be described.

Irregularity <NUM> is formed continuously at the surface of anti-corrosive coating <NUM> using a material for anti-corrosive coating <NUM>. In this irregularity <NUM>, recesses and projections are formed alternately in the form of stripes. The longitudinal direction of each of the recesses and projections of irregularity <NUM> can be formed along the following direction (<NUM>) or (<NUM>): (<NUM>) a helical direction of stranded cable <NUM>; and (<NUM>) a helical direction opposite to the foregoing helical direction of stranded cable <NUM>. In each of the directions (<NUM>) and (<NUM>), optical fiber <NUM> crosses irregularity <NUM> to facilitate increase in friction between optical fiber <NUM> and irregularity <NUM> and friction between irregularity <NUM> and outer coating <NUM>. Hence, optical fiber <NUM> is facilitated to follow expansion and contraction of stranded cable <NUM>. Here, as shown in <FIG>, the longitudinal direction of each of the recesses and projections of irregularity <NUM> is along the helical direction opposite to the helical direction of stranded cable <NUM>. It should be noted that for ease of description, in <FIG>, outer coating <NUM> shown in <FIG> is omitted and optical fiber <NUM> is illustrated to be separated from anti-corrosive coating <NUM> (strand groove <NUM>). In addition to this, thick (thin) portions of anti-corrosive coating <NUM> can be formed in the axial direction at a predetermined interval. Namely, anti-corrosive coating <NUM> can be in a stripe-like shape in which annular projections having a uniform height and annular recesses each having a diameter smaller than that of each of annular projections on the surface of anti-corrosive coating <NUM> are alternately formed in the longitudinal direction.

Coated PC steel stranded cable 1e can be formed by causing coated PC steel stranded cable 1a of the first embodiment to pass through a roller having an inner circumferential surface provided with irregularity after re-twisting outer circumferential elemental wire 21o and before cooling the applied resin in the process of manufacturing coated PC steel stranded cable 1a of the first embodiment.

With reference to <FIG>, a coated PC steel stranded cable 1f of a second embodiment will be described. Coated PC steel stranded cable 1f is mainly different from coated PC steel stranded cable 1a of the first embodiment in that coated PC steel stranded cable 1f is of the inner positioning type in which optical fiber <NUM> is provided in an inner strand groove <NUM> of anti-corrosive coating <NUM>. The following mainly describes this difference, and similar configurations and effects will not be described.

Coated PC steel stranded cable 1f includes stranded cable <NUM>, anti-corrosive coating <NUM>, optical fiber <NUM>, and outer coating <NUM>. The material of anti-corrosive coating <NUM> is used as a PE resin. Optical fiber <NUM> is configured such that the material of each of the core and the clad is quartz glass and an optical fiber elemental wire including a primary coating is employed. Optical fiber <NUM> is disposed at a position corresponding to strand groove <NUM> formed at the triple point surrounded by three adjacent elemental wires <NUM> of stranded cable <NUM> (central elemental wire 21c and two outer circumferential elemental wires 21o). Optical fiber <NUM> is fixed to and is incorporated with stranded cable <NUM> at filler portion <NUM> of anti-corrosive coating <NUM> in this strand groove <NUM>. The description above has discussed the triple point when the stranded cable has seven elemental wires; however, when the stranded cable has <NUM> elemental wires, a space between the various elemental wires, such as a space surrounded by outer and inner circumferential elemental wires, may be employed. Although the triple point depends on the wire sizes of the outer and inner circumferential elemental wires, there may be employed a space surrounded by two outer circumferential elemental wires and one inner circumferential elemental wire.

Coated PC steel stranded cable 1f is manufactured by: preparing a composite wire in which optical fiber <NUM> is disposed at strand groove <NUM> formed at the triple point of stranded cable <NUM>; and forming anti-corrosive coating <NUM> by coating the outer circumference of the composite wire with a PE resin and filling the PE resin between elemental wires <NUM>. The composite wire can be produced by one of the following methods (<NUM>) to (<NUM>).

The outer circumference of stranded cable <NUM> is surrounded by a cylindrical member (not shown) such as a contraction tube in order to avoid fluid from escaping to outside of stranded cable <NUM> and form a flow path in the axial direction of stranded cable <NUM>. Then, optical fiber <NUM> is forced using compressed air into strand groove <NUM> formed at the triple point of stranded cable <NUM>.

When twisting six outer circumferential elemental wires 21o together helically around central elemental wire 21c, optical fiber <NUM> is twisted together with outer circumferential elemental wire 21o such that optical fiber <NUM> is disposed at the triple point of stranded cable <NUM>.

When twisting six outer circumferential elemental wires 21o together helically around central elemental wire 21c, a wire thinner than optical fiber <NUM> is twisted together with outer circumferential elemental wire 21o such that the thinner wire is disposed at the triple point of stranded cable <NUM>. Then, optical fiber <NUM> is connected to the tip of the wire at the one end side of stranded cable <NUM>. Then, by drawing the wire from the other end side of stranded cable <NUM>, optical fiber <NUM> is drawn into the triple point.

Stranded cable <NUM> is produced by twisting six outer circumferential elemental wires 21o together helically around central elemental wire 21c. One outer circumferential elemental wire 21o of this stranded cable <NUM> is untwisted. Accordingly, between outer circumferential elemental wires 21o, a space corresponding to one outer circumferential elemental wire 21o is formed helically. Next, optical fiber <NUM> is disposed in the space. Then, untwisted outer elemental wire 21o is disposed to fill the space.

In accordance with one of the above methods (<NUM>) to (<NUM>), the composite wire is produced, thereby extruding the molten PE resin to the outer circumference of stranded cable <NUM>. On this occasion, stranded cable <NUM> does not need to be untwisted once. Then, pressure is applied from the outer circumference side of stranded cable <NUM> by the PE resin extruded to the outer circumference of stranded cable <NUM>, thereby providing the PE resin between outer circumferential elemental wire 21o and central elemental wires 21c. By cooling the PE resin in this state, anti-corrosive coating <NUM> can be formed in which filler portion <NUM> and outer circumferential portion <NUM> are formed continuously. In filler portion <NUM>, the PE resin is provided without forming a space at the triple point among central elemental wire 21c and two outer circumferential elemental wires 21o. Outer circumferential portion <NUM> is along the helical outline of outer circumferential elemental wire 21o at the outer circumference of outer circumferential elemental wire 21o.

According to coated PC steel stranded cable 1f of the second embodiment, the following effects can be exhibited:.

With reference to <FIG>, the following describes a coated PC steel stranded cable <NUM> of a modification <NUM>-<NUM>. Coated PC steel stranded cable <NUM> is different from coated PC steel stranded cable 1f of the second embodiment in that the diameter of central elemental wire 21c is different from the diameter of outer circumferential elemental wire 21o, and is the same as coated PC steel stranded cable 1f of the second embodiment in the other points. Namely, coated PC steel stranded cable <NUM> includes stranded cable <NUM>, anti-corrosive coating <NUM>, and optical fiber <NUM>, and optical fiber <NUM> is disposed at strand groove <NUM> formed at the triple point of stranded cable <NUM>. The following mainly describes this difference, and similar configurations will not be described.

The diameter of outer circumferential elemental wire 21o and the diameter of central elemental wire 21c may be selected appropriately to be different from each other while satisfying the following conditions (<NUM>) and (<NUM>):.

By satisfying these conditions (<NUM>) and (<NUM>), when a space is secured using an appropriate tool readily insertable between outer circumferential elemental wires 21o (such as a roller-cutter or the like), optical fiber <NUM> can be disposed readily at the triple point and the outer diameter of stranded cable <NUM> (diameter of envelope circle) is unlikely to become large. Here, as compared with the case where the diameter of outer circumferential elemental wire 21o is substantially the same as the diameter of central elemental wire 21c, central elemental wire 21c is slightly made larger and outer circumferential elemental wire 21o is slightly made smaller.

Optical fiber <NUM> may be an optical fiber elemental wire or an optical fiber core wire. Here, optical fiber <NUM> is configured as the optical fiber core wire.

Coated PC steel stranded cable <NUM> can be manufactured as follows. First, stranded cable <NUM> and optical fiber <NUM> are prepared. Next, an interval at one position between adjacent outer circumferential elemental wires 21o in stranded cable <NUM> is widened and the other intervals therebetween are closed. Then, optical fiber <NUM> is disposed to extend from the widened interval along strand groove <NUM> at the triple point of stranded cable <NUM>. Next, an interval is widened between outer circumferential elemental wires 21o at a position facing the position having the widened interval with central elemental wire 21c interposed therebetween, and optical fiber <NUM> is disposed in a similar manner. In this way, the composite wire is produced. Next, a molten PE resin is extruded onto the outer circumference of the composite wire and this PE resin is cooled. Since the diameter of outer circumferential elemental wire 21o is smaller than that of central elemental wire 21c, a space is formed between adjacent outer circumferential elemental wires 21o. Therefore, since the composite wire can be produced by disposing optical fiber <NUM> at the triple point without using the method for manufacturing the composite wire described in the second embodiment, optical fiber <NUM> can be readily disposed. Moreover, for formation of anti-corrosive coating <NUM>, the PE resin can be readily and sufficiently supplied to between outer circumferential elemental wire 21o and central elemental wires 21c without untwisting stranded cable <NUM> or applying pressure from the outer circumference to the molten PE resin.

With reference to <FIG>, the following describes a coated PC steel stranded cable <NUM> of a modification <NUM>-<NUM>. Coated PC steel stranded cable <NUM> is different from coated PC steel stranded cable 1f of the second embodiment in terms of the position of optical fiber <NUM>, and is the same as the second embodiment in terms of the other points. That is, coated PC steel stranded cable <NUM> includes stranded cable <NUM>, anti-corrosive coating <NUM>, and optical fiber <NUM>. The following mainly describes this difference, and similar configurations will not be described.

Optical fiber <NUM> may be an optical fiber elemental wire or an optical fiber core wire. Here, optical fiber <NUM> is the optical fiber core wire. Optical fiber <NUM> is disposed at strand groove <NUM> formed between adjacent outer circumferential elemental wires 21o. Since optical fiber <NUM> is disposed at strand groove <NUM> between adjacent outer circumferential elemental wires 21o, optical fiber <NUM> can be disposed more readily as compared with a case where optical fiber <NUM> is disposed in strand groove <NUM> formed at the triple point of stranded cable <NUM>.

Coated PC steel stranded cable <NUM> can be formed by: preparing stranded cable <NUM> and optical fiber <NUM>; disposing optical fiber <NUM> in strand groove <NUM> between adjacent outer circumferential elemental wires 21o; and then forming anti-corrosive coating <NUM> in the same manner as in the second embodiment.

It should be noted that the scope of the present invention is not limited to the examples described above, is defined by the terms of the claims, and is intended to include any modifications within the scope of the claims. For example, with reference to <FIG> and <FIG>, it has been illustrated in modification <NUM>-<NUM> described above that anti-corrosive coating <NUM> is provided with press-fit groove <NUM>; however, instead of press-fit groove <NUM>, a storage groove wider than press-fit groove <NUM> may be provided to store optical fiber <NUM> therein without permitting optical fiber <NUM> to be press-fitted therein. In this case, optical fiber <NUM> may be fixed using an adhesive agent in the storage groove or optical fiber <NUM> may be disposed in the storage groove, which is then sealed with outer coating <NUM>. In this way, optical fiber <NUM> can be prevented from being detached from the storage groove and optical fiber <NUM> can be facilitated to follow expansion and contraction of stranded cable <NUM>.

The coated PC steel stranded cable according to one embodiment of the present invention can be used suitably to reinforce a concrete structure when embedded inside the concrete structure or disposed outside the concrete structure. Moreover, the coated PC steel stranded cable according to one embodiment of the present invention can be used suitably to check a tension state across the total length of the stranded cable by using the optical fiber as a sensor.

Claim 1:
A coated PC steel stranded cable (<NUM>) comprising:
a stranded cable (<NUM>) in which a plurality of elemental wires (<NUM>) each composed of steel are twisted together;
an anti-corrosive coating (<NUM>) having an outer circumferential portion (<NUM>) that coats an outer circumference of the stranded cable (<NUM>);
an optical fiber (<NUM>) provided at a position inwardly of an outer circumferential surface of the anti-corrosive coating (<NUM>) and corresponding to a first strand groove (<NUM>) in the stranded cable (<NUM>) so as to follow expansion and contraction of the stranded cable (<NUM>), the optical fiber (<NUM>) being a sensor for measuring strain of the plurality of elemental wires (<NUM>); and
an outer coating (<NUM>) that coats an outer circumference of the anti-corrosive coating (<NUM>),
the stranded cable (<NUM>) having an outer circumferential elemental wire (21o) located at an outermost circumference of the stranded cable (<NUM>), and an inner circumferential elemental wire or central elemental wire (21c) adjacent to the outer circumferential elemental wire (21o),
the anti-corrosive coating (<NUM>) having a filler portion (<NUM>) provided at a triple point surrounded by the outer circumferential elemental wire (21o) and the inner circumferential elemental wire or the central elemental wire (21c),
the outer circumferential elemental wire (21o) includes adjacent outermost circumferential elemental wires (21o),
characterized in that
the optical fiber (<NUM>) is disposed at the first strand groove (<NUM>) formed between the adjacent outermost circumferential elemental wires (21o),
the outer circumferential portion (<NUM>) has a surface along an outer circumferential outline of the stranded cable (<NUM>), and
in the surface, a second strand groove (<NUM>) is formed at a position corresponding to the first strand groove (<NUM>).