JPH11256827A - Re-tensioning method of anchor and re-tensioning jig - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable re-tensioning of an anchor without using any exclusive re-tensioning jack. SOLUTION: Under the fitting of a wedge piece 24 along an inside taper surface 22a, a pulling head 22 is fixed to an anchor head 16. The pulling head 22 is moved to a tensioning direction together with an outer pipe 52 interlocking with tensioning action of a tensioning jack 14. By the constitution, the anchor head 16 and a tendon (PC steel strand) 12 are monolithically pulled to tension the anchor again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a jig for re-tensioning an anchor by re-tensioning the anchor by gripping and pulling an anchor head which is a head fixing device for a tension member.

[0002]

2. Description of the Related Art Earth anchors for tensioning and fixing tension members typified by PC steel strands and the like and stabilizing the ground and various structures by the fixing force are widely applied to the ground and various structures. Have been.

In an earth anchor, grout is poured into an anchor hole into which a PC steel stranded wire (tensile material) is inserted, and the solidified length of the PC steel stranded wire is fixed to the ground or the like under the solidification of the grout. It is pulled and tensioned with a predetermined load by a tensioning jack which is a tensioning device. Then, the tensioned PC steel strand is fixed to the end (head) by fixing the anchor head as a head fixing device, and the ground and the like are kept under the tension with the corresponding fixing load. Is established.

Here, in the case of an earth anchor, especially a permanent anchor, the tension state at a required anchoring load must be continuously maintained during the life of the target ground, various structures and the like. Since the anchoring load decreases over time due to displacement of the ground and various structures, elongation of the PC strand, etc., regular inspection (health check) of the anchoring load is required for permanent anchors. Have been.

[0005] Inspection of the anchoring load of a permanent anchor (earth anchor) or the like is usually measured under re-tensioning of a tendon such as PC strand. In addition, when the anchoring load is reduced or when the anchor is additionally struck, the PC steel strand must be re-tensioned.

Therefore, for example, there is provided a re-tensioning jack (re-tensioning device) which grips and fixes an anchor head serving as a head anchor for a permanent anchor, and enables re-tensioning of a PC steel strand by pulling the anchor head. Japanese Utility Model Publication No. 04-037957 discloses a hydraulic anchor maintenance jack.

According to this re-tensioning jack (anchor maintenance jack), a plurality of wedge pieces are pushed out along the tapered surface of the inner cylinder slidably contacting the outer cylinder, and the anchor head is gripped by the wedge pieces, and When the fixing tool is pulled by sliding the inner cylinder in the contraction direction, the PC stranded wire is tensioned (re-tensioned). Then, the hydraulic pressure and the traction displacement are measured with a static strain meter when the PC steel strand is re-tensioned, and the anchoring load of the PC steel strand is obtained from the inflection point of the hydraulic pressure and the displacement graph.

[0008]

However, such a re-tensioning jack is a dedicated re-tensioning device which is generally distinguished from a general tensioning jack used in a tensioning process of a tendon. An increase in the number of devices associated with the construction of the earth anchor is inevitable.

In addition, since this kind of re-tensioning jack has an appropriate tensile load for each model like the tensioning jack, it is necessary to prepare a model corresponding to the tensile load of the anchor. . However, re-tensioning jacks are not as many types as re-tensioning jacks, and this kind of re-tensioning jacks is complicated and expensive. This imposes a heavy burden on capital investment.

[0010] For this reason, the operator usually tries to make the re-tensioning jack of the minimum type compatible with a wide range of tensile load, but re-installs the anchor of the small tensile load depending on the type of the large tensile load. If you are nervous,
Since fine adjustment of the tensile load is not easy, there is a possibility that the soundness check may lack accuracy. In addition, since the number of jacks for re-tensioning is small, if work at a plurality of work sites is required, it is likely that the equipment cannot be covered only by the owned equipment.

An object of the present invention is to provide an anchor re-tensioning method and a re-tensioning jig which enable the anchor to be re-tensioned without using a dedicated re-tensioning jack.

[0012]

In order to achieve this object, the present invention focuses on a general type of tensioning jack having a wide variety of models, and makes use of the tensioning jack for re-tensioning the anchor. I'm sorry. According to the anchor re-tensioning method of the present invention, the pulling head fixed around the anchor head under the insertion of the wedge piece along the inner tapered surface is linked with the tensioning operation of the tensioning jack. By moving the anchor head and the tendon material integrally, the anchor is re-tensioned by moving in the tension direction.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, in a jig 10 for re-tensioning an anchor according to the present invention, a tensioning device which is a tensioning device for tensioning and fixing a tension material (for example, a PC steel strand) 12 of an anchor. A jack 14 can be used as a re-tensioning device for re-tensioning the anchor after anchoring. Then, an anchor head 16 serving as a head fixing tool of the tendon 12 is gripped and fixed, and this anchor head is connected to a tension jack 14.
This re-tensioning jig 10 is configured to be able to re-tension the tension member and thus the anchor by pulling in the tensioning direction (right side in the figure) under the tensioning operation.

An anchor of this type is provided with an extension extending from an anchor plate 18 facing the head of the tendon 12 pulled under a predetermined anchoring load, that is, the surface of the ground 17 to be anchored. At the end, an anchor head 16 serving as a head fixing device is fixed under fitting of a wedge 20 or the like, so that a fixing force caused by a fixing load of the tendon material can be introduced to the ground or the like. .

Since the structure of the anchor itself is not the purpose of the present invention, the description of the anchor itself is omitted here.

In the retensing jig 10 of the present invention, the anchor head 16 can be gripped and fixed by the combination of the pulling head 22 and the wedge piece 24.

As can be seen from FIG. 2 in addition to FIG.
The pooling head 22 is a substantially cylindrical body that can be arranged around the anchor head 16, and the distal end portion, that is, the inner surface of the terminal portion on the anchor plate side is formed as an inner tapered surface 22a having a small diameter at the open end side. . The wedge pieces 24 are supported by the support plate 26 at a plurality of, for example, six, locations at equal angles over the entire circumference of the inner tapered surface 22a so as to be able to swing at least in the radial direction. By gripping the anchor head 16 under the pushing in the end direction, the anchor head and the pooling head 22 can be firmly connected and fixed.

In the retensing jig 10, for example, the pooling head 22 is first disposed around the anchor head 16, and then the wedge piece 24 supported by the support plate 26 is formed into an inner tapered surface. The pooling head 22 is inserted from the rear end of the pooling head 22 into a position along the line 22a. Then, by holding down the support end 24a of the wedge piece, a holding plate 28 for integrally pressing the wedge piece 24 and the support plate 26 is formed.
Is arranged facing the rear surface of the support plate,
A retaining nut 32 is provided so that a spring member 30 for applying a biasing force in the pushing direction to the wedge piece 24, for example, a compression coil spring, is sandwiched between the pressing member and the retaining plate.
Screwed to the rear end of 22.

Next, a coupler 34 is attached to the pooling head 22.
Is fixed. The coupler 34 has a substantially bottomed cylindrical shape that can be arranged so as to cover the pooling head 22, and is fixed to the pooling head, for example, under a screwing between a male screw 36 and a female screw 38. Then, as shown in FIG.
A ram chair (also referred to as a jack chair) 40 is provided so as to further cover 34, and a tension jack 14 is provided under placement on the ram chair.

The tensioning jack 14 is a general center-hole type hydraulic jack used as a tensioning device in the anchor fixing process, and has a flange 42 of the piston 42.
A corresponding port 46 to one of the tension side chamber 44-1 and the return side chamber 44-2 separated and defined by 42a.
The piston 46 slides in the tension direction (right side in the figure) due to pressurized oil being injected from a hydraulic pump (not shown) via the -1 and 46-2, and accompanying discharge of pressurized oil from the other. , A tensioning operation for projecting and a return operation for contracting the piston are possible.

The tension jack 14 is a ram chair 40
Through hole (center hole) 50 of piston 42 in insertion hole 48 of
Are placed on a ram chair with the.

The tensioning jack 14 is used without any modification to a known one, but the structure of the tensioning jack itself is not the purpose of the present invention and will not be described in detail here.

The ram chair 40 itself is also known,
The known one used for tensioning the anchor may be used as it is, but since the ram chair according to the present invention is disposed over the coupler 34, the ram chair is placed over the coupler and tensioned. It is preferable to provide a ram chair for re-tensioning separately from the ram chair for tension, having an inner height that secures a space capable of ensuring the movement of the coupler in the direction (right side in the figure).

Here, the re-tensioning jig 10 of the present invention includes a pair of mutually slidable outer pipes 52 and inner pipes 54. The outer and inner pipes are located at the center of the tensioning jack. It is inserted into the ram chair through the hole (through hole) 50 and the insertion hole 48 of the ram chair. And FIG.
As shown in FIG. 2, the outer pipe 52 is connected and fixed to the coupler 34 and thus to the pooling head 22 under the screwing of the external male screw 58 to the corresponding female screw 56, and the inner pipe 54 is holding nut 32, holding plate
28 continuously penetrates and the external male thread 62 to the corresponding female thread 60
Is connected to and fixed to the support plate 26 under the screwing of.

That is, in the present invention, the outer pipe 52
With the coupler 34, and the pooling head 22,
The inner pipe 54 is the support plate 26, and eventually the wedge piece 24,
Each of them is integrally movable along the axial direction of each pipe.

As shown in FIGS. 1 and 2, when the anchor of the re-tensioning jig 10 is to be re-tensioned, the outer end of the outer pipe 52, that is, the outside of the tensioning jack from the piston 42 is removed. At the extended end of the pipe,
The engageable tension member 64 of b is fixed so as to move integrally with the outer pipe in the axial direction of the outer pipe. For example, a tension nut that can be screwed onto the external thread 66 of the outer pipe 52 can be used as the tension member 64, and this tension nut is normally screwed to the outer pipe to a position adjacent to the rear end 42b of the piston. Be placed.

In the re-tensioning jig 10 assembled as shown in FIG. 1, the tension nut (tension member) 64 is provided at the rear end side of the piston 42 at the piston rear end 42b.
The piston 42 is slid in the tensioning direction (right side in the figure) due to pressurized oil being pressed into the tension side chamber 44-1 through the port 46-1, That is, the outer pipe 52 moves in conjunction with the tension in the tension direction under the engagement between the rear end of the piston and the tension nut due to the tensioning operation of the tensioning jack 14.

Then, the coupler 34 connected to the outer pipe 52 connects the integral pooling head 22 to the anchor head.
16 and the wedge piece 24 in order to pull in tension, the anchor head is further inserted into the inner tapered surface 22a of the pooling head and the outer circumference of the anchor head. It is firmly fixed to the pooling head and is pulled with the pooling head.

As described above, the use of the re-tensioning jig 10 makes it possible to re-tension the anchor using the tensioning jack 14. Then, at the time of re-tensioning under a tensile load corresponding to the anchoring load of the anchor, the soundness of the anchor is checked, for example, by inspection of disclosure using equipment as disclosed in Japanese Utility Model Publication No. 04-037957. Will be

After completion of the health check, the re-tension of the anchor is released by returning the piston 42 under pressure of pressurized oil into the return chamber 44-2 via the port 46-2. . And then, the inner tapered surface of the pooling head
Wedge piece 24 between the outer peripheral surface of anchor head 16 and 22a
By pulling out, the gripping of the anchor head by the pooling head 22 is released, but usually such a wedge piece is formed by vacuum bonding under tight contact of the inner tapered surface and the opposing surface to the outer peripheral surface of the anchor head. , The anchor head and the pooling head may be firmly joined. When this vacuum bonding occurs, a great force is required to separate the inner tapered surface 22a and the outer surface of the anchor head 16 from the wedge piece 24, so that the wedge piece at the time of disassembly of the retensing jig 10 is required. Can not be easily pulled out.

Therefore, in the retensing jig 10 of the present invention, when the wedge piece 24 is pulled out between the inner tapered surface 22a of the pulling head and the outer peripheral surface of the anchor head 16, the tensioning jack 14 is also used. Use is possible.

As shown in FIGS. 1 and 2, for example, a diametric through-hole 68 is formed in the inner pipe 54, and a corresponding axially extending slit 70 which is aligned with the through-hole is formed in the outer pipe 52. Are provided in advance. When the wedge piece 24 is pulled out after the re-tension of the anchor is released, as shown in FIG. 3, the wedge piece 24 is used for re-tension so that the outer pipe 52 cannot be interlocked with the tension operation of the tension jack 14. After the tension nut 64 is removed from the outer pipe or is largely retracted (screw back) with respect to the outer pipe as shown by a dashed line, the piston rear end 42b of the tensioning jack is removed.
Is inserted through the slit 70 of the outer pipe into the through hole 68 of the inner pipe (see FIG. 2).

The pulling key 72 shown in FIG.
In the inserted state, the tension jack 14 is moved to the tension side chamber 44.
If the tension operation is performed under pressure of pressurized oil into -1, the piston 42 moves in the tension direction with a pull-out key, so that the inner pipe 54 does not accompany the outer pipe 52, It is pulled and slid in the direction of tension with respect to the outer pipe.
Since the support plate 26 moves integrally in the corresponding direction under the sliding of the inner pipe 54 in the tensioning direction, the traction force of the tensioning jack 14 under the tensioning operation is reduced by the pulling force. The inner tapered surface 22a of the head becomes a pulling force for pulling out the wedge piece 24 from the outer peripheral surface of the anchor head 16, and under this pulling force, the wedge piece is forcibly pulled out from between the inner tapered surface and the outer peripheral surface of the anchor head. It is.

That is, according to the re-tensioning jig 10 of the present invention, the tensioning jack 14 can be used for pulling out the wedge piece 24, so that the wedge piece is formed on the inner tapered surface 22 a of the pooling head and the anchor head 16. Even if it is vacuum bonded to the outer peripheral surface, the inner tapered surface,
Peeling of the opposing surface of the wedge piece from the outer peripheral surface of the anchor head can be reliably and easily ensured.

In this case, in order to secure a long moving space for the support plate 26 and the holding plate 28 in the pulling-out direction (right in the drawing) inside the pulling head 22, the holding nut 32 is It is preferable that the pooling head be retracted in advance as much as possible.

Although the wedge piece 24 is pulled out using the tensioning jack 14 here, the wedge piece can be forcibly pulled out without using the tensioning jack. As shown in FIG. 4, also in this case,
The tension nut 64 is removed, for example, from the outer pipe 52, after which a withdrawal nut 74 is mounted around the rear end of the inner pipe 54 with a screw on a corresponding male thread 76 (FIG. 2). reference).

Then, as shown in the figure, the rear end of the outer pipe 52
When the withdrawal nut 74 is further rotated in the screwing direction with respect to the inner pipe 54 at the position engaged with 52a, the inner pipe is connected to the outer pipe under the screwing force of the withdrawal nut with respect to the inner pipe. Under this force, the wedge piece 24 is forcibly pulled out from between the inner tapered surface 22a of the pooling head and the outer peripheral surface of the anchor head 16 in order to move in the tension direction.

Such a configuration in which the wedge piece 24 can be pulled out by the pulling nut 74 is effective when the tensile load is relatively small.

Then, the wedge piece 24 is moved by the tensioning operation of the tensioning jack 14 or the rotation of the pulling-out nut 74 to the inner tapered surface 22a of the pulling head and the anchor head 16
After the forcible withdrawal from between the outer peripheral surfaces of the components, if the constituent members are removed under a process reverse to the assembling process, the retensing jig 10 can be easily disassembled.

As described above, according to the anchor re-tensioning method of the present invention, it is sufficient to pull the pulling head 22 fixed to the anchor head 16 under the tensioning operation of the tensioning jack 14, so that the re-tensioning is performed. Without using a jack, the anchor can be re-tensioned by the tension jack. In other words, when re-tensioning the anchor, it is sufficient to re-use the tensioning anchor 14 used in the tensioning work of the anchor, so that re-tensioning with an appropriate tensile load can be easily secured, and excellent accuracy is achieved. You can check the soundness of the anchor.

Since there is no need to arrange a variety of re-tensioning jacks for each tensile load, the increase in the number of associated devices during the installation of the ground anchor can be sufficiently suppressed, and the burden of equipment investment on the installer can be reduced.

Further, the inner tapered surface 22a of the pooling head
The wedge piece 24 firmly fitted between the outer peripheral surface of the anchor head 16 and the wedge piece 24 is easily pulled out under the tensioning operation of the tensioning jack 14 or the rotation of the extraction nut 74, so that after re-tensioning, Work complexity can be prevented.

According to the jig 10 for re-tensioning the anchor of the present invention, the above-described re-tensioning method can be appropriately performed in combination with the jack for tensioning 14, and the re-tensioning of the anchor by the jack for tensioning. Can be easily and surely performed.

Here, in the embodiment of the present invention, there is exemplified a configuration in which the separate coupler 34 and the outer pipe 52 are integrally connected under a screwing between the external thread 58 and the internal thread 56. However, the present invention is not limited to this. For example, the coupler and the inner pipe may be integrally connected and fixed in advance as one member by welding or the like. However, if the coupler 34 and the outer pipe 52 are formed as separate members, the size of the member alone can be prevented, and the work of assembling, disassembling, and transporting can be facilitated.

Further, the coupler 34 is provided with a male screw 36 and a female screw 38.
Although a configuration in which the coupler is connected to and fixed to the pooling head 22 under screwing between them is illustrated, the coupler is detachable from the pooling head and has a traction direction, that is, the inner pipe 52.
It is only necessary to be connected so as to be able to move integrally in the axial direction, such as, for example, a combination of a male screw and a female screw. The spaces may be connected.

In the embodiment of the present invention, the tension nut 64 is exemplified as a tension member that can be screwed to the external thread 66 of the outer pipe 52. However, the tension member is attached to and detached from the outer pipe. As long as it is possible and is only necessary to be connected so as to be integrally movable in the axial direction, it is not limited to a tension nut.For example, a ring-shaped member that can be fixed to the outer pipe by a set screw or the like, or in a diameter direction of the outer pipe. A rod-shaped member or the like that can be disposed through the corresponding through-hole may be used as the tension member.

However, if the tension nut 64 is used as a tension member, workability and reliability of work can be further improved because the attachment to the outer pipe 52 is appropriately performed, although simple attachment and detachment are possible. Be improved.

In the embodiment of the present invention,
Anchor with one PC steel strand as tendon 12
This one anchor head 16 is embodied as an object to be fixed and pulled by the pooling head 22, but the number of PC steel strands is not limited to this, and the number of anchor wires for other numbers is also applicable. It goes without saying that it is good.

Further, the external shape of the anchor head 16 is generally a substantially cylindrical shape, but is not limited to this, and the anchor head 16 may be an anchor having a stepped shape having a step on its peripheral surface or a polygonal planar shape such as a hexagon. A configuration that targets the head may be adopted.

Although the PC strand is embodied as the tendon 12, the present invention is not limited to this, and the present invention can be applied to other tendons, for example, anchors such as PC steel rods.

The embodiments of the present invention described above are intended to explain the present invention, and do not limit the present invention in any way. Modifications, alterations, etc., within the technical scope of the present invention may be made. It goes without saying that all are included in the present invention.

[0053]

As described above, according to the anchor re-tensioning method according to the present invention, the tensioning anchor used in the anchor tensioning work can be used for re-tensioning without using a re-tensioning jack. Therefore, re-tensioning with an appropriate tensile load can be easily ensured, and the soundness of the anchor with excellent accuracy can be checked.

Since there is no need to arrange a variety of re-tensioning jacks for each tensile load, it is possible to sufficiently suppress an increase in the number of associated devices when the earth anchor is installed, and to reduce the burden of equipment investment for the installer.

Further, the wedge piece firmly fitted between the inner tapered surface of the pulling head and the outer peripheral surface of the anchor head can be easily formed by the tensioning operation of the tensioning jack or the rotation of the pull-out nut. Since it is pulled out, complication of work after re-tension can be prevented.

According to the jig for re-tensioning the anchor of the present invention, under the combination with the jack for tensioning,
The above-described re-tensioning method can be appropriately performed, and the re-tensioning of the anchor by the tensioning jack can be easily and reliably performed.

Further, if the tension member is a tension nut that can be screwed into the external thread of the outer pipe, the attachment to the outer pipe is appropriately performed, although the attachment and detachment can be easily performed. And the reliability of the operation is further improved.

If the support plate of the wedge piece can be pushed in under the biasing force of the spring means, the wedge piece can be easily and reliably pushed between the inner tapered surface of the pooling head and the outer peripheral surface of the anchor head. Done in And
By screwing the holding nut to the rear end of the opening of the pulling head, it is possible to easily adjust the strength of the biasing force from the wedge piece.

Further, the coupler and the outer pipe are separately provided,
If the outer pipe can be connected to the pulling head via this coupler, the outer pipe and the pooling head can be connected and fixed without complicating the operation and increasing the size of the member alone.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a partially broken jig for re-tensioning an anchor according to the present invention during re-tensioning.

FIG. 2 is a schematic exploded perspective view of a jig for re-tensioning the anchor.

FIG. 3 is a schematic side view of a partially broken jig for re-tensioning an anchor, showing an embodiment of a step of pulling out a wedge piece.

FIG. 4 is a schematic side view of a partially broken jig for re-tensioning an anchor, showing another form of a step of pulling out a wedge piece.

[Explanation of symbols]

 10 Anchor re-tensioning jig 12 Tensioner (PC steel strand) 14 Tension jack 16 Anchor head 22 Pulling head 22a Inner tapered surface of pulling head 24 Wedge piece 26 Support plate 30 Spring means (compression coil spring) 32 Holding Nut 34 Coupler 52 Outer pipe 54 Inner pipe 64 Tension member (tension nut) 68 Inner pipe through hole 70 Outer pipe slit 72 Extraction key 74 Extraction nut

Claims (10)

[Claims] A tension member pulled under the tensioning operation of a tensioning jack is re-tensioned against an anchor fixed under an anchoring load corresponding to a tensile load by fixing an anchor head at its head. By moving a pulling head fixed around the anchor head under fitting of a wedge piece along an inner tapered surface in a tensioning direction in conjunction with a tensioning operation of the tensioning jack, An anchor re-tensioning method for re-tensioning an anchor by integrally pulling an anchor head and the tension member. 2. A tension member pulled under the tensioning operation of a tensioning jack is re-tensioned to an anchor fixed under an anchoring load corresponding to the tensile load by fixing an anchor head at its head. A pulling head fixed around the anchor head with a wedge piece fitted along the inner tapered surface under the sliding of an outer pipe interlocked with the tensioning operation of the tensioning jack. By moving the anchor head and the tension member integrally to re-tension the anchor by moving in the tensioning direction, and after disabling the pulling head from interlocking with the tensioning operation of the tensioning jack, The pulling head is moved by moving the wedge piece in the tensioning direction while sliding the inner pipe against the outer pipe in conjunction with the tensioning operation of the tensioning jack. Re tensioning method anchor pulled out between the inner tapered surface and the outer peripheral surface of the anchor head. 3. The tension member pulled under the tensioning action of the tensioning jack is re-tensioned against the anchor fixed under an anchoring load corresponding to the tensile load by fixing the anchor head at its head. A pulling head fixed around the anchor head with a wedge piece fitted along the inner tapered surface under the sliding of an outer pipe interlocked with the tensioning operation of the tensioning jack. By moving the anchor head and the tension member integrally to re-tension the anchor by moving in the tensioning direction, and after disabling the pulling head from interlocking with the tensioning operation of the tensioning jack, With the rotation of the extraction nut with respect to the inner pipe at a position where it engages with the outer pipe rear end,
A method of re-tensioning an anchor, wherein the wedge piece is pulled out between an inner tapered surface of a pooling head and an outer peripheral surface of an anchor head. 4. An outer pipe and an inner pipe are arranged by penetrating a tension hole into a center hole provided in a piston, and each pipe is engaged with a rear end of the piston so that each pipe is actuated by the tension jack. The method for re-tensioning an anchor according to claim 2 or 3, wherein the anchor is slid in conjunction with. 5. A pulling head having a substantially cylindrical body which can be arranged around an anchor head and having an inner tapered surface having a small diameter at an open end side on an inner surface of a distal end portion; and a support plate capable of swinging at least in a radial direction. A plurality of wedge pieces that are supported and that fix the pooling head to the anchor head under gripping by fitting along the inner tapered surface of the pooling head; a center hole of the tensioning jack, and a tensioning jack placed thereon. An outer pipe continuously penetrating through the insertion hole of the ram chair and connected at one end to the pooling head; slidably and rotatably inserted into the outer pipe and connected at one end to the support plate of the wedge piece; An inner pipe, which is fixed to the outer pipe so as to be engageable behind the piston of the tensioning jack, with the piston sliding in the tensioning direction. And the pulling head fixed to the anchor head can be pulled in the tensioning direction by moving the outer pipe in conjunction with the tensioning operation of the tensioning jack, and without the outer pipe. A jig for re-tensioning an anchor in which a wedge piece can be pulled out between an inner tapered surface of a pooling head and an outer peripheral surface of an anchor head by pulling an inner pipe in a tensioning direction. 6. The inner pipe has, as a diametric through hole, an insertion hole in which a key for pulling can be inserted, behind the piston of the tensioning jack, and an outer pipe for axially pulling out the key. A slit for ensuring the movement of the key is provided at a corresponding position through the diametrical direction, and after the tension member is removed from the predetermined position and the tensioning operation of the tensioning jack after the insertion of the pull-out key, the inner pipe is moved. The jig for re-tensioning an anchor according to claim 5, wherein the jig can be pulled in a tension direction. 7. The inner pipe is formed with a screw at a rearwardly extending end from the outer pipe, and a pull-out nut is screwed to the male screw to remove the tension member from a predetermined position. Later, and after engagement with the rear end of the outer pipe associated with the screwing of the pulling nut, further rotation of the pulling nut in the screwing direction allows the inner pipe to be moved in the tensioning direction with respect to the outer pipe. A jig for re-tensioning an anchor according to claim 5 or 6. 8. The tension member is a tension nut that can be screwed onto the external thread of the outer pipe, and is fixed so as to be axially immovable around the outer pipe under the threaded connection with the external thread. A jig for re-tensioning an anchor according to claim 5. 9. A pulling nut is screwed to the rear end of the opening of the pulling head, and the pressing nut is interposed between the pressing nut and the support plate, and is biased by a biasing force of a spring member formed of a compression coil spring. 9. The jig for re-tensioning an anchor according to claim 5, wherein the jig is biased in a pushing direction between an inner tapered surface of the head and an outer peripheral surface of the anchor head. 10. The coupling according to claim 5, wherein the coupler is fixed around the pooling head over the pooling head, and the outer pipe is connected to the pooling head via one end fixed to the coupler. Jig for re-tensioning an anchor as described in the above.