JP7822574B2 - Tensioning device and tensioning method for tendons - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. (1) The 30th Symposium on the Development of Prestressed Concrete, October 22, 2021. (2) Publisher: Japan Prestressed Concrete Institute, Publication name: Proceedings of the 30th Symposium of the Japan Prestressed Concrete Institute, Relevant pages: pp. 639-642, Distribution date: October 21, 2021.

The present invention relates to a tensioning device and tensioning method for tendons used to introduce prestress into concrete structures.

Tendons are used to introduce prestress into concrete structures. Tendons are made of steel materials such as PC steel rods and wires, or fiber-reinforced plastic (FRP). FRP tendons do not rust, making them more advantageous than PC steel rods and wires in areas prone to salt damage. Since FRP tendons can be damaged if directly gripped and tensioned, they are tensioned using a temporary attachment that can be fixed to the FRP tendon (see, for example, Patent Document 1).

Figure 9 shows an example of a conventional tensioning device 101 for FRP tendons. The tensioning device 101 includes a temporary anchor 103 into which the end of the tendon 102 is inserted and secured; a PC steel rod 104 connected to the temporary anchor 103; a ram chair 106 supported by a concrete structure 105; a fixing nut 107 threadedly engaged with a thread on the outer surface of the temporary anchor 103 and secured to the ram chair 106; an additional ram chair 108 connected to the ram chair 106; a center hole jack 109 connected to the additional ram chair 108; and a nut 111 threadedly engaged with a thread on the outer surface of the PC steel rod 104 and secured to the center hole jack 109 via a support plate 110. The temporary anchor 103 and the PC steel rod 104 are connected to each other by a connector 112. The connector 112 has a threaded inner surface that screws into threads on the outer surfaces of the temporary mounting body 103 and the PC steel rod 104. The center hole jack 109 includes a cylinder 109a fixed to the additional ram chair 108 and a piston 109b that extends and retracts relative to the cylinder 109a.

When the worker extends the piston 109b from the cylinder 109a, the tensioning member 102 is tensioned and extended. When the extension length of the piston 109b reaches a predetermined length, the worker retracts the piston 109b into the cylinder 109a while the fixing nut 107 is engaged with the ram chair 106. At this time, the tensioning state of the tensioning member 102 is maintained because the fixing nut 107 is engaged with the ram chair 106. By repeating this process, the tensioning member 102 is tensioned to the predetermined tension.

Japanese Patent Application Laid-Open No. 2005-155081

However, with the tensioning method using the above-mentioned tensioning device, when the tendon is long, the amount of elongation in the tendon increases, resulting in an excessively large device, and the need for a large working space for the erection attachment and PC steel rod to move. Increasing the size of the device increases the risk of the tensioning device tipping over due to the tensioning device's axial center becoming eccentric during tensioning, necessitating the need for a long temporary attachment, which is difficult to manufacture.

This problem was particularly pronounced when FRP was used as the tendon. For example, the elastic modulus of aramid FRP is about one-quarter that of PC steel strands, so the amount of elongation caused by the introduction of prestress in aramid FRP is about four times that of PC steel strands, and the above problem occurred even when the tendon was relatively short.

In light of the above background, the present invention aims to provide a tensioning device and tensioning method for tensioning tendons that minimizes the size of the device and does not require a large working space.

In order to solve the above problem, one aspect of the present invention is a tensioning device (1) for tensioning tendons (3) for introducing prestress into a concrete structure (2), comprising: a plurality of elongated members (7) extending in the tensioning direction, having threads on their outer peripheral surfaces, and connected to the tendons in series along the tensioning direction; a connector (8) that detachably connects adjacent elongated members to each other and has an outer contour located inside the outer contour of the elongated members as viewed from the tensioning direction; a ram chair (9) supported by the concrete structure on the relaxation side of the tensioning direction and through which the elongated members are inserted; and a ram chair (9) that can be threaded onto the outer peripheral surface of the elongated members, allowing the connector to slide in the tensioning direction and extending along the outer peripheral surface of the elongated members. the jack (12) includes a base (12a) supported by the additional ram chair on the relaxation side of the tensioning direction, a displacement portion (12b) displaceable between a first position and a second position located on the tensioning side of the tensioning direction relative to the first position, and through which the elongated member can be inserted; and a second nut (14) threadably engageable with the outer peripheral surface of the elongated member, capable of sliding the connecting device, and capable of being engaged with the displacement portion while threadedly engaged with the outer peripheral surface of the elongated member. Here, the terms "tension side" and "relaxation side" refer to relative positions of a member of interest in the tensioning direction, with the "tension side" meaning a position in a direction that increases tension in the tensioning direction of the tendon, and the "relaxation side" meaning a position in a direction that decreases tension.

In this configuration, multiple elongated members are connected in series, ensuring the axial center of the tensioning device necessary for tensioning work. Furthermore, because multiple elongated members can be disconnected, extension members that have moved to the tensioning side of the jack and completed their role can be removed, preventing an increase in the working space required on the tensioning side of the jack. Because the first nut and second nut thread onto the outer peripheral surface of a common elongated member, the portion threaded onto the first nut can be threaded onto the second nut as the tensioning work progresses. Compared to when the portions threaded onto the first and second nuts are separate, the length of the tensioning device in the tensioning direction can be shortened, preventing the tensioning device from becoming too large.

In the above aspect, the tension member (3) may include fiber-reinforced plastic, and the multiple elongated members (7) may be composed of a cylindrical temporary setting body (5) positioned on the most relaxed side in the tensioning direction and into which the end of the tension member is inserted and fixed, and one or more extension members (6) positioned on the tensioning side of the temporary setting body in the tensioning direction.

This aspect allows tensioning of the tendon, which contains fiber-reinforced plastic, without damaging it.

In the above aspect, each of the elongated members (7 (5, 6)) includes a connecting tubular portion (5b, 6a) having a thread on its inner surface at the end in the tension direction facing the other elongated member, and the connector (8) includes a bolt portion (8b) provided at both ends in the tension direction and threadedly engaging with the connecting tubular portion of the elongated member, and an intermediate portion (8a) positioned between the two bolt portions and having an outer circumferential surface with a portion of the circle cut out when viewed from the tension direction.

This configuration allows the connector to be coaxial with the elongated member, and the maximum outer diameter of the connector can be made smaller than the outer diameter of the elongated member. As a result, a simple structure can be realized in which the outer contour of the connector is positioned inside the outer contour of the elongated member when viewed from the tensioning direction, and the first nut and second nut that thread onto the outer peripheral surface of the elongated member can slide in the tensioning direction on the connector.

In the above aspect, the device may further include a nut rotation device (15) that rotates the first nut (10), wherein the additional ram chair (9) includes a side peripheral wall (11a) having a first groove (11b) and a second groove (11c) that are circumferentially spaced from each other, and the nut rotation device may include a support portion (17), a driving portion (18) rotatably supported on the support portion and disposed outside the additional ram chair (11), a driven portion (19) rotatably supported on the support portion and disposed inside the additional ram chair, engaging with the outer peripheral surface of the first nut to rotate together with the first nut, and a band-shaped body (20) that engages with the driving portion and the driven portion to link the rotation of the driving portion and the driven portion, and the nut rotation device may be incorporated into the additional ram chair by partially inserting the support portion into the first groove and the second groove.

In this embodiment, the nut rotation device is incorporated into the additional ram chair, so there is no increased risk even if an operator artificially applies force to rotate the first nut.

In the above aspect, the first groove (11b) and the second groove (11c) have a length in the tension direction that is longer than the distance between the opposing ends of the adjacent elongated members (7), and the side peripheral wall (11a) of the additional ram chair (11) has a window portion (11d) that penetrates radially and opens toward the relaxed side.

In this embodiment, the nut rotation device is movable along the first and second grooves, allowing the first nut received in the additional ram chair to be moved in one go from one elongated member to another elongated member connected via a connector. Furthermore, although the first nut can be moved away from the ram chair, the operator can check through the window whether the first nut is engaged with the ram chair.

In one aspect of the present invention, a method for tensioning the tensioning member (3) using the tensioning device (1) of the above aspect includes repeating the following steps: with the second nut (14) engaged with the displacement portion (12b), displacing the displacement portion from the first position to the second position, and moving the tension-side end of the adjacent elongated member (7) on the relaxed side of the elongated member to which the second nut is threaded toward the tension side relative to the displacement portion at the first position; with the first nut (10) threaded onto the outer peripheral surface of the elongated member and engaged with the ram chair (9), displacing the displacement portion from the second position to the first position; and with the second nut (10) threaded onto the outer peripheral surface of the elongated member and engaged with the ram chair (9), threading the second nut onto the elongated member whose tension-side end has been moved toward the tension side relative to the displacement portion at the first position, and removing the elongated member connected to the tension side of the elongated member from the elongated member.

In this configuration, multiple elongated members are connected in series, ensuring the axial center of the tensioning device necessary for tensioning work. Furthermore, by removing the extension member that has completed its role, the increase in working space required on the tensioning side of the jack is suppressed. Because the first nut and second nut are threaded onto the outer peripheral surface of a common elongated member, as described above, the length of the tensioning device in the tensioning direction can be shortened, suppressing the tensioning device from becoming too large.

The above aspects make it possible to provide a tensioning device and tensioning method for tensioning tendons that minimizes the size of the device and does not require a large working space.

FIG. 1 is a partial cross-sectional side view showing a tensioning method for tensioning a tendon using a tensioning device according to an embodiment. 1A and 1B are diagrams showing a provisionally set body according to an embodiment (A: cross-sectional view along line A-A in FIG. 1B, B: front view (viewed from the tension direction)) 1A and 1B are cross-sectional views of an extension member according to an embodiment of the present invention; FIG. 1B is a front view of the extension member according to an embodiment of the present invention; FIG. 1C is a cross-sectional view of the extension member according to an embodiment of the present invention; 1A and 1B are diagrams showing a connector according to an embodiment (A: side view, B: cross-sectional view along line B-B in FIG. A); 1A and 1B are diagrams showing first and second nuts according to an embodiment (A: side view, B: front view (viewed from the tensioning direction)); FIG. 1 is a perspective view showing a tensioning device according to an embodiment; FIG. 1 is a side view showing an additional ram chair according to an embodiment; FIG. 1 is a perspective view showing a nut rotation device and a first nut according to an embodiment; FIG. 1 is a side view showing a tensioning device according to the prior art;

The tensioning device 1 according to the embodiment will now be described with reference to the drawings. As shown in FIG. 1, the tensioning device 1 is used to tension tendons 3 that introduce prestress into a concrete structure 2. The tendons 3 are composed of rods containing fiber-reinforced plastic (FRP) such as aramid fiber, carbon fiber, or glass fiber. A duct 4 is provided within the concrete structure 2, and multiple tendons 3 may be arranged in one duct 4. The tensioning device 1 tensions the tendons 3 by pulling them at one end. For the purposes of this description, the direction in which tension in the tendon 3 increases (toward the right in FIG. 1) will be referred to as the tensioning side, and the direction in which tension in the tendon 3 decreases (toward the left in FIG. 1) will be referred to as the relaxation side.

The tensioning device 1 comprises a long member 7 including a temporary setting attachment 5 fixed to the end of the tension member 3 and one or more extension members 6 connected in series to the temporary setting attachment 5; a connector 8 connecting adjacent long members 7 to each other; a ram chair 9 supported by the concrete body 2 at the slack side end; a first nut 10 threaded onto the long member 7 and engaged with the ram chair 9; an additional ram chair 11 supported by the ram chair 9 at the slack side end; a jack 12 supported by the additional ram chair 11 at the slack side end; a second nut 14 threaded onto the long member 7 and engaged with the jack 12 via a support plate 13; and a nut rotation device 15 (see Figure 6) that rotates the first nut 10. Note that the temporary setting attachment 5 in Figure 1(A) and the ram chair 9 in Figure 1 are shown in the same cross section as the concrete body 2, and the temporary setting attachment 5 in Figures 1(B) to 1(F) and other components of the tensioning device 1 in Figure 1 are shown from the side.

Of the multiple elongated members 7 connected in series along the tension direction, the one elongated member 7 positioned furthest from the relaxed side is the temporary setting member 5, and one or more elongated members 7 positioned further from the temporary setting member 5 on the tension side are the extension members 6.

As shown in Figures 1 and 2, the temporary attachment 5 is composed of a cylindrical steel pipe extending in the tensioning direction. In the tensioning direction, the temporary attachment 5 is divided into an anchoring tube portion 5a, which is located on the slack side and used to anchor the tendon 3, and a connecting tube portion 5b, which is located on the tensioning side and used to connect to the extension member 6. The anchoring tube portion 5a is longer than the connecting tube portion 5b. The outer surface of the temporary attachment 5 is provided with a thread onto which a first nut 10 can be threaded. After the end of the tendon 3 is inserted into the anchoring tube portion 5a, a filler material 16, such as non-shrink mortar, is filled in. This secures the end of the tendon 3 to the temporary attachment 5. The temporary attachment 5 may also be composed of a material other than steel, such as resin.

As shown in Figures 1 and 3, each extension member 6 is made of a cylindrical steel pipe extending in the tensioning direction. The extension member 6 is divided into two connecting tubular portions 6a provided at both ends in the tensioning direction and an intermediate portion 6b defined between the two connecting tubular portions 6a. The outer surface of the extension member 6 is provided with threads onto which a first nut 10 and a second nut 14 can be threaded. The connecting tubular portion 6a is used for connecting to the temporary attachment body 5 or another extension member 6. It is preferable that each extension member 6 has the same shape. The extension members 6 may also be made of materials other than steel, such as resin.

As shown in Figures 1 and 4, the connector 8 includes an intermediate portion 8a and bolt portions 8b protruding from the intermediate portion 8a at both ends in the tensioning direction. When viewed from the tensioning direction, the intermediate portion 8a has a circular shape with a diameter smaller than the outer diameter of the elongated member 7, with notches 8c cut out by two straight lines arranged parallel to each other across the central axis. The connecting tubular portion 5b (see Figure 2) of the temporary attachment 5 and the connecting tubular portion 6a (see Figure 3) of the extension member 6 are threaded on their inner surfaces, and the bolt portion 8b can be threaded into these connecting tubular portions 6a. By threading the two bolt portions 8b of the connector 8 into the connecting tubular portions 5b and 6a, the temporary attachment 5 and the extension member 6 are connected to each other, or two extension members 6 are connected to each other. The intermediate portion 8a has a smooth surface with no threads on its outer periphery. As a result, the first nut 10 and second nut 14 can separate from one elongated member 7, slide in the tensioning direction on the middle portion 8a, and smoothly engage with the other elongated member 7, regardless of the screw positions on the two elongated members 7 that they connect to each other.

As shown in Figures 1 and 6, the ram chair 9 is a temporary steel frame that has a box or cylindrical shape with a pair of open sides facing each other and through holes in the two bottom walls facing each other in the tensioning direction through which the elongated member 7 is inserted, and is supported at its relaxed end face by the concrete frame 2. Because the elongated member 7 extending in the tensioning direction is inserted through the two bottom walls of the ram chair 9, the elongated member 7 is partially received within the ram chair 9. The tensioning end face of the ram chair 9 can engage a first nut 10 that is threaded onto the outer peripheral surface of the temporary attachment 5 or extension member 6.

As shown in FIG. 5, the first nut 10 and the second nut 14 may be members of the same shape. The first nut 10 and the second nut 14 may be members of different shapes, but the effective diameter and pitch of the threads on their inner surfaces are the same. Furthermore, the effective diameter and pitch of the threads on the outer surfaces of the temporary attachment 5 and all of the extension members 6 are the same so that they can be threaded together.

As shown in Figures 1, 6, and 7, the additional ram chair 11 is a temporary, cylindrical steel frame. The bottom surface of the relaxed side is supported on the bottom surface of the tensioned side of the ram chair 9, through which the temporary mounting member 5 and extension member 6 are inserted. The abutting surfaces of the additional ram chair 11 and the ram chair 9 are provided with an engagement structure (not shown) for aligning their respective centers. The additional ram chair 11 receives the first nut 10 within its cylindrical interior. The peripheral side wall 11a of the additional ram chair 11 has a first groove 11b and a second groove 11c that are spaced apart circumferentially and extend in the tensioned direction, as well as a window 11d that penetrates radially and opens toward the relaxed side. The first groove 11b and the second groove 11c have lengths in the tensioned direction that are longer than the distance between the opposing ends of adjacent elongated members 7 connected by the connector 8. The first groove 11b and the second groove 11c are used to incorporate a nut rotation device 15 into the additional ram chair 11. Through the window 11d, the worker can visually check whether the first nut 10 is engaged with the tension side end face of the ram chair 9.

As shown in Figures 1 and 6, the jack 12 is a well-known center-hole jack. The jack 12 includes a base 12a including a steel cylinder supported on the additional ram chair 11 at its slack end, and a displacement portion 13b including a piston that can be displaced in the tensioning direction relative to the base 12a. The jack 12 is fixed to the additional ram chair 11 by a fastener (not shown) such as a screw. The displacement portion 13b displaces between a first position where it is substantially recessed inside the base 12a and a second position where it partially protrudes from inside the base 12a toward the tensioning side. The jack 12 may be a well-known jack other than a center-hole jack.

As shown in Figures 6 and 8, the nut rotation device 15 includes a support portion 17, a driving portion 18 rotatably supported by the support portion 17 and disposed outside the additional ram chair 11, a driven portion 19 rotatably supported by the support portion 17 and disposed inside the additional ram chair 11, and a band-shaped body 20 such as a chain that engages with the driving portion 18 and the driven portion 19 to link the rotation of the driving portion 18 and the driven portion 19.

As shown in Figure 8, the support part 17 includes a U-shaped frame 17a, a grip part 17b that is connected to the outside of the frame 17a and can be grasped by an operator, and a pair of covers 17c that are attached to the frame 17a with fasteners such as screws (not shown) so as to sandwich the frame 17a from the tension direction and rotatably support the driving part 18 and the driven part 19 (the cover 17c located on the front side of the paper is not shown in Figure 8).

The driving unit 18 includes a plate portion 18a that is perpendicular to the tensioning direction, a shaft portion 18b that protrudes from the center of the plate portion 18a in the tensioning direction and engages with a tool 21 such as a ratchet wrench, and a sprocket 18c that is fixed to the periphery of the plate portion 18a and engages with the band-shaped body 20.

The driven part 19 includes a socket part 19a that engages with the outer peripheral surface of the first nut 10, and a sprocket 19b that is fixed to the periphery of the socket part 19a and meshes with the band-shaped body 20. The socket part 19a is clamped by the fork-shaped cover 17c from a direction perpendicular to the tensioning direction, thereby rotatably supporting the driven part 19 on the support part 17. The band-shaped body 20 causes the driven part 19 to rotate in conjunction with the driving part 18. Therefore, by rotating the driving part 18 with the tool 21, the driven part 19 rotates, and the first nut 10 engaged with the driven part 19 screws forward or backward. The tool 21 may be a hand tool other than a ratchet wrench, or a power tool.

As shown in Figures 6 to 8, the curved portion of the U-shaped frame 17a is positioned outside the additional ram chair 11, one end of the U-shaped frame 17a is inserted into the first groove 11b of the additional ram chair 11, and the other end of the U-shaped frame 17a is inserted into the second groove 11c of the additional ram chair 11. A follower 19 is positioned inside the additional ram chair 11 and connected to both ends of the U-shaped frame 17a. Therefore, the nut rotation device 15 has a ring shape that surrounds the portion between the first groove 11b and the second groove 11c on the side peripheral wall 11a of the additional ram chair 11, and is incorporated into the additional ram chair 11.

Referring to Figure 1, we will explain how to tension the tensioning member 3 using the tensioning device 1.

First, as shown in Figure 1(A), a worker inserts the tendon 3, which has a temporary attachment 5 fixed to its end, into the duct 4 of the concrete structure 2.

Next, as shown in Figure 1(B), the worker connects multiple extension members 6 in series to the temporary attachment 5 via connectors 8, and abuts the ram chair 9 against the concrete structure 2 so that the temporary attachment 5 and extension members 6 are inserted inside. The worker threads the first nut 10 onto the outer surface of the extension member 6 and engages the first nut 10 with the ram chair 9 from the tensioning side in the extension direction. Note that the end of the tendon 3 opposite to the one shown in the figure has a configuration that is approximately symmetrical to the state shown in Figure 1(F). That is, the end of the tendon 3 is fixed to the temporary attachment 5, the ram chair 9 is supported by the concrete structure 2, and the first nut 10 is threaded onto the outer surface of the temporary attachment 5 and engaged with the ram chair 9.

Next, as shown in Figure 1(C), the worker connects the additional ram chair 11 to the ram chair 9 from the tension side so that the extension member 6 is inserted into the additional ram chair 11 and the jack 12, and connects the jack 12 to the additional ram chair 11 from the tension side. At this time, the displacement portion 12b of the jack 12 is positioned in the first position. The worker threads the second nut 14 onto the outer peripheral surface of the extension member 6 positioned most on the tension side, and engages the second nut 14 with the tension side end surface of the displacement portion 12b of the jack 12 via the support plate 13.

Next, the worker displaces the displacement portion 12b to the second position, as shown in FIG. 1(D). At this time, because the second nut 14 threaded onto the extension member 6 is engaged with the displacement portion 12b, the tension member 3 is pulled toward the tensioning side in the tensioning direction, generating a tensile force in the tension member 3 and stretching it. This causes the position of the first nut 10 to also attempt to displace toward the tensioning side. Therefore, in parallel with or alternating with this operation, the worker rotates the first nut 10 using the nut rotation device 15 (see FIG. 6) to engage the first nut 10 (see FIG. 1(B)) with the ram chair 9. Next, with the first nut 10 threaded onto the outer peripheral surface of the extension member 6 or temporary mounting body 5 and engaged with the ram chair 9, the worker displaces the displacement portion 12b to the first position. At this time, because the first nut 10 is engaged with the ram chair 9, the tension generated in the tension member 3 is maintained, and the displacement portion 12b moves away from the second nut 14. The worker then rotates the second nut 14 to move it toward the relaxed side, thereby engaging the displacement portion 12b via the support plate 13. These steps are repeated until the second nut 14 is threaded onto the second elongated member 7 from the tensioning side, i.e., until the tension-side end of the second elongated member 7 from the tensioning side is positioned closer to the tensioning side than the displacement portion 12b in the first position. Note that the jack 12 is selected taking into consideration the stroke length of the displacement portion 12b, the connector 8, and the extension member 6 so that the first nut 10 does not slide on the connector 8 when the displacement portion 12b is returned to the first position, i.e., so that the first nut 10 can engage with the ram chair 9 while threaded onto the elongated member 7.

Once the second nut 14 is threaded onto the second elongated member 7 from the tensioned side, the worker removes the extension member 6 positioned on the most tensioned side of the connected elongated members 7, as shown in Figure 1 (E).

The worker then repeatedly tensions the tension member 3 with the jack 12 and removes the extension member 6, which is positioned on the most tensioned side of the long member 7 during connection. Once the tension member 3 has been tensioned to the specified tensile force, the worker removes the second nut 14, bearing plate 13, jack 12, and additional ram chair 11, completing the tensioning work as shown in Figure 1 (F).

The worker then injects a filler (not shown) such as non-shrink mortar into the duct 4. Once the filler has hardened, the worker removes the first nut 10 and ram chair 9, cuts the tendon 3 between the concrete body 2 and the temporary anchor 5, and removes the temporary anchor 5.

The effects of the tensioning method for tensioning the tensioning member 3 using the tensioning device 1 are explained below.

As shown in Figure 1, multiple long members 7 are connected in series, ensuring the axial center of the tensioning device 1 necessary for tensioning work. Because the tensioning member 3 is tensioned via the temporary setting attachment 5, tensioning can be performed without damaging the tensioning member 3.

Because the connection between multiple long members 7 can be released, the extension member 6 can be removed after moving to the tension side of the jack 12 and completing its role. This prevents the increase in working space required on the tension side of the jack 12 from increasing.

Because the first nut 10 can be threaded not only onto the temporary setting attachment 5 but also onto the extension member 6 to which the second nut 14 is threaded, the length of the temporary setting attachment 5 can be shortened, preventing the tensioning device 1 from becoming too large.

When connecting different components with threads on their outer surfaces, the threads tend to misalign, hindering nut rotation at the connection points. In the above embodiment, the connector 8 connecting adjacent elongated members 7 has an outer contour smaller than that of the elongated members 7 when viewed from the tensioning direction. This allows the first nut 10 and second nut 14 to slide along the connector 8 connecting the elongated members 7 in the tensioning direction. This facilitates smooth movement of the first nut 10 and second nut 14 from one elongated member 7 to another elongated member 7 connected via the connector 8. Furthermore, the smooth surface of the intermediate portion 8a of the connector 8 further facilitates smooth sliding of the first nut 10 and second nut 14 along the intermediate portion 8a. Furthermore, the bolt portion 8b of the connector 8 is threadedly engaged with the connecting tube portions 5b and 6a of the elongated members 7. This means that the bolt portion 8b is necessarily located inside the outer contour of the elongated members 7 when viewed from the tensioning direction. Therefore, if the connector 8 is formed so that the outer contour of the middle portion 8a is positioned inside the outer contour of the elongated member 7 when viewed from the tensioning direction, the first nut 10 and second nut 14 will be able to slide in the tensioning direction on the connector 8. In this way, a structure that allows the first nut 10 and second nut 14 to slide in the tensioning direction on the connector 8 can be achieved with a simple configuration.

As shown in Figure 4, a notch 8c is provided in the middle portion 8a of the connector 8, allowing a wrench (not shown) or similar tool to be engaged with the middle portion 8a, facilitating the connection and disconnection of the elongated member 7.

As shown in Figure 6, the nut rotation device 15 is incorporated into the additional ram chair 11, reducing the risk that an operator will accidentally apply force in a direction that tilts the tensioning device 1, i.e., in a direction that crosses the tensioning direction, thereby improving work safety.

As shown in Figures 1, 6, and 7, the first groove 11b and the second groove 11c of the additional ram chair 11 have a length in the tension direction that is longer than the distance between the opposing ends of adjacent elongated members 7. This allows the first nut 10 received in the additional ram chair 11 to be moved simultaneously from one elongated member 7 to another elongated member 7 connected via the connecting device 8.

Because the additional ram chair 11 has a window 11d, the worker can easily confirm that the first nut 10 is engaged with the ram chair 9 when displacing the displacement portion 12b of the jack 12 to the first position.

This concludes the description of specific embodiments, but the present invention is not limited to the above embodiments and modifications, and can be implemented in a wide variety of ways. Instead of FRP rods, PC steel materials such as PC steel rods and PC steel strands may be used as tendons. For example, when PC steel rods are used as tendons, a temporary attachment may not be used, and a connecting tube with an internal thread may be formed at the end of the PC steel rod. The connector may be threaded onto this connecting tube to connect the PC steel rod tendon and the extension member. Furthermore, when PC steel strands are used as tendons, a temporary attachment may be attached to the outer periphery of the PC steel strands, and the temporary attachment may be used as a permanent anchor. A toothed belt may be used instead of a chain as the band-shaped member, and toothed pulleys may be used as the sprockets in the driving and driven parts.

DESCRIPTION OF SYMBOLS 1: Tensioning device 3: Tensile member 5: Temporarily set attachment 5b: Connecting tube portion 6: Extension member 6a: Connecting tube portion 7: Long member 8: Connector 8b: Bolt portion 8c: Notch portion 9: Ram chair 10: First nut 11: Additional ram chair 11b: First groove 11c: Second groove 11d: Window portion 12: Jack 12a: Base portion 12b: Displacement portion 14: Second nut 15: Nut rotation device 17: Support portion 18: Driving portion 19: Follower portion

Claims (6)

A tensioning device for tensioning tendons for introducing prestress into a concrete structure,
a plurality of elongated members extending in a tensioning direction, having threads on their outer peripheral surfaces, and connected to the tendons in series along the tensioning direction;
a connector that detachably connects adjacent elongate members to each other and has an outer contour that is located inside the outer contour of the elongate members when viewed from the tensioning direction;
a ram chair supported by the concrete frame on the relaxed side in the tension direction and through which the elongated member is inserted;
a first nut that can be threaded onto the outer peripheral surface of the elongated member, that can slide the connector in the tensioning direction, and that can be locked onto the ram chair while threaded onto the outer peripheral surface of the elongated member;
an additional ram chair supported by the ram chair on the relaxed side in the tension direction, through which the elongated member is inserted and which receives the first nut;
a jack including a base supported by the additional ram chair on the relaxation side of the tension direction, and a displacement portion displaceable between a first position and a second position located on the tension side of the tension direction relative to the first position, and through which the elongated member can be inserted;
A tensioning device comprising: a second nut that can be threaded onto the outer peripheral surface of the elongated member, that can slide the connecting device, and that can be engaged with the displacement portion while threaded onto the outer peripheral surface of the elongated member. the tendon includes fiber-reinforced plastic;
The tensioning device described in claim 1, wherein the multiple elongated members are composed of a temporary setting body having a cylindrical shape that is positioned on the most relaxed side in the tensioning direction and into which the end of the tensioning material is inserted and fixed, and one or more extension members that are positioned on the tensioning side of the temporary setting body in the tensioning direction. Each of the elongated members includes a connecting tubular portion having a thread on an inner circumferential surface at an end portion in the tensioning direction that faces the other elongated member,
The tensioning device described in claim 1, wherein the connecting device includes a bolt portion provided at both ends in the tensioning direction and threadedly engaged with the connecting tubular portion of the elongated member, and an intermediate portion disposed between the two bolt portions and having an outer peripheral surface with a portion of a circle cut out when viewed from the tensioning direction. Further provided is a nut rotation device that rotates the first nut,
the additional ram chair includes a peripheral side wall having a first groove and a second groove spaced circumferentially from one another;
The nut rotation device is
A support part;
a prime mover rotatably supported by the support and disposed outside the additional ram chair;
a follower portion rotatably supported by the support portion, disposed inside the additional ram chair, and engaging with an outer peripheral surface of the first nut to rotate together with the first nut;
a band-shaped body that engages with the driving part and the driven part to couple the rotations of the driving part and the driven part,
The tensioning device according to claim 1 , wherein the support portion is partially inserted into the first groove and the second groove, thereby incorporating the nut rotation device into the additional ram chair. the first groove and the second groove have a length in the tensioning direction that is longer than a distance between opposing ends of the adjacent elongated members,
5. The tensioning device according to claim 4, wherein the side peripheral wall of the additional ram chair has a window portion that penetrates radially and opens toward the slack side. A method for tensioning the tendon using the tensioning device according to any one of claims 1 to 5,
a step of displacing the displacement portion from the first position to a second position while the second nut is engaged with the displacement portion, and moving an end portion of the tension side of the elongated member adjacent to the relaxation side of the elongated member to which the second nut is being threaded toward the tension side relative to the displacement portion at the first position;
displacing the displacement portion from the second position to the first position in a state in which the first nut is threadedly engaged with the outer peripheral surface of the elongated member and engaged with the ram chair;
a tensioning method including repeating the steps of threading the second nut onto the elongated member whose end on the tensioning side has been moved closer to the tensioning side than the displacement portion at the first position, and removing the elongated member that was connected to the tensioning side of the elongated member from the elongated member.