Tension structure and construction method for tension structure

Abstract

To provide a tension structure and a construction method for the tension structure that can reduce the amount of tension material protruding from a concrete structure.SOLUTION: The tensioning structure tensions a concrete structure 31 in a predetermined direction with a tendon 32, with one end in the predetermined direction serving as a fixed end and the other end serving as a tensioned end. The tendon 32 has a thread of a predetermined length formed at one end, and only a fixed plate 35 having a bearing area that bears the tension force transmitted by the tendon 32 as a bearing pressure on the concrete structure 31 is screwed onto the thread at the one end, and the tension force is transmitted by a screw joint formed by screwing the thread formed on the fixed plate 35 with the thread formed on the one end of the tendon 32.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tensioning structure in which a concrete structure is tensioned by a tendon, and a construction method for the tensioning structure. [Background technology]

[0002] A known tensioning structure for tensioning a concrete structure with tendons is, for example, the structure described in Patent Document 1. In the tensioning structure of Patent Document 1, one end of the tendon is fixed within a recess formed in the concrete structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-70917 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the amount of protrusion of the tendon into the recess increases, a deeper recess is required and a larger amount of concrete is required. Therefore, there is a need to reduce the amount of protrusion of the tendon from the concrete structure. [Means for solving the problem]

[0005] The tensioning structure that solves the above problem tensions a concrete structure in a predetermined direction with a tendon, with one end in the predetermined direction as a fixed end and the other end as a tensioned end. The tendon has a thread of a predetermined length formed at one end, and only a fixed plate having a bearing area that bears the tension force transmitted by the tendon as a bearing pressure on the concrete structure is screwed onto the thread at the one end, and the tension force is transmitted by a threaded connection between the thread formed on the fixed plate and the thread formed at the one end of the tendon.

[0006] A construction method for a tensioning structure that solves the above-mentioned problems is a construction method for a tensioning structure in which a concrete structure is tensioned in a predetermined direction by a tendon, one end of which in the predetermined direction is a fixed end and the other end is a tensioned end. The construction method for a tensioning structure includes a tendon installation step of installing the tendon so that a fixing plate threadedly connected to a thread formed on one end of the tendon is exposed from the concrete structure and the thread formed on the other end of the tendon protrudes from the concrete structure, a concrete pouring step of pouring concrete into a formwork for the concrete structure after the tendon is installed, and a tensioning step of tightening a nut onto the thread formed on the other end of the tendon while applying a tensile load to the tendon. This allows the amount of protrusion of the tendon from the fixed end of the concrete structure to be reduced.

[0007] In the tensioning structure having the above configuration, it is preferable that the fixing plate is embedded in the concrete structure so that a surface of one end of the fixing plate in the predetermined direction is substantially flush with a surface of the other end of the concrete structure in the predetermined direction, thereby further reducing the amount of protrusion of the tensioning member from the concrete structure.

[0008] In the tensioning structure having the above configuration, the fixing plate may be provided so as to abut from outside against a surface of the concrete structure on one end side in the predetermined direction, thereby reducing the amount of protrusion of the tensioning member from the concrete structure.

[0009] In the tensioned structure having the above configuration, the concrete structure is preferably a part of the upper structure or lower structure of the seismic isolation structure, and has a separation space at one end side of the concrete structure in the predetermined direction that allows relative horizontal displacement of the seismic isolation structure. In this way, even if the upper structure displaces horizontally relative to the lower structure, the displacement can be tolerated by the separation space.

[0010] The tensioned structure of the above configuration may have a living space, a walkway, or a staircase at one end of the concrete structure in the predetermined direction. By allowing horizontal relative displacement of the upper structure with respect to the lower structure, a living space, a walkway, a staircase, etc. can be installed at one end of the concrete structure in the predetermined direction.

[0011] In the tensioning structure having the above configuration, it is preferable that the tendons are enclosed in sheath tubes, so that the gaps between the tendons and the sheath tubes are filled with a filler, thereby suppressing corrosion of the tendons and integrating the tendons with the concrete structure.

[0012] In the tensioning structure having the above configuration, the tendons are preferably unbonded tendons, which eliminates the need to fill the area around the tendons with filler, thereby shortening the construction period.

[0013] In the tensioning structure having the above configuration, the tendon may have a periphery attached to concrete, thereby reducing costs and shortening construction time. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side view schematically showing the general configuration of a seismic isolation structure. [Figure 2] FIG. 1 is a cross-sectional view schematically illustrating one embodiment of a tensioning structure. [Figure 3] 1 is a flowchart showing one embodiment of a construction method for a tension structure. [Figure 4] This is a side view schematically showing the chipped portion of the existing retaining wall. [Figure 5] FIG. 2(a) is a side view showing a schematic state in which the anchor has been driven, and FIG. 2(b) is a plan view showing a schematic state in which the anchor has been driven. [Figure 6] FIG. 2(a) is a side view showing a schematic diagram of the state in which anchors and reinforcing bars are arranged, and FIG. 2(b) is a plan view showing a schematic diagram of the state in which anchors and reinforcing bars are arranged. [Figure 7]FIG. 2A is a side view showing a schematic diagram of the state in which the tendons are installed, and FIG. 2B is a plan view showing a schematic diagram of the state in which the tendons are installed. [Figure 8] FIG. 1(a) is a side view showing a schematic state in which the side formwork has been installed, and FIG. 1(b) is a plan view showing a schematic state in which the side formwork has been installed. [Figure 9] FIG. 2 is a side view schematically showing the state in which the concrete structure is installed, and is a view schematically showing the state in which a tensile load is applied to the tendons. [Figure 10] FIG. 2 is a side view schematically showing the state in which the concrete reinforcement body is installed. [Figure 11] FIG. 1 is a side view schematically showing a state in which a concrete structure is supported by temporary support columns. [Figure 12] This is a side view schematically showing the seismic isolation lower foundation body, seismic isolation device, and seismic isolation upper foundation body installed. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of a tension structure and a construction method for the tension structure will be described with reference to Figures 1 to 12. The tension structure is used to reinforce columns supported by seismic isolation devices, for example, when performing seismic isolation construction to install seismic isolation devices in an existing building.

[0016] As shown in FIG. 1, the seismic isolation structure 10 has a substructure 11, an upper structure 12, and a seismic isolation device 13 provided between the substructure 11 and the upper structure 12. The substructure 11 has a mat slab 15, a lower foundation 16, and a seismic isolation lower foundation body 17. The mat slab 15 is newly installed if it is not already installed in an existing building. The lower foundation 16 is composed of the existing column lower part 26B and a concrete reinforcing body 19 that reinforces the existing column lower part 26B. The seismic isolation lower foundation body 17 is joined to the upper surface of the lower foundation 16. The lower end of the seismic isolation device 13 is joined to the upper surface of the seismic isolation lower foundation body 17.

[0017] The superstructure 12 has columns 21 and beams 22. The superstructure 12 has existing column upper parts 26A below the joints between the columns 21 and beams 22. The existing column upper parts 26A are reinforced by a tensioning structure 30. In the tensioning structure 30, tension is applied to a rectangular parallelepiped concrete structure 31 that covers the existing column upper parts 26A by tensioning members 32 that extend in a predetermined direction. The tensioning members 32 extend left-right or perpendicular to the plane of the paper in Figure 1. The existing column upper parts 26A and the tensioning structure 30 constitute the upper foundation, which is part of the superstructure 12.

[0018] A seismic isolation upper foundation 18 is joined to the underside of the existing column upper portion 26A and the concrete structure 31. The upper end of the seismic isolation device 13 is joined to the underside of the seismic isolation upper foundation 18. In addition, a separation space 20 is formed on the outdoor side of the concrete structure 31 to allow relative horizontal displacement of the upper structure 12 with respect to the substructure 11.

[0019] (tension structure) As shown in Fig. 2, the tendon 32 has a thread of a predetermined length at both ends of the PC steel. The tendon 32 is an unbonded tendon, with the portion of the tendon 32 that is to be placed inside the concrete structure 31 enclosed in a sheath tube 34.

[0020] One end of the tendon 32 is an end that is placed outdoors. One end of the tendon is a fixed end that is fixed to the fixed plate 35 by a screw joint. The fixed plate 35 is formed in a rectangular shape. A thread that threads onto the thread of the tendon 32 is formed through the center of the fixed plate 35. The fixed plate 35 is provided so as to be exposed from the concrete structure 31. More specifically, the fixed plate 35 is embedded in the concrete structure 31 so that the outer surface 35s is approximately flush (almost on the same plane) with the side surface 31s of the concrete structure 31. Note that "approximately flush" here means that the outer surface 35s is flush with the side surface 31s of the concrete structure 31 and that some deviation caused by errors during construction, etc. is allowed.

[0021] The other end of the tendon 32 is an end that is placed indoors. The other end of the tendon 32 is a tensioning end that tensions the tendon 32. The other end of the tendon 32 protrudes from the concrete structure 31. A nut 38 is threadedly engaged with the protruding portion of the other end of the tendon 32. A bearing plate 39 is provided between the concrete structure 31 and the nut 38. The nut 38 is tightened while a tensile load is applied to the tendon 32.

[0022] In this tensioning structure 30, the tension of the tendon 32 is transmitted at one end to the fixed plate 35 by a screw connection between the tendon 32 and the fixed plate 35. The fixed plate 35 has a bearing area that bears the tension of the tendon 32 as a bearing pressure on the concrete structure 31. At the other end of the tendon 32, a bearing plate 39 has a bearing area that bears the tension of the tendon 32 as a bearing pressure on the concrete structure 31.

[0023] (Construction method of tension structure) An example of a construction method for the tension structure described above will be described. In this embodiment, the construction method for the tension structure will be described using an example in which an existing retaining wall 25 (see FIG. 4) is installed around an existing building. Note that the series of steps in the construction method for the tension structure described below is one of the steps performed in the construction method for seismic isolation work. In addition, in the following, it is assumed that the formwork installed for pouring concrete is removed after the concrete has hardened.

[0024] As shown in Figure 3, the construction method of the tensioning structure 30 includes a chipping process (step S101), an anchor placing process (step S102), a reinforcement process (step S103), a tensioning member installation process (step S104), a concrete placing process (step S105), and a tensioning process (step S106).

[0025] As shown in Figure 4, before the seismic isolation work is carried out, the joints between the column 21 and the beam 22 are supported by an existing reinforced concrete column 26. The outdoor side of the existing column 26 is surrounded by an existing retaining wall 25.

[0026] In the chipping process (step S101), the existing retaining wall 25 on the outdoor side of the existing column 26 is chipped. Specifically, the hatched portion 40 of the existing retaining wall 25 is chipped. As a result, a space that functions as the separation space 20 described above is formed.

[0027] As shown in Figures 5(a) and 5(b), in the anchor driving step (step S102), anchors 43 are driven into the existing column 26. The anchors 43 are driven into the portion surrounded by the concrete structure 31. The anchors 43 are driven so as to extend in the extension direction of the beam 22. The anchors 43 are driven so as to line up in the circumferential direction of the existing column 26 and also in the extension direction of the existing column 26.

[0028] In addition, before or after the anchor driving process, a bottom formwork 47, which is one of the forms for the concrete structure 31, is installed. The bottom formwork 47 is installed at a position corresponding to the lower end of the existing column upper part 26A (see Figure 1). The bottom formwork 47 is supported on the mat slab 15 by a plurality of supports 48.

[0029] As shown in FIGS. 6(a) and 6(b), in the reinforcement step (step S103), reinforcing bars 46 to be embedded in the concrete structure 31 are installed. The reinforcing bars 46 are installed so as to surround the existing columns 26. The reinforcing bars 46 are installed so as to be supported by spacers (not shown), such as mortar blocks, placed in the bottom formwork 47. Note that only some of the reinforcing bars 46 are shown in FIGS. 6(a) and 6(b).

[0030] As shown in Figures 7(a) and 7(b), in the tendon installation process (step S104), the tendons 32 are installed in predetermined positions so as to be supported by reinforcing bars 46 (not shown in Figures 7(a) and 7(b)), and a fixing plate 35 is fixed to one end of the tendons 32. The fixing plate 35 may be fixed to the tendons 32 before installation, or may be fixed to the tendons 32 after installation. The tendons 32 are installed so that one end of the fixing plate 35 is exposed from the concrete structure 31 and the other end protrudes from the concrete structure 31. In addition, some of the tendons 32 may be installed so as to pass through through holes formed in the existing columns 26.

[0031] As shown in Figures 8(a) and 8(b), in the concrete pouring step (step S105), a side formwork 49 is installed so as to be in surface contact with the fixed plate 35, and then concrete is poured into the space surrounded by the bottom formwork 47 and the side formwork 49. When the concrete hardens, the concrete structure 31 is formed. Note that in Figure 8(a), the side formwork on the near side of the page is omitted.

[0032] 9, in the tensioning process (step S106), after the support plate 39 is placed, the nuts 38 are tightened to the other ends of the tendons 32 using tensioning jacks 50 while a tensile load is applied to the tendons 32. Once the nuts 38 are tightened using the tensioning jacks 50 for each tendon 32, the construction of the tensioning structure 30 is completed.

[0033] (Continued: Seismic isolation construction method) As shown in Figure 10, once construction of the tensioning structure 30 is complete, the lower foundation reinforcement process is carried out. In the lower foundation reinforcement process, the concrete reinforcement body 19 that constitutes the lower foundation 16 is installed. When installing the concrete reinforcement body 19, first, the reinforcing bars to be embedded in the concrete reinforcement body 19 are arranged. Next, a formwork is installed so as to surround the existing column lower part 26B of the existing column 26. Then, the concrete poured into the formwork hardens, thereby installing the concrete reinforcement body 19.

[0034] As shown in Figure 11, once the concrete reinforcement 19 is installed, a temporary support process and an existing column cutting process are carried out. In the temporary support process, a temporary support column 55, such as a hydraulic jack, that supports the load is installed between the concrete reinforcement 19 and the concrete structure 31. In the existing column cutting process, while the load is supported by the temporary support column 55, a portion of the existing column 26, more specifically, the portion between the existing column upper portion 26A and the existing column lower portion 26B, is cut and removed. This separates the upper foundation (existing column upper portion 26A and concrete structure 31) from the lower foundation 16. In addition, a space is formed between them in which the seismic isolation lower foundation body 17, the seismic isolation device 13, and the seismic isolation upper foundation body 18 can be installed.

[0035] Next, the seismic isolation unit installation process is carried out as shown in Fig. 12. In the seismic isolation unit installation process, the seismic isolation lower foundation body 17, the seismic isolation device 13, and the seismic isolation upper foundation body 18 are installed. In the seismic isolation unit installation process, first, the seismic isolation lower foundation body 17 is installed. The seismic isolation lower foundation body 17 is installed by installing various reinforcing bars such as reinforcing bar anchors to be cast into the lower foundation 16, a lower base plate to which the seismic isolation device 13 is joined, formwork, etc., and then allowing the concrete poured into the formwork to harden.

[0036] Next, the seismic isolation device 13 is installed. The seismic isolation device 13 is installed by being joined to a lower base plate that is integrated with the seismic isolation lower foundation body 17. After installation, an upper base plate that is integrated with the seismic isolation upper foundation body 18 is joined to the seismic isolation device 13.

[0037] Next, the seismic isolation upper foundation body 18 is installed. The seismic isolation upper foundation body 18 is installed by installing various reinforcing bars, such as reinforcing anchors, and formwork to be cast into the upper foundation (existing column upper part 26A and concrete structure 31), and then allowing the concrete cast into the formwork to harden. From the viewpoint of workability, it is preferable that the reinforcing bars used to connect to the upper foundation be installed prior to the installation of the seismic isolation device 13. After the seismic isolation upper foundation body 18 is installed, the temporary support pillars 55 are dismantled, thereby completing the seismic isolation construction.

[0038] The operation and effects of this embodiment will be described. (1) In the tensioning structure 30, only the fixing plate 35, which bears the tension of the tendon 32 as a bearing pressure on the concrete structure 31, is screwed to one end of the tendon 32. This makes it possible to reduce the amount of protrusion of the tendon 32 from the concrete structure 31.

[0039] (2) The fixing plate 35 is embedded in the concrete structure 31 so that the outer surface 35s is substantially flush with the side surface 31s of the concrete structure 31. This allows the tendons 32 to be installed without protruding from the side surface 31s of the concrete structure 31. In addition, the structure of the side formwork 49 installed on one end side of the tendons 32 can be simplified.

[0040] (3) In the seismic isolation structure 10, a separation space 20 is formed between the exterior side of the concrete structure 31 and the existing retaining wall 25 after chipping. This allows the relative horizontal displacement of the superstructure 12 relative to the substructure 11 to be tolerated. Therefore, for example, a living space, a walking space, a staircase, etc. can be installed on one end of the concrete structure 31 in a predetermined direction in which the tendons 32 extend.

[0041] (4) The tendons 32 are unbonded tendons enclosed in the sheath pipes 34 in the concrete structure 31. This eliminates the need to fill the sheath pipes 34 with grout or other filler after the tendons 32 are installed, thereby shortening the construction period.

[0042] This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. The tendons 32 are not limited to unbonded tendons, but may be configured so that concrete is poured while the tendons 32 are enclosed in the sheath tubes 34, and then grout is filled between the tendons 32 and the sheath tubes 34. This makes it possible to integrate the concrete structure 31 and the tendons 32 while suppressing corrosion of the tendons 32.

[0043] The tendon 32 may be configured so that its periphery is attached to concrete, rather than being enclosed in the sheath pipe 34. This reduces costs and shortens the construction period.

[0044] The tensioning structure 30 may be provided not only in the upper structure 12 but also as part of the lower structure 11, for example, in the part where the seismic isolation lower foundation body 17 is joined. The fixing plate 35 may be partially embedded in the concrete structure 31. Alternatively, the fixing plate 35 may not be embedded in the concrete structure 31. That is, the fixing plate 35 may be provided at one end of the tendon 32 so as to abut against the side surface 31s of the concrete structure 31 from the outside and support the side surface 31s. In such a case, in the tendon installation step (step S104), the tendon 32 is installed so that both ends protrude from the concrete structure 31. Then, after the concrete pouring step (step S105), a fixing step is performed in which the fixing plate 35 is fixed to one end of the tendon 32. Even with these configurations, the amount of protrusion of the tendon 32 can be reduced. [Explanation of symbols]

[0045] 10...seismic isolation structure, 11...substructure, 12...superstructure, 13...seismic isolation device, 15...mat slab, 16...lower foundation, 17...seismic isolation lower foundation body, 18...seismic isolation upper foundation body, 19...concrete reinforcement, 20...space, 21...column, 22...beam, 25...existing retaining wall, 26...existing column, 26A...upper part of existing column, 26A...lower part of existing column, 30...tensioning structure, 31...concrete structure, 31s...side, 32...tensioning member, 34...sheath pipe, 35...fixing plate, 35s...outer surface, 38...nut, 39...bearing plate, 40...hatching area, 43...anchor, 46...reinforcing bar, 47...bottom formwork, 48...column, 49...side formwork, 50...tensioning jack, 55...temporary support column.

Claims

1. A tension structure in which a concrete structure is tensioned in a predetermined direction by a tensioning member, one end in the predetermined direction being a fixed end and the other end being a tensioned end, The tendon is A thread of a predetermined length is formed on the one end, Only a fixing plate having a bearing area that bears the tension force transmitted by the tendon as a bearing pressure on the concrete structure is screwed onto the thread at one end, The tension is transmitted by a threaded connection between the screw formed on the fixing plate and the screw formed on the one end of the tendon. tension structure.

2. The fixing plate is The concrete structure is embedded in the concrete structure so that the surface of one end side in the predetermined direction is substantially flush with the surface of one end side in the predetermined direction of the concrete structure. The tensioning structure of claim 1 .

3. The fixing plate is The concrete structure is provided so as to abut from the outside on one end surface in the predetermined direction. The tensioning structure of claim 1 .

4. The concrete structure is a part of a superstructure or a substructure of a seismic isolation structure, A separation space that allows relative horizontal displacement of the seismic isolation structure is provided at one end side of the concrete structure in the predetermined direction. The tensioning structure of claim 1 .

5. The concrete structure has a living space, a walking space, or a staircase on one end side in the predetermined direction. The tensioning structure of claim 1 .

6. The tendon is enclosed in a sheath tube. The tensioning structure of claim 1 .

7. The tendon is an unbonded tendon. The tensioning structure of claim 1 .

8. The tendon is attached to the concrete around its periphery. The tensioning structure of claim 1 .

9. A construction method for a tensioned structure in which a concrete structure is tensioned in a predetermined direction by a tensioning member, one end of which in the predetermined direction is a fixed end and the other end is a tensioned end, a tendon installation process in which the tendon is installed so that a fixing plate threadedly connected to a thread formed at one end of the tendon is exposed from the concrete structure and a thread formed at the other end of the tendon protrudes from the concrete structure; a concrete pouring step of pouring concrete into the formwork of the concrete structure after the tendons are installed; a tensioning step of tightening a nut onto a thread formed on the other end of the tendon while a tensile load is applied to the tendon. Construction method for tension structure.

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