Prestressing member, concrete member joining method, and pile head joint structure

Abstract

To efficiently apply prestress to a joint between adjacent concrete members with a simple configuration and method.SOLUTION: The present invention comprises a plurality of tension members arranged parallelly with a gap therebetween, a support member including a locking plate engaged with one end of the tension members and a strut with an end fixed to the locking plate and arranged in parallel with the tension members, a tension retaining member disposed on the other end of the tension members, which receives a reaction force from the support member to introduce tension into the tension members and retains the introduced tension, and a fixing device disposed between the locking plate and the tension retaining member, which is movable along the tension members and engaged with the tension members.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a prestress introduction member for introducing prestress into concrete, a concrete member joining method, and a pile head joint structure. [Background technology]

[0002] Conventionally, pile head reinforcement structures have been known in which prestress is applied to the pile head joint to reinforce it and resist the pull-out force of a building. For example, in Patent Document 1, when constructing a cast-in-place concrete pile, first, protective bars are attached to a reinforcing bar cage and PC steel wires are inserted into the protective bars. This reinforcing bar cage with protective bars is then inserted into a borehole and concrete is poured.

[0003] Next, the foundation concrete is poured with the PC steel wires pulled out from within the protective reinforcement up to a level above the foundation of the building to be constructed. After the foundation concrete has hardened and the foundation of the building is constructed, the PC steel wires are tensioned on top of the foundation to secure it in place. By applying prestress to the pile head joint in this way, it is expected that the pull-out strength and bending strength will be improved.

[0004] However, the work of applying tension to PC steel wires at the construction site is not only cumbersome but also takes a great deal of time. Therefore, as disclosed in Patent Document 2, the inventors developed a method of connecting a pile to a foundation, in which the lower half of a prestressed member to which tension has been applied in advance is embedded in the concrete on the pile side, and the upper half is embedded in the concrete on the foundation side, and the tension is released after the concrete has hardened. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-220847 [Patent Document 2] Patent Application No. 2023-032220 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the above-mentioned configuration, prestress can be applied to the pile head joint within the desired height range simply by releasing the tension applied to the prestress application member at the construction site, significantly improving workability. However, the prestress application member has a complex structure, as it uses a cylindrical member as the tendon and applies tension using its hollow portion, and a simpler structure is desired.

[0007] The present invention has been made in view of the above-mentioned problems, and its main object is to efficiently apply prestress to the joint between adjacent concrete members using a simple structure and method. [Means for solving the problem]

[0008] In order to achieve this object, the prestress introduction member of the present invention is characterized by comprising: a plurality of tendons arranged in parallel with a gap between them; a support member including a locking plate engaged with one end of the tendons and a strut whose end is fixed to the locking plate and arranged in parallel with the tendons; a tension retaining member arranged on the other end of the tendons, which receives a reaction force from the support member to introduce tension into the tendons and retains the introduced tension; and a fixing device arranged between the locking plate and the tension retaining member, which is movable along the tendons and engaged with the tendons.

[0009] The method for joining concrete members of the present invention is a method for joining concrete members in which one concrete member is constructed and joined to another adjacent concrete member by pouring the other concrete member into the concrete member, and is characterized by comprising the steps of: introducing tension into the tendon of the prestress introduction member of the present invention in advance using the tension retaining member; embedding and fixing one end of the prestress introduction member in the one concrete member; embedding the other end of the prestress introduction member in the other concrete member with the tension retaining member and the fixing device exposed; and abutting the fixing device against the other concrete member after hardening, and then releasing the tension in the tendon.

[0010] The method for joining concrete members of the present invention is characterized in that the one concrete member is a pile body and the other concrete member is a foundation for a building.

[0011] The pile head joint structure of the present invention is characterized by being constructed by the concrete member joining method of the present invention.

[0012] According to the prestress introduction member, concrete member joining method, and pile head joining structure of the present invention, materials that are widely used when applying prestress to concrete, such as PC steel bars, can be used as the tendons that make up the prestress introduction member, and the prestress introduction member can have a simple structure. It becomes possible to do this.

[0013] Furthermore, the prestressing member utilizes a tension-retaining member to allow tension to be introduced into the tendons in advance at the manufacturing plant or construction yard, and the introduced tension can be maintained. Therefore, in the concrete member joining method, prestress can be applied to the desired area between the joints of adjacent concrete members with a simple on-site operation of simply releasing the tension introduced into the prestressing member. This eliminates the need for complicated work such as tension management, greatly improving workability.

[0014] Furthermore, when the adjacent concrete members are a pile body and a foundation, prestress can be applied to the desired height range, including the pile head joint, which is expected to improve not only the pull-out and bending strength of the pile head joint but also the strength of the prestressed area. Furthermore, there are no restrictions on the placement position of the prestressing member in a plan view. Therefore, it can be placed in a rectangular shape in a plan view to avoid interference with the foundation reinforcement, allowing for a high degree of freedom in the design of the pile head joint. [Effects of the Invention]

[0015] According to the present invention, the prestress introduction member has a simple structure, and tension can be introduced into the tendon in advance at a manufacturing factory, etc., and at the site, the simple task of releasing the tension introduced into the prestress introduction member makes it possible to efficiently apply prestress to the desired area, including the joints of adjacent concrete members. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a pile head joint using a prestress introduction member according to this embodiment. [Figure 2] FIG. 1 is a diagram showing a prestress introducing member of the present embodiment (part 1). [Figure 3] FIG. 2 is a diagram showing a prestress introducing member of the present embodiment (part 2). [Figure 4] 1A to 1C are diagrams showing a procedure for joining concrete members using a prestress introducing member according to the present embodiment (part 1). [Figure 5] 10A and 10B are diagrams showing a procedure for joining concrete members using the prestress introducing member of the present embodiment (part 2). [Figure 6] 10A and 10B are diagrams showing other examples of the prestress introducing member of the present embodiment. [Figure 7] 10A and 10B are diagrams showing examples of arrangement of prestress introducing members relative to the head portion of the present embodiment. [Figure 8] FIG. 10 is a diagram showing another example of a pile head joint according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention efficiently applies prestress to the joints between adjacent concrete members, and is particularly suitable for joining the head of a concrete pile to a foundation. Below, we will take as an example a case in which prestress is applied to an area including the pile head joint between a cast-in-place concrete pile and a concrete foundation built on top of the pile, and explain the details with reference to Figures 1 to 8.

[0018] ≪≪≪Pile cap joint structure≫≫≫ As shown in FIG. 1, the head of a building foundation 10 and a pile body 20 are rigidly joined to form a pile head joint 100, and a prestressing member 30 is embedded across both.

[0019] The pile body 20 is made of cast-in-place concrete and is composed of a reinforcing bar cage 21 and concrete 22. The foundation 10 is a cast-in-place concrete structure made of foundation reinforcing bars 11 and concrete 12, and the upper part of the reinforcing bar cage 21 that constitutes the pile body 20 is buried in the concrete 12.

[0020] The prestress introduction member 30 has its lower side (one end) embedded in the head of the pile body 20 and its upper side (the other end) embedded in the foundation 10, and can apply prestress to a predetermined range including the pile head joint 100. Figure 1 shows an example of a state in which prestress is applied to a range of approximately height L1.

[0021] In this way, applying prestress to the pile head joint 100 can improve the pull-out resistance compared to when prestressing is not applied. Also, since the axial compressive force increases, the bending resistance increases. Therefore, even when horizontal and vertical forces act on a building due to an earthquake, for example, the phenomenon of damage to the pile body 20 due to the bending moment generated at the head can be suppressed.

[0022] <<<<Prestressing components>>>> The prestress introducing member 30 is a member into which tension can be introduced in advance at a manufacturing factory or construction yard, and which can be embedded in the concrete 12, 22 while maintaining the introduced tension. Furthermore, the tension can be released after the concrete 12, 22 has hardened.

[0023] As shown in Figures 2(a) and (c), the prestress introduction member 30 comprises four tendons 40 arranged in parallel with a gap between them, a support member 50 arranged so as to be surrounded by the tendons 40, a tension retaining member 60 that introduces tension into the tendons 40 and retains the introduced tension, and a fixing device 70.

[0024] The support member 50 includes a strut 51 and a fixing plate 52. As shown in Figure 2(c), the strut 51 has a cross-shaped cross section, is unbonded over the entire surface, and has the fixing plate 52 fixed to its lower side. The fixing plate 52 is formed in a square shape with an area that is approximately larger than the cross section of the strut 51, and has through holes through which the four tendons 40 pass, formed in the area defined by the cross shape of the strut 51.

[0025] As shown in Figures 2(a) and (c), the tendons 40 are PC steel rods that are longer than the struts 51, and four of them are arranged in parallel so as to surround the struts 51. These may be unbonded coated or in their bare state. Male threads 41, 42 are formed on both ends of each tendon, and the male thread 41 formed on the lower end is inserted into a through-hole formed in the fixing plate 52. A nut 43 is threaded onto this male thread 41 from the underside of the fixing plate 52.

[0026] In this way, the four tendons 40 are respectively arranged within the areas defined by the cross-shaped cross section of the strut 51, and are engaged with the fixed plate 52 in a state in which they will not be pulled out from at least the upper surface side of the fixed plate 52. A tension retaining member 60 is provided on the upper side of the four tendons 40 arranged in this way.

[0027] 2(b) and 3, the tension retaining member 60 includes a retaining plate 61 and a pressing tool 62. The retaining plate 61 is formed in the same shape as the fixed plate 52 that constitutes the support member 50, and as shown in FIG. 2(a), is arranged so that its lower surface abuts against the upper end of the support column 51. Similar to the fixed plate 52, the retaining plate 61 is formed with a through hole through which the tension member 40 passes, and the male screw 42 formed at the upper end of the tension member 40 is inserted into this through hole.

[0028] The pressing tool 62 is a nut that can be threaded onto the male thread 42 formed on the upper end of the tendon 40, and is threaded onto the upper surface of the retaining plate 61. As a result, when the pressing tool 62 is threaded onto the male thread 42 and the retaining plate 61 presses the strut 51, tension can be introduced into the tendon 40. Furthermore, by leaving the pressing tool 62 in place, the state in which tension is introduced into the tendon 40 can be maintained. In this way, a fixing tool 70 is provided between the fixing plate 52 and the retaining plate 61 on the tendon 40, which has the fixing plate 52 of the support member 50 engaged on the lower side and the tension retaining member 60 provided on the upper side.

[0029] 2(a) and 3, the fixing device 70 includes an fixing plate 71 and an fixing plate fixture 72. The fixing plate 71 is a plate material that penetrates the tendon 40, and is disposed between the fixing plate 52 and the retaining plate 61. The fixing plate fixture 72 is a nut that can be threaded onto the male thread 42 formed on the upper end of the tendon 40, and is disposed between the fixing plate 71 and the retaining plate 61 while being fixed to the upper surface of the fixing plate 71.

[0030] <<<<<Pile and foundation joining method>>>> The procedure for applying prestress while joining the head of the pile body 20 and the foundation 10 using the prestress introducing member 30 is as follows.

[0031] ≪≪Preparation process≫≫ Prior to construction, preparation work is carried out for the prestress introduction member 30, as shown in Figure 4(a). The prestress introduction member 30 has the lower ends of the four tendons 40 fastened to the fixing plate 52 that constitutes the support member 50, and a tension retaining member 60 and an anchoring device 70 are placed above each tendon 40.

[0032] The length of each of the struts 51 constituting the tendon 40 and the support member 50 is set so that the fixing plate 52 and the anchoring device 70 can be positioned on either side of the pile head joint 100, as shown in Figure 4(b), and the tension retaining member 60 can be positioned above the uplift surface h1 of the lower half concrete 12a constituting the foundation 10.

[0033] In this state, as shown in Figure 4(a), a desired tension is introduced into the tendon 40 of the prestress introducing member 30. As explained with reference to Figure 2, by screwing a pressing tool 62 onto the male thread 42 and pressing the strut 51 with a holding plate 61, it is possible to apply a reaction force to the strut 51 and introduce tension into the tendon 40. In this way, by changing the screwing position of the pressing tool 62 relative to the male thread 42, it is possible to adjust the tension introduced into the tendon 40.

[0034] <<Pile construction process>> Before or after the preparation process of the prestress introduction member 30, or at the same time, the underground hole H, which has been drilled at the planned construction position of the pile body 20, is filled with a stabilizing solution, and the reinforcing bar cage 21 is erected.

[0035] The prestress introduction member 30, in which tension has been introduced into the tendon 40 in advance in the preparation process described above, is placed at a predetermined position (at a height position spanning the foundation 10 and the pile body 20) in a manner that allows it to be supported by the reinforcing bar cage 21, for example. The prestress introduction member 30 is placed at a position that does not interfere with not only the reinforcing bar cage 21 of the pile body 20 but also the foundation reinforcing bars 11 of the foundation 10.

[0036] After the prestress introduction member 30 is placed at a predetermined planar position and height, concrete 22 is poured into the underground hole H as shown in Figure 4(b). When the concrete 22 hardens, the pile body 20 is constructed with the reinforcing bar cage 21 and the prestress introduction member 30 protruding above the head.

[0037] <<Foundation construction process and prestressing process>> <Constructing the lower half of the foundation> After the concrete 22 has hardened, or around the same time, as shown in FIG. 5(a), the work of placing foundation rebars 11 is carried out in the area of ​​the foundation 10 where construction is planned.

[0038] After this, concrete 12a of the lower half of the foundation 10 is poured, and part of the foundation rebar 11 of the foundation 10 and part of the rebar cage 21, as well as the upper side of the prestress introduction member 30 below the position where the tension retaining member 60 and the fixing device 70 are attached, are buried.

[0039] <Prestressing process> After the lower half concrete 12a of the foundation 10 has hardened, prestress is applied to a predetermined area sandwiching the pile head joint 100 between the pile body 20 and the foundation 10.

[0040] Specifically, as shown in Figure 5(b), the anchoring device 70 is lowered until the anchoring plate 71 constituting the anchoring device 70 abuts against the upturned surface h1 of the lower half concrete 12a of the hardened foundation 10. At this point, the state in which tension is introduced into the tendon 40 is maintained by the tension retaining member 60. When the anchoring plate 71 abuts against the upturned surface h1 of the lower half concrete 12a, the tension introduced into the tendon 40 is released.

[0041] The tension applied to the tendon 40 can be released by removing the tension retaining member 60, as shown in Figure 5(b), or by simply loosening the pressing tool 62. This causes the anchoring plate 71 of the anchoring tool 70 to press the lower half concrete 12a of the foundation 10 from the uplift surface h1. This allows prestress to be applied to a range of approximately height L1, including the pile head joint 100, as shown in Figure 1.

[0042] <Constructing the upper half of the foundation> After these steps are completed, the upper half concrete 12b is poured as shown in Fig. 1, and the exposed parts of the foundation rebar 11, the rebar cage 21, and the prestress introduction member 30 are buried. As the upper half concrete 12b hardens, the foundation 10 and pile body 20 are constructed.

[0043] As described above, the prestress introducing member 30 can use PC steel bars, which are widely used when applying prestress to concrete, as the tendons 40, thereby simplifying the structure of the prestress introducing member 30. Furthermore, by using the tension retaining member 60, tension can be introduced into the tendons 40 in advance at a manufacturing factory or construction yard, and the introduced tension can be maintained.

[0044] Therefore, in the method for joining the pile body 20 and the foundation 10, the desired prestress can be applied to a predetermined height range including the pile head joint 100 between the pile body 20 and the foundation 10 by a simple on-site operation of simply releasing the tension introduced in the prestress introduction member 30. This eliminates the need for complicated work such as tension management, and greatly improves workability.

[0045] 1, prestress is applied to the range of height L1 including the pile head joint 100. Therefore, not only is the pull-out strength and bending strength of the pile head joint 100 improved, but the strength of the range of height L1 where prestress is applied can also be expected to be improved.

[0046] The prestress introduction member, concrete member joining method, and pile head joining structure of the present invention are not limited to the above-described embodiments, and it goes without saying that various modifications are possible within the scope of the spirit of the present invention.

[0047] For example, the cross section of the struts 51 of the support member 50 constituting the prestress introduction member 30 is not limited to a cross shape. It is also possible to use steel pipes with a circular cross section as shown in Fig. 6(a), or shaped steel such as square steel pipes, H-shaped steel, or I-shaped steel as shown in Fig. 6(b). When steel pipes are used for the struts 51 as shown in Fig. 6(a), multiple tendons 40 can be arranged at various intervals as long as they are evenly spaced.

[0048] Therefore, it is possible to adjust the number of tendons 40 provided in the prestress introduction member 30. In this way, since the prestress introduction member 30 allows the length and number of installed tendons 40 to be changed, the number of installed tendons 40 can be adjusted so that the desired prestress can be applied to the pile head joint 100, and one tendon 40 may be placed in the center of the pile body 20, for example.

[0049] Alternatively, multiple prestress introduction members 30 with a reduced number of tendons 40 may be prepared and arranged at intervals within the pile body 20. When multiple prestress introduction members 30 are arranged within the pile body 20, they may be arranged circumferentially along the reinforcing bar cage 21 of the pile body 20, as shown in Figure 7(a), or multiple members may be arranged in a rectangular shape, as shown in Figure 7(b). In this way, there are no restrictions on the arrangement position of the prestress introduction members 30 in a plan view.

[0050] 7(b), it can be placed in any position that avoids interference with the foundation reinforcing bars 11 of the foundation 10 and the reinforcing bar cage 21 of the pile body 20. This allows for a high degree of freedom in the design of the pile head joint 100 between the pile body 20 and the foundation 10.

[0051] Furthermore, the fixing plate 52 of the support member 50 may be formed in any shape, such as a circular shape in plan view or a square shape with rounded corners, as shown in Figure 6(c), as long as it is larger than the cross section of the support column 51 and has an area large enough to provide a through hole through which the tension member 40 passes.

[0052] Furthermore, in this embodiment, an example has been given in which a cast-in-place concrete pile is used for the pile body 20, but the type of pile is not limited in any way. It is possible to use any of a cast-in-place steel pipe concrete pile 80 as shown in Fig. 8, a steel pipe pile, or a precast concrete pile (PHC pile (high-strength prestressed concrete pile), PRC pile (high-toughness prestressed reinforced concrete pile), SC pile (centrifugal concrete pile with outer steel pipe), etc.).

[0053] For example, in a cast-in-place steel pipe concrete pile 80 as shown in Figure 8, the head of the pile body 81 is reinforced with a steel pipe 82. A plurality of pile head reinforcement bars 83 are arranged at equal intervals around the circumferential direction of this steel pipe 82. When prestressing is applied to the pile head joint 100, compressive force is also applied to the steel pipe 82 and the pile head reinforcement bars 83 via the concrete 12, 22.

[0054] This makes it possible to improve the pull-out strength and bending strength without increasing the pile head reinforcement bars 83, and to omit excessive design such as enlarging the cross-sectional diameter of the pile body 20, thereby enabling a rational structure for the pile head joint 100. On the other hand, it is also possible to reduce the pile head reinforcement bars 83 to prevent over-dense reinforcement arrangement, thereby simplifying the reinforcement arrangement in the pile head joint 100.

[0055] Furthermore, when a precast concrete pile is used as the pile body 20, the prestress introduction member 30 is preferably fixed to the concrete filling the hollow portion of the precast concrete pile with concrete filling. The inner circumferential surface of a precast concrete pile is generally made smooth. Therefore, for example, it is recommended to roughen the surface of the precast concrete pile that comes into contact with the concrete filling.

[0056] Furthermore, in this embodiment, after the lower half concrete 12a of the foundation 10 is poured, the anchoring plate 71 of the anchoring device 70 is brought into contact with the raised surface h1 of the foundation 10, thereby applying prestress to the pile head joint 100. However, this method is not limited to this. As shown in Figure 8, after the lower half concrete 12a and the upper half concrete 12b of the foundation 10 are poured and hardened to construct the entire foundation 10, the anchoring plate 71 of the anchoring device 70 may be brought into contact with the raised surface h2 of the upper half concrete 12b, thereby applying prestress to the pile head joint 100. [Explanation of symbols]

[0057] 10 Foundation (one concrete member) 11 Foundation rebar 12 Concrete 12a Lower concrete 12b Upper half concrete 20 Pile body 21 Reinforced Concrete Cage 22 Concrete 23 Steel pipe 30 Prestressing member 40 Tensile material 41 Male thread 42 Male thread 43 Nut 50 Support member 51 Post 52 Fixed plate 60 tension retaining member 61 Holding plate 62 Pressing tool (nut) 70 Fixture 71 Fixing plate 72 Fixing plate fixing device (nut) 80 Cast-in-place steel pipe concrete pile 81 Pile body 82 Steel pipe 83 Pile head reinforcement L1 prestressed height range h1 Upward facing (lower half concrete) h2 Upward facing (upper half concrete) H underground hole

Claims

1. A plurality of tendons arranged in parallel at intervals; a support member including a locking plate that is locked to one end of the tendon, and a support pole that is fixed at an end to the locking plate and is arranged in parallel with the tendon; a tension retaining member that is disposed on the other end side of the tendon, receives a reaction force from the support member, introduces tension into the tendon, and retains the introduced tension; a fixing device disposed between the locking plate and the tension retaining member, movable along the tension member and locked to the tension member; A prestress introducing member comprising:

2. A concrete member joining method in which one concrete member is constructed and joined to another adjacent concrete member, a step of introducing tension into the tendon of the prestress introducing member according to claim 1 in advance using the tension retaining member; a step of embedding and fixing one end of the prestress introducing member in the one concrete member; a step of embedding the other end of the prestress introducing member in the other concrete member with the tension retaining member and the anchoring device exposed; a step of abutting the anchor against the other concrete member after hardening, and then releasing the tension of the tendon; A method for joining concrete members, comprising:

3. The joining method for concrete members according to claim 2, The one concrete member is a pile body, A method for joining concrete members, characterized in that the other concrete member is a foundation for a building.

4. A pile head joint structure constructed by the concrete member joining method according to claim 3.

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