JP3255634B2 - Pile head structure of cast-in-place steel pipe concrete pile - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pile head structure of a cast-in-place steel pipe concrete pile having a pile head formed of a steel pipe concrete pile.

[0002]

2. Description of the Related Art In order to further improve the seismic resistance of a conventional cast-in-place concrete pile with the rise of building structures, as shown in FIG. A cast-in-place concrete pipe pile (composite cast-in-place pile) in which a pile head or the like subjected to shearing force is constituted by a steel pipe concrete pile 110 is used.

[0003] By the way, this steel pipe concrete pile 110
As the joint structure of the pile head consisting of
Conventionally, (1) reinforced cage system, (2) whiskers system, and (3) coupler system have been proposed and put into practical use.

[0004] The steel pipe concrete pile 110 of the above (1) to (3)
In any case, the joint structure between the pile head made of and the footing 109 minimizes the protruding length of the steel pipe concrete pile 110 to the footing 109 and mainly serves as a reinforcing bar (hereinafter, referred to as “anchoring bar”). Is used for fixing.

[0005] Among them, the rebar cage system of (1) is shown in FIG.
As shown in (a), a pre-assembled reinforced basket 102a is inserted into a steel pipe 101 constituting a cast-in-place steel pipe concrete pile, and the upper end of the reinforced basket 102a is extended to a construction position of a footing 109. After being temporarily fixed, the concrete 106 is fixed in the steel pipe 101 by being poured into the steel pipe 101, and the reinforcing bar 102a is used as a fixing bar.

In the beard streak method (2), as shown in FIG. 7 (b), it is fixed on the outer peripheral surface of a steel pipe 101 constituting a cast-in-place steel pipe concrete pile at substantially regular intervals by pre-installation or post-installation. The lower end of the streak 102b is welded, and the upper end of the fixing streak 102b is extended to the position where the footing 109 is constructed.

[0007] The coupler system of (3) is shown in FIG.
As shown in the figure, the coupler 103 is welded to the outer peripheral surface of the steel pipe 101 forming the cast-in-place steel pipe concrete pile at substantially equal intervals, and after removing the excess concrete, the coupler 103 is fixed to the coupler 103 with a threaded reinforcing bar. The lower end of the streak 102c is screwed in, fixed by performing grout injection or tightening with a lock nut.
2c is extended to the construction position of the footing 109.

[0008]

[Problems to be Solved by the Invention] By the way, the above (1) to
Of the joint structures of (3), the reinforced cage system of (1) is the lowest cost and highly reliable structure, but it cannot be used alone due to the recent rise in building structures. It is usually used in combination with the beard streak method of (2) and the coupler method of (3), which requires welding work to fix the anchoring streaks, resulting in low work efficiency and workability. However, there is a problem that costs are required. In addition, in the case of this rebar cage system, the interval between the rebar cage 102a and the steel pipe 101 is usually set to be about 3.0 to 3.5 times the diameter of the rebar. It was difficult to set accurately. Further, in the beard streak method (2) and the coupler method (3), the fixing streaks 102b and 102c are fixed to the outer peripheral surface of the steel pipe 101 directly or via the coupler 103, respectively, only by welding bonding force. For this reason, there is a limit in realizing the currently required improvement in the holding power of the anchoring bars for the steel pipe concrete pile 110 without increasing the cost.

The present invention has been made in view of the above-mentioned problems of the joint structure between a pile head and a footing made of a steel pipe concrete pile, and has realized an improvement in the holding force of anchoring bars to the steel pipe concrete pile without increasing the cost. It is an object of the present invention to provide a pile head structure of a cast-in-place steel pipe concrete pile where possible.

[0010]

In order to achieve the above object, the pile head structure of the cast-in-place steel pipe concrete pile according to the present invention is provided on the inner peripheral surface of the steel pipe constituting the cast-in-place steel pipe concrete pile at substantially regular intervals. , The lower part of the anchoring muscle consisting of high-strength rebar,
The distance between the anchoring muscle and the steel pipe is set to be within 1.5 times the diameter of the anchoring muscle, and an anchoring member is arranged at at least one end of the anchoring muscle. Steel pipe concrete pile where it extends to
In the pile head structure of the above, using the screw rebar as anchoring muscle,
Use female thread members such as lock nuts and couplers as fixing members
And a female screw member arranged at the lower end of the anchor
The fixing member is welded to the inner peripheral surface of the steel pipe .

The pile head structure of the cast-in-place steel pipe concrete pile has a structure in which the lower part of the anchoring bar made of high-strength steel is fixed to the inner peripheral surface of the steel pipe constituting the cast-in-place steel pipe concrete pile at substantially regular intervals. By setting the distance from the steel pipe to 1.5 times or less the diameter of the anchoring bar, the number of anchoring bars can be increased as compared with the reinforced cage system, and the steel bar can be punched inside the steel pipe. The holding power of the anchoring streaks by the concrete to be provided can be improved. In addition, by using anchoring bars made of high-strength rebar, it is possible to reduce the number of anchoring bars required to join a pile head made of a steel pipe concrete pile and a footing with a required strength. In addition to the arrangement of the lower portion of the anchoring muscle with the spacing between the anchoring muscle and the steel pipe set within 1.5 times the diameter of the anchoring muscle, the clearance between adjacent anchoring muscles should be increased. Can be.

In particular, by disposing the anchoring member at at least one end of the anchoring bar, the anchoring member serves as an anchor for the anchoring bar, thereby improving the joint strength between the pile head made of steel pipe concrete pile and the footing. it can.

[0013] In addition, it is possible to use a screw rebar as an anchoring bar.
Simplifies work such as connecting anchoring muscles on site
And can improve work efficiency
In addition, it can improve the integrity with concrete
You.

Furthermore, a female screw disposed at the lower end of the anchoring muscle
Welding the fixing member made of the member to the inner peripheral surface of the steel pipe
With high reliability, the anchoring muscle can be fixed to the steel pipe.
Can be done.

In this case, it is desirable to use a reinforcing bar having a yield point of 490 N / mm ² or more (according to JIS Z 2241) as the high-strength reinforcing bar.

As a result, the number of fixing streaks can be greatly reduced as compared with the case where a reinforcing bar (yield point: 390 N / mm ² ) which has been widely used in the past is used.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pile head structure of a cast-in-place steel pipe concrete pile according to the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an embodiment of a pile head structure of a cast-in-place steel pipe concrete pile according to the present invention. The pile head structure of the cast-in-place steel pipe concrete pile is composed of an anchoring bar 2 made of a high-strength threaded rebar at substantially equal intervals on the inner peripheral surface of the steel pipe 1 constituting the cast-in-place steel pipe concrete pile installed in the ground 7.
Is arranged with the distance d between the anchoring muscle 2 and the steel pipe 1 set within 1.5 times the diameter D of the anchoring muscle, and the upper part of the anchoring muscle 2 is extended to the footing construction position. The configuration is as follows. A lock nut 31 as a fixing member can be screwed into an upper end portion of the fixing streak 2 extending to the footing construction position, and a lower end of the fixing streak 2 located in the steel pipe 1 as necessary. A lock nut 32 as a fixing member can be screwed into the portion. In addition, the fixing line 2
The lock nut 32 screwed to the lower end of the steel pipe 1 can be welded to the inner peripheral surface of the steel pipe 1 if necessary. In this case, after the lock nut 32 is welded to the inner peripheral surface of the steel pipe 1,
The lower end of the fixing streak 2 is screwed and fixed. Further, a fixing hoop 4 for fixing and holding the intermediate position of the anchoring streak 2 by temporary welding to the upper end surface of the steel pipe 1 is attached to the leg member 5.
Can be arranged through. Fixation of the anchoring muscle 2,
The holding can be performed using a member such as a pin.

In this case, as shown in FIG. 2, a spiral steel pipe having a projection 11 for improving the integrity with the concrete 6 cast inside the steel pipe 1 is formed on the inner peripheral surface of the steel pipe 1, as shown in FIG. It is desirable to use.

The anchoring bar 2 made of a high-strength thread rebar has a yield point of 490 N / mm ² or more and a tensile strength of 620 N / mm ^2.
N / mm ² or more, more preferably a yield point of 685 N /
mm ² or more, a tensile strength of 860N / mm ² or more of rebar (JI
According to SZ2241. For example, it is desirable to use “High-strength screw control (USD685)” (trade name) manufactured by Kobe Steel, Ltd., whereby a reinforcing bar (yield point: 390 N / mm ² ), which has been widely used as a fixing bar, is conventionally used. Compared to the case of using a reinforcing bar, the number of anchoring bars is significantly increased (when using a reinforcing bar having a yield point of 685 N / mm ² or more, 4
0% or more), thereby improving the work efficiency and workability of the work of arranging the steel pipe 1 in combination with the fact that the distance s between the adjacent anchoring streaks 2 can be increased. Can be.

Further, as in this embodiment, the lock nuts 31 and 32 may be simply screwed into the fixing member 2 made of a high-strength threaded reinforcing bar. , 32, a grout material can be injected and, as shown in FIG. 3, fixing plates 31c, 32c separately prepared can be tightened by lock nuts 31a, 32a and couplers 31b, 32b. . In this case, the fixing members do not necessarily need to be disposed at both ends of the fixing streaks 2, and may be disposed at only one of the upper end and the lower end. If necessary, a fixing member such as a coupler 32b attached to the lower end of the fixing streak 2 can be welded to the inner peripheral surface of the steel pipe 1.

In this embodiment, a high-strength threaded reinforcing bar is used as the anchoring bar 2, but an anchoring bar made of a high-strength bar (including deformed bar) is used. On the inner peripheral surface of the steel pipe 1, the distance d between the anchoring streaks and the steel pipe 1 can be set at substantially equal intervals within 1.5 times the diameter D of the anchoring streaks. Accordingly, the fixing streaks can be fixed to the inner peripheral surface of the steel pipe 1 by welding or the like.
The fixing of the anchoring muscle is performed before the steel pipe 1 is built in the borehole.
The work can be performed by a so-called post-installation method or by a so-called post-installation method after removing the excess concrete from the cast-in-place concrete pile. Also in this case, it is desirable to provide an appropriate fixing member on the fixing streak.

The pile head structure of the cast-in-place steel pipe concrete pile is constructed such that the upper end portion and, if necessary, the inner peripheral surface of the steel pipe 1 constituting the cast-in-place steel pipe concrete pile to be installed in the ground 7 at substantially equal intervals. The lower end of the fixing bar 2 made of a high-strength threaded rebar in which lock nuts 31 and 32 as fixing members are screwed to the lower end, and the distance d between the fixing bar 2 and the steel pipe 1 is set to 1 of the diameter D of the fixing bar. Set and arrange within 5 times,
The upper end of the anchoring line 2 is extended to the footing construction position, and the intermediate position of the anchoring line 2 is fixed and held. Then, concrete is cast on the ground 7 including the inside of the steel pipe 1 to construct a footing.

As described above, by setting the interval between the anchoring bar 2 made of a high-strength threaded reinforcing bar and the steel pipe 1 within 1.5 times the diameter of the anchoring bar 2, the number of anchoring bars 2 can be reduced. And the holding power of the anchoring streaks 2 by the concrete poured into the steel pipe 1 can be improved,
The lock nuts 31 and 32 become anchors of the anchoring muscle 2,
The joint strength between the pile head made of steel pipe concrete pile and the footing can be improved.

The diameter of the anchoring bars 2, the number of the anchoring bars 2, the length of insertion of the anchoring bars 2 into the steel pipes 1 constituting the cast-in-place steel pipe concrete pile, the anchoring bars 2 upward from the steel pipes 1
Can be set in accordance with a joint structure between a pile head and a footing made of a steel pipe concrete pile, which is conventionally widely used.

Next, FIG. 4 shows a first reference example of the pile head structure of the cast-in-place steel pipe concrete pile of the present invention. As shown in FIG. 4 (c), the pile head structure of this cast-in-place steel pipe concrete pile is composed of a lower anchoring bar 21 and an upper anchoring bar 22, and a lower anchoring bar consisting of a high-strength screw bar. The streaks 21 and the upper anchoring streaks 22 are connected to each other by a coupler 33 as a connecting member at a position near the upper end of the steel pipe 1 constituting the cast-in-place steel pipe concrete pile to be installed in the ground 7. The lower fixing streaks 21 are arranged on the inner peripheral surface of the steel pipe 1 at substantially equal intervals, with the interval between the lower fixing streaks 21 and the steel pipe 1 set within 1.5 times the diameter of the fixing streaks. Starting from the point that the upper fixing streaks 22 are extended to the footing construction position, a lock nut as a fixing member is screwed to the upper end portion of the upper fixing streaks 22 extending to the footing construction position. Further, if necessary, a lock nut as a fixing member can be screwed into the lower end of the lower fixing streak 21 located in the steel pipe 1. The location is the same as the pile head structure of the cast steel pipe concrete pile. The coupler 33 as a connection member screwed to the upper end of the lower fixing streaks 21 can be fixed by temporary welding to the inner peripheral surface of the steel pipe 1 as necessary. Further, as the coupler 33 as the connecting member, a coupler whose outer peripheral surface is formed in an irregular shape (including a “screw wiper”) can be used, thereby improving the integration between the coupler 33 and the concrete to be cast. be able to.

The pile head structure of the cast-in-place steel pipe concrete pile is constructed such that a connection member is formed on the inner peripheral surface of the steel pipe 1 constituting the cast-in-place steel pipe concrete pile installed in the ground 7 at substantially equal intervals and at the upper end portion as a connecting member. The lower anchoring bar 21 made of a high-strength reinforcing bar provided with the coupler 33 is disposed with the distance between the lower anchoring bar 21 and the steel pipe 1 set within 1.5 times the diameter of the lower anchoring bar 21 and temporarily fixed. (FIG. 4 (a)). And coupler 33
After the upper opening of the coupler 33 is closed by disposing a closing member 34 such as a temporary threaded screw piece (FIG. 4 (b)), concrete 6 is cast and the cast-in-place steel pipe concrete pile is removed. To construct. In this case, in addition to the above-mentioned temporary storage screw pieces, a synthetic resin plug member, an easily removable irregular-shaped filler, or the like, is used as the closing member 34 in such a manner that the upper opening of the coupler 33 is closed. Any member that can prevent the provided concrete from entering the upper opening of the coupler 33 can be used. In the case where a temporarily-inserted screw is used as the closing member 34, the temporarily-inserted screw is screwed into the coupler 33, and the lower end surface of the temporarily-inserted screw is brought into contact with the upper end surface of the lower anchoring streak 21. There is an advantage that the lower fixing streaks 21 can be firmly fixed to the coupler 33, but the fixing between the lower fixing streaks 21 and the coupler 33 can also be performed by injecting a grout material or tightening with a lock nut. After constructing the cast-in-place steel pipe concrete pile and removing the excess concrete, the closing member 3 closing the upper opening of the coupler 33 was removed.
4 and the upper anchoring bar 22 made of high-strength steel is connected to the lower anchoring bar 21 buried in the cast-in-place steel pipe concrete pile via a coupler 33, and the upper anchoring bar 22 is extended to the footing construction position. (FIG. 4C). Thereafter, concrete is cast on the ground 7 to build a footing.

As described above, the anchoring bars are constituted by the lower anchoring bars 21 and the upper anchoring bars 22, and the lower anchoring bars 21 and the upper anchoring bars 22 are constructed in a place-punched steel pipe concrete pile in the ground 7. At the position near the upper end of the steel pipe 1, by connecting with a coupler 33 as a connecting member,
After constructing the cast-in-place steel pipe concrete pile and performing the work of removing the excess concrete, it is possible to connect the upper fixation streaks 22 via the coupler 33 to the lower fixation streaks 21 buried in the cast-in-place steel pipe concrete pile, Therefore, the work of removing excess concrete can be efficiently performed, and the occurrence of accidents such as damage to fixing streaks during the removal of excess concrete can be prevented.

Next, FIG. 5 shows a second reference example of the pile head structure of the cast-in-place steel pipe concrete pile of the present invention. The pile head structure of the cast-in-place steel pipe concrete pile of FIG.
As shown in (c), the anchoring bar composed of the high-strength screw bar is composed of the lower anchoring bar 21 and the upper anchoring bar 22, and the lower anchoring bar 21 and the upper anchoring bar 22 are installed in the ground 7. Steel pipes that make up steel piles in place
Are connected by a coupler 33 as a connecting member at a position near the upper end. Then, the lower anchoring muscles 21 and the lower anchoring muscles 2 are provided on the inner peripheral surface of the steel pipe 1 at substantially equal intervals.
Starting from the point that the distance between the steel anchor 1 and the steel pipe 1 is set within 1.5 times the diameter of the anchoring streaks, and the upper anchoring streaks 22 are configured to extend to the footing construction position. Upper anchor muscle 2 extended to the footing construction position
A lock nut as a fixing member can be screwed into the upper end of the second fixing member 2, and a lock nut as a fixing member can also be screwed into the lower end of the lower fixing streak 21 located in the steel pipe 1 as necessary. The basic configuration, such as the ability to be screwed, is the same as the pile head structure of the cast-in-place steel pipe concrete pile of the above embodiment and the first reference example. The coupler 33 as a connection member screwed to the upper end of the lower fixing streaks 21 can be fixed by temporary welding to the inner peripheral surface of the steel pipe 1 as necessary. Further, a coupler 33 as a connecting member
Can be used in which the outer peripheral surface is formed in an irregular shape (including a "screw wiper"), whereby the integration of the coupler 33 and the concrete to be cast can be improved.

The pile head structure of the cast-in-place steel pipe concrete pile has a lower anchoring bar made of high-strength rebar at substantially equal intervals on the inner peripheral surface of the steel pipe 1 constituting the cast-in-place steel pipe concrete pile installed in the ground 7. 21 is provided with the interval between the lower anchoring streak 21 and the steel pipe 1 set within 1.5 times the diameter of the lower anchoring streak 21, temporarily fixed, and made of foamed resin at the upper end of the lower anchoring streak 21. A curing cap 35 such as the one shown in FIG.
(A)). In this case, the temporary fixing of the lower fixing streaks 21 is performed, for example, by temporarily welding a fixing hoop (not shown) to an arbitrary position of the lower fixing streaks 21 and attaching the lower fixing streaks 21 via an appropriate spacer (not shown). It can be performed by temporarily welding to the steel pipe 1. After the concrete 6 is cast and a cast-in-place steel pipe concrete pile is constructed, the excess concrete is removed, the curing cap 35 is removed, and a coupler as a connection member is connected to the upper end of the lower anchoring streak 21. 33 is provided (FIG. 5B). afterwards,
Lower anchorage 21 buried in a steel-pipe concrete pile
Then, the upper anchoring bar 22 made of a high-strength reinforcing bar is connected via a coupler 33, and the upper anchoring bar 22 is extended to the footing construction position (FIG. 5C). In this case,
If necessary, the lower fixing streaks 21 and the upper fixing streaks 22 and the coupler 33 can be fixed by injecting a grout material or tightening with a lock nut. afterwards,
The footing is constructed by placing concrete on the ground 7.

As described above, the anchoring bars are constituted by the lower anchoring bars 21 and the upper anchoring bars 22, and the lower anchoring bars 21 and the upper anchoring bars 22 are formed in a place-punched steel pipe concrete pile in the ground 7. At the position near the upper end of the steel pipe 1, by connecting with a coupler 33 as a connecting member,
After constructing the cast-in-place steel pipe concrete pile and performing the work of removing the excess concrete, it is possible to connect the upper fixation streaks 22 via the coupler 33 to the lower fixation streaks 21 buried in the cast-in-place steel pipe concrete pile, For this reason, the work of removing the excess concrete can be performed more efficiently, and it is possible to prevent the occurrence of an accident such as damage to the fixing streaks during the removal of the excess concrete.

[0032]

According to the pile head structure of the cast-in-place steel pipe concrete pile of the present invention, the anchoring bar composed of the high-strength rebar is provided at substantially equal intervals on the inner peripheral surface of the steel pipe constituting the cast-in-place steel pipe concrete pile. By arranging the lower portion so that the interval between the anchoring bar and the steel pipe is set within 1.5 times the diameter of the anchoring bar, the number of anchoring bars can be increased as compared with the reinforced cage system. In addition, it is possible to improve the holding power of the anchoring streaks by the concrete cast into the inside of the steel pipe. In addition, by using anchoring bars made of high-strength rebar, it is possible to reduce the number of anchoring bars required to join a pile head made of a steel pipe concrete pile and a footing with a required strength. In addition to the arrangement of the lower portion of the anchoring muscle with the spacing between the anchoring muscle and the steel pipe set within 1.5 times the diameter of the anchoring muscle, the clearance between adjacent anchoring muscles should be increased. Thus, the work efficiency and workability of the work of arranging the anchoring streaks can be improved, and the cost required for this can be reduced.

In particular, by disposing the anchoring member at at least one end of the anchoring bar, the anchoring member serves as an anchor for the anchoring bar, and the joint strength between the pile head made of steel pipe concrete pile and the footing can be improved. it can.

Further , it is possible to use a threaded reinforcing bar as an anchoring bar.
Simplifies work such as connecting anchoring muscles on site
And can improve work efficiency
In addition, it can improve the integrity with concrete
You.

Further, a female screw disposed at the lower end of the anchoring muscle
Welding the fixing member made of the member to the inner peripheral surface of the steel pipe
With high reliability, the anchoring muscle can be fixed to the steel pipe.
Can be done.

In addition, a yield point of 490 N / m
By using a reinforcing bar of m ² or more, the number of fixing bars can be significantly reduced as compared with the case of using a reinforcing bar (yield point: 390 N / mm ² ) which has been widely used in the past.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a pile head structure of a cast-in-place steel pipe concrete pile of the present invention, (a) is a longitudinal cross-sectional view,
(B) is a sectional view taken along the line AA of (a), and (c) is a sectional view of B of (a).
FIG. 4 is a cross-sectional view taken along line B.

FIG. 2 shows a steel pipe used for a pile head structure of a cast-in-place steel pipe concrete pile according to the present invention, wherein (a) shows a state where concrete is cast inside, and (b) shows a state before concrete is poured inside. Is shown.

FIG. 3 shows an example of disposing a fixing member with respect to a fixing streak;
(A) is a plan view, (b) is a front view, and (c) is a bottom view.

FIG. 4 is a longitudinal sectional view showing a construction step of a first reference example of the pile head structure of the cast-in-place steel pipe concrete pile of the present invention.

FIG. 5 is a longitudinal sectional view showing a construction step of a second reference example of the pile head structure of the cast-in-place steel pipe concrete pile of the present invention.

FIG. 6 is a schematic diagram of a pile head structure of a cast-in-place steel pipe concrete pile.

FIG. 7 is a longitudinal sectional view showing a pile head structure of a conventional cast-in-place steel pipe concrete pile, in which (a) shows a reinforced cage system, (b) shows a beard bar system, and (c) shows a coupler system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel pipe 2 Anchoring bar 21 Lower anchoring bar 22 Upper anchoring bar 31 Anchoring member (lock nut) 32 Anchoring member (lock nut) 33 Connecting member (coupler) 4 Fixed hoop 5 Leg member 6 Concrete 7 Ground

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-230841 (JP, A) JP-A-3-267422 (JP, A) JP-A-9-250143 (JP, A) JP-A-5-250143 230840 (JP, A) JP-A-7-224434 (JP, A) JP 5-26121 (JP, Y2) JP 3-16898 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) E02D 27/12

Claims (2)

(57) [Claims] 1. An inner peripheral surface of a steel pipe constituting a cast-in-place steel pipe concrete pile, at substantially equal intervals, a lower portion of an anchoring bar made of a high-strength reinforcing bar, and an interval between the anchoring bar and the steel pipe is set to one of the diameter of the anchoring bar. .
Placed steel pipe con- troller which is set up within 5 times and is provided with a fixing member at at least one end of the fixing streak so that the upper part of the fixing streak extends to the footing construction position.
In the pile head structure of the cleat pile,
Use a streak to fix the fixing member with a female such as a lock nut or coupler.
Female member using the same member as the
A pile head structure for a cast-in-place concrete pipe pile, wherein a fixing member made of a screw member is welded to an inner peripheral surface of a steel pipe. 2. The pile head structure of a cast-in-place steel pipe concrete pile according to claim 1, wherein the anchoring bar is made of a high-strength reinforcing bar having a yield point of 490 N / mm ² or more.