JP2005105812A - Pile head reinforcing member, and pile head reinforcing structure using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pile head reinforcing member and a pile head reinforcing structure of simple structure for bonding a pile head of a foundation pile to a foundation structure and capable of reducing the work in a construction field to restrict the construction cost low. <P>SOLUTION: In the pile head reinforcing structure, the pile head reinforcing member 1 provided with a plurality of reinforcing bars 4 by welding to extend upward to be connected to an upper structure is bonded to the periphery of a cylindrical steel ring 2 having an inner diameter a little larger than the outer diameter of the pile head 3a of the foundation pile 3 by fitting the cylindrical steel ring 2 on the pile head 3a of the foundation pile 3, filling a space between outside the pile head of the foundation pile 3 and inside the pile head reinforcing member 1 with a filling and solidifying material 6 selected from mortar and cement paste for solidification. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pile head reinforcing member for reinforcing a pile head of a foundation pile and a pile head reinforcing structure using the same.

  Conventionally, as a pile head joint structure for joining a pile head of a foundation pile and a foundation structure such as a footing, as shown in FIGS. 14 (a) (b) (c), a concrete-filled foundation A structure in which the pile head 3a of the pile 3 is directly embedded and joined in the foundation structure 7 such as a footing (hereinafter referred to as “prior art 1”), or a reinforcing bar 8 is disposed in the pile head 3a of the foundation pile 3. A structure in which the upper part of the reinforcing bar 8 is arranged in the foundation structure 7 and is integrally joined to the foundation structure 7 (hereinafter referred to as “prior art 2”), or a plurality of piles 3a on the inside and outside of the pile head 3a of the foundation pile 3 A structure (hereinafter referred to as “Prior Art 3”) in which the barb reinforcing bars 9 are welded and the barb reinforcing bars 9 are arranged in the base structure 7 and joined to the base structure 7 is well known.

Further, in Japanese Patent No. 3176332, as shown in FIG. 15, a reinforcing ring 10 in which a plurality of reinforcing bars 4 are welded to a pile head 3 a of a foundation pile 3 is installed via a spacing member 11, and a reinforcing ring is provided. The concrete 12 is filled between the inside of the pile 10 and the outside of the pile head 3a so as to be integrated, and the reinforcing bar 4 is arranged on the foundation structure 7 and joined to the foundation structure 7 (hereinafter referred to as “prior art 4”). Is disclosed.
JP 2001-220756 A Japanese Patent No. 3176332

  In the prior art 1, since the pile head of the foundation pile is directly embedded in the foundation structure, it is necessary to thicken the foundation, and the root cut surface is dug deeply, and many soil retaining work, residual soil treatment, and backfilling work are required. Thus, the construction cost increases.

  Since prior art 2 is a structure which joins a pile head and a foundation structure with a reinforcing rod, it has a problem that the pile head fixing degree is small and the earthquake resistance is slightly lowered.

  Prior art 3 has to weld the barbs to the pile head at the site, and the welding conditions tend to be severe, such as welding work in a narrow space or flaring welding upright. It has the problem that it is difficult to guarantee.

  Prior art 4 requires a large amount of filled concrete because the reinforcing bars are welded to the inside of the reinforcing ring and the concrete is filled through the gap retaining material between the outer side of the pile head and the inner side of the reinforcing ring. When a horizontal force acts on the pile head due to an earthquake or the like, a shearing force acts between the pile head and the reinforcing ring, so the strength of the filled concrete must be increased to resist the shearing force. Have

  The present invention solves the problems of the prior art, has a simple structure, requires less on-site work, and is less expensive to construct. Pile head reinforcement for joining the pile head to the foundation structure. It aims at providing a member and a pile head reinforcement structure.

  In order to achieve the above object, the present invention is configured as follows.

  1st invention is a pile head reinforcement structure. WHEREIN: On the outer periphery of the cylindrical steel ring which has an inner diameter slightly larger than the outer diameter of the pile head of a foundation pile, several reinforcement bars for connection with a superstructure are upward. Pile head reinforcing member welded to extend to the base, and the cylindrical steel ring is inserted into the pile head of the foundation pile, and the mortar or cement paste is placed between the pile head outer side of the foundation pile and the inner side of the pile head reinforcing member. It joins by filling and solidifying the filling and solidification material selected from these.

  According to a second aspect of the present invention, in the pile head reinforcement structure, a plurality of reinforcing bars for connection with the upper structure are provided on the inner periphery of a cylindrical steel ring having an outer diameter slightly smaller than the inner diameter of the pile head of the foundation pile. A pile head reinforcing member welded so as to extend upward is inserted into the pile head of the foundation pile, and the mortar or cement is inserted between the pile head inside of the foundation pile and the outside of the pile head reinforcing member. It is characterized by being joined by filling and solidifying a filling / solidifying material selected from pastes.

  3rd invention is 1st or 2nd invention. WHEREIN: As for the slight gap dimension of the pile head of a foundation pile, and a pile head reinforcement member, 90% or more part is 3-30 mm with respect to the perimeter L of the said foundation pile. It is characterized by being.

   A fourth invention is the steel according to the first to third inventions, wherein the cylindrical steel ring has a fixing resistance mechanism (a U-shaped hook, a fixing plate, a stud or the like) with an upper structure instead of a reinforcing bar. The bar is welded.

  A fifth invention is characterized in that, in the first to third inventions, an unbond material is applied to a portion of the reinforcing bar welded to the cylindrical steel ring immediately above the steel ring.

A sixth invention is characterized in that, in the fourth invention, an unbond material is applied to a portion immediately above the steel ring of the steel rod welded to the cylindrical steel ring.

  In the first invention and the second invention, a pile head reinforcement structure that can be easily attached to the pile head of the foundation pile at the site without performing welding work at the site, By providing a slight gap between the pile head reinforcing member and the steel ring inside of the pile head or between the pile head inside and the steel ring outside of the pile head reinforcing member, the pile head and the filling / solidifying material and Enables stress transmission between pile head reinforcement and filling / solidifying material.

  In addition, in the third invention, by setting the gap dimension of the narrow part of at least a predetermined range in the circumferential direction (about 90% or more with respect to the circumferential length L of the foundation pile) within a range of 3 mm to 30 mm, Even if it is outside this numerical value, the desired effect of the present invention can be achieved.

  In the fourth invention, a steel rod having a fixing resistance mechanism (such as a U-shaped hook, a fixing plate or a stud) with an upper structure instead of a steel bar outer periphery or a steel bar welded to the inner periphery of a pile head reinforcing member By welding a plurality of pieces, the fixing length with the upper structure can be made shorter than that of the reinforcing bar, and the upper structure can be made smaller. When the superstructure becomes smaller, not only the superstructure concrete and reinforcing bars can be reduced, but also construction costs can be reduced because there are fewer earth retaining work, residual soil treatment, backfilling work, and the like.

  Moreover, in 5th invention and 6th invention, unbonding material is apply | coated to the steel ring outer periphery of a pile head reinforcement material, or the part directly above the steel ring of several reinforcing bars or steel bars welded to an inner periphery. Therefore, when a horizontal force due to an earthquake or the like is applied, the rebar or steel bar part to which the unbond material has been applied can freely rotate. Therefore, when a certain bending moment is applied, the rebar or steel bar part yields. Since the bending moment applied to the pile head of the foundation pile can be reduced, the cross section of the pile head and the cross section of the underground beam can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 to 3 show Embodiment 1 of the present invention, and FIGS. 4 to 6 show Embodiment 2 of the present invention. In each figure, FIG. 1 and FIG. 4 are the perspective views which show the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 1, 2 to the pile head of a foundation pile, FIG. 2 and FIG. 2 is a partial cross-sectional view showing a pile head reinforcing structure in which the pile head reinforcing member according to 2 is fixed to the pile head of the foundation pile, and FIGS. 3 and 6 show the pile head reinforcing member according to Embodiments 1 and 2 of the foundation pile. It is a top view which shows the pile head reinforcement structure fixed to the pile head.

FIG. 7 is a cross-sectional view showing a simple beam 13 connecting two steel pipes as an analysis model for confirming the function and effect of the joint structure according to the present invention, and FIG. 8 is a simple beam 13 shown in FIG. It is a graph which shows the result of the structural analysis at the time of loading 2 points | pieces concentrated load P.
9 to 11 show Embodiments 3, 4, and 5 of the present invention, in which a steel rod having a fixing resistance mechanism (such as a U-shaped hook, a fixing plate, or a stud) with an upper structure is a steel ring 2. It is sectional drawing which shows the pile head reinforcement structure welded to.

In the first embodiment shown in FIGS. 1 to 3, the pile head reinforcing member 1 has a cylindrical steel ring 2. The steel ring 2 has an inner diameter that is slightly larger than the outer diameter of the pile head 3 a of the foundation pile 3. The main element of the present invention is a slight gap between the steel ring 2 and the pile head 3a. The slight gap is determined on the basis of the gap size derived from the analysis results described later with reference to FIGS. 7 and 8. The filling / solidifying material 6 selected from mortar or cement paste is used for the small gap. By filling and solidifying, the foundation pile 3 and the steel ring 2 can be integrated to exhibit the strength and rigidity required for the pile head joint. Incidentally, the thickness of the steel ring 2 may be the same as or less than the thickness t of the foundation pile 3 described later. Moreover, length L4 of this steel ring 2 may be adjusted in the range in which the following formula | equation (1) is materialized with the outer diameter D of this foundation pile 3. FIG.
L4 = D / 2 to D / 8 (1)

  On the outside of the steel ring 2, the lower ends of the plurality of reinforcing bars 4 are fixed by welding. The reinforcing bars 4 extend upward, and the length of the reinforcing bars 4 is determined in consideration of the fixing property to a foundation structure such as a concrete footing foundation, underground beam, and independent foundation. The reinforcing bar 4 shown in the first embodiment does not have a fixing resistance structure for improving the fixing property with the upper structure. However, as shown in FIGS. Alternatively, a steel rod 14 having a fixing resistance mechanism (U-shaped hook, fixing plate, stud, etc.) with the upper structure may be welded to the steel ring 2.

  That is, in Embodiment 3 of FIG. 9, the lower end part of the some steel bar 14 which has the U-shaped hook 15 in the upper part is being fixed to the outer side of the steel ring 2 by welding. In Embodiment 4 of FIG. 10, the lower end part of the some steel rod 14 which has the fixing plate 16 in the upper part is being fixed to the outer side of the steel rings 2 by welding. In Embodiment 5 of FIG. 11, the lower end part of the some steel rod 14 which has the stud 17 in the upper part is fixed to the outer side of the steel ring 2 by welding. When the steel bar 14 having a U-shaped hook, a fixing plate or a stud is used instead of the reinforcing bar 4 as described above, the length extending upward of the steel bar 14 can be shortened, and a concrete footing foundation or underground beam Can reduce the size of foundation structures such as independent foundations. (In addition, since the other structure of Embodiment 3-5 is the same as Embodiment 1, detailed description is abbreviate | omitted).

Next, in Embodiment 2 shown by FIGS. 4-6, the pile head reinforcement member 1a has the cylindrical steel ring 2a. The steel ring 2 a has an outer diameter slightly smaller than the inner diameter of the pile head 3 a of the foundation pile 3. An important factor also in the second embodiment is a slight gap between the steel ring 2a and the pile head 3a. This slight gap is a gap size derived from the test results described later in FIGS. 7 and 8. By filling and solidifying the small gap with a filling / solidifying material 6 selected from mortar or cement paste. By integrating the foundation pile 3 and the steel ring 2, it is possible to exhibit the strength and rigidity required for the pile head joint. Incidentally, the thickness of the steel ring 2 may be the same as or less than the thickness t of the foundation pile 3 described later. Moreover, length L4 of this steel ring 2 may be adjusted in the range in which the following formula | equation (1) is materialized with the outer diameter D of this foundation pile 3. FIG.
L4 = D / 2 to D / 8 (1)

  Inside the steel ring 2a, the lower ends of the plurality of reinforcing bars 4 are fixed by welding. The reinforcing bars 4 extend upward, and the length of the reinforcing bars 4 is determined in consideration of the fixing property to a foundation structure such as a concrete footing foundation, underground beam, and independent foundation. The reinforcing bar 4 shown in the second embodiment does not have a fixing resistance mechanism for improving the fixing property with the superstructure, but the reinforcing bars as shown in FIGS. 9 to 11 as the third, fourth, and fifth embodiments. Instead of 4, a steel rod 14 having a fixing resistance mechanism (U-shaped hook, fixing plate, stud, etc.) with the upper structure may be welded to the steel ring 2a.

  That is, in Embodiments 3 to 5 of FIGS. 9 to 11, a plurality of steel bars 14 having a U-shaped hook 15, a fixing plate 16, or a stud 17 on the outer side of the steel ring 2 instead of the reinforcing bar 4. It has been explained before that the lower end of the steel plate can be fixed by welding so that the length of the steel bar 14 extending upward can be shortened, and the foundation structures such as concrete footing foundations, underground beams, and independent foundations can be made smaller. As described above, such a fixing resistance mechanism can be incorporated into the second embodiment.

  The main element of the present invention is to form a slight gap dimension between the pile head 3a of the foundation pile 3 and the steel ring 2 or 2a fitted to the outer periphery or inner periphery thereof. explain. The gap dimension between the pile head 3a of the foundation pile 3 and the steel ring 2 fitted to the outer periphery thereof, and the gap dimension between the pile head 3a of the foundation pile 3 and the steel ring 2a fitted to the inner circumference thereof are as follows: The knowledge that when this is filled with the filling / solidifying material 6 greatly affects the bending stress transmission characteristics of the foundation pile 3 and the cylindrical steel ring 2 or 2a of the pile head reinforcing member 1 or 1a. It was.

  The effectiveness of the above knowledge is confirmed by numerical analysis and will be described with reference to FIGS. As shown in FIG. 7, as an analysis model, a simple beam 13 in which two left and right steel pipes 18 are joined using a steel ring 19 and a filling / solidifying material 6 made of mortar or cement paste is formed. Further, the concentrated load P was loaded on the two left and right steel pipes 18 on both outer sides of the steel ring 19.

  The outer diameter of each of the left and right steel pipes is 1000 mm, the wall thickness (t) of 19.0 mm, the length between both fulcrums 20 (L) of 12500 mm, and the clearance (G1) at the center of each steel pipe 18 Is 4 mm, the length (L1) from the central end of each steel pipe 18 to the loading point of the concentrated load P is 2500 mm, and the length (L2) from the loading point of the concentrated load P to each fulcrum 20 is 3750 mm. The outer diameter of the steel ring 19 is 1048 mm, 1098 mm, or 1138 mm, and has a length (L3) of 500 mm and a tube thickness (t1) of 19.0 mm. Further, the gap (G) for filling the filling / solidifying material 6 was changed to 5 mm, 30 mm, and 50 mm. Accordingly, the outer diameter of the steel ring 19 is (D) = 1048 mm when (G) = 5 mm, (D) = 1098 mm when (G) = 30 mm, and (D) = when (G) = 50 mm. It was changed to 1138 mm.

  FIG. 8 shows the structural analysis result when the load P is concentratedly loaded on the simple beam 13. According to FIG. 8, when the gap dimension (G) for filling the filling / solidifying material 6 is 50 mm, it can be confirmed that both the strength and the rigidity are inferior to those when the gap dimension (G) is 5 mm and 30 mm. This decrease in performance is because the gap size (G) is large, so that the filling / solidifying material 6 is likely to deteriorate, and the deterioration of the filling / solidifying material 6 greatly affects the joint strength. In order to prevent a decrease in the proof stress of a joint portion in which a steel pipe and a steel ring are solidified and integrated with a solidified / solidified material, conventionally, a displacement stopper is often used for the filled / solidified material filled portion.

  As described above, in the prior art, as a means for preventing a decrease in the proof stress of the joint between the steel pipe and the steel ring, it is common to use a steel pipe with a stopper or a rib exclusively, and the filling / solidifying material is also concrete. There are many. Therefore, even if there is a misalignment stop or ribbed steel pipe, a space is required between the steel pipe and the steel ring so that the filling / solidifying material can be injected inside (for example, about 100 mm or more). In order to ensure sufficient strength of the joint even if there is no slip stopper or ribbed steel pipe, it is considered to reduce the gap between the steel pipe and the steel ring.

  Since the size of the gap is related to the fluidity of the filling / solidifying material 6 to be filled therein, this will be described. In the present invention, as the minimum value of the gap dimension (G) in the space shape created by the pile head 3a of the foundation pile 3 and the steel ring 2 or 2a, the mortar whose fluidity test has a funnel value of 6 seconds ± 2 seconds is used. In the case of a cement paste having a gap size (G) of 5 mm and a funnel value of 7 seconds ± 2 seconds, it is confirmed by a filling construction test that 3 mm is desirable.

  From the above test results, in the present invention, the minimum value of the gap dimension (G) is set to 3 mm, and the maximum value is set to a range of 30 mm. The gap size of 3 mm to 30 mm is not limited to the case where the pile head 3a and the steel ring 2 or 2a are arranged concentrically and a uniform gap is formed in the circumferential direction. For example, the portion of 90% or more with respect to the circumferential length L of the foundation pile may be 3 to 30 mm, and the portion of 10% or less with respect to the circumferential length L of the remaining foundation pile deviates from the range of 3 to 30 mm. However, the desired effects of the present invention can be achieved.

  The pile head reinforcing member 1 is formed in advance at a factory or the like. Cut the ground so that the pile head 3a of the foundation pile 3 is exposed, insert the pile head reinforcement member 1 into the pile head 3a of the foundation pile 3, and the inside of the steel ring 2 of the pile head reinforcement member 1 and the pile head The gap between the outer side of 3a is filled with a filling / solidifying material 6 of either mortar or cement paste and solidified, and the pile head reinforcing member 1 and the pile head 3a are joined together to form a pile head reinforcing structure. Since the gap between the pile head reinforcing member 1 and the pile head 3a is small, the amount of filling / solidifying material 6 filled in the gap can be reduced, and a horizontal force acts on the pile head due to an earthquake or the like. In this case, since the horizontal force is smoothly transmitted to the pile head reinforcing member 1 through the filling / solidifying material 6 with a slight interval, the filling / solidifying material 6 does not require a large shear strength, and the filling / solidifying material is used. As 6, either general mortar or cement paste can be used.

  The pile head reinforcing member 1a of the second embodiment is the same as described above, and is formed in advance at a factory or the like. Cut the ground so that the pile head 3a of the foundation pile 3 is exposed, insert the pile head reinforcing member 1a into the pile head 3a of the foundation pile 3, and the outside of the steel ring 2a of the pile head reinforcing member 1a and the pile head A filling / solidifying material 6 of either mortar or cement paste is filled in the gap with the inside of 3a and solidified, and the pile head reinforcing member 1a and the pile head 3a are joined together to constitute a pile head reinforcing structure. Since the gap between the pile head reinforcing member 1a and the pile head 3a is small, the amount of filling / solidifying material filled in the gap can be reduced, and a horizontal force acts on the pile head due to an earthquake or the like. In this case, since the horizontal force is smoothly transmitted to the pile head reinforcing member 1a through the filling / solidifying material at a slight interval, the filling / solidifying material does not require a large shear strength, and the general filling / solidifying material is used. The point that can be used is the same as in the first embodiment.

  Pile head reinforcement member 1 or 1a is installed on the part of rebar 4 extending upward from steel ring 2 or 2a, the reinforcement of the foundation structure is placed, concrete is placed, and pile head 3a and The upper structure such as the foundation structure is integrally joined.

  In this foundation structure, the axial force is borne by the foundation pile 3, and the pile head reinforcing member 1 is borne only by bending stress. As shown in FIGS. 12 and 13 (Embodiment 6), the unbond material 5 may be applied to a portion directly above the steel ring 2 of the reinforcing bar 4 of the pile head reinforcing member 1. As a result, when a horizontal force acts on the pile head 3a due to an earthquake or the like, the portion of the pile head reinforcing member 1 to which the unbonded material 5 of the reinforcing bar 4 is applied does not adhere to the concrete of the foundation structure. When a moment is applied, the part yields, and the magnitude of the bending moment acting on the foundation structure such as the pile head 3a and the underground beam can be reduced. The cross section can be reduced. In addition, by adjusting the number and length of the unbond materials 5, it is possible to control the magnitude of the bending moment acting on the foundation structure itself. In addition, the cross-sectional area of the part to which the unbond material 5 is applied among the reinforcing bars 4 (steel bars 14) may be adjusted in advance according to the design specifications. Also in the case of the second embodiment, the same effect as that of the sixth embodiment is achieved by applying the unbond material 5 to the portion directly above the steel ring 2 of the reinforcing bar 4 of the pile head reinforcing member 1a.

It is a perspective view which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 1 to the pile head of a foundation pile. It is a partial sectional view showing the pile head reinforcement structure which fixed the pile head reinforcement member concerning Embodiment 1 to the pile head of a foundation pile. It is a top view which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 1 to the pile head of a foundation pile. It is a perspective view which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 2 to the pile head of a foundation pile. It is a partial cross section figure which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 2 to the pile head of a foundation pile. It is a top view which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 2 to the pile head of a foundation pile. (A) is sectional drawing which shows the simple beam which comprised two steel pipes by the steel ring as an analysis model for confirming the effect of the joining structure of this invention, (b) is (a). A-A 'sectional drawing of (c) is an expanded sectional view of the junction part of a steel pipe and steel rings. It is a figure which shows the structural analysis result at the time of loading the 2 point concentrated load P on the simple beam shown in FIG. It is side sectional drawing which shows Embodiment 3 and shows the pile head reinforcement structure at the time of using the steel bar which has a fixing resistance mechanism (U-shaped hook) with an upper structure instead of a reinforcing bar. FIG. 10 is a side sectional view showing a pile head reinforcing structure in a case where a steel rod having a fixing resistance mechanism (fixing plate) with an upper structure is used instead of a reinforcing bar in the fourth embodiment. FIG. 10 is a side sectional view showing a pile head reinforcing structure in a case where a steel rod having a fixing resistance mechanism (stud) with an upper structure is used instead of a reinforcing bar, showing Embodiment 5. It is a perspective view which shows Embodiment 6 and shows the pile head reinforcement structure at the time of apply | coating an unbond material to the direct upper part of steel rings. It is a partial cross section figure which shows the pile head reinforcement structure which fixed the pile head reinforcement member which concerns on Embodiment 6 to the pile head of a foundation pile. (A) (b) (c) is sectional drawing which shows a prior art. (A) and (b) are sectional drawings which show a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Pile head reinforcement member 2, 2a Steel ring 3 Foundation pile 3a Pile head 4 Reinforcement 5 Unbond material 6 Filling / solidification material 7 Foundation structure 8 Reinforcement rod 9 Beard reinforcement 10 Reinforcement ring 11 Spacing member 12 Concrete 13 Simple Beam 14 Steel rod 15 U-shaped hook 16 Fixing plate 17 Stud 18 Steel pipe 19 Steel ring 20 Support point

Claims (6)

  On the outer periphery of a cylindrical steel ring having an inner diameter slightly larger than the outer diameter of the pile head of the foundation pile, a pile head reinforcing member welded so as to extend upwardly a plurality of reinforcing bars for connection with the upper structure, The cylindrical steel ring is inserted into the pile head of the foundation pile and filled with a filling / solidifying material selected from mortar or cement paste between the outside of the pile head and the inside of the pile head reinforcement member. The pile head reinforcement structure characterized by being joined by doing.   A pile head reinforcement member welded so that a plurality of reinforcing bars for connection with the upper structure are extended upwardly on the inner periphery of a cylindrical steel ring having an outer diameter slightly smaller than the inner diameter of the pile head of the foundation pile. The cylindrical steel ring is inserted into the pile head of the foundation pile, and a filling / solidifying material selected from mortar or cement paste is filled between the inside of the foundation pile and the outside of the pile head reinforcement member. Pile head reinforcement structure characterized by being joined by solidification.   The slight gap dimension between the pile head of the foundation pile and the pile head reinforcing member is such that 90% or more of the circumferential length L of the foundation pile is 3 to 30 mm. Pile head reinforcement structure.   The pile head reinforcement according to any one of claims 1 to 3, wherein a steel rod having a fixing resistance mechanism with an upper structure is welded to the cylindrical steel ring instead of a reinforcing bar. Construction.   The pile head reinforcing structure according to any one of claims 1 to 3, wherein an unbond material is applied to a portion of the reinforcing bar welded to the cylindrical steel ring immediately above the steel ring.   The pile head reinforcing structure according to claim 4, wherein an unbond material is applied to a portion immediately above the steel ring of the steel rod welded to the cylindrical steel ring.

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