Foundation pile

Abstract

The invention discloses a foundation pile (1). A foundation pile (1) is provided with: a central shaft member (10) extending vertically in the vertical direction; a substrate (11) formed at the upper end of the central shaft member (10) so as to fix the upper structure (2) to the upper end of the central shaft member (10); and a peripheral member (20) disposed on the upper periphery of the central shaft member (10) so as to reinforce the upper periphery of the central shaft member (10), the upper surface of the peripheral member (20) being in gapless contact with the lower surface of the substrate (11).

Description

Technical Field

[0001] The present invention relates to a foundation pile that firmly supports a structure combined with its upper part by being driven into the ground. Background Art

[0002] Generally, when installing various structures including road signs or signal poles, a method of driving a foundation pile into the ground and fixing the structure to the upper end of the foundation pile is used.

[0003] A general foundation pile is composed of a tubular body vertically extending in the up and down direction, and a base plate (or flange part) for combining with the upper structure is arranged at the upper end, and it is buried and fixed in the ground in such a way that the base plate slightly protrudes from the ground.

[0004] However, these foundation piles do not have sufficient strength to resist lateral external forces. When the structure fixed on the upper side is subjected to lateral wind pressure or vibration, the upper end part of the foundation pile will move laterally together with the structure, resulting in a weakening of the supporting force of the foundation pile, and finally there is a problem that it is difficult to firmly support the structure.

[0005] In particular, when the upper end of the foundation pile repeatedly and strongly moves laterally, the entire foundation pile is pulled upward, resulting in a further weakening of the supporting force of the foundation pile. This problem not only occurs in the above-mentioned road signs or signal poles, but the same situation also occurs in the foundation piles for supporting all kinds of structures.

[0006] The applicant of the present invention was able to solve this problem and has developed a foundation pile in the past, which includes: a central shaft member with a base plate (or flange part) for fixing the structure arranged at the upper end; and a peripheral member arranged around the central tube body to strengthen the upper side periphery of the central shaft member, and the existing foundation pile technology is disclosed in Korean Patent No. 10-1909396.

[0007] However, as Figure 1 shown, since only a single tube body forming the central axis (i.e., the central shaft member 10) is attached with the base plate 11 in the prior art to support the upper structure 2 combined with the base plate 11, the neck N between the base plate 11 and the peripheral member 20 inevitably becomes a weak structure due to the small cross-sectional area, and thus there is a problem of being vulnerable to damage under the influence of overall horizontal loads or vertical loads.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] (Patent Document 0001) Korean Patent No. 10-1909396 (October 11, 2018) Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] The problem to be solved by the present invention is to provide a foundation pile having excellent strength and durability against vertical loads, horizontal loads, and / or various other loads.

[0013] Means for Solving the Problems

[0014] The foundation pile 1 according to one aspect of the present invention includes: a central axis member 10 vertically extending in the up-down direction; a base plate 11 formed at the upper end of the central axis member 10 to fix an upper structure 2 to the upper end of the central axis member 10; and a peripheral member 20 disposed around the upper side of the central axis member 10 to reinforce the periphery of the upper side of the central axis member 10, and an upper surface of the peripheral member 20 is in contact with a lower surface of the base plate 11 without a gap.

[0015] The foundation pile 1 further includes: a plurality of reinforcing wings joined to the central axis member 10 and the peripheral member 20, the plurality of reinforcing wings including: one or more lower-end reinforcing wings 41 joined to the lower end of the central axis member 10; a plurality of intermediate reinforcing wings 42 joined to the outer periphery of the central axis member 10; and a plurality of upper reinforcing wings (43, 43A, 43B, 43C) joined to the outer periphery of the peripheral member 20.

[0016] The foundation pile 1 further includes: an intermediate extended reinforcing plate 50 joined to an outer peripheral surface of the peripheral member 20 so as to be spaced downward from the base plate 11 and having an area larger than that of the base plate 11 to counter vertical loads, and the foundation pile is installed in such a manner that after being driven into the ground to a degree where the intermediate extended reinforcing plate 50 contacts the bottom surface in a pre-formed buried hole 7, the buried hole 7 is filled again.

[0017] The foundation pile 1 further includes: a plurality of insertion holes 52 formed in the intermediate extended reinforcing plate 50; and a plurality of auxiliary foundation piles 70 inserted into the insertion holes 52 and upper ends of the plurality of auxiliary foundation piles 70 are welded (or other fixing methods) to the intermediate extended reinforcing plate 50, the auxiliary foundation piles 70 including: a base portion 71 at the upper end welded to the intermediate extended reinforcing plate 50; a shaft portion 72 vertically extending downward from a lower surface of the base portion 71; and a reinforcing peripheral portion 73 joined to the shaft portion 72 so as to surround an upper portion of the shaft portion 72 and having a size smaller than that of the base portion 71 and an outer diameter corresponding to the insertion hole 52.

[0018] Advantages of the Invention

[0019] According to the present invention, the foundation pile eliminates the neck that originally existed between the base plate disposed at the upper end of the central shaft member and the peripheral member disposed around the upper side of the central member and is vulnerable to vertical and horizontal loads by closely fitting (or joining) the base plate and the peripheral member, thereby solving the existing problems such as deformation or bending of the neck caused by vertical or horizontal loads.

[0020] In addition, the present invention has excellent strength and durability against vertical loads, horizontal loads, and / or various other loads through a plurality of reinforcing wings disposed on the outer periphery of the foundation pile, an intermediate extended reinforcing plate, and / or an auxiliary foundation pile coupled to the intermediate extended reinforcing plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a diagram for explaining the problems of the conventional technology.

[0022] Figures 2 to 4 is a diagram for explaining the foundation pile according to the first embodiment of the present invention.

[0023] Figure 5 and Figure 6 is a diagram for explaining the foundation pile according to the second embodiment of the present invention.

[0024] Figure 7 and Figure 8 is a diagram for explaining the foundation pile according to the third embodiment of the present invention.

[0025] Figure 9 is a diagram for explaining the foundation pile according to the fourth embodiment of the present invention.

[0026] Figure 10 and Figure 11 is a diagram for explaining the foundation pile according to the fifth embodiment of the present invention.

[0027] Figures 12 to 14 is a diagram for explaining the foundation pile according to the sixth embodiment of the present invention.

[0028] Figure 15 is a diagram showing Figure 6 a modification of

[0029] DESCRIPTION OF THE REFERENCE NUMERALS

[0030] 10: central shaft member; 11: base plate; 20, 20', 20": peripheral member; 50: intermediate extended reinforcing plate; 52: insertion hole; 70: auxiliary foundation pile DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily implement it. The present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0032] When describing the present invention, for the sake of clarity and convenience of description, the size, shape, etc. of the components shown in the drawings may be shown in an exaggerated or simplified manner.

[0033] In addition, terms specifically defined in consideration of the configuration and function of the present invention may vary according to the intention or habit of the user and the operator. Based on the entire content of this specification, these terms should be interpreted as having meanings and concepts consistent with the technical idea of the present invention.

[0034] To clearly describe the present invention, descriptions of parts unrelated to the technical idea of the present invention will be omitted, and the same or similar components are given the same reference numerals throughout the specification.

[0035] In addition, in each embodiment, for components having the same configuration, the same reference numerals will be used to describe only the representative embodiments, and in other embodiments, only the configurations different from the representative embodiments will be described.

[0036] Throughout the specification, when a part is referred to as being "connected" to another part, it not only means the case of "direct connection", but also means the case of "indirect connection" with other elements in between and the case of non-fixed contact with each other. In addition, when the specification mentions that a part "includes" a certain component, unless there is a particularly contrary description, it means that other components may also be included, without excluding other components. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0037] Figures 2 to 4 It is a diagram for explaining a foundation pile according to the first embodiment of the present invention.

[0038] As Figures 2 to 4 shown, the foundation pile 1 according to the first embodiment of the present invention is buried underground to support the structure 2 fixed to the upper end.

[0039] In addition, the foundation pile 1 according to the present embodiment includes: a central axis member 10 extending in the vertical direction and having a base plate 11 formed at the upper end for fixing the upper structure 2; and a peripheral member 20 which is a multi-layer concentric circle type and is arranged at the peripheral portion of the central axis member 10 to strengthen the periphery of the upper side of the central axis member 10.

[0040] In the present embodiment, the central axis member 10 is made of a metal pipe, but it may also be made of a section steel.

[0041] The substrate 11 is fixed to the substrate 2A formed at the lower end of the superstructure 2 by fasteners 3 such as bolts or anchor bolts. Thus, the superstructure 2 can be supported in a state fixed to the foundation pile 1.

[0042] Different from the conventional technique in which the outer peripheral surface of the central axis member is directly exposed between the substrate and the peripheral member to form a neck vulnerable to damage by vertical and horizontal loads, the foundation pile 1 according to the present embodiment is formed such that the upper surface of the peripheral member 20 contacts the lower surface of the substrate 11 without a gap, thereby removing the neck vulnerable to damage by vertical and horizontal loads. At this time, the outer diameter of the substrate 11 is larger than the upper end outer diameter of the peripheral member 20. Therefore, the peripheral area of the substrate 11 is separated from the upper end periphery of the peripheral member 20 and is located outside the peripheral member 20, and a plurality of fixing holes 112 for fastening the fastener 3 may be formed in the peripheral area of the substrate 11. The central axis member 10 is welded to the center of the lower surface of the substrate 11, and the peripheral member 20 is welded around the central axis member 10, thereby forming the foundation pile 1.

[0043] According to an embodiment, the central axis member 10 may use a metal pipe extending vertically, and the substrate 11 may be a circular metal plate welded to the upper end of the central axis member 10 or may be used in various shapes according to the shape of the structure base.

[0044] The substrate 11 may be joined to the upper end of the central axis member 10 by welding, for example, and a plurality of fixing holes 112 may be formed in the peripheral area separated from the upper peripheral edge of the peripheral member 20 to be described later, so that bolts as part of the fastener 3 pass through the plurality of fixing holes 112. The superstructure 2 having a columnar shape is joined to the substrate 11 by the fastener 3, and the fastener 3 includes bolts and nuts passing through holes formed in the lower end substrate 2A of the superstructure 2 and the fixing holes 112.

[0045] In the present embodiment, the peripheral member 20 includes: a plurality of peripheral pipe portions (21, 22, 23) extending vertically and formed of circular tubes each having an inner diameter larger than the inner diameter of the central axis member 10, and arranged to form concentric circles with different inner diameters outside the central axis member 10; and a plurality of fixing ribs 24 extending inward to connect the plurality of peripheral pipe portions (21, 22, 23), and the inner free ends of which are joined to the outer peripheral surface of the central axis member 10.

[0046] The plurality of peripheral pipe portions (21, 22, 23) are configured to have the same upper end height so as to come into overall contact with the lower surface of the substrate 11, and are formed in a multi-layer structure, wherein the length of the peripheral pipe portion disposed on the inner side is greater than the length of the peripheral pipe portion disposed on the outer side, so that the lower end of the peripheral pipe portion disposed on the inner side extends more downward than the lower end of the peripheral pipe portion disposed on the outer side.

[0047] In a state where the lower end of the central shaft member 10 contacts the ground, the foundation pile 1 is driven into the ground using a hammer, a power hammer, an excavator, a pile driver, etc. and the substrate 11 is exposed above the ground GL. Preferably, the foundation pile 1 can be driven until the lower surface of the substrate 11, the upper end of the central shaft member 10, and the upper end of the peripheral member 20 are substantially in a plane at the same height as the ground. After driving the foundation pile 1, it is only necessary to excavate a part of the soil in the peripheral area of the substrate 11 to fasten the fastener 3 for fixing the superstructure 2. This can not only provide the effect of removing the fragile neck between the peripheral member 20 and the substrate 11, but also provide the additional effect of directly supporting the substrate 11 on the ground.

[0048] As described above, the peripheral member 20 includes: a plurality of peripheral pipe portions (21, 22, 23), extending vertically, each formed of a circular tube having an inner diameter larger than the inner diameter of the central shaft member 10, and arranged to form concentric circles with different inner diameters on the outer side of the central shaft member 10; a plurality of fixing ribs 24, extending inward to connect the plurality of peripheral pipe portions (21, 22, 23) and the inner free ends are joined to the outer peripheral surface of the central shaft member 10, and on the upper end side, the upper end surfaces of the plurality of peripheral pipe portions (21, 22, 23) are in a plane at the same height as the lower surface of the substrate 11, but on the lower end side, the lower end of the inner peripheral pipe portion (23 or 22) extends more downward than the lower end of the outer peripheral pipe portion (22 or 21) to form a pointed shape that can be better driven into the ground. When the foundation pile 1 is buried in the ground, the lower end of the central shaft member 10 is first buried in the ground, and then while burying the lower ends in order from the inner peripheral pipe portion to the outer peripheral pipe portion, the soil on the ground is pushed outward, so it has the advantage of being able to effectively bury the foundation pile 1 in the ground.

[0049] Figure 5 and Figure 6 is a view for explaining a foundation pile according to a second embodiment of the present invention.

[0050] Refer to Figure 5 and Figure 6, the foundation pile 1 according to the second embodiment of the present invention is the same as the above-described first embodiment and is buried underground to support the superstructure 2 fixed to the upper end. The foundation pile 1 includes: a central axis member 10 extending in the downward direction and having a base plate 11 formed at the upper end for fixing the superstructure 2; and a multi-axis peripheral member disposed at the peripheral portion of the central axis member 10 to reinforce the periphery of the upper side of the central axis member 10.

[0051] Similar to the above-described first embodiment, the base plate 11 is fixed to the base plate 2A formed at the lower end of the superstructure 2 by fasteners such as bolts or anchor bolts. Thus, the superstructure 2 can be supported in a state fixed to the foundation pile 1. In addition, the foundation pile 1 is formed in the same manner as the above-described first embodiment such that the upper surface of the peripheral member (20, 20', 20") contacts the lower surface of the base plate 11 to remove the neck portion that is vulnerable to damage due to vertical and horizontal loads. At this time, the outer peripheral region of the base plate 11 is located outside the upper end outer peripheral edge of the peripheral member (20, 20', 20"), and a plurality of fixing holes 112 for fastening the fastener 3 may be formed in the outer peripheral region of the base plate 11. The central axis member 10 is welded (or other fixing method) to the center of the lower surface of the base plate 11, and the peripheral member (20, 20', 20") is welded to the periphery of the base plate 11, thereby forming the foundation pile 1.

[0052] In this embodiment, the peripheral member (20, 20', 20") is formed by combining a plurality of peripheral tube portions 25 arranged and joined along the periphery of the central axis member 10. Since the peripheral member (20, 20', 20") in this embodiment is formed by a plurality of peripheral tube portions 25 to form a plurality of axes, it is a multi-axis peripheral member different from the multi-layer concentric circular peripheral member of the above-described embodiment.

[0053] At this time, preferably, the plurality of peripheral tube portions 25 are directly joined to the central axis member 10, but they may also be joined to the central axis member 10 through ribs made of metal plates. The peripheral tube portion 25 is formed in a circular tubular shape extending in the vertical direction.

[0054] At this time, the peripheral tube portion 25 is composed of six and may be arranged on the peripheral surface of the central axis member 10 at an angle of 60°. However, the number of peripheral tube portions 25 does not limit the present invention.

[0055] Figure 7 and Figure 8 are diagrams for explaining the foundation pile according to the third embodiment of the present invention.

[0056] Refer to Figure 7 and Figure 8, the foundation pile 1 according to the third embodiment of the present invention is the same as the above-described first embodiment, and a plurality of concentric circular peripheral members 20 are arranged around the central axis member 10. In order to maximize the horizontal area of the foundation pile so that it can better withstand horizontal loads caused by wind loads or earthquakes, etc., the foundation pile 1 includes: a plurality of reinforcing wings (41, 42, 43A, 43B, 43C), joined (welded) around a plurality of peripheral pipe portions (21, 22, 23) of the central axis member 10 and / or the peripheral member, and the plurality of reinforcing wings (41, 42, 43A, 43B, 43C) integrally include: one or more lower reinforcing wings 41, joined near the lower end of the central axis member 10; a plurality of intermediate reinforcing wings 42, joined to the outer periphery of the central axis member 10; and a plurality of upper reinforcing wings (43A, 43B, 43C), joined to the outer periphery of the peripheral member 20. In this embodiment, the peripheral member 20 includes: a first peripheral pipe portion 21, having the largest outer diameter and the shortest length extending downward; a second peripheral pipe portion 22, having an outer diameter smaller than that of the first peripheral pipe portion 21 and a lower side extension length greater than that of the first peripheral pipe portion 21; and a third peripheral pipe portion 23, having an outer diameter smaller than that of the second peripheral pipe portion 22 and a lower side extension length greater than that of the second peripheral pipe portion 22, and the upper reinforcing wings (43A, 43B, 43C) include: a first upper reinforcing wing 43A, joined to the outer peripheral surface of the first peripheral pipe portion 21; a second upper reinforcing wing 43B, joined to the outer peripheral surface of the second peripheral pipe portion 22; and a third upper reinforcing wing 43C, joined to the outer peripheral surface of the third peripheral pipe portion 23.

[0057] The reinforcing wings (41, 42, 43A, 43B, 43C) can be made of an iron plate (steel plate or steel section) including an inclined surface that slopes downward toward the center of the foundation pile 1, so that the array of reinforcing wings at the same height forms a pointed shape pointing downward, minimizing the resistance when driving the foundation pile 1 into the ground.

[0058] Figure 9 FIG. is for explaining the foundation pile according to the fourth embodiment of the present invention.

[0059] Refer to Figure 9, the foundation pile 1 according to the fourth embodiment of the present invention is provided with multi-axis peripheral members (20, 20', 20"), and the multi-axis peripheral members (20, 20', 20") include a plurality of peripheral pipe portions 25 arranged in a circular pattern around the central axis member 10. In order to maximize the horizontal area of the foundation pile and enable it to better withstand horizontal loads caused by wind loads or earthquakes, etc., the foundation pile 1 includes: a plurality of reinforcing wings (41, 42, 43), joined (welded) around the central axis member 10 and the peripheral member 20, and the plurality of reinforcing wings (41, 42, 43) integrally include: one or more lower reinforcing wings 41, joined near the lower end of the central axis member 10; a plurality of intermediate reinforcing wings 42, joined to the outer periphery of the central axis member 10; and a plurality of upper reinforcing wings 43, respectively joined to each of the peripheral pipe portions 25 of the peripheral members (20, 20', 20"). The remaining configurations are basically the same as those of the above embodiments, so the description thereof is omitted.

[0060] Figure 10 and Figure 11 is a view for explaining the foundation pile according to the fifth embodiment of the present invention.

[0061] Refer to Figure 10 and Figure 11 , the foundation pile 1 according to the fourth embodiment of the present invention is designed to better withstand vertical loads. The foundation pile 1 integrally includes: a central axis member 10, extending in the downward direction and having a circular base plate 11 formed at the upper end for fixing the superstructure 2; a peripheral member 20, disposed at the peripheral portion of the central axis member 10 to strengthen the upper peripheral portion of the central axis member 10, and contacting the lower surface of the base plate 11 at the upper end; and a circular intermediate extended reinforcing plate 50, joined and formed on the outer peripheral surface of the peripheral member 20 at a spaced-apart distance from the base plate 11 downward, and having an area larger than that of the base plate 11 to counteract the vertical load.

[0062] Such a foundation pile 1 can be installed on the ground in the following manner: The ground is pre-excavated to form a buried hole 7 with an area that can accommodate the intermediate extended reinforcing plate 50, and after driving the foundation pile 1 into the ground to the extent that the intermediate extended reinforcing plate 50 contacts the bottom surface in the buried hole 7, the buried hole 7 is filled again.

[0063] In such a foundation pile 1, the central axis member 20 can use steel pipes or steel sections such as H-shaped steel, T-shaped steel, etc. including various cross-sectional shapes (such as circular, rectangular or other shapes), and the intermediate extended reinforcing plate 50 can use a steel plate with an area larger than that of the base plate 11.

[0064] Figures 12 to 14 is a view for explaining the foundation pile according to the sixth embodiment of the present invention.

[0065] Refer toFigures 12 to 14 , the foundation pile 1 according to the sixth embodiment of the present invention integrally includes, in the same manner as the above-described fifth embodiment: a central shaft member 10 that extends in the downward direction and has a base plate 11 formed at the upper end for fixing the superstructure 2; a peripheral member 20 that is disposed at the peripheral portion of the central shaft member 10 to strengthen the upper peripheral portion of the central shaft member 10 and has an upper end that contacts the lower surface of the base plate 11; and an intermediate extended reinforcement plate 50 that is joined in a manner spaced downward from the base plate 11 and formed on the outer peripheral surface of the peripheral member 20 and has an area larger than that of the base plate 11 to resist vertical loads. In addition, it further includes: a plurality of insertion holes 52 formed in the intermediate extended reinforcement plate 50; and a plurality of auxiliary foundation piles 70 that are inserted into the insertion holes 52 and have a base portion 71 at the upper end welded to the intermediate extended reinforcement plate 50.

[0066] The auxiliary foundation pile 70 includes: a base portion 71; a shaft portion 72 that vertically extends downward from the lower surface of the base portion 71; and a reinforced peripheral portion 73 that is joined to the shaft portion 72 in a manner surrounding the upper portion of the shaft portion 72 and has a size smaller than that of the base portion 71 and an inner diameter corresponding to the insertion hole 52.

[0067] After driving the foundation pile 1 into the ground to such an extent that the intermediate extended reinforcement plate 50 contacts the bottom surface in the buried hole 7, the auxiliary foundation piles 70 are respectively inserted into the insertion holes 52 and driven into the ground so that the reinforced peripheral portion 73 is located within the insertion hole 52 and the base portion 71 almost contacts the intermediate extended reinforcement plate 50. Next, the base portion 71 is welded to the intermediate extended reinforcement plate 50. Finally, the buried hole 7 is filled with soil again.

[0068] In the present embodiment, the base plate 11 and the intermediate extended reinforcement plate 50 are configured to be circular, but they may also be configured to be rectangular, polygonal, or other geometric shapes other than these.

[0069] Figure 15 is a diagram showing a modified embodiment of a Figure 6 foundation pile of a multi-axis, multi-layer structure, showing a multi-axis type single-layer structure foundation pile. Referring to Figure 15 , the foundation pile is composed of a peripheral member 20, and the peripheral member 20 includes a plurality of peripheral tube portions 25 having the same height and has a multi-axis type single-layer structure.

[0070] The present invention is not limited to the above embodiments and can be implemented with various modifications.

Claims

1. A foundation pile, characterized in that: include: A central axis member (10) extending vertically in an up-down direction; A base plate (11) formed at the upper end of the central axis member (10) to fix the upper structure (2) to the upper end of the central axis member (10); as well as a peripheral member (20) disposed around the upper side of the central axis member (10) to reinforce the upper side of the central axis member (10); The upper surface of the peripheral member (20) contacts the lower surface of the substrate (11) without a gap.

2. The pile foundation according to claim 1, characterized in that: Also includes: A plurality of reinforcing wings are joined to the central axis member (10) and the peripheral member (20), The plurality of reinforcing wings include: One or more lower end reinforcing wings (41) connected to the lower end of the central axis member (10); A plurality of intermediate reinforcing wings (42) joined to the outer periphery of the central axis member (10); as well as A plurality of upper reinforcing wings (43, 43A, 43B, 43C) are joined to the outer periphery of the peripheral member (20).

3. The pile foundation according to claim 1, characterized in that: Also includes: an intermediate extended reinforcing plate (50) joined to the outer peripheral surface of the peripheral member (20) in a manner spaced apart from the base plate (11) downwardly and having an area larger than that of the base plate (11) to resist vertical loads, Furthermore, the foundation pile is installed in the following manner: after being driven in to such an extent that the intermediate extended reinforcement plate (50) contacts the bottom surface of the pre-formed buried hole (7), the buried hole (7) is refilled.

4. The pile foundation according to claim 3, characterized in that: Also includes: A plurality of insertion holes (52) formed in the intermediate extended reinforcement plate (50); as well as A plurality of auxiliary piles (70) are inserted into the insertion holes (52) and the upper ends of the plurality of auxiliary piles (70) are welded to the middle expansion reinforcement plate (50). The auxiliary pile (70) comprises: a base (71) at the upper end, welded to the intermediate expansion reinforcement plate (50); and a shaft (72) extending vertically downward from the lower surface of the base (71); and a reinforcing peripheral edge portion (73) coupled to the shaft portion (72) in a manner surrounding an upper portion of the shaft portion (72) and having a size smaller than that of the base portion (71) and corresponding to an inner diameter of the insertion hole (52).

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