Method for constructing a pile head seismic isolation structure, and pile head seismic isolation structure

Abstract

To provide a construction method of a pile head seismic isolation structure capable of easily constructing a strong skeleton, and a pile head seismic isolation structure.SOLUTION: A construction method of a pile head seismic isolation structure 20A in which a seismic isolation device 4 is installed at a pile head 21t of a foundation pile 21 using a steel pipe 21m comprises steps of: constructing the foundation pile 21 in the ground G, assembling on the ground a pile head reinforcing bar 30, which comprises a plurality of vertical reinforcing bars 31, radially provided so that one end 31s of each bar is inside, and an annular horizontal reinforcing bar 32 bound to each of the plurality of vertical reinforcing bars 31; installing the pile head reinforcing bar 30 so that one end 31s of the vertical reinforcing bar 31 is installed in a hollow portion 21h provided in the center of a pile horizontal cross section of the pile head 21t of the foundation pile 21, and the other end 31t of the vertical reinforcing bar 31 is installed outside the pile head 21t; and placing concrete around the hollow portion 21h and the pile head 21t to construct a foundation reinforced concrete portion 23A on which the seismic isolation device 4 is installed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for constructing a pile-top seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile, and to the pile-top seismic isolation structure. [Background technology]

[0002] For example, Patent Document 1 discloses a configuration in which a seismic isolation device is attached via a base plate to a concrete base made of concrete filled between the head of a foundation pile and an outer cylinder surrounding the outer periphery of the head, and a bearing ring joined to the outer periphery of the head and extending continuously or intermittently in the circumferential direction is embedded in the concrete base. Furthermore, in this configuration, anchor bars are provided in an evenly distributed manner in the circumferential direction. In this configuration, the bearing ring and anchor bars are embedded in the concrete between the head of the foundation pile and the outer cylinder, thereby increasing the shear strength of the head of the foundation pile and strengthening the strength of the building's framework. Patent Document 2 also discloses a configuration in which a nut is fixed to the top of an expansion ring consisting of an outer steel pipe that surrounds the pile head and a horizontal diaphragm that is inserted into the pile head and fixed to the lower end of the outer steel pipe, concrete is filled into the expansion ring to integrate the expansion ring and the pile head, and a bolt inserted into the lower flange of the seismic isolation device is screwed into the nut of the expansion ring, thereby rigidly connecting the seismic isolation device to the pile head. Patent Document 3 also discloses a configuration comprising a short column connecting a seismic isolation device and a steel pipe pile, and a foundation beam connected to the short column to interconnect the pile heads of a plurality of piles, in which the heads of the steel pipe piles are embedded and held in place in the concrete inside the short column, and a slip-stop plate is attached to the column head of the steel pipe pile so as to surround the steel pipe of the steel pipe pile in a circular shape, and the concrete inside the short column is tightened in the vertical direction by a steel rod. It is desirable to realize a strong pile head for foundation piles. It is also desirable to make the construction easy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-84035 A [Patent Document 2] JP 2009-221769 A [Patent Document 3] JP 2011-256695 A Summary of the Invention [Problem to be solved by the invention]

[0004] The problem that the present invention aims to solve is to provide a method for constructing a pile-top seismic isolation structure that enables a sturdy structure to be easily constructed, and a pile-top seismic isolation structure. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention employs the following means. In other words, the method for constructing a pile-top seismic isolation structure of the present invention is a method for constructing a pile-top seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile made of a steel pipe, and is characterized by including the steps of: constructing a foundation pile in the ground; assembling a pile head reinforcement comprising a plurality of vertical reinforcement bars, each of which is processed into a U-shape and arranged inverted so that the bottom of the U-shape is located at the top, and which are arranged radially so that one end is on the inside, and annular transverse reinforcement bars tied to each of the plurality of vertical reinforcement bars; attaching the pile head reinforcement bars so that one end of the vertical reinforcement bars is installed in a hollow portion provided in the center of the horizontal cross section of the pile head of the foundation pile and the other end of the vertical reinforcement bars is installed on the outside of the pile head; and pouring concrete into the hollow portion and around the pile head to construct a foundation reinforced concrete section in which the seismic isolation device is installed. According to this configuration, the pile head reinforcement bar is assembled in the ground and then attached to the head of the foundation pile. This allows the work of assembling the pile head reinforcement bar to be carried out efficiently, and shortens the construction period. The pile head reinforcement is attached so that one end of the vertical reinforcement is installed in the hollow part of the foundation pile, and the other end located on the outside is installed on the outside of the pile head. By embedding such a pile head reinforcement in the foundation reinforced concrete part formed by concrete poured in the hollow part of the foundation pile and around the pile head, the pile head is restrained by the pile head reinforcement and the foundation reinforced concrete part. This makes it possible to increase the shear strength of the pile head. In particular, since the pile head reinforcement includes a U-shaped vertical reinforcement and annular horizontal reinforcement tied to the vertical reinforcement, the pile head can be reinforced efficiently. Therefore, it is possible to provide a method for constructing a pile head seismic isolation structure that enables a sturdy structure to be easily constructed.

[0006] In one aspect of the present invention, the method for constructing a pile head seismic isolation structure of the present invention further includes a step of installing an outer steel pipe in a position covering the foundation pile from the outside, and in the step of constructing the foundation reinforced concrete portion, concrete is poured into the hollow portion of the foundation pile and between the foundation pile and the outer steel pipe. According to this configuration, the outer steel pipes installed in a position covering the foundation pile from the outside are used as formwork that does not need to be removed, and concrete is poured inside the outer steel pipes to form the foundation reinforced concrete part. Therefore, the pile head seismic isolation structure can be constructed efficiently. Furthermore, with this construction method, the pile head of the foundation pile made of steel pipes is covered with a foundation reinforced concrete section, which is then covered on the outside by an outer steel pipe, forming a concrete pile with a double steel pipe at the pile head. The foundation reinforced concrete section formed inside the outer steel pipe and covering the pile head is uniformly restrained by the pile head reinforcement and the outer steel pipe, further increasing the shear strength. Therefore, there is no need to provide a large concrete section around the pile head to form a pile head seismic isolation structure, and the foundation structure can be made small and compact. In addition, by making the pile head a concrete pile equipped with a double steel pipe, the bending strength and shear strength of the pile head are increased, so there is no need to increase the shear resistance of the foundation piles by connecting them with foundation beams, etc. Therefore, it is possible to realize a pile head seismic isolation structure with an independent footing type without foundation beams, which is strong and capable of shear resistance.

[0007] In one aspect of the present invention, the pile head reinforcement is provided with a height adjustment bar arranged to be positioned inside the U-shape of the vertical reinforcement, and in the process of installing the pile head reinforcement, the height adjustment bar is placed on the top end of the foundation pile to determine the installation height position of the pile head reinforcement. With this configuration, the height adjustment bars provided on the vertical reinforcement of the pile head reinforcement can be placed on the top end of the foundation pile, making it possible to easily and reliably determine the installation height position of the pile head reinforcement relative to the foundation pile.

[0008] The pile-top seismic isolation structure of the present invention is a pile-top seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile, and comprises: the foundation pile made of steel pipes; a foundation reinforced concrete section covering the pile head of the foundation pile and in which the seismic isolation device is installed; and a pile head reinforcement comprising a plurality of vertical reinforcements, each of which is processed into a U-shape and arranged inverted so that the bottom of the U-shape is located on the upper side, and which are arranged radially with one end on the inside, and a circular horizontal reinforcement tied to each of the plurality of vertical reinforcements, and the pile head reinforcement is attached so that one end of the vertical reinforcement is installed in a hollow section provided in the center of the pile horizontal cross section of the pile head of the foundation pile and the other end of the vertical reinforcement is installed on the outside of the pile head, and the entire structure is embedded in the foundation reinforced concrete section. According to this configuration, the pile head reinforcement is arranged so that one end of the vertical reinforcement is installed in the hollow part of the foundation pile, and the other end located on the outside is installed on the outside of the pile head. By embedding such a pile head reinforcement in the foundation reinforced concrete part covering the pile head of the foundation pile, the pile head is restrained by the pile head reinforcement and the foundation reinforced concrete part. This makes it possible to increase the shear strength of the pile head. In particular, since the pile head reinforcement includes a U-shaped vertical reinforcement and annular horizontal reinforcement tied to the vertical reinforcement, the pile head can be reinforced efficiently. The pile head reinforcement is entirely embedded in the reinforced concrete foundation. The reinforced concrete foundation is constructed integrally by pouring concrete into the hollow part of the foundation pile and around the pile head, which makes construction more efficient. Therefore, it is possible to provide a pile head seismic isolation structure that allows for easy construction of a sturdy structure. Effect of the Invention

[0009] According to the present invention, it is possible to provide a method for constructing a pile-top seismic isolation structure that enables a sturdy structure to be easily constructed, and a pile-top seismic isolation structure. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing the configuration of a pile head seismic isolation structure according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along the line II in FIG. [Diagram 3] 1 is a flowchart showing the flow of a method for constructing a pile head seismic isolation structure in this embodiment. [Figure 4] FIG. 11 is a diagram showing a process of installing foundation piles in this embodiment. [Diagram 5] 1A to 1C are diagrams showing a process of installing a pile anchor in this embodiment. [Figure 6] FIG. 4 is a diagram showing a process of installing an outer steel pipe in this embodiment. [Figure 7] FIG. 11 is a diagram showing a process of fixing an outer steel pipe in this embodiment. [Figure 8] FIG. 4 is a diagram showing a process of backfilling the periphery of the outer steel pipe in this embodiment. [Figure 9] FIG. 2 is a diagram showing the process of assembling the pile head reinforcement in the present embodiment. [Figure 10] FIG. 2 is a diagram showing a process of installing a pile head reinforcement in this embodiment. [Figure 11] FIG. 2 is a diagram showing a process of pouring concrete in this embodiment. [Figure 12] 11A to 11C are diagrams showing a process of setting a base plate in the present embodiment. [Figure 13] FIG. 2 is a diagram showing a process of pouring additional concrete in this embodiment. [Figure 14] 1 shows a pile head seismic isolation structure in a second embodiment of the present invention. [Figure 15] FIG. 15 is a cross-sectional view taken along the line II-II of FIG. [Figure 16] 13 is a flowchart showing the flow of a method for constructing a pile head seismic isolation structure in the second embodiment of the present invention. [Figure 17] 1 is a diagram showing the process of assembling a formwork and the process of installing a pile head reinforcement in this embodiment. FIG. [Figure 18] FIG. 2 is a diagram showing a process of pouring concrete in this embodiment. [Figure 19] 1A to 1C are diagrams showing a process of setting a base plate and a process of setting a raised formwork in this embodiment. [Figure 20] FIG. 2 is a diagram showing a process of pouring additional concrete in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention relates to a method for constructing a pile-top seismic isolation structure in which a seismic isolation device is installed at the top of a foundation pile made of a steel pipe, and the pile-top seismic isolation structure. Specifically, the method for constructing a pile-top seismic isolation structure includes installing a pile-top reinforcing bar, which includes a plurality of vertical reinforcing bars assembled on the ground and a circular horizontal reinforcing bar tied to the vertical reinforcing bars, in a hollow portion provided at the top of the foundation pile, and pouring concrete around the hollow portion and the pile head to construct a foundation reinforced concrete portion in which a seismic isolation device is installed. Also, the method is characterized in that an outer steel pipe that also serves as a formwork material is installed at a position that covers the foundation pile from the outside, or in that a height adjustment bar is placed on the top of the foundation pile to determine the installation height position of the pile-top reinforcing bar. Hereinafter, with reference to the attached drawings, a method for constructing a pile top seismic isolation structure according to the present invention and an embodiment for implementing the pile top seismic isolation structure will be described based on the drawings. [First embodiment] FIG. 1 shows a pile-top seismic isolation structure in a first embodiment of the present invention. As shown in Fig. 1, a building 1 includes a foundation 2A constructed in ground G, an upper structure 3 provided on the foundation 2A, and a seismic isolation device 4. The foundation 2A includes a plurality of foundation piles 21. In this embodiment, the framework of the upper structure 3 includes a plurality of columns 5 supported by the plurality of foundation piles 21 via the seismic isolation devices 4, and a beam 6 installed between adjacent columns 5. The seismic isolation device 4 is provided between the foundation piles 21 and the columns 5.

[0012] FIG. 2 is a cross-sectional view taken along line II in FIG. As shown in Figures 1 and 2, each pile head seismic isolation structure 20A includes, in addition to the foundation pile 21 and seismic isolation device 4 described above, an outer steel pipe 22, a foundation reinforced concrete section 23A, and a pile head reinforcement bar 30. The foundation pile 21 is a so-called prefabricated pile made of prefabricated concrete, and is, for example, any one of a reinforced concrete pile (precast concrete pile), a prestressed concrete pile, a high-strength prestressed concrete pile, a high-strength prestressed reinforced concrete pile, and a concrete pile with an outer shell steel pipe. In this embodiment, the foundation pile 21 is a concrete pile with an outer shell steel pipe, in which a steel pipe 21m is provided at the outermost periphery. The foundation pile 21 is formed in a predetermined shape in a factory. The foundation pile 21 includes a pile body 21c, which is a concrete body having a hollow portion 21h in the center of its cross section. The steel pipe 21m is provided so as to cover the outer peripheral surface of the pile body 21c. The hollow portion 21h extends continuously in the vertical direction at the upper part of the pile body 21c, and opens upward at the pile head portion 21t of the foundation pile 21.

[0013] The outer steel pipe 22 is provided radially outside the pile head 21t of the foundation pile 21. As shown in FIG. 1, the outer steel pipe 22 has a length in the vertical direction smaller than that of the foundation pile 21. The ground G is excavated to a certain depth around the foundation pile 21, and gravel 26 is provided on the bottom of the excavation. The outer steel pipe 22 is provided on the mortar concrete 25 provided on the gravel 26. The installation height of the outer steel pipe 22 is adjusted by a plurality of height adjustment fittings 27. The plurality of height adjustment fittings 27 are provided at the lower part of the outer peripheral surface of the outer steel pipe 22 in three or more sets at intervals in the circumferential direction. Each height adjustment fitting 27 includes a base plate 27a arranged on the mortar concrete 25, a female screw member 27b fixed to the outer peripheral surface of the outer steel pipe 22, and a height adjustment bolt 27c. The height adjustment bolt 27c extends in the vertical direction and is screwed into the female screw member 27b, and its lower end abuts against the base plate 27a. The height and subtle inclination of the outer steel pipe 22 are adjusted by rotating the height adjustment bolts 27c with the multiple sets of height adjustment fittings 27. A closing plate 24 is provided on the lower side of the outer steel pipe 22 to close the gap between the lower end of the outer steel pipe 22 and the basing concrete 25. The closing plate 24 may be made of Galvalume Steel Plate (registered trademark) or the like. The outer steel pipe 22 extends above the foundation pile 21. The inner diameter of the outer steel pipe 22 is larger than the outer diameter of the pile head 21t. A base plate 40 on which the seismic isolation device 4 is placed is disposed radially inside the upper end of the outer steel pipe 22. The outer steel pipe 22 and the base plate 40 are not directly joined. A concrete floor 28 is laid on the radially outer side of the outer steel pipe 22. As shown in Figs. 1 and 2, a plurality of dowels 29 to be embedded in the concrete floor 28 are joined to the outer circumferential surface of the outer steel pipe 22. The plurality of dowels 29 are arranged at intervals in the circumferential direction centered on the hollow portion 21h of the foundation pile 21, more specifically, the central axis C of the foundation pile 21 and the hollow portion 21h. The plurality of dowels 29 extend radially outward from the outer circumferential surface of the outer steel pipe 22 and are embedded in the concrete floor 28.

[0014] The foundation reinforced concrete portion 23A is made of concrete poured and filled on the inside of the outer steel pipe 22 at the site. The foundation reinforced concrete portion 23A is provided in the hollow portion 21h of the foundation pile 21 and between the foundation pile 21 and the outer steel pipe 22, and covers the pile head portion 21t of the foundation pile 21 from the radially outer side. The pile head portion 21t of the foundation pile 21 is embedded in the foundation reinforced concrete portion 23A. The foundation reinforced concrete portion 23A forms a footing whose diameter is expanded radially outward from the pile head portion 21t of the foundation pile 21. The foundation reinforced concrete portion 23A is covered from the outside by the outer steel pipe 22. The foundation reinforced concrete part 23A is composed of a lower concrete part 23c formed by concrete poured to a height above the pile head part 21t and below the upper end of the outer steel pipe 22, and an additional concrete part 23d poured on the lower concrete part 23c. A seismic isolation device 4 is provided on the upper end surface of the foundation reinforced concrete part 23A.

[0015] The pile head reinforcement 30 has a plurality of vertical reinforcement bars 31 and horizontal reinforcement bars 32. The multiple vertical reinforcement bars 31 are arranged radially in the hollow portion 21h of the foundation pile 21, more specifically, in a plan view at intervals in the circumferential direction centered on the central axis C of the foundation pile 21 and the hollow portion 21h. The multiple vertical reinforcement bars 31 are arranged at positions that do not interfere with each other in the circumferential direction with respect to the multiple cap nuts 44, which will be described later, joined to the lower surface of the base plate 40. Each of the multiple vertical reinforcement bars 31 is U-shaped as a whole and integrally has a first extension portion 31a, a second extension portion 31b, and a connecting portion 31c. The first extension portion 31a extends in the vertical direction in the hollow portion 21h of the foundation pile 21 and in a portion above the pile head portion 21t. The second extension portion 31b is arranged at an interval on the radial outside of the foundation pile 21 relative to the first extension portion 31a. The second extension portion 31b is arranged radially outside the foundation pile 21 and extends in the vertical direction. The connecting portion 31c connects the upper ends of the first extension portion 31a and the second extension portion 31b to each other. In this manner, the vertical reinforcement 31 is formed in a U-shape, and is oriented so that the bottom of the U-shape is located on the upper side by being inverted. One end 31s, which is the lower end of the first extension portion 31a of each vertical reinforcement bar 31, is embedded in the foundation reinforced concrete portion 23A within the hollow portion 21h of the foundation pile 21. The upper portion of the first extension portion 31a protrudes above the foundation pile 21 and is embedded in the foundation reinforced concrete portion 23A. The connecting portion 31c is embedded in the foundation reinforced concrete portion 23A above the foundation pile 21. The second extension portion 31b of each vertical reinforcement bar 31, including the lower end which is the other end 31t of each vertical reinforcement bar 31, is entirely embedded in the foundation reinforced concrete portion 23A.

[0016] The lateral reinforcement 32 includes inner circumferential lateral reinforcement 32A and outer circumferential lateral reinforcement 32B. The inner periphery horizontal reinforcement 32A is a so-called hoop reinforcement, and is annular when viewed from above, and is provided in a plurality of vertically spaced relation. Each inner periphery horizontal reinforcement 32A is formed to have a circular shape with a diameter smaller than the inner diameter of the hollow portion 21h when viewed in a plan view, and is tied to the first extending portion 31a of the plurality of vertical reinforcement bars 31. Some of the plurality of inner periphery horizontal reinforcement bars 32A are embedded in the foundation reinforced concrete portion 23A within the hollow portion 21h of the foundation pile 21, and the rest are embedded in the foundation reinforced concrete portion 23A above the pile head portion 21t of the foundation pile 21. The outer peripheral horizontal reinforcement 32B is a so-called hoop reinforcement, has a circular shape when viewed from above, and is provided at intervals in the vertical direction. Each outer peripheral horizontal reinforcement 32B is formed to have a circular shape with a diameter larger than the outer diameter of the foundation pile 21 when viewed in a plan view, and is tied to the second extension parts 31b of the multiple vertical reinforcements 31. The multiple outer peripheral horizontal reinforcement 32B is embedded in the foundation reinforced concrete part 23A between the foundation pile 21 and the outer steel pipe 22.

[0017] The pile head reinforcement 30 is provided with height adjustment reinforcement 70. The height adjustment reinforcement 70 is provided so as to be located inside the U-shape of the vertical reinforcement 31. A plurality of height adjustment reinforcement 70 are provided at intervals in the circumferential direction of the foundation pile 21. The height adjustment reinforcement 70 extends in the radial direction of the foundation pile 21 along the horizontal direction. The height adjustment reinforcement 70 is connected to the inner periphery horizontal reinforcement 32A and the outer periphery horizontal reinforcement 32B by welding, wire, or the like. The height adjustment reinforcement 70 is placed in contact with the top end of the foundation pile 21. The joining position of the height adjustment bar 70 in the vertical direction of the pile head reinforcement bar 30 is determined so that when the pile head reinforcement bar 30 is installed so that the height adjustment bar 70 abuts the top end of the foundation pile 21 as described above, the relative position of the pile head reinforcement bar 30 to the foundation pile 21 is appropriate.

[0018] Further, a plurality of pile anchors 35 extending in the vertical direction are provided on the radially outer side of the steel pipe 21m of the foundation pile 21. The plurality of pile anchors 35 are arranged at intervals in the circumferential direction centered on the central axis C. The plurality of pile anchors 35 are arranged at positions that do not interfere with the plurality of vertical reinforcements 31 in the circumferential direction. In particular, in this embodiment, each of the plurality of pile anchors 35 corresponds to a cap nut 44 provided at the upper end of the foundation reinforced concrete portion 23A, which will be described later. When viewed in a plan view as shown in FIG. 2, the pile anchor 35 and the cap nut 44 are positioned so that a straight line passing through the pile anchor 35 and the corresponding cap nut 44 passes through the center of the foundation pile 21 when extended. Each pile anchor 35 is joined to the steel pipe 21m of the foundation pile 21 via a connecting metal 37. The connecting metal 37 is provided with a nut member (not shown). Each pile anchor 35 is a screw reinforcing bar, and its lower end is screwed into the nut member of the connecting metal 37, thereby joining each pile anchor 35 to the foundation pile 21. Each pile anchor 35 extends in the vertical direction, and a fixing device 38 consisting of a plate and a nut is provided at its upper end. In this embodiment, the fixing device 38 is positioned at a height higher than the upper end of the foundation pile 21. Such pile anchor 35 and connecting metal 37 are embedded in the foundation reinforced concrete part 23A. The pile anchor 35 is provided so as to overlap the second extension part 31b of the vertical reinforcing bar 31 of the pile head reinforcing bar 30 by a predetermined length in the vertical direction.

[0019] A plate-shaped base plate 40 is provided along a horizontal plane on the upper end surface of the foundation reinforced concrete portion 23A. Cap nuts 44 are welded to the lower surface of the base plate 40. The cap nuts 44 are provided at multiple locations spaced apart in the circumferential direction. The cap nuts 44 are embedded in the additional concrete portion 23d of the foundation reinforced concrete portion 23A. The base plate 40 has a bolt insertion hole 40h penetrating vertically at a position corresponding to the cap nut 44. A concrete pouring hole 40g penetrating vertically is formed in the center of the base plate 40. The base plate 40 has a plurality of air vent holes 40j formed in positions that do not interfere with the concrete pouring hole 40g and the bolt insertion holes 40h. The seismic isolation device 4 includes a lower base plate 41, an upper base plate 42, and a laminated rubber portion 43. The lower base plate 41 is placed on the base plate 40. The lower base plate 41 is fixed to the upper end of the foundation reinforced concrete part 23A by passing mounting bolts (not shown) through the bolt insertion holes 40h at a plurality of points spaced apart in the circumferential direction and fastening them to the cap nuts 44. The upper base plate 42 is a plate-like shape along a horizontal plane and is provided along the lower end surface of the column 5. A cap nut 45 is embedded in the lower end of the column 5. The upper base plate 42 is fixed to the lower end of the column 5 by passing mounting bolts (not shown) through the upper base plate 42 at a plurality of points spaced apart in the circumferential direction and fastening them to the cap nuts 45. The laminated rubber part 43 is formed by alternately stacking a plurality of rubber layers 43a and a plurality of steel plates 43b one above the other.

[0020] In the pile head seismic isolation structure 20A as described above, when a bending moment acts on the foundation pile 21 and generates a tensile force T, this tensile force T is transmitted to the pile anchor 35 joined to the foundation pile 21. The tensile force transmitted to the pile anchor 35 is transmitted to the seismic isolation device 4 via the vertical reinforcing bar 31 of the pile head reinforcing bar 30 and the cap nut 44. Furthermore, when a compressive axial force in the vertical direction acts from the column 5 to the seismic isolation device 4, this force is transmitted from the lower base plate 41 and the base plate 40 of the seismic isolation device 4 to the foundation pile 21 via the foundation reinforced concrete part 23A between the pile head part 21t of the foundation pile 21 and the base plate 40. The compressive axial force is also transmitted from the base plate 40 to the foundation pile 21 via the foundation reinforced concrete part 23A between the foundation pile 21 and the outer steel pipe 22 on the radial outside of the foundation pile 21, and the basin concrete 25.

[0021] (Construction method of pile head seismic isolation structure) Fig. 3 is a flow chart showing the flow of a method for constructing a pile-head seismic isolation structure in this embodiment. Fig. 4 is a diagram showing a process for installing foundation piles in this embodiment. Fig. 5 is a diagram showing a process for attaching pile anchors in this embodiment. The above-described pile-top seismic isolation structure 20A can be constructed as follows. First, as shown in Fig. 4, a precast concrete foundation pile 21 is constructed by driving the foundation pile 21 into the existing ground to a predetermined depth (step S1). The foundation pile 21 is installed so that the pile head 21t protrudes upward by a predetermined length from the ground G. After that, gravel 26 and mortar concrete 25 are laid on the ground G with a predetermined thickness. Next, as shown in Fig. 5, a plurality of pile anchors 35 are attached to the radially outer side of the steel pipe 21m of the foundation pile 21 (step S2). For this, first, marks are made in advance, for example on a tape measure, at the installation intervals of the plurality of pile anchors 35 in the circumferential direction of the steel pipe 21m, and the tape measure is wrapped around the outer circumferential surface of the steel pipe 21m exposed above the ground G, and the installation positions of each pile anchor 35 are marked out using the positions of the marks as guides. Thereafter, a connecting metal fitting 37 is welded to the outer circumferential surface of the steel pipe 21m in accordance with the marked out positions, and the pile anchor 35 is screwed into the connecting metal fitting 37.

[0022] Fig. 6 is a diagram showing a process of installing an outer steel pipe in this embodiment, Fig. 7 is a diagram showing a process of fixing the outer steel pipe in this embodiment, and Fig. 8 is a diagram showing a process of backfilling the area around the outer steel pipe in this embodiment. Next, as shown in FIG. 6, the outer steel pipe 22 is installed in a position covering the foundation pile 21 from the outside (step S3). The outer steel pipe 22 is hung from above and placed radially outside the pile head 21t of the foundation pile 21. The female screw member 27b of the height adjustment fitting 27 is welded in advance to the lower part of the outer peripheral surface of the outer steel pipe 22. After the laying plate 27a is laid on the mortar concrete 25, the height adjustment bolt 27c is screwed into the female screw member 27b from above, and its tip is abutted against the laying plate 27a. In this state, the lower end of the outer steel pipe 22 can be raised above the mortar concrete 25 by screwing the height adjustment bolt 27c. In this state, the height of the outer steel pipe 22 is adjusted by the multiple height adjustment fittings 27 by rotating the height adjustment bolt 27c. In addition, the height adjustment bolt 27c may be screwed into the female thread member 27b at the stage of hanging the outer steel pipe 22 radially outside the foundation pile 21, and its tip may be allowed to protrude downward below the lower end of the outer steel pipe 22. Next, the lower ends of the height adjustment bolts 27c are welded to the base plate 27a. Furthermore, as shown in Fig. 7, a closing plate 24 is inserted into the gap between the lower end of the outer steel pipe 22 and the mortar concrete 25, and welded to the lower end of the outer steel pipe 22. This fixes the outer steel pipe 22 (step S4). Thereafter, as shown in FIG. 8, the ground G around the outer steel pipe 22 is backfilled to a predetermined height (step S5).

[0023] Fig. 9 is a diagram showing a process of assembling the pile head reinforcing bar in the ground in this embodiment. Fig. 10 is a diagram showing a process of installing the pile head reinforcing bar in this embodiment. Meanwhile, in a work yard or the like on-site, as shown in FIG. 9, the pile head reinforcement 30 is assembled on the ground (step S6). The pile head reinforcement 30 is assembled on the ground using a plurality of vertical reinforcement 31 and a plurality of horizontal reinforcement 32. Each vertical reinforcement 31 is processed into a U-shape and arranged in an inverted manner so that the bottom of the U-shape is located on the upper side. The vertical reinforcement 31 is arranged radially when viewed from above so that one end 31s is on the inside. The inner periphery horizontal reinforcement 32A and the outer periphery horizontal reinforcement 32B as the horizontal reinforcement 32 are arranged at intervals in the vertical direction. Each inner periphery horizontal reinforcement 32A is tied to the first extension portion 31a of the plurality of vertical reinforcement 31. Each outer periphery horizontal reinforcement 32B is tied to the second extension portion 31b of the plurality of vertical reinforcement 31. Furthermore, height adjustment bars 70 are provided so as to be located inside the U-shape of the vertical reinforcement bars 31. The height adjustment bars 70 extend in the radial direction of the foundation pile 21, and are connected to the inner periphery horizontal reinforcement bars 32A and the outer periphery horizontal reinforcement bars 32B by welding, wire, or the like. The height adjustment bars 70 are joined at a position where the relative position of the pile head reinforcement bars 30 to the foundation pile 21 becomes appropriate when the pile head reinforcement bars 30 are provided so that the height adjustment bars 70 abut against the top end of the foundation pile 21. As shown in Fig. 10, the pile head reinforcement bar 30 assembled in the ground is attached to the pile head 21t of the foundation pile 21 that has been subjected to step S5 (step S7). One end 31s of the vertical reinforcement bar 31 of the pile head reinforcement bar 30 is inserted into the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is positioned outside the pile head 21t. At this time, the height adjustment bar 70 is placed on the top end of the foundation pile 21, so that the pile head reinforcement bar 30 is positioned at an appropriate height relative to the foundation pile 21.

[0024] Fig. 11 is a diagram showing a process of pouring concrete in this embodiment, Fig. 12 is a diagram showing a process of setting a base plate in this embodiment, and Fig. 13 is a diagram showing a process of pouring additional concrete in this embodiment. 11, concrete is poured into the hollow portion 21h of the foundation pile 21 and between the foundation pile 21 and the outer steel pipe 22 to construct the lower concrete portion 23c of the foundation reinforced concrete portion 23A (step S8). At this time, the concrete is poured to a height that is a predetermined dimension lower than the upper end of the outer steel pipe 22. The concrete for constructing the lower concrete portion 23c is preferably concrete having a design standard strength of, for example, 36 N / mm 2 In this state, the pile head reinforcement 30 has one end 31s of each of the multiple vertical reinforcements 31 embedded in the lower concrete portion 23c within the hollow portion 21h of the foundation pile 21, and the other end 31t embedded in the lower concrete portion 23c between the foundation pile 21 and the outer steel pipe 22. Concurrently with the construction of the lower concrete portion 23c, or before or after this, the concrete floor 28 is constructed. The concrete used to construct the concrete floor 28 has a design standard strength of, for example, 21 N / mm 2 can be used. Next, as shown in Fig. 12, the base plate 40 is set on the lower concrete portion 23c (step S9). Cap nuts 44 are welded to the lower surface of the base plate 40 at positions corresponding to the bolt insertion holes 40h. The base plate 40 is set to a predetermined height by placing a plurality of cap nuts 44 on the lower concrete portion 23c. At this time, the height of the base plate 40 is adjusted by inserting a shim plate between the cap nuts 44 and the lower concrete portion 23c, if necessary. Next, the raised formwork 80 is set (step S10). In this embodiment, the raised formwork 80 is composed of the upper end of the outer steel pipe 22, which rises above the lower concrete portion 23c, and a crosspiece 81 installed on the outer periphery of the upper surface of the base plate 40. The crosspiece 81 is provided so that its upper end is higher than the upper end of the outer steel pipe 22. In the raised formwork 80, a gap 82 that continues in the circumferential direction is formed between the outer periphery of the base plate 40 and the upper end of the outer steel pipe 22.

[0025] 13, concrete is poured under the base plate 40 to construct the additional concrete portion 23d of the foundation reinforced concrete portion 23A (step S11). To do this, concrete is poured and filled between the base plate 40 and the previously constructed lower concrete portion 23c through concrete pouring holes 40g formed in the base plate 40. The concrete for constructing the additional concrete portion 23d is made of concrete having a design standard strength higher than that of the concrete for constructing the lower concrete portion 23c, for example, 42 N / mm 2 The above-mentioned may be used. Since the base plate 40 has a plurality of air vent holes 40j, concrete can be satisfactorily poured and filled on the lower surface side of the base plate 40 while preventing air bubbles from remaining. The concrete is poured sufficiently until it overflows from the gap 82 between the outer periphery of the base plate 40 and the upper end of the outer steel pipe 22. At this time, since the crosspiece 81 is provided on the outer periphery of the upper surface of the base plate 40, it is possible to prevent the concrete from flowing around to the upper surface side of the base plate 40. In this way, the filling property of the concrete is improved, and the upper surface of the base plate 40 on which the seismic isolation device 4 will be later provided is prevented from being soiled. The poured concrete hardens to form the additional concrete portion 23d. As a result, the foundation reinforced concrete portion 23A consisting of the previously constructed lower concrete portion 23c and the additional concrete portion 23d is formed. In the foundation reinforced concrete section 23A, concrete is poured in stages into the lower concrete section 23c and the additional concrete section 23d, but these are firmly connected by the pile head reinforcement 30 provided between them. This foundation reinforced concrete section 23A firmly supports the base plate 40 at the upper end of the outer steel pipe 22. Thereafter, as shown in FIG. 1, the seismic isolation device 4 is placed on the base plate 40, and the upper structure 3 is constructed above it in sequence.

[0026] (Action and effect) The construction method of the pile-top seismic isolation structure 20A as described above is a construction method of the pile-top seismic isolation structure 20A in which a seismic isolation device 4 is installed on the pile head 21t of the foundation pile 21 using the steel pipe 21m, and includes a step S1 of constructing the foundation pile 21 in the ground G, a step S2 of constructing the foundation pile 21 in the ground G, and a step S3 of constructing the foundation pile 21 in the ground G. The step S2 of constructing the foundation pile 21 in the ground G includes a step S3 of constructing the foundation pile 21 in the ground G, and a step S4 .... The method includes a step S6 of assembling the pile head reinforcement 30 having the reinforcement bars 32 and the pile head reinforcement bar 30a, a step S7 of attaching the pile head reinforcement bar 30 so that one end 31s of the vertical reinforcement bar 31 is placed in a hollow portion 21h provided in the center of the horizontal cross section of the pile head 21t of the foundation pile 21 and the other end 31t of the vertical reinforcement bar 31 is placed on the outside of the pile head 21t, and steps S8 and S11 of pouring concrete into the hollow portion 21h and around the pile head 21t to construct the foundation reinforced concrete portion 23A on which the seismic isolation device 4 will be installed. According to this configuration, the pile head reinforcement bars 30 are assembled in advance, and then attached to the pile heads 21t of the foundation piles 21. This allows the work of assembling the pile head reinforcement bars 30 to be carried out efficiently, and shortens the construction period. The pile head reinforcement 30 is attached so that one end 31s of the vertical reinforcement 31 is installed in the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is installed on the outside of the pile head 21t. By embedding such a pile head reinforcement 30 in the foundation reinforced concrete portion 23A formed by concrete poured in the hollow portion 21h of the foundation pile 21 and around the pile head 21t, the pile head 21t is restrained by the pile head reinforcement 30 and the foundation reinforced concrete portion 23A. This can increase the shear strength of the pile head 21t. In particular, the pile head reinforcement 30 includes a U-shaped vertical reinforcement 31 and an annular horizontal reinforcement 32 tied to the vertical reinforcement 31, so that the pile head 21t can be reinforced efficiently. Therefore, it is possible to provide a method for constructing the pile-top seismic isolation structure 20A that enables a strong framework to be easily constructed.

[0027] In addition, the construction method of the pile head seismic isolation structure 20A further includes a process S3 of installing an outer steel pipe 22 in a position covering the foundation pile 21 from the outside, and in a process S8 of constructing the foundation reinforced concrete section 23A, concrete is poured into the hollow section 21h of the foundation pile 21 and between the foundation pile 21 and the outer steel pipe 22. According to this configuration, the outer steel pipe 22 installed in a position covering the foundation pile 21 from the outside is used as a formwork that does not need to be removed, and concrete is poured inside the outer steel pipe 22 to form the foundation reinforced concrete part 23A. Therefore, the pile-top seismic isolation structure 20A can be constructed efficiently. Furthermore, with this construction method, the pile head 21t of the foundation pile using the steel pipe 21m is covered with the foundation reinforced concrete part 23A, and the outer side of that is further covered by the outer steel pipe 22, so that a concrete pile with the pile head 21t equipped with double steel pipes is formed. The foundation reinforced concrete part 23A formed inside the outer steel pipe 22 and covering the pile head 21t is uniformly restrained by the pile head reinforcing bar 30 and the outer steel pipe 22, so that the shear strength can be further increased. Therefore, it is not necessary to provide a large concrete part around the pile head 21t to form the pile head seismic isolation structure 20A, and the foundation skeleton can be realized small and compact. Furthermore, by making the pile head 21t a concrete pile equipped with double steel pipes, the bending strength and shear strength of the pile head 21t are increased, and therefore it is not necessary to connect the foundation piles 21 with foundation beams or the like to increase the shear resistance of the foundation piles 21. Therefore, it is possible to realize a pile head seismic isolation structure 20A of an independent footing type without a foundation beam, which is strong and capable of shear resistance.

[0028] In addition, the pile head reinforcement 30 is provided with a height adjustment bar 70 arranged to be positioned inside the U-shape of the vertical reinforcement 31, and in process S7 of installing the pile head reinforcement 30, the height adjustment bar 70 is placed on the top end of the foundation pile 21 to determine the installation height position of the pile head reinforcement 30. With this configuration, by placing the height adjustment bar 70 provided on the vertical reinforcement bar 31 of the pile head reinforcement bar 30 on the top end of the foundation pile 21, the installation height position of the pile head reinforcement bar 30 relative to the foundation pile 21 can be easily and reliably determined.

[0029] The pile-top seismic isolation structure 20A is a pile-top seismic isolation structure 20A in which a seismic isolation device 4 is installed on the pile head 21t of the foundation pile 21, and includes a foundation pile 21 using a steel pipe 21m, a foundation reinforced concrete part 23A covering the pile head 21t of the foundation pile 21 and on which the seismic isolation device 4 is installed, and a plurality of vertical reinforcing bars 31, each of which is processed into a U-shape and arranged inverted so that the bottom of the U-shape is located on the upper side, and is radially arranged so that one end 31s is on the inside. and a pile head reinforcement 30 comprising a plurality of vertical reinforcements 31 and annular transverse reinforcements 32 tied to each of the plurality of vertical reinforcements 31. The pile head reinforcement 30 is attached so that one end 31s of the vertical reinforcement 31 is installed in a hollow portion 21h provided in the center of the horizontal cross section of the pile head 21t of the foundation pile 21 and the other end 31t of the vertical reinforcement 31 is installed outside the pile head 21t, and the entire pile is embedded in the foundation reinforced concrete portion 23A. According to this configuration, the pile head reinforcement 30 is arranged so that one end 31s of the vertical reinforcement 31 is installed in the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is installed on the outside of the pile head 21t. By embedding such a pile head reinforcement 30 in the foundation reinforced concrete portion 23A covering the pile head 21t of the foundation pile 21, the pile head 21t is restrained by the pile head reinforcement 30 and the foundation reinforced concrete portion 23A. This can increase the shear strength of the pile head 21t. In particular, since the pile head reinforcement 30 includes the U-shaped vertical reinforcement 31 and the circular ring-shaped horizontal reinforcement 32 tied to the vertical reinforcement 31, the pile head 21t can be reinforced efficiently. The pile head reinforcement bar 30 is entirely embedded in the foundation reinforced concrete part 23A. The foundation reinforced concrete part 23 is integrally constructed by pouring concrete into the hollow part 21h of the foundation pile 21 and around the pile head part 21t, thereby making it possible to improve the efficiency of construction. Therefore, it is possible to provide a pile-top seismic isolation structure 20A that allows for easy construction of a sturdy framework.

[0030] [Second embodiment] A pile-top seismic isolation structure according to the second embodiment of the present invention is shown in Fig. 14. Fig. 15 is a cross-sectional view taken along line II-II in Fig. 14. As shown in FIG. 14, in the pile-top seismic isolation structure in this embodiment, a foundation portion 2B includes a plurality of pile-top seismic isolation structures 20B and a foundation beam 50.

[0031] Each of the plurality of pile-top seismic isolation structures 20B includes a foundation pile 21, a foundation reinforced concrete portion 23B, and a pile-top reinforcing bar 30. The pile-top seismic isolation structure 20B of this embodiment does not include an outer steel pipe 22. The foundation reinforced concrete portion 23B is made of concrete poured on-site radially outside the pile head 21t of the foundation pile 21. The foundation reinforced concrete portion 23B covers the pile head 21t of the foundation pile 21 from the radially outside. The pile head 21t of the foundation pile 21 is embedded in the foundation reinforced concrete portion 23B. The foundation reinforced concrete section 23B has a lower concrete section 23c and an additional concrete section 23d. The additional concrete section 23d is provided on the lower concrete section 23c. The connecting section 31c of the pile head reinforcement 30 extends upward from the lower concrete section 23c and is embedded in the additional concrete section 23d.

[0032] A foundation beam 50 is joined to the lower concrete portion 23c. In the foundation beam 50, beam main reinforcement bars 52 and beam shear reinforcement bars 53 are embedded in beam concrete 51. The beam main reinforcement bars 52 penetrate through the foundation reinforced concrete portion 23B. As shown in FIG. 15, lower concrete portion 23c is formed so as to be larger than additional concrete portion 23d in plan view. In the lower concrete portion 23c, a reinforcing bar cage 62 is embedded on the outer periphery and above the pile head 21t of the foundation pile 21 so as to cover the pile head 21t from the sides and above. The reinforcing bar cage 62 includes horizontal bars 62a arranged in a lattice shape when viewed from above. The horizontal bars 62a are provided in multiple layers at intervals in the vertical direction. The reinforcing bar cage 62 further includes vertical bars 62b extending in the vertical direction to connect the multiple layers of horizontal bars 62a. The reinforcing bar cage 62 is formed so that the outermost periphery forms a rectangle when viewed from above as shown in Fig. 15. Reinforcing bars 61 are provided that extend diagonally when viewed from above so as to connect the centers of adjacent side surfaces of this rectangle.

[0033] In this embodiment, the pile head reinforcement bar 30 is provided at a higher height position than in the first embodiment. The connection metal 37 is provided near the upper end of the foundation pile 21, and the pile anchor 35 extends further upward than the upper end of the foundation pile 21 and is embedded in the foundation reinforced concrete part 23B between the pile head 21t of the foundation pile 21 and the seismic isolation device 4. The height position of the pile head reinforcement bar 30 is adjusted by the height adjustment bar 70 placed on the top end of the foundation pile 21. In this embodiment as well, the pile anchors 35 are provided so as to overlap the vertical reinforcing bars 31 in the vertical direction. As in the first embodiment, a base plate 40 is provided on the foundation reinforced concrete portion 23B, and the seismic isolation device 4 is placed on the base plate 40.

[0034] (Construction method of pile head seismic isolation structure) FIG. 16 is a flowchart showing the flow of the method for constructing a pile-top seismic isolation structure in this embodiment. The above-described pile-top seismic isolation structure 20B can be constructed as follows. First, the precast concrete foundation pile 21 is constructed by driving the foundation pile 21 into the existing ground to a predetermined depth (step S21). The foundation pile 21 is installed so that the pile head 21t protrudes upward by a predetermined length from the ground G. After that, gravel 26 and mortar concrete 25 are laid on the ground G to a predetermined thickness. Next, a plurality of pile anchors 35 are attached to the radially outer side of the steel pipe 21m of the foundation pile 21 (step S22).

[0035] Fig. 17 is a diagram showing a process of assembling a formwork and a process of installing a pile head reinforcement in this embodiment, and Fig. 18 is a diagram showing a process of pouring concrete in this embodiment. 17, a formwork 200 is assembled in a position that covers the foundation pile 21 from the outside (step S23). The formwork 200 is placed on the basing concrete 25. Meanwhile, the pile head reinforcement 30 is assembled in a work yard or the like on the site (step S24). The pile head reinforcement 30 is assembled using a plurality of vertical reinforcement 31 and a plurality of horizontal reinforcement 32. Each vertical reinforcement 31 is processed into a U-shape and arranged in an inverted manner so that the bottom of the U-shape is located on the upper side. The vertical reinforcement 31 is arranged radially when viewed from above so that one end 31s is on the inside. The inner periphery horizontal reinforcement 32A and the outer periphery horizontal reinforcement 32B as the horizontal reinforcement 32 are arranged at intervals in the vertical direction. Each inner periphery horizontal reinforcement 32A is tied to the first extension portion 31a of the plurality of vertical reinforcement 31. Each outer periphery horizontal reinforcement 32B is tied to the second extension portion 31b of the plurality of vertical reinforcement 31. Furthermore, height adjustment bars 70 are provided so as to be located inside the U-shape of the vertical reinforcement bars 31. The height adjustment bars 70 extend in the radial direction of the foundation pile 21, and are connected to the inner periphery horizontal reinforcement bars 32A and the outer periphery horizontal reinforcement bars 32B by welding, wire, or the like. The height adjustment bars 70 are joined at a position where the relative position of the pile head reinforcement bars 30 to the foundation pile 21 becomes appropriate when the pile head reinforcement bars 30 are provided so that the height adjustment bars 70 abut against the top end of the foundation pile 21.

[0036] Thereafter, the pile head reinforcement bar 30 assembled on the ground is attached to the pile head 21t of the foundation pile 21 (step S25). One end 31s of the vertical reinforcement bar 31 of the pile head reinforcement bar 30 is inserted into the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is located on the outside of the pile head 21t. At this time, the height adjustment bar 70 of the pile head reinforcement bar 30 is placed on the top end of the foundation pile 21, so that the pile head reinforcement bar 30 is positioned at an appropriate height with respect to the foundation pile 21. The order of step S23 of assembling the formwork 200 and step S25 of attaching the pile head reinforcement bars 30 may be reversed. 18, concrete is poured inside the formwork 200 to construct the lower concrete portion 23c of the foundation reinforced concrete portion 23B (step S26). The concrete for constructing the lower concrete portion 23c is preferably concrete having a design standard strength of, for example, 42 N / mm 2 In this case, one end 31s of each of the multiple vertical reinforcements 31 of the pile head reinforcement 30 is embedded in the lower concrete portion 23c of the foundation reinforced concrete portion 23B within the hollow portion 21h of the foundation pile 21, and the other end 31t is embedded outside the foundation pile 21 in the lower concrete portion 23c of the foundation reinforced concrete portion 23B. Thereafter, the formwork 200 is dismantled and removed, and the ground G around the foundation reinforced concrete portion 23B is backfilled to a predetermined height (step S27). After constructing the lower concrete portion 23c, the foundation beam 50 is constructed. The concrete for constructing the beam concrete 51 of the foundation beam 50 has a design standard strength of, for example, 30 N / mm 2 can be used.

[0037] Fig. 19 is a diagram showing a process of setting a base plate and a process of setting a raised formwork in this embodiment, and Fig. 20 is a diagram showing a process of pouring additional concrete in this embodiment. Next, as shown in Fig. 19, the base plate 40 is set on the lower concrete portion 23c (step S28). Cap nuts 44 are welded to the lower surface of the base plate 40 at positions corresponding to the bolt insertion holes 40h. The base plate 40 is set to a predetermined height by placing a plurality of cap nuts 44 on the lower concrete portion 23c. At this time, the height of the base plate 40 is adjusted by inserting a shim plate between the cap nuts 44 and the lower concrete portion 23c, if necessary. Next, the raised formwork 90 is set (step S29). In this embodiment, the raised formwork 90 is composed of an outer frame 93 provided so as to rise upward on the lower concrete portion 23c, and crosspieces 91 provided on the outer periphery of the upper surface of the base plate 40. The crosspieces 91 are provided so that their upper ends are higher than the upper end of the outer frame 93. In the raised formwork 90, a gap 92 that continues in the circumferential direction is formed between the outer periphery of the base plate 40 and the upper end of the outer frame 93.

[0038] 20, concrete is poured under the base plate 40 to construct the additional concrete 23d portion of the foundation reinforced concrete portion 23B (step S30). To do this, concrete is poured and filled between the base plate 40 and the previously constructed lower concrete portion 23c through concrete pouring holes 40g formed in the base plate 40. The concrete for constructing the additional concrete portion 23d is selected from concrete pouring holes 40g formed in the base plate 40, and has a design standard strength of, for example, 42 N / mm 2The above-mentioned may be used. Since the base plate 40 has a plurality of air vent holes 40j, concrete can be satisfactorily poured and filled on the lower surface side of the base plate 40 while preventing air bubbles from remaining. The concrete is poured sufficiently until it overflows from the gap 92 between the outer periphery of the base plate 40 and the upper end of the outer frame 93. At this time, since the crosspiece 91 is provided on the outer periphery of the upper surface of the base plate 40, it is possible to prevent the concrete from flowing around to the upper surface side of the base plate 40. In this way, the filling property of the concrete is improved, and the upper surface of the base plate 40 on which the seismic isolation device 4 is later provided is prevented from being soiled. The poured concrete hardens to form the additional concrete portion 23d. As a result, the foundation reinforced concrete portion 23B consisting of the previously constructed lower concrete portion 23c and the additional concrete portion 23d is formed. In the foundation reinforced concrete section 23B, concrete is poured in stages into the lower concrete section 23c and the additional concrete section 23d, but these are firmly connected by the pile head reinforcement 30 provided between them. This foundation reinforced concrete section 23B firmly supports the base plate 40. After this, the outer frame 93 and crosspieces 91 of the raised formwork 90 are removed, and then the seismic isolation device 4 is placed on the base plate 40, as shown in Figure 14, and the upper structure 3 is constructed above it in sequence.

[0039] (Action and effect) The construction method of the pile-top seismic isolation structure 20B as described above is a construction method of the pile-top seismic isolation structure 20B in which a seismic isolation device 4 is installed on the pile head 21t of the foundation pile 21 using the steel pipe 21m, and includes a step S21 of constructing the foundation pile 21 in the ground G, a step S22 of constructing the foundation pile 21 in the ground G, and a step S23 of constructing the foundation pile 21 in the ground G. The step S22 includes a step S23 of constructing the foundation pile 21 in the ground G, and a step S24 of constructing the foundation pile 21 in the ground G. The step S22 includes a step S24 of constructing the foundation pile 21 in the ground G, and a step S25 of constructing the foundation pile 21 in the ground G. The step S22 includes a step S25 of constructing the foundation pile 21 in the ground G, and a step S26 of constructing the foundation pile 21 in the ground G. The step S22 includes a step S26 of constructing the foundation pile 21 in the ground G, and a step S27 of constructing the foundation pile 21 in the ground G. The method includes a step S24 of assembling the pile head reinforcement 30 having the vertical reinforcement 31 and the vertical reinforcement 32; a step S25 of attaching the pile head reinforcement 30 so that one end 31s of the vertical reinforcement 31 is placed in a hollow portion 21h provided in the center of the horizontal cross section of the pile head 21t of the foundation pile 21 and the other end 31t of the vertical reinforcement 31 is placed on the outside of the pile head 21t; and steps S26 and S30 of pouring concrete into the hollow portion 21h and around the pile head 21t to construct the foundation reinforced concrete portion 23B on which the seismic isolation device 4 is to be installed. According to this configuration, the pile head reinforcement bars 30 are assembled in advance, and then attached to the pile heads 21t of the foundation piles 21. This allows the work of assembling the pile head reinforcement bars 30 to be carried out efficiently, and shortens the construction period. The pile head reinforcement 30 is attached so that one end 31s of the vertical reinforcement 31 is installed in the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is installed on the outside of the pile head 21t. By embedding such a pile head reinforcement 30 in the foundation reinforced concrete portion 23B formed by concrete poured in the hollow portion 21h of the foundation pile 21 and around the pile head 21t, the pile head 21t is restrained by the pile head reinforcement 30 and the foundation reinforced concrete portion 23B. This can increase the shear strength of the pile head 21t. In particular, the pile head reinforcement 30 includes a U-shaped vertical reinforcement 31 and an annular horizontal reinforcement 32 tied to the vertical reinforcement 31, so that the pile head 21t can be reinforced efficiently. Therefore, it is possible to provide a method for constructing the pile-top seismic isolation structure 20B that enables a strong framework to be easily constructed.

[0040] In addition, the pile head reinforcement 30 is provided with a height adjustment bar 70 arranged to be positioned inside the U-shape of the vertical reinforcement 31, and in process S25 of installing the pile head reinforcement 30, the height adjustment bar 70 is placed on the top end of the foundation pile 21 to determine the installation height position of the pile head reinforcement 30. With this configuration, by placing the height adjustment bar 70 provided on the vertical reinforcement bar 31 of the pile head reinforcement bar 30 on the top end of the foundation pile 21, the installation height position of the pile head reinforcement bar 30 relative to the foundation pile 21 can be easily and reliably determined.

[0041] The pile-top seismic isolation structure 20B is a pile-top seismic isolation structure 20B in which a seismic isolation device 4 is installed on the pile head 21t of the foundation pile 21, and includes a foundation pile 21 using a steel pipe 21m, a foundation reinforced concrete part 23B covering the pile head 21t of the foundation pile 21 and on which the seismic isolation device 4 is installed, and a plurality of vertical reinforcing bars 31, each of which is processed into a U-shape and arranged inverted so that the bottom of the U-shape is located on the upper side, and is radially arranged so that one end 31s is on the inside. and a pile head reinforcement 30 comprising a plurality of vertical reinforcements 31 and annular transverse reinforcements 32 tied to each of the plurality of vertical reinforcements 31. The pile head reinforcement 30 is attached so that one end 31s of the vertical reinforcement 31 is installed in a hollow portion 21h provided in the center of the horizontal cross section of the pile head 21t of the foundation pile 21 and the other end 31t of the vertical reinforcement 31 is installed outside the pile head 21t, and the entire pile is embedded in the foundation reinforced concrete portion 23B. According to this configuration, the pile head reinforcement 30 is arranged so that one end 31s of the vertical reinforcement 31 is installed in the hollow portion 21h of the foundation pile 21, and the other end 31t located on the outside is installed on the outside of the pile head 21t. By embedding such a pile head reinforcement 30 in the foundation reinforced concrete portion 23B covering the pile head 21t of the foundation pile 21, the pile head 21t is restrained by the pile head reinforcement 30 and the foundation reinforced concrete portion 23B. This can increase the shear strength of the pile head 21t. In particular, since the pile head reinforcement 30 includes the U-shaped vertical reinforcement 31 and the annular horizontal reinforcement 32 tied to the vertical reinforcement 31, the pile head 21t can be efficiently reinforced. The pile head reinforcement bar 30 is entirely embedded in the foundation reinforced concrete part 23B. The foundation reinforced concrete part 23 is integrally constructed by pouring concrete into the hollow part 21h of the foundation pile 21 and around the pile head part 21t, thereby making it possible to improve the efficiency of construction. Therefore, it is possible to provide a pile-top seismic isolation structure 20B that allows for easy construction of a sturdy framework.

[0042] (Modification of the embodiment) The pile top seismic isolation structure of the present invention is not limited to the above-mentioned embodiments described with reference to the drawings, and various modifications are possible within the technical scope. For example, in the above first embodiment, a configuration is provided with the outer steel pipe 22 covering the foundation reinforced concrete part 23A from the outside, but a foundation reinforced concrete part may be provided further outside the outer steel pipe 22 and the outer steel pipe 22 may be covered by the foundation reinforced concrete part, or a configuration is possible without the outer steel pipe 22. Alternatively, in the above second embodiment, a configuration is provided with no outer steel pipe covering the foundation reinforced concrete part 23B from the outside, but a configuration is also possible with an outer steel pipe. In the above embodiment, the height adjustment reinforcement 70 is connected to the inner periphery horizontal reinforcement 32A and the outer periphery horizontal reinforcement 32B, but this is not limited thereto. The height adjustment reinforcement 70 may be connected only to the inner periphery horizontal reinforcement 32A, or only to the inner periphery horizontal reinforcement 32A. Furthermore, the height adjustment reinforcement 70 may be provided such that, for example, its upper end is connected to the connecting portion 31c and extends downward, and its lower end is in contact with the top end of the foundation pile. [Explanation of symbols]

[0043] 4 Seismic isolation device 23d Additional concrete section 20A, 20B Pile head seismic isolation structure 30 Pile head reinforcement 21 Foundation pile 31 Longitudinal reinforcement 21h Hollow portion 31s One end 21m Steel pipe 31t Other end 21t Pile head 32 Horizontal reinforcement 22 Outer steel pipe 70 Height adjustment bar 23A, 23B Foundation reinforced concrete section G Ground 23c Lower concrete section

Claims

1. A method for constructing a pile head seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile using a steel pipe, comprising: constructing foundation piles in the ground; A step of assembling a pile head reinforcement bar comprising a plurality of vertical reinforcement bars, each of which is processed into a U-shape, arranged inverted so that the bottom of the U-shape is located on the upper side, and radially arranged so that one end is on the inside, and a circular ring-shaped horizontal reinforcement bar tied to each of the plurality of vertical reinforcement bars; A step of installing the pile head reinforcement in such a way that one end of the vertical reinforcement is installed in a hollow portion provided in the center of the pile horizontal cross section of the pile head of the foundation pile, and the other end of the vertical reinforcement is installed outside the pile head; A step of pouring concrete around the hollow portion and the pile head to a height above the pile head to construct a lower concrete portion; A step of constructing an additional concrete portion in which the seismic isolation device is to be installed by pouring concrete having a strength higher than that of the lower concrete portion on the lower concrete portion; Including, In the step of constructing the additional concrete portion, the pile head reinforcement is provided across the lower concrete portion and the additional concrete portion. A method for constructing a pile head seismic isolation structure.

2. The method further includes a step of installing an outer steel pipe at a position that covers the foundation pile from the outside, In the step of constructing the lower concrete portion, concrete is poured into the hollow portion of the foundation pile and between the foundation pile and the outer steel pipe, The method further includes a step of setting a base plate on which the seismic isolation device is placed, on the lower concrete portion at a distance from the lower concrete portion; In the step of constructing the additional concrete portion, concrete is poured between the lower concrete portion and the base plate to construct the additional concrete portion, The base plate is set so that a gap is formed between the outer periphery of the base plate and the upper end of the outer steel pipe. A method for constructing a pile head seismic isolation structure according to claim 1.

3. The pile head reinforcement includes a height adjustment reinforcement provided so as to be located inside the U-shape of the vertical reinforcement, A method for constructing a pile head seismic isolation structure as described in claim 1 or 2, characterized in that in the process of installing the pile head reinforcement, the height adjustment reinforcement is placed on the top end of the foundation pile to determine the installation height position of the pile head reinforcement.

4. A pile head seismic isolation structure in which a seismic isolation device is installed at the head of a foundation pile, The foundation pile using a steel pipe; a pile head reinforcement comprising: a plurality of vertical reinforcements, each of which is processed into a U-shape, arranged invertedly so that the bottom of the U-shape is located on the upper side, and radially arranged so that one end is on the inside; and an annular horizontal reinforcement that is tied to each of the plurality of vertical reinforcements; A hollow portion provided in the center of the horizontal cross section of the pile head of the foundation pile, and a lower concrete portion constructed by pouring concrete around the pile head to a height above the pile head; An additional concrete portion in which the seismic isolation device is installed, the additional concrete portion being constructed by pouring concrete having a strength higher than that of the lower concrete portion on the lower concrete portion; Equipped with A pile head seismic isolation structure characterized in that the pile head reinforcement is attached so that one end of the vertical reinforcement is installed in the hollow portion and the other end of the vertical reinforcement is installed on the outside of the pile head, and the entire pile head reinforcement is embedded in the lower concrete portion and the additional concrete portion so as to span between the lower concrete portion and the additional concrete portion.

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