Pile head seismic isolation structure and construction method of pile head seismic isolation structure

Abstract

To provide a pile head base-isolation structure for realizing a strong and compact skeleton.SOLUTION: A pile head base-isolation structure 20A has a seismic isolator 4 at the pile head part 21t of a foundation pile 21, and has the existing concrete foundation pile 21, a foundation reinforced concrete part 23A covering the pile head part 21t of the foundation pile 21 and installed with the seismic isolator 4, and pile head reinforcements 30 embedded in the foundation reinforced concrete part 23A. Each of the pile head reinforcements 30 is formed into a U-shape, and has multiple vertical reinforcements 31 radially arranged in relation to hollow part 21h provided in a sectional center of the foundation pile 21, and annular lateral reinforcements 32 bound to the vertical reinforcements 31. Each of one side material ends 31s of the multiple vertical reinforcements 31 is embedded in a concrete body 24 filled in the hollow part 21h of the foundation pile 21, and each of the other material ends 31t is embedded in the foundation reinforced concrete part 23 A.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] For example, in Patent Document 1, a seismic isolation device is attached via a base plate on a concrete pedestal made of concrete filled between the pile head of a foundation pile and an outer cylindrical body surrounding the outer peripheral side of the pile head, and a bearing ring that is joined to the outer peripheral surface of the pile head and extends continuously or intermittently in the circumferential direction is embedded in the concrete pedestal. Further, in this configuration, anchor bars are provided in an equidistant manner in the circumferential direction. In such a configuration, by embedding the bearing ring and the anchor bars in the concrete between the pile head of the foundation pile and the outer cylindrical body, the shear strength of the pile head portion of the foundation pile is increased, and the strength of the building frame is made strong. Further, in Patent Document 2, a nut is fixed to the upper part of an enlarged head ring composed of an outer steel pipe surrounding the periphery of the pile head portion and a horizontal diaphragm that penetrates the pile head portion and is fixed to the lower end of the outer steel pipe. Filling concrete in the enlarged head ring integrates the enlarged head ring and the pile head portion, and by screwing a bolt inserted through the lower flange of the seismic isolation device into the nut of the enlarged head ring, a configuration in which the seismic isolation device is rigidly joined to the pile head portion is disclosed. Further, in Patent Document 3, a short column that connects the seismic isolation device and the steel pipe pile, and a foundation beam that connects the pile head portions of a plurality of piles to each other by being connected to the short column are provided. The pile head portion of the steel pipe pile is embedded and held in the concrete portion inside the short column, and a displacement preventing plate is provided at the column head portion of the steel pipe pile so as to be embedded in the concrete portion inside the short column and surround the steel pipe of the steel pipe pile in an annular shape. The concrete portion inside the short column is configured to be tightened in the vertical direction by steel bars.

[0003] Generally, it is desirable to increase the strength of the pile head portion of a foundation pile in order to resist tensile forces acting in the vertical direction and shear forces acting in the horizontal direction. In a configuration as disclosed in Patent Documents 1 to 3, if the strength is increased to resist tensile force and shear, the concrete part such as a concrete pedestal will be enlarged.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a pile head seismic isolation structure and a method for constructing a pile head seismic isolation structure that can realize a strong structure compactly.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention adopts the following means. That is, the pile head seismic isolation structure of the present invention is a pile head seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile, and includes the precast concrete foundation pile, a foundation reinforced concrete part that covers the pile head of the foundation pile and where the seismic isolation device is installed, an outer steel pipe that covers the foundation reinforced concrete part from the outside, a plurality of dowel bars joined to the outer peripheral surface of the outer steel pipe and embedded in the soil concrete, and a pile head reinforcement embedded in the foundation reinforced concrete part. Each of the pile head reinforcements is formed in a U shape and has a plurality of longitudinal reinforcements radially provided with respect to a hollow part provided at the center of the cross section of the foundation pile, and a circular horizontal reinforcement bound to the longitudinal reinforcements. One end of each of the plurality of longitudinal reinforcements is embedded in a concrete body filled in the hollow part of the foundation pile, and the other end is embedded in the foundation reinforced concrete part. The concrete body and the foundation reinforced concrete part are cast separately in stages, and the foundation reinforced concrete part is provided so as to be in contact with the upper surface of the concrete body. According to such a configuration, by providing a pile head reinforcement at the pile head of the foundation pile and embedding it in the foundation reinforced concrete part, the pile head is restrained by the pile head reinforcement and the foundation reinforced concrete part, so that the shear strength of the pile head can be increased. In particular, since the pile head reinforcement includes U-shaped longitudinal reinforcements and a circular horizontal reinforcement bound to the longitudinal reinforcements, the pile head can be efficiently reinforced. Furthermore, since one end of the longitudinal reinforcement is embedded in a concrete body filled in the hollow part of the foundation pile, for example, after filling and casting the concrete body so as to embed one end of the longitudinal reinforcement, the foundation reinforced concrete part is formed so as to embed the pile head reinforcement including the other end of the longitudinal reinforcement, and it becomes possible to construct a pile head seismic isolation structure. That is, if the pile head seismic isolation structure is constructed in this way, after filling and casting the concrete body so as to embed one end of the longitudinal reinforcement, the pile head reinforcement is fixed to the foundation pile by the concrete body. Therefore, when forming the foundation reinforced concrete part, it is not necessary to arrange the pile head reinforcement independently using some support material. Since such a support material is not required in this way, the pile head seismic isolation structure can be made compact. Further, even if the concrete body in the hollow portion of the foundation pile and the reinforced concrete portion covering the pile head of the foundation pile are separately placed step by step as described above, one end of each longitudinal reinforcing bar is embedded in the concrete body and the other end is embedded in the reinforced concrete portion, and since the concrete body and the reinforced concrete portion are connected by the longitudinal reinforcing bars, the pile head seismic isolation structure can be made strong. In this way, it is possible to provide a pile head seismic isolation structure capable of realizing a strong structure compactly.

[0007] Also, the construction method of the pile head seismic isolation structure of the present invention is a construction method of a pile head seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile, and includes a foundation pile construction step of constructing the precast concrete foundation pile, and a pile head reinforcing member having a plurality of longitudinal reinforcing bars each formed in a U shape and a circular horizontal reinforcing bar bundled with the longitudinal reinforcing bars. The installation step of the pile head reinforcing member is to install the pile head reinforcing member such that one end of each of the plurality of longitudinal reinforcing bars is located in the hollow portion of the foundation pile and the plurality of longitudinal reinforcing bars are radial in plan view, and the concrete body forming step of filling the hollow portion of the foundation pile with concrete to form a concrete body so as to embed one end of each of the plurality of longitudinal reinforcing bars, and the construction step of the reinforced concrete portion of the foundation pile that covers the pile head of the foundation pile, contacts the upper surface of the concrete body, and embeds the other end of each of the plurality of longitudinal reinforcing bars so as to construct a reinforced concrete portion of the foundation pile where the seismic isolation device is installed. According to such a configuration, as already described with respect to the pile head seismic isolation structure, a strong structure can be realized compactly.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a pile head seismic isolation structure and a construction method of a pile head seismic isolation structure capable of realizing a strong structure compactly.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] The present invention is a pile head seismic isolation structure in which pile head reinforcement and a foundation reinforced concrete portion are provided so as to cover the pile head portion of a foundation pile, and a seismic isolation device is installed on the upper surface of the foundation reinforced concrete portion. Specifically, in the pile head seismic isolation structure, a pile head reinforcement having a plurality of longitudinal reinforcements provided radially with respect to the hollow portion of a precast concrete pile and a circular transverse reinforcement bundled with the longitudinal reinforcements is arranged, and the pile head reinforcement is embedded in a foundation reinforced concrete portion that covers the pile head portion of the foundation pile. Further, one end of the longitudinal reinforcement is embedded in a concrete body filled in the hollow portion of the precast concrete pile, and the other end of the longitudinal reinforcement is embedded in the foundation reinforced concrete portion. The first embodiment is a pile head seismic isolation structure in which a foundation beam is not connected to the foundation reinforced concrete portion, and an outer steel pipe is provided on the outer peripheral portion of the foundation reinforced concrete portion. The second embodiment is a foundation reinforced concrete part with a foundation beam connected to the foundation reinforced concrete part, and a base-isolated structure with a foundation beam in which a base isolation device is installed on the upper surface of the foundation reinforced concrete part with the foundation beam. Hereinafter, with reference to the accompanying drawings, a mode for implementing the base-isolated structure according to the present invention will be described based on the drawings. [First Embodiment] The base-isolated structure in the first embodiment of the present invention is shown in FIG. 1. As shown in FIG. 1, the building 1 includes a foundation part 2A constructed in the ground G, an upper structure part 3 provided on the foundation part 2A, and a base isolation device 4. The foundation part 2A includes a plurality of foundation piles 21. In the present embodiment, the frame of the upper structure part 3 has a plurality of columns 5 supported by each of the plurality of foundation piles 21 via the base isolation device 4, and beams 6 installed between adjacent columns 5. The base isolation device 4 is provided between the foundation pile 21 and the column 5.

[0011] FIG. 2 is a cross-sectional view taken along the line I-I of FIG. 1. As shown in FIGS. 1 and 2, each of the base-isolated structures 20A includes, in addition to the foundation pile 21 and the base isolation device 4 as described above, an outer steel pipe 22, a foundation reinforced concrete part 23A, and a pile head reinforcement 30. The foundation pile 21 is a so-called precast pile made of precast concrete, 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 the present embodiment, the foundation pile 21 is a concrete pile with an outer shell steel pipe provided with a steel pipe 21m on its outermost periphery. The foundation pile 21 is preformed into a predetermined shape in a factory in advance. The foundation pile 21 includes a pile body 21c which is a concrete body having a hollow portion 21h at 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 21t of the foundation pile 21. A concrete body 24 formed by placing and filling concrete is provided in the hollow portion 21h of the foundation pile 21.

[0012] 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 is shorter in the vertical direction than the foundation pile 21. The ground G is excavated at a certain depth around the foundation pile 21, and gravel 26 is provided on the undercut bottom thereof. The outer steel pipe 22 is provided on the leveling concrete 25 provided on the gravel 26, whereby the height at which the outer steel pipe 22 is provided is adjusted. The outer steel pipe 22 and the lower base plate 41 of the seismic isolation device 4 described later are not directly joined. The outer steel pipe 22 extends upward beyond the foundation pile 21. The inner diameter of the outer steel pipe 22 is larger than the outer diameter of the pile head 21t. Soil concrete 28 is laid radially outside the outer steel pipe 22. As shown in FIGS. 1 and 2, a plurality of dowel bars 29 embedded in the soil concrete 28 are joined to the outer peripheral surface of the outer steel pipe 22. The plurality of dowel bars 29 are arranged at intervals in the circumferential direction centered on the hollow portion 21h of the foundation pile 21, more specifically, centered on the central axis C of the foundation pile 21 and the hollow portion 21h. The plurality of dowel bars 29 extend radially outward from the outer peripheral surface of the outer steel pipe 22 and are embedded in the soil concrete 28.

[0013] The base reinforced concrete part 23A is made of concrete cast and filled on site inside the outer steel pipe 22. The base reinforced concrete part 23A is provided between the pile head part 21t of the foundation pile 21 and the outer steel pipe 22, and covers the pile head part 21t of the foundation pile 21 from the radially outer side. The base reinforced concrete part 23A forms a footing whose diameter is enlarged more radially outward than the pile head part 21t of the foundation pile 21. The base reinforced concrete part 23A is covered from the outside by the outer steel pipe 22. The base reinforced concrete part 23A is also provided above the pile head part 21t so as to contact the upper surface of the concrete body 24 of the foundation pile 21. A seismic isolation device 4 is provided on the upper end surface of the base reinforced concrete part 23A. The pile head part 21t of the foundation pile 21 is embedded in the base reinforced concrete part 23A.

[0014] The pile head reinforcing material 30 has a plurality of vertical reinforcing bars 31 and horizontal reinforcing bars 32. The plurality of vertical reinforcing bars 31 are arranged radially in a plan view with intervals in the circumferential direction around the hollow part 21h of the foundation pile 21, more specifically, around the central axis C of the foundation pile 21 and the hollow part 21h. The plurality of vertical reinforcing bars 31 are arranged at positions that do not interfere with each other in the circumferential direction with respect to the plurality of sleeve nuts 44. Each of the plurality of vertical reinforcing bars 31 has an overall U shape and integrally has a first extending part 31a, a second extending part 31b, and a connecting part 31c. The first extending part 31a extends in the vertical direction in the hollow part 21h of the foundation pile 21 and in the part above the pile head part 21t. The second extending part 31b is arranged at an interval from the first extending part 31a on the radially outer side of the foundation pile 21. The second extending part 31b is arranged on the radially outer side of the foundation pile 21 and extends in the vertical direction. The connecting part 31c connects the upper end parts of the first extending part 31a and the second extending part 31b. In this way, the vertical reinforcing bar 31 is formed in a U shape and is positioned as if this U shape is reversed in the vertical direction. One end 31s of one member, which is the lower end of the first extending portion 31a of each vertical reinforcing bar 31, is embedded in the concrete body 24 filled in the hollow portion 21h of the foundation pile 21. The upper portion of the first extending portion 31a is above the foundation pile 21 and is embedded in the foundation reinforced concrete portion 23A. Thereby, the first extending portion 31a is provided so as to straddle the concrete body 24 and the foundation reinforced concrete portion 23A, and connects them. The connecting portion 31c is above the foundation pile 21 and is embedded in the foundation reinforced concrete portion 23A. The second extending portion 31b of each vertical reinforcing bar 31 is entirely embedded in the foundation reinforced concrete portion 23A, and the other end 31t at the lower end is also embedded in the foundation reinforced concrete portion 23A.

[0015] The horizontal reinforcing bar 32 has an inner peripheral horizontal reinforcing bar 32A and an outer peripheral horizontal reinforcing bar 32B. The inner peripheral horizontal reinforcing bar 32A is a so-called hoop bar, is annular when viewed from above, and a plurality of them are provided at intervals in the vertical direction. Each inner peripheral horizontal reinforcing bar 32A is formed into a circle with a diameter smaller than the inner diameter of the hollow portion 21h in plan view, and is bound to the first extending portion 31a of the plurality of vertical reinforcing bars 31. A part of the plurality of inner peripheral horizontal reinforcing bars 32A is embedded in the concrete body 24 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 reinforcing bar 32B is a so-called hoop bar, is annular when viewed from above, and a plurality of them are provided at intervals in the vertical direction. Each outer peripheral horizontal reinforcing bar 32B is formed into a circle with a diameter larger than the outer diameter of the foundation pile 21 in plan view, and is bound to the second extending portion 31b of the plurality of vertical reinforcing bars 31. The plurality of outer peripheral horizontal reinforcing bars 32B are embedded in the foundation reinforced concrete portion 23A between the foundation pile 21 and the outer steel pipe 22.

[0016] In addition, 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 where they do not interfere with the plurality of longitudinal reinforcing bars 31 in the circumferential direction. Particularly in the present embodiment, each of the plurality of pile anchors 35 is associated with a socket nut 44 provided at the upper end of the foundation reinforced concrete part 23A, which will be described later. When viewed in plan as shown in FIG. 2, the pile anchor 35 and the socket nut 44 are positioned such that a straight line passing through the socket nut 44 corresponding to the pile anchor 35 passes through the center of the foundation pile 21. Each pile anchor 35 is joined to the steel pipe 21m of the foundation pile 21 via a connecting fitting 37. The connecting fitting 37 includes a nut member (not shown). Each pile anchor 35 is a threaded bar, and its lower end is screwed into the nut member of the connecting fitting 37, whereby each pile anchor 35 is joined to the foundation pile 21. Each pile anchor 35 extends in the vertical direction, and a fixing tool 38 composed of a plate and a nut is provided at its upper end. In the present embodiment, the fixing tool 38 is positioned at a height above the upper end of the foundation pile 21. Such a pile anchor 35 and the connecting fitting 37 are embedded in the foundation reinforced concrete part 23A. The pile anchor 35 is provided so as to overlap with the second extending portion 31b of the longitudinal reinforcing bar 31 of the pile head reinforcing material 30 by a predetermined length in the vertical direction (the vertical direction).

[0017] The seismic isolation device 4 includes a lower base plate 41, an upper base plate 42, and a laminated rubber part 43. The lower base plate 41 is plate-shaped along the horizontal plane and is provided on the upper end surface of the foundation reinforced concrete part 23A. A socket nut 44 is embedded in the upper end part of the foundation reinforced concrete part 23A. The lower base plate 41 is fixed to the upper end part of the foundation reinforced concrete part 23A by passing mounting bolts (not shown) through the lower base plate 41 at a plurality of locations spaced apart in the circumferential direction and fastening them to the socket nut 44. The upper base plate 42 is plate-shaped along the horizontal plane and is provided along the lower end surface of the column 5. A socket nut 45 is embedded in the lower end part of the column 5. The upper base plate 42 is fixed to the lower end part of the column 5 by passing mounting bolts (not shown) through the upper base plate 42 at a plurality of locations spaced apart in the circumferential direction and fastening them to the socket nut 45. The laminated rubber part 43 is configured by alternately laminating a plurality of rubber layers 43a and a plurality of steel plates 43b vertically.

[0018] In the pile head seismic isolation structure 20A as described above, when a bending moment acts on the foundation pile 21 and a tensile force T is generated, 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 longitudinal reinforcing bar 31 of the pile head reinforcing material 30 and the socket nut 44. Further, when a vertical compressive axial force acts from the column 5 to the seismic isolation device 4, this is transmitted 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 lower base plate 41 from the lower base plate 41 of the seismic isolation device 4. Also, the compressive axial force is transmitted to the foundation pile 21 from the lower base plate 41 via the foundation reinforced concrete part 23A between the foundation pile 21 and the outer steel pipe 22 on the outer side in the radial direction of the foundation pile 21 and the leveling concrete 25.

[0019] (Method for constructing the pile head seismic isolation structure) The pile head seismic isolation structure 20A as described above can be constructed as follows. First, drive the precast concrete foundation pile 21 into the ground. Next, a pile head reinforcing member 30 having a plurality of vertical reinforcing bars 31 each formed in a U shape and an annular horizontal reinforcing bar 32 bound to the vertical reinforcing bars 31 is provided such that one end 31s of each of the plurality of vertical reinforcing bars 31 is located in a hollow portion 21h provided at the center of the cross section of the foundation pile 21, and the plurality of vertical reinforcing bars 31 are spaced apart in the circumferential direction centered on the hollow portion 21h of the foundation pile 21 so as to be radial in plan view. Then, the hollow portion 21h of the foundation pile 21 is filled with concrete to form a concrete body 24, and one end 31s of each of the plurality of vertical reinforcing bars 31 is embedded in the concrete body 24. And a reinforced concrete portion 23A of the foundation is formed so as to cover the pile head portion 21t of the foundation pile 21 and embed the other end 31t of each of the plurality of vertical reinforcing bars 31. Finally, the seismic isolation device 4 is installed on the reinforced concrete portion 23A of the foundation.

[0020] (Function and effect) The pile head seismic isolation structure as described above is a pile head seismic isolation structure 20A in which the seismic isolation device 4 is installed at the pile head portion 21t of the foundation pile 21, and includes a precast concrete foundation pile 21, a reinforced concrete portion 23A of the foundation that covers the pile head portion 21t of the foundation pile 21 and on which the seismic isolation device 4 is installed, and a pile head reinforcing member 30 embedded in the reinforced concrete portion 23A of the foundation. The pile head reinforcing member 30 has a plurality of vertical reinforcing bars 31 each formed in a U shape and radially provided with respect to a hollow portion 21h provided at the center of the cross section of the foundation pile 21, and an annular horizontal reinforcing bar 32 bound to the vertical reinforcing bars 31. One end 31s of each of the plurality of vertical reinforcing bars 31 is embedded in a concrete body 24 filled in the hollow portion 21h of the foundation pile 21, and the other end 31t is embedded in the reinforced concrete portion 23A of the foundation. According to such a configuration, by providing the pile head reinforcing material 30 at the pile head portion 21t of the foundation pile 21 and embedding this in the foundation reinforced concrete portion 23A, the pile head portion 21t is restrained by the pile head reinforcing material 30 and the foundation reinforced concrete portion 23A, so that the shear strength of the pile head portion 21t can be increased. In particular, since the pile head reinforcing material 30 includes a U-shaped longitudinal reinforcing bar 31 and an annular transverse reinforcing bar 32 bound to the longitudinal reinforcing bar 31, the pile head portion 21t can be efficiently reinforced. Furthermore, since one end 31s of the longitudinal reinforcing bar 31 is embedded in the concrete body 24 filled in the hollow portion 21h of the foundation pile 21, for example, after the concrete body 24 is filled and placed so as to embed one end 31s of the longitudinal reinforcing bar 31, the foundation reinforced concrete portion 23A is formed so as to embed the pile head reinforcing material 30 including the other end 31t of the longitudinal reinforcing bar 31, and it becomes possible to construct the pile head seismic isolation structure 20A. That is, if the pile head seismic isolation structure 20A is constructed in this way, after the concrete body 24 is filled and placed so as to embed one end 31s of the longitudinal reinforcing bar 31, the pile head reinforcing material 30 is fixed to the foundation pile 21 by the concrete body 24. Therefore, when forming the foundation reinforced concrete portion 23A, there is no need to arrange the pile head reinforcing material 30 to stand on its own using some support material. Since such a support material becomes unnecessary in this way, the pile head seismic isolation structure 20A can be made compact. Therefore, through the concrete body 24 in the hollow portion, the foundation pile 21 and the pile head reinforcing material 30 are integrated to increase the structural performance of the foundation pile 21. Also, by embedding one end 31s of the longitudinal reinforcing bar 31 in the concrete body 24 filled in the hollow portion 21h of the foundation pile 21, the concrete body 24 also serves as a height adjustment function for the longitudinal reinforcing bar 31. Also, even if, as described above, the concrete body 24 in the hollow portion 21h of the foundation pile 21 and the foundation reinforced concrete portion 23A covering the pile head portion 21t of the foundation pile 21 are placed separately in stages, one end 31s of the longitudinal reinforcing bar 31 is embedded in the concrete body 24 and the other end 31t is embedded in the foundation reinforced concrete portion 23A, respectively, and since the concrete body 24 and the foundation reinforced concrete portion 23A are connected by the longitudinal reinforcing bar 31, the pile head seismic isolation structure 20A can be made strong. In this way, it is possible to provide the pile head seismic isolation structure 20A that can realize a strong and compact body.

[0021] Further, the pile head seismic isolation structure 20A further includes an outer steel pipe 22 that covers the foundation reinforced concrete part 23A from the outside. According to such a configuration, the foundation reinforced concrete part 23A that covers the pile head part 21t is covered from the outside by the outer steel pipe 22, and only the pile head part 21t forms a concrete pile with an outer shell steel pipe composed of a double steel pipe. Therefore, since the foundation reinforced concrete part 23A that covers the pile head part 21t is uniformly restrained by the pile head reinforcing bars 20 and the outer steel pipe 22, the shear strength can be further increased. Therefore, it is not necessary to provide a large concrete part around the pile head part 21t to form the pile head seismic isolation structure 20A, and it is possible to provide the pile head seismic isolation structure 20A that can reduce the size of the foundation body. In addition, by using a concrete pile with an outer shell steel pipe composed of a double steel pipe only for the pile head part 21t, the bending strength and shear strength of the pile head part 21t are increased, so it is not necessary to connect the foundation piles 21 to each other with a foundation beam or the like to increase the shear resistance of the foundation piles 21. Even a pile head seismic isolation structure in an independent footing form without a foundation beam can have shear resistance, and the foundation body can be reduced.

[0022] Furthermore, the outer steel pipe 22 is provided on the level concrete 25. Thereby, the installation height of the outer steel pipe 22 can be adjusted by the level concrete 25. Furthermore, the outer steel pipe 22 is not joined to the lower base plate 41 of the seismic isolation device 4 and is non-joined. Thereby, the deformation during an earthquake does not affect the lower base plate 41.

[0023] In addition, the foundation pile 21 is any one of a reinforced 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. According to such a configuration, it is possible to provide a head seismic isolation structure 20A that can increase the shear strength of the head portion 21t of the foundation pile 21, which is any one of a reinforced 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, and can realize a strong structure compactly. In addition, by adopting a precast concrete pile for the foundation pile 21, it is not necessary to arrange construction machinery for constructing a cast-in-place pile at the construction site, and the construction efficiency can be improved and the construction period can be shortened. Also, the head seismic isolation structure 20A of the present invention can be realized even on a relatively narrow construction site.

[0024] Particularly in the present embodiment, the foundation pile 21 is a concrete pile with an outer shell steel pipe in which a steel pipe 21m is provided on the outermost periphery, and a pile anchor 35 that extends in the vertical direction and is provided so as to overlap the longitudinal reinforcing bar 31 in the vertical direction is joined to the outside of the steel pipe 21m. According to such a configuration, the tensile force acting on the foundation pile 21 can be efficiently transmitted to the seismic isolation device 4.

[0025] In addition, in the construction method of the head seismic isolation structure 20A in which the seismic isolation device 4 is installed on the head portion 21t of the foundation pile 21 as described above, a precast concrete foundation pile 21 is driven into the ground, and a plurality of longitudinal reinforcing bars 31 each formed in a U shape and a horizontal reinforcing bar 32 formed in an annular shape and bound to the longitudinal reinforcing bars 31 are provided. The head reinforcing material 30 is provided such that one end 31s of each of the plurality of longitudinal reinforcing bars 31 is located in the hollow portion 21h provided at the center of the cross section of the foundation pile 21, and the plurality of longitudinal reinforcing bars 31 are spaced apart in the circumferential direction centered on the hollow portion 21h of the foundation pile 21 and are radially arranged in plan view. Concrete is filled into the hollow portion 21h of the foundation pile 21 to form a concrete body 24, one end 31s of each of the plurality of longitudinal reinforcing bars 31 is embedded in the concrete body 24, the head portion 21t of the foundation pile 21 is covered, and a foundation reinforced concrete portion 23A is formed so as to embed the other end 31t of each of the plurality of longitudinal reinforcing bars 31, and the seismic isolation device 4 is installed on the foundation reinforced concrete portion 23A. According to such a configuration, it is possible to realize the pile head seismic isolation structure 20A that can realize a strong and compact body.

[0026] [Second Embodiment] The pile head seismic isolation structure in the second embodiment of the present invention is shown in FIG. 3. FIG. 4 is a sectional view taken along the arrow II-II in FIG. 3. As shown in FIG. 3, in the pile head seismic isolation structure in this embodiment, the base portion 2B includes a plurality of pile head seismic isolation structures 20B and a foundation beam 50.

[0027] Each of the plurality of pile head seismic isolation structures 20B includes a foundation pile 21, a foundation reinforced concrete portion 23B, and a pile head reinforcement 30. The pile head 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 cast on-site on the radially outer side of the pile head portion 21t of the foundation pile 21. The foundation reinforced concrete portion 23B 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 23B. The foundation reinforced concrete portion 23B integrally has a seismic isolation device support portion 231 and a foundation beam joint portion 232. The seismic isolation device support portion 231 is provided on the foundation beam joint portion 232. The connecting portion 31c of the pile head reinforcement 30 extends above the foundation beam joint portion 232 and is embedded in the seismic isolation device support portion 231.

[0028] The foundation beam 50 is joined to the foundation beam joint portion 232. In the beam concrete 51 of the foundation beam 50, a beam main reinforcement 52 and a beam shear reinforcement 53 are embedded. The beam main reinforcement 52 penetrates through the foundation reinforced concrete portion 23B. As shown in FIG. 4, the foundation beam joint portion 232 is formed to be larger than the seismic isolation device support portion 231 in plan view. In the joint portion 232 of the foundation beam, a reinforcing cage 62 is embedded on the outer peripheral side and above the pile head portion 21t of the foundation pile 21 so as to cover the pile head portion 21t from the side and above. The reinforcing cage 62 includes horizontal bars 62a assembled in a lattice pattern when viewed from above. The horizontal bars 62a are provided in a plurality of layers at intervals in the vertical direction. The reinforcing cage 62 further includes vertical bars 62b extending in the vertical direction and connecting the horizontal bars 62a of the plurality of layers. As shown in FIG. 4, when viewed in plan, the outermost contour of the reinforcing cage 62 is formed in a rectangular shape. A reinforcing bar 61 extending in an oblique direction is provided when viewed in plan so as to connect the centers of adjacent side surfaces of this rectangular shape.

[0029] In the present embodiment, the pile head reinforcing member 30 is provided at a height position higher than that in the first embodiment. More specifically, the connecting hardware 37 is provided near the upper end portion of the foundation pile 21, and the pile anchor 35 extends further above the upper end portion of the foundation pile 21 and is embedded in the foundation reinforced concrete portion 23B between the pile head portion 21t of the foundation pile 21 and the seismic isolation device 4. Also in the present embodiment, the pile anchor 35 is provided so as to overlap with the longitudinal reinforcing bar 31 in the vertical direction.

[0030] Also in the pile head seismic isolation structure as described above, similar to the first embodiment, by providing the pile head reinforcing member 30 on the pile head portion 21t of the foundation pile 21 and embedding it in the foundation reinforced concrete portion 23B, the pile head portion 21t is restrained by the pile head reinforcing member 30 and the foundation reinforced concrete portion 23B, so that the shear strength of the pile head portion 21t can be increased. In particular, since the pile head reinforcing member 30 includes a U-shaped longitudinal reinforcing bar 31 and an annular horizontal reinforcing bar 32 bundled to the longitudinal reinforcing bar 31, the pile head portion 21t can be efficiently reinforced. Furthermore, since one end 31s of the vertical reinforcing bar 31 is embedded in the concrete body 24 filled in the hollow portion 21h of the foundation pile 21, for example, after the concrete body 24 is filled and placed so as to embed one end 31s of the vertical reinforcing bar 31, the foundation reinforcing concrete portion 23B is formed so as to embed the pile head reinforcing material 30 including the other end 31t of the vertical reinforcing bar 31, and the pile head seismic isolation structure 20B can be constructed. That is, if the pile head seismic isolation structure 20B is constructed in this way, after the concrete body 24 is filled and placed so as to embed one end 31s of the vertical reinforcing bar 31, the pile head reinforcing material 30 is fixed to the foundation pile 21 by the concrete body 24. Therefore, when forming the foundation reinforcing concrete portion 23B, it is not necessary to arrange the pile head reinforcing material 30 independently using some support material. Since such a support material is not required in this way, the pile head seismic isolation structure 20B can be made compact. Also, even if the concrete body 24 in the hollow portion 21h of the foundation pile 21 and the foundation reinforcing concrete portion 23A covering the pile head portion 21t of the foundation pile 21 are separately placed in stages as described above, one end 31s of the vertical reinforcing bar 31 is embedded in the concrete body 24 and the other end 31t is embedded in the foundation reinforcing concrete portion 23B, respectively, and the concrete body 24 and the foundation reinforcing concrete portion 23B are connected by the vertical reinforcing bar 31. Therefore, the pile head seismic isolation structure 20B can be made strong. In this way, it is possible to provide a pile head seismic isolation structure 20B that can realize a strong structure in a compact form.

[0031] (Modification of the embodiment) Note that the pile head seismic isolation structure of the present invention is not limited to the above-described embodiments described with reference to the drawings, and various modifications can be considered within its technical scope. For example, in the above-described first embodiment, the structure is provided with the outer steel pipe 22 that covers the basic reinforced concrete part 23A from the outside. However, a basic reinforced concrete part may be provided even further outside the outer steel pipe 22, and the outer steel pipe 22 may be covered with the basic reinforced concrete part. Alternatively, it is also possible to adopt a configuration without the outer steel pipe 22. Or, in the above-described second embodiment, the structure is configured without the outer steel pipe that covers the basic reinforced concrete part 23B from the outside, but it is also possible to adopt a configuration with the outer steel pipe.

[0032] (Study Example 1) Specific studies were conducted on the pile head seismic isolation structure 20A provided with the outer steel pipe 22 as shown in the above-described first embodiment, and the study examples are shown below. FIG. 5 is a diagram showing the pile head design stress acting on the pile head in the study example of the pile head seismic isolation structure according to the first embodiment. First, as shown in FIG. 5, two different types of piles (reference numerals F110A and F120A in FIG. 5) were set for the pile head design stress (axial force N, shear force Q, bending moment M). Also, the outer diameter D of the foundation pile 21 was 1200 mm, and the embedding height h of the pile head portion 21t of the foundation pile 21 with respect to the basic reinforced concrete part 23A was 1200 mm. The concrete strength used for the basic reinforced concrete part 23A was Fc36, the reinforcing bar material was SD390, and the main reinforcing bars were 12 - D32. Next, the concrete strength was studied. The shear force generated in the pile head portion 21t of the foundation pile 21 is transmitted by the bearing pressure from the foundation pile 21 to the basic reinforced concrete part 23A inside the outer steel pipe 22. Assuming that the stress block height of the basic reinforced concrete part 23A that resists the shear force is 0.3 times (0.3h) the embedding height h of the pile head portion 21t with respect to the basic reinforced concrete part 23A, and as shown in FIG. 6, when the stress spread angle θ from the center of the hollow portion 21h of the foundation pile 21 is 30 degrees, the bearing area Acc of the basic reinforced concrete part 23A is Acc = h×0.3×Dπ×2θ / 360 = 1200×0.3×1200π×60 / 360 = 226080mm 2 It becomes. Therefore, the compressive stress intensity for working on the foundation reinforced concrete part 23A inside the outer steel pipe 22 is Q / Acc = 600×10 3 N / 226080mm 2 = 2.654N / mm 2 It becomes. Since the concrete strength of the foundation reinforced concrete part 23A is Fc36, the allowable short-term compressive stress intensity is 24N / mm 2 It becomes. Therefore, 2.654 / 24 = 0.11 < 1.0 Since it is, it was confirmed that there is no problem with the concrete strength.

[0033] Also, regarding the outer steel pipe 22, the pressure received from the foundation reinforced concrete part 23A was calculated. The outer steel pipe 22 had a diameter D of 1800mm, a plate thickness t of 12mm, and a material of STK490. Also, the stress block height that resists the shear force was set to 0.3 times the embedding height h of the pile head part 21t with respect to the foundation reinforced concrete part 23A, and the stress spread angle θ from the center of the hollow part 21h of the foundation pile 21 to the outer steel pipe 22 was set to 30 degrees. Considering the construction error of 100mm of the foundation pile 21, the distance L from the center (pile center) of the foundation pile 21 to the inner surface (plate thickness t = 12mm) of the outer steel pipe 22 is L = 1200 / 2 + (300 - 100) - 12 = 788mm Then, the pressure receiving area on the inner surface of the outer steel pipe 22 is Acs = 788×2π×1 / 6×1200×0.3 = 296918mm 2 The internal pressure amount P acting on the outer steel pipe 22 is P = Q×Acs = 600×10 3 N / 296918mm 2 = 2.02N / mm 2 It becomes.

[0034] The circumferential stress intensity σ acting on the outer steel pipe 22 is σ = P·D / 2t = 2.02×1800 / (2×12) = 152 N / mm 2 It becomes as follows. The short-term test value of the outer steel pipe 22 is 152 / 325 = 0.47 < 1.0 Therefore, it was confirmed that the pressure received by the outer steel pipe 22 from the foundation reinforced concrete part 23A is below the short-term allowable stress of the outer steel pipe 22. Based on the above examination results, the steel pipe diameter of the outer steel pipe 22, the pile anchor 35, the longitudinal reinforcing bars 31, and the transverse reinforcing bars 32 were set as shown in Fig. 7.

[0035] (Examination Example 2) For the pile head seismic isolation structure 20B without the outer steel pipe 22 as shown in the above second embodiment and to which the foundation beam 50 is joined, specific examinations were conducted, and the examination examples are shown below. First, as shown in Fig. 8, three different types of piles (codes F100, F110, F120) were set for the pile head design stresses (axial force N, shear force Q, bending moment M) acting on the pile head. Also, the outer diameter D of the foundation pile 21 was 1200 mm, the embedding height h of the pile head 21t of the foundation pile 21 with respect to the foundation reinforced concrete part 23B was 1200 mm, the concrete strength used for the foundation reinforced concrete part 23B was Fc42, the reinforcing bar material was SD490, and the main reinforcing bars were 17 - D38.

[0036] Next, the concrete strength is examined. The shear force generated at the pile head 21t of the foundation pile 21 is transmitted by the short-term allowable shear force obtained by adding the shear force transmitted by the friction at the pile head 21t and the shear force resisted by the edge settlement of the foundation reinforced concrete part 23B (pile cap). Assuming the design shear force Q is 1382 kN and the design stress is the axial force N considering the vertical movement is 5889 kN, the short-term allowable shear force Qcr is Qcr = N·μ = 5945×0.5 = 2973 kN Therefore, the short-term test value is 1382 / 2973 = 0.48 < 1.0 Therefore, it was confirmed that the reinforced concrete part 23B to which the foundation beam 50 is joined can transmit the shear force by the friction between the concretes at the pile head part 21t. Based on the above examination results, the reinforced concrete part 23B, the pile anchor 35, the vertical reinforcing bar 31, and the horizontal reinforcing bar 32 were set as shown in FIG. 9.

Explanation of reference numerals

[0037] 4 Seismic isolation device 28 Earthen concrete 20A, 20B Pile head seismic isolation structure 30 Pile head reinforcing material 21 Foundation pile 31 Vertical reinforcing bar 21h Hollow part 31s One end of the member 21m Steel pipe 31t The other end of the member 21t Pile head part 32 Horizontal reinforcing bar 22 Outer steel pipe 35 Pile anchor 23A, 23B Reinforced concrete part 50 Foundation beam 24 Concrete body

Claims

1. A pile head seismic isolation structure in which a seismic isolation device is installed at the pile head of a foundation pile, comprising: the precast concrete foundation pile; a foundation reinforced concrete part that covers the pile head of the foundation pile and in which the seismic isolation device is installed; an outer steel pipe that covers the foundation reinforced concrete part from the outside; a plurality of dowel bars joined to the outer peripheral surface of the outer steel pipe and embedded in the slab concrete; a pile head reinforcement embedded in the foundation reinforced concrete part, wherein the pile head reinforcement has a plurality of vertical reinforcements each formed in a U shape and radially provided with respect to a hollow part provided at the center of the cross section of the foundation pile, and a horizontal reinforcement forming an annular shape bound to the vertical reinforcements; one end of each of the plurality of vertical reinforcements is embedded in a concrete body filled in the hollow part of the foundation pile, and the other end is embedded in the foundation reinforced concrete part; the concrete body and the foundation reinforced concrete part are cast separately in stages, and the foundation reinforced concrete part is provided so as to be in contact with the upper surface of the concrete body. A pile head seismic isolation structure characterized by this.

2. 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, comprising: a foundation pile construction step of constructing the precast concrete foundation pile; a pile head reinforcement installation step of installing a pile head reinforcement having a plurality of vertical reinforcements each formed in a U shape and a horizontal reinforcement forming an annular shape bound to the vertical reinforcements, such that one end of each of the plurality of vertical reinforcements is located in the hollow part of the foundation pile and the plurality of vertical reinforcements are radial in plan view; a concrete body forming step of filling the hollow part of the foundation pile with concrete to form a concrete body so as to embed one end of each of the plurality of vertical reinforcements; a foundation reinforced concrete part construction step of constructing a foundation reinforced concrete part in which the seismic isolation device is installed so as to cover the pile head of the foundation pile, be in contact with the upper surface of the concrete body, and embed the other end of each of the plurality of vertical reinforcements; A method for constructing a pile head seismic isolation structure, characterized by including this.

Images