Pile foundation structure

Abstract

To provide a pile foundation structure allowing construction to be easily carried out as suppressing skeleton volume of a basement and an excavation amount of the ground.SOLUTION: A pile foundation structure 1 including a pile 3 and a pressure-resistant slab 6 supporting a building 2 is provided with: the pile 3; a column type foundation member 4 connected on a pile head part 3t of the pile 3 and disposed in the subsurface so as to extend upward from the pile head part 3t; a column 5 disposed on an upper part of the foundation member 4; the pressure-resistant slab 6 connected on a lower part of the foundation member 4; and a horizontal resistant member 7 connected on the foundation member 4 at a position above the pressure-resistant slab 6. A column leg part 51 of the column 5 is semi-rigidly connected on an upper surface of the foundation member 4 or the column leg part 51 of the column 5 is smaller in a sectional area than the foundation member 4 and both are rigidly connected to each other.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a pile foundation structure including piles supporting a building and a pressure-resistant plate.

Background Art

[0002] When constructing a building, it is widely practiced to drive piles into the ground and provide a pressure-resistant plate on the ground to support the load of the building structure so as to be connected to the piles. For example, Patent Document 1 describes a configuration including a foundation pile buried in the ground and a foundation slab as a pressure-resistant plate joined to the head of the foundation pile. Further, Patent Document 2 describes a configuration including a footing disposed above the pile head of a pile and connected to a foundation beam, and a pressure-resistant plate provided in a region surrounded by the foundation beam connected to the footing. Furthermore, Patent Document 3 describes a configuration including an existing pressure-resistant plate supported by an existing pile, improved ground provided on the existing pressure-resistant plate, and dirt floor concrete provided on the improved ground.

[0003] Here, when an earthquake occurs, a bending moment acts on the pile head of the pile. In Patent Documents 1 to 3, basically, it is necessary to resist such a bending moment only by the pressure-resistant plate. For this reason, it is necessary to configure the pressure-resistant plate robustly and thickly so that the pressure-resistant plate can resist the bending moment. Also, in order to construct such a pressure-resistant plate, it is necessary to deeply excavate the ground. Therefore, the construction is not easy.

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 foundation structure with excellent structural safety that can be easily constructed by suppressing the amount of building structure in the basement floor and the amount of ground excavation.

Means for Solving the Problems

[0006] The inventors of the present invention arranged a column-shaped foundation member between the pile and the column on the ground floor, joined a pressure-resistant plate to the lower side of the foundation member, and joined a horizontal resistance member (floor slab or beam) to the upper side of the foundation member to form a rigidly joined structure. By doing so, not only the pressure-resistant plate but also the entire structure resists the bending moment acting on the pile head integrally, so that the thickness of the pressure-resistant plate can be reduced, and the amount of building structure in the basement floor and the amount of ground excavation can be reduced. As a result, the amount of building structure in the basement floor and the ground excavation work can be reduced, and the present invention has been achieved by focusing on the fact that a more efficient pile foundation structure can be realized. Specifically, in the pile foundation structure, the column foot of the column arranged on the upper part of the foundation member is semi-rigidly joined to the upper surface of the foundation member, or the column foot of the column has a smaller cross-sectional area than the foundation member, and both are rigidly joined, and the pressure-resistant plate, the foundation member, and the horizontal resistance member are rigidly joined to form a structure. In order to solve the above problems, the present invention adopts the following means. That is, the pile foundation structure of the present invention is a pile foundation structure including a pile supporting a building and a pressure-resistant plate, the pile, a column-shaped foundation member provided underground, which is joined to the pile head of the pile and extends upward from the pile head, a column arranged on the upper part of the foundation member, the pressure-resistant plate joined to the lower part of the foundation member, and a horizontal resistance member joined to the foundation member at a position above the pressure-resistant plate, and the column foot of the column is semi-rigidly joined to the upper surface of the foundation member, or the column foot of the column has a smaller cross-sectional area than the foundation member, and both are rigidly joined. The horizontal resistance member is a floor slab or a beam. According to the above configuration, a columnar foundation member provided underground and extending upward from the pile head of the pile is joined to the pile head of the pile. A pressure-resistant plate is joined to the lower part of this columnar foundation member, and horizontal resistance members (floor slab, beam) are joined to the foundation member at a position above the pressure-resistant plate. In this way, the pressure-resistant plate, the horizontal resistance members, and the foundation member are formed into a robust and integral structure having a certain thickness as a whole. Since the column is arranged above such a foundation member, even if the column is, for example, a column on the outer periphery of a building and a large load acts on it, the load can be transmitted from above downward to the pressure-resistant plate and the ground under the pressure-resistant plate. In this way, even in the case of a column on which a large load of a building acts, the axial rigidity of the structure supporting the column can be increased, and as a result, the structural safety can be enhanced. Here, since the columnar foundation member is provided so as to extend upward from the pile head of the pile, the pressure-resistant plate joined to the lower part of the foundation member is provided near the pile head. Since the horizontal resistance members (floor slab, beam) are joined to the foundation member at a position above such a pressure-resistant plate, the horizontal resistance members are configured to be joined to the foundation member at a position a certain height above the pile head of the pile. In such a configuration, when an earthquake occurs and a bending moment acts on the pile head of the pile, this is transmitted to the pressure-resistant plate, and at the same time, a couple force that acts in the direction opposite to the bending moment at a position different from the bending moment of the pile head acts on the horizontal resistance member formed integrally with the pressure-resistant plate via the columnar foundation member. Due to this couple force, the bending moment of the pile head is canceled out and the bending moment is reduced. In this way, since the bending moment of the pile head that should originally be resisted by the pressure-resistant plate is reduced by the foundation member and the horizontal resistance members, it is not necessary to resist the bending moment only by the pressure-resistant plate. Therefore, compared with the case where the foundation member is not provided, the pressure-resistant plate can be made thinner, so that the amount of building structure in the basement and the amount of ground excavation can be suppressed. In addition, the column base of the column is semi-rigidly joined to the upper surface of the column-shaped foundation member, or the cross-sectional area of the column base of the column is made smaller than the cross-sectional area of the column-shaped foundation member, and the column base and the foundation member are rigidly joined. As a result, during an earthquake, the horizontal force transmitted from the foundation member to the column base of the column is suppressed, and the building above the ground can enhance the structural stability against earthquakes and vibrations while ensuring a certain degree of flexibility. In particular, since the transmission of the bending moment is suppressed between the column base and the foundation member, the necessity of making the foundation member more robust than necessary for the purpose of resisting the bending moment between the column base and the foundation member is reduced. Therefore, when constructing the foundation member, for example, by reducing the cross-sectional area of the foundation member or reducing the number of shear reinforcement bars, the foundation member can be constructed compactly. The above effects are synergistic, making it possible to provide a pile foundation structure with excellent structural safety that can suppress the amount of building structure in the basement floor and the amount of ground excavation and can be easily constructed.

[0007] In one aspect of the present invention, the foundation member is arranged in the vertical direction compared to the horizontal foundation bar capacity in the horizontal direction, which is the product of the cross-sectional area of the horizontally arranged foundation horizontal bars and the tensile strength indicating the material properties of the foundation horizontal bars. The vertical foundation bars are arranged such that the vertical foundation bar capacity, which is the product of the cross-sectional area of the vertically arranged foundation vertical bars and the tensile strength indicating the material properties of the foundation vertical bars, is larger. According to such a configuration, since the vertical foundation bar capacity in the foundation member is larger than the horizontal foundation bar capacity, by enhancing the integrality of the bearing plate and the horizontal resistance member by the foundation member, when a bending moment acts on the pile head of the pile during an earthquake, the resistance to the bending moment can be increased.

[0008] In one aspect of the present invention, the pile foundation structure of the present invention further includes a core reinforcing bar extending vertically between the foundation member and the column such that the upper end is embedded in the column and the lower end is embedded in the foundation member. In the pile foundation structure, when the column and the foundation member are semi-rigidly joined, the lower end of the column is formed in a tapered shape to have an inclined surface, and the lower surface of the column abuts against the upper surface of the foundation member, and the column is provided so as to be tiltable with respect to the foundation member. According to such a configuration, by providing a core reinforcing bar extending vertically between the column and the foundation member and forming the lower end of the column in a tapered shape to have an inclined surface, the column is formed so that the column foot portion of the column is semi-rigidly joined to the upper surface of the foundation member, and the column can be provided so as to be tiltable with respect to the foundation member. Thereby, while ensuring a certain degree of flexibility between the column and the foundation member, the durability and stability of the structure against earthquakes and vibrations can be improved.

Effects of the Invention

[0009] According to the present invention, it is possible to realize a pile foundation structure excellent in structural safety that can easily perform construction by suppressing the building volume of the basement floor and the amount of ground excavation.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Best Mode for Carrying Out the Invention

[0011] The present invention is a pile foundation structure including piles and a pressure-resistant slab. As shown in FIG. 1, the pile foundation structure includes a column-shaped foundation member and a pressure-resistant slab disposed between the pile and the column on the ground floor, and a pressure-resistant slab joined to the lower side of the foundation member and a horizontal resistance member (floor slab or beam) joined to the upper side of the foundation member. In the pile foundation structure, the column foot of the column on the directly upper floor is semi-rigidly joined to the upper surface of the foundation member, and the column foot of the column on the directly upper floor has a smaller cross-sectional area than the foundation member, and both are rigidly joined. And the pressure-resistant slab, the column-shaped foundation member, and the horizontal resistance member are rigidly joined. The feature of this structure is that, with respect to the bending moment acting on the pile head, the pressure-resistant slab and the column-shaped foundation member and the horizontal resistance member disposed above it act integrally to resist, and by reducing the thickness of the pressure-resistant slab, the building volume of the basement floor and the amount of ground excavation are reduced. Hereinafter, with reference to the accompanying drawings, a form for implementing the pile foundation structure according to the present invention will be described based on the drawings. FIG. 1 shows a view showing the configuration of a building provided with the pile foundation structure according to an embodiment of the present invention. As shown in FIG. 1, the pile foundation structure 1 according to the present embodiment supports the building 2. More specifically, the pile foundation structure 1 includes a pile 3, a foundation member 4, a column 5, a pressure-resistant slab 6 (see FIG. 3), and a beam 7. The pile foundation structure 1 supports the column 5 from below by the pile 3, the foundation member 4, the pressure-resistant slab 6, and the beam 7.

[0012] FIG. 2 is a structural floor beam laying diagram of the I-I portion of FIG. 1. The building 2 of the present embodiment has a rectangular shape such that its outer peripheral surface 2f extends in each of a first direction D1 in the horizontal plane and a second direction D2 orthogonal to the first direction D1 in the horizontal plane when viewed in plan. The column 5 constitutes the framework of the building 2. As shown in FIGS. 1 and 2, in this embodiment, the column 5 is arranged on the outer peripheral portion of the building 2. A plurality of columns 5 are provided at intervals in the horizontal direction along the outer peripheral portion of the building 2. Each column 5 is provided so as to be exposed on the outer peripheral surface 2f of the building 2. That is, each column 5 constitutes a part of the outer peripheral surface 2f of the building 2. As shown in FIG. 1, each column 5 extends in the vertical direction H. At the column base portion 51 of each column 5, one side surface 51s in the column width direction along the outer peripheral surface 2f extends in the vertical direction H, while the other side surface 51t in the column width direction extends obliquely so as to approach the center portion in the column width direction of the column 5 from above to below. Thereby, the column base portion 51 is formed such that the dimension in the column width direction along the outer peripheral surface 2f of the building 2 gradually decreases from above to below. In the portion 52 above the column base portion 51 of each column 5, one side surface 52s in the column width direction and the other side surface 52t in the column width direction extend in the vertical direction H, and the dimension in the column width direction is made constant in the vertical direction H.

[0013] The columns 5 adjacent to each other in the horizontal direction along the outer peripheral surface 2f of the building 2 are connected via the outer peripheral beams 22 provided on each floor of the building 2. The outer peripheral beam 22 is, for example, of a steel frame structure and extends in the horizontal direction along the outer peripheral surface 2f of the building 2. An outer wall (not shown) is formed between the adjacent columns 5. In the building 2, the outer peripheral beam 22M provided on the intermediate floor of the column 5 serves as a vibration damping beam provided with a vibration damping panel 26 at the central position. The outer peripheral beam 22M formed as this vibration damping beam is separated from the floor slab of each floor and is configured not to support the floor slab.

[0014] Hereinafter, the structure of the pile foundation structure 1 in the portion viewed from arrow A in FIGS. 1 and 2 will be described with reference to the drawings. Similar explanations can also be made for other portions of the pile foundation structure 1 hereinafter. FIG. 3 is a longitudinal sectional view of the portion taken along line II-II in FIG. 2. FIG. 4 is a longitudinal sectional view of the portion taken along line III-III in FIG. 2. FIG. 5 is a cross-sectional view of the portion taken along line IV-IV in FIG. 3. FIG. 6 is a cross-sectional view of the portion taken along line V-V in FIG. 4. As shown in FIG. 3, the pile 3 is provided in the ground G vertically below the column 5. The pile 3 is, for example, a concrete-filled steel pipe pile, and includes a steel pipe 31 extending in the vertical direction H and concrete (not shown) filled in the steel pipe 31.

[0015] The foundation member 4 is provided underground. The foundation member 4 extends upward from the pile head 3t of the pile 3. The foundation member 4 is formed in a columnar shape extending in the vertical direction H. As shown in FIGS. 3 to 5, the foundation member 4 has a concrete part 41, a plurality of bending reinforcement bars 42 embedded in the concrete part 41, and a plurality of shear reinforcement bars 43 embedded in the concrete part 41. In the present embodiment, the concrete part 41 is formed in a rectangular parallelepiped shape extending in the vertical direction H as a whole. As shown in FIGS. 3 and 5, the concrete part 41 is formed so as to project to the outer peripheral side of the pile head 3t of the pile 3. That is, the cross-sectional area of the foundation member 4 is larger than the cross-sectional area of the pile 3. The pile head 3t of the pile 3 is embedded in the lower part of the concrete part 41. A plurality of anchor bars 35 are joined to the steel pipe 31 of the pile 3 so as to extend upward from the pile head 3t. The plurality of anchor bars 35 are embedded in the concrete part 41 of the foundation member 4 together with the pile head 3t. Thereby, the foundation member 4 is firmly joined to the pile head 3t of the pile 3. The plurality of bending reinforcement bars 42 extend in the vertical direction H. The lower end of each bending reinforcement bar 42 is provided at a position overlapping the pile head 3t of the pile 3, the anchor bar 35, and a pressure-resistant plate 6 described later in the vertical direction H. The upper end of each bending reinforcement bar 42 is provided at a position overlapping a beam 7 described later in the vertical direction H. The plurality of shear reinforcement bars 43 are provided at intervals in the vertical direction H. Each shear reinforcement bar 43 is provided so as to surround the plurality of bending reinforcement bars 42 in the concrete part 41.

[0016] As shown in FIGS. 3 and 4, the base member 4 is provided with a column support portion 45 at its upper part. The column support portion 45 is formed in such a shape that the concrete portion 41 protrudes more upward. The column support portion 45 is provided on the concrete portion 41. The column support portion 45 has a concrete portion 46, a plurality of anchor bars 47 embedded in the concrete portion 46, and a horizontal bar 48 embedded in the concrete portion 46 and provided orthogonally to the plurality of anchor bars 47. The plurality of anchor bars 47 protrude downward from the lower surface of the concrete portion 46 and are embedded in the concrete portion 41.

[0017] As shown in FIGS. 3 and 4, the column foot portion 51 of the column 5 is disposed above the column support portion 45 of the base member 4. The column foot portion 51 of the column 5 is semi-rigidly joined to the upper surface of the base member 4. As shown in FIGS. 3, 4, and 6, the column 5 has a concrete portion 56, a plurality of column main bars 57, and a plurality of shear reinforcement bars 58 embedded in the concrete portion 56. The concrete portion 56 is formed in a rectangular shape in a plan cross-sectional view. The cross-sectional area of the column foot portion 51 of the column 5 is smaller than the cross-sectional area of the concrete portion 41 of the base member 4. That is, the cross-sectional area of the base member 4 is larger than the cross-sectional area of the column foot portion 51.

[0018] In the column foot portion 51 of the column 5, the lower end of the concrete portion 56 is formed in a tapered shape and has an inclined surface 56s inclined toward the central portion side of the column 5 from above to below. The inclined surface 56s is formed over the entire circumference of the column 5. That is, the inclined surface 56s is formed on both the surface of the concrete portion 56 along the column width direction (first direction D1) and the surface along the column thickness direction (second direction D2). The lower surface 56b of the concrete portion 56 of the column 5 is provided in contact with the upper surface 45t of the column support portion 45 of the base member 4. Between the inclined surface 56s and the upper surface 45t of the column support portion 45, styrofoam (registered trademark) 59 is provided so as to fill the gap between the inclined surface 56s and the upper surface 45t of the column support portion 45. In the present embodiment, the styrofoam 59 is provided as a part of the formwork in order to form the inclined surface 56s when placing the concrete that forms the concrete portion 56. The styrofoam 59 may be removed after the formation of the concrete portion 56 including the inclined surface 56s, or may be left as it is.

[0019] The plurality of column main reinforcements 57 are embedded in the concrete portion 56 at the outer peripheral portion of the column foot portion 51 of the column 5. As shown in FIG. 4, among the plurality of column main reinforcements 57, the column main reinforcement 57S provided on one side in the column width direction (first direction D1) extends in the vertical direction H. Among the plurality of column main reinforcements 57, the column main reinforcement 57T provided on the other side in the column width direction extends obliquely so as to approach the center portion in the column width direction of the column 5 from above downward in parallel with the side surface 51t. The lower ends of the plurality of column main reinforcements 57 terminate within the concrete portion 56. That is, the plurality of column main reinforcements 57 do not protrude downward from the concrete portion 56 and are not embedded in the lower base member 4. The plurality of shear reinforcing bars 58 are embedded in the concrete portion 56 at intervals in the vertical direction H. Each of the plurality of shear reinforcing bars 58 is provided so as to surround the plurality of column main reinforcements 57. As will be described later, the column 5 is semi-rigidly joined to the column support portion 45 so as to be tiltable with respect to the base member 4. When an earthquake occurs and the column 5 tilts, a large compressive force acts near the lower end of the column foot portion 51 of the column 5 that contacts the base member 4. In order to resist this, the shear reinforcing bars 58 are concentratedly provided particularly near the lower end of the column foot portion 51.

[0020] The pile foundation structure 1 of the present embodiment further includes a plurality of core reinforcing bars 8. The plurality of core reinforcing bars 8 are provided at the joint between the foundation member 4 and the column 5. As shown in FIG. 6, when viewed in plan, the plurality of core reinforcing bars 8 are provided at the central portion of the column 5. The core reinforcing bars 8 are arranged, for example, three in number, at intervals in the column width direction (first direction D1). The core reinforcing bars 8 are arranged, for example, two in number, side by side in the column thickness direction (second direction D2) orthogonal to the column width direction in the horizontal plane. As shown in FIG. 3, each core reinforcing bar 8 is provided to extend in the vertical direction H between the foundation member 4 and the column 5. The upper end 8t of each core reinforcing bar 8 protrudes upward from the foundation member 4 and is embedded in the column 5. The lower end 8b of each core reinforcing bar 8 is embedded in the foundation member 4. The lower end 8b of each core reinforcing bar 8 is located above the pile head portion 3t of the pile 3 at the lower part of the foundation member 4.

[0021] With the above configuration, the concrete portion 56 of the column 5 and the concrete portions 41 and 46 of the foundation member 4 are not integrally formed, but are separate, different concrete bodies. For this reason, the column 5 and the foundation member 4 (the column support portion 45 thereof) are joined only by the core reinforcing bars 8 provided at the central portion of the column 5 as described above. Therefore, for example, when an earthquake occurs and a horizontal force acts on the pile 3, causing the foundation member 4 to displace in the horizontal directions D1 and D2 together with the pile 3, the column 5 tends to stay in place due to the inertial force. As a result, with a point on the outer periphery of the lower surface 56b of the column 5 as the center, the side opposite to the point is lifted upward, and the upper surface 45t of the foundation member 4 and the lower surface 56b of the column 5 are separated. In this way, the column 5 tilts and inclines with respect to the foundation member 4. Here, since the lower end of the column 5 has the inclined surface 56s and is formed in a tapered shape as described above, the above-described tilting is performed smoothly. In this way, the column 5 is semi-rigidly joined to the foundation member 4 and is provided so as to be tiltable with respect to the foundation member 4.

[0022] As described above, the column 5 is semi-rigidly joined to the column support portion 45 of the foundation member 4 so as to be tiltable with respect to the foundation member 4, and the lower surface 56b of the column 5 and the upper surface 45t of the foundation member 4 (the column support portion 45 thereof) are not joined. For this reason, there is a possibility that rainwater may enter from the outside of the building 2 through this interface. In order to suppress this, when the column 5 is particularly located on the outer peripheral portion of the building 2 as in the present embodiment, it is preferable to seal the joint portion between the column base portion 51 of the column 5 and the foundation member 4 with an appropriate sealing material for waterproofing. Further, it is desirable to apply rust preventive paint to the surface of the portion of the core reinforcing bar 8 located in the vicinity of this interface in the vertical direction H to suppress rusting of the core reinforcing bar 8 due to water entering the interface. Furthermore, in the present embodiment, the concrete portion 46 has a stepped portion 45d that protrudes upward on the inner side of the building 2. Thereby, when rainwater enters the inside of the column 5 from the outside of the building 2 through the above interface, further intrusion of the rainwater into the inside of the building 2 is suppressed.

[0023] The pressure-resistant plate 6 is joined to the lower part of the foundation member 4. As shown in FIGS. 3 and 5, the pressure-resistant plate 6 extends along a horizontal plane so as to cover the piles 3 and the ground around the foundation member 4. The pressure-resistant plate 6 is, for example, made of reinforced concrete, and has a concrete portion 61 and pressure-resistant plate reinforcing bars 62 embedded in the concrete portion 61. The pressure-resistant plate reinforcing bars 62 are, for example, assembled in a lattice shape in plan view. The pressure-resistant plate reinforcing bars 62 are provided at intervals in the vertical direction H at the upper and lower parts of the pressure-resistant plate 6. A part of the pressure-resistant plate reinforcing bars 62 protrudes laterally from the pressure-resistant plate 6 and is embedded in the concrete portion 41 of the foundation member 4. Thereby, the pressure-resistant plate 6 is firmly joined to the lower part of the foundation member 4.

[0024] FIG. 7 is a cross-sectional view of the portion taken along the arrow VI-VI in FIG. 3. FIG. 8 is a longitudinal sectional view of the portion taken along the arrow VII-VII in FIG. 3. The beam 7 (horizontal resistance member) supports the lowest floor of the building 2 (on the ground floor). The beam 7 is provided at a position above the pressure-resistant slab 6. The beam 7 is joined to the upper part of the foundation member 4. The beam 7 extends in the horizontal direction (second direction D2). As shown in FIGS. 3, 7, and 8, the beam 7 is, for example, made of reinforced concrete and has a concrete part 71, a plurality of main beam reinforcing bars 72, and beam shear reinforcing bars 73. As shown in FIGS. 3 and 7, the plurality of main beam reinforcing bars 72 are provided at intervals vertically in the upper and lower parts of the beam 7. In each of the upper and lower parts of the beam 7, the plurality of main beam reinforcing bars 72 are provided at intervals in the beam width direction (first direction D1) orthogonal to the extending direction (second direction D2) of the beam 7. Each main beam reinforcing bar 72 extends in the extending direction of the beam 7. The end portions of each main beam reinforcing bar 72 project from the concrete part 71 in the extending direction of the beam 7 and are embedded in the concrete part 41 of the foundation member 4. The end portions 72s of each main beam reinforcing bar 72 extend in the extending direction of the beam 7 within the concrete part 41 to a position overlapping the core reinforcing bar 8. The end portions 72s of each main beam reinforcing bar 72 terminate after being bent upward or downward. A plurality of beam shear reinforcing bars 73 are provided at intervals in the extending direction of the beam 7. Each beam shear reinforcing bar 73 is provided in the concrete part 71 so as to surround the plurality of main beam reinforcing bars 72.

[0025] Further, as shown in FIGS. 3 and 8, connection reinforcing bars 75 are provided at the joint between the beam 7 and the foundation member 4. The connection reinforcing bars 75 extend in the horizontal direction (second direction D2), one end of which is embedded in the concrete portion 41 of the foundation member 4, and the other end of which is embedded in the concrete portion 71 of the beam 7. In the present embodiment, a plurality of connection reinforcing bars 75 are provided. The plurality of connection reinforcing bars 75 are provided in two upper and lower stages at the middle portion in the vertical direction H of the beam 7. The connection reinforcing bars 75 provided in two upper and lower stages are arranged in a plurality of rows at intervals in the beam width direction (first direction D1) orthogonal to the extending direction of the beam 7 in the horizontal plane at each stage. The end portion 75s of the connection reinforcing bar 75 embedded in the foundation member 4 is bent downward and then terminated. The end portion 75s of the connection reinforcing bar 75 extends to a position beyond the region where the plurality of core reinforcing bars 8 are provided in the extending direction of the beam 7.

[0026] In the configuration as described above, when an earthquake occurs and a bending moment M acts on the pile head 3t of the pile 3, as shown in FIG. 3, the force F due to this bending moment M is transmitted to the pressure-resistant plate 6, and at the same time, a force -F of the same magnitude as the force F, that is, a couple, is generated in the opposite direction at a position different from the bending moment M of the pile head 3t with respect to the beam 7 integrally formed with the pressure-resistant plate 6 via the columnar foundation member 4. Due to this couple, the bending moment M of the pile head 3t is canceled out, and as shown in the stress diagram depicted as the bending moment M in FIG. 3, the stress of the foundation member 4 is reduced as it goes upward. In particular, at the height where the beam 7 is joined to the upper end of the foundation member 4, the bending moment M is substantially equal to zero. In this way, in the present embodiment, the beam 7 serves as a horizontal resistance member that resists the bending moment M integrally with the foundation member 4 and the pressure-resistant plate 6. Here, in the present embodiment, the foundation horizontal reinforcement 40H including the pressure-resistant slab reinforcement 62, the beam main reinforcement 72, and the connection reinforcement 75 arranged in the horizontal direction D2, and the foundation vertical reinforcement 40V including the bending reinforcement 42 and the core reinforcement 8 arranged in the vertical direction H are arranged such that the vertical foundation reinforcement capacity obtained by multiplying the cross-sectional area of the foundation vertical reinforcement 40V by the tensile strength indicating the material properties of the foundation vertical reinforcement 40V is larger than the horizontal foundation reinforcement capacity obtained by multiplying the cross-sectional area of the foundation horizontal reinforcement 40H by the tensile strength indicating the material properties of the foundation horizontal reinforcement 40H. Thereby, the integrality between the pressure-resistant slab 6 and the beam 7 by the foundation member 4 is enhanced, and the resistance when the bending moment M acts on the pile head 3t of the pile 3 as described above is enhanced.

[0027] The pile foundation structure 1 as described above is a pile foundation structure 1 including the pile 3 that supports the building 2 and the pressure-resistant slab 6, and is joined to the pile head 3t of the pile 3 and extends upward from the pile head 3t. It includes a columnar foundation member 4 provided underground, a column 5 arranged above the foundation member 4, a pressure-resistant slab 6 joined to the lower part of the foundation member 4, and a beam (horizontal resistance member) 7 joined to the foundation member 4 at a position above the pressure-resistant slab 6. The column foot 51 of the column 5 is semi-rigidly joined to the upper surface of the foundation member 4. According to the above configuration, the pile head 3t of the pile 3 is joined to a columnar foundation member 4 provided underground and extending upward from the pile head 3t. A pressure-resistant slab 6 is joined to the lower part of the columnar foundation member 4, and a beam (horizontal resistance member) 7 is joined to the foundation member 4 at a position above the pressure-resistant slab 6. In this way, the pressure-resistant slab 6, the beam 7, and the foundation member 4 are formed to have a strong and integral structure with a certain thickness as a whole. Since the column 5 is arranged above such a foundation member 4, even if the column 5 is, for example, a large-load acting column such as an outer peripheral column of the building 2, the load can be transmitted from above to below to the pressure-resistant slab 6 and the ground under the pressure-resistant slab. In this way, even in the column 5 where a large load of the building 2 acts, the axial rigidity of the structure supporting the column 5 is enhanced, and as a result, the structural safety can be enhanced. Here, since the columnar base member 4 extends upward from the pile head portion 3t of the pile 3, the pressure-resistant plate 6 joined to the lower part of the base member 4 is provided near the pile head portion 3t. Since the beam 7 is joined to the base member 4 at a position above such a pressure-resistant plate 6, the beam 7 is configured to be joined to the base member 4 at a position higher by a certain height than the pile head portion 3t of the pile 3. In such a configuration, when an earthquake occurs and a bending moment M acts on the pile head portion 3t of the pile 3, this is transmitted to the pressure-resistant plate 6, and at the same time, a couple force that acts in the direction opposite to the bending moment M at a position different from the bending moment M of the pile head portion 3t is generated with respect to the beam 7 formed integrally with the pressure-resistant plate 6 via the columnar base member 4. Due to this couple force, the bending moment M of the pile head portion 3t is offset and the bending moment M is reduced. In this way, since the bending moment M of the pile head portion 3t that should originally be resisted by the pressure-resistant plate 6 is reduced by the base member 4 and the beam 7, it is not necessary to resist the bending moment M only by the pressure-resistant plate 6. Therefore, compared with the case where the base member 4 is not provided, it is possible to make the pressure-resistant plate 6 thinner, so that the building volume of the basement floor and the amount of ground excavation can be suppressed. Further, the column foot portion 51 of the column 5 is semi-rigidly joined to the upper surface 45t of the columnar base member 4. Thereby, at the time of an earthquake, the horizontal force transmitted from the base member 4 to the column foot portion 51 of the column 5 is suppressed, and the building 2 on the ground portion can enhance the structural stability against earthquakes and vibrations while ensuring a certain flexibility. In particular, since the transmission of the bending moment M is suppressed between the column foot portion 51 and the base member 4, the necessity of making the base member 4 more robust than necessary for the purpose of resisting the bending moment M between the column foot portion 51 and the base member 4 is reduced. Therefore, when constructing the base member 4, for example, by reducing the cross-sectional area of the base member 4 or reducing the number of shear reinforcement bars, the base member 4 can be constructed compactly. By the synergistic effect of the above effects, it is possible to provide a pile foundation structure 1 with excellent structural safety that can suppress the building volume of the basement floor and the amount of ground excavation and can be easily constructed.

[0028] Further, the base member 4 is arranged such that the base bar capacity in the vertical direction H, which is obtained by multiplying the cross-sectional area of the base horizontal bars 40H arranged in the horizontal direction D2 by the tensile strength indicating the material properties of the base horizontal bars 40H, is smaller than the base bar capacity in the vertical direction H, which is obtained by multiplying the cross-sectional area of the base vertical bars 40V arranged in the vertical direction H by the tensile strength indicating the material properties of the base vertical bars 40V. According to such a configuration, since the base bar capacity in the vertical direction H is larger than the base bar capacity in the horizontal direction D2 in the base member 4, by enhancing the integrality of the pressure-resistant plate 6 and the beam (horizontal resistance member) 7 by the base member 4, when a bending moment M acts on the pile head 3t of the pile 3 during an earthquake, the resistance to the bending moment M can be enhanced.

[0029] Further, the pile foundation structure 1 further includes a core bar 8 extending in the vertical direction H between the base member 4 and the column 5 such that the upper end 8t is embedded in the column 5 and the lower end 8b is embedded in the base member 4. The column 5 has an inclined surface 56s by forming the lower end in a tapered shape, and the lower surface 56b of the column 5 abuts against the upper surface 45t of the base member 4, and the column 5 is provided so as to be tiltable with respect to the base member 4. According to such a configuration, by providing the core bar 8 extending in the vertical direction H between the column 5 and the base member 4 and forming the column 5 such that the lower end of the column 5 has an inclined surface 56s by being formed in a tapered shape, the column foot portion 51 of the column 5 can be provided as a semi-rigid joint structure on the upper surface 45t of the base member 4, and the column 5 can be provided so as to be tiltable with respect to the base member 4. Thereby, while ensuring a certain degree of flexibility between the column 5 and the base member 4, the durability and stability of the structure against earthquakes and vibrations can be improved.

[0030] Further, bending reinforcement bars 42 are provided vertically on the base member 4 to resist the couple force generated between the pressure-resistant plate 6 and the beam 7 by the horizontal force due to an earthquake. According to such a configuration, the resistance to the couple force in the base member 4 can be enhanced, the bending moment M of the pile head 3t can be offset, and the effect of reducing the bending moment M can be enhanced.

[0031] In addition, the pile foundation structure 1 in the above-described embodiment further includes a connection reinforcing bar 75 that extends in the horizontal direction D2 and is embedded in each of the foundation member 4 and the beam 7 to connect the foundation member 4 and the beam 7. The end portion 75s of the connection reinforcing bar 75 embedded in the foundation member 4 is terminated after being bent downward. According to such a configuration, the joint strength between the foundation member 4 and the beam 7 is increased, and when a bending moment M acts on the pile head portion 3t of the pile 3 and a couple force acts on the beam 7, it is possible to effectively resist this.

[0032] In addition, in the pile foundation structure 1 in the above-described embodiment, the pile 3 is a concrete-filled steel pipe pile. An anchor bar 35 is joined to the steel pipe 31 of the pile 3 so as to extend upward from the pile head portion 3t. The pile head portion 3t is embedded in the foundation member 4 together with the anchor bar 35, whereby the pile 3 and the foundation member 4 are joined. According to such a configuration, the pile head portion 3t is embedded in the foundation member 4 together with the anchor bar 35, so that the pile 3 and the foundation member 4 are joined more firmly.

[0033] In addition, in the pile foundation structure 1 in the above-described embodiment, the cross-sectional area of the foundation member 4 is larger than the cross-sectional area of the column base portion 51. According to such a configuration, even if the column 5 is subjected to a large load such as an outer peripheral column of the building 2, the load can be transmitted from above downward to the pressure-resistant plate 6 and the ground under the pressure-resistant plate. Thereby, the axial rigidity of the structure supporting the column 5 is increased, and as a result, the structural safety can be enhanced, and the settlement and deformation of the ground can also be suppressed.

[0034] Note that the pressure-resistant plate 6 not only supports the vertical load of the basement floor, but also, since the lower part of the foundation member 4 is rigidly joined to the pressure-resistant plate 6, a part of the vertical load of the building 2 can be transmitted from the upper column 5 to the foundation member 4 and the pressure-resistant plate 6. In this way, by the pile 3 and the pressure-resistant plate 6 supporting the vertical load of the building 2, the structural safety of the building 2 can be enhanced.

[0035] (First Modification of the Embodiment) Note that the pile foundation structure of the present invention is not limited to the above-described embodiment described with reference to the drawings, and various modifications can be considered within its technical scope. For example, in the above embodiment, the beam 7 joined to the foundation member 4 is provided at a position above the pressure-resistant plate 6. However, as a horizontal resistance member, instead of the beam 7, a floor slab may be provided.

[0036] Such a pile foundation structure 1 includes a pile 3 that supports the building 2 and a pile foundation structure 1 including a pressure-resistant plate 6, and is joined to the pile head 3t of the pile 3 and extends upward from the pile head 3t. A columnar foundation member 4 provided underground, a column 5 disposed above the foundation member 4, a pressure-resistant plate 6 joined to the lower part of the foundation member 4, and a floor slab joined to the foundation member 4 at a position above the pressure-resistant plate 6. The column leg portion 51 of the column 5 is semi-rigidly joined to the upper surface of the foundation member 4. Needless to say, even in such a case, the same effects as those of the above embodiment can be obtained. Particularly in such a case, the floor slab is realized as one in which the beam-shaped portion is buried, and it is desirable that this beam-shaped portion be configured such that one end is joined to the foundation member 4 as the beam 7 as described in the above embodiment.

[0037] (Second Modification of the Embodiment) Also, in the above embodiment, the column leg portion 51 of the column 5 is configured to be semi-rigidly joined to the upper surface of the foundation member 4, but it is not limited to this. After forming the column leg portion 51 of the column 5 so that its cross-sectional area is smaller than that of the foundation member 4, both the column 5 and the foundation member 4 may be configured to be rigidly joined.

[0038] Such a pile foundation structure 1 is a pile foundation structure 1 including piles 3 supporting a building 2 and a pressure-resistant slab 6, and includes a pile 3, a columnar foundation member 4 provided underground, which is joined to the pile head 3t of the pile 3 and extends upward from the pile head 3t, a column 5 disposed above the foundation member 4, a pressure-resistant slab 6 joined to the lower part of the foundation member 4, and a floor slab joined to the foundation member 4 at a position above the pressure-resistant slab 6. The column base portion 51 of the column 5 has a smaller cross-sectional area than the foundation member 4, and both are rigidly joined. In such a configuration, the cross-sectional area of the column base portion 51 of the column 5 is made smaller than the cross-sectional area of the columnar foundation member 4, and the column base portion 51 and the foundation member 4 are rigidly joined. Thereby, at the time of an earthquake, the horizontal force transmitted from the foundation member 4 to the column base portion 51 of the column 5 is suppressed, and the above-ground building 2 can enhance the structural stability against earthquakes and vibrations while ensuring a certain degree of flexibility. In particular, since the transmission of the bending moment M is suppressed between the column base portion 51 and the foundation member 4, the necessity of making the foundation member 4 more robust than necessary for the purpose of resisting the bending moment M between the column base portion 51 and the foundation member 4 is reduced. Therefore, when constructing the foundation member 4, for example, the foundation member 4 can be constructed compactly by reducing the cross-sectional area of the foundation member 4 or reducing the number of shear reinforcement bars.

[0039] (Other modifications) Further, in the above embodiment, among the side surfaces 51s and 51t of the column 5, the dimension of the column base portion 51 in the column width direction gradually decreases from top to bottom by inclining the other side 51t in the column width direction. However, the present invention is not limited to this, and the column 5 may have any cross-sectional shape. Further, in the above embodiment, in all the columns 5 located at the outer peripheral portion of the building 2, the dimension of the column base portion 51 in the column width direction gradually decreases from top to bottom. However, the present invention is not limited to this. Among a plurality of columns 5 located at the outer peripheral portion of the building 2, in some of the columns 5, the dimension of the column base portion 51 in the column width direction may gradually decrease from top to bottom. In addition, as long as it does not deviate from the gist of the present invention, it is possible to make selections from the configurations exemplified in the above embodiments or to appropriately change them to other configurations.

Explanation of Reference Numerals

[0040] 1 Pile foundation structure 8b Lower end 2 Building 8t Upper end 3 Pile 40H Foundation horizontal reinforcing bar 3t Pile head 40V Foundation vertical reinforcing bar 4 Foundation member 45t Upper surface of foundation member 5 Column 51 Column foot 6 Pressure-resistant plate 56b Lower surface of column 7 Beam (horizontal resistance member) 56s Inclined surface 8 Core reinforcing bar

Claims

1. A pile foundation structure including piles supporting a building and a pressure-resistant plate, wherein the piles, a columnar foundation member provided underground, which is joined to the pile heads of the piles and extends upward from the pile heads, a column disposed above the foundation member, the pressure-resistant plate joined to the lower part of the foundation member, a horizontal resistance member joined to the foundation member at a position above the pressure-resistant plate, are provided, wherein the column foot of the column is semi-rigidly joined to the upper surface of the foundation member, or the column foot of the column has a smaller cross-sectional area than the foundation member and both are rigidly joined, and the pile foundation structure is characterized by this.

2. The pile foundation structure according to claim 1, wherein the foundation member is reinforced such that the vertical foundation reinforcement capacity obtained by multiplying the cross-sectional area of the vertically disposed foundation vertical reinforcement by the tensile strength indicating the material properties of the foundation vertical reinforcement is larger than the horizontal foundation reinforcement capacity obtained by multiplying the cross-sectional area of the horizontally disposed foundation horizontal reinforcement by the tensile strength indicating the material properties of the foundation horizontal reinforcement.

3. further comprising a core reinforcement provided to extend in the vertical direction between the foundation member and the column such that the upper end and the lower end are respectively embedded in the column and the foundation member, when the column and the foundation member are semi-rigidly joined, the column has an inclined surface by forming the lower end in a tapered shape, and the lower surface of the column abuts against the upper surface of the foundation member, and the column is provided so as to be tiltable with respect to the foundation member, and the pile foundation structure according to claim 1 or 2 is characterized by this.

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