JP7469645B2 - Pile head joint structure, earthquake-resistance reinforcement method for existing structures, and repair method for pile head joints of existing structures - Google Patents

Description

The present invention relates to a pile head joint structure, a method for seismic reinforcement of an existing structure, and a method for repairing a pile head joint of an existing structure.

In the past, the joints between the superstructures of office buildings and apartment buildings and the piles were rigidly connected, i.e. completely fixed, without allowing any rotation. Therefore, in the event of a major earthquake, the pile heads and foundation beams would be damaged by large stresses, and as a result, the piles would lose their ability to retain axial force, causing the superstructures of office buildings and apartment buildings to tilt and sink. To prevent this, it is common to increase the strength of the pile heads and foundation beams by making them larger in cross section, but this is costly.
Therefore, in recent years, in order to reduce the stress generated in the pile heads and foundation beams, semi-rigid connections that allow some rotation, or pin connections that allow complete rotation, are increasingly being used at the connections between the superstructure and the piles.

As such an energy absorbing structure for a pile head, structures such as those shown in Patent Documents 1, 2 and 3 are known.
Patent Document 1 describes a structure in which the pile head, which is semi-rigidly or pin-jointed, is composed of a main pile, an outer pipe pile, and rod-shaped energy absorbing members installed inside the main pile and the footing, and the majority of the earthquake energy is absorbed by deformation of the outer pipe pile and the energy absorbing members, thereby reducing the energy input to the main pile.

Patent documents 2 and 3 describe a structure in which an energy absorbing member made of a viscoelastic body or lead and a steel rod is provided inside the footing at the head of the pile, and the energy of the earthquake is absorbed by the flow or shear deformation caused by the relative displacement between the viscoelastic body or lead and the steel rod, thereby reducing the energy input to the pile.

JP 2004-218196 A JP 2001-32295 A JP 2004-324154 A

However, the conventional pile head joint structure had the following problems.
Once an energy absorbing member is damaged, it needs to be replaced in order to cope with a new earthquake. The energy absorbing members described in Patent Documents 1 to 3 are provided inside the pile or footing, so there is a problem that the replacement work is difficult, and there is room for improvement in this respect.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a pile head joint structure that allows easy replacement of energy absorbing members, a method for seismic reinforcement of an existing structure, and a method for repairing pile head joints of an existing structure.

In order to achieve the above-mentioned objective, the pile head joint structure of the present invention is a pile head joint structure for connecting the foundation of a superstructure to a main pile, wherein the connection portion between the foundation and the main pile is joined by a semi-rigid joint that allows partial rotation of the foundation, or a pin joint that allows the rotation completely, and is characterized in that it comprises an energy absorbing member connected to the radial outside of the main pile, and an energy absorbing member receiver that is fixed to the foundation and connects the energy absorbing member to the foundation, and an outer pipe pile is provided that is arranged coaxially with the main pile so as to surround the periphery of the main pile, and the energy absorbing member is connected to the radial outside of the outer pipe pile .
In addition, the pile head joint structure of the present invention is a pile head joint structure for connecting the foundation of a superstructure to a main pile, and the connection portion between the foundation and the main pile is joined by a semi-rigid joint that allows partial rotation of the foundation, or a pin joint that allows the rotation completely, and is characterized in that it comprises an energy absorbing member connected to the radial outside of the main pile, and an energy absorbing member receiver that is fixed to the foundation and connects the energy absorbing member to the foundation, and the energy absorbing member is a flat plate member with its in-plane direction oriented vertically.
In addition, the pile head joint structure of the present invention is a pile head joint structure for connecting the foundation of a superstructure and the main pile, wherein the connection portion between the foundation and the main pile is joined by a semi-rigid joint that allows partial rotation of the foundation, or a pin joint that allows the rotation completely, and the pile comprises an energy absorbing member connected to the radial outside of the main pile, and an energy absorbing member receiver that is fixed to the foundation and connects the energy absorbing member to the foundation, wherein the energy absorbing member is a U-shaped member having a curved portion curved in a U-shape, and the U-shaped member is arranged so as to be curved in the vertical direction by the curved portion.
In addition, the pile head joint structure of the present invention is a pile head joint structure for connecting the foundation of a superstructure to a main pile, wherein the connection portion between the foundation and the main pile is joined by a semi-rigid joint that allows partial rotation of the foundation, or a pin joint that allows the rotation completely, and is characterized in that it comprises an energy absorbing member connected to the radial outside of the main pile, and an energy absorbing member receiver that is fixed to the foundation and connects the energy absorbing member to the foundation, and the rotational rigidity between the foundation and the main pile added by the energy absorbing member is greater than or equal to the rotational rigidity between the foundation and the main pile added by the connection portion between the foundation and the main pile.

The method for seismic reinforcement of an existing structure according to the present invention is a method for seismic reinforcement of an existing structure using the above-mentioned pile head joint structure, and is characterized by having the steps of joining the connection between the foundation of the existing structure and the main pile by the semi-rigid joint or the pin joint, connecting the energy absorbing member to the radial outside of the main pile, and fixing an energy absorbing member receiver that connects the energy absorbing member to the foundation to the foundation.

The method for repairing a pile head joint of an existing structure according to the present invention is characterized by replacing the energy absorbing member of the above-mentioned pile head joint structure.

In the present invention, when an earthquake occurs, the connection between the pile and the foundation is allowed to rotate partially in the case of a semi-rigid joint, or completely in the case of a pin joint. The shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure are absorbed mostly by the shear deformation of the energy absorbing member, making it possible to increase the amount of energy absorption, with only a portion of the force being borne by the pile. This allows the cross section of the pile to be made smaller, reducing construction costs.
In addition, in the present invention, the pile is hardly damaged by the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure, so the pile can maintain its axial force. Therefore, the superstructure does not tilt or sink, and excessive displacement can be prevented, so the superstructure can be stably supported even after a major earthquake.

In addition, in the present invention, unlike the conventional structure in which the energy absorbing members are installed inside the main pile or foundation, they are installed on the outside of the main pile, making it easy to replace energy absorbing members that have been damaged. Therefore, by replacing damaged energy absorbing members with new ones, it is possible to prepare for new earthquakes. In particular, for main piles on the periphery of the superstructure, which are prone to damage during earthquakes, they can be easily replaced by excavating the ground from the periphery of the superstructure.

Moreover, in this invention, by using steel as an energy absorbing member in the pile head, a stable history can be obtained without the need for maintenance. This eliminates the need for underground space and basement floors for maintenance that are normally required when using vibration control dampers or seismic isolation dampers, making it possible to reduce the construction costs of the superstructure.

The pile head joint structure according to the present invention may also be characterized in that an outer pipe pile is arranged coaxially with the main pile so as to surround the periphery of the main pile, and the energy absorbing member is connected to the radial outside of the outer pipe pile.

In the present invention, the outer pipe pile, the energy absorbing member, and the energy absorbing member receiver can be partially or completely integrated and then installed concentrically with the main pile, improving workability. In addition, the outer pipe pile can prevent damage to the main pile caused by the compressive force acting on the main pile from the energy absorbing member during an earthquake.

The pile head joint structure of the present invention may also be characterized in that the energy absorbing member is connected to the foundation and the outer pipe pile, or to the foundation and the main pile, by bolt fastening.

In this case, the connection between the outer pipe pile and the energy absorbing member, and the connection between the energy absorbing member receiver and the energy absorbing member can be performed mechanically by bolt fastening, so that replacement work can be carried out efficiently.
Specifically, when constructing a new pile head joint structure, it can be constructed simply by fastening the bolts to the pile. Also, when reinforcing an existing pile head joint structure, for example, a half steel pipe is placed on the outside of the pile and welded to form an outer pipe pile, and an energy absorbing member is attached to the outer pipe pile with bolts, which can be easily constructed.

The pile head joint structure according to the present invention may also be characterized in that the energy absorbing member is a flat plate member whose in-plane direction is oriented vertically.

According to the present invention, by using an energy absorbing member, a pile head joint structure can be constructed using a simple member with the plate surface oriented vertically.
Furthermore, according to the present invention, the area of the ground to be excavated can be made smaller since it only needs to be matched to the width of the plate.

In addition, in the pile head joint structure according to the present invention, the energy absorbing member may be characterized by comprising the plate member and a U-shaped member having a curved portion curved in a U-shape, and the U-shaped member is arranged so as to be curved in the left-right direction by the curved portion.

With this configuration, the energy absorbing member is a combination of a plate member and a U-shaped member. By providing a U-shaped member that utilizes the deformation of a U-shaped curved surface as part of the energy absorbing member, the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure can be effectively absorbed by the U-shaped member.

In addition, in the pile head joint structure according to the present invention, the energy absorbing member may be characterized by comprising the plate member and a U-shaped member having a curved portion curved in a U-shape, and the U-shaped member is arranged so as to be curved in the up-down direction by the curved portion.

With this configuration, the energy absorbing member is a combination of a plate member and a U-shaped member. By providing a U-shaped member that utilizes the deformation of a U-shaped curved surface as part of the energy absorbing member, the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure can be effectively absorbed by the U-shaped member.

The pile head joint structure according to the present invention may also be characterized in that the plate member has a burring hole formed therein.

With this configuration, the energy absorbing member is burred, so it is possible to maintain a stable shear strength even if it is significantly deformed, resulting in greater energy absorption per weight of steel and efficient shear resistance.

In addition, in the pile head joint structure according to the present invention, the energy absorbing member may be a U-shaped member having a curved portion curved in a U-shape, and the U-shaped member may be arranged so as to be curved in the left-right direction by the curved portion.

With this configuration, the energy absorbing member is a U-shaped member, and by utilizing the deformation of the U-shaped curved surface, the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure can be effectively absorbed by the U-shaped member.

In addition, in the pile head joint structure according to the present invention, the energy absorbing member may be a U-shaped member having a curved portion curved in a U-shape, and the U-shaped member may be arranged so as to be curved in the up-down direction by the curved portion.

With this configuration, the energy absorbing member is a U-shaped member, and by utilizing the deformation of the U-shaped curved surface, the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure can be effectively absorbed by the U-shaped member.

Furthermore, in the pile head joint structure according to the present invention, the rotational stiffness between the foundation and the main pile added by the energy absorbing member may be greater than or equal to the rotational stiffness between the foundation and the main pile added by the connection between the foundation and the main pile.

With this configuration, rotation acting on the foundation during an earthquake is tolerated at the connection between the foundation and the main pile, so the load of the foundation caused by that rotation is more likely to flow to the energy absorbing member. This improves the efficiency of force transmission, making it possible to more reliably reduce the cross-section of the main pile, thereby reducing construction costs.

In addition, in the pile head joint structure of the present invention, it is preferable that a filler material is filled between the outer pipe pile and the main pile.

In this case, a filler such as mortar or concrete is filled between the main pile and the outer pipe pile, which prevents the outer pipe pile from being deformed and damaged by the compressive force received from the energy absorbing member during an earthquake.

The pile head joint structure according to the present invention may also be characterized in that protrusions are provided on the inner pipe surface on the radially inner side of the outer pipe pile, the outer pile surface on the radially outer side of the main pile, or on both the inner pipe surface and the outer pile surface.

This configuration increases the adhesion strength of the filler material, such as mortar or concrete, filled between the main pile and the outer pipe pile to the outer pipe pile or the main pile, making it possible to integrate them.

The pile head joint structure, method for seismic reinforcement of an existing structure, and method for repairing pile head joints of an existing structure of the present invention ensure the axial force retention function of the pile at low cost when the pile head is semi-rigid or pin-jointed, and can prevent the superstructure from tilting, subsidence, or excessive displacement, and can be easily replaced once damaged.

FIG. 2 is a longitudinal sectional view showing a pile head joint structure according to the first embodiment of the present invention. This is a view taken along the line AA in Figure 1, and is a plan view of the pile head joint structure seen from above. 3A and 3B are diagrams showing an arrangement of a flat energy absorbing member according to a modified example, and correspond to FIG. 2 . 1A and 1B are diagrams showing a flat-plate energy absorbing member, in which (a) is a side view and (b) is a cross-sectional view taken along line BB shown in (a). 13A to 13C are side views showing modified flat energy absorbing members. FIG. 2 is a vertical cross-sectional view showing the pile head joint structure according to the first embodiment during an earthquake. A vertical cross-sectional view showing a pile head joint structure according to a second embodiment. FIG. 11 is a vertical cross-sectional view showing a pile head joint structure according to the second embodiment during an earthquake. A vertical cross-sectional view showing a pile head joint structure according to a third embodiment. This is a view taken along the CC line in Figure 9, and is a plan view of the pile head joint structure according to the third embodiment seen from above. A vertical cross-sectional view showing a pile head joint structure according to the third embodiment during an earthquake. A vertical cross-sectional view showing a pile head joint structure according to a fourth embodiment. A vertical cross-sectional view showing a pile head joint structure according to the fourth embodiment during an earthquake. A vertical cross-sectional view showing a pile head joint structure according to the fifth embodiment. This is a view taken along the line DD shown in Figure 14, and is a plan view of the pile head joint structure according to the fifth embodiment seen from above. A vertical cross-sectional view showing a pile head joint structure according to the fifth embodiment during an earthquake. 5A and 5B are plan views showing the arrangement of a pile head joint structure according to a first modified example, and correspond to FIG. 3 . 13A and 13B are plan views showing the arrangement of a pile head joint structure according to a second modified example, and correspond to FIG. 3 . A vertical cross-sectional view showing a pile head joint structure according to a third modified example.

Below, the pile head joint structure according to an embodiment of the present invention, the method for seismic reinforcement of an existing structure, and the method for repairing the pile head joint of an existing structure will be described with reference to the drawings.

First Embodiment
As shown in Fig. 1, the pile head joint structure 1 according to this embodiment is a joint structure for joining a pile head 2A of a main pile 2 to a foundation 3 of a superstructure (not shown). The connection between the foundation 3 and the main pile 2 according to this embodiment is joined by a semi-rigid joint that allows some rotation.

The pile head joint structure 1 comprises a cylindrical outer pipe pile 4 arranged radially outward of the main pile 2 and coaxially therewith, a plurality of flat plate energy absorbing members 5 (energy absorbing members) (four in this embodiment as shown in Figure 2) connected to the radially outward side of the outer pipe pile 4, and a ring-shaped support member 6 (energy absorbing member support) fixed to the foundation 3 and connecting the flat plate energy absorbing members 5 to the foundation 3.

Materials constituting the pile 2 include, for example, steel and concrete. Specifically, the pile 2 may be, for example, a steel pipe pile, a cast-in-place steel pipe concrete pile, a concrete pile with a steel shell (SC pile), a centrifugal prestressed reinforced concrete pile (PRC pile), or a pretensioned centrifugal high-strength prestressed concrete pile (PHC pile). The pile 2 is entirely buried in the ground, and the inside of the pile head 2A is filled with concrete.

On the outer circumferential surface 2b of the pile 2, a pile projection 22 that protrudes radially outward is formed in the area of the pile head 2A surrounded by the outer pipe pile 4. The shape of the pile projection 22 is not limited, and may be, for example, a partial projection or a circumferentially extending protrusion. By providing such a pile projection 22, the adhesion strength with the concrete 43 (filler) filled between the pile 2 and the outer steel pipe 41 of the outer pipe pile 4 can be increased.

A pile head cap 21 is fitted onto the upper end 2a of the pile head 2A to cover the upper opening. The pile head cap 21 is made of steel and formed into a cylindrical shape with a top, and is attached to the upper end 2a of the pile head 2A by a fixing means so that it covers the upper end 2a from above. The top surface 21a of the pile head cap 21 is a contact surface that forms a horizontal plane on which the pile receiving plate 31 described later is grounded.

The foundation 3 is a concrete footing that supports the columns of the superstructure from below. In this embodiment, the lower half is buried in the ground. A pile receiving plate 31 is provided on the underside 3a of the foundation 3 directly above the pile head 2A, coaxially with the pile 2. The pile receiving plate 31 is buried in the foundation 3, with its underside 31a in surface contact with the top surface 21a of the pile head cap 21 attached to the pile head 2A. The vertical load received by the foundation 3 is transmitted to the pile 2 via the pile receiving plate 31 and the pile head cap 21. A receiving member 6 is buried in the underside 3a of the foundation 3.

As shown in Figs. 1 and 2, the ring-shaped support member 6 is formed into a ring shape made of steel, and is embedded in the concrete of the foundation 3 with the lower surface 6a of the ring-shaped support member 6 flush with the lower surface 3a of the foundation 3. The outer and inner diameters of the ring-shaped support member 6 are determined so that all of the first connection portions 5a of the four flat energy absorbing members 5 are connected. A number of anchoring bars 61 that extend upward and are anchored in the concrete of the foundation 3 are welded to the ring-shaped support member 6 by butt welding or stud welding.

A first mounting flange 62 is provided on the underside 6a of the ring-shaped receiving member 6 to which one end (first connection portion 5a) of the flat-plate energy absorbing member 5 is connected. The first mounting flange 62 is plate-shaped and welded to the ring-shaped receiving member 6 with its length oriented horizontally. The first mounting flange 62 has a bolt hole (not shown) that penetrates in the thickness direction.

The outer pipe pile 4 has a larger outer diameter than the main pile 2. The outer pipe pile 4 is equipped with a cylindrical outer steel pipe 41 that surrounds the pile head 2A, and concrete 43 (filler) that is filled between the outer steel pipe 41 and the pile head 2A. The outer pipe pile 4 is positioned, for example, by placing it on a receiving member (not shown) that is fixed in advance at a predetermined position of the main pile 2, and is joined to the pile head 2A so that it is coaxial with the pile axis of the pile head 2A.

The inner peripheral surface 41a of the outer steel pipe 41 is formed with an outer steel pipe protrusion 44 that is convex radially inward. The shape of the outer steel pipe protrusion 44 is not limited, and may be, for example, a partial protrusion or a circumferentially extending protrusion. By providing such an outer steel pipe protrusion 44, it is possible to increase the adhesion strength with the concrete 43 filled between the main pile 2 and the outer steel pipe 41 of the outer pipe pile 4.

A second mounting flange 45 is provided on the outer peripheral surface 41b of the outer steel pipe 41 to which the other end (second connection portion 5b) of the flat-plate energy absorbing member 5 is connected. The second mounting flange 45 is plate-shaped and welded to the outer steel pipe 41 with its length facing up and down. The second mounting flange 45 has a bolt hole (not shown) that penetrates in the thickness direction.

The filler filled inside the outer steel pipe 41 is not limited to concrete 43 as in this embodiment, but may be mortar or other materials. In this way, by filling the space between the main pile 2 and the outer pipe pile 4 with concrete 43, damage to the outer steel pipe 41 of the outer pipe pile 4 due to the pressing force of the flat plate energy absorbing member 5 can be prevented.

The flat-plate energy absorbing member 5 is bent in the in-plane direction at the midpoint of its length. For the flat-plate energy absorbing member 5, ordinary steel or a material with high energy absorbing performance such as low-yield-point steel is used. The flat-plate energy absorbing member 5 has a first connection portion 5a at one end connected to a ring-shaped receiving member 6 provided on the foundation 3 via a first mounting flange 62, and a second connection portion 5b at the other end connected to a second mounting flange 45 provided on the outer pipe pile 4. The first connection portion 5a and the second connection portion 5b are fixed to the first mounting flange 62 and the second mounting flange 45, respectively, by bolting. Since the flat-plate energy absorbing member 5 is connected with bolts in this way, it is easy to replace when damaged.

As shown in Fig. 2, the four flat plate energy absorbing members 5 are arranged at regular intervals (here, at 45 degree intervals) in the circumferential direction around the main pile 2. The number of installed flat plate energy absorbing members 5 can be changed appropriately depending on conditions such as the diameter dimension of the main pile 2 (outer pipe pile 4), the rotational rigidity received from the foundation 3, and the material, shape, and thickness dimension of the flat plate energy absorbing members 5 themselves. For example, as shown in Fig. 3(a), six flat plate energy absorbing members 5 may be arranged at regular intervals in the circumferential direction, or as shown in Fig. 3(b), eight flat plate energy absorbing members 5 may be arranged at regular intervals in the circumferential direction.
3(a) and 3(b), the flat plate energy absorbing member 5 and the outer pipe pile 4 are not connected by welding, but rather a locking protrusion 53 with a T-shaped cross section provided on the first connecting portion 5a of the flat plate energy absorbing member 5 is inserted from above and below into a slit member 47 provided on the outer circumferential surface 41b of the outer pipe pile 4. This allows the flat plate energy absorbing member 5 to be connected in a state where its movement in the lateral direction (left and right direction) is restricted.

As shown in Figures 4(a) and (b), the flat energy absorbing member 5 has multiple (here, two) burring holes 51 formed at appropriate positions that penetrate the plate in the thickness direction. The burring holes 51 are holes that have flange portions 51a that rise from the plate surface at the hole edges, and are shaped to enable stable shear strength to be maintained even during large deformations.

The number, arrangement, hole diameter, and other configurations of the burring holes 51 can be set appropriately according to the rigidity of the flat energy absorption member 5 required by design. For example, Fig. 5(a) shows a case where only one burring hole 51 is provided, Fig. 5(b) shows a case where three burring holes 51 are provided, and Fig. 5(c) shows a case where multiple burring holes 51 are provided.

As shown in Figure 6, the rotational stiffness of the connection between the flat-plate energy absorbing member 5 and the ring-shaped support member 6 is set to be equal to or greater than the rotational stiffness between the foundation 3 and the main pile 2 added by the connection between the main pile 2 and the foundation 3, so that the load can easily flow to the flat-plate energy absorbing member 5. In other words, it is preferable to completely fix the ring-shaped support member 6 with fixing bars 61 such as whisker bars.

Here, a construction method (pile head joint method) for the pile head joint structure 1 having the above-described configuration will be described.
First, as shown in Fig. 1, the pile 2 is driven into the ground by, for example, a rotary press-in method, with the pile head 2A positioned underground.
Next, a cylindrical outer pipe pile 4 is placed radially outward of the main pile 2 and coaxially with the main pile 2. Specifically, the ground around the pile head 2A of the main pile 2 driven into the ground is excavated to secure a construction space. A pile head cap 21 is fitted onto the upper end 2a of the main pile 2.

Then, the outer steel pipe 41 of the outer pipe pile 4 is placed so as to cover the radial outside of the pile head 2A. The second mounting flange 45 is welded to the outer peripheral surface 41b of the outer steel pipe 41 in advance.

Next, the foundation 3 is installed above the pile 2. A formwork is set up in a specified area for the foundation 3, and the pile receiving plate 31 and ring-shaped receiving member 6 are placed on the underside 3a of the foundation 3, and concrete is then poured into the formwork. At this time, the underside 31a of the pile receiving plate 31 is in contact with the top surface 21a of the pile head cap 21 installed on the upper end 2a of the pile 2. The first mounting flange 62 is welded to the underside 6a of the ring-shaped receiving member 6 in advance.

Next, the second mounting flange 45 of the outer pipe pile 4 and the first mounting flange 62 of the ring-shaped receiving member 6 are connected by bolting with the flat plate energy absorbing member 5. Note that concrete may be poured into the formwork for the foundation 3 after the second mounting flange 45 of the outer pipe pile 4 and the first mounting flange 62 of the ring-shaped receiving member 6 are bolted with the flat plate energy absorbing member 5.
The outer pipe pile 4, flat plate energy absorbing member 5 and ring-shaped receiving member 6 may be preassembled in a factory and brought to the site, or may be assembled on-site before installation at the pile head 2A. After installing a damming treatment to prevent concrete from leaking out from the gap between the outer steel pipe 41 and the pile head 2A, concrete 43 is filled between the outer steel pipe 41 and the pile head 2A and allowed to harden. After that, the excavated area around the pile head 2A is backfilled with soil. This completes the construction of the pile head joint structure 1.
Furthermore, a superstructure is constructed above the foundation 3.

Next, the functions of the above-mentioned pile head joint structure, the method for seismic reinforcement of an existing structure, and the method for repairing a pile head joint of an existing structure will be described in detail with reference to the drawings.
In the pile head joint structure 1 according to this embodiment, as shown in Fig. 6, when an earthquake occurs, in the case of a semi-rigid joint as in this embodiment, some rotation (symbol F in Fig. 6) of the connection part between the main pile 2 and the foundation 3 is permitted. Furthermore, the shear force and bending moment acting on the pile head 2A due to the inertial force acting on the superstructure are absorbed mostly by the shear deformation of the flat plate energy absorbing member 5, making it possible to increase the amount of energy absorption, and only a portion of the energy is borne by the main pile 2. Therefore, the cross section of the main pile 2 can be made small, and construction costs can be reduced.

In addition, in this embodiment, the pile 2 is not damaged by the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure, so the axial force retention function can be guaranteed. Therefore, the superstructure does not tilt or sink, and excessive displacement can be prevented, so the superstructure can be stably supported even after a major earthquake.

Furthermore, in this embodiment, instead of the conventional structure in which the energy absorption member is provided inside the main pile 2 or the foundation 3, the flat plate energy absorption member 5 is provided on the outside of the main pile 2, which makes it easy to replace the flat plate energy absorption member 5 that has been damaged.
Therefore, it is possible to prepare for a new earthquake by replacing the damaged flat-plate energy absorbing members 5 with new ones. In particular, the main piles 2 on the periphery of the superstructure, which are easily damaged during an earthquake, can be easily replaced by excavating the ground from the periphery side of the superstructure.

Moreover, in this embodiment, by using steel material as the flat plate energy absorption member 5 in the pile head portion, a stable history can be obtained without the need for maintenance. This eliminates the need for underground space and basement floors for maintenance that are normally required when using vibration control dampers or seismic isolation dampers, making it possible to reduce the construction costs of the superstructure.

In addition, in this embodiment, the connection between the outer pipe pile 4 and the flat plate energy absorption member 5, and the connection between the ring-shaped receiving member 6 and the flat plate energy absorption member 5 can be mechanically performed by bolt fastening, allowing replacement work to be performed efficiently.
Specifically, when constructing a new pile head joint structure 1, construction can be performed simply by placing the outer pipe pile 4 over the main pile 2 from above and then fastening it with bolts. In addition, when reinforcing an existing pile head joint structure 1, construction can be easily performed by forming the outer pipe pile 4 by, for example, placing a half steel pipe on the outside of the main pile 2 and welding it, and then attaching the flat plate energy absorbing member 5 to the outer pipe pile 4 with bolts.

In addition, in this embodiment, by using a flat plate energy absorption member 5, the pile head joint structure 1 can be constructed using a simple member with the plate surface oriented vertically.

Furthermore, in the case of the pile head joint structure 1 according to this embodiment, burring holes 51 are formed in the flat plate energy absorption member 5 by burring processing, so that the energy absorption per weight of steel material is increased and shear resistance can be efficiently exerted.

In addition, in this embodiment, the rotational stiffness of the connection between the foundation 3 and the flat plate energy absorbing member 5 is set to be equal to or greater than the rotational stiffness between the foundation 3 and the main pile 2 added by the connection between the foundation 3 and the main pile 2, so that the rotation acting on the foundation 3 during an earthquake is fully tolerated by the connection between the foundation 3 and the main pile 2, and the load of the foundation 3 due to this rotation is more likely to flow to the flat plate energy absorbing member 5. This further improves the efficiency of force transmission, making it possible to more reliably reduce the cross section of the main pile 2, thereby reducing construction costs.

Furthermore, in this embodiment, concrete 43 is filled between the main pile 2 and the outer pipe pile 4, so that deformation and damage to the outer pipe pile 4 due to the pressing force received from the flat plate energy absorbing member 5 during an earthquake can be suppressed.

Furthermore, in this embodiment, protrusions are provided on both the radially inner pipe inner surface of the outer pipe pile 4 and the radially outer pile outer surface of the main pile 2, so that the adhesion strength of the concrete 43 filled between the main pile 2 and the outer pipe pile 4 to the outer pipe pile 4 or the main pile 2 can be increased, making it possible to integrate them.

In the pile head joint structure, the method for seismic reinforcement of an existing structure, and the method for repairing a pile head joint of an existing structure according to the present embodiment described above, when the pile head 2A is semi-rigidly joined, the axial force retention function of the pile 2 can be ensured at low cost, the inclination, settlement, and excessive displacement of the superstructure can be prevented, and it can be easily replaced once it is damaged.

Next, other embodiments of the pile head joint structure, the method for seismic reinforcement of an existing structure, and the method for repairing the pile head joint of an existing structure of the present invention will be described with reference to the attached drawings. The same reference numerals will be used for the same or similar members and parts as those in the above-mentioned embodiment, and the description will be omitted. Configurations that differ from the embodiment will be described.

Second Embodiment
As shown in Fig. 7, the pile head joint structure 1A according to the second embodiment is a structure in which the piles are joined by pin joints that completely allow rotation. In the pile head joint structure 1A of the second embodiment, the main pile 2, the outer pipe pile 4, the flat plate energy absorbing member 5, and the ring-shaped receiving member 6 are configured in the same manner as in the first embodiment described above.

The second pile head cap 23, which has a spherical convex surface 23a that is convex upward, is fitted to the upper end 2a of the pile 2. A second pile receiving plate 33 that can slide on the convex surface 23a of the second pile head cap 23 is embedded in the foundation 3. The lower surface of the second receiving plate 33 is formed with a concave surface 33a that has a curved surface equivalent to the convex surface 23a. The second pile head cap 23 and the second receiving plate 33 are provided with the convex surface 23a and the concave surface 33a in surface contact, and can slide along the contact surface. Therefore, the pile 2 and the foundation 3 can rotate smoothly around the contact part between the convex surface 23a and the concave surface 33a, and the vertical load of the foundation 3 is transmitted to the pile 2.

As shown in Figure 8, in the pile head joint structure 1A according to the second embodiment, when an earthquake occurs, because it is a pin joint, rotation of the connection between the main pile 2 and the foundation 3 (symbol F in Figure 8) is fully permitted. Furthermore, the shear force and bending moment acting on the pile head 2A due to the inertial force acting on the superstructure is absorbed mostly by the shear deformation of the flat plate energy absorbing member 5, and only a portion of it is borne by the main pile 2. Therefore, the cross section of the main pile 2 can be made smaller, reducing construction costs.

In addition, in the second embodiment, the pile 2 is not damaged by the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure, so the axial force retention function can be guaranteed. Therefore, the superstructure does not tilt or sink, and excessive displacement can be prevented, so the superstructure can be stably supported even after a major earthquake.

Furthermore, in the second embodiment, unlike the conventional structure in which the energy absorbing member is provided inside the main pile 2 or foundation 3, the plate energy absorbing member 5 is provided on the outside of the main pile 2, which makes it easy to replace a damaged plate energy absorbing member 5. Therefore, by replacing a damaged plate energy absorbing member 5 with a new one, it is possible to prepare for a new earthquake. In particular, for the main piles 2 on the periphery of the superstructure, which are prone to damage during an earthquake, they can be easily replaced by excavating the ground from the periphery side of the superstructure.

Third Embodiment
Next, the pile head joint structure 1B according to the third embodiment shown in Figures 9 and 10 has a configuration in which a first U-shaped energy absorption member 7 (energy absorption member, U-shaped member) is provided instead of the flat energy absorption member 5 (see Figure 1) in the first embodiment described above.

The first U-shaped energy absorbing member 7 is a plate-like member having a curved portion 71 curved in a U-shape at the middle portion. The first U-shaped energy absorbing member 7 is arranged so that the curved portion 71 is located radially outward from both ends (an end 72a of the first plate surface 72 and an end 73a of the second plate surface 73, which will be described later). One of the first plate surfaces 72 sandwiching the curved portion 71 is arranged facing the lower surface 3a of the foundation 3 and is fixed by bolt fastening to the ring-shaped receiving member 6 buried in the foundation 3. The other second plate surface 73 is fixed by bolt fastening in a state in which it is placed on the second mounting flange 46 protruding radially outward from the outer peripheral surface 41b of the outer pipe pile 4. The second mounting flange 46 is arranged so that the flange surface faces the lower surface 3a of the foundation 3.
As shown in FIG. 10, four first U-shaped energy absorbing members 7 are arranged at regular intervals (here, at 45° intervals) in the circumferential direction.

According to this configuration, as shown in Figure 11, by using the first U-shaped energy absorption member 7 as the energy absorption member, the deformation of the U-shaped curved portion 71 can be utilized, so that the shear force and bending moment acting on the pile head 2A due to the inertial force acting on the superstructure can be effectively absorbed by the first U-shaped energy absorption member 7.
Moreover, in the case of the first U-shaped energy absorbing member 7, since the amount of deformation due to the U-shaped curved portion 71 can be made large, damage to the first U-shaped energy absorbing member 7 itself can be kept small.

Fourth Embodiment
Next, the pile head joint structure 1C according to the fourth embodiment shown in Fig. 12 is a structure in which the pile head joint structure 1B of the third embodiment (see Fig. 9) is joined by a pin joint that completely allows rotation. In the pile head joint structure 1C of the fourth embodiment, the main pile 2, the outer pipe pile 4, the first U-shaped energy absorbing member 7, and the ring-shaped receiving member 6 are configured similarly to those of the first embodiment.

The second pile head cap 23, which has a spherical convex surface 23a that is convex upward, is fitted to the upper end 2a of the pile 2. A second pile receiving plate 33 that can slide on the convex surface 23a of the second pile head cap 23 is embedded in the foundation 3. The lower surface of the second receiving plate 33 is formed with a concave surface 33a that has a curved surface equivalent to the convex surface 23a. The second pile head cap 23 and the second receiving plate 33 are provided with the convex surface 23a and the concave surface 33a in surface contact, and can slide along the contact surface. Therefore, the pile 2 and the foundation 3 can rotate smoothly around the contact part between the convex surface 23a and the concave surface 33a, and the vertical load of the foundation 3 is transmitted to the pile 2.

As shown in FIG. 13, in the pile head joint structure 1C according to the fourth embodiment, when an earthquake occurs, rotation F of the connection between the main pile 2 and the foundation 3 is completely permitted because it is a pin joint. Furthermore, the shear force and bending moment acting on the pile head 2A due to the inertial force acting on the superstructure is absorbed mostly by the shear deformation of the first U-shaped energy absorbing member 7, and only a portion of it is borne by the main pile 2. Therefore, the cross section of the main pile 2 can be made smaller, reducing construction costs.

In addition, in the fourth embodiment, the pile 2 is not damaged by the shear force and bending moment acting on the pile head due to the inertial force acting on the superstructure, so the axial force retention function can be guaranteed. Therefore, the superstructure does not tilt or sink, and excessive displacement can be prevented, so the superstructure can be stably supported even after a major earthquake.

Furthermore, in the fourth embodiment, unlike the conventional structure in which the energy absorbing member is provided inside the main pile 2 or foundation 3, the flat energy absorbing member 5 is provided on the outside of the main pile 2, making it easy to replace the first U-shaped energy absorbing member 7 that has been damaged. Therefore, by replacing the damaged first U-shaped energy absorbing member 7 with a new one, it is possible to prepare for a new earthquake. In particular, for the main piles 2 on the periphery of the superstructure, which are prone to damage during earthquakes, they can be easily replaced by excavating the ground from the periphery side of the superstructure.

Fifth Embodiment
Next, the pile head joint structure 1D according to the fifth embodiment shown in Figure 14 is configured to use a second U-shaped energy absorbing member 7A (energy absorbing member) in which the mounting orientation of the first U-shaped energy absorbing member 7 according to the third embodiment described above is changed.
The second U-shaped energy absorbing member 7A is arranged with the curved portion 71 facing upward, and the end 72a of the first plate surface 72 and the end 73a of the second plate surface 73 facing downward. The first plate surface 72 and the second plate surface 73 sandwiching the curved portion 71 are arranged in directions perpendicular to the radial direction. The first plate surface 72 is fixed by bolt fastening to a plate-shaped support bracket 63 extending downward from the lower surface 6a of the ring-shaped receiving member 6 embedded in the foundation 3. The second plate surface 73 is fixed by bolt fastening to the outer peripheral surface 41b of the outer pipe pile 4. The plate surface 63a of the support bracket 63 is arranged so that the surfaces are parallel to the first plate surface 72.

As shown in FIG. 15, four second U-shaped energy absorbing members 7 are arranged at regular intervals (here, at 45 degree intervals) in the circumferential direction.

As shown in Figure 16, in the fifth embodiment, the energy absorbing member is a second U-shaped energy absorbing member 7A, and by utilizing the deformation of the U-shaped curved surface, the shear force and bending moment acting on the pile head 2A due to the inertial force acting on the superstructure can be effectively absorbed by the second U-shaped energy absorbing member 7A.
Moreover, in the case of the second U-shaped energy absorbing member 7A, the amount of deformation due to the U-shaped curved surface can be made large, so that damage to the second U-shaped energy absorbing member 7A itself can be kept small.

The above describes embodiments of the pile head joint structure, the method for seismic reinforcement of an existing structure, and the method for repairing the pile head joint of an existing structure according to the present invention, but the present invention is not limited to the above-mentioned embodiments and can be modified as appropriate without departing from the spirit of the invention.

For example, as in the first modified example shown in Figures 17(a) and (b), a configuration in which the flat plate energy absorption member 5 and the first U-shaped energy absorption member 7 described in the above embodiment are combined for one main pile 2 may be used. In addition, the configuration is not limited to alternating arrangement of the flat plate energy absorption member 5 and the first U-shaped energy absorption member 7 in the circumferential direction.

In addition, in the above-described embodiment, the ring-shaped receiving member 6 extending in the circumferential direction is embedded in the foundation 3 as a connection part for the energy absorbing member, but is not limited to being ring-shaped. For example, as shown in Figures 18(a) and (b), the receiving member 6A (energy absorbing member receiving member) may be divided in the circumferential direction. In other words, it is also possible to configure the receiving member 6A to be provided individually for each energy absorbing member (flat-plate energy absorbing member 5).

In addition, in this embodiment, concrete 43 is filled between the outer pipe pile 4 and the pile head 2A of the main pile 2, but it may be filled with a fillable material such as molten lead or resin, and it is also possible to omit the filler material such as concrete 43.

In addition, in this embodiment, the flat energy absorbing member 5 is configured to have one or more burring holes 51, but the burring holes 51 may be omitted. In other words, the flat energy absorbing member 5 may not have the burring holes 51.

Furthermore, in this embodiment, the energy absorbing members 5, 7, and 7A are configured to be connected to the outer pipe pile 4 and the energy absorbing member receiver by bolt fastening, but the connection means is not limited to bolt fastening and may be connected by other methods such as welding.

Moreover, a pile head joint structure 1E in a third modified example shown in Fig. 19 is configured such that the outer pipe pile 4 (see Fig. 1, etc.) of the above-mentioned embodiment is omitted, and a flat plate energy absorbing member 5 is directly connected to the pile head 2A of the main pile 2. That is, in the third modified example, a first connection portion 5a at one end of the flat plate energy absorbing member 5 is connected to the foundation 3 via a ring-shaped receiving member 6, and a second connection portion 5b at the other end is connected by bolt fastening via a connection plate 24 connected to the outer circumferential surface 2b of the main pile 2. In this case, the cost and labor required for providing the outer pipe pile can be reduced.
In this way, even if the flat plate energy absorption member 5 is connected directly to the main pile 2 without the interposition of an outer pipe pile, if the pile head 2A is made a semi-rigid connection, as in the case of providing an outer pipe pile, the axial force retention function of the main pile 2 can be ensured at low cost, and tilting, settlement, and excessive displacement of the superstructure can be prevented, and it has the advantage of being easily replaced once damaged.

In addition, the components in the above-described embodiments may be replaced with well-known components as appropriate without departing from the spirit of the present invention.

1, 1A, 1B, 1C, 1D, 1E Pile head joint structure 2 Pile 2A Pile head 3 Foundation 4 Outer pipe pile 5 Flat plate energy absorption member (energy absorption member)
6 Ring-shaped receiving member (energy absorbing receiving member)
6A Receiving member (energy absorbing receiving member)
7 First U-shaped energy absorbing member (energy absorbing member, U-shaped member)
7A Second U-shaped energy absorbing member (energy absorbing member, U-shaped member)
21, 23 Pile head cap 22 Pile projection 31, 33 Pile receiving plate 41 Outer steel pipe 43 Concrete (filler)
44 Outer steel pipe projection 45 Second mounting flange 51 Burring hole 61 Anchoring bar 62 First mounting flange

Claims (32)

A pile head joint structure for connecting the foundation of the superstructure and the main pile,
The connection between the foundation and the pile is made by a semi-rigid joint that allows some rotation of the foundation, or a pin joint that allows the rotation completely,
An energy absorbing member connected to the radially outer side of the pile;
an energy absorbing member receiver fixed to the foundation and connecting the energy absorbing member to the foundation;
Equipped with
An outer pipe pile is provided, the outer pipe pile being arranged coaxially with the main pile so as to surround the main pile;
A pile head joint structure characterized in that the energy absorbing member is connected to the radially outer side of the outer pipe pile . The pile head joint structure according to claim 1 , characterized in that the energy absorbing member is connected to the foundation and the outer pipe pile, or to the foundation and the main pile, by bolting. The pile head joint structure according to claim 1 or 2 , characterized in that the energy absorbing member is a flat plate member whose in-plane direction is oriented vertically. The energy absorbing member includes the plate member and a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 3 , characterized in that the U-shaped member is arranged so as to be curved in the left-right direction by the curved portion. The energy absorbing member includes the plate member and a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 3 , characterized in that the U-shaped member is arranged so as to be curved in the vertical direction by the curved portion. The pile head joint structure according to any one of claims 3 to 5 , characterized in that the plate member is formed with a burring hole. The energy absorbing member is a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 1 or 2 , characterized in that the U-shaped member is arranged so as to be curved in the left-right direction by the curved portion. The energy absorbing member is a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 1 or 2 , characterized in that the U-shaped member is arranged so as to be curved in the vertical direction by the curved portion. A pile head joint structure described in any one of claims 1 to 8, characterized in that the rotational rigidity between the foundation and the main pile added by the energy absorbing member is greater than or equal to the rotational rigidity between the foundation and the main pile added by the connection between the foundation and the main pile. The pile head joint structure according to claim 1 or 2 , characterized in that a filler material is filled between the outer pipe pile and the main pile. A pile head joint structure as described in claim 1 or 2, characterized in that protrusions are provided on the radially inner pipe inner surface of the outer pipe pile, the radially outer pile outer surface of the main pile, or both the pipe inner surface and the pile outer surface. A pile head joint structure for connecting the foundation of the superstructure and the main pile,
The connection between the foundation and the pile is made by a semi-rigid joint that allows some rotation of the foundation, or a pin joint that allows the rotation completely,
An energy absorbing member connected to the radially outer side of the pile;
an energy absorbing member receiver fixed to the foundation and connecting the energy absorbing member to the foundation;
Equipped with
A pile head joint structure characterized in that the energy absorbing member is a flat plate member with its in-plane direction oriented vertically. An outer pipe pile is provided, the outer pipe pile being arranged coaxially with the main pile so as to surround the main pile;
The pile head joint structure according to claim 12, characterized in that the energy absorbing member is connected to the radially outer side of the outer pipe pile. The pile head joint structure according to claim 13, characterized in that the energy absorbing member is connected to the foundation and the outer pipe pile, or to the foundation and the main pile, by bolting. The energy absorbing member includes the plate member and a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 12, characterized in that the U-shaped member is arranged so as to be curved in the left-right direction by the curved portion. The energy absorbing member includes the plate member and a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to claim 12, characterized in that the U-shaped member is arranged so as to be curved in the up and down direction by the curved portion. The energy absorbing member is a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to any one of claims 12 to 14, characterized in that the U-shaped member is arranged so as to be curved in the left-right direction by the curved portion. The energy absorbing member is a U-shaped member having a curved portion curved in a U shape,
The pile head joint structure according to any one of claims 12 to 14, characterized in that the U-shaped member is arranged so as to be curved in the up and down direction by the curved portion. The pile head joint structure according to claim 13 or 14, characterized in that a filler material is filled between the outer pipe pile and the main pile. A pile head joint structure as described in claim 13 or 14, characterized in that protrusions are provided on the radially inner pipe inner surface of the outer pipe pile, the radially outer pile outer surface of the main pile, or both the pipe inner surface and the pile outer surface. A pile head joint structure for connecting the foundation of the superstructure and the main pile,
The connection between the foundation and the pile is made by a semi-rigid joint that allows some rotation of the foundation, or a pin joint that allows the rotation completely,
An energy absorbing member connected to the radially outer side of the pile;
an energy absorbing member receiver fixed to the foundation and connecting the energy absorbing member to the foundation;
Equipped with
The energy absorbing member is a U-shaped member having a curved portion curved in a U shape,
A pile head joint structure characterized in that the U-shaped member is arranged so as to be curved in the vertical direction by the curved portion. An outer pipe pile is provided, which is arranged coaxially with the main pile so as to surround the main pile,
The pile head joint structure according to claim 21, characterized in that the energy absorbing member is connected to the radially outer side of the outer pipe pile. The pile head joint structure according to claim 22, characterized in that the energy absorbing member is connected to the foundation and the outer pipe pile, or to the foundation and the main pile, by bolting. The pile head joint structure according to claim 22 or 23, characterized in that a filler material is filled between the outer pipe pile and the main pile. A pile head joint structure as described in claim 22 or 23, characterized in that protrusions are provided on the radially inner pipe inner surface of the outer pipe pile, the radially outer pile outer surface of the main pile, or both the pipe inner surface and the pile outer surface. A pile head joint structure for connecting the foundation of the superstructure and the main pile,
The connection between the foundation and the pile is made by a semi-rigid joint that allows some rotation of the foundation, or a pin joint that allows the rotation completely,
An energy absorbing member connected to the radially outer side of the pile;
an energy absorbing member receiver fixed to the foundation and connecting the energy absorbing member to the foundation;
Equipped with
A pile head joint structure, characterized in that the rotational rigidity between the foundation and the main pile added by the energy absorbing member is greater than or equal to the rotational rigidity between the foundation and the main pile added by the connection between the foundation and the main pile. An outer pipe pile is provided, which is arranged coaxially with the main pile so as to surround the main pile,
The pile head joint structure according to claim 26, characterized in that the energy absorbing member is connected to the radially outer side of the outer pipe pile. The pile head joint structure according to claim 27, characterized in that the energy absorbing member is connected to the foundation and the outer pipe pile, or to the foundation and the main pile, by bolting. The pile head joint structure according to claim 27 or 28, characterized in that a filler material is filled between the outer pipe pile and the main pile. A pile head joint structure as described in claim 27 or 28, characterized in that protrusions are provided on the radially inner pipe inner surface of the outer pipe pile, the radially outer pile outer surface of the main pile, or both the pipe inner surface and the pile outer surface. A method for seismic reinforcement of an existing structure, comprising:
A step of joining the connection portion of the foundation of the existing structure and the pile by the semi-rigid joint or the pin joint;
Connecting the energy absorbing member to the radially outer side of the pile;
a step of fixing an energy absorbing member receiver to the foundation, the energy absorbing member receiver connecting the energy absorbing member to the foundation;
A method for seismic reinforcement of an existing structure, comprising: A method for repairing a pile head joint of an existing structure, comprising replacing the energy absorbing member of the pile head joint structure according to any one of claims 1 to 30.

Images