JP2001234549A - Joint structure between pile and foundation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure which eases the joint degree between a pile head and a foundation, decreases bending moment in the event of an earthquake, and absorbs earthquake energy at a joint portion. SOLUTION: According to the joint structure between a pile and the foundation, a head portion of the pile 1, i.e., the pile head 2, is connected to the foundation 3 of an upper structure, not shown, via a connecting member 4. The connecting member 4 is formed of a so-called steel pipe with infilled concrete (CFT), and consists of a hollow steel pipe 5 and concrete 6 filled therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a joint structure between a pile and a foundation.

[0002]

2. Description of the Related Art There are two types of pile foundations: a support pile type and a friction pile type. In the former, when a good quality support layer is deep underground, an upper structure is constructed on a pile driven into the support layer. Accordingly, the structure is a type in which the weight of the structure is stably supported by the support layer, and the latter is a basic type in which the upper structure is supported by the frictional force with the surrounding ground when there is no high-quality support layer.

[0003] Naturally, these piles must be able to reliably support the weight of the superstructure, but in the event of an earthquake, a large shear force or bending moment acts on the pile head due to the horizontal force from the superstructure. Therefore, when designing and constructing, it is necessary to give due consideration to earthquake safety.

Conventionally, as a method of joining a pile and a foundation slab, a pile head of a cast-in-place concrete pile is attached to the foundation slab.
There has been a method of embedding a main bar of a pile, which has been embedded in about 0 cm and put out in advance, on a foundation slab, or embedding a pile head of a ready-made pile in a foundation slab to a length corresponding to a pile diameter.

[0005]

However, in these joining methods, the degree of fixation α is 1.0, that is, almost rigid, and an excessive shear force or bending moment acts on the pile head during a huge earthquake. This could lead to unexpected situations such as breakage of piles and collapse of superstructures.

The present invention has been made in consideration of the above-described circumstances, and is intended to reduce the joint moment between a pile head and a foundation to reduce a bending moment during an earthquake and to absorb energy during an earthquake at a joint. It is an object of the present invention to provide a possible joint structure between a pile and a foundation.

[0007]

In order to achieve the above object, a joint structure between a pile and a foundation according to the present invention has a hollow structure in which the head of the pile and the foundation of the upper structure are hollow. It is joined via a joining member consisting of a steel pipe and concrete filled therein.

Further, in the joint structure of a pile and a foundation according to the present invention, an end of the joining member penetrates a predetermined length into the head of the pile or the foundation so that a gap is formed around the end. In addition, the gap is filled with a filler that can expand and contract.

In the joint structure between a pile and a foundation according to the present invention, a communication opening is provided at an end of the hollow steel pipe, and concrete filled in the hollow steel pipe through the communication opening is filled with the pile or the concrete. It is to be integrated with the foundation concrete.

In the joint structure between a pile and a foundation according to the present invention, the head of the pile and the foundation of the superstructure are joined to each other via a joining member composed of a hollow steel pipe and concrete filled therein. is there. The joining member can secure high strength by the synergistic action of the strength of the hollow steel pipe itself and the increase in the compressive strength of the concrete due to the restraining effect of the hollow steel pipe.

Therefore, it is possible to reduce the bending stiffness by reducing the cross-sectional area of the joining member without impairing the function of supporting the vertical load of the upper structure at all. The degree of bonding is reduced.

Further, a large bending deformation occurs in the joining member with a decrease in bending stiffness. The bending deformation exerts a hysteretic damping of the hollow steel pipe, and energy during an earthquake is reduced.
It is quickly absorbed by such a joining member.

[0013] The joining member composed of the hollow steel pipe and the concrete filled therein is mainly intended for a structural member called a concrete filled steel pipe (CFT). , RCFT) and whether to use high-strength concrete are arbitrary. Also, it goes without saying that hollow steel pipes having various cross-sectional shapes including circular steel pipes and square steel pipes can be used.

[0014] It is optional how the joining member is joined to the head of the pile. The lower end of the joining member is fixed in the head of the cast-in-place concrete pile by a predetermined length. Various types of connection are conceivable, such as bolting using a reinforcing bar protruding from the head of the pile, or fixing directly to the head by welding if the pile is a steel pipe pile. When the lower end of the joining member is fixed within the head of the pile by a predetermined length, studs or ribs are protruded from the peripheral surface of the hollow steel pipe, or the end of the reinforcing steel provided in the hollow steel pipe is connected to the pile. It is needless to say that the fixing strength between the lower end of the joining member and the head of the pile can be increased by fixing in the head.

The same applies to the case of joining to the foundation, in which the upper end of the joining member is fixed within the foundation by a predetermined length.
Various connection types are conceivable, such as bolting using an anchor bolt embedded in the foundation or directly fixing to a plate embedded in the foundation by welding. In addition, when fixing the upper end of the joining member by a predetermined length in the foundation,
About studs and ribs protruding from the peripheral surface of the hollow steel pipe, or fixing the end of the reinforcing steel provided in the hollow steel pipe to the foundation, to increase the anchoring strength between the upper end of the joining member and the foundation The same is true for

In joining the head of the pile and the foundation of the superstructure through a joining member composed of a hollow steel pipe and concrete filled therein, as long as the joining member undergoes a predetermined bending deformation, How to set the length is optional, and whether the joint member is exposed to the surrounding ground is also optional, but the end of the joint member is formed so that a gap is formed around it. If the head of the pile or the foundation penetrates a predetermined length and the gap is filled with an expandable / contractible filler, the joint member will not be exposed to the surrounding ground or groundwater, so that the corrosion of the joint member is anticipated. Can be prevented.

[0017] In this configuration, the joining member can be bent and deformed almost without being restrained from the surroundings by the filler that can be expanded and contracted filled in the gap, and the filler filled in the gap can be deformed. There is no concern that interfering substances such as sand and gravel that may inhibit bending deformation due to the material will enter the gap.

The concrete filled in the hollow steel pipe is
A communication opening may be provided at the end of the hollow steel pipe, and the concrete filled in the hollow steel pipe through the communication opening may be separated from the pile head or the concrete of the foundation. Or, if it is made to be integrated with the concrete of the foundation, it becomes possible to transmit the axial force from the upper structure downward through the hollow steel pipe and the entire cross section of the concrete therein.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view showing an embodiment of a joint structure between a pile and a foundation according to the present invention. It is to be noted that the same reference numerals are given to components and the like that are substantially the same as those in the conventional technology, and description thereof will be omitted.

FIG. 1 shows a joint structure between a pile and a foundation according to the present embodiment. As can be seen from the figure, the joint structure between the pile and the foundation according to the present embodiment is obtained by joining the head of the pile 1, ie, the pile head 2, to the foundation 3 of the upper structure (not shown) via the joining member 4. The joining member 4 is a so-called concrete-filled steel pipe (CFT), and includes a hollow steel pipe 5 and concrete 6 filled therein.

It is conceivable that the joining member 4 is transported to the site with, for example, concrete filled therein.

In order to construct the joint structure between the pile and the foundation according to the present embodiment, when the pile 1 is, for example, a cast-in-place concrete pile, the lower end of the joint member 4 is connected to the pile when the cast-in-place concrete pile is constructed. When the concrete work of the foundation 3 is performed, the upper end of the joining member 4 may be buried in the foundation 2 when the concrete work of the foundation 3 is performed.

In the joint structure between the pile and the foundation according to the present invention, the pile head 2 and the foundation 3 of the superstructure are joined via the joining member 4 which is a concrete-filled steel pipe. The joining member 4 is secured with high strength by the synergistic effect of the strength of the hollow steel pipe 5 itself and the increase in the compressive strength of the concrete 6 due to the restraining effect of the hollow steel pipe.

As described above, according to the joint structure between the pile and the foundation according to the present embodiment, the synergistic effect of the strength of the hollow steel pipe 5 itself and the increase in the compressive strength of the concrete 6 due to the restraining effect of the hollow steel pipe is achieved. Since the joining member 4 formed with high strength is interposed between the pile head 2 and the foundation 3, without impairing the function of supporting the vertical load of the superstructure at all,
It is possible to reduce the bending stiffness by reducing the cross-sectional area of the joining member 4.

Therefore, the foundation 3 of the superstructure and the pile head 2
The connection state with the conventional rigid connection is shifted to, for example, a semi-fixed state, and the rotation constraint of the pile head 2 against the horizontal force from the upper structure is greatly reduced. When acting from the upper structure, only a small bending moment is generated at the pile head 2, and thus the pile head damage due to the bending moment is prevented beforehand.

Further, according to the joint structure between the pile and the foundation according to the present embodiment, since the joining member 4 is formed of a concrete-filled steel pipe having excellent toughness, the hysteresis damping performance of the joining member during an earthquake is exhibited. , Energy during an earthquake is quickly absorbed.

Further, according to the joint structure between the pile and the foundation according to the present embodiment, the joining state between the foundation 3 and the pile head 2 of the upper structure becomes a semi-fixed state. The natural frequency of the object-coupled system decreases. Therefore, although it depends on the prevailing frequency of the surface ground and the vibration characteristics of the input seismic wave, in general, the level of earthquake input to the upper structure is reduced, and it is possible to improve the seismic resistance of the upper structure. Become.

Further, according to the joint structure between the pile and the foundation according to the present embodiment, the bending moment generated at the pile head can be suppressed to a small value. According to the present embodiment, even in the case where the cross section of the pile is determined, the bending moment at the pile head does not become critical in design, so that the cross section of the pile is reduced, and the construction cost of the pile is reduced. Can be reduced.

In the present embodiment, it is assumed that the joining member 4 in which the concrete 6 has been filled in the hollow steel pipe 5 in advance is carried on site, but a configuration shown in FIG. 2 may be used instead.

In the joint structure between the pile and the foundation according to the modification shown in FIG. 3, the pile head 2 and the foundation 3 are joined via a joint member 14 which is a concrete-filled steel pipe, similarly to the above-described embodiment. However, an annular plate 17 having a communication opening 18 is attached to each of the upper and lower ends of the joining member 14.

In order to construct the joint structure between the pile and the foundation according to the present modification using the joint member 14, the lower end of the joint member 14 is embedded in the pile head 2 when the cast-in-place concrete pile 1 is constructed. Erect. At this time, the fresh concrete of the cast-in-place concrete pile 1 enters the hollow steel pipe 15 through the communication opening 18 of the annular plate 17 provided at the lower end of the joining member 14, but the poor quality concrete enters the hollow steel pipe 15. Perform slime treatment as necessary to prevent the slime from entering.

Next, the communication opening 1 on the upper end side of the joining member 14
8 is filled with, for example, high-strength concrete 16, and the concrete is filled into the hollow steel pipe 15 through a communication opening 18 on the lower end side.
Integrate with the concrete on the pile side that has entered inside.

Next, in parallel with the concrete work of the foundation 3, fresh concrete of the foundation 3 is poured from the communication opening 18 on the upper end side of the joining member 14, so that the concrete on the foundation side has a high strength in the hollow steel pipe 15. Concrete 16 and hollow steel pipe 15 are integrated.

According to this structure, the stress transmission becomes smooth due to the integration of the concrete, and the axial force from the upper structure can be reliably transmitted downward through the entire cross section of the hollow steel pipe and the concrete inside the hollow steel pipe. Becomes

In this modification, studs 19 are provided on the outer peripheral surfaces of the lower end and the upper end of the joining member 14 so that the pile head 2
And the fixing strength with the base 3 is improved.

As described above, in order to increase the fixing strength between the joining member 4 or the joining member 14 and the pile head 2 or the foundation 3, as shown in FIG. Alternatively, as shown in FIG. 4, as shown in FIG. 4, the reinforcing steel 31 is passed through the hollow steel pipe 5 and the hollow steel pipe 15, and the upper end is fixed to the foundation 3 and the lower end is fixed to the pile head 2. You may do so. In such a case, the joining member 4 is a reinforced concrete filled steel pipe (RCFT).

Although not specifically mentioned in the present embodiment, a joint structure between a pile and a foundation according to the modified example shown in FIGS. 5 and 6 may be adopted instead of the embodiment shown in FIG. .

As can be seen from the figure, the joint structure between the pile and the foundation according to this modification is similar to that of the above-described embodiment.
Although the pile head 2 and the foundation 3 are joined by, in this modification,
The lower end of the joining member 4 penetrates the pile head 2 by a predetermined length so that a gap δ is formed around the lower end thereof, and the gap is filled with an expandable and contractible filler 41.

As the expandable / contractible filler 41, for example, it is conceivable to form a rubber-based material or a porous elastic material.

According to such a configuration, since the joining member 4 is not exposed to the surrounding ground or groundwater, it is possible to prevent corrosion of the joining member.

In this configuration, the joining member 4 can be bent and deformed with almost no restraint from the surroundings by the expandable and contractible filler 41 filled in the gap δ, There is no concern that an interfering substance such as gravel or the like that impedes bending deformation due to the filled filler 41 enters the gap.

The gap δ may be provided on the foundation 3 as shown in FIG. 7A, or may be provided over the foundation 3 and the pile head 2.

[0043]

As described above, according to the joint structure of a pile and a foundation according to the present invention, the cross-sectional area of the joint member can be reduced without impairing the function of supporting the vertical load of the upper structure. Bending rigidity can be reduced.

Therefore, the joining condition between the foundation of the upper structure and the pile head shifts from the conventional rigid connection to, for example, a semi-fixed state, and the rotation constraint of the pile head against the horizontal force from the upper structure is reduced. It is greatly reduced, and when a horizontal force due to an earthquake or wind is applied from the upper structure, only a small bending moment is generated at the pile head, thus preventing the pile head from being damaged due to the bending moment.

[0045]

[Brief description of the drawings]

FIG. 1 is a side view showing a part of a joint structure between a pile and a foundation according to an embodiment in a cross section.

FIG. 2 is a side view showing a part of a joint structure between a pile and a foundation according to a modification in a cross section.

FIG. 3 is a side view partially showing a joint structure between a pile and a foundation according to another modified example in a cross section.

FIG. 4 is a side view showing a part of a joint structure between a pile and a foundation according to another modification in a cross section.

FIG. 5 is a side view showing a part of a joint structure between a pile and a foundation according to another modification in a cross section.

FIG. 6 is a horizontal sectional view along AA.

FIG. 7 is a side view showing a joint structure between a pile and a foundation according to another modification.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 pile 2 pile head (pile head) 3 foundation 4 joining member 5 hollow steel pipe 6 concrete 41 expandable / contractible filler

Claims (3)

[Claims] 1. A joint structure between a pile and a foundation, wherein the head of the pile and the foundation of the upper structure are joined via a joining member composed of a hollow steel pipe and concrete filled therein. 2. An end portion of the joining member is penetrated a predetermined length into the head or the foundation of the pile so that a gap is formed around the joining member, and the gap is filled with an expandable and contractible filler. A joint structure between the pile according to claim 1 and a foundation. 3. A communication opening is provided at an end of the hollow steel pipe,
2. The joint structure between a pile and a foundation according to claim 1, wherein the concrete filled in the hollow steel pipe through the communication opening is integrated with the pile or the concrete of the foundation. 3.