JP2000087367A - Joint method of pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rationally design a cross section of a pile by accurately grasping stress efficiency around the pile head in the case of an earthquake. SOLUTION: Joint structure of a pile is so constituted that PC steel wires 3 projected from the head of a PC pile 1 are made to pass through a footing slab 2 to anchor the ends of the PC steel wires 3 on the upper surface of the footing slab. Anchorage structure in the ends of the PC steel wires 3 is constituted of anchor members 7 and energy absorption members 4 provided between the anchor members and footing slab 2. The energy absorption members 4 are crushed ahead of the PC steel wires at yield strength or less than fracture strength of the PC steel wires 3. While, tensile force is introduced to the PC steel wires 3 in the case anchorage work is carried out by the anchor members 7, and its strength is properly set so that the head of the PC pile 1 can be rotationally deformed for the footing slab 2 in the case bending moment acting on the head of the PC pile 1 exceeds M1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joint structure between a base of an upper structure such as a foundation slab and a pile head.

[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] These piles are joined to the foundation slab of the superstructure at the pile head.
In addition to a compressive force acting as a long-term load, during an earthquake, a pulling force caused by the overturning moment of the upper structure, a shear force or a bending moment caused by a horizontal force acts.

[0004] Therefore, when joining the pile head and the foundation slab, first, whether to handle rigidly or non-rigidly in the design at the joint is determined by the structural type, scale, and importance of the upper structure. Determining in consideration of the degree, pile diameter, number of piles, etc., then select a joining method that satisfies such joining conditions and design so that the soundness of the joint is maintained against the above-mentioned load There is a need.

[0005] Incidentally, as a joining method that can be regarded as a rigid connection, in the case of a cast-in-place concrete pile, a pile head is buried about 10 cm in a foundation slab, and a main bar of the pile previously set is fixed to the foundation slab. Alternatively, in the case of a ready-made stake, there is a method of embedding the stake in a foundation slab about a pile diameter length.

On the other hand, non-rigid joining methods include PC
In the case of piles or PHC piles, embedding in the foundation slab is 1
In addition to performing about 0 cm, the method of fixing the PC steel wire or steel rod left at the time of cutting the pile to the foundation slab, or in the case of a steel pipe pile or a ready-made concrete pile with an outer shell steel pipe, attach a reinforcing bar to the pile head. There is a method of attaching by welding in advance, and then fixing the joining rebar to the base slab.

[0007]

However, the rigidity of the pile head is considerably increased by the above-mentioned joining method even in the case of rigid joining and not rigid joining. A large bending moment acts on the pile head.

On the other hand, in the event of an earthquake, in addition to the bending moment, the above-described shearing force and pulling-out force act on the pile head in a complicated manner. There is a limit to accurately grasp the stress properties near the head.

Therefore, in order to prevent the pile head from being damaged by the bending moment described above, there has been a problem that the pile must be excessively designed.

The present invention has been made in consideration of the above-described circumstances, and a pile head capable of rationally designing a cross section of a pile by accurately grasping stress properties near the pile head during an earthquake. It is an object of the present invention to provide a joint structure.

[0011]

In order to achieve the above object, a joint structure for a pile according to the present invention, as described in claim 1, connects the head of the pile and the base of the upper structure via a tension member. And a predetermined tension is introduced into the tendon so that the head of the pile is rotationally deformed with respect to the base when a predetermined bending moment acts on the head of the pile. .

In the joint structure for a pile according to the present invention, an anchoring structure provided at an end of the tendon at the base side side is provided with an energy absorbing member that breaks down at a yield strength or breaking strength or less of the tendon. And the energy absorbing member can be replaced freely.

In the joint structure for a pile according to the present invention, the head of the pile and the base of the upper structure are joined in a state where a predetermined tension is introduced, so that there is a space between the pile head and the base. , A compressive force interacts as a reaction force of the tension. And
As long as this compressive force is present, the head of the pile will not rotate and deform (creating an angle of rotation) and will not leave the base of the superstructure. In other words, the head of the pile is kept in rigid contact with the base of the superstructure.

On the other hand, as the magnitude of the earthquake increases,
That is, as the bending moment caused by the horizontal force during an earthquake increases, the above-described compressive force decreases, and the compressive force eventually disappears, and the pile head starts rotating and deforming with respect to the base of the superstructure.

That is, when the bending moment is small,
The connection between the head of the pile and the base of the superstructure maintains a rigid connection, but when a certain bending moment is reached, in other words, when the earthquake exceeds a certain scale, the two parts are connected. The state shifts from rigid to non-rigid, and the bending moment acting on the head of the pile is suppressed much more than in the rigid state.

The turning point at which the joint between the head of the pile and the base of the upper structure shifts from rigid to non-rigid can be freely set by adjusting the magnitude of the tension. It is possible to perform an optimal design for each property.

Here, the base of the upper structure means a portion of the upper structure to which the head of the pile is joined. If the upper structure is, for example, a normal building, the foundation slab corresponds to the upper structure. If it is a pier, the base of the pier corresponds. The base is mainly made of reinforced concrete, but its material is arbitrary. The base includes not only concrete structures other than RC (for example, PC structures) but also steel structures.

The types of piles are arbitrary, and include cast-in-place concrete piles, steel pipe piles, concrete piles,
It can be applied to ready-made piles such as C pile and PHC pile.
Further, as the tension member, for example, a PC steel wire or a PC steel rod can be used.

The joining method between the tendon and the pile is arbitrary,
When using a PC pile, a PC steel wire protruding from the pile may be used, and when using a steel pipe pile, a PC steel rod may be directly or pre-determined on the pile head of the steel pipe pile. It may be mounted by welding or the like via the mounting bracket.

The fixing structure provided at the base-side end of the tendon material may be arbitrarily configured. However, the fixing structure may include an energy absorbing member that breaks at a yield strength or breaking strength equal to or lower than the yield strength of the tendon material. In addition, if the energy absorbing member is freely replaceable, even if the energy absorbing member is damaged by the compressive force received from the tension member during a large earthquake, the energy absorbing member is removed after the earthquake and replaced with a new one, and a predetermined tension is applied. With the introduction of force, it can be restored.

As a specific example of the fixing structure, for example, a known fixing member for fixing a PC steel wire is modified so as to cause premature breakage so as to serve also as an energy absorbing member, or a known fixing member and an upper structure are used. For example, a method of separately interposing an energy absorbing member between the base and the base may be considered.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a joint structure for piles according to the present invention will be described with reference to the accompanying drawings.
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.

FIGS. 1 to 3 show a joint structure of a pile according to this embodiment. As can be seen from these figures, the joint structure of the pile according to the present embodiment penetrates a PC steel wire 3 as a tendon from the head of the PC pile 1 into the base slab 2 which is the base of the upper structure. Then, by fixing the end of the PC steel wire 3 on the upper surface of the base slab, the head of the PC pile 1 and the base slab 2 are joined to each other via the PC steel wire 3.

Here, the fixing structure at the end of the PC steel wire 3 includes a female cone 5 and a three-divided male cone 6 fitted into the female cone, as can be clearly seen from the exploded perspective view of FIG. It comprises a member 7 and an energy absorbing member 4 interposed between the fixing member and the base slab 2.

The energy absorbing member 4 is formed as a concrete cylinder having an insertion hole 8 formed in the center thereof, through which the PC steel wire 3 is inserted. It collapses ahead of the line. As can be seen from the figure, the energy absorbing member 4 can be replaced with a new one after the crushing, with the fixing member 7 removed.

On the other hand, tension is introduced into the PC steel wire 3 during the fixing operation by the fixing member 7, and the bending moment acting on the head of the PC pile 1 reaches M ₁ . Previously, not rotational deformation (angle of rotation) occurs in the head of the PC pile 1, when exceeded M _1, there are appropriately determined so that the head of the PC pile 1 is rotated deformed relative to the base slab 2 .

M ₁ means a turning point from a rigid state to a non-rigid state as described later, and how to determine this may be appropriately examined from a design point of view.

In the pile joining structure according to the present embodiment, the head of the PC pile 1 and the foundation slab 2 are joined in a state where the above-described tension is introduced. As shown in FIG. 4, a compressive force P acts from the base slab 2 as a reaction force of the tension. And the horizontal force H during an earthquake
As a stress state combined with the bending moment M acting on the pile head due to the above, the head of the PC pile 1 is rotationally deformed as long as the value of the stress σ ₂ is compression as shown in FIG. It does not leave the base slab 2 (causing a rotation angle). In other words, the head of the PC pile 1 is kept in rigid contact with the base slab 2. Incidentally, such a rigid connection state as long as the bending moment M acting on the pile head is below the M ₁ as described above, is maintained.

FIG. 5 shows the rotation angle θ at the pile head of the PC pile 1.
5 is a graph showing the relationship between the bending moment M acting on the pile head and the rigid contact state described above corresponds to a path from the origin to point A on the graph.

On the other hand, as the magnitude of the earthquake increases,
That is, as the bending moment M caused by the horizontal force H during an earthquake increases, the value of the above-described stress σ ₂ decreases. When the value of the stress σ ₂ exceeds the above-described M ₁ , the stress σ ₂ changes from FIG.
As shown in (f), it is in a tension state, and the head of the PC pile 1 is
Rotational deformation of the base slab 2 is started. In other words, the head of the PC pile 1 shifts to a state close to the pin connection with the base slab 2 (point A in FIG. 5).

Next, when the horizontal force H at the time of the earthquake further increases from this state, the bending moment acting on the pile head continues to increase. Is small (from point A in FIG. 5).
B point). When the compressive force acting on the energy absorbing member 4 as a reaction force of the tensile force generated in the PC steel wire 3 reaches a predetermined magnitude, the energy absorbing member 4 is crushed (point B in FIG. 5). .

As described above, according to the joint structure of a pile according to the present embodiment, when the bending moment M acting on the pile head of the PC pile 1 is small, in other words, when the small-to-medium-sized earthquake occurs, the PC pile 1 the head and the bonding state of the base slab 2 is rigid connection is maintained as a boundary when it reaches a certain bending moment M _1, for a certain size or more seismic other words, both the bonding state of Shifts from rigid to non-rigid, it is possible to greatly suppress the bending moment M acting on the head of the PC pile 1, and thus to use a large earthquake without using a pile having an excessive cross section. In this case, it is possible to prevent the pile head from being damaged at the time and the upper structure from being damaged.

Further, according to the joint structure of the pile according to the present embodiment, the transition point at which the joint state between the head of the PC pile 1 and the foundation slab 2 shifts from rigid to non-rigid (point A in FIG. 5). ), PC
Since the tension can be set freely by adjusting the magnitude of the tension introduced into the steel wire 3, it is possible to perform an optimal design for each property.

Further, according to the pile joining structure according to the present embodiment, the fixing structure of the PC steel wire 3 is constituted by the fixing member 7 and the energy absorbing member 4, and the energy absorbing member 4 is damaged in the event of a large earthquake. As a result, the location of the damage in the event of a large earthquake is actively provided, so that the behavior of the superstructure and the pile during the large earthquake becomes clear, and as a result, the elasto-plastic design becomes easier.

Further, according to the pile joint structure according to the present embodiment, the energy absorbing member 4 which is prematurely damaged at a yield strength or breaking strength of the PC steel wire 3 or less is replaced between the fixing member 7 and the foundation slab 2. Because it was freely interposed, even if it was damaged by the compressive force received from PC steel wire 3 after a large earthquake,
If this is removed and replaced with a new one to introduce a predetermined tension, it becomes possible to restore the original condition.

In the present embodiment, the PC pile 1 is used as a pile, and the PC steel wire 3 protruding from the PC pile is used as a tension member. However, when a steel pipe pile is used instead of the PC pile,
As shown in FIG. 6, a PC steel rod 13 as a tendon is fixed to an annular steel plate 12 as a mounting bracket in advance by welding or the like.
The annular steel plate 12 may be fixed to the steel pipe pile 11 by welding or the like, or the PC steel rod 13 may be fixed to the steel pipe pile 11 directly by welding or the like as shown in FIG. As shown in FIG. 7, a flange 14 having a notch 16 is provided at the pile head of the steel pipe pile 11, and a PC steel bar 13 having an engaging plate 15 provided at an end thereof is fitted into the notch 16. It is also possible to mount it in such a way.

In this embodiment, a concrete cylinder is used as the energy absorbing member. Instead of this, the energy absorbing member is formed of, for example, a hollow steel pipe, and is broken by local buckling of the hollow steel pipe. You may. Further, the energy absorbing member may be omitted, and the fixing member 7 itself may be damaged.

Further, in the present embodiment, the tension member PC
The fixing structure of the steel wire 3 includes the fixing member 7 and the energy absorbing member 4.
And the energy absorbing member is freely replaceable. However, in some cases, the energy absorbing member may not be replaceable. With such a configuration, restoration after a large earthquake is impossible, but in other respects, the same operational effects as described above can be obtained.

Further, in the present embodiment, the PC which is a tendon material is used.
Although the fixing structure of the steel wire 3 is damaged, the fixing structure may not be damaged in some cases. In such a configuration, the above-described operation and effect cannot be obtained with respect to the clarity of the elasto-plastic design at the time of a large earthquake, but in other respects, the same operation and effect as described above can be obtained.

[0040]

As described above, according to the pile joint structure of the present invention according to the first aspect, when the bending moment acting on the pile head is small, in other words, when a small-to-medium-sized earthquake occurs,
Although the connection between the pile head and the base remains rigid, the connection between the two ends when the bending moment reaches a certain value, in other words, for an earthquake of a certain scale or more. Since the transition to rigid connection, the bending moment acting on the pile head can be greatly reduced, and even if a pile with an excessive cross section is not used, damage to the pile head and damage to the superstructure during a large earthquake can be achieved. Can be prevented beforehand. In addition, the turning point at which the connection between the pile head and the base transitions from rigid to non-rigid can be set freely by adjusting the magnitude of the tension introduced into the tendon, making it ideal for each property It is possible to perform a simple design.

According to the joint structure of a pile according to the second aspect of the present invention, even if the energy absorbing member is damaged by the compressive force received from the tendon during a large earthquake, it is removed and replaced with a new one. If a predetermined tension is introduced, it is possible to restore the original condition.

[0042]

[Brief description of the drawings]

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

FIG. 2 is a plan view seen from the direction of the line AA in FIG. 1;

FIG. 3 is an exploded perspective view showing a joint structure of the pile according to the embodiment.

FIG. 4 is a diagram showing an operation of the pile joint structure according to the embodiment.

FIG. 5 is a view showing the operation of the pile joint structure according to the embodiment.

FIG. 6 is a perspective view showing a modification of the fixing structure between the pile head and the tension member.

FIG. 7 is a perspective view showing a modification of the fixing structure between the pile head and the tension member.

[Description of Signs] 1 Pile 2 Foundation slab (base) 3 PC steel wire (tensile material) 4 Energy absorbing member (fixing structure) 7 Fixing member (fixing structure)

Claims (2)

[Claims] 1. A head of a pile and a base of an upper structure are joined to each other via a tension member, and the head of the pile is connected to the base when a predetermined bending moment acts on the head of the pile. A pile joining structure, wherein a predetermined tension is applied to the tension member so as to be rotationally deformed. 2. An anchoring structure provided at an end portion of the tendon member on the base side side is provided with an energy absorbing member which breaks down earlier than the yield strength or breaking strength of the tendon material, and the energy absorbing member is replaceable. The joint structure for a pile according to claim 1.