JP2002212958A - Pile foundation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pile foundation structure which can exert excellent earthquake resistant performance and base-isolation performance. SOLUTION: According to the pile foundation structure, a footing 6 is borne by a pile head which is an upper surface of a foundation pile, via a pin-connecting means and a drawing resistance applying means 20. The pin-connecting means connects the pile head and the footing 6 to each other in a relatively rotatable manner. The drawing resistance applying means 20 fixes a plurality of reinforcements 21 to the foundation pile such that their upper end portions 21a protrude from the pile head. Then, a plurality of reinforcement insertion passages 22 which each have a inner diameter D larger than a reinforcement diameter d, are formed in the footing 6 in a vertically penetrating manner, and the reinforcements 21 are inserted into the respective reinforcement insertion passages 22 such that the upper end portions 21a of the reinforcements 21 protrude from the footing 6. Further, a slipout preventive body 23a is attached to each reinforcement portion 21b protruding from the footing 6, and a spring member 24 is interposed between each slipout preventive body 23a and a footing upper surface 6b. The spring member 24 functions to urgingly bias the footing 6 in a downward direction with respect to the reinforcements 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete footing (foundation of a structure) fixed to an architectural / civil engineering-related structure such as a building or a bridge and embedded in the underground ground. Pile foundation structure supported by the pile head, which is the upper end of (a tip support pile that transmits to and supports a deep layer such as a hard bed layer, or a friction pile that is supported by the frictional force between the pile outer surface and soil and sand) It is about.

[0002]

2. Description of the Related Art In this type of pile foundation structure, as shown in FIG. 10, a foundation pile 82 as a structural unit is generally cast on an underground ground 81, and a pile head 82a and an upper layer are placed on the foundation pile 82. Usually, the concrete footing 83 is rigidly connected to the concrete footing 83 by embedding a plurality of pile reinforcing bars 84 in both the concrete 82 and 83 by casting concrete. The footing 83 is fixed to the column 85 and the foundation beam 86 on the upper structure side.

[0003]

However, in such a rigid joint structure, when an excessive force due to an earthquake or the like (hereinafter referred to as "seismic force") acts, stress is applied to a pile head joint part which is a boundary between the two. When a large earthquake occurs, the pile head 82a and the lower part of the footing 83 are easily damaged or broken, which may cause damage such as collapse of the upper structure. In addition, because of the rigid connection, the stress acting on the joint portion of the pile head is increased. Therefore, it is necessary to increase the number of reinforcing bars 84 to be buried more than necessary and to increase the cross sections of the pile 82 and the footing 83. is there. As a result, not only the construction becomes complicated, but also the construction cost increases due to an increase in reinforcement arrangement work. Also,
When the pile head joint is damaged or damaged, it is necessary to restore the point. However, the pile head joint is supported by a pile 82 which is concretely cast as a structural unit on the underground ground 81. Due to the low substructure, the workability of the recovery work itself is extremely poor and a huge recovery cost is required.

An object of the present invention is to provide a pile foundation structure capable of exhibiting excellent seismic performance and seismic isolation performance without causing such problems.

[0005]

A pile foundation structure according to the present invention which solves the above problem has a footing supported on a pile head, which is an upper end portion of a foundation pile, via a pin joining means and a pull-out resistance applying means. It is. Thus, the pin joining means is configured to load the elastic member between the lower support member provided on the pile head and the upper support member provided on the lower end of the footing, thereby relatively rotating the pile head and the footing. The pull-out resistance applying means connects a plurality of rebars,
A plurality of rebar insertion passages, which are fixed to the foundation pile and whose inner diameter is larger than the rebar diameter, are connected to the footing while their upper end portions protrude from the pile head and pass through the outer peripheral annular area of the joint portion by the pin joining means. Formed vertically, penetrate the upper end side of each reinforcing bar into each reinforcing bar insertion passage so as to protrude on the footing, attach a retaining body to each reinforcing bar portion protruding on the footing, and attach each retaining body and footing A spring member that presses and biases the footing downward against the rebar is interposed between the upper surface and the upper surface.

In the pull-out resistance applying means, it is preferable that each rebar insertion passage is formed by embedding a tubular member having a diameter larger than the rebar diameter in a footing. Also,
Each reinforcing bar projecting above the footing penetrates a metal supporting plate placed on the upper surface of the footing, and a spring member such as a coil spring or a disc spring is loaded between the supporting plate and the retaining body. Is preferred. It is preferable that a sliding layer made of a low friction material is formed between the upper surface of the footing and the support plate. Further, it is preferable that a lid member for securing a space for securing a horizontal displacement area and a vertical displacement area of each reinforcing bar with respect to the footing is disposed on the footing.

[0007]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be specifically described with reference to FIGS.

FIG. 1 to FIG. 5 show an embodiment of the present invention.
As shown in FIG. 1, the pile head 2a, which is the upper end of the foundation pile 2, and the footing 6 disposed above the pile head 2a are connected to the pin joining means 7.
And the pull-out resistance applying means 20 is connected so as to allow relative rotation by the pin connection. In addition, the foundation pile 2 is a reinforced concrete pile having a solid circular cross section formed by cast-in-place on the underground ground 1 (generally referred to as a “cast-in-place pile” or a “placed in-situ pile”). It is made of concrete which is fixed to a pillar 4 and a foundation beam 5 extending downward integrally from a building 3 as an upper structure and embedded in the ground.

[0009] The pin joining means 7 is shown in FIGS.
As shown in the figure, an elastic member 13 is loaded between a lower support member 10 provided on the pile head 2a and an upper support member 6a provided on the lower end of the footing 6. That is, the lower bearing member 10 places a shoe composed of a metal base plate 8 and a metal cylindrical wall 9 fixed to the upper surface of the shoe at the center of the pile head 2a, and places the shoe on the pile head 2a. The outer moat concrete layer 11 surrounding the shoes 8 and 9 is formed by casting concrete. Tube wall 9 and concrete layer 1
The upper surface position of 1 is set at the level of the pile construction excavation surface.
The upper support member 6a is formed integrally with the lower surface of the footing 6 so as to protrude therefrom.
Is fitted. The cross-sectional shape of the cylindrical wall (shoe) 9, that is, the concave portion 12 is square or circular, and in this example, square. The cross-sectional shape of the upper bearing member 6a has a similar shape smaller than the cross-sectional shape of the concave portion 12. An elastic member 13, between the two support members 6a, 10
A shim plate 14, a lateral displacement restraining member 15, a metal plate 16, and a cushion material 17 are loaded. That is, between the base plate (shoe) 8 constituting the bottom surface of the concave portion 12 and the lower end surface of the upper support member 6a fitted in the concave portion 12, an elastic member 13 placed on the base plate 8 and an elastic member Shim plate 1 placed on 13
4 and the metal plate 1 placed on the shim plate 14
6 and the lateral displacement restraining member 15 are loaded. The elastic member 13 has a flat plate shape that matches the cross-sectional shape of the concave portion 12, and is generally made of a rubber elastic material having excellent compression / restoring characteristics or an elastomer material made of a rubber base material. Thereby, the relative rotational displacement between the pile head 2a and the footing 6 is allowed. In addition, as a constituent material of the elastic member 13, it is possible to use lead, a lead alloy, a viscoelastic body, or the like, which has fluid deformability. Shim plate 14 is PT
The elastic member 1 is made of a low friction resin material such as FE.
3 has the same cross-sectional shape. Metal plate 16
In the figure, the peripheral portion 16a rises in an inclined shape extending upward. The lateral displacement restricting member 15 is an annular body filled between the peripheral surface 16 a of the metal plate 16 and the opposing surface of the cylindrical wall 9, and the inner peripheral surface 15 a is a tapered surface that closely contacts the peripheral surface 16 a of the metal plate 16. It is formed in. The constituent material of the lateral displacement restraining member 15 is PTFE, PF
It is preferable to use a fluorine resin such as A or Gore-Tex or a fluorine rubber, but it is also possible to use a copper alloy such as copper or a mirror. A cylindrical cushion member 17 is filled between the opposing surfaces of the upper support member 6 a and the cylindrical wall 9 above the lateral displacement restricting member 15. Further, between the upper surface of the lower support member 10 and the lower surface of the footing 6, a cushion member 18 having an annular plate shape fitted to the upper support member 6a is loaded. These cushion members 17 and 18 function as discarding frames when the footing 6 and the upper support member 6a integrally formed therewith are constructed (when concrete is cast), and after the concrete is hardened, the pile head 2a is formed. It functions as a clearance forming member for allowing relative horizontal displacement and relative rotational displacement between the motor and the footing 6. As a constituent material of the cushion members 17 and 18, a material which has a necessary strength as a concrete scrap frame and which can be compressed and deformed to allow a relative relative displacement between the footing 6 and the pile head 2 a, for example, styrene foam A cardboard material or the like whose inner surface is waterproofed by spray application of a waterproofing agent or pasting of waterproofing paper is used.

In the joint structure of the pile head by the pin joining means 7 described above, when the seismic force acts, the pile head 2
a and the footing 6 relatively horizontally move within a predetermined range within the concave portion 12 regulated by the cushioning material 17, and not only the energy at that time is absorbed by the cushioning material 17 but also the cushioning material 17. , 18 and the elastic member 13 accommodated in the bottom of the concave portion 12, the pile head 2 a and the footing 6 are relatively rotationally displaced in all directions, and the energy at that time is transmitted to the elastic member 13 and the cushion members 17, 18. Will be absorbed. As a result, stress concentration at the joint between the pile head 2a and the footing 6 when seismic force acts is significantly reduced, so that the cross sections of the pile 2 and the footing 6 are reduced to the minimum necessary in strength. In addition, while reducing the amount of reinforcement, the ease of construction and the cost are reduced, and even when an excessive horizontal force is applied, the pile head 2a and the footing 6 are prevented from being damaged or broken. Seismic performance and seismic isolation performance can be demonstrated.

By the way, the weight of the upper structure acts as a long-term vertical load on the elastic member 13 accommodated in the concave portion 12 through the footing 6, and further, when seismic force acts, the pile head 2a A strong offset load acts on the elastic member 13 in accordance with the relative rotational displacement between the footing 6 and the footing 6. At this time, the inner peripheral surface of the recess 12 (the inner peripheral surface of the cylindrical wall 9) and the upper support of the footing 6 Even if there is a slight gap between the elastic member 13 and the member 6a, the peripheral portion of the elastic member 13 protrudes into the gap, so that the elastic member 13 is easily damaged (cracked, etc.), and accordingly, a predetermined energy absorbing function is impaired. there is a possibility.

However, a shim plate 14 is laid on the entire upper surface of the elastic member 13 housed in the concave portion 12, and an upward tapered surface 1 is provided on the shim plate 14.
Since the lateral displacement restraining member 15 having the upper surface 5a is mounted on the shim plate 1, the upper surface of the elastic member 13 is worn or damaged when the pile head 2a and the footing 6 move relative to each other horizontally.
In addition to being blocked by the elastic member 13, when a long-term vertical load or an eccentric load due to the relative rotational displacement between the pile head 2 a and the footing 6 acts on the elastic member 13, the load is reduced by the tapered surface of the lateral displacement restraining member 15. The pressing force on the elastic member 13 side and the pressing force on the inner peripheral surface side of the cylindrical wall 9 are divided by a component 15a, and the lower surface of the lateral displacement restricting member 15 is received by the shim plate 14. Therefore, the pressing force of the lateral displacement restricting member 15 on the inner peripheral surface side of the cylindrical wall 9 is increased.

Therefore, even when an earthquake or the like occurs,
Inner peripheral surface of recess 12 formed by cylindrical wall 9 and upper support member 6
No gap is generated between the elastic member 13 and the elastic member 13, thereby preventing damage such as a crack due to protrusion of the peripheral portion of the elastic member 13, and at the same time, reducing corrosion and deterioration of the elastic member 13. This makes it possible to maintain the above-described excellent seismic performance and seismic isolation performance of the elastic member 13 stably over a long period of time.

The lateral displacement restraining member 15 is surrounded by the inner peripheral surface of the cylindrical wall 9, the shim plate 14, and the downward tapered surface 16a of the metal plate 16, so that the relative horizontal movement between the footing 6 and the pile head 2a is achieved. And the side displacement restricting member 15 itself is prevented from being damaged by direct contact with the concrete at the time of relative rotational displacement or being deformed by deformation, and the function of preventing the original elastic member from protruding by the side displacement restricting member 15 is further enhanced. By maintaining it stably, it is possible to more reliably exhibit the predetermined seismic performance and seismic isolation performance even after a long period of time.

Further, a configuration is adopted in which a metal plate 16 is disposed on the upper surface of the shim plate 14, and a downward tapered surface facing the upward tapered surface of the lateral displacement restraint member 15 is formed on the peripheral edge of the metal plate 16. As a result, the lateral displacement restraining member 15 rises and is surrounded by the inner peripheral surface of the cylindrical wall 9 and the downward tapered surface 16a of the shim plate 14 and the metal plate 16, and the relative horizontal movement and relative rotational displacement between the footing 6 and the pile head 2a are formed. Sometimes, the side displacement restraining member 15 itself is prevented from being damaged or deformed, and the function of preventing the original elastic member from protruding by the side displacement restraining member 15 is stably maintained. The seismic performance and seismic isolation performance of can be fully demonstrated. Also,
It is possible to provide a sliding function due to low friction between the metal plate 16 and the shim plate 14, and it is possible to more effectively absorb the rotational force due to an earthquake or the like. Further, by arranging the distal end of the metal plate 16 in the clearance, damage to the lateral displacement restricting member 15 due to the distal end of the metal plate 16 biting into the lateral displacement restricting member 15 is possible. Thus, the original elastic member protruding prevention function can be stably held for a long period of time. As shown in FIG. 6 or FIG. 7, the metal plate 16 is formed in a flat plate shape whose peripheral edge does not rise, and the outer peripheral edge of the lower end of the upper support member 6 a is formed on a tapered surface which is in close contact with the tapered surface 15 a of the lateral displacement restraining member 15. Also in the case where the elastic member is formed, the function of preventing the protrusion of the elastic member substantially the same as the case described above can be exerted.

By the way, a large pull-out force may be applied to the pillars (particularly corner pillars) 4 on the outer peripheral portion of the middle and high-rise building due to seismic force or buoyancy of water.
In the pile foundation structure in which the footing 6 and the footing 6 are joined by the above-mentioned pin joining means 7, the pulling force cannot be sufficiently countered, and the footing 6 is relatively moved from the footing 6 to the foundation pile 2.
May come off. In such a state, the balance of the force of the entire structure is suddenly broken, and the structure is seriously damaged. Therefore, in the pile foundation structure according to the present invention, by connecting the pile head 2a and the footing 6 with the pull-out resistance applying means 20 as described below, the above-described seismic function by the pin joining means 7 is achieved. , It is devised so as to ensure a resistance (pull-out resistance) enough to oppose the pull-out force without impairing the seismic isolation function.

That is, as shown in FIGS. 2, 3 and 5, the pull-out resistance applying means 20 comprises a plurality of rebars 21. 7 and fixed to the foundation pile 2 while passing through the outer peripheral annular region of the joint portion (the fitting portion between the upper bearing member 6a and the lower bearing member 10 (the concave portion 12)), and the inner diameter D is larger than the rebar diameter d. Are formed in the footing 6 in a vertically penetrating manner, and the upper end portions 21a of the reinforcing bars 21 are inserted into the reinforcing bar insertion passages 22 so as to protrude above the footing 6, and the footing 6 is placed on the footing 6. A retaining body 23 is attached to each protruding reinforcing bar portion 21b, and each retaining body 2
3 and the footing upper surface (footing top surface) 6b,
The footing 6 is provided with a spring member 24 for urging the reinforcing bar 21 to press the footing 6 downward.

As shown in FIG. 2 and FIG.
The pile 21 is buried and fixed in the foundation pile 2 in a state of being arranged at equal pitch on a circle concentric with the foundation pile 2 and penetrating the concrete layer 11, and the upper end side portion 21a exceeds the footing top surface 6b by a predetermined amount. It extends vertically upward to the position. Each reinforcing bar 21 is a main reinforcing bar or a PC steel material in which a screw portion 21c is engraved on an upper end portion 21b protruding above the footing top surface 6b. The portions of the reinforcing bars 21 buried in the foundation pile 2 (and the concrete layer 11) are interconnected by a band reinforcing bar (not shown) in the above-described circular arrangement.

As shown in FIG. 3, the rebar insertion passages 22 are formed in the footing 6 in the same arrangement form as the rebars 21, and each rebar 21 is located at the center of each rebar insertion passage 22. It is inserted in the state where it was done. As shown in FIG. 5, the rebar portion 21a inserted into the rebar insertion passage 22
In the range corresponding to the diameter difference D-d between the reinforcing bars 1a and 22, it is possible to relatively displace in the horizontal direction with respect to the reinforcing bar insertion passage 22, but the diameter D of the reinforcing bar insertion passage 22 in the horizontal direction of the reinforcing bar portion 21a. The relative displacement between the pile head 2a and the footing 6 in the horizontal direction (the relative displacement in the horizontal direction caused by the relative rotational displacement of the two 2a and 6 to absorb seismic force) for which the relative displacement is permitted by the pin joining means 7 ) Is set according to the rebar diameter d so as to coincide with or substantially coincide with the diameter d. Each rebar insertion passage 22 has a tubular member 22 having an inner diameter D.
a is buried in the footing 6. That is, the footing 6 having the rebar insertion passages 22 is formed by casting concrete using the tubular members 22a as a part of the mold for forming the footing (discarded form). Therefore, the tubular member 22a may have a rigidity enough to withstand the pressure during concrete casting and concrete hardening (not to be crushed), such as a metal pipe such as a steel pipe, a resin pipe, or a paper pipe. Pipe making (capo stack etc.) can be used.

As shown in FIG. 5, the upper end portion of each reinforcing bar 21, that is, the reinforcing bar portion 21b protruding above the footing top surface 6b, is formed of a metal annular plate having a diameter larger than the reinforcing bar insertion passage 22 in order from the bottom. The pressure plate 25, the annular washer 26, the annular spring member 24, and the annular washer 27 are inserted, and the retaining body 23 is attached. The support plate 25 is formed with a through-hole having a diameter necessary and sufficient for the reinforcing bar portion 21b to pass therethrough at the center thereof. The supporting plate 25 follows a reinforcing bar displacement (horizontal displacement) in the reinforcing bar insertion passage 22 and a footing top surface. 6b. As the spring member 24, a compression coil spring (a coil having a circular or square cross section) or a stack of a plurality of disc springs is used. In the illustrated example, a compression coil spring having a circular coil cross section is used. Have been. The retaining body 23 is a pair of nuts (double nuts) 23 a and 23 a screwed to the screw portion 21 c of the reinforcing bar 21. Thus, the footing 6 is urged downward by the spring member 24 against the rebar 21, and the urging force can be adjusted by changing the amount of tightening by the nuts 23a, 23a. In the range where the vertical relative displacement of the pile head 2a and the footing 6 allowed by the joining means 7 (the vertical relative displacement caused by the relative rotational displacement of the two 2a and 6 to absorb the seismic force) is not hindered. It is set to such an extent that the pulling out of the stake 2 from the footing 6 can be sufficiently prevented.

Therefore, according to the pull-out resistance applying means 20, the foundation pile 2 can be reliably pulled out from the footing 6 without hindering the relative displacement between the pile head 2a and the footing 6 by the pin connecting means 7. Can be prevented. That is, the relative displacement in the vertical direction between the pile head 2a and the footing 6 is absorbed by the expansion and contraction of the spring member 24, and the displacement in the horizontal direction of the two members 2a and 6 is caused by the movement of the rebar in the rebar insertion passage 22 (sliding of the support plate 25). ), The seismic function and seismic isolation function of the pin joining means 7 are not impaired. Further, pulling out of the foundation pile 2 is reliably prevented by the retaining body 23. Therefore, according to the pile foundation structure in which the pile head 2a and the footing 6 are joined and connected by both means 7 and 20, the seismic performance and seismic isolation performance of the building 3 can be greatly improved.

In some cases, concrete beams such as foundation beams, slabs, and columns are cast on the footing top surface 6b. In such a case, as shown in FIG. 5, each reinforcing bar is placed on the footing top surface 6b. A space 28 for securing a horizontal displacement area (sliding area of the support plate 25) and a vertical displacement area (expandable area of the spring member 24) with respect to the footing 6 of 21.
A cover member 28 for securing a is arranged. The cover member 28 is a discarded frame, and may be made of metal or resin as long as it has a compressive strength enough to withstand the pressure during concrete casting and concrete hardening (not to be crushed). Can be used. As shown in FIG. 8, instead of such a cover member 28, the space corresponding to the space 28a has a compressive strength enough to withstand the pressure during concrete placing and concrete hardening, and An elastic layer 29 made of urethane foam or the like having an elasticity that does not hinder the sliding of the support plate 25 and the expansion and contraction of the spring member 24 may be filled in advance.

A sliding layer 30 made of a low-friction material is formed between the footing top surface 6b and the support plate 25 so that the support plate 25 slides smoothly on the footing top surface 6b. Preferably. The sliding layer 30 is
The support plate 25 may be formed integrally with the support plate 25 as shown in FIG. 8, or may be formed separately from the support plate 25 as shown in FIG. That is, in the embodiment shown in FIG. 8, the sliding layer 30 is formed by coating the lower surface of the support plate 25 with a low friction material such as PTFE. In FIG. 9, the sliding layer 30 is formed of a sliding plate made of a low friction material such as PTFE, which is fitted and fixed to the upper end of the tubular member 22a slightly projecting from the footing top surface 6b. ing.

[0024]

As described above, according to the pile foundation structure of the present invention, seismic performance and seismic isolation performance of a building can be significantly improved without the problems described at the outset. In particular, the pull-out resistance applying means can satisfactorily withstand the pull-out force acting on the pillars (particularly corner pillars) on the outer peripheral portion of the middle and high-rise building by seismic force or buoyancy of water without impairing the pin joining function. .

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing an example of a pile foundation structure according to the present invention.

FIG. 2 is an enlarged detailed view showing a main part (a peripheral part of a corner post) of FIG. 1;

FIG. 3 is a cross-sectional plan view taken along the line III-III in FIG. 2;

FIG. 4 is an enlarged view of a main part of FIG. 2 (a peripheral part of a pin joining unit).

FIG. 5 is a main part of FIG. 2 (a part around the pull-out resistance applying means);
FIG.

FIG. 6 is a longitudinal sectional front view corresponding to FIG. 4 showing a modification of the pin joining means.

FIG. 7 is a longitudinal sectional front view corresponding to FIG. 4, showing another modification of the pin joining means.

8 is a longitudinal sectional front view corresponding to FIG. 7, showing a modification of the pull-out resistance applying means.

FIG. 9 is a longitudinal sectional front view corresponding to FIG. 7, showing another modification of the pull-out resistance applying means.

FIG. 10 is a vertical sectional front view showing a conventional pile foundation structure.

[Explanation of symbols]

2 ... foundation pile, 2a ... pile head, 6 ... footing, 6a ... upper support member, 6b ... toping top surface (upper surface of footing), 7 ... pin joining means, 10 ... lower support member, 13 ...
Elastic member, 20 ... pull-out resistance applying means, 21 ... rebar, 2
1a: upper end side portion of the reinforcing bar, 21b: a reinforcing bar portion projecting on the footing, 22: a reinforcing bar insertion passage, 22a: a tubular member,
Reference numeral 23: retaining body, 23a: nut (preventing body), 24: spring member, 25: supporting plate, 28: lid member, 28a: space, 3
0: sliding layer, D: diameter of reinforcing bar insertion passage, d: diameter of reinforcing bar.

Claims (5)

[Claims] 1. A footing is supported on a pile head, which is an upper end portion of a foundation pile, via a pin connecting means and a pull-out resistance applying means, wherein the pin connecting means comprises a lower bearing member provided on the pile head. The pile head and the footing are relatively rotatably joined by loading an elastic member between the pile head and the upper bearing member provided at the lower end of the footing, and the pull-out resistance applying means comprises a plurality of reinforcing bars. Are fixed to the foundation pile in a state where their upper end portions protrude from the pile head and pass through the outer peripheral annular region of the joint portion by the pin joining means,
A plurality of rebar insertion passages whose inner diameter is larger than the rebar diameter are formed in the footing so as to penetrate vertically, and the upper end side of each rebar is inserted into each rebar insertion passage in a state protruding on the footing,
A retaining member is attached to each reinforcing bar portion protruding above the footing, and a spring member that presses and biases the footing downward with respect to the reinforcing bar is interposed between each retaining member and the upper surface of the footing. A pile foundation structure characterized by the following. 2. The pile foundation structure according to claim 1, wherein each rebar insertion passage is formed by embedding a tubular member having a diameter larger than the rebar diameter in a footing. 3. Reinforcing bars projecting on the footing are:
3. The spring according to claim 1, wherein a metal supporting plate mounted on the footing upper surface is penetrated, and a spring member is mounted between the supporting plate and the retaining body. Pile foundation structure. 4. The pile foundation structure according to claim 3, wherein a sliding layer made of a low friction material is formed between the upper surface of the footing and the support plate. 5. A cover member for securing a space for securing a horizontal displacement area and a vertical displacement area of each reinforcing bar with respect to the footing is arranged on the footing. The pile foundation structure according to claim 2, 3, or 4.