JP7699035B2 - Pile head semi-rigid joint structure - Google Patents

Description

The present invention relates to a semi-rigid pile head joint structure.

Conventionally, a semi-rigid pile head joint structure that does not completely restrain the rotation of the pile head is known as a method of connecting a pile supporting a structure to the foundation of the structure. The semi-rigid pile head joint structure is a structure that improves the earthquake resistance performance of the pile foundation by distributing the bending moment between the pile head and the underground in a balanced manner by controlling the degree of fixation against rotation of the pile head. Conventional semi-rigid pile head joint structures are generally configured such that the pile head is embedded in the foundation and constructed as a single unit, as in Patent Document 1, for example.

JP 2020-90867 A

However, the semi-rigid pile head joint structure with the above configuration has the problem that because the foundation and pile head are integrated, when external forces such as earthquakes or wind act on the building, large shear forces and bending stresses are transmitted from the foundation to the pile head, which is integrated with the foundation. As a result, there is a risk that the pile head will break at the joint between the pile head and the foundation due to the large shear forces and bending stresses acting on it. In particular, since existing piles may not be designed to withstand horizontal resistance during earthquakes, conventional semi-rigid pile head joint structures using existing piles have the problem that the shear forces transmitted to the pile head will be greater than the allowable value of the existing piles.

The present invention was made in consideration of the above circumstances, and aims to provide a semi-rigid pile head joint structure that can reduce the shear force and bending stress transmitted from the foundation to the pile head.

In order to achieve the above-mentioned objective, the semi-rigid pile head joint structure of the present invention comprises a foundation located below a structure, a pile body penetrating the ground and positioned away from the lower end of the foundation, a joint portion including a reinforcing steel pipe surrounding the pile head of the pile body, and a filling portion formed by filling the inside of the reinforcing steel pipe with a filling material, and an edge cutting portion disposed between the foundation and the joint portion, abutting against the lower end of the foundation and the upper end of the joint portion, and having an abutment surface formed larger than the upper end surface of the reinforcing steel pipe.

By using the above configuration, the pile body and the foundation are joined by the joint, resulting in a semi-rigid pile head joint structure in which the pile head is not completely restrained against external forces. In the semi-rigid pile head joint structure, the joint and the foundation are separated by the edge separation section, and the pile body, the joint and the foundation are formed as separate bodies, so that the shear force and bending stress transmitted from the foundation to the pile head can be reduced. Therefore, the pile body can be prevented from breaking even when a large shear force acts on the foundation.

In addition, in the semi-rigid pile head joint structure according to the present invention, the filling section has a tapered section that slopes downward from the upper end in a direction expanding in diameter, and the upper end surface of the tapered section abuts against the abutment surface of the edge cutting section, and the upper end of the pile body may be formed smaller than the upper surface of the smoothly cut cutting section.

By adopting the above configuration, the semi-rigid pile head joint structure can reduce the rotational rigidity of the joint by forming the upper end surface of the tapered portion with a smaller cross section than the upper surface of the cut portion. This can reduce the bending stress generated in the pile body, and can prevent the pile body from bending and breaking even when a large bending stress acts on the foundation of the pile body.

In addition, in the semi-rigid pile head joint structure according to the present invention, the edge cutting section may be provided between the foundation and the joint section and include a steel plate formed larger than the upper end surface of the tapered section.

With the above configuration, the semi-rigid pile head joint structure can prevent unevenness between the foundation and the joint by providing a steel plate between the foundation and the joint, and can keep the contact point between the foundation and the joint in a uniform state. This makes it possible to make the stress acting on the contact point uniform, preventing damage to the contact point due to the action of localized stress. In addition, because the steel plate has a small coefficient of friction, it is possible to improve the shear resistance of the contact point.

The semi-rigid pile head joint structure according to the present invention may also have an L-shaped external shape, multiple ribs connected to the upper surface of the steel plate at equal intervals in a plan view, and fixed to the foundation.

By adopting the above configuration, the semi-rigid pile head joint structure can improve the adhesion between the steel plate and the foundation, thereby preventing the occurrence of positional shifts caused by the action of large horizontal displacements, etc.

In addition, in the semi-rigid pile head joint structure according to the present invention, the edge cut-off portion is disposed between the lower end portion of the foundation and the reinforcing steel pipe, and has an outer edge cut-off portion provided on the periphery of the tapered portion, and the outer edge cut-off portion may be formed larger than the opposing surface of the reinforcing steel pipe.

The above configuration allows the foundation and the joint to be securely separated and separated even in a configuration in which a portion of the cross section of the reinforcing steel pipe in plan view is larger than the tapered portion, such as when a portion of the reinforcing steel pipe protrudes outward from the end of the tapered portion in plan view.

The semi-rigid pile head joint structure according to the present invention may also include a basal concrete layer provided on the periphery of the pile body and abutting the lower end of the reinforcing steel pipe, and a crushed stone layer provided on the periphery of the pile body and abutting the lower part of the basal concrete layer.

By using the above configuration, the semi-rigid pile head joint structure can be firmly supported at the lower end of the reinforcing steel pipe by the basin concrete layer and the crushed stone layer. This makes it possible to prevent the position of each part from shifting due to subsidence of the ground at the installation location of the reinforcing steel pipe.

The present invention provides a semi-rigid pile head joint structure that can reduce the shear force and bending stress transmitted from the foundation to the pile head.

FIG. 2 is a cross-sectional view showing an example of a semi-rigid pile head joint structure according to an embodiment of the present invention. 1A is a plan view cross-sectional view showing an example of a semi-rigid pile head joint structure according to an embodiment of the present invention, (a) is a plan view cross-sectional view taken along line A-A in FIG. 1, (b) is a plan view cross-sectional view taken along line B-B in FIG. 1, and (c) is a plan view cross-sectional view taken along line CC in FIG. 1.

Hereinafter, a semi-rigid pile head joint structure according to an embodiment of the present invention will be described with reference to Figures 1 and 2. The dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.
As shown in FIG. 1 , the semi-rigid pile head joint structure 1 according to this embodiment includes a foundation 2 , a pile body 3 , a reinforcing steel pipe 4 , an edge cutting portion 5 , and a filling portion 6 .

The foundation 2 is placed on the ground G and supports a structure to be newly constructed above the foundation 2. In this embodiment, the foundation 2 is composed of columns and pile caps (not shown), and the lower part of the pile cap is placed on the ground G. The configuration of the foundation 2 is not limited to the above, and it may be a footing foundation in which a foundation slab is placed on the ground G.

As shown in Figures 1 and 2(a), the pile body 3 is inserted into the ground G as an existing pile 3 that supported a structure that was removed before the foundation 2 was placed on the ground G (hereinafter, the "pile body 3" will be referred to as the "existing pile 3"). The existing pile 3 has a cylindrical shape and is installed with the central axis of the cylinder approximately aligned in the vertical direction.

The existing pile 3 is a cast-in-place concrete pile constructed directly in a circular plan-view hole 31 formed by excavating the ground G. The existing pile 3 has a concrete pile portion 32 and a reinforcing bar cage 33 arranged inside the concrete pile portion 32. The existing pile 3 is installed by placing the reinforcing bar cage 33 at a predetermined position in the hole 31 and pouring known concrete material into the pile without any gaps to form the concrete pile portion 32.

The existing pile 3 is located under the foundation 2, and the upper end 341 of the pile head 34 facing closely to the foundation 2 is smoothly cut in the radial direction of the pile body 3 to form a cut portion 35. The cut portion 35 is formed at a position spaced a distance D1 from the lower end 21 of the foundation 2 in the penetration direction of the existing pile 3.

The reinforcing bar cage 33 comprises multiple hoops 331 and multiple main reinforcements 332. The reinforcing bar cage 33 is arranged within the concrete pile section 32 of the existing pile 3, and the concrete pile section 32 and the reinforcing bar cage 33 are fixed together, thereby improving the pile bearing capacity.

The tie bars 331 have an outer shape that is annular when viewed from above, and are arranged at regular intervals in the direction of penetration of the existing pile 3. The main bars 332 abut against the inner edge 331a of each of the tie bars 331, and are arranged at regular intervals in the circumferential direction of the tie bars 331. The tie bars 331 and the main bars 332 are connected at the abutment points on each inner edge 331a to form a reinforcing bar cage 33.

The reinforcing steel pipe 4 is formed in a circular shape in plan view, and its diameter in plan view is larger than that of the existing pile 3. The reinforcing steel pipe 4 protrudes upward from the upper end 341, and surrounds the pile head 34 and part of the filling section 6 in plan view. A gap 7 that is annular in plan view is formed between the reinforcing steel pipe 4 and the existing pile 3. Due to the gap 7, the semi-rigid pile head joint structure 1 can eliminate construction errors that occur during construction of the semi-rigid pile head joint structure 1.

The edge cutting section 5 is disposed between the foundation 2 and the reinforcing steel pipe 4. In this embodiment, the edge cutting section 5 includes a steel plate 51 disposed between the foundation 2 and the filling section 6, and an outer edge cutting section 52 disposed between the lower end 21 and the upper end 41 of the reinforcing steel pipe 4. The steel plate 51 is disposed above the outer edge cutting section 52.

The steel plate 51 is a stainless steel plate having a rectangular and plate-like shape in a plan view. The steel plate 51 has high rigidity. The coefficient of friction of the upper surface 511 and the lower surface 512 of the steel plate 51 is smaller than the coefficient of friction of the lower end surface 211 of the lower end portion 21.

The outer edge cut portion 52 has a hollow circular shape in a plan view. The outer edge cut portion 52 is formed larger than the upper end surface 42 of the upper end portion 41 of the opposing reinforcing steel pipe 4. The inner circumferential surface 521a of the hollow hole 521 of the outer edge cut portion 52 is formed with a tapered portion 522 that is inclined in a direction of increasing in diameter from the upper end inner circumferential surface 521b of the hollow hole 521 along the inner circumferential surface 521a toward the lower end inner circumferential surface 521c of the hollow hole 521.

The filling section 6 is provided inside the reinforcing steel pipe 4 and the outer edge cutting section 52. The filling section 6 is also provided between the existing pile 3 and the steel plate 51. In other words, the filling section 6 is surrounded by the existing pile 3, the reinforcing steel pipe 4, and the cutting section 5. The filling section 6 is formed by filling the filling material 61 from the hollow hole 521 into the area surrounded by the existing pile 3, the reinforcing steel pipe 4, and the cutting section 5, including the gap 7, without leaving any gaps. The filling material 61 is a known concrete material. The formation of the filling section 6 allows the existing pile 3 and the reinforcing steel pipe 4 to be integrated.

The filling section 6 has a tapered section 64 formed on the upper outer peripheral surface 62 that abuts against the outer edge cutting section 52, which is inclined in a direction that expands in diameter downward from the peripheral portion 631 of the abutment portion 63 with the lower surface 512 along the upper outer peripheral surface 62 from the abutment portion 63 to the depth of the lower end portion 523 of the outer edge cutting section 52. The abutment portion 63 is the upper end portion 63 of the filling section 6.

As shown in FIG. 2(b), the upper end surface 641 of the tapered portion 64 abuts the lower surface 512 and is smaller than the cut surface 351, which is the upper surface of the cut portion 35. The tapered portions 522 and 64 have approximately the same tapered shape and abut against each other. The reinforcing steel pipe 4 and the filling portion 6 are provided as a joint 8 between the pile head portion 34 and the foundation 2.

As shown in FIG. 1, the filling section 6 has reinforcing bars 65 and a number of spacers 66 provided between the lower end 642 of the tapered section 64 and the upper end 341 of the existing pile 3. The reinforcing bars 65 and the number of spacers 66 are installed before filling with the filling material 61.

The reinforcing bars 65 are formed in a grid shape in plan view, installed on a number of spacers 66, and positioned above the cutting surface 351 with a predetermined vertical cover. The reinforcing bars 65 are formed so as not to come into contact with the inner circumferential surface of the reinforcing steel pipe 4.

The multiple spacers 66 are arranged at a predetermined interval on the cut surface 351. For example, the spacers 66 may be known block-type spacers with a groove formed on the upper surface for placing reinforcing bars. The multiple spacers 66 may further include a spacer that ensures a predetermined horizontal coverage of the reinforcing steel pipe 4. For example, a hollow disk-shaped spacer with a hole formed through which the reinforcing bar adjacent to the inner surface of the reinforcing steel pipe 4 can be inserted may be used.

The semi-rigid pile head joint structure 1 has the above-mentioned configuration, and by providing reinforcing bars 65 in the filled section 6, the strength of the filled section 6 against external forces can be improved and cracks in the filled section 6 can be prevented.

The steel plate 51 is provided between the lower end 21 and the upper end 81 of the joint 8 and the upper end 524 of the outer edge cutting portion 52. The upper surface 511 of the steel plate 51 abuts the lower end 21, and the lower surface 512 abuts the upper end surface 82 of the joint 8 and the upper end surface 525 of the outer edge cutting portion 52 (hereinafter, the "upper end surface 82" will be referred to as the "abutment surface 82"). The lower surface 512 of the steel plate 51 is formed larger than the abutment surface 82. With the above configuration, the steel plate 51 completely cuts off the lower end surface 211 of the foundation 2 and the abutment surface 82 of the joint 8, as shown in FIG. 2(c). The lower surface 512 is also the abutment surface with the abutment surface 82 of the steel plate 51.

The outer edge cutting section 52 completely cuts off the foundation 2 and the steel plate 51 from the upper end 41 of the reinforcing steel pipe 4 at the periphery of the tapered section 522. The outer edge cutting section 52 is also used as a throw-away formwork when pouring the filling material 61 to form the filling section 6.

The above configuration forms a joint 8 between the foundation 2 and the existing pile 3, and a semi-rigid pile head joint structure 1 is formed in which the foundation 2 and the joint 8 are completely separated by the edge separation section 5. In addition, the foundation 2, the joint 8, and the existing pile 3 are formed as separate entities.

A sacrificial concrete layer G1 that abuts against the lower end 43 of the reinforcing steel pipe 4 and a crushed stone layer G2 that abuts against the lower part of the sacrificial concrete layer G1 are provided on the peripheral portion 36 of the existing pile 3. The sacrificial concrete layer G1 and the crushed stone layer G2 are layered in the ground G to support the semi-rigid pile head joint structure 1. The sacrificial concrete layer G1 and the crushed stone layer G2 are formed with a compaction strength that prevents the ground G from sinking due to the semi-rigid pile head joint structure 1.

The steel plate 51 has an L-shaped outer shape on the upper surface 511, and is provided with a plurality of whisker ridges 9 joined to the upper surface 511 at equal intervals in a plan view. The plurality of whisker ridges 9 are arranged at equal intervals on the peripheral portion 511a of the upper surface 511.

In Figures 1 and 2, the dimensions of each component of the semi-rigid pile head joint structure 1 are exaggerated for the sake of explanation, but the actual dimensions are, for example, that the existing pile 3 has a diameter D2 of 1000 mm, and the reinforcing steel pipe 4 has a diameter D3 of 1200 mm and a thickness T1 of 12 mm. In addition, by placing the existing pile 3 of the above dimensions in the center of the reinforcing steel pipe 4 in a plan view, the annular gap 7 in a plan view is formed with a diameter length L1 of 88 mm.

Next, the operation and effects of the semi-rigid pile head joint structure 1 according to the embodiment of the present invention described above will be explained with reference to the drawings.

In the semi-rigid pile head connection structure 1 according to this embodiment, the connection part 8 consisting of the reinforcing steel pipe 4 and the filling part 6 is disposed between the foundation 2 and the existing pile 3, so that the pile head 34 is not completely restrained against external forces having directional properties such as rotational or shear directions. In the semi-rigid pile head connection structure 1, the edge separation part 5 is provided between the foundation 2 and the connection part 8, so that the foundation 2, the existing pile 3, and the connection part 8 are formed as separate entities completely separated by the edge separation part 5.
With the above-mentioned configuration, the semi-rigid pile head connection structure 1 can reduce the shear force and bending stress transmitted from the foundation 2 to the pile head 34 of the existing pile 3. Therefore, even if an excessively large shear force acts on the foundation 2, the existing pile 3 can be prevented from breaking.

A tapered portion 64 is formed on the upper outer peripheral surface 62 of the filling portion 6, the tapered portion 64 being inclined in a direction of increasing in diameter downward from a peripheral edge portion 631 of the abutment portion 63 with the lower surface 512 along the upper outer peripheral surface 62 from the abutment portion 63 to the depth of the lower end portion 523 of the outer edge cutting portion 52. An upper end surface 641 of the tapered portion 64 abuts the lower surface 512, and is formed smaller than the cutting surface 351 which is the upper surface of the cutting portion 35.
With the above configuration, the semi-rigid pile head joint structure 1 can reduce the rotational rigidity of the joint 8 because the abutment surface 82 of the joint 8 is formed smaller than the cut surface 351 by the tapered portion 64. Therefore, the semi-rigid pile head joint structure 1 can reduce the bending stress generated in the existing pile 3, and can prevent bending failure of the existing pile 3 even when excessive bending stress acts on the foundation 2 for the existing pile 3. The tapered shape of the tapered portion 64 also makes it possible to prevent chipping and cracking of the corners of the joint 8.

The steel plate 51 is provided between the lower end 21 and the upper end 81 of the joint 8 and the upper end 524 of the outer edge cutting portion 52, with the upper surface 511 abutting the lower end 21 and the lower surface 512 abutting the abutment surface 82 and the upper end surface 525. The lower surface 512 of the steel plate 51 is formed larger than the abutment surface 82. With the above configuration, the lower end surface 211 of the foundation 2 and the abutment surface 82 of the joint 8 can be completely cut off by the steel plate 51.
The semi-rigid pile head joint structure 1 prevents unevenness with the joint 8 by providing the high-rigidity steel plate 51, and can keep the abutment part 513 with the joint 8 in a uniform state. Therefore, the stress acting on the abutment part 513 can be made uniform, and damage to the abutment part 513 due to the action of local stress can be prevented. Since the friction coefficient of the steel plate 51 is smaller than that of the foundation 2, the shear force resistance of the abutment part 513 against the shear force transmitted from the foundation 2 to the existing pile 3 can be improved.

The steel plate 51 has an L-shaped outer shape on an upper surface 511, and is provided with a plurality of whisker ridges 9 joined at equal intervals in a plan view on the upper surface 511. The plurality of whisker ridges 9 are arranged at equal intervals on a peripheral portion 511a of the upper surface 511.
With the above-mentioned configuration, the pile head semi-rigid joint structure 1 can improve the adhesion between the foundation 2 and the steel plate 51, thereby preventing the installation position of the steel plate 51 from shifting due to the action of large horizontal displacement, etc.

The outer edge cutting portion 52 is provided on the periphery of the tapered portion 64 and is disposed between the lower end portion 21 and the lower surface 512 and the upper end portion 41 of the reinforcing steel pipe 4, with the tapered portion 522 and the tapered portion 64 abutting against each other. The outer edge cutting portion 52 is formed in a circular shape in a plan view and is formed larger than the upper end surface 42 which is the opposing surface to the lower end portion 523 of the outer edge cutting portion 52 of the reinforcing steel pipe 4.
With the above-mentioned configuration, the pile head semi-rigid joint structure 1 can reliably separate the foundation 2 and the joint 8 by the outer edge cutting portion 52, making them into separate bodies.

A sacrificial concrete layer G1 abutting the lower end 43 of the reinforcing steel pipe 4, and a crushed stone layer G2 abutting the lower part of the sacrificial concrete layer G1 are provided on the peripheral portion 36 of the existing pile 3.
From the above-mentioned configuration, the pile head semi-rigid joint structure 1 can be configured such that the lower end portion 43 is firmly supported by the laminated configuration of the basin concrete layer G1 and the crushed stone layer G2. Therefore, it is possible to prevent the installation positions of each part from shifting due to subsidence of the ground at the installation location of the reinforcing steel pipe 4.

The semi-rigid pile head joint structure 1 according to this embodiment makes it possible to easily reuse the existing piles 3 as the pile bodies of the newly constructed foundation 2. By reusing the existing piles 3, it is possible to reduce the construction costs of the structure, shorten the construction period, and reduce the environmental burden caused by vibrations and noise associated with the construction of new piles and the disposal of existing piles.

The above describes an embodiment of the semi-rigid pile head joint structure according to the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the invention.
For example, in the above embodiment, the existing pile 3, the joint 8, and the outer edge cutting portion 52 are formed in a circular shape when viewed from above, but may be formed in a rectangular shape when viewed from above.

For example, in the above embodiment, the tapered portion 64 is formed on the upper outer peripheral surface 62, which is a part of the outer peripheral surface of the filling portion 6, but the tapered portion 64 may be formed depending on the configuration of the filling portion 6. For example, the tapered portion 64 may be formed on the entire outer peripheral surface of the filling portion 6.

For example, in the above embodiment, the edge cutting portion 5 includes a steel plate 51 and an outer edge cutting portion 52, but the edge cutting portion 5 may be configured with a steel plate 51 that is larger than the upper end surface 42.

For example, in the above embodiment, multiple bolts 9 are provided on the upper surface 511 of the steel plate 51, but the configuration may also be such that bolt holes are drilled in the steel plate 51 and anchor bolts that penetrate the steel plate 51 are driven into the foundation 2.

For example, in the above embodiment, a basal concrete layer G1 and a crushed stone layer G2 are provided at the bottom of the reinforcing steel pipe 4, but the crushed stone layer G2 may be formed in two layers based on the grain size of the crushed stone.

1. Semi-rigid pile head structure 2. Foundation 3. Existing pile (pile body)
4 Reinforcing steel pipe 5 Edge cutting portion 6 Filling portion 8 Joint portion 9 Wire rib 21 Lower end portion 34 Pile head portion 35 Cut portion 36 Periphery portion 42 Upper end surface (opposite surface)
43 Lower end portion 51 Steel plate 52 Outer edge cutting portion 61 Filler material 63 Contact portion (upper end portion)
64 Tapered portion 81 Upper end portion 351 Cut surface (upper surface)
512 Bottom surface (contact surface)
641 Top surface G Ground G1 Concrete layer G2 Crushed stone layer

Claims (6)

A foundation located below the structure;
A pile body penetrated into the ground and disposed away from the lower end of the foundation;
A joint portion including a reinforcing steel pipe surrounding the periphery of the pile head of the pile body and a filling portion formed by filling the inside of the reinforcing steel pipe with a filler material;
a cutting edge portion disposed between the foundation and the joint portion, abutting against a lower end portion of the foundation and an upper end portion of the joint portion, and having an abutment surface formed larger than an upper end surface of the reinforcing steel pipe;
Equipped with
Pile head semi-rigid joint structure. The filling portion has a tapered portion that is inclined in a direction in which the diameter of the filling portion increases downward from an upper end portion,
The upper end surface of the tapered portion abuts against the abutment surface of the edge cutting portion, and the upper end of the pile body is formed smaller than the upper surface of the smoothly cut cut portion.
The pile head semi-rigid joint structure according to claim 1. The edge cutting portion is provided between the foundation and the joint portion and includes a steel plate formed larger than the upper end surface of the tapered portion.
The pile head semi-rigid joint structure according to claim 2. The steel plate has an L-shaped outer shape, is connected to the upper surface of the steel plate at equal intervals in a plan view, and is fixed to the foundation.
The pile head semi-rigid joint structure according to claim 3. The edge termination portion is disposed between the lower end portion of the foundation and the reinforcing steel pipe, and has an outer edge termination portion provided on the periphery of the tapered portion,
The outer edge cutting portion is formed larger than the opposing surface of the reinforcing steel pipe.
A pile head semi-rigid joint structure according to any one of claims 2 to 4. A basing concrete layer provided on the periphery of the pile body and abutting the lower end of the reinforcing steel pipe;
A crushed stone layer provided on the periphery of the pile body and abutting the lower part of the sacrificial concrete layer;
Equipped with
A pile head semi-rigid joint structure according to any one of claims 1 to 5.

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