JP2016199861A - Pile foundation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pile foundation structure that suppresses increase in construction costs and elongation of a construction period.SOLUTION: A pile foundation structure 1 is for supporting a building, and includes a below-column pile 10 having a column erected on a top of the pile, a non-below-column pile 20 without a column erected on a top of the pile, and a foundation beam 30 connecting the below-column pile 10 and the non-below-column pile 20. The non-below-column pile 20 is arranged between the below-column piles 10, 10, and a pile bottom end of the non-below-column pile 20 is supported on a bearing layer 4. Desirably, a foundation footing 31 should be formed on the foundation beam 30 above the non-below-column pile 20, and the non-below-column pile 20, the foundation footing 31, and the foundation beam 30 should be connected.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a pile foundation structure provided by using in combination a columnar pile including a column at the top of the pile and a non-columnar pile without a column at the top of the pile.

In recent years, with the advancement of land use (higher buildings, deeper underground, etc.), simply providing a single pile for a single pillar can cause problems with lack of support and subsidence. There is. Measures against this problem included increasing the bearing capacity of the pile (expansion of the pile diameter, installation of an intermediate enlarged portion of the pile, improvement of the pile surrounding ground, etc.).
As another countermeasure, Patent Document 1 discloses a structure in which a pile (hereinafter referred to as “non-pillar pile” in this specification) is provided even at a position where there is no column. In addition, in this specification, the pile provided below the pillar is referred to as a “pillar pile”.
Patent Document 2 discloses a pile foundation structure that resists a horizontal load acting during an earthquake by providing an auxiliary pile under the foundation beam. The pile foundation structure of Patent Literature 2 is to distribute the horizontal load not only to the foundation pile but also to the auxiliary pile, thereby reducing the horizontal load acting on the foundation pile. That is, the auxiliary pile is provided in order to resist the horizontal load, and it is not assumed that the auxiliary pile supports the vertical load of the upper building. Therefore, since the building load on the upper side of the pile body is not positively transmitted to the auxiliary pile, the upward shearing force generated on the circumferential surface of the pile is small, and the pile body is arranged within the beam width of the foundation beam.

Japanese Patent No. 3695550 JP-A-63-171924

By the way, when supporting a vertical load also to an auxiliary pile, like the foundation structure of patent document 1, it is necessary to connect a non-column pile (auxiliary pile) to the mat slab which has high horizontal rigidity. However, when mat slabs are formed to connect non-column piles, there is a problem that the construction cost becomes high and the construction period becomes long.
From such a viewpoint, this invention makes it a subject to provide the pile foundation structure which can suppress the increase in construction cost and the lengthening of a construction period, implement | achieving the high support performance of a pile.

The inventors of the present invention have provided a column base provided below a column as a pile foundation structure capable of suppressing an increase in construction costs and a prolonged construction period while realizing excellent vertical support performance and horizontal support performance. Excavation to the extent that mat slabs are formed while providing high support performance by providing non-pillar piles by joining not only piles but also foundation beams provided between columns on the lower floors of the building It came to invent the pile foundation structure which is not necessary.
In addition, the present inventors provide a foundation footing to widen the beam width on the foundation beam to be joined to the non-column pile, thereby increasing the degree of fixation between the non-column pile and the foundation beam. It was made possible to cope with the case where construction position shift occurred. Furthermore, the present inventors have made the joint rigidity between the non-column pile and the foundation beam lower than the joint stiffness between the column pile and the foundation beam, so that the bending stress between the non-column pile and the foundation beam generated during an earthquake is reduced. Paying attention to the point that the damage can be prevented by reducing the degree, the pile foundation structure in which the pile head of the non-column pile was semi-rigidly joined was invented.
In order to solve the above-mentioned problem, the pile foundation structure of the first invention is a pile foundation structure that supports a structure, and is provided with a pillar under a pile provided with a pillar at the top of the pile, and a pillar provided at the top of the pile. A non-pillar pile, and a foundation beam connecting the pillar pillar and the non-pillar pile, wherein the non-pillar pile is disposed between the pillar piles, and The lower end portion of the pile under the pillar is supported by a support layer.
In the pile foundation structure of the second invention, a foundation footing is formed on the foundation beam on the non-columnar pile, and the non-columnar pile, the foundation footing, and the foundation beam are connected to each other. Features. Moreover, the pile foundation structure of 3rd invention is characterized by the joining rigidity of the said non-column pile and the said foundation footing being smaller than the joint rigidity of the said pillar pile and the said foundation beam. Furthermore, the pile foundation structure of the fourth invention is characterized in that a vertical haunch part is formed at an end part of the foundation beam. In addition, in order to oppose the ground reaction force, the vertical hunch part is preferably provided upward on the upper end side of the foundation beam.

According to the pile foundation structure as described above, the non-column piles are arranged between the column piles and the lower end of the pile is supported by the support layer, so that the foundation beam is passed through the non-column piles. Thus, a vertical load acting on the column can be transmitted to the support layer. Therefore, the lack of bearing capacity of the pile can be solved. In addition, since it is not necessary to form a mat slab as in the prior art, it is possible to suppress an increase in construction costs and a prolonged construction period.
Further, the non-column pile is connected to the foundation beam provided with the foundation footing, and the fixing region of the pile head of the non-column pile is joined to the wide foundation footing so that the pile head Can be made to resist shear by fixing the pile head in the foundation footing against the punching shear failure from below the pile. Furthermore, the joint stiffness between the non-column pile and the foundation beam is lower than that between the column pile and the foundation beam (the non-column pile and the foundation beam have a semi-rigid joint structure). The horizontal force that is sometimes borne is smaller than the pile under the pillar, and the bending stress generated at the joint between the pile head of the non-pillar pile and the lower end of the foundation beam during the earthquake is reduced. And damage to the foundation beam. In addition, the bending strength of the foundation beam was improved by providing a vertical hunch at the end of the foundation beam. The present invention provides a foundation beam between pillars at the lowest layer of a building in a shallow excavated soil region without providing a large concrete plate with a large plate thickness like a mat slab. By building a foundation beam with high bending rigidity, a part of the vertical load of the building is borne by the non-column pile.

  According to the pile foundation structure using both the pillar pile and the non-pillar pile according to the present invention, it is possible to prevent excessive settlement by realizing the high support performance of the pile and eliminating the lack of the bearing capacity of the pile. . Moreover, since it is not necessary to form a mat slab, it is possible to suppress an increase in the construction cost and an increase in the construction period.

It is sectional drawing which showed the pile foundation structure which concerns on 1st embodiment of this invention. It is the top view which showed the pile foundation structure which concerns on 1st embodiment of this invention. It is a principal part expanded sectional view which showed the pile foundation structure which concerns on 1st embodiment of this invention. It is sectional drawing which showed the pile foundation structure which concerns on 2nd embodiment of this invention. (A) And (b) is the top view which showed the modification of the pile foundation structure which concerns on embodiment of this invention. (A) And (b) is sectional drawing which showed the further modification of the pile foundation structure which concerns on embodiment of this invention.

(First embodiment)
The pile foundation structure 1 which concerns on 1st embodiment is a foundation connected with a pillar pile which has a pillar in the upper part of a pile, a non-pillar pile without a pillar in the pile upper part, and a pillar pile and a non-pillar pile. It is a structure that improves the bearing capacity of the pile by transmitting a vertical load from the foundation beam to the support layer via the non-column pile. As a result, it is not necessary to form a mat slab, so that the construction cost can be increased and the construction period can be prevented from being prolonged.
In addition, the pile foundation structure 1 forms foundation footings on the foundation beams on the non-column piles, and connects the non-column piles, foundation footings, and foundation beams to ensure stress transmission between the pile and the foundation beams. It is easy to cope with the construction position shift of the pile.
Furthermore, the pile foundation structure 1 makes the joint stiffness between the non-columnar pile and the foundation beam (foundation footing) smaller than the joint stiffness between the columnar pile and the foundation beam by narrowing the pile head of the non-columnar pile. It is low. Thereby, the bending stress of the pile head part of the non-column pile under the earthquake and the edge part of the foundation beam to connect can be reduced, and these damages can be prevented. Furthermore, the pile foundation structure 1 is improving the bending strength of the edge part of a foundation beam by forming a vertical haunch part in the edge part of a foundation beam.

As shown in FIGS. 1 and 2, the pile foundation structure 1 according to the first embodiment includes a columnar pile 10, a non-columnar pile 20, and a foundation beam 30.
The pillar pile 10 is provided below the pillar 2. That is, the pillar 2 pile 10 is provided with the pillar 2 above the pillar pile 10 (upper pile). A post-column footing 3 is formed under the column 2, and a column-pile 10 is disposed under the column-base footing 3. The under-column footing 3 is an independent foundation (independent footing foundation) that supports one pillar 2. One pillar pile 3 may be provided under one pillar pillar footing 3, or a plurality of pillar pillars 3 may be provided. The pillar pile 10 is a pile having a general shape constructed by using a general construction machine. The lower end portion of the pillar pile 10 is supported in a state where a predetermined depth is embedded in the underground support layer 4. Although the pillar pile 10 of this embodiment is comprised by the cast-in-place pile which has an expanded bottom part, you may employ | adopt other pile types, such as a ready-made concrete pile and a steel pipe pile.

The non-pillar pile 20 is provided between adjacent pillar pillars 10, 10 and is not connected to the pillar pillar footing 3. That is, the column is not provided above the non-pillar pile 20 (upper pile). In the present embodiment, one non-pillar pile 20 is provided between the pillar piles 10 and 10. The non-pillar pile 20 is a pile constructed using a general construction machine. The lower end portion of the non-pillar pile 20 is supported in a state where a predetermined depth is embedded in the support layer 4 similarly to the pillar pile 10. Although the non-pillar pile 20 is configured by a cast-in-place pile having an expanded bottom portion, other pile types such as a ready-made concrete pile and a steel pipe pile may be employed.
The pile head of the non-columnar pile 20 has a reduced diameter than the pile body portion on the lower side of the non-columnar pile 20. Specifically, the pile head is provided with a tapered portion 21 that gradually narrows upward (see FIGS. 1 and 3). The non-columnar pile 20 is connected to the foundation footing 31 by a semi-rigid joint having a lower degree of fixation than the rigid joint. In this embodiment, by placing the foundation footing 31 on the pile head reduced in taper shape, the pile head is allowed to rotate while transmitting the shearing force. A pulling resistance steel rod (anchor bar) (not shown) may be installed at a location where the pulling force acts.
In addition, semi-rigid joining is not limited to the said structure, Other structures may be sufficient. For example, by covering a pile head of the non-pillar pile 20 with a cap member (not shown) and building a tapered clearance at the root portion, rotation of the pile head is allowed while transmitting shearing force. It may be a configuration. Moreover, you may provide a taper part in the lower part of a foundation footing instead of a pile head. In this case, the tapered portion becomes narrower downward.
The under-column footings 3 and the under-column piles 10 are connected by a rigid joint structure or a semi-rigid joint structure having a higher degree of fixation than the non-column bottom pile 20.

The foundation beam 30 is constructed so as to be bridged between the lower end portions of the adjacent columns 2 and 2, and is coupled to the columnar pile 10 and the non-columnar pile 20. In other words, the columnar pile 10 and the non-columnar pile 20 are connected by the foundation beam 30. One end of the main bar (not shown) of the foundation beam 30 extends to the inside of one column 2 of the adjacent columns 2 and 2, and the other end of the main bar is the inside of the other column 2. It has been extended and established. That is, the foundation beam 30 is continuously formed between the columns 2 and 2.
A foundation footing 31 is formed on a portion of the foundation beam 30 on the non-columnar pile 20. That is, the foundation footing 31 is formed between the foundation beam 30 and the non-columnar pile 20, and the upper end portion of the non-columnar pile 20 and the foundation beam 30 are connected via the foundation footing 31. . The foundation footing 31 is formed to protrude downward from the lower end of the foundation beam 30. The foundation footing 31 constitutes a widened portion that widens on both sides in the width direction with respect to the beam width, and has a rectangular shape in plan view (in this embodiment, a square). The main reinforcement (main reinforcement extending in the horizontal direction) of the foundation beam 30 in the portion where the foundation footing 31 is provided passes through the foundation footing 31 continuously.

As shown in FIG. 3, a shear reinforcement bar 34 is provided on the foundation beam 30 above the non-columnar pile 20. The shear reinforcement bar 34 includes a reinforcement bar extending in the horizontal direction and a reinforcement bar extending in the vertical direction. The shear reinforcement bars 34 extending in the horizontal direction are arranged in a plurality of stages within the cross section height of the foundation beam 30 or the foundation footing 31 so as to cross the virtual fracture surface 35 of the punching shear fracture. A plurality of shear reinforcement bars 34 extending in the vertical and horizontal directions are provided, and at least a part of the shear reinforcement bars 34 are arranged so as to straddle the virtual fracture surface 35 in the vertical direction. Beam foundation bars and shear reinforcement bars (both not shown) are arranged on the foundation beam 30 other than the joint with the non-column piles 20. Further, the base footing 31 is provided with a glutinous mesh reinforcing bar and a shear reinforcing bar (both not shown).
A vertical hunch 33 is formed at the end of the foundation beam 30 upward. The vertical haunch portions 33 are respectively formed at the end portions on both sides of the foundation beam 30. The vertical haunch portion 33 is inclined upward from the upper surface of the foundation beam 30 and joined to the side surface of the column 2 to increase the bending rigidity of the foundation beam 30 and the bonding strength between the column 2 and the foundation beam 30. .

In designing the pile foundation structure 1 having the above-described configuration, the vertical load sharing and subsidence of the columnar pile 10 and the non-columnar pile 20 are determined by the interaction between the columnar pile 10 and the noncolumnar pile 20 and the pile. It is preferable to calculate by analysis considering the rigidity of the foundation beam. Specifically, an analysis method such as a finite element method (FEM) or a hybrid method may be employed.
By making the shaft diameter and concrete strength of the non-columnar pile 20 larger than that of the columnar pile 10, the load transmission effect to the non-columnar pile 20 may be enhanced.

According to the pile foundation structure 1 according to the first embodiment, the non-columnar pile 20 is disposed between the adjacent columnar piles 10 and 10, and the lower ends of the columnar pile 10 and the non-columnar pile 20 are supported. By being supported by the layer 4, a vertical load can be transmitted from the foundation beam 30 to the support layer 4 through the non-columnar pile 20. As a result, the vertical load acting on the under-pile pile 10 is reduced by being distributed to the non-post-column pile 20, so that excessive subsidence can be prevented without making the under-pile pile 10 a special shape. In addition, since the columnar pile 10 and the non-columnar pile 20 are integrated via the foundation beam 30, the rigidity of the foundation beam 30 suppresses the uneven settlement of the columnar pile 10 and the noncolumnar pile 20. .
Furthermore, since it is not necessary to form a mat slab as in the prior art, the amount of ground excavation and the amount of use of concrete and reinforcing bars can be reduced. Moreover, in the pile foundation structure 1 which concerns on 1st embodiment, the excavation amount of a ground and the utilization amount of concrete and a reinforcing bar may be less than the large cross-section foundation beam using a continuous footing. Therefore, according to the pile foundation structure 1, the increase in construction cost and the lengthening of the construction period can be significantly suppressed. Moreover, since the pillar pile 10 is not a special shape, it can be constructed using a general machine. As a result, an increase in construction costs can be suppressed.
Further, by connecting the non-columnar pile 20, the foundation footing 31, and the foundation beam 30, the stress transmission of the vertical load of the non-columnar pile 20 and the foundation beam 30 is ensured. Furthermore, since the area of the connection surface (the bottom face of the foundation footing 31) with the non-pillar pile 20 becomes large, even if the construction position shift of the non-pillar pile 20 occurs, the non-pillar pile 20 and the foundation footing 31 Can be securely connected.
Furthermore, the fixed degree of the non-columnar pile 20 and the foundation beam 30 can be lowered by reducing the diameter of the pile body of the pile head of the non-columnar pile 20 and semi-rigidly joining the foundation footing 31. Thereby, the bending stress of the pile head of the non-column pile 20 and the lower end of the foundation beam to be connected (foundation footing 31) at the time of an earthquake can be reduced, and damage to the non-column pile 20, foundation footing 31 and foundation beam 30 can be reduced. Can be prevented.
When there is no foundation beam connected in the orthogonal direction of the foundation beam 30 (position of the non-columnar pile 20) as in the present embodiment, if seismic force acts in the orthogonal direction of the foundation beam 30, the foundation beam 30 Although shear stress and torsional stress occur in the direction perpendicular to the axis of the material, semi-rigid bonding also works effectively to suppress damage caused by these. This is because the fixing degree between the non-column pile 20 and the foundation beam 30 is lower than the fixing degree between the column pillar 10 and the foundation beam 30, so that the horizontal rigidity of the non-column pile is relatively small. This is because the non-pillar pile can reduce the horizontal force borne by the earthquake.
Thus, since the non-pillar pile 2 can reduce the strength to withstand the horizontal force at the time of an earthquake, the non-pillar pile 2 can have a simpler structure than the pillarless pile 10. Therefore, the construction cost of the non-pillar pile 20 can be suppressed.
Furthermore, in the first embodiment, the bending strength of the foundation beam 30 can be improved by forming the upward vertical haunch part 33 at the end of the foundation beam 30. Moreover, since the shear reinforcement bar 34 of the foundation beam 30 above the non-pillar pile 20 is provided, the punching shear failure by the non-pillar pile 20 can be prevented.

(Second embodiment)
As shown in FIG. 4, the pile foundation structure 1 a according to the second embodiment is applied when the intermediate layer 5 exists above the support layer 4 of the ground. The intermediate layer 5 has an N value equivalent to that of the support layer 4 but is thinner than the support layer 4. In the pile foundation structure 1 according to the first embodiment, the non-columnar pile 20 is supported by the support layer 4, whereas in the pile foundation structure 1 a, the non-columnar pile 20 is supported by the intermediate layer 5 in the middle. By doing so, the length of the non-pillar pile 20 is reduced, and the construction cost is increased and the construction period is prolonged.
In the pile foundation structure 1 a according to the second embodiment, the lower end portion of the non-columnar pile 20 is disposed on the intermediate layer 5 positioned above the support layer 4. That is, the non-pillar pile 20 is supported in a state where the intermediate layer 5 has a predetermined depth. The pillar pile 10 extends through the intermediate layer 5 to the lower support layer 4.
The foundation footing 31 of the first embodiment is provided at the same excavation depth position as the foundation footing 3 connected to the upper part of the underarm pile 2 (see FIG. 1), whereas the second embodiment In the foundation footing 31, the bottom surface of the foundation footing 31 is the same as the bottom surface of the foundation beam 30, and the non-columnar pile 20 is joined to the foundation footing 31 (see FIG. 4).
In addition, about another structure, since it is equivalent to the pile foundation structure 1 which concerns on 1st embodiment, the same code | symbol is attached | subjected to the same component and description is abbreviate | omitted.
According to the pile foundation structure 1a which concerns on 2nd embodiment, the effect similar to the pile foundation structure 1 which concerns on 1st embodiment is obtained. Furthermore, according to the pile foundation structure 1a, the distance between the lower end portion of the enlarged middle point pile and the under-column pile is increased, the interaction is reduced, and the vertical force can be supported. Moreover, since the length of the non-column pile 20 can be shortened compared with 1st embodiment, the excavation amount of a ground and the usage-amount of concrete and a reinforcing bar can be reduced further, and workability | operativity is good. Moreover, the amount of excavation is reduced by making the installation depth of the foundation footing 31 shallow. Therefore, it is possible to further suppress an increase in construction cost and a prolonged construction period.

As mentioned above, although the form for implementing this invention was demonstrated, this invention is not the meaning limited to the said embodiment, A design change is possible suitably in the range which does not deviate from the meaning of this invention. For example, in the said embodiment, although the one non-pillar pile 20 is provided between the adjacent pillar piles 10 and 10, it is not limited to one. As shown to (a) of FIG. 5, you may make it line the two non-pillar piles 20 and 20 in a line. In this case, the foundation footing 31a is widened according to the installation area of the non-pillar pile 20. In addition, you may provide the more non-pillar pile 20 more. According to such a configuration, since the vertical load borne by the non-column pile 20 can be increased, the vertical load acting on the column pile 10 can be further reduced.
As another configuration, as shown in FIG. 5 (b), a foundation beam 30a is provided between the foundation beams 30, 30 adjacent to each other in parallel, and the foundation beam 30a extending in the X direction and the Y beam in the Y direction. A foundation footing 31 may be formed at the intersection with the extending foundation beam 30a to be connected to the non-columnar pile 20. According to such a structure, the space | interval of the columnar pile 10 and the non-columnar pile 20 can be enlarged.

In the above embodiment, the upward vertical hunch portions 33 are formed at both ends of the foundation beam 30 to improve the bending strength of the foundation beam 30, but as shown in FIG. A stagnation portion 36 may be formed between the upper vertical hunch portions 33 of the 30. If it does in this way, the cross-sectional size of the foundation beam 30 will become large, and the bending strength, the shear strength, and the twisting strength of the foundation beam 30 can be increased.
Further, as shown in FIG. 6B, a wall 37 may be formed on the upper side of the foundation beam 30 so as to be in contact with the foundation beam 30. The wall 37 is formed integrally with the foundation beam 30, the columns 2, 2 and the upper floor beam 38 above the non-columnar pile 20. According to such a configuration, the vertical load of the pillar 2 is transmitted not only to the foundation beam 30 but also to the non-columnar pile 20 through the wall 37, so that the burden on the foundation beam 30 can be reduced. In this case, the vertical haunch portion is not necessary.

  Moreover, in the said embodiment, the non-column lower pile 20 is connected to the foundation footing 31 by a semi-rigid joint, so that the fixing degree between the non-column lower pile 20 and the foundation beam 30 is lowered, and the non-column lower pile 20 Reduces the horizontal force that is borne by the earthquake, but the non-column pile 20 and the foundation footing 31 and the foundation beam 30 are rigidly connected, so that the horizontal force during an earthquake can be The pile 20 may be equally burdened.

1,1a Pile foundation structure 2 Column 4 Support layer 10 Column pile 20 Non-column pile 30 Foundation beam 31 Foundation footing

Claims (4)

A pile foundation structure that supports the structure,
Under-pillar piles with columns at the top of the piles;
A non-pillar pile without a column at the top of the pile,
A foundation beam connecting the under-pile pile and the non-post-column pile, and
A pile foundation structure, wherein the non-column piles are arranged between the column piles, and a pile lower end portion of the non-column piles is supported by a support layer. Foundation footings are formed on the foundation beams on the non-column piles,
The pile foundation structure according to claim 1, wherein the non-pillar pile, the foundation footing, and the foundation beam are connected.   The pile foundation structure according to claim 2, wherein a joint rigidity between the non-column pile and the foundation footing is smaller than a joint rigidity between the column pillar and the foundation beam.   The pile foundation structure according to any one of claims 1 to 3, wherein a vertical haunch part is formed at an end of the foundation beam.

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