JP7457670B2 - Pile foundation structure, building - Google Patents

Description

The present invention relates to pile foundation structures and buildings.

Foundation piles and footings are widely used as foundation structures that support buildings.
For example, Patent Document 1 discloses a pile foundation structure including footing concrete cast on the pile heads of a plurality of piles, and a steel foundation beam whose joint portion with a column is buried in the footing concrete. There is. In this pile foundation structure, columns placed on footing concrete are supported by multiple piles.
Furthermore, Patent Document 2 describes a precast foundation footing that is manufactured integrally with a precast column member and has a connecting beam embedded therein, and a plurality of foundation piles that are provided at positions away from the sides of the foundation footing. A foundation structure is disclosed that includes a steel frame that connects the pile cap of a foundation pile and a connecting beam. Also in this foundation structure, the column members provided on the foundation footing are supported by a plurality of foundation piles.
Furthermore, in Patent Document 3, vertical loads are reduced by providing a structural pile directly under a column and a midpoint pile other than directly below the column, and integrating the foundation slab, structural pile, and midpoint pile. A configuration is disclosed in which the load is borne by both the center point pile and the center point pile.

In the configurations disclosed in Patent Documents 1 to 3, the foundation piles are all configured to support vertical loads, and the vertical load acting on the columns is distributed and borne by multiple piles.
During an earthquake, horizontal shear forces are concentrated on the pile heads. In order to resist the horizontal shear forces acting on the pile heads, it may be possible to increase the number of foundation piles. However, increasing the number of foundation piles would result in longer construction periods and higher construction costs.
In addition, if the number of foundation piles is increased to resist the horizontal shear force acting on the pile head, the result may be that the vertical load support capacity becomes excessive relative to the horizontal shear force resistance capacity. For this reason, it is desirable to have a good balance between the vertical load support capacity and the capacity to resist the horizontal shear force acting on the pile head.

JP 2016-14273 A JP2017-122343A Patent No. 3695550

The problem that this invention aims to solve is to provide a pile foundation structure and building that can efficiently resist the horizontal shear force acting on the pile head during an earthquake while suppressing increases in construction costs.

In order to solve the above problems, the present invention employs the following means.
That is, the pile foundation structure of the present invention is a pile foundation structure in which a footing foundation part and a foundation pile are joined, and the foundation pile includes at least a long pile provided directly below a column material and a long pile provided directly below the column material. a short pile provided spaced apart from the long pile along one side of the pile, the footing foundation section being composed of a truncated pyramid or truncated conical footing and a foundation slab, and the footing includes: The pile head of the foundation pile is buried.
According to such a configuration, the pile foundation structure includes, as the foundation pile, a long pile provided directly below the column material, and a long pile provided apart from the long pile along at least one pile side of the long pile. It is equipped with short piles that can be used. As a result, the vertical load of the superstructure provided on the pile foundation structure is mainly borne by the long piles.
Moreover, the pile heads of the long piles and short piles that constitute the foundation piles are buried in the footing. For this reason, the pile head of a long pile and the pile head of a short pile are arranged at the upper part of the foundation pile joined to the footing. As a result, in the upper part of the foundation pile, the total cross-sectional area of the pile heads of the long piles and the pile heads of the short piles becomes large, and the resistance to horizontal shear force can be increased.
Extensive footings are typically required at the pile heads of such piles to resist horizontal forces. On the other hand, in the above configuration, since the short pile is provided along at least one side of the long pile, the footings connected to these are integrated, and the long pile is attached to one footing. and short piles can be joined together. Thereby, the overall volume of the footing can be made smaller while providing a structure that can sufficiently resist horizontal forces than when a footing is individually provided for each pile.
Furthermore, since there is no need for a large horizontal resistance force at the bottom of the foundation pile where shear force is not as large as the pile head, only long piles are present and short piles are not present. Therefore, it is possible to suppress the lengthening of the construction period for constructing foundation piles and the increase in construction costs. In this way, the ability to support vertical loads and the ability to resist horizontal shear forces acting on the pile head can be provided in a well-balanced manner.
Therefore, it is possible to provide a pile foundation structure that can efficiently resist the horizontal shear force that acts on the pile head during an earthquake while suppressing an increase in construction costs.

In one aspect of the present invention, a plurality of the short piles are provided around one of the long piles.
According to such a configuration, by providing a plurality of short piles around one long pile, the total cross section of the pile heads of the long piles and the pile heads of the short piles at the top of the foundation pile can be The area can be increased. Therefore, resistance to horizontal shear force can be more effectively increased.

In one aspect of the present invention, the building of the present invention is a building having a pile foundation structure as described above, and only piles having the same length as the long piles are placed directly under the outer peripheral columns. The pile foundation structure is placed directly below the internal column.
Normally, piles placed on the outside of a building have a slab attached to only one side of the pile, while piles placed on the inside have slabs attached to both sides of the pile. In this case, the resistance force of the slab, which can bear the burden of the shear force acting on the pile head together with the pile, is often greater.
Therefore, a pile foundation structure consisting of long piles and short piles is placed directly under the internal columns to increase the total cross-sectional area of the pile heads of the long piles and the pile heads of the short piles. This allows it to resist large shear forces. In addition, in order to make the cross-sectional area of the pile heads smaller than the internal piles directly under the outer peripheral pillars, and to create a suitable structure that allows the slab to resist, only piles of the same length as long piles are installed. Do not place piles of the same length as short piles. As a result, it is possible to suppress the provision of an excessive number of piles in proportion to the resistance force of the slab, and it is possible to realize a well-balanced and rational configuration.

According to the present invention, it is possible to provide a pile foundation structure and a building that can efficiently resist horizontal shear force acting on the pile head during an earthquake while suppressing an increase in construction costs.

It is a figure showing an example of arrangement of a peripheral column, an internal column, a long pile, a short pile, and a pile in a pile foundation structure concerning an embodiment of the present invention. FIG. 2 is a sectional view taken along the line II in FIG. 1; It is a sectional view showing the connection structure of the pile head of a long pile and a short pile to a footing foundation part in the above-mentioned pile foundation structure. It is a figure which shows the study result of the bending moment of a long pile and a short pile in the case where the pile head is fixed and when the degree of fixation of the pile head is set as a pin. This figure shows the results of a study on the horizontal displacement of long and short piles when the pile head is fixed and when the pile head is fixed to a pin degree. This is a comparison table showing the shear force sharing ratio of long piles and short piles based on analysis results using different methods of fixing the pile heads of foundation piles. This is a table showing the ratio of the initial stiffness of the horizontal ground spring when the ground deformation coefficient is E ₀ = 700N (corresponding to soft ground) and when calculated from the Francis equation (corresponding to hard ground). be. Bending of long piles and short piles in the case where the initial stiffness of the ground spring is E ₀ = 700N (corresponding to soft ground) and the case where the ground spring is determined by the Francis formula (corresponding to hard ground) FIG. 3 is a diagram showing the result of moment study. Horizontality of long piles and short piles in the case where the initial stiffness of the ground spring is E ₀ = 700N (corresponding to soft ground) and the case where the ground spring is determined by the Francis formula (corresponding to hard ground) It is a figure showing the result of examination of displacement. This is a comparison table showing the shear force sharing ratio of long piles and short piles based on analysis results with different ground characteristics around the piles.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to an accompanying drawing, the form for implementing the pile foundation structure and building by this invention is demonstrated based on a drawing.
FIG. 1 shows an example of the arrangement of outer columns, inner columns, long piles, short piles, and piles in the pile foundation structure according to this embodiment. FIG. 2 is a sectional view taken along the line II in FIG. 1. FIG. 3 is a sectional view showing the connection structure of the long pile and the pile head of the short pile with respect to the footing foundation in the above-mentioned pile foundation structure.
The building 1 has a lower structure 2 constructed in the ground G and an upper structure 3 provided on the lower structure 2.
The upper structure 3 includes a plurality of columns 30 extending in the vertical direction and beams 34 installed between the columns 30 adjacent to each other. The superstructure 3 includes a plurality of columns 30, including a plurality of outer peripheral columns 31 arranged along the outer periphery 1s of the building 1, and a plurality of pillar members arranged inside the outer periphery 1s of the building 1. An internal column 32 as C.

The substructure 2 comprises a pile foundation structure 10 provided on the inside side of the building 1 and piles 25 provided on the outer periphery side of the building 1.
As shown in Figures 2 and 3, the pile foundation structure 10 is disposed below the internal column 32 of the superstructure 3. The pile foundation structure 10 includes a foundation pile 20 and a footing base portion 11.
The footing base 11 integrally includes a foundation slab 12 and a footing 13. The foundation slab 12 is, for example, a mat slab made of reinforced concrete. In this embodiment, the foundation slab 12 does not include a foundation beam. The footing 13 is, for example, made of reinforced concrete, and is provided in a part of the foundation slab 12 including a part directly below the internal column 32. That is, the footing 13 is provided in a part of the foundation slab 12 provided in the substructure 2. The footing 13 is formed so as to protrude downward from the lower surface of the foundation slab 12. The footing 13 is formed in a rectangular or circular shape when viewed from above. The diameter dimension of the footing 13 gradually decreases from the top to the bottom. That is, the footing 13 is formed in a truncated pyramid or truncated cone shape, and is provided upside down with the lower bottom surface with a larger area positioned on the upper side and the upper bottom surface with a smaller area positioned on the lower side. By providing the footing 13, the footing base 11 has a concrete thickness in the vertical direction that is greater than the thickness of the foundation slab 12 in the portion where the footing 13 is not provided.

The foundation pile 20 includes a long pile 21 and a short pile 22. The long pile 21 is provided directly below the internal column 32 serving as the column material C. The short pile 22 is provided along at least one pile side surface 21s of the long pile 21. In the pile foundation structure 10, a plurality of short piles 22 are provided around one long pile 21. In this embodiment, the short piles 22 are provided on both sides of the long pile 21. As shown in FIG. 1, when viewed from above, the two short piles 22 are arranged in a straight line with respect to the long pile 21. Note that the short piles 22 may be arranged, for example, on all four sides of the long pile 21.

As shown in FIG. 3, the pile head 21t of the long pile 21 and the pile head 22t of the short pile 22 are each buried in the footing foundation 11 in which the footing 13 is provided. The pile heads 21t and 22t are provided with pile head fixing bars 21m and 22m, respectively, which extend upward. The pile head anchoring bars 21m and 22m are fixed to the concrete that constitutes the footing foundation 11.

The footing base part 11 is integrally provided with a column joint part 15 that projects upward from the upper surface of the footing base part 11. The column joint portion 15 is arranged directly below the internal column 32. The column joint part 15 is made of concrete, for example, and integrally includes an extending part 15a extending upward from the upper surface of the footing foundation part 11, and an enlarged diameter part 15b extending in diameter along a horizontal plane from the upper end of the extending part 15a. has.
A seismic isolation sliding support 16 is fixed to the upper surface of the enlarged diameter portion 15b. The seismic isolation sliding support 16 includes an upper flange 16a, a lower flange 16b, and a laminated rubber portion 16c. The lower flange 16b is provided on the upper surface of the enlarged diameter portion 15b. A sliding plate (not shown) is fixed to the upper surface of the lower flange 16b. The laminated rubber portion 16c is fixed to the lower side of the upper flange 16a, and a sliding material (not shown) is provided at the lower end. Since the sliding material of the laminated rubber portion 16c is provided opposite to and in contact with the sliding plate of the lower flange 16b, the upper structure including the upper flange 16a is able to withstand force when horizontal force is applied due to an earthquake or the like. , slides against the lower structure including the lower flange 16b.
The lower end 32b of the internal column 32 is joined to the upper surface of the upper flange 16a.

As shown in FIG. 2, the long pile 21 has a longer vertical length than the short pile 22. The short pile 22 has a smaller vertical length than the long pile 21. The pile tip 21b of the long pile 21 is embedded in a strong lower layer G2 having a higher N value, for example, 50 or more, than the upper layer G1 of the ground G. Thereby, the long pile 21 is made into a support pile whose supporting capacity against vertical loads is ensured. The long pile 21 transmits a vertical load to the lower layer G2 serving as a support layer.
The pile tip 22b of the short pile 22 has not reached the lower part G2 where the N value is high, but remains in the upper part G1 where the N value is lower than the lower part G2, for example, less than 30. The short pile 22 is installed only in the upper layer G1 of the ground G so that the entire pile is located in the upper layer G1, and the pile tip 22b is embedded in the upper layer G1 where the N value is smaller than 30. Thereby, the short pile 22 functions as a horizontal resistance pile that mainly resists horizontal force.
In this embodiment, the short piles 22 do not function as support piles. The dead weight of the short pile 22 is supported by the adjacent long pile 21 via the footing foundation 11 to which the pile head 22t of the short pile 22 is joined. In this way, since the short piles 22 are supported by the long piles 21, the upper layer G1 is buried soil, a fine sand layer where liquefaction may occur, or a loose silt layer with an N value of 3 or less. The stratum may be such that it cannot support the weight of the short pile 22.
In this embodiment, the length of the long pile 21 is, for example, 66 to 68 m, and the length of the short pile 22 is, for example, 15 m. Note that the lengths of the long piles 21 and the short piles 22 vary depending on the composition of the ground G on which the building 1 is installed (the soil quality of the upper layer G1, the depth of the lower layer G2 with a high N value, etc.), and the lengths are different from the above values. is just one example.

As shown in FIG. 3, the punch-out shear failure surface B is set so as to expand downward from the footing foundation 11 from the joining position J between the footing foundation 11 and the lowest end surface of the internal column 32. The punch-out shear failure surface B is inclined downwardly from the joining position J of the footing base portion 11 and the lowest end surface of the internal column 32 in a direction that widens by 45 degrees.
At the height position where the footing base part 11 is provided, which is inside the punching shear failure surface B, the footing 13 is provided extending over the entire area in the horizontal direction. That is, on the inner side of the push-out shear failure surface B, the cross-section of the concrete is thicker than on the outer side, where only the foundation slab 12 exists. As a result, push-out shear failure is suppressed even in the footing foundation portion 11 that does not have a foundation beam.
The pile head 22t of the short pile 22 is joined to the footing foundation 11 within the range surrounded by the push-out shear failure surface B.

As shown in FIGS. 1 and 2, the pile 25 is arranged directly below the outer peripheral column 31. As shown in FIGS. The pile 25 has the same length as the long pile 21. The pile tip 25b of the pile 25 is embedded in the strong lower layer G2. Thereby, the pile 25 is made into a support pile whose supporting force against the vertical load acting on the outer peripheral column 31 is ensured. The pile 25 transmits a vertical load to the lower layer G2 serving as a support layer.

According to the pile foundation structure 10 as described above, the footing foundation part 11 and the foundation pile 20 are joined together, and the foundation pile 20 is a long pile 21 provided directly below the column material C. , and a short pile 22 provided along at least one pile side surface 21s of the long pile 21. 13, the pile heads 21t and 22t of the foundation pile 20 are buried.
According to such a configuration, the pile foundation structure 10 includes, as the foundation pile 20, a long pile 21 provided directly under the column C, and a long pile 21 along the pile side surface 21s of at least one of the long piles 21. A short pile 22 provided apart from the pile 21 is provided. Thereby, the vertical load of the superstructure 3 provided on the pile foundation structure 10 is mainly borne by the long piles 21.
Further, the pile heads 21t and 22t of the long pile 21 and the short pile 22 that constitute the foundation pile 20 are buried in the footing 13. For this reason, a pile head 21t of the long pile 21 and a pile head 22t of the short pile 22 are arranged above the foundation pile 20 joined to the footing 13. As a result, in the upper part of the foundation pile 20, the total cross-sectional area of the pile head 21t of the long pile 21 and the pile head 22t of the short pile 22 increases, and the resistance to horizontal shear force is increased. Can be done.
Extensive footings are typically required at the pile heads of such piles to resist horizontal forces. On the other hand, in the above configuration, since the short pile 22 is provided along at least one pile side surface 21s of the long pile 21, the footing 13 joined to these is integrated, and The long pile 21 and the short pile 22 can be joined together. Thereby, the overall volume of the footing 13 can be made smaller while providing a structure that can sufficiently resist horizontal forces than in the case where footings are individually provided for each of the piles 21 and 22.
Furthermore, since a large horizontal resistance force is not required on the lower side of the foundation pile 20 where shear force as large as the pile heads 21t and 22t does not act, only the long piles 21 are present and the short piles 22 are not present. It is said that Therefore, it is possible to suppress the lengthening of the construction period for constructing the foundation piles 20 and the increase in construction costs. In this way, the ability to support vertical loads and the ability to resist horizontal shearing forces acting on the pile heads 21t and 22t can be provided in a well-balanced manner.
Therefore, it is possible to provide the pile foundation structure 10 that can efficiently resist the horizontal shear force that acts on the pile heads 21t and 22t during an earthquake while suppressing an increase in construction costs.

Particularly in this embodiment, as already explained, the short pile 22 is supported by the long pile 21 via the footing foundation 11. Therefore, even if the upper layer G1 into which the short piles 22 are embedded is buried soil, a fine sand layer where liquefaction may occur, or a loose silty stratum with an N value of 3 or less, the short piles The pile 22 can be supported.
Furthermore, the footing 13 is a footing in an area surrounded by a push-out shear failure surface B that is set to expand downward from the joint position J of the footing foundation 11 and the column C. The base portion 11 is provided over the entire horizontal area at the height position where the base portion 11 is provided. For this reason, the cross section of the concrete is formed thicker on the inner side of the push-out shear failure surface B, and thereby, push-out shear failure is suppressed even in the footing foundation portion 11 that does not have a foundation beam. In particular, in this embodiment, the foundation slab 12 is a matte slab without a foundation beam, which reduces the amount of mining required when constructing the foundation beam 12, thereby reducing the construction period and construction cost. Ru.

Moreover, in the pile foundation structure 10, a plurality of short piles 22 are provided around one long pile 21.
According to such a configuration, by providing a plurality of short piles 22 around one long pile 21, the pile head 21t of the long pile 21 and the short pile 22 in the upper part of the foundation pile 20 are The total cross-sectional area of the pile head 22t can be increased. Therefore, resistance to horizontal shear force can be more effectively increased.

In addition, the building 1 is a building 1 equipped with the pile foundation structure 10 as described above, in which only the piles 25 having the same length as the long piles 21 are arranged directly under the outer peripheral pillars 31, and the internal pillars The pile foundation structure 10 is placed directly under the pile foundation 32 .
Usually, for piles placed around the outside of building 1, the slab is attached to only one side of the pile, whereas for piles placed inside, the slab is attached to both sides of the pile, so it is placed on the inside side. In many cases, piles have a greater resistance to the shear force acting on the pile head due to the slab that can bear the load along with the pile.
Therefore, the pile foundation structure 10 composed of the long piles 21 and the short piles 22 is arranged directly under the internal columns 32, and the pile head 21t of the long pile 21 and the pile head of the short pile 22 are arranged. The large total cross-sectional area of 22t resists large shear forces. Directly below the outer peripheral pillar 31, a pile of the same length as the long pile 21 is installed, in order to make the cross-sectional area of the pile head smaller than that of the internal pile, and to create a suitable structure that allows the slab to resist. Only the short piles 25 are arranged, and no piles having the same length as the short piles 22 are arranged. As a result, it is possible to suppress the provision of an excessive number of piles in proportion to the resistance force of the slab, and it is possible to realize a well-balanced and rational configuration.

(Modified example of embodiment)
Note that the pile foundation structure and building of the present invention are not limited to the above-described embodiments described with reference to the drawings, and various modifications can be made within the technical scope thereof.
For example, in the embodiment described above, the footing foundation 11 includes the foundation slab 12 and the footing 13, and does not include a foundation beam. If the foundation slab 12 alone cannot resist the stress (bending moment) acting on the internal column 32 provided on the footing foundation 11, a foundation beam may be provided in addition to the foundation slab 12.
Further, in the above embodiment, the long piles 21 constituting the foundation piles are supported by the lower part G2, but they may be provided as friction piles in the ground G without being buried in the lower part G2. The short piles 22 constituting the foundation piles are installed in one place on each side of the long pile 21, and are installed in a total of two places, but when one place is installed only on one side of the long pile 21, or , the long piles 21 may be installed at two locations in each of the two horizontal directions, and may be installed at four locations in total.
Further, in the above embodiment, a mat slab is used as the foundation slab 12, but the foundation slab 12 is not limited to a mat slab, and may be a slab provided with a foundation beam.
In addition to this, it is possible to select the configurations mentioned in the above embodiments or to change them to other configurations as appropriate, without departing from the gist of the present invention.

(Example of consideration)
In the configuration shown in the above embodiment, the effect of the pile head fixation degree on the shear force of the short pile (horizontal resistance pile) and the ground characteristics around the pile were examined, and the results are shown below. The difference between soft ground and hard ground as the ground characteristics around the pile was examined by changing the value of the ground spring connected to the pile.
In buildings with the above configuration, support piles (long piles) that reach the supporting layer directly below the columns and horizontal resistance piles (short piles) that provide horizontal resistance against earthquake forces are used. In this study, it was confirmed that the shear force distribution rate of the horizontal resistance piles does not change significantly between support piles and horizontal resistance piles depending on the pile head fixation degree and the soil spring value.
(1) Effect of pile head fixation First, stress analysis was conducted for the case in which the pile head was fixed (indicated as "pile head fixed" in the following figures) and the case in which the pile head was pinned (indicated as "pile head pinned" in the following figures), and the bending moment, deformation, and shear force load ratio were calculated for the support piles and horizontal resistance piles.
Fig. 4 shows the results of the study on bending moment of the support pile and horizontal resistance pile when the pile head is fixed and when the pile head is fixed with a pin. Fig. 5 shows the results of the study on deformation of the support pile and horizontal resistance pile when the pile head is fixed and when the pile head is fixed with a pin. Fig. 6 shows the shear force sharing rate of the support pile and horizontal resistance pile when the pile head is fixed and when the pile head is fixed with a pin.
As shown in Figures 4 to 6, the shear force distribution rate of the horizontal resistance pile does not change significantly when the pile head is fixed, even when the pile head fixation degree is pinned, and it was confirmed that the effect of the pile head fixation degree is small.

上式（１）において、ｋ_Ｂは水平地盤バネ定数（ｋＮ／ｍ^３）、Ｂは杭径（ｃｍ）、Ｅ_０は地盤の変形係数（ｋｇ／ｃｍ^２）、νはポアソン比、ＥＩは杭の曲げ剛性（ｋｇ・ｃｍ^２）である。
地盤バネの初期剛性を、上式（１）のＦｒａｎｃｉｓの式より求め、杭水平変位による剛性低下については、杭の変形の１／２乗に比例して低減するモデルとした。
地盤の変形係数をＥ_０＝７００Ｎとした（軟弱地盤を模擬した）場合と、上式（１）より求めた（硬質地盤を模擬した）場合との、水平地盤バネの初期剛性の比を、図７に示す。上式（１）により求めた地盤バネの初期剛性は、軟弱地盤を模擬した解析条件による地盤の変形係数をＥ_０＝７００Ｎとした場合の１．４～２１．７倍となっている。
また、図８は、地盤バネの初期剛性をＥ_０＝７００Ｎとした場合と、地盤バネをＦｒａｎｃｉｓの式より求めた場合とにおける、長尺杭（支持杭）および短尺杭（水平抵抗杭）の曲げモーメントの検討結果を示す図である。図９は、地盤バネの初期剛性をＥ_０＝７００Ｎとした場合と、地盤バネをＦｒａｎｃｉｓの式より求めた場合とにおける、長尺杭（支持杭）および短尺杭（水平抵抗杭）の水平変位の検討結果を示す図である。図１０は、地盤バネの初期剛性をＥ_０＝７００Ｎとした場合と、地盤バネをＦｒａｎｃｉｓの式より求めた場合とにおける、長尺杭（支持杭）および短尺杭（水平抵抗杭）のせん断力分担率を示す。
図８～図１０に示すように、短尺杭（水平抵抗杭）のせん断力分担率は、地盤バネの値を大きくしても大きく変わらず、地盤バネの影響が小さいことを確認した。
上述のように、長尺杭（支持杭）と短尺杭（水平抵抗杭）が組み合わされた基礎杭は、杭頭部の固定方法、及び杭周辺の地盤特性が異なる場合であっても、共に一定割合でせん断力を負担している。また、杭頭部での水平変位について、共に一定割合が発生しており、安定した構造性能を実現できる点が確認された。 In addition, by simulating hard ground, the shear force ratios borne by long piles (support piles) and short piles (horizontal resistance piles) were calculated when the ground spring was calculated from the following Francis equation (1).

In the above formula (1), k _B is the horizontal ground spring constant (kN/m ³ ), B is the pile diameter (cm), E ₀ is the ground deformation coefficient (kg/cm ² ), ν is Poisson's ratio, and EI is This is the bending rigidity (kg·cm ² ) of the pile.
The initial stiffness of the ground spring was determined using the Francis equation (1) above, and a model was used in which the stiffness reduction due to horizontal displacement of the pile was reduced in proportion to the 1/2 power of the deformation of the pile.
The ratio of the initial stiffness of the horizontal ground spring between the case where the ground deformation coefficient is E ₀ = 700N (simulating soft ground) and the case obtained from the above formula (1) (simulating hard ground) is: It is shown in FIG. The initial stiffness of the ground spring determined by the above equation (1) is 1.4 to 21.7 times the deformation coefficient of the ground based on the analytical conditions simulating soft ground when E ₀ =700N.
In addition, Figure 8 shows the long piles (support piles) and short piles (horizontal resistance piles) when the initial stiffness of the ground spring is E ₀ = 700N and when the ground spring is calculated using the Francis equation. It is a figure which shows the examination result of a bending moment. Figure 9 shows the horizontal displacement of long piles (support piles) and short piles (horizontal resistance piles) when the initial stiffness of the ground spring is E ₀ = 700N and when the ground spring is calculated using the Francis equation. FIG. Figure 10 shows the shear forces of long piles (support piles) and short piles (horizontal resistance piles) when the initial stiffness of the ground spring is E ₀ = 700N and when the ground spring is calculated using the Francis equation. Indicates the share.
As shown in Figures 8 to 10, the shear force sharing ratio of short piles (horizontal resistance piles) did not change significantly even when the value of the ground spring was increased, confirming that the influence of the ground spring was small.
As mentioned above, foundation piles that are a combination of long piles (support piles) and short piles (horizontal resistance piles) can be used together even if the method of fixing the pile head and the ground characteristics around the pile are different. The shear force is borne at a certain rate. Additionally, a certain percentage of horizontal displacement occurred at the pile head, confirming that stable structural performance could be achieved.

1 Building 21s Pile side 2 Lower structure 21t, 22t Pile head 3 Upper structure 22 Short pile 10 Pile foundation structure 25 Pile 11 Footing foundation 30 Column 12 Foundation slab 31 Peripheral column 13 Footing 32 Internal column 20 Foundation pile 34 Beam 21 Length Shaku pile C pillar material

Claims (3)

A pile foundation structure in which a footing foundation and a foundation pile are joined,
The foundation pile includes a long pile provided directly below the column material, and a short pile provided apart from the long pile along at least one side of the long pile,
The pile foundation structure is characterized in that the footing foundation includes a footing in the shape of a truncated pyramid or a truncated cone and a foundation slab, and a pile head of the foundation pile is buried in the footing. The pile foundation structure according to claim 1, wherein a plurality of the short piles are provided around one of the long piles. A building equipped with the pile foundation structure according to claim 1 or 2,
Directly below the outer perimeter columns, only piles of the same length as the long piles are placed,
A building characterized in that the pile foundation structure is disposed directly below the interior columns.

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