Building underground structure
By introducing a softer buffer material between concrete piles and foundations, the underground structure mitigates pile head bending moments, enabling cost-effective construction with reduced pile and foundation sizes.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- OHBAYASHI GUMI LTD
- Filing Date
- 2024-11-15
- Publication Date
- 2026-05-27
AI Technical Summary
The conventional underground structure of a building constructed by the reverse casting method experiences increased bending moment at the pile head due to rigid joining of the concrete foundation with cast-in-place concrete piles, necessitating larger and stronger structures, thereby increasing costs.
Incorporating a buffer material softer than concrete, such as expanded polystyrene, between the cast-in-place concrete piles and the concrete foundation to separate them, reducing direct load transmission during horizontal forces like earthquakes.
This design reduces the bending moment at the pile head, allowing for smaller and less costly cast-in-place concrete piles and foundations by distributing loads through the inverted support columns.
Smart Images
Figure 2026087412000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the underground structure of a building constructed by the reverse casting method.
Background Art
[0002] Conventionally, as an underground structure of a building constructed by the reverse casting method, there is known one having cast-in-place concrete piles provided in the ground, a concrete foundation provided on the cast-in-place concrete piles, and a reverse cast column supported by the cast-in-place concrete piles on the lower end side and at least partially embedded in the concrete foundation (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the above conventional underground structure of a building, a concrete foundation is rigidly joined to the cast-in-place concrete piles by placing concrete on the cast-in-place concrete piles with reinforcing bars protruding upward in advance from the upper end surface of the cast-in-place concrete piles. Therefore, when a horizontal load is applied to the building during an earthquake or the like, there is a problem that the bending moment of the pile head transmitted from the cast-in-place concrete piles to the concrete foundation increases.
[0005] When the bending moment of the pile head transmitted from the cast-in-place concrete piles to the concrete foundation increases, in order to cope with this, it is necessary to make the cast-in-place concrete piles and the concrete foundation into a larger-sized structure with higher strength, and accordingly, the cost of the underground structure of the building increases.
[0006] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a building's underground structure that can reduce the bending moment at the pile head transmitted from the cast-in-place concrete pile to the concrete foundation. [Means for solving the problem]
[0007] The underground structure of the building according to the present invention is characterized by comprising: cast-in-place concrete piles installed in the ground; a concrete foundation installed on the cast-in-place concrete piles; inverted support columns supported by the cast-in-place concrete piles at their lower ends and at least a portion of which is embedded in the concrete foundation; and a buffer material made of a material softer than concrete, installed between the cast-in-place concrete piles and the concrete foundation to separate the cast-in-place concrete piles and the concrete foundation.
[0008] In the underground structure of the building of the present invention, it is preferable that the cushioning material is made of expanded polystyrene. [Effects of the Invention]
[0009] According to the present invention, it is possible to provide a building's underground structure that can reduce the bending moment at the pile head transmitted from the cast-in-place concrete pile to the concrete foundation. [Brief explanation of the drawing]
[0010] [Figure 1] This is a cross-sectional view of a key part of the underground structure of a building according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Figure 3] Figure 1 is an explanatory diagram showing the procedure for constructing the underground structure of the building shown. [Figure 4] Figure 1 is an explanatory diagram showing the procedure for constructing the underground structure of the building shown. [Figure 5] Figure 1 is an explanatory diagram showing the procedure for constructing the underground structure of the building shown. [Modes for carrying out the invention]
[0011] The following describes in detail an example of a building's underground structure according to one embodiment of the present invention, with reference to the drawings.
[0012] The underground structure 1 of the building shown in Figure 1 is constructed below ground level by excavating the ground 2 using the top-down construction method. The underground structure 1 of the building includes cast-in-place concrete piles 10, concrete foundations 20, top-down support columns 30, and buffer materials 40.
[0013] The cast-in-place concrete pile 10 is a reinforced concrete pile also called an inverted pile. In the inverted construction method, the cast-in-place concrete pile 10 is installed inside the pile hole 11, i.e., underground, by pouring concrete to a predetermined height inside the pile hole 11, which is made in the ground before the ground 2 is excavated. The underground structure 1 of the building according to this embodiment has multiple cast-in-place concrete piles 10, but for convenience, only one cast-in-place concrete pile 10 is shown in Figure 1.
[0014] Furthermore, the number of cast-in-place concrete piles 10 installed in the building's underground structure 1 is not particularly limited.
[0015] As shown in Figure 2, in this embodiment, the cast-in-place concrete pile 10 has a circular cross-section. Inside the cast-in-place concrete pile 10, multiple reinforcing bars 12a extending in the vertical direction are arranged at intervals in the circumferential direction, and multiple reinforcing bars 12b arranged in a ring shape surrounding these reinforcing bars 12a are also arranged at intervals in the vertical direction. In Figures 1 and 2, for convenience, only one reinforcing bar 12a and one reinforcing bar 12b are each labeled with a reference numeral. Each reinforcing bar 12a and one reinforcing bar 12b is located only inside the cast-in-place concrete pile 10 and does not protrude upward from the upper end surface 13 of the cast-in-place concrete pile 10 toward the concrete foundation 20.
[0016] Note that the cross-sectional shape of the cast-in-place concrete pile 10 is not limited to circular. Also, the placement location, number, and presence or absence of the reinforcing bars 12 inside the cast-in-place concrete pile 10 can be appropriately changed.
[0017] The concrete foundation 20 is a part provided at the lowermost part of the underground structure 1 of the building. The concrete foundation 20 is constructed by placing concrete on the bottom surface 2a of the ground 2 excavated to a predetermined depth in the top-down construction method and is provided on the cast-in-place concrete pile 10. Although not shown in detail, the concrete foundation 20 has a reinforced concrete structure with reinforcing bars arranged inside. The reinforcing bars provided in the concrete foundation 20 are also arranged only inside the concrete foundation 20 and do not protrude toward the side of the cast-in-place concrete pile 10.
[0018] The concrete foundation 20 may be configured to have a foundation beam portion 21. In the present embodiment, the foundation beam portion 21 of the concrete foundation 20 is arranged on the cast-in-place concrete pile 10.
[0019] The top-down column 30 is supported by the cast-in-place concrete pile 10 at the lower end side and at least a part of it is embedded in the concrete foundation 20.
[0020] In the present embodiment, the top-down column 30 is formed into a straight columnar shape of a predetermined length by a cross steel frame (cross H-shaped steel) having a web portion 31 configured such that the cross section perpendicular to the vertical direction is a cross and four flange portions 32 fixed to the outer ends of the web portion 31, respectively. The lower end side of the top-down column 30, that is, the portion from the lower end to a predetermined height, is a rooting portion 33, and a plurality of studs 34 are fixed to the outer surfaces of the flange portions 32 in the portion of the rooting portion 33. In FIG. 1, for the sake of convenience, only some of the studs 34 are labeled.
[0021] When the in-situ concrete pile 10 is formed, the embedment part 33 of the reverse batter column 30 is inserted into the concrete placed in the pile hole 11 to form the in-situ concrete pile 10. As the concrete hardens, the reverse batter column 30 is supported by the in-situ concrete pile 10 at the embedment part 33 on the lower end side. Also, at least a part of the portion of the reverse batter column 30 protruding upward from the in-situ concrete pile 10 is embedded in the concrete foundation 20.
[0022] Note that the reverse batter column 30 is not limited to the cross-shaped steel frame described above, and may be formed of a steel frame having other shapes such as a square steel pipe. Further, by covering the portion of the reverse batter column 30 protruding upward from the concrete foundation 20 with a concrete portion 23 that is continuously connected to the concrete foundation 20 integrally, it may be configured as a column 24 made of reinforced concrete.
[0023] The buffer material 40 is formed of a member softer than concrete and is provided between the in-situ concrete pile 10 and the concrete foundation 20 to separate the in-situ concrete pile 10 and the concrete foundation 20.
[0024] More specifically, the buffer material 40 is formed in a disk shape having the same diameter as the upper end surface 13 of the in-situ concrete pile 10, and is disposed on the upper end surface 13 of the in-situ concrete pile 10 to cover the entire portion other than the portion where the reverse batter column 30 protruding from the upper end surface 13. Also, the buffer material 40 is disposed inside the pile hole 11 and contacts the lower surface 22 of the concrete foundation 20 on its upper surface. The reverse batter column 30 penetrates the buffer material 40 between the in-situ concrete pile 10 and the concrete foundation 20.
[0025] The buffer material 40 is preferably softer than concrete and has a strength or hardness such that it can support the weight of the concrete for forming the concrete foundation 20. In the present embodiment, the buffer material 40 is made of expanded polystyrene that satisfies the above conditions. More specifically, the buffer material 40 is formed of Styrofoam (registered trademark).
[0026] The cushioning material 40 is not limited to expanded polystyrene; it may be made of various materials as long as they are softer than concrete.
[0027] The cast-in-place concrete pile 10 and the concrete foundation 20 are separated from each other by the presence of a buffer material 40 between them, preventing them from becoming one. As a result, the cast-in-place concrete pile 10 and the concrete foundation 20 are connected to each other only by the inverted support column 30. Therefore, when a horizontal load is applied to the building's underground structure 1, such as during an earthquake, the horizontal load is not applied directly to the pile head of the cast-in-place concrete pile 10, but rather to the inverted support column 30 supported by the cast-in-place concrete pile 10. Furthermore, even if the concrete foundation 20 moves downward toward the upper end surface 13 of the cast-in-place concrete pile 10 when a horizontal load is applied to the building's underground structure 1, the buffer material 40 is compressed, preventing the load from being transmitted to the cast-in-place concrete pile 10.
[0028] Thus, in the underground structure 1 of the building according to this embodiment, a buffer material 40 made of a material softer than concrete is provided between the cast-in-place concrete pile 10 and the concrete foundation 20, thereby separating the cast-in-place concrete pile 10 and the concrete foundation 20. As a result, the cross-sectional performance of the pile head of the cast-in-place concrete pile 10 can be determined solely by the steel cross-section of the inverted support column 30 supported by the cast-in-place concrete pile 10. This reduces the bending stiffness of the pile head of the cast-in-place concrete pile 10, thereby reducing the bending moment of the pile head transmitted from the cast-in-place concrete pile 10 to the concrete foundation 20 when a horizontal load is applied to the underground structure 1 of the building, such as during an earthquake.
[0029] Furthermore, when a horizontal load is applied to the building's underground structure 1, the bending moment at the pile head transmitted from the cast-in-place concrete pile 10 to the concrete foundation 20 can be reduced. As a result, the cost of the building's underground structure 1 can be reduced by decreasing the diameter of the cast-in-place concrete pile 10 or by reducing the thickness of the concrete foundation 20.
[0030] Next, the procedure for constructing the underground structure 1 of the building according to this embodiment will be described.
[0031] First, a cast-in-place concrete pile 10 is formed inside the pile hole 11, and an inverted support column 30 is erected in the pile hole 11 to support the cast-in-place concrete pile 10. Then, as shown in Figure 3(a), the ground 2 is excavated so that the bottom surface 2a of the ground 2 is higher than the upper end surface 13 of the cast-in-place concrete pile 10 by a height corresponding to the thickness of the buffer material 40.
[0032] Next, as shown in Figure 3(b), a buffer material 40 is placed on the upper end surface 13 of the cast-in-place concrete pile 10. At this time, it is preferable, but not limited to, that the upper surface of the buffer material 40 be at the same height as the bottom surface 2a of the ground 2.
[0033] Next, as shown in Figure 3(c), concrete is poured onto the bottom surface 2a of the ground 2 to form a concrete foundation 20 on top of the cast-in-place concrete pile 10. At this time, in the area where the cast-in-place concrete pile 10 is installed, a buffer material 40 is placed on the upper end surface 13 of the cast-in-place concrete pile 10, so the concrete is poured on top of the buffer material 40 and does not come into contact with the upper end surface 13 of the cast-in-place concrete pile 10.
[0034] Thus, the underground structure 1 of a building having the above configuration can be easily constructed by a simple method that involves placing a buffer material 40 made of a material softer than concrete on the upper end surface 13 of the cast-in-place concrete pile 10 before pouring the concrete to form the concrete foundation 20.
[0035] Furthermore, in this embodiment, since the buffer material 40 is made of expanded polystyrene, the buffer material 40 can reliably separate the cast-in-place concrete pile 10 from the concrete foundation 20, and prevents the buffer material 40 from being crushed by the weight of the concrete when concrete is poured to form the concrete foundation 20, thereby making it easier to construct the underground structure 1 of a building having the above configuration.
[0036] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]
[0037] 1. The underground structure of the building 2 Ground 2a Bottom 10. Cast-in concrete piles 11 Pile holes 12a Reinforcement bars 12b Reinforcement bars 13 Upper end surface 20 Concrete foundation 21 Foundation beam section 22 Bottom side 23 Concrete section 24 pillars 30 Reverse-mounted support posts 31 Web section 32 Flange section 33 Root portion 34 studs 40 Cushioning material
Claims
1. Cast-in-place concrete piles installed underground, A concrete foundation is provided on top of the aforementioned cast-in-place concrete pile, A cast-in-place concrete pile is supported at the lower end and at least a portion of it is embedded in the concrete foundation, An underground structure for a building, characterized by having a buffer material made of a material softer than concrete, which is provided between the cast-in-place concrete pile and the concrete foundation to separate the cast-in-place concrete pile and the concrete foundation.
2. The underground structure of a building according to claim 1, wherein the cushioning material is made of expanded polystyrene.