Building foundation structure

Abstract

To provide a building foundation structure capable of making the number of piles fewer.SOLUTION: A building foundation structure 1 of the present invention is provided with a flat plate 2 of a first floor in which slave reinforcements are buried, and which is supported with a plurality of piles 3 and is in direct contact with the ground. A first shearing reinforcement area 8 is formed on a flat plate 2 from an outer peripheral surface of a footing 4 in a circumferential direction of the footing 4 at a predetermined width dimension, and a second shearing reinforcement area 9 is formed in a strip shape from a boundary of the first shearing reinforcement area 8 to a predetermined length dimension by arranging higher rigid slab reinforcements 23 than circumferential slab reinforcements 21 from a pile 3 toward an adjacent pile 3, and a plurality of shearing reinforcements 25 arranged in the first shearing reinforcement area 8 and the second shearing reinforcement area 9 is formed in an almost U-shape having a hook part 25c engaging one end reinforcement of one side in a vertical direction of the higher rigid slab reinforcements and a flat part 25b hooked on the other end reinforcement of the other side in the vertical direction of the higher rigid slab reinforcements.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a building foundation structure. [Background technology]

[0002] BACKGROUND ART Conventionally, a building foundation structure is known in which a reinforced concrete slab laid on the ground is supported by a plurality of piles (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 01-10846 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional building foundation structures, when the first floor supported by piles is made up of flat plates, the thickness of the floor plates is uniform and there is no difference in rigidity, so the piles must be installed at intervals that do not cause harmful deformation. This means that a relatively large number of piles must be installed to support the flat plate on the first floor. In view of the above, an object of the present invention is to provide a building foundation structure that can reduce the number of piles. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides A building foundation structure with a first floor flat plate in direct contact with the ground, in which slab reinforcement is buried and supported by multiple piles, A footing wider than the piles is provided on top of the piles, A first shear reinforcement area is formed on the flat plate along the circumferential direction of the footing from the outer peripheral surface of the footing with a predetermined width dimension, and slab reinforcement having higher rigidity than the surrounding slab reinforcement is arranged from the pile toward the other adjacent piles, and a band-shaped second shear reinforcement area is formed from the boundary of the first shear reinforcement area to a predetermined length dimension, The multiple shear reinforcement bars arranged in the first shear reinforcement area and the second shear reinforcement area are characterized by being formed in an approximately U-shape, having a hook portion that engages with one end reinforcement on one side of the high-rigidity slab reinforcement in the vertical direction, and a flat portion that can be hung on the other end reinforcement on the other side of the high-rigidity slab reinforcement in the vertical direction.

[0006] According to the present invention, the flat plate has a first shear reinforcement area extending from the pile surface along the circumferential direction of the pile with a predetermined width, and slab reinforcement having higher rigidity than the surrounding slab reinforcement is arranged from the pile toward other adjacent piles, and a band-shaped second shear reinforcement area is provided extending from the boundary of the first shear reinforcement area to a predetermined length, thereby enabling the number of piles to be reduced compared to conventional methods.

[0007] In addition, in the present invention, it is preferable that the flat plate is provided with inter-column bands and column row bands, and that the footing is provided with column head reinforcement bars in accordance with the stress from the column row bands, which serve as the column head portion when the piles are considered as columns.

[0008] In the present invention, it is preferable to arrange predetermined reinforcement using the footing as a foundation pillar, which makes it possible to easily install pillars on the footing. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view schematically showing a building foundation structure according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram schematically illustrating a building according to an embodiment of the present invention. [Figure 3] FIG. 2 is an explanatory diagram showing a first shear reinforcement region and a second shear reinforcement region of the present embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing the footing of the present embodiment from the side. [Figure 5] FIG. 2 is an explanatory diagram showing an example of a shear reinforcement bar according to the present embodiment. [Figure 6] FIG. 2 is an explanatory diagram showing a footing located on the outer periphery of the building foundation structure of this embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along line AA in FIG. 6. [Figure 8] FIG. 7 is a cross-sectional view taken along line BB in FIG. 6. [Figure 9] FIG. 1 is an explanatory diagram showing a conventional building foundation structure. DETAILED DESCRIPTION OF THE INVENTION

[0010] A building foundation structure according to an embodiment of the present invention will be described with reference to Figures 1 to 8. Referring to Figure 1, the building foundation structure 1 of this embodiment includes a first-floor flat plate 2 with no beams, in direct contact with the ground, and with slab reinforcement buried therein. The flat plate 2 is supported from below by a plurality of piles 3 with circular cross-sections buried in the ground. The piles 3 are provided at their upper ends with footings 4 with rectangular cross-sections that are wider than the main body of the piles 3 buried in the ground. Normal beam-type foundation beams 12 are installed around the periphery of the building foundation structure 1.

[0011] The flat plate 2 is provided with column bands 5, which are lattice-shaped areas between adjacent piles 3 and include the footings 4 of the piles 3, and are subjected to a larger bending moment than other areas. The other area, intercolumn bands 6, are provided in the remaining areas other than the column bands 5. In addition to the slab reinforcement that penetrates the footings 4 of the piles 3, the column bands 5 also use high-rigidity slab reinforcement (high-rigidity slab reinforcement 23) for the slab reinforcement adjacent to the footing 4, and high-rigidity slab reinforcement (high-rigidity slab reinforcement 23) is also arranged around the footing 4. The high-rigidity slab reinforcement 23 may have a larger diameter or be made of a stronger material than the surrounding slab reinforcement (low-rigidity slab reinforcement 21). Ordinary low-rigidity slab reinforcement 21 is arranged in the intercolumn bands 6.

[0012] The footing 4, which is the head portion of the pile 3 when considered as a column, has column head reinforcement bars 7a and 7b arranged in the X and Y directions in accordance with the stress from the column band 5. Furthermore, the footing 4 is arranged with the required reinforcement as a foundation column, i.e., at least 0.8% of the cross section (at least 0.6% if the shape of the foundation column is excessively large compared to the stress) as the main reinforcement bars 31 of the foundation column. This allows the column 14 (see Figure 2) to be easily installed on the footing 4. The shape of the footing 4 is determined so that the input from the flat plate 2 can be transmitted by the pile 3, and the height of the footing 4 is determined by the anchorage lengths of the main reinforcement bars 31 of the foundation column and the column head reinforcement bars 7a and 7b in the X and Y directions. The footing 4 is designed to have a shape that prevents punching by the pile 3.

[0013] The flat plate 2 forms a first shear reinforcement area 8 of a predetermined width from the surface of the footing 4, which is the upper surface of the pile 3, along the circumferential direction of the pile 3, and arranges slab reinforcement (high-rigidity slab reinforcement 23) with higher rigidity than the surrounding slab reinforcement (low-rigidity slab reinforcement 21) from the footing 4 of the pile 3 toward the footing 4 of another adjacent pile 3, and forms a band-shaped second shear reinforcement area 9 from the boundary of the first shear reinforcement area 8 to a predetermined length.

[0014] The slab reinforcement of the flat plate 2 is composed of upper Y-direction reinforcement bars arranged at an appropriate interval in the vertical direction of the flat plate 2 (hereinafter referred to as the Y direction), upper X-direction reinforcement bars arranged at an appropriate interval in the horizontal direction of the flat plate 2 (hereinafter referred to as the X direction), lower Y-direction reinforcement bars arranged below the upper Y-direction reinforcement bars in alignment with the upper Y-direction reinforcement bars, and lower X-direction reinforcement bars arranged below the upper X-direction reinforcement bars in alignment with the upper Y-direction reinforcement bars. The slab reinforcement is composed, for example, of upper Y-direction reinforcement bars sandwiched between upper and lower X-direction reinforcement bars, with the upper Y-direction reinforcement bars and the lower Y-direction reinforcement bars intersecting each other vertically and horizontally. The flat plate 2 may be cast in place or made of precast concrete.

[0015] The first shear reinforcement region 8 is formed along the circumferential direction of the footing 4 of the pile 3, extending from the side surface of the footing 4 of the pile 3 by a predetermined width dimension W, with its outer peripheral edge forming the boundary. Specifically, the first shear reinforcement region 8 is formed in a ring shape around the footing 4 of the pile 3 so as to surround it. In the footing 4 of the pile 3 located on the outer periphery of the building 10, the first shear reinforcement region 8 is formed only along the side facing inward of the building 10.

[0016] The second shear reinforcement region 9 is formed in a strip shape from the boundary of the first shear reinforcement region 8 to a predetermined length dimension L, extending from the footing 4 of one pile 3 toward the footing 4 of another adjacent pile 3. Since the piles 3 are usually arranged in a grid pattern, the second shear reinforcement region 9 in the portion corresponding to the pile 3 located inside the building 10 is formed in a cross shape, extending toward the adjacent piles 3 on the front, back, left, and right. If the other piles 3 are located diagonally, the second shear reinforcement region 9 can also be formed diagonally toward the other piles 3.

[0017] In addition to the slab reinforcement that penetrates the footing 4 of the piles 3, high-rigidity slab reinforcement (high-rigidity slab reinforcement 23) is also used for the slab reinforcement close to the footing 4, and high-rigidity slab reinforcement (high-rigidity slab reinforcement 23) is arranged immediately around the footing 4. For example, the high-rigidity slab reinforcement 23 is made of rebar with a larger diameter or made of a stronger material than the surrounding slab reinforcement (low-rigidity slab reinforcement 21).

[0018] Next, we will explain the shear reinforcement 25 arranged in the first shear reinforcement region 8 and the second shear reinforcement region 9. The shear reinforcement 25 is formed into a substantially U-shape, consisting of a main body portion 25a extending in the thickness direction of the flat plate 2, a flat portion 25b formed at the bottom of the main body portion 25a by bending it horizontally at approximately 90°, and a hook portion 25c formed at the top of the main body portion 25a on the same side as the flat portion 25b and bent diagonally downward. The downward inclination angle of the hook portion 25c is set to, for example, 45° with respect to the main body portion 25a.

[0019] The shear reinforcement 25 is inserted into the upper and lower end reinforcing bars of the high-rigidity slab reinforcement 23, slipping from one side to the other. The hook portion 25c engages with the upper end reinforcing bar of the intersecting upper end reinforcing bars from above, and the flat portion 25b engages with the lower end reinforcing bar of the intersecting lower end reinforcing bars from below. This ensures sufficient restraint of the high-rigidity slab reinforcement 23 by the shear reinforcement 25, thereby enhancing the shear strength. The protrusion length of the hook portion 25c and the flat portion 25b from the main portion 25a is set shorter than the reinforcing pitch of the high-rigidity slab reinforcement 23. A plurality of such shear reinforcement 25 is arranged at an appropriate pitch along the length of each slab reinforcement in the first shear reinforcement region 8 and the second shear reinforcement region 9.

[0020] The shear reinforcement 25 is arranged so that the open side of the U-shape faces the center of the footing 4 of the pile 3, with all the shear reinforcement on the left side of the width of the footing 4 facing left and all the shear reinforcement on the right side facing right, with the center of the footing 4 as the boundary. Therefore, the shear reinforcement 25 is arranged so that the reinforcement arranged at the same position along the length of each slab reinforcement faces each other toward the center of the footing 4. The shear reinforcement 25 is basically arranged in the high-stiffness slab reinforcement 23, but it may also be arranged in the normal slab reinforcement (low-stiffness slab reinforcement 21) arranged outside the high-stiffness slab reinforcement 23. The adjacent shear reinforcement 25 that face each other are not directly joined to each other and form a closed reinforcement arrangement between them.

[0021] The arrangement of the shear reinforcement bars 25 in the second shear reinforcement region 9 is the same as that in the first shear reinforcement region 8, but the shear reinforcement bars 25 are arranged with more spacing between them than in the first shear reinforcement region 8 (in the illustrated example, with a spacing of three slab reinforcements).

[0022] The shear reinforcement structure of the flat plate 2 according to this embodiment configured as described above has been verified in a past experiment as follows. In this experiment, a load test corresponding to the mechanism of punching failure was carried out on a test specimen of the flat plate 2. Specifically, when the cross-sectional area of ​​the shear reinforcement 25 in the first shear reinforcement region 8 is set to 0.44% of the area of ​​the first shear reinforcement region 8 and the cross-sectional area of ​​the shear reinforcement in the second shear reinforcement region 9 is set to 0.2% of the area of ​​the second shear reinforcement region 9, the out-of-plane deformation R due to a cyclic repeated load Qs is +5×10 -3 After rad, first, the slab reinforcement at the critical cross section of the flat plate at the column center position within the column width yields, and the out-of-plane deformation R=+10×10 -3 The column side surface gradually yielded up to rad. After that, the out-of-plane deformation R=+15×10 -3 By rad, all high-stiffness slab reinforcement had yielded and the load had risen to near the maximum load (Qsmax). After the maximum load, no sudden decrease in load was observed.

[0023] With the above structure, effective shear reinforcement performance can be ensured by setting the width dimension W of the first shear reinforcement region 8 to be equivalent to the thickness T of the flat plate 2 and the length dimension L of the second shear reinforcement region 9 to be approximately 1 / 4 of the span S between footings 4. Here, the span S between footings 4 refers to the dimension between the opposing faces of adjacent footings 4.

[0024] Furthermore, in the case of a footing 4 having corners, i.e., a footing 4 with a polygonal cross section, the first shear reinforcement region 8 may be formed excluding the corners. That is, the first shear reinforcement region 8 may be formed within the width dimension of each face of the footing 4 rather than annularly around the footing 4. Punching failure occurs due to a combination of out-of-plane shear failure on the front and rear faces of the footing 4 and torsional failure on the side faces of the footing 4 in the direction of seismic force application. For example, in the case of a footing 4 with a rectangular cross section, the first shear reinforcement region 8 and the second shear reinforcement region 9 may be provided in a cross-shaped manner within a range equivalent to the width of the face of the footing 4, based on the front, rear, and left and right faces of the footing 4. However, the effectiveness of shear strength enhancement against punching failure in the area between the cross-shaped regions and extending from the corners of the footing 4 is low. Therefore, excluding this area from the first shear reinforcement region 8 can reduce the amount of shear reinforcement and the construction effort required, thereby reducing costs.

[0025] In the case of cast-in-place construction, slab reinforcement and shear reinforcement bars are similarly arranged in formwork installed in the predetermined positions, and then concrete is poured, thereby ensuring connections with columns, etc., and the formwork is then removed. In this way, in the case of cast-in-place construction, a building foundation can be constructed that includes flat plates 2 that form first shear reinforcement regions 8 and second shear reinforcement regions 9.

[0026] In the building foundation structure 1 according to this embodiment, a first shear reinforcement region 8 is formed in the flat plate 2 along the circumferential direction of the pile 3, with a predetermined width W from the top surface of the pile. Furthermore, slab reinforcement (high-stiffness slab reinforcement 23) with higher stiffness than the surrounding slab reinforcement (low-stiffness slab reinforcement 21) is arranged from the pile 3 toward the adjacent pile 3. Furthermore, a strip-shaped second shear reinforcement region 9 is formed from the boundary of the first shear reinforcement region 8 to a predetermined length L. Therefore, the combination of the first shear reinforcement region 8 and the second shear reinforcement region 9, coupled with the action of the high-stiffness slab reinforcement (high-stiffness slab reinforcement 23) arranged from the footing 4 of the pile 3 toward the footing 4 of the adjacent pile 3, can rationally improve the shear strength against punching failure, which occurs when out-of-plane shear failure on the front and rear surfaces of the footing 4 of the pile 3 and torsional failure on the side surfaces of the footing 4 of the pile 3 are combined. This improves the deformation capacity as well, enabling the construction of a flat plate 2 with excellent toughness.

[0027] By appropriately specifying the reinforcement area in this way, even when the number of piles 3 and the span between the piles 3 are reduced and the span between the piles 3 is lengthened, the amount of shear reinforcement 25 used to increase shear strength can be reduced, reducing the amount of steel used. Furthermore, the tangled reinforcement can be reduced, improving the ease of reinforcement placement, thereby achieving cost reductions. The high-rigidity slab reinforcement (high-rigidity slab reinforcement 23) placed between the footings 4 of the piles 3 ensures the ductility of the second shear reinforcement region 9 formed between the footings 4 of the piles 3. Furthermore, for the first shear reinforcement region 8 and the second shear reinforcement region 9, which are combined to mutually increase shear strength, increasing the amount of shear reinforcement in either one region can reduce the amount of shear reinforcement in the other region. For example, reducing the reinforcement in the first shear reinforcement region 8 can reduce the tangled reinforcement around the piles 3 and enable the shear reinforcement placement plan to take concrete filling into consideration, further improving the ease of concrete filling and reinforcement placement.

[0028] The predetermined width dimension W of the first shear reinforcement region 8 is set to a width dimension equivalent to the thickness T of the flat plate 2, and the predetermined length dimension L of the second shear reinforcement region 9 is set to a length dimension approximately 1 / 4 of the pile-to-pile span S between one pile 3 and another adjacent pile 3, thereby ensuring just the right shear strength for the flat plate 2. In addition, the shear reinforcement 25 is formed in a roughly U-shape with a hook portion 25c at the top that engages with the upper end reinforcement from above and a flat portion 25b at the bottom that can be hung on the lower end reinforcement, so that the reinforcement work can be completed simply by hooking it onto the slab reinforcement, which simplifies the work and improves workability compared to so-called closed-type shear reinforcement.

[0029] Furthermore, the U-shaped shear reinforcement bars 25 are arranged in the same direction on both the left and right sides of the width direction of the footing 4 of the pile 3, facing each other toward the center of the footing 4 of the pile 3. Therefore, if the directions were alternated, for example, the closed type reinforcement shape would become larger and large gaps would be created between the shear reinforcement bars 25, and if they were all lined up in the same direction, the reinforcement would become uneven on the left and right sides of the width direction of the column. In contrast, the reinforcement can be arranged uniformly in the left-right direction around the pile 3, and good shear reinforcement can be achieved by arranging a series of shear reinforcement bars 25 in small closed type reinforcement with almost no gaps.

[0030] Furthermore, in the first shear reinforcement region 8, the cross-sectional area of ​​the shear reinforcement 25 is set to approximately 0.45% of the area of ​​the first shear reinforcement region 8, and in the second shear reinforcement region 9, the cross-sectional area of ​​the shear reinforcement is set to approximately 0.2% of the area of ​​the second shear reinforcement region 9.This sets a high shear strength in the first shear reinforcement region 8 around the pile 3, including the footing 4, where shear force is basically concentrated and strain increases accordingly, and the second shear reinforcement region 9, which is located away from the pile 3, can rationally bear part of the shear force acting on the first shear reinforcement region 8.This reduces the amount of reinforcement, improves workability, and also achieves cost reductions, while sufficiently ensuring the required shear strength and appropriately preventing the occurrence of punching failure.

[0031] According to the building foundation structure 1 of this embodiment, the flat plate 2 includes a first shear reinforcement region 8 extending circumferentially from the surface of the footing 4 of the pile 3 to a predetermined width. Furthermore, slab reinforcement (high-stiffness slab reinforcement 23) with higher stiffness than the surrounding slab reinforcement (low-stiffness slab reinforcement 21) is arranged from the pile 3 toward the adjacent piles 3. Furthermore, a strip-shaped second shear reinforcement region 9 is provided extending from the boundary of the first shear reinforcement region 8 to a predetermined length. Therefore, although the diameter of the piles 3 is larger, the number of piles 3 can be reduced compared to conventional methods. Figure 9 shows the number of piles required in conventional methods. Furthermore, according to the building foundation structure 1 of this embodiment, the entire structure is flat except for the footing 4, improving the ease of construction of ground works such as flooring.

[0032] In this embodiment, the shear reinforcement 25 has been described as having a hook portion 25c at the upper end of the main body 25a and a flat portion 25b at the lower end of the main body 25a, but the shear reinforcement of the invention is not limited to this, and it is sufficient that the shear reinforcement is formed in a roughly U-shape having a hook portion that engages with one end reinforcing bar on one side of the high-rigidity slab reinforcement in the vertical direction and a flat portion that is hung on the other end reinforcing bar on the other side of the high-rigidity slab reinforcement in the vertical direction. Therefore, the shear reinforcement of the invention may have a hook portion at the lower end of the main body and a flat portion at the upper end of the main body. [Explanation of symbols]

[0033] 1 Building foundation structure 2 Flat Plates 3 stakes 4 Footing 5 Colonnade 6. Hashirama Belt 7a Column reinforcement 7b Column reinforcement 8 First shear reinforcement zone 9 Second shear reinforcement zone 10 Building 12 Foundation beam 14 pillars 21 Low stiffness slab reinforcement 23 High-rigidity slab reinforcement 25 Shear reinforcement 25a Main body 25b Flat part 25c hook 31 Main reinforcement 41 Ground W: specified width L: specified length

Claims

1. A building foundation structure in which a flat plate without a beam formed in direct contact with the ground in an area surrounded by beam-type foundation beams installed on the periphery is supported from below by multiple piles with a circular cross section buried in the ground, The plurality of piles are arranged in a grid pattern at intervals both vertically and horizontally in the area surrounded by the foundation beams, and a footing having a rectangular cross section and a width wider than the main body of the pile is provided at the upper end of each pile to which the flat plate is joined, The flat plate is provided with pile row bands, which are strip-shaped ranges between adjacent piles and include the footings of the piles, arranged in a grid pattern, High-rigidity slab reinforcement is arranged in the pile band so as to penetrate the footing at the upper end of the pile, and reinforcing bars are arranged in the footing according to the stress from the pile band, The flat plate has a first shear reinforcement region in which shear reinforcement is arranged along the circumferential direction of the footing and a predetermined width from the top surface of the footing, and a second shear reinforcement region in which shear reinforcement is arranged is formed in a strip shape with a predetermined length from the boundary of the first shear reinforcement region from the footing to another adjacent footing.

2. A building foundation structure as described in claim 1, characterized in that the high-rigidity slab reinforcement arranged to penetrate the footing has a two-stage structure including upper end reinforcement and lower end reinforcement, and the multiple shear reinforcement bars arranged in the first shear reinforcement area and the second shear reinforcement area are formed in an approximately U-shape, having a hook portion that engages with one side of the upper end reinforcement or the lower end reinforcement, and a flat portion that can be hung on the other side.

3. A building foundation structure as described in claim 1 or 2, characterized in that the specified width dimension of the first shear reinforcement area is a width dimension equivalent to the thickness of the flat plate, and the specified length dimension of the second shear reinforcement area from the boundary of the first shear reinforcement area is a length dimension that is 1 / 4 of the pile-to-pile span.

Images