Flat slab construction

Abstract

To provide a flat slab structure capable of easily constructing an underground pit with high degree of freedom in piping.SOLUTION: A flat slab structure 10 forming a first stage floor 2 of a building comprises: an independent footing foundation supporting a flat slab 11; and a concrete layer 12 provided on a surface of a ground G at a lower side of the flat slab 11. In the ground G, there is provided a sloped portion 102 formed so that the surface of the ground G descends from an outer peripheral portion 11s side toward a center portion 11c side of the flat slab 11. An underground pit P is provided between the flat slab 11 and the concrete layer 12.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to flat slab construction. [Background technology]

[0002] An underground pit to house equipment, piping, etc. may be provided under the first floor of a structure. For example, Patent Document 1 discloses a configuration in which a pit is formed between the foundation bottom plate and the slab of a structure. In this configuration, the slab is provided on a plurality of foundation beams provided on the foundation bottom plate. The foundation beams are composed of an inverted haunch portion provided in the center in the longitudinal direction and cast-in-place concrete beam portions provided at both longitudinal ends. A sub-beam is provided at the boundary between the inverted haunch portion and the cast-in-place concrete beam portion. The beam depth of the inverted haunch portion is lower than the beam depth of the cast-in-place concrete beam portion and the sub-beam, forming a space, and a piping unit is provided in this space. In the configuration disclosed in Patent Document 1, in order to form a pit, it is necessary to install foundation beams on the foundation bottom slab in accordance with the height of the pit, which requires a lot of work and construction time. Furthermore, since the piping unit needs to be provided in the space above the inverted haunch portion configured as described above, it cannot be said that the degree of freedom in designing the piping is high.

[0003] Moreover, Patent Document 2 discloses an underground pit equipped with a soil cement column row wall having a plurality of soil cement columns on a bottom concrete slab, and a post-cast concrete wall. In the case of an underground pit such as that disclosed in Patent Document 2, in order to form the underground pit, it is necessary to install a soil cement column wall corresponding to the height of the underground pit and a post-cast concrete wall on the bottom concrete slab, which requires a lot of work and construction time.

[0004] Patent document 3 also discloses a configuration in which a pit space is formed between the foundation slab and the lowest floor slab of the upper building part, and the pit space is provided with a column-under-the-column foundation riser provided at the bottom of the column of the upper building part, and a connecting beam column provided in a non-column-under portion other than the column-under portion. Even in the configuration disclosed in Patent Document 3, in order to form a pit, it is necessary to provide a column foundation riser according to the height of the pit and a connecting column on the foundation slab, which takes time for construction. Also, since multiple connecting columns are provided in addition to the column foundation riser in the space inside the pit, the piping etc. to be placed in the space inside the pit must be laid out to avoid these. It is desirable to realize an underground pit that allows a high degree of freedom in piping design and is easy to construct. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-97861 A [Patent Document 2] JP 2004-162350 A [Patent Document 3] JP 2017-115499 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a flat slab structure that enables easy construction of underground pits with a high degree of freedom in piping. [Means for solving the problem]

[0007] The inventors arrived at the present invention by focusing on the fact that, as a slab structure above an underground pit in which a building's equipment piping is installed, the floor surface forming the underground pit is constructed as a sloped concrete layer (level concrete), and the slab is constructed without foundation beams, as a flat slab with a rectangular and approximately uniform cross-section, allowing for a high degree of freedom in terms of the installation location of the piping and allowing for relatively easy construction. In order to solve the above problems, the present invention employs the following means. In other words, the flat slab structure of the present invention is a flat slab structure that forms the first floor of a building, and is characterized in that it comprises an independent footing foundation that supports the flat slab, and a concrete layer provided on the surface of the ground below the flat slab, and that the ground is provided with a sloped portion formed so that the surface of the ground descends from the outer periphery side of the flat slab toward the center side, and an underground pit is provided between the flat slab and the concrete layer. According to this configuration, the flat slab is supported by the independent footing foundation. The underground pit is formed below the flat slab between the flat slab and a concrete layer provided on the surface of the ground. A slope is formed in the ground so that the surface of the ground descends from the outer periphery side to the center side of the flat slab, and the height of the ground on the outer periphery side is higher than the height of the ground on the center side. Therefore, when constructing an underground pit between the concrete layer and the flat slab, it is possible to suppress the collapse of the soil around the underground pit during construction without providing an earth retaining wall to surround the underground pit. This reduces the need to provide an earth retaining wall, and the underground pit can be easily constructed. Furthermore, as described above, a slope is formed in the ground so that the surface slopes downward from the outer periphery of the flat slab toward the center, and therefore, particularly near the center of the flat slab, a large space height can be secured within the underground pit, allowing for a high degree of freedom in piping. Furthermore, since the underground pit is formed by the flat slab, basically no protrusions such as foundation beams that protrude significantly downward from the underside of the flat slab, i.e., into the underground pit, are provided, which increases the flexibility of piping. In this way, it is possible to realize a flat slab structure that allows for easy construction of underground pits with high flexibility in piping.

[0008] In one aspect of the present invention, the flat slab structure of the present invention has an independent footing foundation comprising a footing and a foundation column erected approximately at the center of the footing, and a capital portion is integrally formed on the underside of the flat slab and supported by the footing, or a foundation reinforcement portion is provided above the footing and supports the flat slab. According to this configuration, the horizontal cross-sectional area of ​​the concrete at the joint between the flat slab and the independent footing is increased by providing a capital or foundation increase portion at the joint between the flat slab and the independent footing, which allows the flat slab and the independent footing to be joined with high joint strength and high rigidity. In addition, the load acting on the flat slab can be efficiently transferred to the independent footing foundation.

[0009] In one aspect of the present invention, in the flat slab structure of the present invention, the height of the flat slab relative to the concrete layer on the outer periphery side of the flat slab is smaller than the height of the flat slab relative to the concrete layer on the central side of the flat slab. With this configuration, the above-mentioned flat slab structure can be efficiently realized. Effect of the Invention

[0010] According to the present invention, a flat slab structure is provided that allows for easy construction of an underground pit. [Brief description of the drawings]

[0011] [Figure 1]1 is a plan view showing the first floor of a building partially including a flat slab structure according to an embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view taken along the line II in FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional view taken along the line II-II in FIG. [Figure 4] FIG. 2 is a cross-sectional view showing the configuration of a first modified example of a flat slab structure according to an embodiment of the present invention. [Diagram 5] FIG. 4 is a cross-sectional view showing a configuration of a second modified example of a flat slab structure according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention is a flat slab structure in which an underground pit is formed without foundation beams by a flat slab, a slope being provided in the ground, and a sloped concrete layer (level concrete) being provided on the surface of the ground. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a flat slab structure according to the present invention will be described with reference to the accompanying drawings. A plan view showing the first floor of a building partially including the flat slab structure according to this embodiment is shown in Fig. 1. Fig. 2 is a cross-sectional view taken along line II in Fig. 1. Fig. 3 is a cross-sectional view taken along line II-II in Fig. 1. As shown in Figs. 1 to 3, a flat slab structure 10 according to this embodiment forms the first floor 2 of a building 1. The first floor 2 is formed by a flat slab 11. An underground pit P capable of accommodating piping, equipment, etc. is formed below a partial area of ​​the flat slab 11. As will be described later, the flat slab 11 is supported on the ground G or on foundation piles or ground improvement bodies 110, 112 provided in the ground G.

[0013] As shown in FIG. 2, the flat slab structure 10 includes a flat slab 11, a concrete layer 12 provided below the flat slab 11, and an independent footing foundation 20. The flat slab 11 will be described in detail later. The concrete layer 12 is provided below the flat slab 11. The concrete layer 12 is made of concrete poured to a predetermined thickness and is provided so as to cover the surface of the ground G. In this embodiment, the concrete layer 12 is provided for the purpose of adjusting the height position of the space and structures provided thereon, and no structural reinforcing bars are arranged in the concrete layer 12, but a welding wire mesh is embedded in the concrete layer 12 to suppress cracks. The concrete layer 12 may be unreinforced in relation to the arrangement position of the independent footing foundation 20 constituting the flat slab structure 10. The flat slab structure 10 has an underground pit P between the flat slab 11 and the concrete layer 12. The surface of the pit P is formed by the lower surface of the flat slab 11 and the upper surface of the concrete layer 12. As shown in FIG. 1, in this embodiment, the underground pit P is not provided below the entire flat slab 11, but is provided only below a part of the flat slab 11.

[0014] As shown in Figures 1 and 2, foundation piles or soil improvement body 110 are partially provided on the outer periphery 11s of the flat slab 11 in the area where the underground pit P is provided. A peripheral capital portion 16 that protrudes downward from the flat slab 11 is integrally provided on the portion of the flat slab 11 that corresponds to the foundation piles or soil improvement body 110. The peripheral capital portion 16 is supported on the foundation piles or soil improvement body 110. As a result, the flat slab 11 is supported on the foundation piles or soil improvement body 110. Also, as shown in Figure 3, in the area where the underground pit P is provided, in the portion of the outer periphery 11s of the flat slab 11 where no foundation piles or ground improvement bodies 110 are provided, the flat slab 11 is placed on a concrete layer 12 provided on the ground G and is supported by the ground G.

[0015] The independent footing foundation 20 is provided on the foundation piles or soil improvement body 112 on the inner side of the area where the underground pit P is formed. The independent footing foundation 20 supports the flat slab 11. In this embodiment, a plurality of independent footing foundations 20 are provided at intervals in the horizontal direction in the area where the underground pit P is formed. The plurality of independent footing foundations 20 are provided on the outer periphery 11s and / or center 11c side of the flat slab 11 in the area where the underground pit P is provided. Each independent footing foundation 20 is, for example, made of reinforced concrete. The independent footing foundation 20 may be formed as precast concrete. Each independent footing foundation 20 integrally includes a footing 21 and a foundation column 22. The footing 21 is provided on a foundation pile or a ground improvement body 112 provided on the ground G via a level concrete 25 for adjusting the height. The footing 21 is formed to have a predetermined thickness in the vertical direction. The footing 21 is formed so as to spread in the horizontal direction on the level concrete 25. The foundation column 22 protrudes upward from the center of the footing 21. The foundation column 22 supports the first floor column 3 that extends upward from the first floor floor 2.

[0016] The flat slab 11 has a predetermined thickness and is formed so that its cross section is substantially uniform. In particular, in this embodiment, the flat slab 11 is formed so that its lower surface is a flat plane and no protrusions are provided downward from the lower surface. In this embodiment, a capital portion 15 protruding downward from the flat slab 11 is integrally formed in the flat slab 11 at a portion where the independent footing foundation 20 is provided. The capital portion 15 is provided so as to be located at the outer periphery of the foundation column 22, and contacts the upper surface of the footing 21 at the outer periphery of the foundation column 22. The capital portion 15 firmly supports the flat slab 11 at the portion where the independent footing foundation 20 is provided. In this embodiment, the capital portion 15 and the footing 21 are designed to resist shear forces only by the concrete that constitutes them, and therefore, the capital portion 15 and the footing 21 are not provided with shear reinforcement bars. The flat slab 11 does not have a foundation beam that is erected between the foundation columns. The flat slab 11 functions as a horizontal member like a beam by being erected between adjacent independent footing foundations 20, or between the independent footing foundations 20 and the foundation piles or ground improvement body 110 or the ground G. The flat slab 11 transmits the vertical load acting on the flat slab 11 to the independent footing foundations 20, the foundation piles or ground improvement body 110, and the ground G. In the flat slab 11, reinforcing bars (main bars, and reinforcing bars arranged in a direction crossing the main bars) (not shown) are arranged in the horizontal direction to resist bending properties (bending stress) and punching failure (out-of-plane shear stress). In this embodiment, the flat slab 11 is not provided with face material shear reinforcement, and the concrete forming the slab thickness of the flat slab 11 resists the stress borne by the face material shear reinforcement.

[0017] In the region where the underground pit P is provided, the ground G has an upper surface formed by excavating downward below the flat slab 11 or by partially backfilling the excavated soil and sand. In the region where the underground pit P is provided, the ground G has a sloped portion 102. The sloped portion 102 is formed so that the surface of the ground G descends from the outer periphery 11s side to the center 11c side of the flat slab 11 in the region where the underground pit P is provided. In the area where the underground pit P is provided, on the outer periphery 11s of the flat slab 11 where the foundation piles or ground improvement body 110 are provided, the sloped portion 102 is formed so that the surface of the ground G descends from the foundation piles or ground improvement body 110 toward the central portion 11c of the flat slab 11. Also, as shown in Figure 3, in the area where the underground pit P is provided, in the outer periphery 11s of the flat slab 11 where no foundation piles or ground improvement body 110 are provided, the sloped portion 102 is formed so that the surface of the ground G descends from the portion where the underside of the flat slab 11 contacts the concrete layer 12 toward the central portion 11c of the flat slab 11. 2, the ground G has a footing outer peripheral inclined surface 105 around the portion where the independent footing foundation 20 is provided on the central portion 11c side of the flat slab 11. The footing outer peripheral inclined surface 105 is formed so as to descend with increasing distance from the outer periphery of the footing 21 of the independent footing foundation 20. The ground G has a flat portion 107 between the slope portion 102 and the footing outer peripheral slope 105. The flat portion 107 is formed so as to connect the lower end of the slope portion 102 and the lower end of the footing outer peripheral slope 105.

[0018] The concrete layer 12 is provided so as to cover the sloped portion 102, the footing outer peripheral inclined surface 105, and the flat portion 107 formed on the surface of the ground G. As shown in Fig. 3, the concrete layer 12 is in contact with the lower surface of the flat slab 11 at the outer peripheral portion 11s of the flat slab 11 in the region where the underground pit P is provided. As shown in Fig. 2, in the outer peripheral portion 11s of the flat slab 11, in the portion where the foundation pile or the ground improvement body 110 is provided, the concrete layer 12 is sandwiched between the foundation pile or the ground improvement body 110 and the outer peripheral capital portion 16 of the flat slab 11.

[0019] In the underground pit P thus formed, the height Hs of the flat slab 11 relative to the concrete layer 12 on the outer periphery 11s side of the flat slab 11 is smaller than the height Hc of the flat slab 11 relative to the concrete layer 12 on the central portion 11c side of the flat slab 11. In other words, the height Hs of the underground pit P on the outer periphery 11s side is smaller than the height Hc of the underground pit P on the central portion 11c side.

[0020] According to the flat slab structure 10 as described above, the flat slab structure 10 forms the first floor 2 of the building 1, and comprises an independent footing foundation 20 supporting the flat slab 11, and a concrete layer 12 provided on the surface of the ground G below the flat slab 11, and a sloped portion 102 is provided in the ground G so that the surface of the ground G slopes downward from the outer periphery 11s side of the flat slab 11 toward the central portion 11c side, and an underground pit P is provided between the flat slab 11 and the concrete layer 12. According to this configuration, the flat slab 11 is supported by the independent footing foundation 20. The underground pit P is formed below the flat slab 11 between the concrete layer 12 provided on the surface of the ground G and the flat slab 11. The ground G has a slope 102 formed such that the surface of the ground G descends from the outer periphery 11s side to the center 11c side of the flat slab 11, and the height of the ground G on the outer periphery 11s side is higher than the height of the ground G on the center 11c side. Therefore, when constructing the underground pit P between the concrete layer 12 and the flat slab 11, it is possible to suppress the collapse of the soil around the underground pit P during construction without providing an earth retaining wall to surround the underground pit P. Therefore, the need for providing an earth retaining wall is reduced, and the underground pit P can be easily constructed. Furthermore, as described above, the ground G has a sloping portion 102 formed such that the surface slopes downward from the outer peripheral side 11s to the central side 11c of the flat slab 11. Therefore, particularly on the central side 11c of the flat slab 11, the height of the space within the underground pit P can be secured to be large, providing a high degree of freedom in piping. Furthermore, since the underground pit P is formed by the flat slab 11, basically no protrusions such as foundation beams that protrude significantly downward from the underside of the flat slab 11, i.e., into the underground pit P, are provided. This allows for greater flexibility in piping. In this way, it is possible to realize a flat slab structure 10 that enables easy construction of an underground pit P with a high degree of freedom in piping.

[0021] In particular, in this embodiment, as described above, the flat slab 11 does not have a foundation beam. In other words, since the underground pit P is formed by the flat slab 11, which can be constructed without using a foundation beam, there is no need to provide a foundation beam in the underground pit P. This increases the degree of freedom in piping. Also, in the case of a typical slab with foundation beams, it is necessary to provide a manhole in the foundation beam for the purpose of inspection work inside the underground pit, but this is no longer necessary, and the degree of freedom in piping is further increased. In addition, in general, foundation beams require a lot of design work because they need to be designed so that components such as main reinforcement, ribs, and width stoppers are contained within a certain volume while ensuring the covering of the reinforcing bars. In the flat slab structure 10 of this embodiment, the design work for such foundation beams can be reduced, making construction easier in this respect as well.

[0022] In addition, when constructing a building 1 in which the first floor is realized as a concrete floor, for example, if the steel frame is erected using heavy machinery after the foundation beams are constructed, the concrete floor can be constructed at an appropriate time while the main body of the building 1 is being constructed, so the travel area of ​​the heavy machinery can be freely set. Therefore, construction efficiency is good. On the other hand, if the first floor is a structural slab, special reinforcement may be required to allow heavy machinery to pass above, which results in more construction constraints and higher construction costs. In the above-mentioned flat slab structure 10, the flat slab 11 functions as a structural slab that resists vertical loads, bending properties (bending stress), and punching failure (out-of-plane shear stress), as already explained. In addition, by appropriately adjusting the size of the capital portion 15 and the footing 21 and by preventing the reinforcing bars from protruding into the area where heavy machinery travels, it is possible to ensure an area for heavy machinery to travel, just like with a concrete floor.

[0023] The independent footing foundation 20 also comprises a footing 21 and a foundation column 22 erected approximately in the center of the footing 21, and a capital portion 15 is formed integrally with the underside of the flat slab 11, and the capital portion 15 is supported by the footing 21. According to this configuration, the horizontal cross-sectional area of ​​the concrete at the joint is increased by providing the capital portion 15 at the joint between the flat slab 11 and the independent footing foundation 20. Therefore, the flat slab 11 and the independent footing foundation 20 are joined with high joint strength and high rigidity. In addition, the load acting on the flat slab 11 can be efficiently transmitted to the independent footing foundation 20.

[0024] In addition, in the area where the underground pit P is provided, the height Hs of the flat slab 11 relative to the concrete layer 12 on the outer periphery 11s side of the flat slab 11 is smaller than the height Hc of the flat slab 11 relative to the concrete layer 12 on the central portion 11c side of the flat slab 11. With this configuration, the flat slab structure 10 as described above can be efficiently realized.

[0025] (First Modification of the Embodiment) The flat slab structure of the present invention is not limited to the above-mentioned embodiment described with reference to the drawings, and various modifications are possible within the technical scope. For example, in the above embodiment, the capital portion 15 is integrally formed on the underside of the flat slab 11, and the capital portion 15 is supported by the footing 21, but the present invention is not limited to this. For example, as shown in Fig. 4, a foundation increase part 30 may be provided above the footing 21, and the flat slab 11 may be supported by the foundation increase part 30. In this case, the flat slab 11 may be provided with main reinforcement bars 18, and connecting reinforcement bars 19 may be provided to connect the flat slab 11 and the foundation increase part 30. According to this configuration, the horizontal cross-sectional area of ​​the concrete at the joint is increased by providing the foundation increase portion 30 at the joint between the flat slab 11 and the independent footing foundation 20. Therefore, the flat slab 11 and the independent footing foundation 20 are joined with high joint strength and high rigidity.

[0026] (Second Modification of the Embodiment) In addition, in the above embodiment, as explained using Figure 3, the concrete layer 12 forming the bottom surface of the underground pit P is configured to contact the underside of the flat slab 11 at the outer peripheral portion 11s of the flat slab 11, but this is not limited to this. As shown in FIG. 5, an earth retaining wall 50 may be provided between the outer periphery 11s of the flat slab 11 and the concrete layer 12 on the outer periphery of the area where the underground pit P is provided.

[0027] (Third Modification of the Embodiment) In the above embodiment, a footing outer peripheral sloped surface 105 having a slope is provided between the independent footing foundation 20 at the center of the flat slab 11 and the concrete layer 12 forming the underground pit P, but an underground pit may be formed by making the flat portion 107 extend toward the independent footing foundation 20 without providing the footing outer peripheral sloped surface 105. Therefore, in this embodiment, by not providing the footing outer peripheral sloped surface 105 at the center of the flat slab 11, it is possible to ensure a wide underground pit P. The flat slab in the above embodiment is a slab whose cross section is formed substantially uniformly in a rectangular shape. In this specification, the flat slab also includes a flat slab in which flat beams are provided in a lattice shape without providing foundation beams between foundation columns. A flat slab having flat beams requires a large number of flat beams compared to a structure in which a foundation beam with a large cross section is erected between foundation columns, but the cross section of each beam is small, and the lower surface of each flat beam is essentially the lower surface of the flat slab. Therefore, even when a flat slab having flat beams is used, no protrusions are provided that protrude significantly downward, i.e., into the underground pit, from the lower surface of the flat slab, so that the degree of freedom of piping can be increased as in the above embodiment. In addition, in the above embodiment, the independent footing foundation is installed on the top of the foundation beam or the ground improvement body, but the independent footing foundation may be installed without providing the foundation beam or the ground improvement body. In addition, in the above embodiment, the underground pit P is provided to accommodate piping, equipment, etc., but the underground pit P can also be used as a water tank. In addition, in the above embodiment, the flat slab is supported by an independent footing foundation via a capital portion or a foundation extension portion, but the flat slab may have a uniform cross section without a capital portion or a foundation extension portion, and may be supported by an independent footing foundation consisting of a footing and a foundation column. In addition, the configurations described in the above embodiments can be selected or changed as appropriate without departing from the spirit of the present invention. [Explanation of symbols]

[0028] 1 Building 20 Independent footing foundation 2 1st floor 21 Footing 3 pillars 22 foundation pillars 10 Flat slab structure 30 Foundation extension 11 Flat slab 102 Slope section 11c Central part 110, 112 Ground improvement body 11s Outer area G Ground 12 Height of concrete layer Hc, Hs 15 Capital P Underground Pit

Claims

1. A flat slab structure forming the first floor of a building, An independent footing supporting a flat slab; A concrete layer is provided on the surface of the ground below the flat slab, The concrete layer is provided so as to contact the lower surface of the flat slab at the outer periphery of the flat slab, and the flat slab is placed on the concrete layer; The ground is provided with a sloped portion formed so that the surface of the ground descends from the portion of the outer periphery of the flat slab where the underside of the flat slab and the concrete layer contact toward the center of the flat slab; A flat slab structure characterized in that an underground pit is provided between the flat slab and the concrete layer.

2. The independent footing foundation includes a footing and a foundation column erected at approximately the center of the footing, The flat slab structure described in claim 1, characterized in that a capital portion is integrally formed on the underside of the flat slab so as to protrude downward from the flat slab, and the capital portion is arranged so as to contact the upper surface of the footing at the outer periphery of the foundation column, thereby supporting the capital portion with the footing.

3. The independent footing foundation comprises a footing and a foundation column erected at approximately the center of the footing, A foundation reinforcement part is provided above the footing, and the foundation reinforcement part supports the flat slab.

2. The flat slab structure according to claim 1 .

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