Opening and constructing and burying method, opening formwork and closing member

Abstract

To provide means by which an opening can be closed (buried) after being constructed in a concrete floor of an upper floor, eliminating the need for formwork support work for a floor bottom formwork or joint work between upper and lower floors, and reducing the labor required for assembling and dismantling the formwork and the generation of residual materials.SOLUTION: An opening 2 has an upper draft surface 3a having an inward draft slope downward from an entire upper end periphery 2a, and a lower steep slope surface 3b below the upper draft surface, which is a surface that is steeper inward than the draft slope. An open formwork 10 has an upper outer peripheral surface 12 that abuts against the upper draft surface, and a lower outer peripheral surface 14 that abuts against the lower steep slope surface. A closing member 20 has a plate-shaped portion 22 that fits into the inner lower end of the opening, and an inclined lower surface 22a that abuts against the lower steep slope surface on both lower ends in the width direction or length direction. The opening construction and burying method is a method in which the opening 2 is constructed in a concrete floor 1, and then the opening 2 is closed and buried, and includes an opening construction step S1, a form removal step S2, a material lifting step S3, and an opening burying step S4, in this order.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an opening construction and burying method in which an opening is constructed in a concrete floor of an upper floor, and then the opening is closed and buried, and to an opening formwork and a closing member used in this construction method. [Background technology]

[0002] In reinforced concrete construction, a construction method is sometimes used in which an opening is made in the floor of the upper floor for lifting materials in order to reuse the formwork support on the upper floor, and then, after the materials have been lifted, a hole-bottom formwork is installed in the floor opening and post-construction concrete is poured to seal the opening. This method will be referred to hereinafter as the “opening construction and burying method.” Among these methods, the method of closing the opening is disclosed in, for example, Patent Document 1.

[0003] The "Floor opening hole filling method and formwork used therefor" in Patent Document 1 involves installing formwork (hole bottom formwork) and filling in floor openings only on the floor where renovation work is being carried out. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6085151 Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional opening construction buried construction method, the floor bottom formwork corresponding to the floor bottom of the upper floor is supported by the formwork shoring of the floor below, and an opening formwork for the opening is made out of plywood or the like at the position where the opening is to be made, and concrete is poured around it to construct the concrete floor of the upper floor with an opening. Next, after the concrete floor on the upper floor has hardened, the floor base formwork and formwork supports are disassembled (removed from the formwork), and the formwork supports used on the lower floor are moved to the upper floor through the opening in the upper floor. After that, reinforcement is placed inside the opening and concrete is poured to close (bury) the opening.

[0006] However, when closing the opening (burying the concrete), a formwork for closing the opening and a formwork support for supporting the formwork on the floor below are required, which requires the labor of assembling and dismantling the formwork. In addition, materials are left over after the formwork is dismantled.

[0007] In Patent Document 1, after reinforcing bars are placed in the opening, the bottom hole formwork for closing the opening is suspended from the reinforcing bars in the opening, eliminating the need for formwork support on the lower floor. However, this reinforcing bar placement work needs to be carried out jointly by workers on both the upper and lower floors, and similarly, the work of assembling and dismantling the formwork is laborious. In addition, materials are left over after the formwork is dismantled.

[0008] The present invention has been invented to solve such problems. That is, the object of the present invention is to provide a means by which an opening can be closed (buried) after it has been constructed in the concrete floor of the upper floor, without the need for joint work on the bottom of the hole and its support work by the upper and lower floors, and with almost no labor involved in assembling and dismantling the formwork, and with almost no waste material. [Means for solving the problem]

[0009] According to the present invention, there is provided an opening construction and burying method in which an opening is constructed in a concrete floor of an upper floor, and then the opening is closed and buried, an opening construction process in which the floor bottom formwork of the upper floor is supported by a formwork support of the floor below, an opening formwork is installed on the floor bottom formwork at a position where the opening is to be formed, and concrete is poured around the opening formwork to construct the concrete floor having the opening; a demolding process in which, after the concrete floor has hardened, the open formwork is pulled upward as a whole to expose the inner surface of the opening; After the concrete floor has hardened, a material lifting process is performed in which the floor bottom formwork and the formwork support are disassembled and the formwork support is moved to the upper floor through the opening; and an opening embedding step of closing the bottom of the opening with a closing member, arranging reinforcement in the opening, and pouring concrete into the opening to embed the opening, the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end thereof, and a lower steeply inclined surface located continuously downward from an entire circumference of a lower end of the upper draft surface and having an inward slope steeper than the draft slope; An opening construction burying method is provided in which the closing member has a plate-shaped portion that fits into the inner lower end of the opening, and the plate-shaped portion has inclined lower surfaces at both ends in the width or length direction that abut the lower steeply sloping surface.

[0010] According to the present invention, there is also provided an opening form for constructing an opening in a concrete floor of an upper floor, comprising: the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end, and a lower steeply inclined surface that is located continuously downward from an entire circumference of a lower end of the upper draft surface and is a surface that is steeper inwardly than the draft slope, The open-ended form is a one-piece form that can be repeatedly reused, and has an upper outer peripheral surface that abuts the upper draft surface and a lower outer peripheral surface that abuts the lower steep surface.

[0011] Further according to the present invention there is provided a closure member for closing an opening in a concrete floor, comprising: the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end, and a lower steeply inclined surface that is located continuously downward from an entire circumference of a lower end of the upper draft surface and is a surface that is steeper inwardly than the draft slope, The closure member has a plate-like portion that fits into the inner lower end of the opening, and the plate-like portion has inclined lower surfaces at both ends in the width or length direction that abut the lower steeply inclined surface. Effect of the Invention

[0012] According to the above-mentioned configuration of the present invention, the opening construction and burying method has an opening construction process and an opening burying process, so that after an opening is constructed in the concrete floor of the upper floor in the opening construction process, the opening can be closed and concrete can be poured into the opening and buried in the opening burying process.

[0013] In addition, since the opening has an upper draft surface and a lower steeply inclined surface, and the open-type formwork has an upper outer peripheral surface that abuts on the upper draft surface and a lower outer peripheral surface that abuts on the lower steeply inclined surface, the use of the open-type formwork makes it possible to construct an opening with high dimensional accuracy. In addition, since the open-type formwork is an integrated formwork that can be repeatedly reused, the labor required for assembling and dismantling the formwork and the generation of leftover materials can be prevented.

[0014] Furthermore, since the closure member has a plate-shaped portion that fits into the inner lower end of the opening and an inclined lower surface on the underside of both ends of this plate-shaped portion that abuts against the lower steeply sloping surface, the bottom of the opening can be easily closed with the closure member during the opening embedding process.

[0015] In addition, since the bottom of the opening is closed with a closing member in the opening embedding process, the hole bottom formwork for closing the opening is no longer necessary. After the opening is closed, reinforcement is placed in the opening and concrete is poured into the opening to embed the opening, so the hole bottom formwork and its formwork support work and the joint work of the upper and lower floors are not required, and the labor required for assembling and dismantling the formwork and the generation of leftover materials can be prevented. [Brief description of the drawings]

[0016] [Figure 1] An explanatory diagram of an opening in the concrete floor on the upper floor. [Diagram 2] FIG. 2 is an overall configuration diagram of an open formwork. [Diagram 3] FIG. 2 is an overall configuration diagram of a closing member. [Figure 4] FIG. 2 is an explanatory diagram of the opening construction and burying method according to the present invention. [Diagram 5] This is an explanatory diagram of a method for installing an insert metal fitting for a reinforcing bar. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, common parts in each drawing are given the same reference numerals, and duplicated explanations will be omitted.

[0018] Fig. 1 is an explanatory diagram of an opening 2 in an upper floor concrete floor 1. In this figure, (A) is a top view, (B) is a BB cross-sectional view of (A), and (C) is a CC cross-sectional view of (A). As shown in this figure, an opening 2 is provided in a concrete floor 1 and penetrates it in the vertical direction. The thickness of the concrete floor 1 in the position surrounding the opening 2 is preset to a constant value. The thickness is, for example, 200 mm.

[0019] In FIG. 1(A), the opening 2 is rectangular in shape that is long in the length direction and short in the width direction when viewed from above, and the length and width are set to be constant. Hereinafter, the length direction is called the X direction, and the width direction is called the Y direction.

[0020] 1(A), the upper end perimeter 2a of the opening 2 is located outside the lower end perimeter 2b in a plan view. The lower end opening surrounded by the lower end perimeter 2b is set to a size that allows a formwork support 6 (described later) to be moved from the lower floor to the upper floor.

[0021] In Figs. 1(B) and (C), the opening 2 has an upper draft surface 3a and a lower steeply inclined surface 3b between the upper end circumference 2a and the lower end circumference 2b. The upper draft surface 3a has an inward draft angle downward from the entire upper end periphery 2a of the opening 2. The draft angle is an angle at which the open-ended formwork 10 (see FIG. 2) can be easily pulled upward as a unit in the demolding step S2 described below, and is, for example, 15 to 25° inward with respect to the vertical plane, more preferably 18 to 22°. In addition, the lower steeply inclined surface 3b is located continuously downward from the entire circumference of the lower end of the upper draft surface 3a and is a surface that is steeper inwardly inclined than the draft of the upper draft surface 3a, for example, at an inward angle of 25 to 45°, more preferably 30 to 40°, relative to the vertical plane. Furthermore, it is preferable that the upper draft surface 3a and the lower steeply inclined surface 3b are smooth flat surfaces. The overall height of the lower steeply inclined surface 3b is, for example, 50 to 60 mm from the lower end.

[0022] FIG. 2 is a diagram showing the overall configuration of the open formwork 10, where (A) is a top view, (B) is a view taken along the line BB in (A), and (C) is a view taken along the line CC in (A).

[0023] In this example, the open formwork 10 is made entirely of aluminum to reduce weight so that workers can carry it by hand, and is a one-piece formwork that can be repeatedly reused. A handle 15 for carrying the open-type formwork 10 is attached to the upper part of the open-type formwork 10. The handle 15 is preferably of a retractable type that is retracted downward when not in use, but may be of a removable type or a fixed type.

[0024] Furthermore, since aluminum is easily corroded by alkaline concrete, the entire outer surface of the open formwork 10 is coated with a corrosion prevention material 11 (for example, fluororesin).

[0025] The open formwork 10 is set in length and width so as to occupy the entire inside of the opening 2 in the concrete floor 1 described above. 2(A), the length of the open-ended formwork 10 in the X direction is set equal to the length of the opening 2, and the width in the Y direction is set equal to the width of the opening 2. The height of the open-ended formwork 10 is preferably equal to or greater than the thickness of the opening 2.

[0026] In FIGS. 2(B) and 2(C), an open form 10 has an upper outer peripheral surface 12 and a lower outer peripheral surface 14. Upper outer peripheral surface 12 is the surface that comes into contact with upper draft surface 3a of opening 2, and has an inward draft angle downward from the upper end. This draft angle is set at the same angle as upper draft surface 3a of opening 2, for example, 15 to 25°, more preferably 18 to 22°, inward with respect to the vertical plane. Further, the lower outer peripheral surface 14 is a surface that abuts against the lower steeply inclined surface 3b of the opening 2, is located continuously below the upper outer peripheral surface 12, and has a surface that is inwardly inclined steeper than the draft angle of the upper outer peripheral surface 12. This inclined surface is set at the same angle as the lower steeply inclined surface 3b of the opening 2, for example, 25 to 45°, more preferably 30 to 40°, inward with respect to the vertical plane.

[0027] In Fig. 2(B) and (C), the open formwork 10 has an insert mounting hole 13 on the upper outer peripheral surface 12 for mounting an insert metal fitting 7 (described later) for inserting reinforcement. The insert mounting holes 13 are provided at opposing positions offset from each other on both sides in the width direction and both sides in the length direction of the open-type formwork 10. The amount of offset is preferably equal to or greater than the diameter of the insert reinforcing bars.

[0028] In FIG. 2(A), the open formwork 10 further has a bottom plate 16 . The bottom plate 16 has a bottom plate opening 16a on the inside, and is set so as to be in close contact with the top surface of the floor bottom formwork 5 (described later) of the upper floor. The bottom plate opening 16a is provided to reduce the weight of the open formwork 10 and to allow construction tools to be moved from the lower floor to the upper floor while the concrete floor is still unhardened. In FIG. 2(A), the bottom plate 16 has nail holes 17 for fixing the bottom plate 16 to the floor bottom formwork 5 with nails or screws.

[0029] FIG. 3 is an overall configuration diagram of the closing member 20, where (A) is a top view, (B) is a view taken along the line BB in (A), and (C) is a view taken along the line CC in (A). As shown in this figure, the closing member 20 is set to a length, width and height sufficient to occupy the inner lower end of the opening 2 in the concrete floor 1 described above.

[0030] In this example, in FIG. 3(A), the closing member 20 is composed of two closing members 20a and 20b separated at the center position in the X direction so that the closing member 20 can be easily carried by an operator. The two closure members 20a, 20b are identical and have a plate-like portion 22 that fits into the inner lower end of the opening 2. The thickness of the plate-like portion 22 is set to be substantially the same as the height of the lower steeply inclined surface 3b of the opening 2. This thickness is, for example, 50 mm. It should be noted that the closing member 20 is not limited to this example, and may be one piece or divided into three or more parts.

[0031] 3(B) and (C), the plate-like portion 22 has inclined lower surfaces 22a that come into contact with the lower steeply inclined surface 3b of the opening 2 on the lower surfaces at both ends in the width direction or length direction (width direction in this example). In this example, the inclined lower surfaces 22a are provided in three directions in total, including the lower surfaces at both ends in the width direction (Y direction) and the lower surface at one end in the length direction (X direction). In this example, the other end in the length direction (X direction) of the plate-like portion 22 is provided on a vertical surface 22b. With this configuration, by bringing the vertical surfaces 22b of the two closing members 20a, 20b into close contact with each other, the entire four sides of the lower steeply inclined surface 3b of the opening 2 can be closed with almost no gaps as a whole.

[0032] In FIG. 3, the closure element 20, i.e. the two closure elements 20a, 20b, have trusses 24 which are lower than the overall height of the opening 2. Moreover, the plate-like portion 22 is a precast concrete plate in which the lower portions of the truss reinforcement bars 24 are embedded. The upper parts of the truss bars 24 exposed above the plate-like portion 22 function as reinforcing bars (reinforcing bars) in the opening when concrete is poured in the opening filling step S4 described below. In addition, this portion (the exposed portion of the truss reinforcement 24) also functions as a handle for a worker to carry the closure member 20 by hand when closing the bottom (inner lower end) of the opening 2 in the opening embedding step S4.

[0033] FIG. 4 is an explanatory diagram of the opening construction and burying method according to the present invention. The opening construction and burying method according to the present invention is a method in which an opening 2 is constructed in a concrete floor 1 on the upper floor, and then the opening 2 is closed and buried, and includes, in order, an opening construction process S1, a form removal process S2, a material lifting process S3, and an opening burying process S4.

[0034] The opening construction process S1 includes a floor bottom formwork support assembling process (A), an opening formwork installation process (B), a reinforcing bar insert installation process (C), and a floor concrete pouring process (D) as shown in FIG.

[0035] That is, in the floor bottom formwork shoring assembly process (A), the floor bottom formwork 5 of the upper floor is supported by the formwork shoring 6 of the floor below, and in the open formwork installation process (B), an open formwork 10 is installed on top of the floor bottom formwork 5 at a position where the opening 2 will be formed. Furthermore, after the reinforcing bar insert installation process (C), concrete is poured around the open formwork 10 in the floor concrete pouring process (D) to construct the concrete floor 1 with the opening 2.

[0036] In the insert fitting process (C), after the open formwork 10 is set, the insert metal fittings 7 for the insert bars are fitted into the insert fitting holes 13 provided in the open formwork 10. The insert mounting holes 13 are provided at offset opposing positions on both sides in the width direction and on both sides in the length direction of the open-type formwork 10, so the insert metal fittings 7 are also provided at offset opposing positions on both sides in the width direction and on both sides in the length direction. This offset is equal to or greater than the diameter of the insert reinforcing bars.

[0037] The demolding step S2 corresponds to (E) of FIG. 4, in which, after the concrete floor 1 has hardened, the open formwork 10 is pulled upward as a unit to expose the inner surface of the opening 2. The material lifting process S3 also corresponds to (E) of FIG. 4. After the concrete floor 1 has hardened, the floor bottom formwork 5 and formwork support 6 are disassembled and the formwork support 6 is moved through the opening 2 to the upper floor.

[0038] The opening embedding step S4 includes a closing member installing step (F), an insert reinforcing bar arranging step (G), and an opening concrete pouring step (H) in FIG. That is, in the closing member installation process (F), the bottom of the opening 2 is closed with a closing member 20, in the insert reinforcement process (G), reinforcement is placed in the opening, and in the opening concrete pouring process (H), concrete is poured into the opening to fill it. With this configuration, the bottom of the opening is closed with the closing member 20 in the opening filling step S4, making it possible to eliminate the need for a conventional hole bottom form for closing the opening.

[0039] In addition, in the reinforcing bar arrangement process (G), the insert hardware 7 for the reinforcing bars is located in opposing positions offset from each other on both sides in the width direction and both sides in the length direction, so that the center parts of two reinforcing bars (steel bars) whose one ends are screwed into the insert hardware 7 in opposing positions can be firmly bound together. In addition, the opening 2 embedded in the opening concrete pouring process (H) has sufficient reinforcement in the plate-shaped portion and its upper portion, so it has the same bending rigidity as the concrete floor 1 and becomes part of the concrete floor 1.

[0040] Fig. 5 is an explanatory diagram of a method for installing the insert metal fitting 7 for the reinforcing bars. In this figure, (A) corresponds to the insert fitting step (C) in Fig. 4(C), and (B) corresponds to the demolding step S2 in Fig. 4(E). In this example, the insert metal fitting 7 for the insert bar is a cylindrical member with a flange having a large diameter part and a small diameter part, and a bottomed female screw part is provided at the axis center of the small diameter part. In addition, a hollow cylindrical resin cap 7a is fixed to the outside of the small diameter part so as to be slidable in the axial direction.

[0041] 5(A), the male thread of the bolt 8 is passed through the insert mounting hole 13 from the inside of the open-type formwork 10, and the male thread of the bolt 8 is screwed into the female thread of the insert metal fitting 7, and the outer circumferential surface of the open-type formwork 10 is sandwiched between the bolt 8 and the insert metal fitting 7 and fixed in place. At this time, the resin cap 7a is in close contact with the outer circumferential surface of the open-type formwork 10, so that no gap is generated between the outer circumferential surfaces of the insert metal fitting 7 and the open-type formwork 10. In the state shown in FIG. 5(A), concrete is poured around the open formwork 10 in the floor concrete pouring step (D) to construct a concrete floor 1 having an opening 2.

[0042] In Fig. 5(B), the insert metal fittings 7 are embedded in the concrete floor 1. When removing the open formwork 10 after pouring concrete, the bolts 8 are removed from the inside of the open formwork 10, and then the open formwork 10 is pulled upward as a whole to expose the inner surface of the opening 2.

[0043] With the above-mentioned configuration, the open formwork 10 can be embedded to construct the concrete floor 1 with the insert metal fittings 7 attached to the insert mounting holes 13. After the concrete floor 1 has hardened, the open formwork 10 can be removed as a unit with the insert metal fittings 7 remaining embedded in the concrete floor 1.

[0044] According to an embodiment of the present invention, the opening construction and burying method has an opening construction step S1 and an opening burying step S4, so that after constructing an opening 2 in the concrete floor 1 of the upper floor in the opening construction step S1, the opening 2 can be closed and concrete can be poured into the opening and buried in the opening burying step S4.

[0045] In addition, since the open-ended formwork 10 has an upper outer peripheral surface 12 that abuts against the upper draft slope surface 3a of the opening 2 and a lower outer peripheral surface 14 that abuts against the lower steep slope surface 3b of the opening 2, the opening 2 can be constructed with high dimensional accuracy by using the open-ended formwork 10. In addition, since the open-ended formwork 10 is an integrated formwork that can be repeatedly reused, it is possible to prevent the labor of assembling and dismantling the formwork and the generation of leftover materials.

[0046] Furthermore, since the closure member 20 has a plate-shaped portion 22 that fits into the inner lower end of the opening 2 and an inclined lower surface 22a on the underside of both ends of this plate-shaped portion 22 that abuts against the lower steeply inclined surface 3b, the bottom of the opening 2 can be easily closed with the closure member 20 in the opening embedding step S4.

[0047] Furthermore, in the opening filling step S4, the opening bottom is closed with the closing member 20, which eliminates the need for a conventional hole bottom form for closing the opening. In addition, after the opening is closed, reinforcement is placed inside the opening and concrete is poured into the opening to fill the opening 2, so there is no need for joint work on the bottom of the hole and its formwork supports by the upper and lower floors, and the effort required for assembling and dismantling the formwork and the generation of leftover materials can be prevented.

[0048] The scope of the present invention is not limited to the above-described embodiment, but is indicated by the claims, and further includes all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0049] S1 Opening construction process, S2 Form removal process, S3 Material lifting process, S4 Opening burying process, 1 Concrete floor, 2 Opening, 2a Upper end all around, 2b Lower end all around, 3a Upper draft slope surface, 3b Lower steep slope surface, 5 Floor bottom formwork, 6 Formwork support, 7 Insert metal, 7a Resin cap, 8 Bolt, 10 Opening formwork, 11 Corrosion prevention material, 12 Upper outer peripheral surface, 13 Insert mounting hole, 14 Lower outer peripheral surface, 15 Handle, 16 Bottom plate, 16a Bottom plate opening, 17 Nail hole, 20, 20a, 20b Closure member, 22 Plate-shaped portion, 22a Sloping lower surface, 22b Vertical surface, 24 Truss reinforcement

Claims

1. An opening construction and burying method in which an opening is constructed in a concrete floor of an upper floor, and then the opening is closed and buried, an opening construction process in which the floor bottom formwork of the upper floor is supported by a formwork support of the floor below, an opening formwork is installed on the floor bottom formwork at a position where the opening is to be formed, and concrete is poured around the opening formwork to construct the concrete floor having the opening; a demolding process in which, after the concrete floor has hardened, the open formwork is pulled upward as a whole to expose the inner surface of the opening; After the concrete floor has hardened, a material lifting process is performed in which the floor bottom formwork and the formwork support are disassembled and the formwork support is moved to the upper floor through the opening; and an opening embedding step of closing the bottom of the opening with a closing member, arranging reinforcement in the opening, and pouring concrete into the opening to embed the opening, the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end thereof, and a lower steeply inclined surface located continuously downward from an entire circumference of a lower end of the upper draft surface and having an inward slope steeper than the draft slope; An opening construction burying method, wherein the closing member has a plate-shaped portion that fits into the inner lower end of the opening, and the plate-shaped portion has inclined lower surfaces at both ends in the width or length direction that abut the lower steeply inclined surface.

2. The opening construction burying method according to claim 1, wherein the opening construction process includes a reinforcing bar insert installation process for installing an insert metal fitting for reinforcing bar into an insert installation hole provided in the opening formwork after the opening formwork is installed.

3. The opening construction and embedding method according to claim 2, wherein the opening embedding step includes a reinforcing bar arrangement step of arranging reinforcing bars in the opening using the insert metal fittings after closing the bottom of the opening with the closing member.

4. An opening form for constructing an opening in a concrete floor of an upper floor, the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end, and a lower steeply inclined surface that is located continuously downward from an entire circumference of a lower end of the upper draft surface and is a surface that is steeper inwardly than the draft slope, The open-ended form is a one-piece form that can be repeatedly reused, and has an upper outer peripheral surface that abuts against the upper draft surface and a lower outer peripheral surface that abuts against the lower steep surface.

5. 5. The open formwork according to claim 4, further comprising an insert mounting hole on the upper outer peripheral surface for mounting an insert metal fitting for a reinforcing bar.

6. A bottom plate is attached to the upper surface of the floor bottom formwork of the upper floor and has a bottom plate opening on the inside, The open formwork according to claim 4 , wherein the bottom plate has nail holes for fastening the bottom plate to the floor bottom formwork with nails or screws.

7. The whole is made of aluminum, 7. The open formwork according to claim 6, wherein the entire outer surface is coated with a corrosion inhibitor.

8. A closure member for closing an opening in a concrete floor, comprising: the opening has an upper draft surface having an inward draft slope extending downward from an entire circumference of an upper end, and a lower steeply inclined surface that is located continuously downward from an entire circumference of a lower end of the upper draft surface and is a surface that is steeper inwardly than the draft slope, The closure member has a plate-shaped portion that fits into the inner lower end of the opening, and the plate-shaped portion has inclined lower surfaces at both ends in the width or length direction that abut the lower steeply inclined surface.

9. The opening has a truss bar that is lower than the overall height of the opening. The closure member according to claim 8 , wherein the plate-shaped portion is a precast concrete plate in which the lower portion of the truss reinforcement is embedded.

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