Inner formwork for forming hollow spaces in precast concrete members

Abstract

To provide an inner mold form for manufacturing a precast concrete (PCa) member having a hollow part provided with a cotter, the inner mold form capable of supporting a part that forms the cotter and easily removable.SOLUTION: An inner mold form 1 includes: a cylindrical-shaped cotter formation member 12; a core member 13 to be inserted inside the cotter formation member 12; and a slider 14 arranged between the cotter formation member 12 and the core member 13. The slider 14 includes a plurality of rolling elements 18 capable of rolling at least one of an inside surface of the cotter formation member 12 and an outside surface of the core member 13.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an inner formwork for forming a hollow portion in a precast concrete member (hereinafter referred to as "PCa member"). [Background technology]

[0002] Precast concrete members are sometimes used in the construction of architectural or civil engineering structures. For example, in buildings, columns and beams are sometimes made of precast concrete members to shorten construction time and improve quality. Precast concrete members are manufactured in factories, transported to the construction site, and then placed in their designated positions using lifting equipment such as cranes.

[0003] In buildings with large spans between columns, such as logistics facilities, the distance from the lifting machine to the installation position of the PCa members becomes long, making it necessary to either increase the size of the lifting machine or reduce the weight of the PCa members. By providing a hollow section in the PCa member, the PCa member can be made lighter, preventing the need for a larger lifting machine. PCa members with hollow sections are installed in the designated position at the construction site using a lifting machine, and concrete is then poured into the hollow section. To improve the bond between the PCa member and the concrete that will be poured later, cotters are provided on the inner surface that defines the hollow section. Various inner formworks have been proposed that allow the formation of cotters but still be removable.

[0004] For example, Patent Document 1 describes an inner formwork comprising a cylindrical cotter forming formwork, a core member placed inside the cotter forming formwork, and a mat-like air panel disposed between them. Concrete for constructing a PCa member is poured into this inner formwork with the air panel filled with air, and when demolding, the air is released from the air panel to create a gap between the cotter forming formwork and the core member, the air panel and core member are removed, and then the cotter forming formwork is removed.

[0005] Furthermore, Patent Document 2 describes a formwork device that includes a truncated quadrangular pyramid-shaped hollow formwork that tapers toward its tip, and a cotter formwork adhered to the surface of the hollow formwork. When the hollow formwork is pulled out after the concrete has hardened, the cotter formwork peels off from the hollow formwork, and is then removed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-191320 [Patent Document 2] Japanese Patent Publication No. 2022-46053 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with the inner formwork described in Patent Document 1, there was a risk that the support of the cotter forming formwork by the air panels would become unstable. Also, with the inner formwork described in Patent Document 2, the cotter forming formwork tends to remain in the cotter (recess) even after the hollow formwork is removed, so in the case of a relatively long PCa member such as a pillar, it was difficult to remove the cotter formwork remaining in the center of the PCa member in the extension direction.

[0008] In view of the above background, the present invention aims to provide an inner formwork for forming a hollow portion in which a cotter is provided in a PCa member, which can stably support the portion in which the cotter is formed and can be easily removed. [Means for solving the problem]

[0009] In order to solve the above problem, one aspect of the present invention is an inner formwork (1) for forming a hollow portion (5) extending along a predetermined axial direction in a precast concrete member (3), the formwork comprising: a cylindrical cotter forming member (12) extending along the axial direction and having an outer surface with irregularities and an inner surface; a core member (13) inserted into the cotter forming member, extending along the axial direction and having an outer surface; and a slider (14) arranged between the inner surface of the cotter forming member and the outer surface of the core member, the slider including a plurality of rolling elements (18) that can roll on at least one of the inner surface of the cotter forming member and the outer surface of the core member, the portion on which the rolling elements roll on at least one of the inner surface of the cotter forming member and the outer surface of the core member extending parallel to the axial direction, and the inner surface of the cotter forming member being supported by the outer surface of the core member substantially only via the slider. Here, "substantially only through the slider" means that when the core member is moved axially relative to the cotter-forming member, no member that generates a frictional force greater than that of the slider is used. Furthermore, the terms "outer surface" and "inner surface" include not only flat surfaces but also curved surfaces, for example, the outer and inner peripheral surfaces of a cylinder.

[0010] According to this embodiment, the cotter forming member is supported by the core member 13 via the slider, so it remains stable even when subjected to pressure from the poured concrete. In addition, frictional force is reduced by the rolling elements, so the core member can be easily removed from the cotter forming member when demolding.

[0011] In the above aspect, the inner surface of the cotter forming member (12) and the outer surface of the core member (13) may form a polygon having the same number of angles in a cross section perpendicular to the axial direction, the opposing surfaces of the inner surface of the cotter forming member and the outer surface of the core member may be parallel to each other, and the slider (14) may abut against all planes on the inner surface of the cotter forming member and the outer surface of the core member that are bounded by the angles of the polygon.

[0012] According to this aspect, the inner surface of the cotter forming member and the outer surface of the core member face each other in parallel, so that the structure of the slider disposed therebetween can be made relatively simple.

[0013] In the above embodiment, the slider (14) may be fixed to the outer surface of the core member (13) and roll on the inner surface of the cotter-forming member (12).

[0014] According to this aspect, it becomes easier to insert the core member and slider into the cotter forming member when assembling the inner formwork, and it becomes easier to remove the cotter forming member when demolding compared to when the slider is fixed to the cotter forming member.

[0015] In the above aspect, the polygon may be a rectangle, and the core member (13) may include a square steel pipe.

[0016] According to this aspect, commercially available square steel pipes can be used as the core members, thereby reducing material costs. [Effects of the Invention]

[0017] According to the above aspect, it is possible to provide an inner formwork for forming a hollow portion in a PCa member in which a cotter is provided, which can stably support the portion in which the cotter is formed and can be easily removed. [Brief explanation of the drawings]

[0018] [Figure 1] A partial cross-sectional side view showing the state in which the inner formwork according to the embodiment is erected. [Figure 2] 1 is a cross-sectional view of the inner formwork taken along line II-II in FIG. 1; [Figure 3] FIG. 1 is a partial cross-sectional side view showing a manufacturing process of a PCa member using an inner formwork according to an embodiment (after concrete is poured, and the illustration of reinforcing bars is omitted). [Figure 4] 1 is a cross-sectional view showing a manufacturing process of a PCa member using an inner formwork according to an embodiment (the state in which the steel plate portion is being pulled out, and the illustration of the reinforcing bars is omitted). [Figure 5] 1 is a cross-sectional view showing a manufacturing process of a PCa member using an inner formwork according to an embodiment (the core member is being pulled out, and the reinforcing bars are not shown). DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a partial cross-sectional side view showing a state in which a formwork 2 including an inner formwork 1 according to an embodiment has been erected. Fig. 2 is a cross-sectional view of the inner formwork 1, and Figs. 3 to 5 are cross-sectional views showing a manufacturing process of a PCa member 3 using the inner formwork 1 (in Fig. 3, the inner formwork 1 is shown from the side).

[0020] As shown in FIG. 5, the PCa member 3 to be manufactured has a hollow portion 5 in which a cotter 4 is provided. The PCa member 3 is, for example, a member used to construct a pillar of a building. The PCa member 3 extends along a predetermined axial direction, but the axial direction of the PCa member 3 during manufacture may differ from the axial direction (vertical direction) when the PCa member 3 is installed in a building; in the illustrated example, it is horizontal. The hollow portion 5 extends along the axial direction and is open at both ends in the axial direction. The cotter 4 is a recess provided on the inner surface of the hollow portion 5, and multiple cotters 4 are provided spaced apart from each other in the axial direction, and each cotter 4 extends around the entire circumference in the circumferential direction relative to the axial direction. As shown in FIGS. 1 and 5, the PCa member 3 includes reinforcing bars 6 and a concrete portion 7.

[0021] As shown in FIG. 1, the formwork 2 includes an outer formwork 8 for defining the outer shape of the concrete section 7 (see FIG. 5) and an inner formwork 1 for defining the hollow section 5 (see FIG. 5). Note that in FIG. 1, only the outer formwork 8 is shown in vertical cross section, and the other members are shown in side view. The outer formwork 8 is, for example, a steel formwork in the shape of a rectangular parallelepiped box with the entire top surface open. The reinforcing bars 6 include main reinforcements 9 extending in the axial direction and hoops 10 extending circumferentially so as to intersect with the main reinforcements 9. One axial end of the main reinforcements 9 is joined to a mechanical joint 11 located within the outer formwork 8, and the other end protrudes from the outer formwork 8.

[0022] The inner formwork 1 comprises a cylindrical cotter forming member 12 that extends along the axial direction and has an outer surface with unevenness, a core member 13 that is inserted into the cotter forming member 12 and extends along the axial direction, and a plurality of sliders 14 that are arranged between the cotter forming member 12 and the core member 13.

[0023] The cotter-forming member 12 includes four sheathing plates 15 arranged to form a rectangular cylindrical shape and multiple protrusions 16 fixed to the outer surface of each sheathing plate 15. The sheathing plates 15 are flat and formed, for example, from steel plates. Two adjacent sheathing plates 15 are releasably connected. The multiple protrusions 16 are spaced apart from one another in the axial direction. Each protrusion 16 is arranged along the surface of the sheathing plate 15 in a direction perpendicular to the axial direction. Each protrusion 16 may extend across the entire width of the sheathing plate 15 or partially across the entire width. In the illustrated example, the protrusions 16 on different sheathing plates 15 are aligned circumferentially, but they do not need to be aligned. When the protrusions 16 extend to the middle of the width of each sheathing plate 15 as shown in the figure, the cotter 4 of the PCa member 3 is formed in a portion of the inner circumferential surface of the hollow portion 5 other than the corners. The ridges 16 are formed, for example, from a steel plate having a predetermined thickness. By fixing the ridges 16 to the surface of the flat sheathing 15, unevenness is formed on the outer surface of the cotter forming member 12. It is preferable that two cotter forming members 12 are provided adjacent to each other in the axial direction, and a core member 13 and a slider 14 are provided for each cotter forming member 12.

[0024] The core member 13 is a cylindrical or columnar member having a predetermined rigidity and is preferably made of steel, for example, a square steel pipe. The core member 13 is placed inside the cotter-forming member 12 so that the outer surface of the core member 13 is parallel to the inner surface of the opposing cotter-forming member 12.

[0025] One or more sliders 14 are fixed to each outer surface of the core member 13. Each slider 14 includes a base 17 fixed to the outer surface of the core member 13 and a plurality of rolling elements 18 rotatably supported on the base 17 and capable of rolling in the axial direction on the inner surface of the cotter forming member 12. The rolling elements 18 are configured as rollers that rotate around a rotation axis extending along the outer surface of the core member 13 in a direction perpendicular to the axial direction. The rolling elements 18 are spaced apart from one another in the axial direction, but it is preferable that many of them are provided close to one another. It is preferable that one or more sliders 14 provided on each outer surface of the core member 13 are arranged so as to cover substantially the entire outer surface of the core member 13. Note that the rolling elements 18 may be spheres instead of rollers, or a combination of rollers and spheres may be used.

[0026] The entire inner surface of the cotter-forming member 12 is spaced apart from the outer surface of the core member 13, and the cotter-forming member 12 is supported by the core member 13 substantially only via the slider 14. For this reason, the greatest resistance when the core member 13 is displaced axially relative to the cotter-forming member 12 is the frictional force between the rolling elements 18 and the cotter-forming member 12.

[0027] The cotter-forming member 12, on whose inner surface the rolling elements 18 roll, may have a polygonal cylindrical shape other than a rectangle. Furthermore, when only spheres are used as the rolling elements 18, the portion of the cotter-forming member 12 on which the rolling elements 18 roll is parallel to the axial direction, but may also be curved in the circumferential direction. The shape of the outer surface of the core member 13, to which the mount 17 is fixed on its outer surface, is not limited as long as the slider 14 is positioned so that the rolling elements 18 can roll on the inner surface of the cotter-forming member 12, and the outer shape of the core member 13 in a cross section perpendicular to the axial direction may be a shape other than a rectangle.

[0028] The slider 14 may be fixed to the inner surface of the cotter-forming member 12 and roll on the outer surface of the core member 13, or it may be unfixed to the cotter-forming member 12 or the core member 13 and roll on both. The inner surface of the cotter-forming member 12 and the outer surface of the core member 13 on which the rolling elements 18 roll must be parallel to the axial direction. When the slider 14 is fixed to the inner surface of the cotter-forming member 12, the shape of the inner surface of the cotter-forming member 12 is not limited as long as the slider 14 is positioned so that the rolling elements 18 can roll on the outer surface of the core member 13; for example, the cotter-forming member 12 may be cylindrical.

[0029] A method for manufacturing the PCa member 3 using the inner formwork 1 will be described.

[0030] As shown in Figure 1, workers assemble the reinforcing bars 6, place the inner form 1, with the core member 13 and slider 14 inserted into the cotter forming member 12, inside the cylindrical assembly of the reinforcing bars 6, and assemble the outer form 8. The inner form 1 may be inserted into the assembly of the reinforcing bars 6 from the axial direction, or may be inserted from above before attaching the upper parts of the ties 10 to the main reinforcement 9, and then the upper parts of the ties 10 may be attached to the main reinforcement 9.

[0031] Next, as shown in FIG. 3, workers pour concrete into the outer form 8 so that the inner form 1 is buried.

[0032] Next, when the concrete portion 7 has hardened to the extent that it can be removed from the form, the worker removes the outer formwork 8 and rolls the rolling elements 18 to pull out the core member 13 from the cotter-forming member 12, as shown in FIG.

[0033] Next, as shown in Figure 5, the worker releases the connections between the sheathing boards 15 in the cotter forming member 12 and removes each sheathing board 15 from the hollow portion 5 of the PCa member 3. Because the protrusions 16 are fixed to the sheathing boards 15, they are removed from the hollow portion 5 together with the sheathing boards 15.

[0034] The function and effect of the inner formwork 1 will be described.

[0035] Because the rolling elements 18 reduce friction, the core member 13 can be easily pulled out from within the cotter forming member 12, even after the concrete has been poured. Furthermore, because the cotter forming member 12 is supported by the core member 13 via the slider 14, the core member 13 can stably support the cotter forming member 12 against the pressure of the poured concrete.

[0036] Material costs can be reduced because a commercially available steel pipe can be used as the core member 13. In addition, the cotter forming member 12 can be easily produced by processing a commercially available steel plate or the like.

[0037] Since the inner surface of the cotter forming member 12 and the outer surface of the core member 13 are parallel to each other, the slider 14 can have a relatively simple structure.

[0038] By fixing the slider 14 to the core member 13, it becomes easier to insert the core member 13 and the slider 14 into the cotter-forming member 12 when assembling the inner form 1. In addition, it becomes easier to remove the cotter-forming member 12 when demolding compared to when the slider 14 is fixed to the cotter-forming member 12.

[0039] Although the description of the specific embodiment has been completed above, the present invention is not limited to the above embodiment and its modifications, and can be implemented in a wide variety of modifications. The PCa member 3 may be a part of an architectural or civil engineering structure other than a column, such as a beam. The core member 13 may be removed by pushing it out from the opposite side instead of by pulling it out. [Explanation of symbols]

[0040] 1: Inner formwork 3: PCa (precast concrete) members 4: Cotter 5: Hollow part 12: Cotter forming member 13: Core member 14: Slider 18: Rolling element

Claims

1. An inner form for forming a hollow portion extending along a predetermined axial direction in a precast concrete member, a cylindrical cotter forming member extending along the axial direction and having an outer surface and an inner surface with irregularities; a core member inserted within the cotter-forming member, extending along the axial direction, and having an outer surface; a slider disposed between an inner surface of the cotter forming member and the outer surface of the core member, the slider including a plurality of rolling elements capable of rolling on at least one of the inner surface of the cotter forming member and the outer surface of the core member; a portion of at least one of the inner surface of the cotter forming member and the outer surface of the core member on which the rolling elements roll extends parallel to the axial direction; An inner form, wherein the inner surface of the cotter-forming member is supported on the outer surface of the core member substantially only via the slider.

2. the inner surface of the cotter-forming member and the outer surface of the core member form polygons having the same number of angles in a cross section perpendicular to the axial direction, the inner surface of the cotter-forming member and the outer surface of the core member facing each other are parallel to each other; The inner form according to claim 1 , wherein the slider abuts against all flat surfaces bounded by corners of the polygon on the inner surface of the cotter-forming member and the outer surface of the core member.

3. The inner form according to claim 2 , wherein the slider is fixed to the outer surface of the core member and rolls on the inner surface of the cotter-forming member.

4. the polygon is a quadrilateral, The inner formwork according to claim 3 , wherein the core member comprises a square steel pipe.

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