Shear reinforcement method and shear reinforcement structure

Abstract

To provide a shear reinforcement method and a shear reinforcement structure which enable efficient arrangement of shear reinforcements for suppressing enlargement of a crack width.SOLUTION: A flat slab 20 is composed of reinforced concrete having upper end reinforcements 21 and lower end reinforcements 22, and extends in a horizontal direction. The flat slab 20 includes engagement parts 31a engaged with the upper end reinforcements 21, reinforcement parts 31b extending to the vicinity of the lower end reinforcements 22 from the engagement parts 31a, and a plurality of shear reinforcements 30 having fixing plates 32 provided on the lower ends of the reinforcement parts 31b. The engagement parts 31a of the shear reinforcements 30 are engaged with the upper end reinforcements 21, the shear reinforcements 30 are suspended from the upper end reinforcements 21, then concrete is placed in a non-engagement state of the reinforcement parts 31b of the shear reinforcements 30 and the fixing plates 32, and thereby the flat slab 20 is constructed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a shear reinforcement method and a shear reinforcement structure for suppressing the expansion of shear crack width that occurs in horizontal members extending in the horizontal direction, such as cross members such as beams and flat slabs. [Background technology]

[0002] Traditionally, flat slabs have been designed to prevent punching shear failure, and for long-term or short-term loads, they are often designed to prevent excessive cracking by suppressing the expansion of crack width even if shear cracks occur.

[0003] Therefore, in order to suppress the width of cracks caused by punching shear, a large number of shear reinforcement bars are provided in flat slabs (see, for example, Patent Document 1). In this document, a first column shear reinforcement area is formed in a flat plate with a first predetermined length dimension, and slab reinforcement bars with higher rigidity than the surrounding slab reinforcement bars are arranged. Furthermore, a second shear reinforcement area is formed with a second predetermined length dimension from the boundary of the first shear reinforcement area. In this case, in the shear reinforcement area, the upper flat part of the shear reinforcement bar is hooked to the upper end reinforcement of the high-rigidity slab reinforcement bar, and the lower hook part of the shear reinforcement bar is hooked to the lower end reinforcement of the high-rigidity slab reinforcement bar.

[0004] FIG. 9 shows two specific examples of shear reinforcement bars used in a conventional flat slab 90. The left side of FIG. 9 shows a shear reinforcement bar 95 whose upper and lower ends are bent at 180°. The upper and lower ends of this shear reinforcement bar 95 are hooked to upper end reinforcement bars 91 and lower end reinforcement bars 92 of the flat slab 90, respectively. The right side of FIG. 9 shows a shear reinforcement bar 96 with head bars fixed to both sides of the reinforcing bar. Each head bar of this shear reinforcement bar 96 is hooked to upper end reinforcement bars 91 and lower end reinforcement bars 92 of the flat slab 90, respectively. This makes it possible to suppress the expansion of cracks C9 even if they occur in the flat slab 90. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-208576 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the task of hooking the shear reinforcement bars onto the upper and lower end reinforcements of the flat slab is time-consuming and difficult, making the method difficult to install. [Means for solving the problem]

[0007] The shear reinforcement method for solving the above problem is a shear reinforcement method for reinforcing a horizontal member that is made of reinforced concrete with an upper reinforcing bar arranged at the top and a lower reinforcing bar arranged at the bottom and extends in the horizontal direction, using a shear reinforcement bar. The shear reinforcement bar has a hook part that hooks onto the upper reinforcing bar and a reinforcing part that extends from the hook part to the vicinity of the lower reinforcing bar while the hook part hooks onto the upper reinforcing bar. After the hook part of the shear reinforcement bar is hooked onto the upper reinforcing bar to hang the reinforcing part, concrete is poured while the reinforcing part is not hooked onto the lower reinforcing bar. Here, the horizontal member is not limited to a flat slab, and may be any member that extends in the horizontal direction, such as a beam or a floor. In addition, extending to the vicinity of the lower reinforcing bar may be a length that reaches the lower reinforcing bar, or may be a length that does not reach the lower reinforcing bar, as long as it extends to a length that can suppress the width of cracks in the horizontal member. Effect of the Invention

[0008] According to the present invention, it is possible to efficiently arrange shear reinforcement bars that suppress the expansion of crack width. [Brief description of the drawings]

[0009] [Figure 1] FIG. 3 is a cross-sectional view of a flat slab using a shear reinforcement structure according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of a flat slab using a shear reinforcement structure according to an embodiment. [Diagram 3] Cross-sectional view of a key part of a flat slab using a shear reinforcement structure in the first modified example. [Figure 4] Cross-sectional view of a key part of a flat slab using a shear reinforcement structure in the second modified example. [Diagram 5] Cross-sectional view of a key part of a flat slab using a shear reinforcement structure in the third modified example. [Figure 6] Cross-sectional view of a key part of a flat slab using a shear reinforcement structure in the fourth modified example. [Figure 7] Cross-sectional view of a key part of a beam using a shear reinforcement structure in a fifth modified example. [Figure 8] FIG. 13 is a perspective view of a reinforcing bar cage constituting a beam using a shear reinforcement structure in a fifth modified example. [Figure 9] FIG. 1 is a cross-sectional view of a flat slab illustrating a conventional shear reinforcement structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of a shear reinforcement method and a shear reinforcement structure will be described with reference to Figures 1 and 2. In this embodiment, a shear reinforcement method and a shear reinforcement structure that suppress the width of cracks caused by punching shear in a flat slab will be described.

[0011] As shown in FIG. 1, a flat slab 20 is provided around a column 15 as a horizontal member. The column 15 and the flat slab 20 are made of reinforced concrete. Specifically, the flat slab 20 includes a plurality of upper end reinforcements 21, lower end reinforcements 22, and shear reinforcement bars 30. The upper end reinforcements 21 are upper reinforcing bars arranged in a lattice pattern on the upper part of the flat slab 20, and the lower end reinforcements 22 are lower reinforcing bars arranged in a lattice pattern on the lower part of the flat slab 20. The upper end reinforcements 21, lower end reinforcements 22, and shear reinforcement bars 30 are embedded in concrete 25 to form the flat slab 20 extending in a plane.

[0012] The shear reinforcement 30 includes a central hook 31a, two reinforcing parts 31b connected to both ends of the hook 31a and extending downward, and an anchoring plate 32 provided at the lower end of each reinforcing part 31b. In this embodiment, one reinforcing bar 31 is bent into a U-shape to form the hook 31a and the reinforcing parts 31b. The hook 31a has a length corresponding to the spacing of the lattice of the upper end reinforcing bar 21. The reinforcing part 31b extends from the upper end reinforcing bar 21 to the vicinity of the lower end reinforcing bar 22 (a position several millimeters above the upper surface of the lower end reinforcing bar 22) so that the crack C1 does not expand when it occurs. The anchoring plate 32 is made of metal or the like, and is an anchoring part that anchors the reinforcing bar 31 of the shear reinforcement 30 into the concrete 25.

[0013] (Flat slab construction method) Next, a method for constructing the flat slab 20 using the above-mentioned shear reinforcement structure will be described.

[0014] As shown in Figure 2, the bottom end bars 22 of the flat slab 20 are arranged in a lattice pattern around the columns 15, and the intersections are fastened. Then, above the bottom end bars 22, the top end bars 21 are arranged in a lattice pattern, spaced apart from the bottom end bars 22, and the intersections are fastened.

[0015] Next, multiple shear reinforcement bars 30 are suspended from the upper end bars 21 of the flat slab 20. In this case, as shown in Fig. 1, the hooking portion 31a of the shear reinforcement 30 is lowered from above so as to hook onto two adjacent upper end reinforcements 21. The fixing plate 32 of the shear reinforcement 30 is placed above the lower end reinforcements 22 by several mm.

[0016] As shown in Fig. 2, the shear reinforcement bars 30 are arranged at appropriate intervals in the shear reinforcement area around the column 15. Here, the shear reinforcement area is, for example, an area where cracks C1 (Fig. 1) may occur. The extending direction of the hook portions 31a of the shear reinforcement bars 30 is arbitrary. Then, as described above, after the upper end reinforcement 21, the lower end reinforcement 22, and the shear reinforcement 30 are arranged, concrete is poured. With the above steps, the flat slab 20 is completed.

[0017] (action) The flat slab 20 is constructed by hanging the shear reinforcement 30 from the upper end reinforcement 21 of the flat slab 20 and pouring concrete with the anchor plate 32 at the lower end of the shear reinforcement 30 in the unhung state. In this case, the reinforcing part 31b of the shear reinforcement 30 is arranged from the upper end reinforcement 21 to the vicinity of the lower end reinforcement 22. This makes it possible to suppress the expansion of cracks even if the lower end of the shear reinforcement 30 is not hooked onto the lower end reinforcement 22 of the flat slab 20.

[0018] According to this embodiment, the following effects can be obtained. (1) In this embodiment, the hanging portion 31a of the shear reinforcement 30 is hooked onto the upper end reinforcement 21 of the flat slab 20 to place the shear reinforcement 30. This reduces the workload of placing the shear reinforcement 30, since the lower portion of the shear reinforcement 30 is not fixed to the lower end reinforcement 22 of the flat slab 20.

[0019] (2) Each reinforcing portion 31b of the shear reinforcement 30 in this embodiment extends from the upper end reinforcement 21 to the vicinity of the lower end reinforcement 22. This makes it possible to suppress the crack C1 from expanding even if it occurs. In the design method in the RC Standards of the Japan Society of Mechanical Engineers, the strength of a flat slab is determined only by the cross-sectional thickness of the flat slab and the concrete strength, and the fixing of the lower end reinforcement 22 of the shear reinforcement 30 is not taken into consideration in the ultimate design of the flat slab 20. Therefore, even if the shear reinforcement 30 is not fixed to the lower end reinforcement 22, the strength of the flat slab can be maintained as in the conventional case, as long as the cross-sectional thickness of the flat slab and the concrete strength are ensured.

[0020] (3) The shear reinforcement 30 of this embodiment includes a hook portion 31a that hooks onto the two upper end reinforcements 21, and the hook portion 31a has a length corresponding to the two upper end reinforcements 21. This makes it possible to suppress the swaying and displacement of the shear reinforcement 30 even when concrete is poured into the flat slab 20.

[0021] (4) The shear reinforcement 30 of this embodiment has a U-shape, which allows the two reinforcing parts 31b to be efficiently arranged in one operation. (5) In the present embodiment, the hanging portion 31a and the reinforcing portion 31b of the shear reinforcement bar 30 are formed from a single steel bar, so that the shear reinforcement bar 30 can be realized with a simple structure.

[0022] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction. In the above embodiment, the length of the reinforcing portion 31b of the shear reinforcement 30 is determined so that the anchor plate 32 is positioned several millimeters above the bottom end reinforcement 22 when the shear reinforcement 30 is suspended from the top end reinforcement 21 of the flat slab 20. The length of the reinforcing portion 31b of the shear reinforcement 30 is not limited to this as long as it is a length that can suppress the width of cracks in the horizontal member.

[0023] For example, as shown in FIG. 3, a shear reinforcement 35 may be used in which the reinforcing portion 36b extends to the bottom end bar 22 of the flat slab 40. The shear reinforcement 35 includes a central hanging portion 36a, reinforcing portions 36b connected to both ends of the hanging portion 36a, and an anchor plate 32 provided at the bottom end of the reinforcing portion 36b. The hanging portion 36a and the two reinforcing portions 36b are composed of one reinforcing bar 36. Furthermore, the shear reinforcement 35 may have a shape in which the distance between the two reinforcing portions 36b increases downward. This allows the shear reinforcement 35 to be arranged efficiently. Furthermore, the reinforcing portion of the shear reinforcement bar need only be in a non-hooked state relative to the lower reinforcing bar, and may be temporarily attached to another member when the concrete is poured, for example.

[0024] In the above embodiment, the hook portion 31a of the shear reinforcement 30 is hooked to two adjacent upper end reinforcements 21. As long as the hook portion of the shear reinforcement can be hooked to the upper end reinforcement 21, it is not limited to a structure in which it is hooked to two adjacent upper end reinforcements.

[0025] For example, as shown in Fig. 4, the length of the hanging portion 38a of the shear reinforcement bar 37 embedded in the flat slab 41 is set to a length that spans three upper end bars 21. The shear reinforcement bar 37 may be configured such that the hanging portion 38a is brought into contact with the three upper end bars 21, and then the reinforcing portion 38b connected to the hanging portion 38a extends downward. Here, the hanging portion 38a and the two reinforcing portions 38b connected thereto are composed of one reinforcing bar 38.

[0026] The shear reinforcement bar 30 in the above embodiment has two reinforcing portions 31b. The number of reinforcing portions of the shear reinforcement bar 30 is not limited to two. For example, as shown in Fig. 5, a flat slab 42 may be used that uses a shear reinforcement 50 having only one reinforcing portion 51b. This shear reinforcement 50 has a reinforcing portion 51b that is connected only to one end of a substantially flat hanging portion 51a. The hanging portion 51a and one reinforcing portion 51b of the shear reinforcement are composed of one reinforcing bar 51. Furthermore, the shear reinforcement has an anchoring plate 52 provided at the lower end of the reinforcing portion 51b.

[0027] In the above embodiment, the shear reinforcement 30 has an anchoring plate 32 at each of the lower ends of the two reinforcing parts 31b. The anchoring parts for fixing the reinforcing parts of the shear reinforcement are not limited to anchoring plates as long as they are provided at the lower ends of the reinforcing parts.

[0028] For example, as shown in FIG. 6, instead of the anchor plate, the anchoring portion may be formed of a reinforcing bar having a length equal to or greater than the bent anchoring length. In this case, a shear reinforcement bar 55 formed of a single reinforcing bar may be used in the flat slab 43. This shear reinforcement bar 55 includes a central hook portion 55a, reinforcing portions 55b connected to both sides of the hook portion 55a, and anchoring portions 55c connected to each reinforcing portion 55b. The reinforcing portion 55b has a length extending from the upper end reinforcing bar 21 to the vicinity of the lower end reinforcing bar 22 when the hook portion 55a hooks onto the upper end reinforcing bar 21, similar to the reinforcing portion 31b. The anchoring portion 55c extends in the extension direction of the surface of the flat slab 43 by a length equal to or greater than the anchoring length. Furthermore, in the case where the reinforcing portion is structured such that it is difficult for the reinforcing portion to come out of the concrete, the anchoring portion may be omitted.

[0029] The hanging portion 31a and the reinforcing portion 31b of the shear reinforcement 30 in the above embodiment are U-shaped with a flat center. The hanging portion and the reinforcing portion of the shear reinforcement are not limited to this shape, and may be, for example, a shear reinforcement having an arc-shaped hanging portion as long as it can be embedded in the concrete 25 of the flat slab 43. Also, although the hanging portion 31a and the reinforcing portion 31b of the shear reinforcement 30 are made of a single reinforcing bar, they may be made of different members.

[0030] In the above embodiment, the flat slab 20 is provided with the shear reinforcement 30. The structure of the shear reinforcement of the present invention is not limited to flat slabs, but may be any horizontal member extending in the horizontal direction, and may be applied to, for example, normal floors and beams.

[0031] FIG. 7 shows a vertical cross section of a beam 70, and FIG. 8 shows the structure of reinforcing bars embedded in concrete 75 of the beam 70. As shown in FIG. 7, a beam 70 serving as a horizontal member is formed by embedding a reinforcing bar cage 71 in concrete 75 .

[0032] As shown in FIG. 8, the reinforcing bar cage 71 includes a plurality of main reinforcements 72 and a plurality of tie bars 73 arranged in parallel with a space therebetween. The tie bars 73 surround the outer periphery of the main reinforcements 72 in an annular shape. A plurality of shear reinforcements 80 are arranged on the main reinforcements 72 arranged at the upper part of the reinforcing bar cage 71. The shear reinforcements 80 include a hook portion 81a, reinforcing portions 81b provided on both sides of the hook portion 81a, and fixing plates 82 provided at the lower end of each reinforcing portion 81b. The hook portion 81a and the two reinforcing portions 81b are configured in a substantially U-shape with one reinforcing bar 81. The reinforcing portions 81b have a length that extends from the main reinforcements 72 arranged at the upper part to the vicinity of the main reinforcements 72 arranged at the lower part when the hook portion 81a hooks on the upper main reinforcements 72 according to the spacing between the main reinforcements 72 in the vertical direction. When placing the reinforcing bar cage 71, the shear reinforcement bars 80 are lowered from above onto the main reinforcements 72 at the top of the reinforcing bar cage 71, and the hanging portions 81a of the shear reinforcement bars 80 are hooked onto and suspended by two adjacent main reinforcements 72. Thereafter, concrete is poured into the reinforcing bar group in which the shear reinforcement bars 80 are placed in the reinforcing bar cage 71 to construct the beam 70. In this case, the shear reinforcement 80 is hooked onto the main reinforcement 72 placed on the upper part of the reinforcing bar cage 71, but if there is no need to increase the cover thickness of the concrete 75 of the beam 70, the shear reinforcement 80 may be arranged by hooking it onto the tie bars 73 of the reinforcing bar cage 71.

[0033] Next, the technical ideas that can be understood from the above embodiment and other examples will be described below. (a) The shear reinforcement structure according to claim 2, characterized in that the hanging portion of the shear reinforcement bar is hung on two of the upper reinforcing bars. (b) the shear reinforcement has two reinforcement parts connected to both sides of the hanging part; The shear reinforcement structure described in (a) above, characterized in that the two reinforcing parts and the hanging part are formed by bending a single reinforcing bar. (c) the horizontal member is a flat slab; A shear reinforcement structure as described in (a) or (b), characterized in that the hanging portion has a length corresponding to the spacing of the lattice of the upper end reinforcement of the flat slab. [Explanation of symbols]

[0034] 15...column, 20,40,41,42,43...flat slab as horizontal member, 21...upper end bar as upper reinforcing bar, 22...lower end bar as lower reinforcing bar, 25,75...concrete, 30,35,37,50,55,80...shear reinforcement, 31,36,38,51,81...reinforcing bar, 31a,36a,38a,51a,55a,81a...hanging part, 31b,36b,38b,51b,55b,81b...reinforcement part, 32,52,82...anchoring plate as anchoring part, 55c...anchoring part, 70...beam, 71...reinforcing bar cage, 72...main bar, 73...hoop.

Claims

1. A shear reinforcement method for reinforcing a horizontally extending flat slab made of reinforced concrete with an upper reinforcing bar placed at the top and a lower reinforcing bar placed at the bottom, using a shear reinforcement bar, The shear reinforcement is A hook portion that hooks onto the upper reinforcing bar; A reinforcing portion extending from the hanging portion to a position near the lower reinforcing bar and above the lower reinforcing bar when the hanging portion is hung on the upper reinforcing bar, After the hanging portion of the shear reinforcement is hung on the upper reinforcing bar, the reinforcing portion is suspended, A shear reinforcement method characterized in that concrete is poured in an unhung state in which the reinforcing portion is not closed to the lower reinforcing bar.

2. In a shear reinforcement structure, a flat slab extending horizontally and made of reinforced concrete with an upper reinforcing bar placed at the top and a lower reinforcing bar placed at the bottom is reinforced with shear reinforcement. The shear reinforcement is A hook portion that hooks onto the upper reinforcing bar; A reinforcing portion extending from the hanging portion to a position near the lower reinforcing bar and above the lower reinforcing bar when the hanging portion is hung on the upper reinforcing bar, A shear reinforcement structure characterized in that the shear reinforcement is embedded in concrete in a suspended state by hanging the hanging portion of the shear reinforcement on the upper reinforcing bar, and in an unhanging state in which the reinforcing portion is not closed to the lower reinforcing bar.

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