Reinforced concrete member, method for constructing reinforced concrete member, and reinforcement support used in this construction method.

Abstract

This reduces the width of cracks caused by in-plane shear forces in reinforced concrete slabs. [Solution] A reinforced concrete member constituting a slab or wall of a reinforced concrete structure, comprising: a first grid reinforcement consisting of a plurality of reinforcing bars extending in two orthogonal directions in a plane; a second grid reinforcement consisting of a plurality of reinforcing bars extending in the two orthogonal directions in a plane spaced apart from the first grid reinforcement in the thickness direction of the reinforced concrete member; and an oblique grid reinforcement consisting of a plurality of reinforcing bars that are inclined with respect to the reinforcing bars of the first and second grid reinforcement and extend in two mutually orthogonal directions in the plane between the first and second grid reinforcement, wherein the reinforcing bars constituting the oblique grid reinforcement are anchored to another reinforced concrete member joined to the slab or wall, or are anchored inside the reinforced concrete member near the periphery of the slab or wall.

Description

Technical Field

[0001] The present invention relates to a reinforced concrete member constituting a slab or a wall of a reinforced concrete structure, a construction method of the reinforced concrete member, and a reinforcing tool used in this construction method.

Background Art

[0002] Large in-plane shear forces may act on the slab of a reinforced concrete structure during an earthquake. FIGS. 1 and 2 show typical examples where large in-plane shear forces act on the slab. FIG. 1 shows a structure where, when rebuilding an existing building, the underground part uses the existing underground structure 1 as it is, and the above-ground part is newly built with a setback from the underground structure 1. FIG. (a) of the same figure is a cross-sectional view, and (b) is a perspective view of an enlarged part A of FIG. (a).

[0003] In the structure shown in FIG. 1, the upper and lower seismic elements (the upper seismic wall 2a and the lower basement seismic wall 1a) of the slab 3 on the first floor of the newly built building 2 are discontinuous. Therefore, when a shear force F due to an earthquake acts on the newly built building 2, this shear force F is transmitted to the underground structure 1 through the slab 3, and thus a large in-plane shear force acts on the slab 3.

[0004] FIG. 2 is a plan view of a structure 5 with a complicated planar shape of the underground outer wall, where the shape changes discontinuously at the connection between the underground part 6 of building A and the underground part 7 of building B. Since the structures of buildings A and B are different and their behaviors during an earthquake are also different, when a shear force F acts on the underground part 6 of building A, a large in-plane shear force acts on the slab 8 provided at the connection with the underground part 7 of building B.

[0005] Regarding the design of slabs subjected to such large in-plane shear forces, Non-Patent Document 1 states that, when applying the rigid floor assumption, it is desirable to keep the shear stress below the short-term allowable shear stress of the concrete used to prevent shear cracking in the slab. Conventionally, it has been common practice to design slabs according to the standards described in Non-Patent Document 1. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Architectural Institute of Japan, "Calculation Standards and Commentary for Reinforced Concrete Structures 2018," pp. 281-282, "4. Design for Shear Forces on Slabs," December 5, 2018, 9th edition, 1st printing. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, conventional designs that keep the shear stress below the short-term allowable shear stress of concrete have the problem that the slab thickness can become very large, for example, exceeding 1 meter.

[0008] On the other hand, in actual reinforced concrete buildings, while minute cracks in the slab may be acceptable, wide cracks are generally not tolerated from the standpoint of appearance and durability.

[0009] This invention has been made in view of the above points, and aims to rationalize the design and construction of reinforced concrete members by allowing the occurrence of cracks while keeping the crack width small when a large in-plane shear force acts on a planar reinforced concrete member, such as a slab or wall that constitutes a reinforced concrete structure. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a reinforced concrete member constituting a slab or wall of a reinforced concrete structure, comprising: a first grid reinforcement consisting of a plurality of reinforcing bars extending in two orthogonal directions in a plane; a second grid reinforcement consisting of a plurality of reinforcing bars extending in the two orthogonal directions in a plane spaced apart from the first grid reinforcement in the thickness direction of the reinforced concrete member; and an oblique grid reinforcement consisting of a plurality of reinforcing bars extending in two mutually orthogonal directions, inclined with respect to the reinforcing bars of the first and second grid reinforcement and in a plane between the first and second grid reinforcement, wherein the reinforcing bars constituting the oblique grid reinforcement are anchored to another reinforced concrete member joined to the slab or wall, or are anchored inside the reinforced concrete member near the periphery of the slab or wall.

[0011] According to the present invention, since the diagonal grid reinforcement bars are provided in a direction inclined with respect to the first and second grid reinforcement bars, the diagonal grid reinforcement bars are present in a direction that crosses the cracks that occur when an in-plane shear force acts on a concrete structure. The ends of the diagonal grid reinforcement bars are anchored inside other reinforced concrete members joined to the reinforced concrete member or inside the reinforced concrete member itself, so the diagonal grid reinforcement bars crossing the crack resist the tensile force that would widen the crack and transmit the force between the concrete on both sides of the crack. This suppresses the widening of the crack and keeps the crack width small.

[0012] The tensile force transmitted to the diagonal grid reinforcement is then transmitted to other parts of the reinforced concrete member, causing further cracks. The diagonal grid reinforcement crossing these cracks prevents them from widening, and further causes other cracks to form. This process is repeated, resulting in the formation of numerous small cracks. Thus, according to the present invention, the diagonal grid reinforcement allows for the dispersion of cracks, and the width of each crack can be kept small.

[0013] In the present invention, the diagonal grid reinforcement bars may be provided at a central position between the first grid reinforcement bars and the second grid reinforcement bars. Furthermore, the reinforcing bars constituting the diagonal grid reinforcement may be inclined at an angle of 45° with respect to the reinforcing bars constituting the first grid reinforcement and the second grid reinforcement. Furthermore, the reinforced concrete member may constitute a slab, and the other members may constitute beams.

[0014] Furthermore, the present invention relates to a method for constructing the above-mentioned reinforced concrete member, wherein the reinforced concrete member constitutes a slab, the first grid reinforcement is a lower reinforcement, and the second grid reinforcement is an upper reinforcement, and comprises: a first step of supporting the first grid reinforcement at a predetermined height; a second step of temporarily placing the diagonal grid reinforcement on the first grid reinforcement; a third step of supporting the second grid reinforcement at a predetermined height; and a third step of supporting the diagonal grid reinforcement at a predetermined height by hooking one hook portion of a reinforcement support device, which has hook portions at both ends, onto the second grid reinforcement and hooking the diagonal grid reinforcement onto the other hook portion.

[0015] According to the present invention, since the diagonal grid reinforcement is supported by reinforcement support devices hooked onto the upper reinforcement bars, the reinforcement support frame only needs to be provided for the upper reinforcement bars, thereby eliminating the complexity of arranging the reinforcement support frame.

[0016] In this method for constructing a reinforced concrete member, the reinforcing bar support is adjustable in overall length, and the one hook portion and the other hook portion are rotatable relative to each other around the length of the reinforcing bar support. The third step may further include adjusting the relative angle of the hook portions around the axis so that each hook portion is oriented according to the orientation of the reinforcing bar hooked onto each hook portion, and so that the height of the diagonal grid reinforcing bar hooked onto the other hook portion remains constant, as well as adjusting the length of the reinforcing bar support.

[0017] By doing so, since the relative angle around the longitudinal direction between one hook portion and the other hook portion can be adjusted, the diagonal lattice reinforcing bars in a direction different from that of the upper end bars can be surely supported by the reinforcing bar support hooked on the upper end bars. Further, since the entire length of the reinforcing bar support can be adjusted, the diagonal lattice reinforcing bars can be supported at a constant height regardless of whether the reinforcing bar support is hooked on any reinforcing bars above or below the upper end bars and the diagonal lattice reinforcing bars.

[0018] In this case, the reinforcing bar support may be configured to include a nut member and first and second hook portions respectively screwed into both ends of the nut member. The present invention also includes a reinforcing bar support used in the method for manufacturing the above concrete member.

Effects of the Invention

[0019] According to the present invention, when a large in-plane shear force acts on a planar reinforced concrete member which is a slab or a wall constituting a concrete structure, by allowing the occurrence of cracks while suppressing the crack width to be small, rationalization in the design and construction of the reinforced concrete member can be achieved.

Brief Description of the Drawings

[0020] [Figure 1] A typical first example in which a large in-plane shear force acts on a slab is shown, where (a) is a vertical sectional view and (b) is a perspective view of part A in (a). [Figure 2] A typical second example in which a large in-plane shear force acts on a slab is shown. [Figure 3] It is a vertical sectional view of a slab which is an embodiment of the present invention. [Figure 4] It is an enlarged view of part IV in FIG. 3. [Figure 5] It is a plan view of the location shown in FIG. 4. [Figure 6] It is a diagram for explaining that the crack width due to the in-plane shear force can be reduced by providing diagonal lattice reinforcing bars. [Figure 7]This figure shows the test specimen used in the effectiveness verification experiment of this embodiment. (a) is a plan view of a test specimen without diagonal grid reinforcement as a comparative example, and (b) is a plan view of a test specimen with diagonal grid reinforcement as an example. [Figure 8] This figure shows the relationship between the deformation angle (horizontal axis) and the horizontal load (vertical axis) when an alternating load is applied to a comparative example specimen. [Figure 9] This figure shows the relationship between the deformation angle (horizontal axis) and the horizontal load (vertical axis) when an alternating load is applied to the test specimen of the example. [Figure 10] This figure shows the distribution of crack widths that occurred in the comparative example specimen after the effectiveness verification experiment was completed. [Figure 11] This figure shows the distribution of crack widths that occurred in the test specimens used in the example after the effectiveness verification experiment was completed. [Figure 12] This diagram shows a disassembled view of the reinforcing bar support used when installing diagonal grid reinforcing bars in the slab construction method of this embodiment. [Figure 13] This figure shows the slab construction steps (a) to (f) in this embodiment. [Modes for carrying out the invention]

[0021] Figure 3 is a vertical cross-sectional view of a reinforced concrete slab 10 and beam 12, which is one embodiment of the present invention. Figure 4 is an enlarged view of section IV in Figure 3, and Figure 5 is a plan view of the same section shown in Figure 4. The slab 10 constitutes the floor of the reinforced concrete structure.

[0022] The slab 10 is rectangular in shape and is joined to the beam 12 around its perimeter. Inside the slab 10 are bottom reinforcement bars 14, top reinforcement bars 16, and diagonal grid reinforcement bars 18. The bottom reinforcement bars 14 are located on the lower side of the slab 10 in the thickness direction, in a plane parallel to the surface of the slab 10. The top reinforcement bars 16 are located on the upper side of the slab 10 in the thickness direction, in a plane parallel to the surface of the slab 10. The diagonal grid reinforcement bars 18 are located in the plane between the bottom reinforcement bars 14 and the top reinforcement bars 16. The lower reinforcement bar 14 corresponds to the first grid reinforcement of the present invention, and the upper reinforcement bar 16 corresponds to the second grid reinforcement of the present invention.

[0023] The lower reinforcement bars 14 are a grid-like reinforcement made up of multiple upper lower reinforcement bars 14a that extend parallel to each other at predetermined intervals in the direction of one side of the slab 10 (left-right direction in Figure 4), and multiple lower reinforcement bars 14b that extend parallel to each other at predetermined intervals, perpendicular to the upper lower reinforcement bars 14a.

[0024] The upper reinforcement bars 16 are a grid-like structure of reinforcing bars formed by combining a plurality of upper upper reinforcement bars 16a that extend parallel to each other at predetermined intervals in the direction of one side of the slab 10 (the depth direction of the paper in Figure 4), and a plurality of lower upper reinforcement bars 16b that extend parallel to each other at predetermined intervals, perpendicular to the upper upper reinforcement bars 16a.

[0025] The diagonal grid reinforcement bars 18 are arranged in a grid pattern in Figure 5, extending from the upper right to the lower left, and consist of multiple upper diagonal reinforcement bars 18a that extend parallel to each other at predetermined intervals, and multiple lower diagonal reinforcement bars 18b that are perpendicular to the upper diagonal reinforcement bars 18a and extend parallel to each other at predetermined intervals. Therefore, the upper diagonal reinforcement bars 18a and lower diagonal reinforcement bars 18b that make up the diagonal grid reinforcement bars 18 are arranged in a direction roughly diagonal to the slab 10.

[0026] The diagonal grid reinforcement bars 18 are provided in a plane located between the lower reinforcement bars 14 and the upper reinforcement bars 16, preferably in the center between the lower reinforcement bars 14 and the upper reinforcement bars 16. Furthermore, each of the reinforcing bars constituting the lower reinforcement 14, upper reinforcement 16, and diagonal grid reinforcement 18 extends into the interior of the beam 12 joined to the slab 10 and is anchored inside the beam 12. The reinforcement can be anchored, for example, by anchoring plates or by hooks with the ends of the reinforcement bars folded back into a U-shape.

[0027] In this embodiment, the reinforcing bars constituting the lower bar 14, upper bar 16, and diagonal grid reinforcing bars 18 are all of the same diameter, and their spacing is also the same. Therefore, the lower bar 14 and upper bar 16 are arranged to overlap in a plan view. Furthermore, the diagonal grid reinforcing bars 18 are arranged to be inclined at an angle of preferably 45° with respect to the lower bar 14 and upper bar 16.

[0028] The slab 10 of this embodiment is characterized by the fact that, by providing diagonal grid reinforcement bars 18, the width of cracks that occur when in-plane shear force is applied is kept small. This characteristic feature will be described below with reference to Figure 6.

[0029] Figure 6 shows the state of deformation of slab 10 when a shear force is applied to it. Note that the deformation of slab 10 is exaggerated in Figure 6. As shown in Figure 6, consider a state in which a rectangular slab 10 is deformed into a rhombus shape due to a shear force acting on it, causing one diagonal A1 to stretch and the other diagonal A2 to contract. In this state, a tensile force T acts on the slab 10 in the direction of diagonal A1. When the tensile force T exceeds the tensile strength of the concrete, cracks C occur with the direction of diagonal A1 as the width direction and the direction of diagonal A2 as the length direction.

[0030] In this case, if there is no reinforcing bar crossing crack C, the tensile force T will not be transmitted between the concrete on both sides of crack C, and the crack width will expand due to the tensile force T acting on both sides of crack C.

[0031] In contrast, in this embodiment, the diagonal grid reinforcement bars 18 are provided so as to extend in a direction roughly diagonally across the slab 10, so there are reinforcement bars that cross the crack C in the width direction (roughly in the direction of diagonal A1 in the example of Figure 6) (hereinafter, among the reinforcement bars constituting the diagonal grid reinforcement bars 18, the reinforcement bars that cross the crack C are referred to as diagonal reinforcement bars 18A). Since the ends of the diagonal grid reinforcement bars 18 are anchored to the beams 12 surrounding the slab 10, the diagonal reinforcement bars 18A resist the tensile force T that tries to widen the crack C and transmit the tensile force T between the concrete on both sides of the crack C. As a result, the expansion of the crack width is suppressed and the crack width can be kept small. The tensile force T is then transmitted to other locations in the slab 10 by the diagonal reinforcement bars 18A, causing another crack, and the diagonal reinforcement bars 18A that cross that crack suppress the expansion of the crack width in the same way as above, and further cause the occurrence of another crack C. As this process is repeated, numerous small cracks C are dispersed and generated.

[0032] Furthermore, the sum of the widths of the multiple cracks C that occur when the slab 10 deforms due to in-plane shear force will be a value corresponding to the amount of shear deformation of the slab 10. In other words, if minute deformations of the concrete portion are ignored, the sum of the widths of the resulting cracks C will be constant if the amount of shear deformation of the slab 10 is the same. Therefore, from this perspective as well, it can be said that the width of each crack C can be kept small by distributing the generation of numerous cracks C through the action of the diagonal grid reinforcement bars 18.

[0033] As explained above, according to the slab 10 of this embodiment, the width of the cracks C that occur can be kept small by providing the diagonal grid reinforcement bars 18.

[0034] Furthermore, by setting the inclination angle of the diagonal grid reinforcement 18 with respect to the lower reinforcement 14 and upper reinforcement 16 to 45°, the diagonal reinforcement 18A traverses the crack C in a direction almost perpendicular to the crack C (i.e., in approximately the same direction as the tensile force T). As a result, the tensile force T is efficiently transmitted as an axial tensile force to the diagonal reinforcement 18A, thus more effectively suppressing the crack width. Moreover, since the diagonal grid reinforcement 18 is composed of multiple reinforcements, the dispersion effect of the crack C is enhanced, and the width of the crack C can be more effectively reduced.

[0035] Furthermore, if the slab 10 undergoes shear deformation in the direction shown in Figure 6, it will extend in the direction of diagonal A1, and the reinforcing bars in the diagonal grid reinforcement 18 that are oriented in the direction of diagonal A1 will suppress the crack width. On the other hand, if it undergoes shear deformation in the opposite direction (the upper side is oriented to the left in Figure 6), the slab 10 will extend in the direction of diagonal A2, and the reinforcing bars oriented in the direction of diagonal A2 will contribute to suppressing the crack width. In other words, because the diagonal grid reinforcement 18 has a grid of reinforcing bars, the crack width can be kept small for shear deformation in either direction.

[0036] Next, we conducted a verification experiment to confirm the crack width suppression effect of the diagonal grid reinforcement bars 18, and we will now explain the experimental method and results. Figure 7 shows the test specimens used in this verification experiment. Figure 7(a) is a plan view of test specimen 30 without the diagonal grid reinforcement bars 18, as a comparative example, and Figure 7(b) is a plan view of test specimen 40 with the diagonal grid reinforcement bars 18, as an example.

[0037] In both test specimens 30 and 40, the lower reinforcement bars 14 and upper reinforcement bars 16 are made of D6 diameter reinforcing bars spaced 80 mm apart. In addition, test specimen 40, which is an embodiment, has diagonal grid reinforcement bars 18, which are made of reinforcing bars with the same diameter and spacing as the lower reinforcement bars 14 and upper reinforcement bars 16, but are inclined at 45° and placed at the center in the thickness direction between the lower reinforcement bars 14 and upper reinforcement bars 16.

[0038] As shown in Figure 7, the main beam reinforcement bars 12a constituting the beam 12 were provided only near the left and right sides of the test specimens 30 and 40 in the figure, while stubs 50 and 52 were joined to the top and bottom sides in the figure. The ends of the bottom reinforcement bars 14 and top reinforcement bars 16 of the test specimens 30 and 40, and the ends of the diagonal grid reinforcement bars 18 of the test specimen 40, were extended and anchored into the beam 12 and stubs 50 and 52 by an equivalent length. In other words, the stubs 50 and 52 mimic the beams 12 on the top and bottom sides, thereby achieving a state similar to that of an actual slab 10 in which beams 12 are joined to all four sides of the test specimens 30 and 40.

[0039] In this verification experiment, one stub 50 was fixed, and an alternating load was applied to the other stub 52 in the left-right direction to determine the relationship between the shear deformation angle and the load. In this experiment, the test conditions were set to apply an alternating load so that the amplitude of the deformation angle was ±0.1%, 0.2%, 0.3%, 0.4%, 0.67%, and 1%. However, as described below, the experiment was stopped for both test specimens 30 and 40 midway through the cycle in which a displacement of ±1% was applied. Furthermore, in this experiment, the crack occurrence in test specimens 30 and 40 was observed when the aforementioned deformation was reached and when the load was returned to zero from that deformation.

[0040] Figures 8 and 9 show the relationship between the deformation angle (horizontal axis) and the horizontal load (vertical axis) when the above alternating load is applied to the comparative example specimen 30 and the example specimen 40, respectively.

[0041] As shown in Figure 8, in the comparative example test specimen 30, the horizontal load reached its maximum (approximately 1000 kN; indicated by a circle in Figure 8) when the displacement angle was around +0.55% and -0.6% during the cycle in which a displacement angle of ±0.67% was applied, and the load tended to decrease beyond this displacement angle. Furthermore, during the process in which a deformation angle of +1% was applied, the horizontal load remained lower than the above maximum load, so the experiment was terminated when the load returned to zero (indicated as "End" in Figure 8).

[0042] On the other hand, as shown in Figure 9, in the example test specimen 40, the horizontal load did not exceed the maximum value of the horizontal load in the previous ±0.67% cycle (approximately 1300 kN; indicated by a circle in Figure 9) during the process of applying a displacement angle of +1%. Therefore, after reaching a displacement angle of +1%, the experiment was terminated when the load returned to zero (indicated as "End" in Figure 9), and the crack initiation status was observed.

[0043] Comparing Figure 8 and Figure 9, after cracks occur (indicated by squares in each figure), the rate of decrease in the rise of the horizontal load (i.e., the degree of decrease in stiffness) is more gradual in the embodiment shown in Figure 9 than in the comparative example in Figure 8. Consequently, the maximum load (indicated by circles in the figure) is greater in the embodiment shown in Figure 9 than in the comparative example in Figure 8. In other words, it can be seen that the maximum shear strength is increased by providing the diagonal grid reinforcement bars 18.

[0044] Next, we will explain the results of crack observation in the comparative examples and examples. Figures 10 and 11 show the distribution of crack widths that occurred in test specimens 30 and 40 when the load was returned to zero after reaching a deformation angle of 0.3%. Specifically, the crack widths that occurred in test specimens 30 and 40 were measured and indicated by the intensity of the color. The crack width values ​​in the figures (0.1 mm, 0.3 mm) are the values ​​obtained by converting the crack widths in test specimens 30 and 40 to the expected crack widths in a slab of actual size.

[0045] Comparing Figure 10 and Figure 11, the comparative example shown in Figure 10 shows cracks with a width of 0.3 mm or more, whereas the example shown in Figure 11 does not show cracks with a width of 0.3 mm or more. Furthermore, the number of cracks with a width of 0.1 mm or more is also smaller in the example shown in Figure 11 compared to the comparative example shown in Figure 10.

[0046] Thus, the results of this verification experiment showed that in the example with diagonal grid reinforcement bars 18, the crack width was kept smaller than in the comparative example without diagonal grid reinforcement bars 18. This confirmed that diagonal grid reinforcement bars 18 have a crack width suppression effect.

[0047] As explained above, verification experiments have confirmed that, according to the slab 10 of this embodiment, by providing diagonal grid reinforcement bars 18 between the lower reinforcement bars 14 and the upper reinforcement bars 16, the width of cracks that occur when a shear load is applied to the slab 10 can be kept small. Therefore, compared to conventional design methods, which aim to prevent crack occurrence by setting the shear stress below the short-term allowable shear stress of concrete, it is possible to reduce the required thickness of the slab 10 and perform rational design and construction of the slab 10.

[0048] In the above embodiment, the slab 10 is assumed to be joined to the beam 12 all around, but it is not limited to this, and may be joined to the beam 12 on at least two opposing sides. In places where the beam 12 is not joined, the diagonal grid reinforcement bars 18 cannot be anchored to the beam 12, but in that case, they can be anchored inside the slab 10 near the periphery (at a position where the required cover thickness of 30 to 50 mm can be secured, as close to the periphery of the slab 10 as possible, i.e., 30 to 50 mm from the periphery).

[0049] Furthermore, in the above embodiment, the diagonal grid reinforcement bars 18, which are made up of reinforcing bars at regular intervals, are provided over the entire surface of the slab 10. However, the present invention is not limited to this, and may be provided only near the diagonals of the slab 10 where cracks are likely to occur due to in-plane shear force, or the reinforcing bars of the diagonal grid reinforcement bars 18 may be made denser (the spacing between reinforcing bars becomes smaller) near the diagonals.

[0050] Furthermore, although the slab 10 is assumed to be rectangular in the above embodiment, the slab may be a polygon other than a rectangle, such as a triangle, depending on the structure of the building, and the present invention is also applicable in such cases.

[0051] Furthermore, although the above embodiment was described with reference to a slab 10, large in-plane shear forces can also act on reinforced concrete walls, and the present invention is applicable to such reinforced concrete walls as well.

[0052] Next, the method for constructing the slab 10 in this embodiment will be described. Figure 12 is a diagram showing an exploded view of the reinforcing bar support 60 used when installing the diagonal grid reinforcing bars 18 in the construction method of the slab 10 in this embodiment.

[0053] As shown in the figure, the rebar support 60 comprises a long nut 62, a first hook portion 63, and a second hook portion 64. The base ends of the first hook portion 63 and the second hook portion 64 are provided with threaded portions 63a and 64a, respectively, and the rebar support 60 is integrated by screwing the threaded portions 63a and 64a onto both sides of the long nut 62.

[0054] With the rebar support 60, the overall length of the rebar support 60 can be adjusted according to the amount that the first hook portion 63 and the second hook portion 64 are screwed into the long nut 62, and the relative angle between the first hook portion 63 and the second hook portion 64 around their axes (i.e., around the length of the rebar support 60) can be adjusted. However, the configuration of the rebar support 60 is not limited to that shown in Figure 12; any configuration that has hooks on both sides, allows for adjustment of the overall length, and allows for adjustment of the relative angle of the two hooks around their axes is acceptable.

[0055] Figure 13 shows the construction process (a) to (f) of slab 10. First, in step (a), a spacer 68 is placed on the lower formwork 66, the lower reinforcement bars 14 are assembled on the spacer 68, and these lower reinforcement bars 14 are supported by the spacer 68. Next, in step (b), the diagonal grid reinforcement bars 18 are assembled and temporarily placed on the lower reinforcement bars 14. Next, in step (c), the rebar support frame 70 is installed on the formwork 66 in a position that does not interfere with the lower reinforcing bars 14 or the diagonal grid reinforcing bars 18. Then, the upper reinforcing bars 16 are assembled and supported by the rebar support frame 70.

[0056] Next, in step (d), the rebar support 60 is inserted from above the upper reinforcement bar 16, the second hook portion 64 of the rebar support 60 is hooked onto the diagonal grid reinforcement bar 18 to lift the diagonal grid reinforcement bar 18, and the first hook portion 63 is hooked onto the upper reinforcement bar 16 to support the lifted diagonal grid reinforcement bar 18. By performing this work over the entire slab 10 as in step (e), the reinforcement work, including the installation of the diagonal grid reinforcement bar 18, is completed.

[0057] In step (e), when supporting the diagonal grid reinforcing bars 18 with the rebar support 60, the orientation of the reinforcing bars of the upper reinforcing bars 16 and the orientation of the reinforcing bars of the diagonal grid reinforcing bars 18 differ by 45° clockwise or counterclockwise. Therefore, the relative angle around the axis of the first hook portion 63 and the second hook portion 64 is adjusted accordingly. Specifically, the relative angle around the axis of the first hook portion 63 and the second hook portion 64 is adjusted so that the upper reinforcing bars 16 are perpendicular to the first hook portion 63 and the diagonal grid reinforcing bars 18 are perpendicular to the second hook portion 64. This allows the rebar support 60 to support the diagonal grid reinforcing bars 18 in a stable state.

[0058] Furthermore, in step (e), the diagonal grid reinforcing bars 18 are supported by the second hook portion 64 of the reinforcing bar support 60, which has its first hook portion 63 hooked onto the upper reinforcing bars 16 at multiple locations. For this reason, the location on which of the upper and lower upper reinforcing bars 16a and 16b of the upper reinforcing bars 16 the first hook portion 63 is hooked, and the location on which of the upper and lower diagonal reinforcing bars 18a and 18b of the diagonal grid reinforcing bars 18 is hooked onto the second hook portion 64, will differ. Depending on whether the first hook portion 63 is hooked onto the upper reinforcing bars 16, the height between the hooking position of the first hook portion 63 on the upper reinforcing bars 16 and the hooking position of the diagonal grid reinforcing bars 18 on the second hook portion 64 will differ.

[0059] Therefore, in step (e), in order to support the diagonal grid reinforcement bars 18 at a constant height, the total length of the reinforcement support 60 is adjusted by changing the amount that the first hook portion 63 or the second hook portion 64 is screwed into the long nut 62, depending on whether the upper or lower reinforcement is hooked onto the hook portion of each reinforcement support 60.

[0060] As described above, once the reinforcement is complete, in step (f), concrete 80 is poured into the formwork up to the floor level FL, and then cured to complete the construction of the slab.

[0061] By the way, when installing the diagonal grid reinforcement bars 18, since the diagonal grid reinforcement bars 18 are installed at a height midway along the thickness direction of the slab 10, ready-made spacers may not be able to accommodate the height of the diagonal grid reinforcement bars 18. On the other hand, if the diagonal grid reinforcement bars 18 are to be supported by a reinforcement support frame, it is necessary to manufacture a separate reinforcement support frame from the reinforcement support frame 70 for the upper reinforcement bars 16, and the reinforcement support frame must be fixed to the formwork 66 while avoiding the lower reinforcement bars 14 and the diagonal grid reinforcement bars 18, making the placement work complicated.

[0062] In contrast, in this embodiment, the diagonal grid reinforcement bars 18 are supported by reinforcement support devices 60 that hook onto the upper reinforcement bars 16. Therefore, only one type of reinforcement frame 70 is needed for the upper reinforcement bars 16, thereby eliminating the complexity of manufacturing and arranging new reinforcement frames. Furthermore, since the diagonal grid reinforcing bars 18 are suspended by the reinforcing bar support 60, tensile force acts on the reinforcing bar support 60, eliminating the risk of buckling, thus allowing the cross-sectional area of ​​the reinforcing bar support 60 to be reduced.

[0063] Furthermore, since the rebar support 60 is configured such that the first hook portion 63 and the second hook portion 64 are screwed into the long nut 62, the relative angle around the axis of the first hook portion 63 and the second hook portion 64 can be adjusted. This allows the rebar support 60 hooked onto the upper reinforcing bar 16 to reliably support the diagonal grid reinforcing bars 18 that are facing a different direction from the upper reinforcing bar 16.

[0064] Furthermore, since the overall length of the rebar support 60 can be adjusted by the amount the first hook portion 63 and the second hook portion 64 are screwed into the long nut 62, the diagonal grid rebar 18 can be supported at a constant height regardless of whether the upper or lower rebars of the upper rebar 16 and the diagonal grid rebar 18 are hooked onto the respective hook portions.

[0065] Thus, with the rebar support 60 of this embodiment, the length and angle of the hook portion can be adjusted, which increases the degree of freedom in the support position of the diagonal grid rebars 18 by the rebar support 60, making it easier to position the rebar support 60 while avoiding the lower rebars 14 and the diagonal grid rebars 18. [Explanation of Symbols]

[0066] 10 Slabs 12 Beam 14 Bottom reinforcement 14a Upper bottom reinforcement 14b Lower bottom reinforcement 16 Top bar 16a Upper upper end reinforcement 16b Lower upper end reinforcement 18 Diagonal grid reinforcement bars 18a Upper diagonal reinforcement bars 18b Lower diagonal reinforcement bars 18A Diagonal rebar 30, 40 test specimens 50, 52 stubs 60 Rebar support 62 Long nuts 63 First hook section 64 Second hook section 66 formwork 68 Spacers 70 Reinforcement Bar Stand

Claims

1. A reinforced concrete member that constitutes a slab or wall of a reinforced concrete structure, A first grid reinforcement consisting of multiple reinforcing bars extending in two orthogonal directions within a plane, A second grid reinforcement consisting of multiple reinforcing bars extending in the two orthogonal directions, located in a plane spaced apart from the first grid reinforcement in the thickness direction of the reinforced concrete member, The invention comprises a plurality of diagonal grid bars that are inclined with respect to the first and second grid bars and extend in two mutually perpendicular directions within the plane between the first grid bars and the second grid bars, The reinforcing bars constituting the diagonal grid reinforcement are anchored to other reinforced concrete members joined to the slab or wall, or are anchored inside the reinforced concrete member near the periphery of the slab or wall.

2. The reinforced concrete member according to claim 1, wherein the diagonal grid reinforcement is provided at the central position between the first grid reinforcement and the second grid reinforcement.

3. The reinforced concrete member according to claim 1 or 2, wherein the reinforcing bars constituting the diagonal grid reinforcement are inclined at an angle of 45° with respect to the reinforcing bars constituting the first grid reinforcement and the second grid reinforcement.

4. The reinforced concrete member according to claim 1 or 2, wherein the aforementioned reinforced concrete member constitutes a slab, and the other member constitutes a beam.

5. A method for constructing a reinforced concrete member according to claim 1 or 2, The aforementioned reinforced concrete member constitutes a slab. The first grid reinforcement is the bottom reinforcement, and the second grid reinforcement is the top reinforcement. The first step is to support the first grid reinforcement at a predetermined height, A second step involves temporarily placing the diagonal grid reinforcement bars on top of the first grid reinforcement bars, A third step of supporting the second grid reinforcement at a predetermined height, A third step involves supporting the diagonal grid reinforcing bars at a predetermined height by hooking one hook portion of a reinforcing bar support device, which has hook portions at both ends, onto the second grid reinforcing bar, and hooking the other hook portion onto the diagonal grid reinforcing bar. A method for constructing reinforced concrete members equipped with [a specific feature / feature].

6. The rebar support is adjustable in overall length, and the one hook portion and the other hook portion are rotatable relative to each other around the length of the rebar support. The method for constructing a reinforced concrete member according to claim 5, further comprising the step of adjusting the relative angle around the axis of the hook portion so that the hook portion is oriented in accordance with the orientation of the reinforcing bars hooked onto each hook portion, and so that the height of the diagonal grid reinforcing bars hooked onto the other hook portion is constant, and adjusting the length of the reinforcing bar support.

7. The method for constructing a reinforced concrete member according to claim 5, wherein the reinforcing bar support comprises a nut member and first and second hook portions that are screwed into both ends of the nut member, respectively.

8. A reinforcing bar support used in the method of claim 5, A rebar support comprising a nut member and first and second hook portions that are screwed into both ends of the nut member, respectively.

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