Joint structure and slab construction method

Abstract

To provide a joint structure that facilitates the construction of slabs using half-precast members. [Solution] The joint structure 1 is used when erecting a concrete half-precast member 3 between a pair of side sections 2 and constructing a slab by pouring concrete Con on top of the side sections 2 and the half-precast member 3. The half-precast member 3 has main steel members 32 extending in the direction connecting the pair of side sections 2 on the top surface of a concrete precast slab 31, and the main steel members 32 are arranged so as not to extend outward from the precast slab 31 in that direction. Joint reinforcing bars 4 are arranged so as to extend from above the side sections 2 toward the half-precast member 3, and a lap joint is formed between the joint reinforcing bars 4 and the main steel members 32.

Description

[Technical Field]

[0001] The present invention relates to a joint structure and a method for constructing a slab. [Background technology]

[0002] One method that shortens construction time and improves workability when constructing reinforced concrete slabs is the half-precast method, in which half-precast members that serve as buried formwork are erected between a pair of sides, rebar is then assembled in place on top of the half-precast members, and concrete is poured to construct the slab.

[0003] Patent Document 1 describes a half-precast member in which a plate-shaped precast slab is reinforced with steel. By adding rigidity with the steel, it is possible to omit the support work required for the bottom of the precast slab when pouring concrete. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-167478 Summary of the Invention [Problem to be solved by the invention]

[0005] The main role of the steel is to ensure the bending rigidity required during construction, but by extending the steel to the outside of the precast slab and anchoring it in the concrete at the upper part of the side, the steel can also function as structural steel for the slab.

[0006] However, in this case, the overall length of the steel material and therefore the overall length of the half-precast member increases, which reduces the efficiency of work such as transporting and erecting the half-precast member. Furthermore, extending the steel material may result in its length exceeding the standard length, in which case it becomes necessary to join additional steel material to the end of the standard-length steel material by welding or bolts, significantly increasing costs and construction labor.

[0007] The present invention has been made in consideration of the above problems, and aims to provide a joint structure, etc. that facilitates the construction of slabs using half-precast members. [Means for solving the problem]

[0008] The first invention for solving the above-mentioned problems is a joint structure used when erecting a concrete half-precast member between a pair of side sections and pouring concrete on top of the side sections and the half-precast member to construct a slab, wherein the half-precast member has steel material extending in the direction connecting the pair of side sections on the top surface of a concrete precast plate, the steel material being arranged so as not to extend outward from the precast plate in that direction, joint steel bars being arranged so as to extend from above the side sections toward the half-precast member, and a lap joint being formed between the joint steel bars and the steel material.

[0009] According to the present invention, the steel members of the half-precast members do not extend outward from the precast slab, making the half-precast members easy to transport and erect, and preventing the total length of the steel members from exceeding the standard length. Furthermore, in the joint structure, the steel members are fixed to the sides via joint rebar, ensuring the rigidity of the precast slab and functioning as structural steel for the slab, eliminating the need for slab reinforcement. For these reasons, the present invention allows slabs to be easily constructed using half-precast members, resulting in reduced costs, shorter construction times, and improved workability.

[0010] The steel material may have protrusions or holes. This ensures the integrity of the steel material and the concrete of the slab.

[0011] An anchoring portion may be provided at an end portion of the joint reinforcing bar on the side portion side. Also, an anchoring portion may be provided at an end portion of the joint reinforcing bar on the half precast member side. This allows the anchorage length on the side of the joint steel bar and the joint length on the half-precast member side to be shortened.

[0012] The joint reinforcing bars are reinforcing bars adjacent to each other in the axial direction connected by a mechanical joint, and the reinforcing bars on the side and the mechanical joint may be embedded in the outer part above the side, and the concrete may be poured inside the outer part. By using mechanical joints to connect the rebars, the installation of the rebars becomes easier. For example, it is possible to install the rebars on the side and the mechanical joints in the outer upper part of the side before erecting the half-precast member, and then connect the rebars on the half-precast member side to the mechanical joints after erecting the half-precast member. This allows the rebars to be installed in advance (part of them), while preventing them from interfering with the erection of the half-precast member.

[0013] The second invention is a method for constructing a slab using the joint structure of the first invention, characterized in that a slab is constructed from the concrete by steps of erecting the half-precast members between a pair of the side portions and pouring concrete on top of the side portions and the half-precast members, and in the process forming a lap joint between the joint reinforcing bars and the steel material. [Effects of the Invention]

[0014] According to the present invention, a joint structure, etc. can be provided that facilitates the construction of slabs using half-precast members. [Brief explanation of the drawings]

[0015] [Figure 1]A diagram showing a portion of a box culvert including a joint structure 1. [Figure 2] A diagram showing the construction of a box culvert. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. [Figure 4] FIG. 2 is a diagram showing an example of the arrangement of main steel members 32. [Figure 5] FIG. 10 is a diagram showing another example of the main steel material 32. [Figure 6] FIG. 4 shows a joint reinforcing bar 4a. [Figure 7] FIG. 10 is a diagram showing the outer portion 71 of the corner portion 7 and the joint reinforcing bar 4b. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0017] Fig. 1 is a diagram showing a part of a box culvert, which is a structure including a joint structure 1 according to an embodiment of the present invention, Fig. 2 is a diagram showing the box culvert in the middle of construction, and Fig. 3 is a cross section taken along line AA in Fig. 2.

[0018] A box culvert is formed by erecting a concrete half-precast member 3 between a pair of widthwise side members 2, and then pouring concrete Con on top of the side members 2 and half-precast members 3 to construct a top slab. Figure 2 shows the state before the concrete Con is poured.

[0019] The width direction of the box culvert is the direction connecting the pair of side sections 2, and is perpendicular to the axial direction of the box culvert in a plan view. The axial direction of the box culvert corresponds to the normal to the paper surface of Figures 1 and 2, and the width direction of the box culvert corresponds to the left-right direction in Figures 1 and 2. Also, Figures 1 and 2 show the joint structure 1 on one side 2 of the box culvert in the width direction, but a similar joint structure 1 is also formed on the other side 2.

[0020] The side portion 2 is a wall-like member made of reinforced concrete. The side portion 2 may be formed by pouring concrete on-site, or the side portion 2 may be manufactured as a precast member in a factory or the like, transported to the construction site, and installed at the construction site.

[0021] Above the side 2 is the corner 7 between the top slab and the side 2, and reinforcing bars 21 are placed in the corner 7. The reinforcing bars 21 are embedded in the side 2 and protrude from the top surface of the side 2, with their protruding ends bent at approximately 90° toward the other side 2. The reinforcing bars 21 are placed at intervals in the axial direction of the box culvert, i.e., in the extension direction on the plane of the side 2.

[0022] The half precast member 3 is a bottom formwork used when pouring the concrete Con for the top slab, and is also an embedded formwork that remains after the concrete Con is poured to form part of the top slab. The half precast member 3 has main steel members 32 attached to the top surface of a concrete precast plate 31. If necessary, multiple half precast members 3 are arranged side by side in the axial direction of the box culvert.

[0023] The precast slab 31 is a plate-shaped member, and both ends of the box culvert in the width direction are placed on a pair of side portions 2 of the box culvert in the width direction. Both ends of the precast slab 31 in the box culvert in the width direction may be placed on brackets (not shown) provided on the inside of the pair of side portions 2. The "inside" corresponds to the center side of the box culvert in the width direction.

[0024] The main steel members 32 are steel members arranged to extend in the width direction of the box culvert. As shown in Figure 3, in this embodiment, the main steel members 32 are flat steel members, and their plate surfaces are used in the vertical direction. A plurality of main steel members 32 are arranged at intervals in the axial direction of the box culvert (corresponding to the left-right direction in Figure 3), and the lower parts of these main steel members 32 are embedded in one precast slab 31.

[0025] The main steel member 32 imparts bending rigidity to the precast slab 31 to prevent deformation when the concrete Con is poured, and also functions as structural steel for the underside of the top slab after the concrete Con is poured.

[0026] In particular, in this embodiment, both ends of the main steel members 32 do not extend outward from the precast slab 31 in the width direction of the box culvert, and the main steel members 32 are positioned so that they fit within the range of the precast slab 31. The length of the main steel members 32 is, for example, approximately the same as the distance between the pair of side members 2, but is not limited to this and may be any length necessary to ensure sufficient rigidity so that support work on the bottom surface of the half precast member 3 can be omitted. "Outward" refers to the direction away from the center of the box culvert in the width direction.

[0027] In this embodiment, the joint rebar 4 is arranged so as to extend from the upper corner 7 of the side portion 2 toward the half precast member 3, and a joint structure 1 is formed by a lap joint between the joint rebar 4 and the main steel member 32 of the half precast member 3. In other words, the end of the joint rebar 4 on the half precast member 3 side in the axial direction and the end of the main steel member 32 on the side portion 2 side in the axial direction are arranged so as to overlap in the width direction of the box culvert.

[0028] 3, a plurality of joint reinforcing bars 4 (three in the illustrated example) are arranged in the height direction on both sides of the main steel material 32. It is desirable to use deformed reinforcing bars as the joint reinforcing bars 4.

[0029] Reference numeral 5 in Figure 1 indicates the portion where the joint rebar 4 and the main steel member 32 overlap, and this will be referred to as the joint section hereinafter. The length of the joint section 5 is the larger of the required anchorage lengths of the joint rebar 4 and the main steel member 32. The cross-sectional area of ​​the joint rebar 4 is set so that the bending strength of the slab cross section calculated based on the arrangement and cross-sectional dimensions, etc. of the joint rebars 4 on both sides of the main steel member 32 (without considering the main steel member 32) exceeds the bending strength of the slab cross section calculated based on the arrangement and cross-sectional dimensions, etc. of the main steel member 32 (without considering the joint rebar 4). The "slab cross section" is the cross section in the axial direction of the box culvert.

[0030] In addition, reference numeral 8 in Fig. 1 denotes a reinforcing bar on the upper side of the slab, which is arranged so as to extend in the width direction of the box culvert. The end of the reinforcing bar 8 is connected to the reinforcing bar 21 by a mechanical joint 6. Note that, as with the joint structure 1, a joint reinforcing bar may be used to form a lap joint with the reinforcing bar 21.

[0031] When forming a box culvert, after erecting half precast members 3 between a pair of side sections 2, joint rebars 4 are placed as shown in Figure 2, lapped over the joint rebars 4 and the main steel member 32, and reinforcing bars 8 are placed on top of the half precast members 3, connecting them to reinforcing bars 21 with mechanical joints 6. Thereafter, concrete Con is poured on top of the side sections 2 and half precast members 3 as shown in Figure 1, and a top slab is constructed, thereby forming a box culvert including a joint structure 1. The joint rebars 4 may be placed before erecting the half precast members 3.

[0032] In the joint structure 1, stress is transmitted between the joint rebar 4 and the main steel member 32 via the concrete Con of the slab. In addition, the end of the joint rebar 4 on the side 2 side is fixed to the concrete Con of the corner portion 7. Therefore, the main steel member 32 is fixed in the concrete Con of the corner portion 7 via the joint rebar 4, and the main steel member 32 can function as structural steel for the slab.

[0033] As explained above, in this embodiment, the main steel members 32 do not extend outward from the precast slab 31, making it easy to transport and erect the half precast member 3, and preventing the total length of the main steel members 32 from exceeding the standard length for steel members. Furthermore, in the joint structure 1, the main steel members 32 are fixed to the corner portions 7 via the joint reinforcing bars 4, so the main steel members 32 ensure the rigidity of the precast slab 31 and function as structural steel members for the slab, eliminating the need for arranging reinforcement for the slab. For these reasons, in this embodiment, slabs can be easily constructed using half precast members 3, reducing costs, shortening construction time, and improving workability.

[0034] However, the present invention is not limited to the above embodiment. For example, the shape of the half precast member 3 is not limited to the above, and it is sufficient that steel members extending in the width direction of the box culvert (the direction connecting the pair of side portions 2) are provided on the upper surface of a concrete precast slab 31. As an example, as shown in Figure 4, the main steel members 32 may be supported by steel legs 33, and the lower parts of the legs 33 may be embedded in the precast slab 31.

[0035] Furthermore, although the joint structure 1 of this embodiment is applied to a box culvert, the structure to which the joint structure 1 is applied is not limited to this, and may be any structure in which a concrete slab is formed on a pair of side sections 2. The configuration and shape of the side sections 2 are not particularly important.

[0036] As shown in Figure 5(a), protrusions 321 such as studs can be provided on the main steel member 32. Holes can be provided instead of the protrusions 321, or perforated steel dowels can be attached. By providing the main steel member 32 with protrusions 321 or holes in this way, it is possible to ensure the unity with the concrete Con.

[0037] In addition, although the main steel material 32 in this embodiment is flat steel, it may be other shaped steel. For example, as shown in Fig. 5(b), an H-shaped steel may be used, or a channel steel may be used. In these cases, the joint reinforcing bars 4 may be placed directly above the main steel material 32.

[0038] In this embodiment, the joint rebar 4 is fixed to the corner 7 simply by adhering it to the concrete Con, but as shown in Figure 6, a hook 41 may be provided as a fixing part at the end of the side portion 2 of the joint rebar 4a, thereby improving the fixing ability to the corner 7 and reducing the fixing length of the joint rebar 4a to the corner 7 (the length within the corner 7). By providing a similar hook 41 at the end of the joint rebar 4 on the half precast member 3 side, the joint length (the length of the joint section 5) can also be shortened.

[0039] In addition, as an anchoring part other than the hook 41, an anchoring body that is wider than the main body of the joint rebar 4 may be provided at one or both ends of the joint rebar 4, and the same effect as above can be obtained. For the main steel material 32, the length of the joint can also be shortened by providing a plate-like member such as a bearing plate that is perpendicular to the axial direction at the end in the axial direction as an anchoring part.

[0040] 7(a), the outer portion 71 of the corner 7 may be formed in advance before erecting the half precast member 3, so that the joint rebar 4 protrudes from the outer portion 71 toward the half precast member 3. The outer portion 71 is formed within a range that does not interfere with the precast slab 31. The outer portion 71 may be formed simultaneously with the side portion 2 by pouring concrete on-site, or a precast member integrating the side portion 2 and the outer portion 71 may be fabricated in advance in a factory or the like and installed at the construction site. Alternatively, the outer portion 71 may be formed by pouring concrete on top of the side portion 2 after the side portion 2 is installed, or the outer portion 71 may be fabricated in advance in a factory or the like as a precast member and installed on top of the side portion 2 after the side portion 2 is installed.

[0041] 7(b), the installation of the joint reinforcing bars 4b can be facilitated by connecting axially adjacent reinforcing bars 42 with mechanical joints 43. As the mechanical joint 43, for example, one that fits the ends of the reinforcing bars 42 with screws is used, but the present invention is not limited to this.

[0042] In the example of Figure 7(b), the reinforcing bars 42 on the side 2 side and the mechanical joint 43 are embedded in the outer portion 71, and the reinforcing bars 42 on the half precast member 3 side are connected to the mechanical joint 43 after the half precast member 3 is erected. Then, concrete Con is poured inside the outer portion 71 (the remaining part of the corner portion 7 and above the half precast member 3) to form the top slab. In this case, by installing the reinforcing bars 42 on the half precast member 3 side later, it is possible to install (part of) the joint reinforcing bars 4b in advance and prevent the joint reinforcing bars 4b from interfering with the erection of the half precast member 3.

[0043] Furthermore, if the stress generated in the joint section 5 is high and damage (plastic hinge) at the end of the side section 2 of the joint section 5 may extend into the corner section 7, or if the width of the bending crack at the plastic hinge occurrence location becomes a design issue, the plastic hinge occurrence location may be moved toward the half precast member 3 (hinge relocation) by increasing the amount of joint reinforcing bars 4 or adding rebar or steel other than the joint reinforcing bars 4. For example, the distance from the corner section 7 to the plastic hinge occurrence location may be set to at least 0.2 times the thickness of the slab, and the ratio of the bending strength / acting bending moment of the joint section 5 may be set to be greater than that of the plastic hinge occurrence location (e.g., approximately 1.1 times or greater). The plastic hinge occurrence location is the location where a plastic hinge occurs first due to the bending moment when the vertical downward load acting on the slab is increased, and can be confirmed by performing simulations, etc.

[0044] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that those skilled in the art can conceive of various modifications or alterations within the scope of the technical ideas disclosed herein, and it is understood that these modifications also fall within the technical scope of the present invention. [Explanation of symbols]

[0045] 1: Joint structure 2: Side 3: Half precast members 4, 4a, 4b: Reinforcement bars for joints 5: Joint section 7: Corner 31: Precast version 32: Main steel material (steel material) 41: Hook (fixing part) 42: Reinforced concrete 43: Mechanical coupling 71:Outer part

Claims

1. A joint structure used when constructing a slab by erecting a concrete half-precast member between a pair of side sections and pouring concrete on the side sections and the half-precast member, The half precast member is a member in which a steel member extending in a direction connecting the pair of side portions is provided on the upper surface of a concrete precast plate, The steel members are arranged so as not to extend outward from the precast slab in that direction; A joint reinforcing bar is arranged so as to extend from above the side portion toward the half precast member, A joint structure characterized in that a lap joint is formed between the joint reinforcing bar and the steel material.

2. 2. The joint structure according to claim 1, wherein the steel material has a projection or a hole.

3. 2. The joint structure according to claim 1, wherein an anchoring portion is provided at an end portion on the side portion side of the joint reinforcing bar.

4. 2. A joint structure according to claim 1, characterized in that an anchoring portion is provided at the end of the joint reinforcing bar on the half precast member side.

5. The joint reinforcing bars are reinforcing bars adjacent to each other in the axial direction connected by a mechanical joint, The side reinforcing bars and the mechanical joints are embedded in the outer portion above the side, 2. The joint structure according to claim 1, wherein the concrete is poured inside the outer portion.

6. A slab construction method for constructing the slab using the joint structure according to any one of claims 1 to 5, a step of erecting the half precast member between the pair of side portions; pouring concrete onto the side portions and the half precast members; Therefore, A method for constructing a slab, comprising constructing a slab using the concrete, and forming a lap joint between the joint reinforcing bar and the steel material.

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