Reinforced concrete beam

Abstract

To provide a reinforced concrete beam that has a highly strong beam bar excellent in workability and hardly causes cracking.SOLUTION: A reinforced concrete beam 200 has a beam bar 100 inside concrete. The beam bar 100 comprises: a lower stirrup unit 50 in which a plurality of first stirrups 10 are disposed at a predetermined pitch and a top edge main reinforcement 30 is full-strength welded; an upper stirrup unit 60 in which a plurality of second stirrups 20 are disposed at a predetermined pitch, a horizontal reinforcement 40 is welded, and no hook is provided on an end of a hanging reinforcement part 22; and a bottom edge main reinforcement 70 connected to the inside of the first stirrups 10. The horizontal reinforcement 40 is disposed on the lateral side of a bottom reinforcement part 11 and has a cross section orthogonal to a longitudinal direction in an inverted T-shape in which a lower rectangular part 150 having a first width w1 and an upper rectangular part 160 having a second width w2 narrower than the first width w1 continue. The horizontal reinforcement 40 is included in the lower rectangular part 150.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to reinforced concrete beams. [Background technology]

[0002] In arranging beam bars that constitute foundation beams or beams that connect columns of a building, a construction method using so-called welded reinforcing bars is sometimes applied to streamline the work of arranging multiple stirrups while measuring the pitch between the stirrups along the longitudinal direction of the beam bars, attaching horizontal bars (abdominal bars) to the vertical bars that constitute the stirrups by bundling, etc., and connecting multiple main bars to the upper and lower insides of the stirrups. This welded reinforcing bar is, for example, a unit made by welding the stirrups and horizontal bars in advance in a factory, etc., and such welded reinforcing bars are brought to the site and, for example, the upper unit and the lower unit are connected on site to arrange closed stirrups. Then, the upper end main bars and lower end main bars are arranged on the upper and lower insides of the closed stirrups and bundling, etc., to arrange the beam bars.

[0003] Here, a reinforcement structure and method for beam reinforcement has been proposed in which a lower unit in which multiple stirrups are unitized by upper end main reinforcement and lower end main reinforcement is covered with a cap tie that does not have a hook and reinforced (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-29249 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the beam reinforcement described in Patent Document 1, the upper stirrup reinforcement, which is a cap tie, does not have a hook, and in addition, the cap tie is only slightly wrapped around the lower stirrup reinforcement, so it is unclear whether the beam reinforcement has sufficient strength.

[0006] According to the Guidelines and Commentary for Reinforcement of Reinforced Concrete Structures 2021 (Architectural Institute of Japan), the above-mentioned cap-tie type reinforcement has a specification in which, for example, a 135-degree hook is provided at the upper end of the lower stirrup and the lower stirrup and the cap tie are overlapped with a lap joint length of 6d (d is the name of deformed reinforcing bar). In view of such general specifications, it must be said that it is unclear whether the strength of the cap-tie type beam reinforcement described in Patent Document 1 is sufficient, in other words, whether the upper and lower stirrup reinforcements form a closed type reinforcement in a strong manner.

[0007] In particular, with closed-type reinforcing bars having a small beam depth, it is difficult to ensure a sufficient lap joint length as described above, and therefore it is difficult to form closed-type reinforcing bars having sufficient strength.

[0008] In this way, in the case of closed-type reinforcing bars with a small beam shape, a plurality of upper stirrups also having a U-shape opening downwards are arranged so as to cover a plurality of lower stirrups having a U-shape opening upwards, and then a plurality of tiers (e.g., two tiers) of horizontal bars are welded to the plurality of downward hanging bar parts constituting the upper stirrups, and the horizontal bars are used as hook substitutes for the upper stirrups. This makes it possible to shorten the lap splice length between the upper stirrups and the lower stirrups as much as possible, and thus makes it possible to form a closed-type reinforcing bar with a small beam shape that has sufficient strength.

[0009] However, since multiple rows of horizontal reinforcement are arranged protruding from the sides of the upper stirrups, there is a risk that the horizontal reinforcement will become the starting point of cracks and exacerbate the cracks.

[0010] The present invention has been made in consideration of the above problems, and aims to provide a reinforced concrete beam that has beam bars with high strength and excellent workability, and is less likely to crack. [Means for solving the problem]

[0011] In order to achieve the above object, one embodiment of a reinforced concrete beam according to the present invention is as follows: A reinforced concrete beam having a beam bar inside the concrete, The beam reinforcement is A lower stirrup unit is formed by first stirrups arranged at a predetermined pitch, each having a U-shape that opens upward and a bottom reinforcement part and a rising reinforcement part that rises upward from the left and right ends of the bottom reinforcement part, and each first stirrup is connected to the corresponding left and right rising reinforcement parts by full strength welding of the upper end main reinforcement at the inside of the upper ends of the corresponding left and right rising reinforcement parts; an upper stirrup unit in which second stirrups are arranged at a predetermined pitch, each having a U-shape that opens downward and a top end portion and a hanging portion that hangs down from the left and right ends of the top end portion to the bottom portion, each second stirrup is connected to the corresponding left and right hanging portion by welding a horizontal bar at a predetermined position outside the hanging portion, and no hook is provided at the end of the hanging portion; The bottom reinforcement portion forms the first stirrup and has a lower end main reinforcement connected to the inside of the bent portion at the boundary between the bottom reinforcement portion and the rising reinforcement portion, When the upper stirrup unit is placed over the lower stirrup unit, the rising portion of the corresponding first stirrup and the hanging portion of the corresponding second stirrup overlap, and the horizontal reinforcement is disposed on the side of the bottom reinforcement or the side of the lower end main reinforcement, The cross-sectional shape of the reinforced concrete beam perpendicular to the longitudinal direction is an inverted T shape in which a lower rectangular portion having a first width and an upper rectangular portion having a second width narrower than the first width are connected, The horizontal bars are included in the lower rectangular portion.

[0012] According to this embodiment, the rising reinforcement part of the lower stirrup unit, in which multiple first stirrups are integrated with the upper end main reinforcement, and the hanging reinforcement part of the upper stirrup unit, in which multiple second stirrups are integrated with the horizontal reinforcement, overlap, and the horizontal reinforcement is arranged on the side of the bottom reinforcement part or the side of the lower end main reinforcement, thereby forming a beam reinforcement with high strength and excellent workability. Furthermore, the cross-sectional shape perpendicular to the longitudinal direction of the reinforced concrete beam is an inverted T shape consisting of a lower rectangular part with a first width and an upper rectangular part with a second width narrower than the first width, and the horizontal reinforcement is included in the lower rectangular part, so that sufficient cover is secured on the side of the horizontal reinforcement, and the horizontal reinforcement is prevented from becoming a crack starting point, resulting in a reinforced concrete beam with excellent deformation performance and less cracking.

[0013] Here, the "full strength welding" where the first stirrup and the upper main bar are connected in the lower stirrup unit is also called "full strength rebar cross welding" and means spot welding where the weld has strength equal to or greater than the JIS standard yield point of the stirrup, the elongation of the main bar is equal to or greater than the JIS standard value of the rebar before welding, and the shear strength of the weld is equal to or greater than the short-term allowable tensile strength of the stirrup. Note that normal spot welding guarantees that the weld is about 1 / 3 to 2 / 3 of the JIS standard yield point of the rebar. This full strength welding is a welding method where normal spot welding is repeated two or more times, and the second spot welding is performed after one spot welding to anneal the weld before it is rapidly cooled.

[0014] The lower end main reinforcement, which is not necessarily included in the lower stirrup unit, is connected to the inside of the bent part at the boundary between the bottom reinforcement part and the rising reinforcement part that form the first stirrup. This lower end main reinforcement may also be connected to the first stirrup by full strength welding, or may be tied with a tie wire, etc. On the other hand, the "welding" that connects the multiple second stirrup reinforcements and the horizontal reinforcements in the upper stirrup unit means welding in a broad sense, which means not only full strength welding but also general spot welding.

[0015] In the upper stirrup unit, a horizontal bar is welded to the lower end or near the lower end of the hanging bar part of the second stirrup bars, so that the welded horizontal bar becomes a hook substitute bar in the second stirrup bars. Similarly, in the lower stirrup unit, the welded upper end main bar becomes a hook substitute bar in the first stirrup bars. By providing the horizontal bar as a hook substitute bar, the hook can be eliminated from the second stirrup bars. Similarly, by providing the upper end main bar as a hook substitute bar, the hook can be eliminated from the first stirrup bars.

[0016] In this embodiment, the corresponding first stirrup reinforcement part and the corresponding second stirrup reinforcement part overlap, but the overlap length does not need to satisfy the specified lap joint length, and in principle there is no restriction on the lap length. For example, in a beam with a low beam depth, if a specified lap joint length is required for the overlap part of the rising reinforcement part and the hanging reinforcement part, there may be cases where the specified lap joint length is not satisfied. Therefore, in this embodiment, although the overlap part of the rising reinforcement part and the hanging reinforcement part does not have the specified lap joint length, the corresponding first stirrup reinforcement and the second stirrup reinforcement are integrated by arranging a horizontal bar at the lower end position of the beam reinforcement height (side of the bottom reinforcement part and the lower end main reinforcement).

[0017] Another aspect of the reinforced concrete beam according to the present invention is as follows: The present invention is characterized in that a first covering of the horizontal stripes in the lower rectangular portion is larger than a second covering of the hanging stripes in the upper rectangular portion.

[0018] According to this embodiment, the first cover of the horizontal reinforcement in the lower rectangular portion is larger than the second cover of the hanging reinforcement portion in the upper rectangular portion, thereby preventing the horizontal reinforcement from becoming the starting point of cracks, resulting in a reinforced concrete beam that is less susceptible to cracks.

[0019] Another aspect of the reinforced concrete beam according to the present invention is as follows: The first fog is set to twice the second fog.

[0020] According to this embodiment, the first cover thickness is set to twice the second cover thickness, which prevents the horizontal bars from becoming the starting point of cracks, resulting in a reinforced concrete beam that is less susceptible to cracks.

[0021] Another aspect of the reinforced concrete beam according to the present invention is as follows: It is characterized by a beam depth of 500 mm or less.

[0022] According to this aspect, in a reinforced concrete beam with a small beam depth of 500 mm or less, the lapped portion of the rising reinforcement and the hanging reinforcement does not have a predetermined lap joint length, but the horizontal reinforcement is provided at the lower end position of the beam reinforcement (the side of the bottom reinforcement or the side of the lower end main reinforcement), so that a reinforced concrete beam with a beam reinforcement in which the first stirrup and the second stirrup are integrated can be formed. Here, "column depth of 500 mm or less" can mean, for example, a beam depth of 400 mm to 500 mm.

[0023] Another aspect of the reinforced concrete beam according to the present invention is as follows: The present invention is characterized in that the cross bars are connected by full strength welding on the outside of the hanging bars.

[0024] According to this embodiment, the second stirrups and the cross bars are connected by full strength welding instead of the usual spot welding, so that a reinforced concrete beam having beam bars with even higher strength can be formed. Effect of the Invention

[0025] As can be understood from the above explanation, according to the reinforced concrete beam of the present invention, it is possible to provide a reinforced concrete beam that is equipped with beam bars that are high in strength and have excellent workability, and is less susceptible to cracking. [Brief description of the drawings]

[0026] [Figure 1]1A to 1C are diagrams illustrating an example of a method for forming beam reinforcement to form a reinforced concrete beam according to an embodiment. [Diagram 2] 1A to 1C are diagrams illustrating an example of a method for forming beam reinforcement. [Diagram 3] 2, this is a diagram illustrating an example of a method for forming beam reinforcement. [Figure 4] FIG. 2 is a perspective view of an example of a reinforced concrete beam according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, a reinforced concrete beam according to an embodiment will be described with reference to the accompanying drawings, together with its constituent elements, the beam bars, and a method for forming the beam bars. In this specification and the drawings, substantially identical components are designated by the same reference numerals, and duplicated descriptions may be omitted.

[0028] [Reinforced concrete beam according to the embodiment] An example of a reinforced concrete beam according to an embodiment will be described together with its constituent beam bars and a method for forming the beam bars with reference to Fig. 1 to Fig. 4. Fig. 1 to Fig. 3 are views for explaining an example of a method for forming the beam bars that form the reinforced concrete beam according to the embodiment. Fig. 4 is a perspective view of an example of a reinforced concrete beam according to the embodiment.

[0029] As shown in FIG. 1, the lower stirrup unit 50 has an upwardly open U-shape, and is formed by arranging first stirrups 10 having a bottom reinforcement portion 11 and rising reinforcement portions 12 rising upward from the left and right ends of the bottom reinforcement portion 11 at a predetermined pitch S in the Z direction, which is the longitudinal direction of the beam reinforcement, and connecting each first stirrup 10 to the inside of the upper ends of the corresponding left and right rising reinforcement portions 12 by the upper end main reinforcement 30.

[0030] Here, the rising reinforcing bars 12 and the upper end main reinforcing bars 30 are connected by full strength welding. This full strength welding is a welding method in which ordinary spot welding is repeated two or more times, and a second spot welding is performed before the welded part is quenched after one spot welding, so that the welded part is annealed. By this full strength welding, the welded part between the first stirrup 10 and the upper end main reinforcing bars 30 has a strength equal to or greater than the JIS standard yield point of the first stirrup 10, the elongation of the reinforcing bars is equal to or greater than the JIS standard value of the reinforcing bars before welding, and the shear strength of the welded part is equal to or greater than the short-term allowable tensile strength of the stirrup, so that both members are connected with high connection strength.

[0031] The illustrated predetermined pitch S is 150 mm, 200 mm, etc., and is determined based on the amount of reinforcing bars required in the concrete. The first stirrups 10 are formed, for example, from deformed steel bars, and reinforcing bars with diameters of 10 mm (D10), D13, etc. are applied, and this is also determined based on the amount of reinforcing bars required in relation to the above-mentioned predetermined pitch S.

[0032] A deformed steel bar of a predetermined diameter is applied to the upper end main reinforcement 30, and since there are two upper end main reinforcement 30 in the illustrated example, the diameter is set to satisfy the design bending moment, design shear force, etc. From the viewpoint of the required amount of reinforcing bars, one or more additional upper end main reinforcement 30 may be arranged between the two upper end main reinforcement 30 in the final reinforcement arrangement state. For example, in the illustrated example, deformed steel bars such as D19 and D22 can be applied.

[0033] On the other hand, the upper stirrup unit 60 has a U-shape that opens downwards, and the second stirrup 20 having a top end reinforcement section 21 and hanging reinforcement sections 22 hanging downward from the left and right ends of the top end reinforcement section 21 is arranged at a predetermined pitch S in the Z direction, which is the longitudinal direction of the beam reinforcement, similar to the first stirrup 10, and each second stirrup 20 is formed by connecting the cross reinforcement 40 by welding at a predetermined position outside the corresponding left and right hanging reinforcement sections 22.

[0034] Here, the length of the hanging reinforcement portion 22 is L, and has a length that reaches the bottom reinforcement portion 11 of the first stirrup 10 when the beam reinforcement intermediate body 100' shown in Fig. 2 is formed. The attachment position of the cross reinforcement 40 is the lower end or a position near the lower end of the hanging reinforcement portion 22 (a lateral position of the bottom reinforcement portion 11 in Fig. 2, or a lateral position of the lower end main reinforcement 70 of the beam reinforcement 100 shown in Fig. 3).

[0035] The horizontal bars 40 are connected to the hanging bars 22 by welding. This welding may be a normal spot welding, but it is preferable to connect them by full strength welding, similar to the welding of the first stirrup 10 and the upper end main bar 30 in the lower stirrup unit 50.

[0036] Also, the lower end of the hanging reinforcing bar portion 22 of the second stirrup 20 does not have a hook, and the horizontal reinforcing bar 40 is connected by welding at or near the lower end, so that the horizontal reinforcing bar 40 serves as a hook substitute. In this way, although the second stirrup 20 does not have a hook at the end of the hanging reinforcing bar portion 22, the horizontal reinforcing bar 40 is connected by welding, preferably by full strength welding, so that the good anchorage of the second stirrup 20 in the concrete expected from the hook is guaranteed.

[0037] Similarly, in the lower stirrup unit 50, the first stirrup 10 does not have a hook at the end of the rising reinforcing part 12, but the upper end main reinforcing bar 30 is connected by welding, so that the upper end main reinforcing bar 30 serves as a hook substitute reinforcing bar. In this way, the upper end main reinforcing bar 30 is connected to the end of the first stirrup 10 by full strength welding, so that the good anchorage of the first stirrup 10 in the concrete expected from the hook is guaranteed.

[0038] In addition, the lower stirrup unit 50 and the upper stirrup unit 60 in the illustrated example each have five first stirrups 10 and five second stirrups 20 at the same pitch S, but from the standpoint of transportability to the site as well as workability such as transportability at the site, the unit may have six or more stirrups and be as long as possible in the Z direction.

[0039] For example, since the lower stirrup unit 50 has only the upper end main reinforcement 30 as the main reinforcement and does not have the lower end main reinforcement, the weight of the lower stirrup unit 50 is as light as possible compared to the configuration in which the lower stirrup unit already has the lower end main reinforcement. Therefore, the lower stirrup unit 50 can be made longer in the Z direction compared to the configuration in which the lower stirrup unit has the lower end main reinforcement. In addition, when such a longer lower stirrup unit 50 is prepared, the upper stirrup unit 60 is also prepared with a length corresponding to this longer lower stirrup unit 50.

[0040] As shown in FIG. 1, the upper stirrup unit 60 is placed over the lower stirrup unit 50 in the X1 direction, and the corresponding rising reinforcement portion 12 of the first stirrup 10 and the hanging reinforcement portion 22 of the second stirrup 20 are overlapped and connected to form a beam reinforcement intermediate body 100' as shown in FIG. 2.

[0041] In forming this beam reinforcement intermediate body 100', since the lower stirrup unit 50 has the upper end main reinforcement 30, when the second stirrup reinforcement 20 constituting the upper stirrup reinforcement unit 60 is placed over the lower stirrup reinforcement unit 50 from above, the second stirrup reinforcement 20 can be placed on top of the two upper end main reinforcements 30.

[0042] Next, as shown in Fig. 3, the lower end main reinforcement 70 is arranged in the X2 direction and connected to the inside of the bent part at the boundary between the bottom reinforcement part 11 and the rising reinforcement part 12 that form each first stirrup 10, thereby forming the beam reinforcement 100. Here, the lower end main reinforcement 70 is connected to the first stirrup 10 by bundling with a bundling wire or the like, but may also be joined by welding.

[0043] The beam bar 100 in the illustrated example is a beam bar of a reinforced concrete beam with a low beam depth of 500 mm or less. More specifically, as shown in Fig. 4, the beam depth H of a reinforced concrete beam 200 is set in the range of 400 mm to 500 mm, and the beam bar 100 shown in Fig. 3 is a beam bar that forms this reinforced concrete beam 200. Therefore, the length of the lap portion of the rising reinforcement portion 12 and the hanging reinforcement portion 22 (lap length is the length L of the rising reinforcement portion 12 and the hanging reinforcement portion 22) is set to be equal to or longer than a predetermined hook overlap length L. 1h does not have

[0044] If a specified lap joint length were required at the lap point between the rising reinforcement section 12 and the hanging reinforcement section 22 for a reinforced concrete beam 200 with such a low beam depth, there may be cases where the specified lap joint length is not met.

[0045] Therefore, in the beam reinforcement 100, although the lap portion between the rising reinforcement portion 12 and the hanging reinforcement portion 22 does not have a specified lap joint length, the lap length of the lap portion is ensured to be the height L of the beam reinforcement 100, and a cross reinforcement 40 is arranged at the lower end position of the beam reinforcement 100 (to the side of the bottom reinforcement portion 11 and the lower end main reinforcement 70), so that the corresponding first stirrup reinforcement 10 and second stirrup reinforcement 20 can be integrated with high strength.

[0046] In addition, by arranging the cross bars 40 at the lower end position of the height of the beam bars 100 (to the side of the bottom reinforcement portion 11 and the lower end main reinforcement 70), a reinforced concrete beam 200 in which brittle fracture is suppressed can be formed.

[0047] 4, the reinforced concrete beam 200 has a lower rectangular portion 150 having a first width w1 and an upper rectangular portion 160 having a second width w2 narrower than the first width w1, and its cross section perpendicular to the longitudinal direction has an inverted T shape. As described above, the beam depth H of the reinforced concrete beam is small, having a beam depth H of 500 mm or less.

[0048] A horizontal bar 40 is included inside a lower rectangular portion 150 having a first width w1, and a cover t1 of the horizontal bar 40 is set larger than a cover t2 of the hanging bar portion 22 and the rising bar portion 12 in the upper rectangular portion 160.

[0049] Specifically, the fog t1 is set to about twice the fog t2, and when the fog t2 is 50 mm, the fog t1 is set to 100 mm.

[0050] In this way, by making the cross-sectional shape perpendicular to the longitudinal direction of the reinforced concrete beam 200 an inverted T-shape and making the first cover t1 on the side of the cross reinforcement 40 sufficiently large and larger than the second cover t2 of the hanging reinforcement section 22 and the rising reinforcement section 12 located above it, the cross reinforcement 40, which is located on the outermost side of the beam reinforcement 100, is prevented from becoming the starting point of cracks, and a reinforced concrete beam 200 that is less susceptible to cracks and has excellent deformation performance can be formed.

[0051] In addition, the present invention is not limited to the configuration shown here, and may be implemented in other embodiments in which other components are combined with the configurations and the like of the above-mentioned embodiment. In this regard, the present invention may be modified within the scope of the gist of the present invention, and may be appropriately determined according to the application form. [Explanation of symbols]

[0052] 10: First stirrup 11: Bottom reinforcement 12:Rising muscle section 20: Second stirrup 21: Top muscle section 22: Hanging muscle 30:Top main reinforcement 40: Horizontal stripes 50: Lower stirrup unit 60: Upper stirrup unit 70: Bottom main reinforcement 100: Beam reinforcement 150: Lower rectangular part 160: Upper rectangular part 200: Reinforced concrete beam

Claims

1. A reinforced concrete beam having a beam bar inside the concrete, The beam reinforcement is a lower stirrup unit in which first stirrups are arranged at a predetermined pitch, each having a U-shape that opens upward and a bottom reinforcement portion and a rising reinforcement portion that rises upward from the left and right ends of the bottom reinforcement portion, and each first stirrup is connected to the corresponding left and right rising reinforcement portions by full strength welding of the upper end main reinforcement at the inside of the upper ends of the corresponding left and right rising reinforcement portions; an upper stirrup unit in which second stirrups are arranged at a predetermined pitch, each having a U-shape that opens downward and a top end portion and a hanging portion that hangs down from the left and right ends of the top end portion to the bottom portion, each second stirrup is connected to the corresponding left and right hanging portion by welding a horizontal bar at a predetermined position outside the hanging portion, and no hook is provided at the end of the hanging portion; The bottom reinforcement portion and the rising reinforcement portion are connected to the inside of the bent portion at the boundary between the bottom reinforcement portion and the rising reinforcement portion that form the first stirrup. When the upper stirrup unit is placed over the lower stirrup unit, the rising portion of the corresponding first stirrup and the hanging portion of the corresponding second stirrup overlap, and the horizontal reinforcement is disposed on the side of the bottom reinforcement or the side of the lower end main reinforcement, The cross-sectional shape of the reinforced concrete beam perpendicular to the longitudinal direction is an inverted T shape in which a lower rectangular portion having a first width and an upper rectangular portion having a second width narrower than the first width are connected, A reinforced concrete beam, characterized in that the cross bars are included in the lower rectangular portion.

2. 2. The reinforced concrete beam according to claim 1, wherein a first cover of the transverse reinforcement in the lower rectangular portion is greater than a second cover of the hanging reinforcement in the upper rectangular portion.

3. 3. The reinforced concrete beam according to claim 2, wherein the first cover is set to twice the second cover.

4. 3. A reinforced concrete beam according to claim 1 or 2, characterized in that the beam depth is 500 mm or less.

5. 3. The reinforced concrete beam according to claim 1, wherein the horizontal reinforcement is connected by full-strength welding on the outside of the hanging reinforcement portion.

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