JP7328004B2 - Reinforcing bar and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reinforcing bar having a bending portion and a bending apparatus for the reinforcing bar.

Various design standards stipulate that the ends of reinforcing bars in reinforced concrete members are fixed to concrete by standard hooks having a bent portion and a straight portion. The bent portion is most commonly arcuate (semicircular) with a central angle of 180°, but may be arcuate (1/4 circle) with a central angle of 90°. Loop joints in which ends of U-shaped reinforcing bars having semicircular bent portions are overlapped are also often used in precast floor slabs of highway bridges (for example, Patent Documents 1 and 2).

The reason why these bent portions are arcuate largely depends on the bending device that bends the reinforcing bars. In this type of bending device, a circular bending roller is placed outside the disc (collar) while the reinforcing bar is placed against the collar. is moved on a circular orbit centered on . As a result, the reinforcing bar is bent into an arc shape (for example, Patent Documents 3, 4, etc.).

Japanese Patent Application Laid-Open No. 2009-264040 JP 2010-236258 A JP-A-9-10851 JP 2012-16719 A

When a tensile force is applied to the reinforcing bars in the concrete, bearing stress is generated in the concrete inside the bent portion. The processing radius (inner radius) of the bending portion is set to about 2.0 to 5.0 times the diameter of the reinforcing bar, but if it is too small, the bearing pressure stress of the concrete inside the bending portion increases, and splitting failure may occur in the concrete. There is

Focusing on the mechanical mechanism in which the tensile force of the reinforcing bar becomes the bearing pressure of the concrete and is transmitted to the concrete and fixed, it is desirable that the distribution of the bearing stress degree along the axial direction of the reinforcing bar is uniform. In the case where the bent portion is arc-shaped, the distribution is not uniform in practice, and there are places where the degree of bearing stress is locally increased. From this point of view, the arc-shaped bent portion cannot be said to have a rational shape.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a reinforcing bar or the like having a bent portion with a rational shape.

A first invention for solving the above-described problems has an elliptical arc-shaped bent portion having a major axis direction along the longitudinal direction of the reinforcing bar body at the end, and the end is a reinforcing bar. is a hook portion that is bent into a hook shape, and the hook portion has the bent portion that continues from the reinforcing bar body and a straight portion that extends from the end point of the bent portion, and the ellipse of the bent portion It is a reinforcing bar characterized by the ratio of the major axis to the minor axis of the arc being 2:1 .

The present inventors diligently studied the shape of the bent portion so that the bearing stress of the concrete inside the bent portion would have a more uniform distribution with respect to the tensile force of the reinforcing bar, and the above elliptical arc shape is almost ideal. I found that it has a typical shape. By processing the end portion of the reinforcing bar into such a shape, it becomes possible to equalize the bearing stress of the concrete inside the bent portion. Further, in this case, it is possible to flatten the bent portion and reduce its width, and since the maximum value of the bearing stress is reduced, cracking of the concrete does not occur. As a result, the bent portion can be made compact, and there is no problem of tangled reinforcing bars even in places where reinforcing bars are densely arranged.

In the present invention , the degree of bearing stress of the concrete inside the bent portion can be made more uniform.

The bent portion of the present invention is a part of the hook portion for anchoring the reinforcing bar. can be made more uniform.

A second aspect of the present invention has an elliptical arc-shaped bent portion having a long axis direction along the longitudinal direction of the reinforcing bar body at the end, and the end is a hook formed by bending the reinforcing bar into a hook shape. wherein the hook portion has the bent portion continuing from the reinforcing bar main body and a straight portion extending from the end point of the bent portion. A manufacturing method for bending a reinforcing bar by a device, wherein the bending device includes a collar and a bending roller, the collar and the bending roller have an elliptical arc, and the collar has an elliptical arc. The major axis and the minor axis are the same as the major axis and the minor axis of the elliptical arc of the bending roller, respectively, the collar and the bending roller are arranged with a gap for arranging the reinforcing bar, and the bending roller is the The manufacturing method is characterized in that the bending roller can rotate around the center of the elliptical arc of the bending roller, and that the rotation axis moves in a circular orbit around the center of the elliptical arc of the collar.

The shape of the bent portion described above is novel and cannot be processed by a conventional bending apparatus. Accordingly, the present inventor devised a bending apparatus as described above, which makes it possible to easily perform the bending process described above.

ADVANTAGE OF THE INVENTION By this invention, the reinforcing bar etc. which have a bent part of a rational shape can be provided.

The figure which shows the reinforcing bars 1 and 2. FIG. The figure explaining the bearing pressure stress of concrete. An example of modeling the reinforcing bar R. The figure which shows the reinforcement of Case 1-4. The figure which shows an analysis result. The figure which shows bearing pressure stress (sigma). The figure which shows the bending apparatus 100. FIG. FIG. 4 shows the movement of the bending roller 120; An example of exchanging the collar 110 and the bending roller 120 according to the reinforcing bar diameter. The figure which shows reinforcing bars 1a and 1b.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

(1. Reinforcing bars 1 and 2)
1(a) and 1(b) are diagrams showing reinforcing bars 1 and 2 according to an embodiment of the present invention.

A reinforcing bar 1 shown in FIG. 1(a) has an end portion bent into a hook shape to form a fixing hook portion, and has a reinforcing bar main body 10, a bent portion 11, a linear portion 12, and the like. The reinforcing bar main body 10 is a portion up to the position where the bending of the reinforcing bar 1 is performed (the starting point of the bending portion 11), and the bending portion 11 and the straight portion 12 constitute the hook portion described above.

The bent portion 11 is an elliptical arc-shaped portion continuous from the reinforcing bar body 10 . This elliptical arc is a part of an ellipse whose major axis is in the direction along the longitudinal direction of the reinforcing bar body 10, and the bending part 11 divides the ellipse in half at the minor axis position. It is elliptical. In this embodiment, the ratio a:b of the major axis a to the minor axis b of the ellipse is 2:1. Here, the major axis a and the minor axis b of the ellipse are assumed to be based on the position of the center line (core) of the reinforcing bar 1 . This is the same for reinforcing bars 2 and reinforcing bars R, which will be described later.

The straight portion 12 is a portion extending parallel to the reinforcing bar body 10 from the end point of the bent portion 11 toward the reinforcing bar body 10 side.

A reinforcing bar 2 shown in FIG. 1B has a loop portion forming one end of a loop joint, and has a reinforcing bar main body 20 and a bent portion 21 . The reinforcing bar main body 20 is a portion up to the position where the reinforcing bar 2 is bent (the starting point or the terminal point of the bending portion 21), and the bending portion 21 constitutes the loop portion.

The bent portion 21 is an elliptical arc-shaped portion that connects a pair of parallel reinforcing bar main bodies 20 at the ends of the reinforcing bar 2 . This elliptical arc is also a part of an ellipse whose major axis direction is the direction along the longitudinal direction of the reinforcing bar body 20, and the bending part 21 divides the ellipse in half at the minor axis position. It is elliptical. In this embodiment, the ratio a:b of the major axis a to the minor axis b of the ellipse is 3:2.

(2. Bearing stress of concrete)
As shown in FIG. 2(a), when the reinforcing bar body 10 of the reinforcing bar 1 embedded in concrete receives a tensile force, the reinforcing bar 1 tends to be displaced in the axial direction and the axis-perpendicular direction. This displacement is resisted in the axial direction by the adhesion of the reinforcing bars 1 and the concrete, and in the direction perpendicular to the axis by the bearing pressure of the concrete.

At this time, a bearing stress σ in the direction perpendicular to the axis of the reinforcing bar 1 is generated in the concrete inside the bent portion 11, and this bearing stress σ causes the concrete to split in the direction normal to the paper surface of FIG. 2(a). becomes. This is the same when both reinforcing bar bodies 20 of the reinforcing bars 2 embedded in concrete receive the tensile force T as shown in FIG. 2(b).

In order to study the distribution of the bearing stress of concrete, as shown in FIG. The distribution of the bearing stress when a tensile force T was applied to the main body of the reinforcing bar was analyzed. The springs S1 and S2 are provided in the direction perpendicular to the axis of the reinforcing bar R and in the axial direction, respectively. The former spring S1 expresses the bearing pressure of the concrete, and the latter spring S2 expresses the adhesion action of the reinforcing bars R by the joints.

The diameter of the reinforcing bar R (reinforcing bar diameter) φ is 22.2 mm. The spring constant of S2 was set in consideration of the shear elastic modulus of concrete and the range of stress transmission from the node of the reinforcing bar R to the concrete.

A, B, C, D, and E in FIG. 3 respectively represent the loading position of tensile force T, the bending start point, the top of the hook, the bending end point, and the tip of the hook. A section up to the hook tip E was modeled. The length of the reinforcing bar R from the loading position A of the tensile force T to the bending start point B is the same as the length of the reinforcing bar R from the bending end point D to the hook tip E (4φ=88.8 mm).

As shown in FIG. 4, the shape of the bent portion of the reinforcing bar R is Case 1 (semicircular), Case 2 (semielliptical with the short axis direction along the longitudinal direction of the reinforcing bar body), Case 3, 4 (a semi-elliptical shape with the long axis direction along the longitudinal direction of the main body of the reinforcing bar) were compared. In Case 3, the ratio a:b between the major axis a and the minor axis b was 2:1, and in Case 4, the ratio a:b was 3:2. In Case 2, the ratio of the major axis to the minor axis is 2:1.

In each case 1 to 4, the length of the reinforcing bar R from the bending start point B to the bending end point D is the same. Note that FIG. 4 shows, in the coordinate system used for the analysis, the nodes when the reinforcing bar R is divided into elements during the analysis by circles having a size corresponding to the diameter of the reinforcing bar.

The analysis results of cases 1 to 4 are shown in FIGS. 5(a) and 5(b). 5(a) shows the relationship between the distance from the loading position A (distance in the axial direction of the reinforcing bar R) and the axial force (tensile force) of the reinforcing bar R, and FIG. and the deformation amount of the spring S1. The amount of deformation of the spring S1 corresponds to the bearing stress of the concrete.

As shown in FIG. 5(a), the tensile force T of the reinforcing bar R decreases as the tip E of the hook is approached. This is due to the adhesion resistance of concrete, and the value depends on the distance from the loading position A regardless of the shape of the bent portion.

On the other hand, as shown in FIG. 5(b), the bearing stress of the concrete (deformation amount of the spring S1) reaches one peak in common near the bending starting point B, but the distribution of the bearing stress is different from the case 1 to 4 differ. This is because, as shown in FIG. 6, the bearing stress σ is represented by the resultant force of the tensile stress t, and its magnitude varies depending on the shape of the bent portion and the tensile force T.

Comparing Cases 1 to 4, the bearing stress of the concrete near the bending start point B is smaller for Case 2>1>4>3. In Cases 3 and 4, which have elliptical arc-shaped bent portions along the direction, the distribution of the bearing stress can be made more uniform than the other Cases 1 and 2, and the maximum value of the bearing stress can be reduced. It can be seen that it can be reduced.

Comparing Cases 3 and 4, in Case 4 where the ratio a:b of the major axis a to the minor axis b is 3:2, the bearing stress of the concrete near the bending start point B is the same as that near the hook apex C. about twice the value. On the other hand, in case 3 where the ratio a:b is 2:1, the concrete bearing stress near the bending start point B is about the same as the value near the hook apex C, and the concrete bearing stress is higher. uniform. Therefore, when bending the end portion of the reinforcing bar into a hook shape, Case 3, in which the ratio a:b between the major axis a and the minor axis b is 2:1, is more preferable.

On the other hand, as shown in FIG. 1(b), considering the case of the rebar 2 with the end portion as the loop portion, the distribution of the bearing stress degree when the tensile force T is applied to both rebar main bodies 20 is as shown in FIG. 5(b) ) is added with the distribution of bearing stress obtained by horizontally reversing the above distribution.

Therefore, in the case of the reinforcing bar 2, if the ratio a:b between the major axis a and the minor axis b of the elliptical arc of the bent portion 21 is 2:1 as in case 3, the bearing stress near the hook apex C increases, It can be seen that setting the ratio a:b to 3:2 as in case 4 is preferable because the distribution of the bearing stress can be made more uniform.

(3. Bending device 100)
Bending portions 11 and 21 having elliptical arcs as shown in FIGS. 1A and 1B cannot be processed by a conventional bending apparatus. Therefore, a new bending device is required. FIG. 7 is a diagram schematically showing a bending apparatus 100 for bending a bending portion 11 (21) of a reinforcing bar 1 (2) having an elliptical arc.

A bending apparatus 100 shown in FIG. 7 has a collar 110, a bending roller 120 and a stopper 130 provided on a housing.

The collar 110 and the bending roller 120 have an elliptical arc in the plane and are arranged side by side in the plane with a gap for placing the rebar 1 . The major and minor diameters of the elliptical arc of collar 110 are the same as the major and minor diameters of the elliptical arc of bending roller 120, respectively.

The bending roller 120 can rotate around the center of the elliptical arc as the rotation axis 121 . On the other hand, the collar 110 is fixed to the housing, and the bending roller 120 rotates the collar 110 so that its rotating shaft 121 draws a circular orbit (see F in FIG. 8 to be described later) about the center 111 of the elliptical arc of the collar 110. It is movable around the center 111 of 110 .

A groove 140 for moving the rotary shaft 121 is formed in the housing along the circular orbit. In this embodiment, when the rotating shaft 121 of the bending roller 120 moves 180° around the center 111 of the collar 110, the reinforcing bar 1 is bent into a hook shape and the bending process is completed (see the dotted line in FIG. 7). is shaped like a semicircle.

The mechanism for moving the bending roller 120 is not particularly limited, but in this embodiment, elliptical gears are used, and the elliptical gears provided inside the housing so as to correspond to the collar 110 and the bending roller 120 are engaged with each other.

Reference numerals 112 and 122 in FIG. 8(a) show the elliptical gears provided in the housing corresponding to the collar 110 and the bending roller 120, respectively, in plan view. The elliptical gears 112 and 122 are gears arranged at equal intervals on an elliptical arc, and both the elliptical gears 112 and 122 have the same major axis, minor axis and number of teeth of the elliptical arc.

The minor and major axes of the elliptical arcs of the elliptical gears 112 and 122 coincide with the minor and major axes of the elliptical arcs of the collar 110 and the bending roller 120, respectively, and the centers of the elliptical arcs of the elliptical gears 112 and 122 are aligned. coincide in the plane with the centers of the elliptical arcs of collar 110 and bending roller 120, respectively. The elliptical gear 122 can rotate integrally with the bending roller 120 around the rotating shaft 121 .

In this embodiment, both the elliptical gears 112 and 122 are meshed so that the minor axis of the elliptical gear 112 and the major axis of the elliptical gear 122 are coaxial at the initial position of the bending roller 120 shown in FIG. 8(a). At this time, the minor axis of the collar 110 and the major axis of the bending roller 120 are also coaxial.

Then, the rotation shaft 121 of the elliptical gear 122 is moved along the circular orbit F using a drive mechanism (not shown) such as a motor. Then, as shown in FIGS. 8(b) to 8(f), the elliptical gear 122 rotates about the rotation axis 121 while maintaining a constant distance between the rotation axis 121 and the center 111 of the elliptical gear 112. It moves on a circular orbit F around the center 111 of the elliptical gear 112 while rotating in the direction indicated by the arrow G in the figure.

In the above example, as the elliptical gear 122 moves on the circular orbit F, the elliptical gear 122 is driven to rotate. The elliptical gear 122 may rotate in the direction indicated by the arrow G.

In any case, the elliptical gear 122 should move on the circular orbit F around the center 111 of the elliptical gear 112 while rotating about the rotation axis 121 . As a result, the bending roller 120 provided corresponding to the elliptical gear 122 moves on the circular orbit F around the center 111 of the collar 110 while also rotating about the rotating shaft 121 . The bending roller 120 presses the reinforcing bar 1 against the collar 110 side, so that the end portion of the reinforcing bar 1 disposed between the collar 110 and the bending roller 120 is bent into an elliptical arc shape.

After the reinforcing bar 1 has been bent, the reinforcing bar 1 is removed and the bending roller 120 is returned to its initial position. 130 in the figure is a stopper, which fixes the position of the main body of the reinforcing bar when bending the end of the reinforcing bar 1 . The thickness of the collar 110 and the bending roller 120 should be about the diameter of the reinforcing bar to be processed.

Also, if the shape of the center line of the reinforcing bar in the bent portion is the same elliptical arc shape, only the collar 110 and the bending roller 120 can be replaced according to the diameter of the reinforcing bar as shown in FIGS. 9(a) and 9(b). Therefore, the reinforcing bar 1 having a plurality of diameters can be bent. In this case, the position of the stopper 130 is adjusted according to the diameter of the reinforcing bar.

As described above, the reinforcing bars 1 and 2 of the present embodiment have the elliptical arc-shaped bent portions 11 and 21 whose major axis direction is the longitudinal direction of the reinforcing bar bodies 10 and 20. It is possible to realize a rational shape in which the degree of bearing stress of the concrete inside 21 is uniformed.

In addition, the elliptical arc-shaped bent portions 11 and 21 whose long axis direction is the longitudinal direction of the reinforcing bar bodies 10 and 20 are flatter than the conventional semicircular bent portions, and the width (from the bending start point B The linear distance to the bending end point D) can be reduced. Moreover, since the maximum value of bearing stress is also reduced, cracking of concrete does not occur. As a result, the bent parts 11 and 21 can be made compact, and the reinforcing bars 1 and 2 can be arranged more freely without causing a problem of tangled reinforcing bars even in places where the reinforcing bars are densely arranged. In addition, when a loop joint is provided in the floor slab, the thickness of the floor slab is determined by the width of the bent portion of the loop joint, and in some cases the thickness of the floor slab is greater than necessary. It is possible to reduce the floor slab thickness by forming the bent portion 21 having a small width as shown in FIG.

Especially in recent years, the strength of reinforcing bars has been increasing, and high-strength reinforcing bars that bear a large tensile force also increase the bearing pressure stress of concrete. Miniaturization of the bent portion is desired. Forming the bent portions 11 and 21 in the shape of an elliptical arc as in this embodiment also meets such a requirement.

Concerning the major axis and the minor axis of the elliptical arc, by setting the ratio of the minor axis to the major axis to be 2/3 or less, the degree of bearing stress of the concrete inside the bent portions 11 and 21 can be made more uniform.

In particular, when the bent portion 11 is used as a part of the hook portion for anchoring the reinforcing bar as shown in FIG. Concrete bearing stress can be made more uniform. On the other hand, when the bent portion 21 is used as a loop portion forming one side of the loop joint as shown in FIG. The bearing stress of the concrete can be made more uniform.

Further, as in the present embodiment, by using the bending apparatus 100 in which the bending roller 120 having an elliptical arc rotates and moves on a circular orbit around the center of the collar 110 having an elliptical arc, the elliptical shape as described above is used. Arc-shaped reinforcing bars can be easily bent. A configuration in which a circular bending roller is biased toward the collar 110 by a spring and presses the reinforcing bar against the collar 110 while the bending roller moves along the elliptical arc of the collar 110 is also possible. It is conceivable, but in this case, processing of the reinforcing bar 1 requires a considerably large spring reaction force, so it is not realistic.

However, the invention is not limited to the above embodiments. For example, in the reinforcing bar 1 of this embodiment, the bent portion 11 has a semi-elliptical shape with a central angle of 180°, but as shown in the reinforcing bar 1a in FIG. It may be elliptical, and in this case, the processing by the bending apparatus 100 may be finished at the time shown in FIG. 8(e). Alternatively, as shown in the reinforcing bar 1a in FIG. 10(b), the bent portion 11 may have an elliptical arc shape with a central angle of more than 90° and less than 180°.

Moreover, the bending apparatus 100 only needs to have the collar 110 and the bending roller 120 described above, and other configurations are not particularly limited. Further, the bending apparatus 100 may be a portable apparatus capable of performing reinforcement processing at a construction site, or may be a stationary apparatus performing processing at a factory.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the technical ideas disclosed in the present application, and these also belong to the technical scope of the present invention. Understood.

1, 1a, 1b, 2: reinforcing bars 10, 20: reinforcing bar bodies 11, 21: bending part 12: straight part 100: bending device 110: collar 111: center 112, 122: elliptical gear 120: bending roller 121: rotation Shaft 130: Stopper 140: Groove

Claims (2)

An elliptical arc-shaped bent portion having a major axis direction along the longitudinal direction of the reinforcing bar body is provided at the end,
The end portion is a hook portion in which a reinforcing bar is bent into a hook shape,
The hook portion has the bent portion continuing from the reinforcing bar body and a straight portion extending from the end point of the bent portion,
A reinforcing bar characterized in that the ratio of the major axis to the minor axis of the elliptical arc of the bent portion is 2:1 . An elliptical arc-shaped bent portion having a major axis direction along the longitudinal direction of the reinforcing bar body is provided at the end,
The end portion is a hook portion in which a reinforcing bar is bent into a hook shape,
The hook portion has a bending portion continuing from the reinforcing bar main body and a straight portion extending from an end point of the bending portion. A manufacturing method for manufacturing by bending,
The bending device is
Equipped with collars and bending rollers,
said collar and said bending roller having an elliptical arc;
the major axis and minor axis of the elliptical arc of the collar are the same as the major axis and minor axis of the elliptical arc of the bending roller, respectively;
said collar and said bending roller are arranged with a gap for placing rebar;
The bending roller is rotatable around the center of the elliptical arc of the bending roller as a rotation axis, and the rotation axis moves in a circular orbit around the center of the elliptical arc of the collar. Method.

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