JP7699437B2 - Box culvert - Google Patents

Description

The present invention relates to a box culvert made of precast concrete.

Conventionally, when constructing underground waterways, roads, etc., box culverts, which are cylindrical bodies with a hollow cross section, have been widely used (see, for example, Patent Documents 1 and 2). Box culverts are often constructed by casting in place, but when it is necessary to shorten the process, etc., underground structures such as waterways and roads may be constructed by burying precast products in the ground while connecting them in the longitudinal direction.

Conventional box culverts, whether cast-in-place or precast, are often constructed with a rectangular cross section that has a haunch at the corner of the edge shape. Precast box culverts are manufactured in factories, so there is a greater degree of freedom in the form shape compared to cast-in-place products, but they have cross-bar arrangements such as rebar that runs along the haunch and corner reinforcement bars that mimic the shape of cast-in-place products. This means that arranging the reinforcement at the corners during production requires a great deal of effort, and it is difficult to streamline the amount and placement of rebar.

In order to solve these problems, the applicant for this patent has already proposed a precast concrete box culvert described in Patent Document 3. As shown in Figure 4, the box culvert in Patent Document 3 is equipped with a body 2 made of concrete with a roughly rectangular cross section, with corners 1 (corners) formed in an arc shape (arch shape), main reinforcements 3 arranged in the circumferential direction when viewed in cross section on both the outside and inside of the body 2, and tie reinforcements 4 arranged in the circumferential direction at a specified interval and surrounding the main reinforcements 3.

Japanese Patent Application Publication No. 5-163760 JP 2001-173368 A Patent Application No. 2019-204843 (currently unpublished)

The box culvert of the conventional Patent Document 3 is installed by erecting the side wall member 6 and the top plate member 7 on the bottom plate member 5, which is approximately U-shaped, as shown in FIG. 5. When the side wall member 6 and the top plate member 7 are erected, the side 8 of the bottom plate member 5 is in a cantilevered state because it is in an arc shape. At this time, the stress state is different from that when the ring of the box culvert is completed, and there is a risk that undesigned strain will occur in the reinforcing bars of the span of the bottom plate member 5. As a countermeasure against this cantilevered state, for example, it is possible to install a support on the side of the bottom plate member 5 or to backfill under the side. However, such a countermeasure increases the amount of work and there is a risk of delaying the construction process. In addition, it is necessary to select a material that does not require compaction, such as liquefied treated soil, for backfilling under the side. For this reason, a technology that ensures the quality of the structure and does not delay the construction process was required.

The present invention was made in consideration of the above, and aims to provide a precast concrete box culvert that can ensure the quality of the structure and does not delay the construction process.

In order to solve the above problems and achieve the objectives, the box culvert of the present invention is a precast concrete box culvert consisting of a body with a substantially rectangular cross section with the corners formed in an arch shape, and is characterized by comprising a substantially U-shaped base plate member with both left and right ends forming corners, side wall members arranged opposite each other on both left and right ends of the base plate member, a top plate member that connects the upper parts of the side wall members and is arranged opposite the base plate member, and camber materials provided under the corners at both left and right ends of the base plate member to reduce stress and strain that occurs in the cantilevered base plate member when the side wall members and top plate member are erected.

The box culvert according to the present invention is characterized in that in the above-mentioned invention, the camber material is made of concrete, steel, or a composite material of these formed on the underside of the corner portion.

The box culvert according to the present invention is characterized in that in the above-mentioned invention, the side line of the camber material is located on an extension of the central axis of the side wall member.

The box culvert according to the present invention is characterized in that, in the above-mentioned invention, it is provided with main reinforcements arranged in the circumferential direction in cross-sectional view on the outside and inside of the interior of the body, and tie reinforcements arranged in the circumferential direction at a predetermined interval and surrounding the main reinforcements.

According to the box culvert of the present invention, the box culvert is made of precast concrete and has a rectangular cross-section with arched corners. The box culvert is made of a U-shaped base plate member with both left and right ends forming corners, side wall members arranged on both left and right ends of the base plate member, a top plate member that connects the upper parts of the side wall members and is arranged opposite the base plate member, and camber members arranged under the corners on both left and right ends of the base plate member to reduce the stress and strain that occurs in the cantilevered base plate member when the side wall members and the top plate member are erected. Therefore, the load due to the weight of the side wall members and the top plate member is transmitted to the installation surface as an axial force by the camber members, and the bending moment and strain of the reinforcing bars that occur in the span of the base plate member during the construction process can be reduced. This has the effect of ensuring the quality of the base plate and providing a precast concrete box culvert that does not delay the construction process.

In addition, with the box culvert of the present invention, the camber material is made of concrete, steel, or a composite material of these formed on the underside of the corner portion, which has the effect of allowing the camber material to be installed relatively easily and at low cost.

In addition, with the box culvert of the present invention, the side line of the camber material is located on an extension of the central axis of the side wall member, which effectively reduces the bending moment and strain of the reinforcing bar that occurs in the span portion of the base slab member during the construction process, and also optimizes the volume of the camber material.

In addition, the box culvert of the present invention is equipped with main reinforcements arranged in the circumferential direction in cross-sectional view on both the outside and inside of the interior of the body, and tie reinforcements arranged in multiple circumferential directions at a specified interval and surrounding the multiple main reinforcements, making it possible to eliminate the need for cross reinforcement such as corner reinforcement that exists in conventional box culverts with rectangular cross sections. This has the effect of reducing the effort required for reinforcement work during construction.

FIG. 1 is a partial perspective view of a main portion showing a first embodiment of a box culvert according to the present invention. FIG. 2 is a photograph of a main part showing a second embodiment of a box culvert according to the present invention. FIG. 3 is a cross-sectional view of a main part showing a third embodiment of a box culvert according to the present invention. FIG. 4 is a cross-sectional view showing a conventional box culvert. FIG. 5 is a diagram showing the load acting during installation.

Below, an embodiment of a box culvert according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment.

(Basic configuration)
First, a basic configuration of the embodiment of the present invention will be described.
The box culvert according to this embodiment is applied to the lower left and right portions of a box culvert as shown in Fig. 4, and therefore, an outline of this box culvert will be described. The box culvert in Fig. 4 includes a skeleton 2 made of precast concrete with a substantially rectangular cross section in which corner portions 1 are formed in an arch shape, axial reinforcing bars 3 (main reinforcing bars), and tie bars 4 (tie bars). The corner portions 1 being arch-shaped means that the contour line of the skeleton 2 at the corner portions 1 is a rounded shape (R-shape) having a predetermined curvature in the cross-sectional view of the box culvert.

The structure 2 is composed of a top plate 10 (top plate member) and a bottom plate 12 (bottom plate member) that are arranged vertically opposite each other and have different thicknesses, and side walls 14, 14 (side wall members) that are arranged opposite each other on the left and right ends of the bottom plate 12. As shown in FIG. 5, the bottom plate 12 is a roughly U-shaped member whose left and right ends form corner portions 1. The top plate 10 is arranged to connect the upper parts of the side walls 14. In this embodiment, the height of the inner cross section of the structure 2 is assumed to be about 6000 mm and the width is assumed to be about 5700 mm, and an unequal thickness shape is assumed in which the top plate 10 is about 850 mm thick, the bottom plate 12 is about 900 mm thick, and the left and right side walls 14 are about 650 mm thick, but this is not limited to this. In other words, an unequal thickness shape with other combinations of dimensions may be used, or an equal thickness shape in which each member has the same thickness may be used.

The radius of curvature of the structural line of the corner section 1 is larger on the outer side than on the inner side (inner space side), and the centers of the circle of curvature R1 on the inner side and the circle of curvature R2 on the outer side are at different positions. In this way, a box culvert with an unequal thickness shape can be realized, in which the material thicknesses of the top plate 10, bottom plate 12, and side walls 14 are different. In this embodiment, the radius of curvature of the structural line on the inner side of the corner section 1 is assumed to be 1000 mm, but this is not limited to this.

The axial rebars 3 are arranged in the circumferential direction in a cross-sectional view on both the outside and inside of the interior of the body 2. The tie bars 4 are hoop bars arranged at a predetermined interval in the circumferential direction and surrounding the axial rebars 3. The axial rebars 3 are arranged at a predetermined interval in the longitudinal direction (extension direction of the box culvert). The tie bars 4 have annular first and second tie bars arranged in a row with a slight offset in the longitudinal direction. The first and second tie bars overlap and surround the axial rebars 3 between them. By not using an intermediate tie bar in this way and by using two tie bars 4, the efficiency of the reinforcing bar arrangement work during production is improved. This makes it possible to produce the product in a short period of time.

In addition, in the corner section 1, it is preferable to set the tie bars 4 restraining the inner axial rebars 3 so that when the tensile stress reaches the yield stress, the tie bars 4 are set to below the yield stress. By doing so, when an external force (axial force, moment) acts in the direction that opens the corner section 1 in the event of a large deformation such as an earthquake, it is possible to prevent the concrete cover on the inside from spalling against the action (abdominal pressure) that pushes the concrete on the inside of the corner section 1 away.

A small protrusion 16 (for example, about 50 mm high) may be provided on the underside (outer surface) between the lower arch-shaped corner portion 1 and the base plate 12 connected thereto. By providing the protrusion 16, it is possible to ensure the filling of the backfill material under the corner portion 1 of the base plate 12 that is placed on the installation surface.

According to the box culvert in Figure 4, there is no corner reinforcement, which was present in conventional box culverts with rectangular cross sections, so the rebars do not cross. Since there are no crossing rebars and the problem of rebars interfering with each other is eliminated, the effort required for rebar arrangement during construction can be reduced. Also, inspection of the corners can be omitted. Furthermore, because the corner section 1 is R-shaped, the aesthetic appearance of the inside of the box culvert viewed from the interior space side is improved.

In addition, by shifting the center positions of the curvature circles R1, R2 on the outer and inner sides of the corner section 1, it is possible to realize a box culvert with an unequal thickness shape in which the material thicknesses of the top plate 20, bottom plate 22, and side walls 14 are changed. Even with an unequal thickness shape, the bending shape of the axial reinforcing bars 3 in the corner section 1 can be set to the shape of a single circle, which is easy to bend.

(Embodiment 1)
Next, a first embodiment of the present invention that is applied to a box culvert having the above-mentioned basic configuration will be described.
Fig. 1 is a perspective view of a main part of a box culvert 100 according to the first embodiment. As shown in this figure, the box culvert 100 is provided with camber members 18 provided on the undersides of the corner portions 1 at both the left and right ends of the bottom slab 12. The camber members 18 are intended to reduce stress and strain that occur in the cantilevered bottom slab 12 when the side walls 14 and the top slab 10 are erected.

The camber material 18 is composed of a concrete member 20 in the shape of a roughly right-angled triangle plate. The front and rear sides of the concrete member 20 are provided with lattice-shaped crack prevention bars 22 (wire mesh). The concrete member 20 is fixed to the underside of the corner portion 1 by a fixing member 26, sandwiching a hard rubber plate 24 between them. The fixing member 26 is composed of angle members 28 such as shaped steel that are arranged across the lower surface of the corner portion 1 and the front and rear surfaces of the concrete member 20, and bolts 30 that are inserted into through holes provided in the angle members 28. The camber material 18 can also be attached to the underside of the corner portion 1 afterwards. In this embodiment 1, the thickness T of the bottom slab 12 in the depth direction is assumed to be about 1000 mm, and the thickness t of the camber material 16 is assumed to be about 300 mm, but this is not limited to this.

According to this embodiment 1, the load due to the weight of the side wall 14 and top plate 10 is transmitted to the installation surface as an axial force by the camber material 18, and the bending moment and strain of the reinforcing bars that occur in the span of the bottom plate 12 during the construction process can be reduced. Therefore, it is possible to provide a box culvert made of precast concrete that can ensure the quality of the structure and does not delay the construction process. In addition, since the camber material 18 is made of a composite material of concrete and steel, it can be installed relatively easily and at low cost.

(Embodiment 2)
Next, a second embodiment of the present invention will be described.
As shown in Fig. 2, the box culvert 200 according to the second embodiment includes camber materials 32 provided under the corner portions 1 at both the left and right ends of the bottom slab 12. The camber materials 32 are intended to reduce stress and strain that occurs in the bottom slab 12 in a cantilevered state when erecting the side walls 14 and the top slab 10. The camber materials 32 are made of concrete that is cast integrally with the bottom slab 12. A lattice-shaped crack prevention bar (wire mesh) (not shown) is provided on the front and rear sides of the interior of the camber materials 32.

According to this second embodiment, the load due to the weight of the side wall 14 and top plate 10 is transmitted to the installation surface as an axial force by the camber material 32, and the bending moment and strain of the reinforcing bars that occur in the span of the bottom plate 12 during the construction process can be reduced. Therefore, it is possible to provide a box culvert made of precast concrete that can ensure the quality of the structure and does not delay the construction process. In addition, this integrated camber material 32 makes it possible to carry out construction using ordinary materials such as locally generated soil as backfill material.

(Embodiment 3)
Next, a third embodiment of the present invention will be described.
As shown in Figure 3, the box culvert 300 according to the third embodiment includes camber materials 34 provided under the corner portions 1 at both the left and right ends of the bottom slab 12. The camber materials 34 are intended to reduce stress and strain that occurs in the cantilevered bottom slab 12 when erecting the side walls 14 and the top plate 10. A side line 36 of the camber material 34 is located on an extension of the central axis C of the side walls 14 in a cross-sectional view.

In this way, by aligning the side line 36 of the camber material 34 with the central axis C of the side wall 14, it is possible to effectively reduce the bending moment and the strain of the reinforcing bars that occur in the span portion of the base slab member during the construction process. This makes it possible to provide a precast concrete box culvert that ensures the quality of the structure and does not delay the construction process. In addition, the volume of the camber material 34 can be reduced, making it possible to set (optimize) it to an optimal size.

As described above, the box culvert according to the present invention is a precast concrete box culvert consisting of a body with a substantially rectangular cross section with arched corners, and includes a substantially U-shaped bottom plate member with both left and right ends forming corners, side wall members arranged opposite each other on both left and right ends of the bottom plate member, a top plate member connecting the upper parts of the side wall members and arranged opposite the bottom plate member, and camber materials arranged under the corners at both left and right ends of the bottom plate member to reduce the stress and strain generated in the cantilevered bottom plate member when the side wall members and the top plate member are erected. Therefore, the load due to the weight of the side wall members and the top plate member is transmitted to the installation surface as an axial force by the camber materials, and the bending moment and strain of the reinforcing bars generated in the span of the bottom plate member during the construction process can be reduced. Therefore, it is possible to provide a precast concrete box culvert that can ensure the quality of the body and does not delay the construction process.

In addition, with the box culvert of the present invention, the camber material is made of concrete, steel, or a composite material formed on the underside of the corner portion, so the camber material can be installed relatively easily and at low cost.

In addition, with the box culvert of the present invention, the side line of the camber material is located on an extension of the central axis of the side wall member, so that the bending moment and strain of the reinforcing bar generated in the span portion of the base slab member during the construction process can be effectively reduced, and the volume of the camber material can be optimized.

In addition, the box culvert of the present invention is equipped with main reinforcements arranged in the circumferential direction in cross-sectional view on both the outside and inside of the interior of the body, and tie reinforcements arranged in multiple circumferential directions at a specified interval and surrounding the multiple main reinforcements, making it possible to eliminate the need for cross reinforcement such as corner reinforcement that exists in conventional box culverts with rectangular cross sections. This reduces the effort required for reinforcement work during construction.

As described above, the box culvert of the present invention is useful for box culverts used as underground structures such as underground waterways and roads, and is particularly suitable for reducing the stress and strain of the cantilevered bottom plate member when erecting the side wall members and top plate member.

1 Corner part 2 Body 3 Axial reinforcement (main reinforcement)
4. Tie-down reinforcement (tie-down)
10 Top plate (top plate member)
12 Bottom plate (bottom plate member)
14 Side wall (side wall member)
16 Protrusion 18, 32, 34 Camber material 20 Concrete member 22 Crack prevention bar 24 Rubber plate 26 Fixing member 28 Angle material 30 Bolt 36 Side line 100, 200, 300 Box culvert

Claims (3)

A precast concrete box culvert having a rectangular cross-section with arched corners, main reinforcements arranged in the circumferential direction in cross-sectional view on the outside and inside of the body, and hoops arranged at predetermined intervals in the circumferential direction and surrounding the main reinforcements,
The present invention comprises a substantially U-shaped bottom plate member, the left and right ends of which form the corner portions, side wall members arranged on the left and right ends of the bottom plate member facing each other, a top plate member connecting the upper portions of the side wall members and arranged facing the bottom plate member, and a camber material provided under the corner portions at the left and right ends of the bottom plate member in order to reduce stress and strain generated in the bottom plate member in a cantilevered state when the side wall members and the top plate member are erected,
This box culvert is characterized in that when the tensile stress of the main reinforcement arranged inside the corner portion reaches the yield stress, the tensile stress of the tie reinforcement restraining the main reinforcement is below the yield stress, thereby preventing the cover concrete from spalling against pressure acting in a direction to push away the cover concrete on the inside of the corner portion. A precast concrete box culvert consisting of a body having a substantially rectangular cross section with arched corners,
The present invention comprises a substantially U-shaped bottom plate member, the left and right ends of which form the corner portions, side wall members arranged on the left and right ends of the bottom plate member facing each other, a top plate member connecting the upper portions of the side wall members and arranged facing the bottom plate member, and a camber material provided under the corner portions at the left and right ends of the bottom plate member in order to reduce stress and strain generated in the bottom plate member in a cantilevered state when the side wall members and the top plate member are erected,
A box culvert characterized in that the side line of the camber material is located on an extension of the central axis of the side wall member. The box culvert according to claim 1 or 2, characterized in that the camber material is made of concrete, steel, or a composite material thereof formed on the underside of the corner portion.

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