Box culvert

Abstract

To provide a box culvert made of precast concrete, the box culvert being able to secure the quality of its skeleton and preventing a delay in its construction process.SOLUTION: A box culvert 100 made of precast concrete and having a substantially rectangle cross-section formed in an arch shape at a corner part 1 comprises: a bottom-slab member 12 substantially U-shaped and including right and left ends each forming the corner part 1; side wall members 14 disposed facing each other on both right and left ends of the bottom-slab member 12; a top-slab member connecting upper parts of the side wall members 14 with each other and disposed facing the bottom-slab member 12; and a camber member 18 disposed in the lower side of the corner part 1 of each of the right and left ends of the bottom-slab member 12 in order to reduce stress and strain generated in the bottom-slab member 12 in a cantilever state when constructing the side wall members 14 and the top-slab member.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a box culvert made of precast concrete.

Background Art

[0002] Conventionally, when constructing a waterway or a road passing underground, a box culvert having a hollow cylindrical cross-section has been widely used (see, for example, Patent Documents 1 and 2). The construction of the box culvert is often carried out on-site, but when it is necessary to shorten the process, etc., an underground structure such as a waterway or a road may be constructed by burying precast products while connecting them in the longitudinal direction.

[0003] Many conventional box culverts are configured with a rectangular cross-section having a haunch at the corner portion of the edge shape, regardless of whether they are cast-in-place or precast products. The box culvert of the precast product is a factory-made product, so it has a higher degree of freedom in the formwork shape than the cast-in-place one, but it has cross-reinforcement such as reinforcing bars along the haunch and corner reinforcement bars following the shape of the cast-in-place one. For this reason, a great deal of labor is required for the reinforcement work at the corner portion during production, and it has been difficult to rationalize the amount of reinforcing bars and the arrangement of the reinforcing bars.

[0004] In order to solve such problems, the applicant of the present patent has already proposed a precast concrete box culvert described in Patent Document 3. As shown in FIG. 4, the box culvert of this Patent Document 3 includes a body 2 made of concrete having a substantially rectangular cross-section in which a corner portion 1 (corner portion) is formed in an arc shape (arch shape), main reinforcing bars 3 arranged in the circumferential direction in a cross-sectional view on the outer side and the inner side inside the body 2, and stirrups 4 arranged at a predetermined interval in the circumferential direction and surrounding the plurality of main reinforcing bars 3.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] By the way, as shown in FIG. 5, the box culvert of the above-mentioned conventional Patent Document 3 is installed by erecting a side wall member 6 and a top plate member 7 on a substantially U-shaped bottom plate member 5. When erecting the side wall member 6 and the top plate member 7, since the side portion 8 of the bottom plate member 5 is arc-shaped, it is in a cantilever state. At this time, due to a stress state different from that at the time of ring completion of the box culvert, there is a possibility that an out-of-design strain may occur in the reinforcing bars at the support intervals of the bottom plate member 5. As a countermeasure against this cantilever state, for example, it is conceivable to install a support on the side portion of the bottom plate member 5 or to backfill under the side portion. However, with such countermeasures, the work labor increases, and there is a possibility that the construction process may be delayed. In addition, for the backfill under the side portion, it is necessary to select a material that does not require rolling pressure such as fluidized treated soil. For this reason, a technique that ensures the quality of the structure and does not delay the construction process has been demanded.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a precast concrete box culvert that can ensure the quality of the structure and does not delay the construction process. [Means for Solving the Problems]

[0008] In order to solve the above-described problems and achieve the object, the box culvert according to the present invention is a precast concrete box culvert having a housing with a substantially rectangular cross-section in which the corner portions are formed in an arch shape, and includes substantially U-shaped bottom plate members at both left and right ends that form the corner portions, side wall members disposed opposite to each other above the left and right ends of the bottom plate members, a top plate member that connects the upper portions of the side wall members and is disposed opposite to the bottom plate member, and a camber material provided below the corner portions at both left and right ends of the bottom plate member in order to reduce the stress and strain generated in the bottom plate member in a cantilever state when the side wall members and the top plate member are erected.

[0009] Further, the box culvert according to the present invention is characterized in that, in the above-described invention, the camber material is made of concrete, steel material, or a composite material thereof formed below the corner portion.

[0010] Further, the box culvert according to the present invention is characterized in that, in the above-described invention, the side line of the camber material is located on the extension of the central axis of the side wall member.

[0011] Further, the box culvert according to the present invention is characterized in that, in the above-described invention, main reinforcement bars are arranged in the circumferential direction in a cross-sectional view on the outer side and the inner side inside the housing, and a plurality of stirrups are arranged at predetermined intervals in the circumferential direction and surround the plurality of main reinforcement bars.

Effect of the Invention

[0012] According to the box culvert of the present invention, it is a precast concrete box culvert composed of a housing with a substantially rectangular cross-section in which the corner portions are formed in an arch shape, and includes a substantially U-shaped bottom plate member whose left and right ends form corner portions, side wall members disposed opposite to the upper portions of the left and right ends of the bottom plate member, a top plate member that connects the upper portions of the side wall members and is disposed opposite to the bottom plate member, and a camber material provided below the corner portions at the left and right ends of the bottom plate member in order 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 self-weight of the side wall members and the top plate member is transmitted to the installation surface as an axial force by the camber material, and it is possible to reduce the bending moment and the strain of the reinforcing bars generated in the span portion of the bottom plate member during the construction process. Accordingly, it is possible to ensure the quality of the housing and to provide a precast concrete box culvert that does not delay the construction process.

[0013] Moreover, according to the box culvert of the present invention, since the camber material is made of concrete, steel material, or a composite material thereof formed below the corner portion, it is possible to provide the camber material relatively easily and at low cost.

[0014] Furthermore, according to the box culvert of the present invention, since the side line of the camber material is located on the extension of the central axis of the side wall member, it is possible to effectively reduce the bending moment and the strain of the reinforcing bars generated in the span portion of the bottom plate member during the construction process, and to optimize the volume of the camber material.

[0015] In addition, according to the box culvert of the present invention, main reinforcement bars are arranged circumferentially in a cross-sectional view on the outer and inner sides of the body, respectively, and a plurality of stirrups are arranged at predetermined intervals in the circumferential direction and surround the plurality of main reinforcement bars. Therefore, it is possible to eliminate the cross reinforcement such as corner reinforcement bars that existed in the conventional box culvert with a rectangular cross section. For this reason, it is possible to reduce the labor of the reinforcement work during production, which has the effect of reducing the labor of the reinforcement work during production.

Brief Description of Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the 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 by this embodiment.

[0018] (Basic Configuration) First, the 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 parts of the box culvert as shown in FIG. 4, and thus a schematic description of this box culvert will be given. The box culvert in FIG. 4 includes a body 2 made of precast concrete with a substantially rectangular cross-section in which a corner portion 1 is formed in an arch shape, axial reinforcing bars 3 (main bars), and strap bars 4 (strap bars). The fact that the corner portion 1 is in an arch shape means that the contour line of the body 2 of the corner portion 1 has a rounded shape (R shape) with a predetermined curvature in a cross-sectional view of the box culvert.

[0019] The body 2 consists of a top plate 10 (top plate member) and a bottom plate 12 (bottom plate member) that are arranged opposite to each other vertically and have different thicknesses, and side walls 14, 14 (side wall members) that are arranged opposite to each other above the left and right ends of the bottom plate 12. As shown in FIG. 5, the bottom plate 12 is a substantially U-shaped member whose left and right ends form the corner portion 1. The top plate 10 is arranged so as to connect the upper parts of the side walls 14. In this embodiment, it is assumed that the height of the inner cross-section of the body 2 is about 6000 mm and the width is about 5700 mm, and an unequal thickness shape with a thickness of about 850 mm for the top plate 10, a thickness of about 900 mm for the bottom plate 12, and a thickness of about 650 mm for the left and right side walls 14 is assumed, but it is not limited to this. That is, an unequal thickness shape with other combinations of dimensions may be used, or an equal thickness shape with the same thickness for each member may be used.

[0020] The radius of curvature of the body line of the corner portion 1 is such that the radius of curvature on the outer surface side is larger than the radius of curvature on the inner surface side (inner space side), and the centers of the curvature circles R1 on the inner surface side and R2 on the outer surface side are at different positions. By doing so, a box culvert with an unequal thickness shape in which the member thicknesses of the top plate 10, the bottom plate 12, and the side wall 14 are different can be realized. In this embodiment, it is assumed that the radius of curvature of the body line on the inner surface side of the corner portion 1 is 1000 mm, but it is not limited to this.

[0021] The axial reinforcement bars 3 are arranged circumferentially in a sectional view on the outer and inner sides inside the body 2 respectively. The strip reinforcement bars 4 are hoop bars that are arranged in a plurality at predetermined intervals in the circumferential direction and surround the plurality of axial reinforcement bars 3. A plurality of axial reinforcement bars 3 are arranged at predetermined intervals in the longitudinal direction (the extending direction of the box culvert). The strip reinforcement bars 4 have an annular first strip bar and a second strip bar that are arranged in a continuous manner with a slight shift in the longitudinal direction. The first strip bar and the second strip bar overlap and surround the plurality of axial reinforcement bars 3 therebetween. By adopting the two - series strip reinforcement bars 4 without using intermediate strip reinforcement bars in this way, the efficiency of the steel bar placement work during production is improved. As a result, it becomes possible to manufacture in a short period of time.

[0022] In addition, in the corner portion 1, it is preferable to set the strip reinforcement bar 4 that restrains the inner axial reinforcement bar 3 when its tensile stress reaches the yield stress so that it is below the yield stress. By doing so, when an external force (axial force, moment) acts in the direction in which the corner portion 1 opens when a large deformation occurs during an earthquake or the like, it is possible to prevent the peeling of the inner cover concrete against the action (diaphragm pressure) that causes the concrete inside the corner portion 1 to be peeled off.

[0023] Also, a protrusion 16 with a small amount (for example, about 50 mm in height) may be provided on the lower surface (outer surface) between the lower arch - shaped corner portion 1 and the bottom plate 12 connected thereto. By providing the protrusion 16, it is possible to ensure the filling property of the backfill material on the lower side of the corner portion 1 of the bottom plate 12 installed on the installation surface.

[0024] According to the box culvert in FIG. 4, since there are no corner reinforcement bars existing in the conventional box culvert with a rectangular cross - section, there is no need to intersect the steel bars. Since there are no intersecting steel bars and there is no problem of interference between the steel bars, the labor of the steel bar placement work during production can be reduced. Also, the inspection of the corner portion can be omitted. Furthermore, since the corner portion 1 has an R - shape, the aesthetics inside the box culvert seen from the inner space side is improved.

[0025] In addition, by shifting the center positions of the curvature circles R1 and R2 on the outer surface side and the inner surface side of the corner portion 1, it is possible to realize a box culvert with an unequal thickness shape in which the member thicknesses of the top plate 20, the bottom plate 22, and the side wall 14 are changed. Further, even in the case of an unequal thickness shape, the bending shape of the axial reinforcing bar 3 in the corner portion 1 can be set to a single-center circle shape that is easy to bend.

[0026] (Embodiment 1) Next, Embodiment 1 of the present invention applied to the box culvert having the above basic configuration will be described. FIG. 1 is a perspective view of a main part of a box culvert 100 according to Embodiment 1 of the present invention. As shown in this figure, the box culvert 100 includes a camber material 18 provided below the corner portions 1 at both left and right ends of the bottom plate 12. The camber material 18 is for reducing the stress and strain generated in the cantilevered bottom plate 12 when the side wall 14 and the top plate 10 are erected.

[0027] This camber material 18 is composed of a concrete member 20 in the shape of a substantially right-angled triangle plate. Lattice-shaped crack prevention bars 22 (wire meshes) are provided on the front side and the rear side in the concrete member 20. The concrete member 20 is fixed to the lower side of the corner portion 1 with a fixing member 26 with a hard rubber plate 24 interposed therebetween. The fixing member 26 is composed of an angle material 28 such as a section steel arranged across the lower surface of the corner portion 1 and the front and rear surfaces of the concrete member 20, and a bolt 30 inserted through a through hole provided in the angle material 28. This camber material 18 can also be attached to the lower side of the corner portion 1 by retrofitting. In Embodiment 1, the thickness T in the depth direction of the bottom plate 12 is assumed to be about 1000 mm, and the thickness t of the camber material 16 is assumed to be about 300 mm, but it is not limited thereto.

[0028] According to the first embodiment, the load due to the self-weight of the side wall 14 and the top plate 10 is transmitted as an axial force to the installation surface by the camber material 18, and the bending moment and the strain of the reinforcing bars generated at the span of the bottom plate 12 during the construction process can be reduced. Therefore, it is possible to ensure the quality of the structure and provide a precast concrete box culvert that does not delay the construction process. Further, since the camber material 18 is made of a composite material of concrete and steel, it can be provided relatively easily and at low cost.

[0029] (Second Embodiment) 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 a camber material 32 provided below the corner portions 1 at both left and right ends of the bottom plate 12. The camber material 32 is for reducing the stress and strain generated in the bottom plate 12 in a cantilever state when the side wall 14 and the top plate 10 are erected. This camber material 32 is composed of concrete produced by casting concrete integrally with the bottom plate 12. Lattice-shaped crack prevention bars (wire mesh) (not shown) are provided on the front side and the rear side inside the camber material 32.

[0030] According to the second embodiment, the load due to the self-weight of the side wall 14 and the top plate 10 is transmitted as an axial force to the installation surface by the camber material 32, and the bending moment and the strain of the reinforcing bars generated at the span of the bottom plate 12 during the construction process can be reduced. Therefore, it is possible to ensure the quality of the structure and provide a precast concrete box culvert that does not delay the construction process. Further, according to this integral camber material 32, it is possible to perform construction using normal materials such as locally generated soil as backfill material.

[0031] (Third Embodiment) Next, a third embodiment of the present invention will be described. As shown in FIG. 3, the box culvert 300 according to the third embodiment includes a camber material 34 provided below the corner portions 1 at both left and right ends of the bottom plate 12. The camber material 34 is for reducing the stress and strain generated in the bottom plate 12 in a cantilever state when the side walls 14 and the top plate 10 are erected. The side line 36 of the camber material 34 is located on the extension of the central axis C of the side wall 14 in a cross-sectional view.

[0032] In this way, when the side line 36 of the camber material 34 is aligned with the central axis C of the side wall 14, the bending moment generated in the span portion of the bottom plate member and the strain of the reinforcing bars during the construction process can be effectively reduced. Therefore, it is possible to provide a precast concrete box culvert that can ensure the quality of the structure and does not delay the construction process. In addition, the volume of the camber material 34 can be reduced, and it can be set (optimized) to an optimal size.

[0033] As described above, according to the box culvert according to the present invention, it is a precast concrete box culvert having a structure with a substantially rectangular cross-section in which the corner portions are formed in an arch shape, and includes a substantially U-shaped bottom plate member whose left and right ends form corner portions, side wall members disposed opposite to the left and right ends of the bottom plate member, a top plate member that connects the upper portions of the side wall members and is disposed opposite to the bottom plate member, and a camber material provided below the corner portions at both left and right ends of the bottom plate member in order to reduce the stress and strain generated in the bottom plate member in a cantilever state when the side wall members and the top plate member are erected. Therefore, the load due to the self-weight of the side wall members and the top plate member is transmitted to the installation surface as an axial force by the camber material, and the bending moment generated in the span portion of the bottom plate member and the strain of the reinforcing bars 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 structure and does not delay the construction process.

[0034] Further, according to the box culvert of the present invention, since the camber material is made of concrete, steel, or a composite material thereof formed on the lower side of the corner portion, the camber material can be provided relatively easily and at low cost.

[0035] Further, according to the box culvert of the present invention, since the side line of the camber material is located on the extension of the central axis of the side wall member, the bending moment generated at the support interval of the bottom plate member and the strain of the reinforcing bars in the construction process can be effectively reduced, and the volume of the camber material can be optimized.

[0036] Further, according to the box culvert of the present invention, since it includes main reinforcing bars arranged circumferentially in a cross-sectional view on the outer and inner sides of the body, respectively, and a plurality of hoop bars arranged at a predetermined interval in the circumferential direction and surrounding the plurality of main reinforcing bars, it is possible to eliminate the intersecting reinforcement such as corner reinforcing bars existing in the conventional box culvert with a rectangular cross-section. For this reason, the labor of the reinforcement work during production can be reduced.

Industrial Applicability

[0037] As described above, the box culvert according to the present invention is useful for a box culvert used as an underground structure such as a waterway or a road passing underground, and is particularly suitable for reducing the stress and strain of the bottom plate member in a cantilever state during the erection of the side wall member and the top plate member.

Explanation of Reference Numerals

[0038] 1 Corner portion 2 Body 3 Axial reinforcing bars (main reinforcing bars) 4 Hoop reinforcing bars (hoop bars) 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 ribs 24 Rubber plate 26 Fixing member 28 Angle material 30 Bolt 36 Side line 100, 200, 300 Box culvert

Claims

1. A precast concrete box culvert comprising a housing having a substantially rectangular cross-section with corner portions formed in an arch shape, main reinforcement bars arranged circumferentially in cross-section on the outer and inner sides of the interior of the housing, and hoop bars arranged in a plurality at predetermined intervals in the circumferential direction and surrounding the plurality of main reinforcement bars, a substantially U-shaped bottom plate member whose left and right ends form the corner portions, side wall members oppositely arranged on the left and right ends of the bottom plate member, a top plate member connecting the upper portions of the side wall members and oppositely arranged with respect to the bottom plate member, and a camber material provided on the lower sides of the corner portions at the left and right ends of the bottom plate member in order to reduce the stress and strain generated in the bottom plate member in a cantilever state when the side wall members and the top plate member are erected, wherein the tensile stress of the hoop bar that restrains the main reinforcement bar when the tensile stress of the main reinforcement bar arranged inside the corner portion reaches the yield stress is below the yield stress, and it prevents the peeling of the cover concrete against the pressure acting in the direction of pushing off the cover concrete inside the corner portion. A box culvert characterized by this.

2. A precast concrete box culvert comprising a housing having a substantially rectangular cross-section with corner portions formed in an arch shape, a substantially U-shaped bottom plate member whose left and right ends form the corner portions, side wall members oppositely arranged on the left and right ends of the bottom plate member, a top plate member connecting the upper portions of the side wall members and oppositely arranged with respect to the bottom plate member, and a camber material provided on the lower sides of the corner portions at the left and right ends of the bottom plate member in order to reduce the stress and strain generated in the bottom plate member in a cantilever state when the side wall members and the top plate member are erected, A box culvert characterized in that the center line of the camber material is located on the extension of the central axis of the side wall member.

3. The box culvert according to claim 1 or 2, wherein the camber material is made of concrete, steel material or a composite material thereof formed on the lower side of the corner portion.

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