JP2002146722A - Box girder bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a crack by solving such problems that compressive force is not sufficiently provided to a PC floor slab itself when a cast-in-place PC floor slab is used on a steel-made box girder bridge and that tensile stress acts on the PC floor slab when the drying shrinkage occurs in a concrete. SOLUTION: The upper surface of the box girder is constituted of a flexible dog leg shaped plate or the like, and the deformation of the PC floor slab is not restricted by making a space between the upper surface and the PC floor slab. Accordingly, prestress can be sufficiently provided to the PC floor slab itself, and tensile stress does not act on the PC floor slab even if the drying shrinkage occurs in the concrete.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel box girder bridge, and more particularly to a box girder bridge using a cast-in-place prestressed concrete slab (hereinafter referred to as a cast-in-place PC slab). .

[0002]

2. Description of the Related Art FIG. 4 is a cross-sectional view of a conventional box girder bridge combined with a cast-in-place PC slab, viewed in the bridge axis direction. In FIG. 4, a cast-in-place PC floor slab 1 is installed on a box girder 2. On both side edges of the upper surface 21 of the box girder 2, the dowels 3, 4 are installed. The dowels 3, 4 are taken in, the concrete is cast in place, and after the concrete is solidified, the prestressing (in the direction perpendicular to the bridge axis) is performed. , Indicated by arrows in FIG. 4).

[0003]

However, the above-mentioned prior art has the following problems. 1) When the prestress is introduced, a part of the prestress force is transmitted to the box girder via the above-mentioned givels 3 and 4, so that between the dowel 3 and the dowel 4, the cast-in-place PC floor slab 1
The compressive force acting on itself is reduced. For this reason, cracks may be generated in the cast-in-place PC slab 1. 2) Since the box girder 2 restrains the deformation of the cast-in-place PC slab 1, when the concrete dries and shrinks,
Tensile stress acts on the cast-in-place PC slab 1 between the dowel 3 and the dovetail 4. For this reason, it causes cracks to occur in the cast-in-place PC slab 2. 3) In particular, when the rigidity of the upper surface 21 of the box girder 2 is high, the above problem becomes remarkable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. The upper surface of a box girder is made to have a flexible structure so that a prestress can be reliably introduced and restraint when concrete is dried and shrunk. An object of the present invention is to provide a box girder bridge that can be opened.

[0005]

The box girder bridge of the present invention for solving such a problem is as follows. [1] A box girder bridge having a substantially rectangular steel box girder and a cast-in-place prestressed concrete slab installed on the box girder, wherein the upper surface of the box girder has a rectangular cross section or The cast-in-place prestressed concrete slab is formed by either an arc-shaped plate or a corrugated cross section, and the cast-in-place prestressed concrete slab is fixed to both side edges of the upper surface. A gap is provided between the lower surface of the prestressed concrete slab and the upper surface of the box girder, or after applying a prestress to the cast-in-place prestressed concrete slab, the lower surface of the cast-in-place prestressed concrete slab and the A gap is formed between the box girder and the upper surface of the box girder. [2] A box girder bridge having a substantially rectangular steel box girder and a cast-in-place prestressed concrete slab installed on the box girder, wherein a side surface of the box girder protrudes above an upper surface,
The cast-in-place prestressed concrete slab is fixed to the tip of the protruding side surface.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 shows an embodiment of a box girder bridge according to the present invention, and is a cross-sectional view as viewed in a bridge axis direction. In FIG. 1, a cast-in-place PC floor slab 1 is installed on a steel box girder 2 having a substantially rectangular cross section. Steel box girder 2
Is manufactured at the factory and transported to the site. The cast-in-place PC floor slab 1 is used to cast concrete at the site using a movable formwork or a fixed formwork, and after the concrete is hardened, prestress (in the direction perpendicular to the bridge axis, indicated by an arrow in FIG. 1) is introduced. . The cast-in-place PC floor slab 1 is fixed to the steel box girder 2 by stoppers 3 and 4. Further, the upper surface 21 of the steel box girder 2 has a roof shape with a “C-shaped cross section” bent at substantially the center,
A gap is provided between the lower surface 11 of the cast-in-place PC floor slab 1 in the range facing the roof shape and the upper surface 21 of the steel box girder 2, and urethane is disposed here. That is, even when the upper surface 21 of the steel box girder 2 is deformed to have flexibility and increase its bending angle, the upper surface 21 can be cast in place.
There is no contact with the lower surface 11 of the C slab 1. Therefore, when a prestress is introduced, even if a part of the prestress force is transmitted to the box girder via the slip stoppers 3 and 4, the upper surface 21 of the steel box girder 2 is easily bent and deformed. Thus, it is ensured that a compressive force is introduced into the cast-in-place PC slab 1 itself.

Further, since the degree to which the steel box girder 2 restrains the deformation of the cast-in-place PC slab 1 is reduced, when the concrete dries and shrinks, the tensile stress acting on the cast-in-place PC slab 1 is reduced. Decrease. For these, cast-in-place PC floor slabs 2
Cracking is reduced.

The shape of the upper surface of the steel box girder of the present invention and the shape of the lower surface of the cast-in-place PC slab are not limited to those described above. A corrugated plate having a trapezoidal or arc-shaped cross section formed of a continuous arc, a corrugated plate having a zigzag cross section, or the like may be used. In the case of a rectangular cross section, the bending angle is a design matter. Furthermore, the gap is not limited to the space being arranged, but means the gap of the present invention as long as the exchange of force can be ignored even if the opposing surfaces are in contact with each other. . [Embodiment 2] Fig. 2 shows another embodiment of a box girder bridge according to the present invention, and is a cross-sectional view seen in the bridge axis direction. In FIG. 2, a cast-in-place PC floor slab 1 is installed on a steel box girder 2 having a substantially rectangular cross section. The steel box girder 2 is manufactured at the factory and is carried to the site. The cast-in-place PC floor slab 1 places concrete using a movable formwork or a fixed formwork on site, and after the concrete is hardened, prestress (in the direction perpendicular to the bridge axis, indicated by an arrow in FIG. 2) is introduced. . Cast in place P
The C floor slab 1 is fixed to the steel box girder 2 by stoppers 3 and 4. The upper surface 21 of the steel box girder 2 has an arcuate cross-section projecting downward substantially at the center, and the lower surface 11 of the cast-in-place PC floor slab 1 in the area facing the roof shape has the same arcuate cross-section. . That is, the upper surface 21 of the steel box girder 2 has flexibility, and when the upper surface 21 is deformed so as to protrude downward, the upper surface 21 is further away from the lower surface 11 of the cast-in-place PC floor slab 1. Become. Therefore, when a prestress is introduced, even if a part of the prestress force is transmitted to the box girder via the slip stoppers 3 and 4, the upper surface 21 of the steel box girder 2 projects downward and deforms. For the site-cast PC
It is ensured that a compressive force is introduced into the floor slab 1 itself.

Further, since the degree to which the steel box girder 2 restrains the deformation of the cast-in-place PC slab 1 is reduced, when the concrete dries and shrinks, the tensile stress acting on the cast-in-place PC slab 1 is reduced. Decrease. For these, cast-in-place PC floor slabs 2
Cracking is reduced.

The shape of the upper surface of the steel box girder of the present invention and the shape of the lower surface of the cast-in-place PC floor slab are not limited to those described above. A corrugated plate having a trapezoidal cross section, an arc-shaped cross section formed of a continuous arc, or a corrugated plate having a zigzag cross section may be used. Further, in the case of a circular cross section, the radius of curvature is a design matter. Further, a gap may be provided in advance between the lower surface of the cast-in-place PC floor slab and the upper surface of the steel box girder, and urethane or the like may be disposed here. [Embodiment 3] Fig. 3 shows another embodiment of a box girder bridge according to the present invention, and is a cross-sectional view as viewed in the bridge axis direction. In FIG. 2, a cast-in-place PC floor slab 1 is installed on a steel box girder 2 having a substantially rectangular cross section. Sides 22, 23 of steel box girder 2
Are protruded above the upper surface 21 and are provided with flanges 24 and 25 at their ends, are manufactured in a factory, and are carried into the site. The cast-in-place PC slab 1 casts concrete on the site using a movable formwork or a fixed formwork, and after the effect of the concrete, prestress (in the direction perpendicular to the bridge axis, indicated by an arrow in FIG. 3) is introduced. . The cast-in-place PC floor slab 1 is fixed to the steel box girder 2 by the slip stoppers 3 and 4 installed on the flanges 24 and 25. Therefore, when a prestress is introduced, even if a part of the prestress force is transmitted to the box girder via the slip stoppers 3 and 4, the projecting ranges of the side surfaces 22 and 23 of the steel box girder 2 can be easily formed. It is ensured that a compressive force is introduced into the cast-in-place PC slab 1 itself in order to cause the slab to fall down.

Further, since the extent to which the steel box girder 2 restrains the deformation of the cast-in-place PC slab 1 is reduced, when the concrete dries and shrinks, the tensile stress acting on the cast-in-place PC slab 1 is reduced. Decrease. For these, cast-in-place PC floor slabs 2
Cracking is reduced.

The shape of the upper surface of the steel box girder and the shape of the lower surface of the cast-in-place PC slab according to the present invention may be the same as those described in the first or second embodiment. Further, the thickness of the protruding portion on the side surface, the protruding distance, and the like are design matters.

[0013]

According to the box girder bridge of the present invention described above,
The following remarkable effects can be obtained. 1) It is ensured that a compressive force is introduced into the cast-in-place PC slab itself. 2) The constraint of deformation of the cast-in-place PC slab itself is reduced. Therefore, the fatigue durability of the cast-in-place PC floor slab is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a box girder bridge according to the present invention, as viewed in a bridge axis direction.

FIG. 2 shows another embodiment of the box girder bridge according to the present invention, and is a cross-sectional view as viewed in a bridge axis direction.

FIG. 3 shows another embodiment of the box girder bridge according to the present invention, and is a cross-sectional view as viewed in the bridge axis direction.

FIG. 4 is a cross-sectional view of a box girder bridge combined with a conventional cast-in-place PC slab, viewed in the bridge axis direction.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 Cast-in-place PC slab 2 Steel box girder 3 Stopper 4 Stopper 11 Lower surface of cast-in-place PC slab 21 Upper surface of steel box girder 22 Side face of steel box girder 23 Side face of steel box girder 24 Flange 25 Flange

Claims (2)

[Claims] 1. A box girder bridge having a substantially rectangular steel box girder and a cast-in-place prestressed concrete slab installed on the box girder, wherein an upper surface of the box girder has a rectangular cross section. The cast-in-place prestressed concrete slab is fixed to both side edges of the upper surface, and is formed by any of a plate or a cross-section arc-shaped plate or a corrugated plate. A gap is provided between the lower surface of the cast-in-place prestressed concrete slab and the upper surface of the box girder, or after applying a prestress to the cast-in-place prestressed concrete slab, the lower surface of the cast-in-place prestressed concrete slab And a gap is formed between the box girder and the upper surface of the box girder. 2. A box girder bridge having a substantially rectangular steel box girder and a cast-in-place prestressed concrete slab installed on the box girder, wherein a side surface of the box girder protrudes above an upper surface. A box girder bridge, wherein the cast-in-place prestressed concrete slab is fixed to a tip of the protruding side surface.