JP6370508B1 - Bridge PC floor slab with fiber reinforced concrete - Google Patents

Abstract

[PROBLEMS] To reduce the manufacturing cost of a member by reducing the thickness of fiber-reinforced concrete formed on the tension side of a precast concrete floor slab member and eliminating the need for reinforcing bars, and to provide a high-strength floor slab Provide a precast PC deck for bridges that can be obtained. A bridge floor slab in which a floor slab member 1 having a lower cross section 1a formed of fiber reinforced concrete having a predetermined thickness and an upper cross section 1b formed of high-strength concrete is arranged side by side. In the upper cross section of the member 1, pre-stressing prestress is introduced by the tension steel material 6b in the direction perpendicular to the bridge axis, and in the bridge axis direction, the pre-stress is applied to the floor slab member 1 by the post-tension method by tension fixation of the PC steel material 6a. Precast PC for bridges in which the floor slab member 1 is integrated by stress bonding and the bi-directional prestress is applied to the entire cross section of the floor slab, and the entire cross section of the floor slab is unreinforced. Floor slab. [Selection] Figure 1

Description

The present invention relates to a fiber reinforced concrete or a bridge PC slab provided with an ultra-high strength fiber reinforced concrete part.
In the present specification, “PC” means a prestressed concrete structure.

Fiber reinforced concrete is a mixture of short fibers and concrete, and has high tensile strength and high toughness. As the fibers to be mixed, synthetic fibers having relatively high strength and elastic modulus such as steel fibers, carbon fibers, glass fibers, aramid fibers, polyolefin fibers such as polypropylene and polyethylene, and vinylon fibers are used.
Ultra high strength fiber reinforced concrete is fiber reinforced concrete in which fibers are mixed in high strength cement in which fine particles are closely packed in the gaps between cement particles, and its compressive strength reaches 200 N / mm ^2. Yes, it is a highly durable material. The fine grain material added to the ultra high strength fiber reinforced concrete is silica fume, silica dust, fly ash, slag and the like.

Fiber reinforced concrete has the advantages of suppressing cracking, improving toughness, and improving bending strength, and is often used for the production of precast concrete members because it can reduce the weight and durability of concrete members. In addition, ultra-high-strength fiber reinforced concrete is much larger than ordinary concrete in both compressive strength and tensile strength, and has a large contribution to shear strength. It is known that it is possible to reduce or eliminate shear reinforcement bars.
Patent Document 1 discloses a technique related to a composite concrete member formed by using high-strength fiber reinforced concrete as an embedded form and integrated with ordinary concrete.
Hereinafter, unless otherwise specified, in this specification, “fiber reinforced concrete” also includes ultra high strength fiber reinforced concrete.

JP 2013-1583 A

When the entire floor slab member is formed of fiber reinforced concrete, the strength of the entire floor slab member is significantly increased, but the cost of the mixed fibers is also reflected, which is reflected in the manufacturing cost of the member and is inferior in economic efficiency and practicality. It will be.
In Patent Document 1 (Japanese Patent Laid-Open No. 2013-1583), a reinforcing bar 8B is arranged on the bottom surface of a U-shaped embedded form 8A made of fiber reinforced concrete mixed with metal fibers or organic fibers constituting the beam member 8. By doing so, it is disclosed that the strength of the beam member 8 as a whole can be increased, and as a result, the shear reinforcement can be omitted, the manufacture of the beam member can be simplified, and a composite beam member having excellent load resistance and durability can be obtained. ing. However, the reinforcing bar 8B must be disposed on the bottom surface portion 81 of the U-shaped embedded form 8A. Paragraph 0033 states that “the amount of reinforcing bars is a reinforcing bar area of 2 to 15 relative to the cross-sectional area of the bottom surface portion. % Is preferable, and 2 to 10% is more preferable. ”, Reinforcing bars are indispensable, and reinforcing bar arrangement work is necessary. And since prestress is not introduced into the beam member, this beam member is classified as an RC member. This means that in the case of RC beam members, even if high strength fiber reinforced concrete is used for the main part of the member cross section, a certain amount of reinforcing bars must be placed in order to function as a structural member (beam member) The problem in terms of reducing member costs and construction costs by omitting reinforcing bar arrangement work has not been solved, and it is assumed that fiber reinforced concrete was also used in the floor slab In the same way, reinforcing bars must be arranged.
The present invention uses fiber reinforced concrete for a part of the cross section of a PC floor slab member of a bridge, and makes use of the merit that fiber reinforced concrete has high strength, thereby making reinforcing bar arrangement unnecessary in all cross sections. Accordingly, it is an object to reduce the manufacturing cost of the member and to obtain a high-strength floor slab.

  In the present invention, the entire cross-section of the precast concrete floor slab member of the bridge is a composite of the lower cross-section and the upper cross-section, the lower cross-section is made of fiber reinforced concrete of a predetermined thickness, and the upper cross-section is made of high-strength concrete In the upper section, prestressing prestress is introduced in the direction perpendicular to the bridge axis, and in the bridge axis direction, prestressing due to post-tensioning due to tension fixation of the PC steel material is introduced, and the PC precast floor slab member A precast PC floor slab for bridges characterized in that the two are pre-stressed together, bi-directional prestress is applied to the entire cross section of the floor slab, and the entire cross section of the floor slab is unreinforced.

The precast PC floor slab provided with the fiber-reinforced concrete part of the present invention has the following advantages.
(1) The PC floor slab formed with the lower cross-section made of fiber reinforced concrete and bi-directional pre-stress applied to all cross-sections has high pre-stress due to the bi-directional pre-stress and the fiber reinforced concrete. The tensile strength greatly improves the bending cracking resistance of the floor slab, so it is possible to prevent the occurrence of cracks.
Moreover, since the arrangement of reinforcing bars in both directions is not required in the cross section, the manufacturing process is simplified and the cost is reduced.
(2) The cost reduction is achieved by combining the lower cross section with fiber reinforced concrete without introducing the entire cross section of the floor slab member into fiber reinforced concrete and introducing bi-directional prestress into the entire cross section, and the application field of fiber reinforced concrete. It expands the possibilities of expansion.
(3) Since the entire cross section of the PC slab is made of reinforcing steel, the floor slab is lightened.
(4) By setting the thickness of the lower cross section made of fiber reinforced concrete to 1/8 to 1/12 of the thickness of the entire cross section of the floor slab member, the tensile strength is higher than the bending tensile stress generated in the cross section of the floor slab. Since the concrete area having strength is sufficiently secured, it is possible to reliably prevent cracking.

The layout of a precast PC floor slab member (plan view, AA cross section, BB cross section). The partial perspective view of a precast PC floor slab. Sectional drawing of the standard part (general part other than a fulcrum part) of a precast PC floor slab member. The stress distribution figure in a floor slab member cross section. Detailed sectional drawing of a crimping | joining junction part. 2 is a detailed cross-sectional view of a stopper hole and a detailed cross-sectional view of a level adjusting hole. Sectional drawing of the conventional composite beam which consists of fiber reinforced concrete and plain concrete.

FIG. 1 is an example of a layout (plane, AA cross section, BB cross section) of a precast PC floor slab member 1 for a bridge according to the present invention, and FIG. 2 is a perspective view.
Precast PC floor slab members 1, 1,... Formed as a single piece on three steel girders 3 with a predetermined width (bridge axis direction) and no longitudinally (bridge axis perpendicular) direction. Are arranged side by side in the bridge axis direction, and the entire cross section of the standard part (general part other than the fulcrum part) of the precast PC slab member 1 is composed of the lower cross section 1a and the upper cross section 1b as shown in FIG. The lower cross section 1a is made of fiber reinforced concrete having a predetermined thickness, and the upper cross section 1b is made of high strength concrete and integrated.
In the upper cross-section 1b, a plurality of PC steel materials 6b are arranged in the longitudinal direction (perpendicular to the bridge axis) of the precast PC floor slab member 1 and are tension-fixed by a pre-tension method to give pre-stress to each composite section of the floor slab. Has been. In the width direction of the precast PC floor slab member 1 (bridge axis direction), a plurality of precast PC floor slab members 1 in which a plurality of PC steel materials 6a are arranged side by side are continuously disposed, Prestress is applied to the plurality of precast PC floor slab members 1 by fixing the tension, and the plurality of precast PC floor slab members 1 are joined by pressure bonding.
In the cross section of the standard portion of the PC floor slab member, the tension steel material 6b for pretension is appropriately disposed so as to pass above and below the PC steel material 6a for post tension so as to correspond to the bending stress in the span.
Thus, prestress is applied to the entire cross section of the precast PC floor slab member 1 in two directions, ie, the bridge axis direction and the direction perpendicular to the bridge axis, and the precast PC floor slab is in a two-way compressed state. The lower cross section 1a of the member 1 is formed of fiber reinforced concrete having high tensile strength and high toughness, and it is not necessary to provide reinforcing bars for reinforcement in both cross sections in two directions (width and length).

The precast PC floor slab member 1 is preferably a single floor slab without providing a joint in the direction perpendicular to the bridge axis (width direction). However, if the width is large and it is difficult to make a single precast floor slab due to manufacturing equipment or transportation, it is necessary to divide the PC steel material through the sheath provided in the width direction by dividing it and providing a joint. The precast floor slab member 1 can be integrated by applying a prestress by a tension method and performing pressure bonding.
The length of the precast PC floor slab member 1 in the direction of the bridge axis needs to be determined according to restrictions in transportation and the capacity of the lifting machine.

  By using a combination of pre-stress due to tension fixation of fiber reinforced concrete and PC steel wire, it is not necessary to arrange reinforcing bars for reinforcement, reducing material costs by omitting reinforcing bars, and reinforcing bar reinforcement work The construction cost can be reduced due to the fact that it is unnecessary, so the economy has been greatly improved.

The precast PC floor slab member 1 is manufactured by first placing a fiber reinforced concrete having a predetermined thickness to form a lower section, and arranging a PC steel material 6b in the longitudinal direction on the upper surface and a sheath for PC steel material in the width direction. A precast PC floor slab with a composite cross-section that is integrated with the lower cross-section by placing high-strength concrete without forming any reinforcing bars to form the upper cross-section and hardening the concrete 1 is obtained.
Although illustration is omitted, the connection between the lower cross section 1a and the upper cross section 1b is strengthened by making a seam at the joint between the lower cross section 1a and the upper cross section 1b, or a shear cotter and the like are added to the joint. By installing, the lower cross section 1a and the upper cross section 1b are firmly integrated.

Further, the lower cross section 1a is first made of fiber reinforced concrete to be a precast member, and the lower member 1a of the precast floor slab made of fiber reinforced concrete is used as a bed frame, and high strength concrete is placed thereon. It is also possible to manufacture by the manufacturing method to synthesize.
The thickness of the lower section 1a is 1/8 to 1/12 of the thickness of the entire section, and most preferably 1/10. As shown in the stress distribution diagram of FIG. 4, the distribution of the bending tensile stress degree generated in the cross section of the floor slab member decreases in proportion to the distance from the lower end of the cross section to the neutral axis toward the neutral axis of the cross section. Therefore, pre-stress is applied to the maximum bending tensile stress (σ _tmax ) generated at the lower end of the cross section, and fiber reinforced concrete having high tensile concrete strength is used. If the thickness of the lower cross section of fiber reinforced concrete is about 10% of the thickness of the entire cross section, the bending tensile stress level in the upper cross section area is lower than the maximum edge stress level at the lower end. It is possible to reliably achieve the prevention of bending cracks by introducing a prestress into the high-strength concrete to cope with the degree of bending tensile stress generated in.
When entering the region of the upper cross section, the bending tensile stress level becomes σ _t1 or less, which is greatly reduced compared to the maximum edge stress level σ _tmax at the lower end, making it possible to cope with a conventional high strength concrete cross section with prestress introduced. Become. If the bending tensile stress degree σ _t1 generated in the upper cross section is canceled by the introduced pre-stress, it can be ensured that no bending crack is generated.
The lower cross section is preferably formed using ultra high strength fiber reinforced concrete.

The precast PC floor slab members 1 arranged side by side are pressure-bonded and joined by the tension introduced into the PC steel 6a. About this crimping | compression-bonding surface, as shown in FIG. 5, it can select from two types, a dry construction method and a wet construction method.
In the dry method, it is preferable to apply an adhesive between the precast PC floor slab members 1 and 1 and provide a gap of about 2 to 5 mm in consideration of manufacturing errors of the floor slab member 1. Sponge rubber 61 is affixed so that rainwater and adhesive do not flow into the inside of the sheath 60 from the joint portion of the sheath 60 for inserting the tension steel wire.
In the wet method, a joint 20 having a diameter of 10 to 20 mm is provided between the precast PC floor slab members 1 and 1, and the joint 7 is filled with the non-shrink mortar 71. Sponge rubber 61 is attached to the seam of the sheath so as not to flow into the inside, and the non-shrink mortar 71 is filled to fill the joint 7.
If the precast PC floor slab member 1 is warped or deformed by bending by arranging the tension steel material 6b in the direction perpendicular to the bridge axis and introducing prestress, a wet construction method can be adopted. it can.

  FIG. 6 (1) is a detailed cross-sectional view of the slip prevention hole 12 provided in the precast PC floor slab member 1. In order to absorb the installation error of the precast PC floor slab member 1, a sole rubber 4 is laid between the upper surface of the flange 31 of the precast PC floor slab member 1 and the steel girder 3 to provide a gap. After installing on the flange 31 of the girder 3, the gap is filled with non-shrink mortar 71, the non-shrinkage hole 12 is filled with the expanded concrete 2, and the precast PC floor slab member 1 and the steel girder 3 through the stud bolt 32. Are joined and integrated to prevent slippage. Instead of the non-shrink mortar 71, an expanded mortar can be used.

  FIG. 6 (2) is a detailed sectional view of the level adjusting hole 13 for adjusting the level of the precast PC floor slab member 1, and a level adjusting insert 8 with an internal screw is driven into the precast PC floor slab member 1. The level adjusting hole 13 is provided in the upper part of the insert 8. When the precast PC floor slab member 1 is installed on the steel girder, the precast PC floor slab member 1 is laid between the precast PC floor slab member 1 and the upper surface of the flange 31 of the steel girder 3 so that a gap is formed. The plate member 1 is installed. After the installation, the level adjusting bolt 50 is screwed into the insert 8 through the hole 13, and the level of the precast PC floor slab member 1 is adjusted by the adjusting bolt 50. After the adjustment, the non-shrink mortar 71 is filled in the gap and the level adjusting hole 13 to maintain the level state of the precast PC floor slab.

DESCRIPTION OF SYMBOLS 1 Floor slab member 1a Upper cross section 1b Lower cross section 12 Shift stop hole 13 Level adjustment hole 2 Expanded concrete 3 Steel girder 31 Flange 4 Sole rubber 32 Stud bolt 50 Level adjustment bolt 6a 6b PC steel 60 Sheath 61 Sponge rubber 7 Joint 71 No shrinkage Mortar 8 insert

Claims (2)

Bridge floor slab with precast floor slab members with a composite cross-section with a lower cross-section formed of fiber-reinforced concrete of a predetermined thickness and an upper cross-section formed of high-strength concrete and integrated in the bridge axis direction In the upper cross section of the floor slab member, PC steel is arranged in the direction perpendicular to the bridge axis and in the direction of the bridge axis, and the two directions of prestress are applied to the entire cross section of the floor slab member by fixing the PC steel. In addition, a precast PC floor slab for bridges, in which floor slab members are bonded and integrated with each other, and the entire cross section of the floor slab is straight. The bridge precast PC slab according to claim 1, wherein the thickness of the lower cross section made of fiber reinforced concrete is 1/8 to 1/12 of the thickness of the floor slab.