JP2612977B2 - Prevention method of crack of post-cast concrete in composite slab. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite slab made of a semi-precast concrete member and a post-reinforced reinforced concrete, which prevents cracking of the post-cast concrete at a joint extending in the longitudinal direction between adjacent half-precast concrete members. Pertains to the method.

[0002]

2. Description of the Related Art According to a reinforced concrete composite slab construction method in which a semi-precast concrete member and a cast-in-place concrete cast on the same member are combined, a half-precast concrete member manufactured in advance in a factory is opposed to a corresponding beam. A bridge is laid over the shoulders of the members, and the concrete is laid with reinforcing bars arranged on each of the members.

[0003] The semi-precast concrete member has various cross-sectional shapes, but recently, it has a rib shape or a void shape having a convex, T-shaped or double T-shaped cross section.
The number of devices that can be applied to a large span of about 5 to 10 m in length is increasing. In this case, due to the restrictions on truck transport, many of these are elongated and have a width of about 1 to 2 m.

Further, the semi-precast concrete member and the post-cast concrete portion have a composite slab structure integrally resisting external force by a shearing bar, shear cutter or the like.

[0005]

In the above-mentioned composite slab, while the concrete of the semi-precast concrete member has been dried and shrunk to a considerable extent and is in a substantially stable state, the post-cast concrete has a high stability. After drying, drying shrinkage proceeds. Furthermore, compared to slabs by the conventional method, after-cast concrete has a large drying shrinkage because it is thinner by the thickness of the half-cast concrete member, and it is often applied to a large span, so the area is large, Cracks are likely to occur by nature. Most of the cracks occur along the seam extending in the longitudinal direction between the adjacent semi-precast concrete members, for the following reasons. That is, in the longitudinal direction which is the main reinforcement direction of the semi-precast concrete member, there is no seam between the bridges of the member, and the drying shrinkage strain of the post-cast concrete is relatively uniformly restrained, and cracks hardly occur. On the other hand, in the lateral direction of the half-PC precast concrete member, there are some seams between the beams because the members are simply laid side by side. For this reason, the drying shrinkage strain of the post-cast concrete in the transverse direction is restrained by the adhesion to the semi-precast concrete member and the dowel effect of the shearing bars and main bars embedded in the member, and the joint shrinks due to the drying shrinkage. Tensile stress caused by strain acts intensively. This results in cracks in the post-cast concrete along the longitudinal seams of the semi-precast concrete member. At present, this seam is dealt with by providing force bars and reinforcing bars inside the post-cast concrete, but this alone has little effect. These cracks are likely to be connected to the seam of the semi-precast concrete member and penetrate therethrough, which is a disadvantage not only in terms of appearance but also in terms of waterproofing, sound insulation, and repair.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned problems of the prior art, and the object thereof is to provide a simple slab composed of a semi-precast concrete member and a post-cast concrete portion. It is an object of the present invention to provide a method for reliably preventing cracks in post-cast concrete which occurs at a longitudinal seam position of a semi-precast concrete member.

[0007]

According to the present invention, there is provided, according to the present invention, a semi-precast concrete member spanned and laid between opposing beam members, and is cast on the same portion. In a composite slab comprising a post-cast reinforced concrete part, a plastic sheet having a T-shaped section continuous along the seam is interposed between seams in the longitudinal direction of the adjacent semi-precast concrete members, and the vertical side of the plastic sheet is perpendicular to the seam. A part is sandwiched between the two adjacent members, and a horizontal part is straddled over each upper surface of the two adjacent members. It is to be cast.

[0008]

According to the present invention, a plastic sheet having a T-shaped cross section is interposed along a longitudinal seam of an adjacent semi-precast concrete member in the composite slab, and a plastic sheet having a T-shaped cross section is interposed along the seam. The vertical piece is sandwiched between the semi-precast concrete members that are adjacent to each other in the width direction, and adhesion of the semi-precast concrete member and the post-cast concrete is prevented only at this portion, so that the post-cast concrete on the same member is prevented. The concentration of stress generated at the joint position of the member due to the drying shrinkage of the member is prevented.

As a result, the occurrence of cracks in the post-cast concrete, which is generated at the position of the seam in the longitudinal direction of the semi-precast concrete member, is prevented.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Numeral 1 is a semi-precast concrete member spanned between shoulders of opposing beams (not shown). In the illustrated embodiment, the semi-precast concrete member has a double T-shaped cross section. Has been arranged.

Reference numeral 4 denotes a plastic sheet having a T-shaped cross section, which is a longitudinal seam 5 of the semi-precast concrete member 1.
And a vertical piece 4a of the plastic sheet 4
Are sandwiched between the end faces in the width direction of the adjacent half-cast concrete members 1 and 1, and the horizontal pieces 4 b are disposed across the upper surfaces of the respective horizontal plates of the adjacent half-cast concrete members 1 and 1. I have. (See FIG. 2) When the placement of the plastic sheet 4 is completed, a slab bar 6 is arranged on the semi-precast concrete member, and a post-cast concrete 7 is cast.

The illustrated embodiment is constructed as described above, so that only the longitudinal seam 5 of the adjacent precast concrete member 1 is joined by the plastic sheet 4 to the semi-precast concrete member 1 and the post-cast concrete 7. This prevents the concentration of stress generated at the joint 5 due to drying shrinkage of the post-cast concrete 7, thereby preventing the post-cast concrete 7 from cracking at the joint 5 position.

Note that the width of the T-type plastic sheet 4 is 2 to 4 times the thickness of the post-cast concrete 7 in consideration of the effect of preventing cracks and minimizing the adhesion area between concrete. The thickness is set to 1 mm or less so as not to cause a sectional defect of the post-cast concrete.

[0014]

According to the present invention, there is provided a composite slab comprising a semi-precast concrete member laid over and laid between beam members and a post-cast reinforced concrete portion cast on the member. A plastic film having a T-shaped cross section is provided at the joint in the longitudinal direction of the member.
The vertical piece of the film is sandwiched between the adjacent semi-precast concrete members, and the horizontal piece is interposed so as to be straddled on each upper surface of the adjacent member. The aftercast concrete of the longitudinal seam of the semi-precast concrete member is freed from the stress concentration caused by drying shrinkage by the plastic sheet. As a result, cracks in the post-cast concrete generated at the joints can be significantly reduced. Even when complete prevention is difficult, cracks can be controlled by appropriately arranging a place where this is installed and a place where it is not installed. Furthermore, even if the post-cast concrete is to lead to the occurrence of penetration cracks, the T-type plastic sheet is not cut because a large force does not act on the T-type plastic sheet. Repair of cracks becomes easy.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a method for preventing cracks in post-cast concrete in a composite slab according to the present invention, showing a process of disposing a plastic sheet having a T-shaped cross section.

FIG. 2 is a longitudinal sectional view showing a state in which the crack preventing method is completed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semi-precast concrete member 4 Plastic sheet 4a Vertical part 4b Horizontal part 5 Seam 6 Slab streak 7 Post-cast concrete

Claims (1)

(57) [Claims] 1. A composite slab comprising a semi-precast concrete member laid over and laid between opposing beam members and a post-cast reinforced concrete portion cast on the same portion, wherein the adjacent semi-precast concrete member is provided. A plastic sheet having a T-shaped section continuous along the seam is interposed at the seam in the longitudinal direction of the member, and a vertical piece of the plastic sheet is sandwiched between the adjacent two members, and a horizontal part is formed. A method for preventing cracking of post-cast concrete in a composite slab, wherein a piece is straddled over each upper surface of the adjacent two members, and is then arranged on the member, and post-cast concrete is poured. .