JPH041135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to improving the strength of precast concrete plates.

[Conventional technology]

Usually, precast concrete plates with truss reinforcements are used for the floors and walls of buildings, and one side has a smooth finished surface and doubles as a formwork.

It is desirable that this precast concrete plate be as light as possible in consideration of ease of transportation and handling on site, and therefore, a thin plate with parallel upper and lower surfaces is usually used.

However, as shown in FIG. 4, even if the reinforcing truss bars 1 are planted in the concrete 2, when the area of the precast concrete plate 3 becomes large, it becomes difficult to transport the concrete plate 3. When pouring concrete by constructing a frame with the concrete plates 3 and 3, the concrete plates 3
A support part (not shown) that supports the
Is required. This is because the strength of the concrete plate 3 is weak, so that the concrete plate 3 is easily bent by its own weight or external force. In this case, the larger the area of the concrete plate 3 or the thinner the plate thickness, the more supporting members must be provided. Note that FIG. 4 is a perspective view showing a conventional precast concrete plate 3 being lifted up by a lifting device 4. As shown in FIG.

[Problem that the invention seeks to solve]

With the conventional precast concrete plate whose upper and lower surfaces are parallel as described above, it is necessary to provide a support member to support the concrete plate, which makes the above-mentioned transportation and concrete pouring work complicated. There was a problem.

The present invention has been made to solve these problems, and an object of the present invention is to obtain a precast concrete plate that can reduce or eliminate the need for supporting members that support the precast concrete plate.

[Means to solve the problem]

The precast concrete plate according to the present invention has truss reinforcements planted thereon, the lower surface is flat, and the upper surface where the truss reinforcements are implanted has a central part that is gradually thickened from the periphery and has an arc-shaped cross section. It is molded.

[Effect]

In this invention, since the central part of the upper surface of the precast concrete plate is formed into a medium-height shape with an arcuate cross-section that is gradually thicker than the peripheral part, the shape of this concrete plate is what is called a "beam of equal strength".
This means that if the same amount of concrete is used as before, the maximum stress of the concrete plate can be increased.

〔Example〕

The present invention will be explained below based on illustrated embodiments. FIG. 1 is a cross-sectional view showing an embodiment of a precast concrete plate 3 according to the present invention. 1 consists of a plurality of convex portions 1a with continuous convex portions as shown in FIGS. 2 and 3, and a lower end truss 1b is formed between each convex portion 1a. This truss reinforcement 1 is the same as that used in the conventional concrete plate 3 mentioned above.

As shown in FIG. 1, this concrete plate 3 has a lower surface 2a having a substantially flat plate shape, and an upper surface 2a on which the truss reinforcements 1 are installed.
In b, the center part is formed to be gradually thicker than the peripheral part, and this embodiment shows the case where the center part bulges in an arcuate cross-section. Note that FIG. 2 shows a cross section of the central portion of the concrete plate 3, and FIG. 3 shows a cross section of the peripheral portion of the concrete plate 3.

Therefore, in the precast concrete plate of the present invention configured as described above, for example, when the concrete plate 3 is placed or lifted using the left and right ends in FIG. 1 as fulcrums, or when the concrete plate 3 is When it is installed at a construction site to serve as a formwork and concrete is poured into the frame, the force due to its own weight or external force is applied from the top to the bottom in the figure as a uniformly distributed load or a concentrated load. Due to this force, a tensile force acts on the flat lower surface 2a of the concrete plate 3, while a compressive force acts on the upper surface 2b, which has an arcuate cross-section and a swollen central portion.

By the way, a conventional precast concrete plate can be considered as a "beam with a uniform cross section" in terms of material mechanics, whereas the precast concrete board 3 according to the present invention has a "beam with uniform strength". It has a shape similar to that of a "beam" (a beam designed so that the tensile and compressive circumferential stresses of the square cross section are constant in the axial direction). This is because among the "beams of equal strength", beams like this example, which are supported at both ends and have a rectangular cross section, have a middle-height shape in which the center part is gradually thicker than the peripheral part. It is. In comparing this "beam with equal strength" and "beam with a uniform cross section", if the maximum stress of both beams is the same, the volume of the "beam with equal strength" will be significantly reduced. This is known mechanically. Therefore, in the concrete plate 3 according to the present invention when the same amount of concrete as the conventional one is used, the maximum allowable stress can be significantly increased.

Note that the lower surface 2a of the concrete 2 of the concrete plate 3 in this invention only needs to be substantially flat, and may not be perfectly flat, but may be curved or have some irregularities, for example.

In addition, although the above description has been given in the case of a thin precast concrete plate 3, even if the plate is thick to some extent, the concrete plate 3 can be made into a concrete plate 3 with improved strength due to the above structure.

By the way, in the above explanation, we explained the case where the strength of the concrete plate is increased using the same amount of concrete as before, but if the maximum stress is to be the same as before, it is necessary to use a much larger amount of concrete than before. This can reduce the weight of the concrete plate.

〔Effect of the invention〕

As explained above, this invention has a structure in which the central part of the upper surface of concrete in which truss bars are planted is gradually thickened from the periphery to a medium-height shape, and is formed into an arcuate cross-section, thereby achieving uniform strength. The strength of the precast concrete plate is increased through the acquisition of beams, and there is a significant effect that the number of supporting members supporting the concrete plate can be reduced compared to the conventional method or completely eliminated.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a precast concrete plate showing an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing a part of the cross section along the - line in FIG. 1, and FIG.
The figure is an enlarged sectional view showing a part of the cross section taken along the - line in Fig. 1, and Fig. 4 is a perspective view showing a conventional precast concrete plate. 1... Truss muscle, 2a... Lower surface, 2b... Upper surface, 3...
Precast concrete board. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a precast concrete plate on which truss reinforcements are planted, the lower surface is flat, and the upper surface on which the truss reinforcements are implanted is formed into a medium-high shape with an arcuate cross-section where the center part is gradually thicker than the periphery. A precast concrete board featuring: