JPH04334405A - Manufacture of precast concrete beam - Google Patents

Abstract

PURPOSE:To secure the integrity of a lower end main bar and a stirrup with concrete while retaining a wire mesh forming an inner template of concrete of U-shaped section and pressing a thick concrete plate. CONSTITUTION:A wire mesh 4 forming an inner template is stuck to a lower end main bar 1 and a stirrup 2 of a reinforced squirrel cage C assembled with the lower end main bar 1 and the stirrup 2, and said reinforced squirrel cage C is disposed on lower templates 6, 6 with the lower end main bar 1 facing upward, and outer plates 5, 5 are disposed on both outsides of the reinforced squirrel cage C. After that, concrete 3 is filled between said outer templates 5, 5 and the wire mesh 4 and a precast concrete beam B is manufactured. The integrity of the lower end main bar 1 and the stirrup 2 with concrete 3 is secured by sticking the wire mesh 4 on the inner peripheral sides of the lower end main bar 1 and the stirrup 2, and the lower end main bar 1 is functioned as a tension steel bar of the precast concrete beam B, and the necessity of supporting at the time of placing in-site concrete 8 is eliminated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a precast concrete beam, which is a method of manufacturing a precast beam having a U-shaped cross section.

0002

[Prior Art and Problems to be Solved by the Invention] To reduce the weight of precast concrete beam members and to facilitate transportation to the site, at the same time, to eliminate the need for formwork for cast-in-place concrete, the beam members were started. There is a tendency to use a method of burying the wrap and bottom main reinforcement in concrete and precasting it into a U-shaped cross-section.
Conventional precast concrete beams are usually manufactured by using wire mesh for the inner formwork and burying the stirrup lower part and lower end main reinforcement in the concrete to save the time and effort of demolding.

[0003] In this conventional manufacturing method, the stirrup is completely buried in concrete except for the upper part, so the wire mesh is placed in a state supported by the stirrup. Because of the distance, it is difficult to maintain that state when filling with concrete.
In addition, there are other problems such as an increase in weight due to the thickness of the concrete being larger than necessary. Focusing on this problem, a beam to solve this problem was proposed in Japanese Patent Application Laid-Open No. 61-49049.

[0004] This solves the problem of retaining the wire mesh and increasing its weight by positioning the wire mesh on the outer periphery of the stirrup. However, in this structure, the attachment of the stirrup and lower end main reinforcement to the concrete is substantially reduced. Because the integrity of the two is lost, the main reinforcement at the bottom cannot resist the load during concrete pouring on site as a main reinforcement as part of the beam; It is essential to install supports, and problems such as a decrease in construction efficiency have been pointed out.

[0005] The present invention has been made in consideration of the actual situation of conventional U-shaped beams, and aims to propose a new method for manufacturing a beam having a structure that overcomes the above-mentioned problems.

[0006]

[Means for Solving the Problems] In the present invention, a wire mesh serving as the inner formwork of concrete with a U-shaped cross section is attached to the inner circumferential side of the main reinforcement at the lower end and the stirrup, thereby holding the wire mesh and at the same time suppressing the plate thickness. At the same time, it ensures the integrity of the lower end main reinforcement and stirrup with the concrete, and in particular allows the lower end main reinforcement to function effectively as a tension reinforcing bar, eliminating the need for support when pouring concrete on site.

[0007] By positioning the wire mesh on the inner circumferential side of the lower end main reinforcing bars and stirrups, the lower end main reinforcing bars and stirrups are buried in the concrete and become integral with the concrete, and the lower end main reinforcing bars have a U-shaped cross section and are cast in situ into the concrete. The U-shaped precast concrete beam effectively resists tension during concrete pouring, and can stand alone against the poured concrete.

[0008] By eliminating the need for supports, the main reinforcement at the bottom resists tension during concrete pouring at the site, but especially when the span is large and supports need to be installed, the upper end of the cross section on the support is in tension. Therefore, abdominal reinforcement to resist this is placed near the upper end of the concrete with a U-shaped cross section.

[0009] The wire mesh is held in place even when concrete is filled by being attached to the lower end main reinforcements and stirrups.
Also, by placing it in close contact with the stirrup, the thickness of the concrete plate can be kept to the required size.

[0010] In manufacturing a precast concrete beam, a reinforcing bar cage is assembled in advance from a lower end main reinforcing bar and a stirrup, and a wire mesh serving as an inner formwork is pasted on the inner circumferential side of the lower end main reinforcing bar and stirrup, and this reinforcing bar cage is After installing the main reinforcement on the lower formwork with the main reinforcement facing upwards and placing the outer formwork on both outsides of the reinforcing bar cage, concrete is filled between the outer formwork and the wire mesh, and after the concrete hardens, the outer formwork is replaced. This will be done in the following manner:

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on drawings showing one embodiment.

The present invention is a method for manufacturing a precast concrete beam (hereinafter referred to as a PC beam) B having a U-shaped cross section as shown in FIG.

As shown in the figure, the PC beam B is manufactured by embedding the lower end main reinforcement 1 and the stirrup 2 in concrete 3 with a U-shaped cross section, and the upper part of the stirrup 2 is the anchorage part from the top of the concrete 3 to the slab. only stands out.

In the reinforcing bar cage C assembled from the lower end main reinforcing bars 1 and the stirrups 2, a wire mesh 4 is provided on the inner peripheral side of the lower end main reinforcing bars 1 and the stirrups 2 to serve as an inner formwork when filling with concrete 3.
is pasted.

As shown in FIGS. 1 and 2, the wire mesh 4 is bent into a U shape along the inner peripheral surface of the concrete 3 and attached to the inner peripheral side of the lower end main reinforcement 1 and stirrup 2, and when filling the concrete 3. The pressure is maintained by the reinforcing bar cage C. The wire mesh 4 is made of expanded metal, punched metal, or the like.

Concrete 3 is made using this wire mesh 4 as an inner formwork.
By being filled with the reinforcing bar cage C, the reinforcing bar cage C becomes in a state equivalent to being reinforced inside the beam, and it already has a load-bearing capacity when the PC beam B is manufactured.

The procedure for manufacturing the PC beam B will now be explained with reference to FIGS. 2 to 6.

First, as shown in FIG. 2, as described above, a wire mesh 4 is attached to the inner circumference of the reinforcing bar cage C consisting of the lower end main reinforcement 1 and the stirrup 2, while the outer circumferential side of the concrete 3 is attached as shown in FIG. Assemble the outer forms 5, 5. wire mesh 4
Since the reinforcing bar cage C with attached reinforcing bars C is left upside down until the concrete 3 hardens, the outer formwork 5 is installed on the lower formwork 6 located on the top side of the concrete 3.

When the PC beam B is not supported by a support, the lower end main reinforcement 1 on the tension side bears the pouring load of the cast-in-place concrete 8 over the entire length of the span and becomes self-supporting, but especially in the center of the span, etc. When an intermediate support is erected, in order to resist the tensile force on the support, that is, in the section where the upper side of the cross section is tensile, if necessary, the abdominal muscles 7 that take charge of this upper tensile force are set as shown in Figs. 1 and 2. Reinforcement is placed near the upper end of the concrete 3 and tied to the stirrup 2. These abdominal muscles 7 also have the role of resisting the tensile force that acts on the lower side of the PC beam B due to the fact that the upper and lower sides of the PC beam B are reversed when the outer formwork 5 is lifted for curing after being demolded. .

As shown in FIG. 4, the lower formwork 6 has a height equal to or greater than the protrusion length of the stirrup 2 from the top of the concrete 3, and is calculated by subtracting the cover thickness of the stirrup 2 from the thickness of the concrete 3. It protrudes from the side surface of the outer formwork 5 toward the inner periphery by the same width, and supports the reinforcing bar cage C from filling with concrete 3 to hardening. In the embodiment, in order to restrain and hold the reinforcing bar cage C, a groove 6a in which the stirrup 2 is accommodated is formed on the inner peripheral side of the lower formwork 6, as shown in FIG.

As shown in FIG. 4, on the lower formworks 6, 6,
The reinforcing bar cage C is sandwiched between the outer formworks 5, 5, and the lower end main bar 1
is placed facing upward, and then concrete 3 is filled between the outer forms 5, 5 and the wire mesh 4 as shown in FIG. When filling the concrete 3, the wire mesh 4 becomes the inner formwork as described above. A slight amount of concrete 3 oozes out from the holes of this wire mesh 4, but the slag hardens as it is, creating unevenness on the inner circumference side of the PC beam B, and serves to enhance the adhesion effect with the cast-in-place concrete 8. There is.

After the concrete 3 hardens, the outer forms 5, 5 are removed to complete the PC beam B as shown in FIG.

FIG. 7 shows the state in which this PC beam B is used. After the PC beam B is installed between the columns, the projecting part of the stirrup 2 is installed as shown in FIGS. 7 and 1. This is done by arranging the upper main reinforcements 9 and placing the concrete 8 at the same time as the slab. At this time, as mentioned above, since the reinforcing bar cage C is integrated with the concrete 3, the pouring load of the concrete 8 cast in the field is borne by the lower end main reinforcement 1, and the PC beam B is not dependent on the support of the supports and is placed in the concrete 3. Resist 8. In Fig. 1, the reinforcing bars on the lower end main reinforcement 1 are constructed across the lower end main reinforcing bars 1, 1 of the PC beams B and B facing each other on the column, and the connecting reinforcement 10 is connected to this with a lap joint.
shows.

[0024]

[Effects of the Invention] This invention is as described above, and since the wire mesh serving as the inner formwork is attached to the inner peripheral side of the lower end main reinforcement and stirrup, the wire mesh can be held securely and the thickness of the plate can be suppressed. , it is possible to ensure the integrity of the bottom main reinforcement and stirrup with the concrete, and when pouring concrete on-site, the bottom main reinforcement effectively functions as a tension reinforcing bar, making the precast concrete beam self-supporting against the load of the poured concrete. You can make them resist.

[0025] As a result, no support is required, and construction efficiency can be increased.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of manufacturing a precast concrete beam.

FIG. 2 is a perspective view showing an assembled state of the reinforcing bar cage.

FIG. 3 is a perspective view showing the assembled state of the lower formwork and the outer formwork.

FIG. 4 is a perspective view showing a reinforcing bar cage installed on the lower formwork.

FIG. 5 is a perspective view showing how concrete is filled between the outer formwork and the wire mesh.

FIG. 6 is a perspective view showing how the outer formwork is removed from the mold.

FIG. 7 is a sectional view showing a precast concrete beam in use.

[Explanation of symbols]

B...Precast concrete beam, C...Reinforced cage, 1
... Bottom main reinforcement, 2 ... Stirrup, 3 ... Concrete, 4 ... Wire mesh, 5 ... Outer formwork, 6 ... Lower formwork, 6a...
...Groove, 7...Abdominal reinforcement, 8...Concrete, 9...Top main reinforcement, 10...Connection reinforcement.

Claims (2)

[Claims] [Claim 1] A method for manufacturing a precast concrete beam in which the lower end main reinforcement and stirrup are buried in concrete having a U-shaped cross section, and the upper part of the stirrup protrudes from the top of the concrete. A wire mesh that will become the inner formwork of the concrete is pasted on the inner circumferential side of the lower end main reinforcement and stirrup of the reinforcing bar cage assembled from the main reinforcing bars and stirrups, and the reinforcing bar cage is placed on the lower formwork with the lower end main reinforcing bars facing upward. After placing outer formwork on both outsides of the reinforcing bar cage, concrete is filled between the outer formwork and the wire mesh.
A method for manufacturing precast concrete beams that consists of the process of removing the outer formwork after the concrete has hardened. 2. The method for manufacturing a precast concrete beam according to claim 1, wherein the reinforcing bar cage is assembled by arranging abdominal reinforcement on the outer peripheral side of the stirrup at a position near the upper end of the concrete.