JPH0510001A - Precast concrete beam - Google Patents

Abstract

PURPOSE:To utilize prestress introduced into concrete without loss by a method in which a precast concrete beam having high tensile strength, light weight, high handleability, and high workability is formed by reducing the restricting force between shape steel and concrete, CONSTITUTION:In a reinforcing bar cage 2 for reinforcing beams surrounding shape steel 1 and the shape steel 1 of beams, the portion excluding both ends of the shape steel 1 from the upper end to the lower part of the base bars 2b of the cage 2 is buried in concrete 3. Tensed steels 4 to be introduced with prestress are set in the concrete 3. In the shape steel 1 for beam, the flange- corresponding portion of the lower side in the concrete 3 is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaped steel material for a beam and a reinforcing steel cage surrounding the shaped steel material for reinforcing a beam, wherein both ends of the shaped steel material are located below the upper end of the rib of the reinforcing steel cage. The present invention relates to a precast concrete beam in which a portion excluding a portion is previously embedded in concrete and a tension steel material for introducing prestress is arranged in the concrete.

[0002]

2. Description of the Related Art In the above-mentioned precast concrete beams, conventionally, H-section steel is used as a section steel material with the same cross section over the entire length thereof, and the H-section steel embedded in the concrete is pre-cast under the H-section steel embedded in the concrete. It is known that both side flanges and upper flanges exposed from concrete are provided with ribs constituting a rebar cage (see, for example, JP-A-59-165752).

[0003]

However, the above-mentioned conventional precast concrete beams have the following problems. In other words, this type of precast concrete beam is used as a formwork, for example, by burying the upper part of the ribs protruding from the precast concrete beam part in the concrete that is cast on site together with the slab. It is one that constitutes an integral rigid frame structure, for example, by making a tensile steel material inserted into a sheath material in concrete in that state and applying a compressive force to the concrete, it is possible to obtain a larger tensile strength. However, in that state, the tension steel material mainly opposes the tensile force.Therefore, in the conventional structure in which the beam section pre-concretely cast and the other sections use the section steel material of the same cross section, The lower flange portion of the shaped steel material had almost no effect on tensile strength and merely increased the beam weight. Moreover, since a large binding force is generated between the lower flange and the concrete, when the concrete dries and shrinks, the direction of the binding force is opposite to the direction of the force for introducing the prestress. Therefore, the prestressing force is weakened, and there is a fear that the prestressed structure at the corner cannot be fully utilized. In view of the above situation, an object of the present invention is to provide a precast concrete beam that can utilize the introduced prestress without waste.

[0004]

A characteristic construction of a precast concrete beam according to the present invention is that a lower flange-corresponding portion in the concrete is removed from a beam-shaped steel material partially buried in concrete in advance. Especially.

[0005]

[Function] In other words, when bending of a precast concrete beam of this kind is incorporated in a rigid frame structure, if there is no prestressing tension steel, the beam for the beam will bear. Since the applied prestress force resists the applied force, it is not necessary for the shaped steel material for the beam itself to have a large tensile strength, so by removing the portion corresponding to the lower flange of the shaped steel material, the beam weight In addition, the restraining force between the shaped steel material and the concrete is reduced as much as possible to prevent the generation of a force that significantly weakens the prestressing force when the concrete dries and shrinks.

[0006]

As a result, the precast beam with prestress introduced has a large tensile strength and is excellent in workability, but the weight of the beam is reduced to improve the handleability and cause the attenuation of the prestress force. As a result of being able to reduce the restraining force between the shaped steel material and the concrete, it has become possible to provide an excellent precast concrete beam that can utilize the introduced prestress without waste.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, in a precast concrete beam according to the present invention, a portion of a beam-shaped steel material 1 and a reinforcing bar cage 2 surrounding the shaped steel material 1 is placed in concrete 3. It is buried. The concrete 3 is located below the upper ends of the ribs 2b that form the rebar cage 2 together with the main ribs 2a, and occupies a portion of the shaped steel material 1 excluding both ends thereof, and is above the ribs 2b. It is configured so as to form a beam together with the concrete cast on site where the part is buried. Further, in this concrete 3, a tension steel material 4 for introducing prestress for increasing the bending resistance of the finished beam is arranged. The tension steel material 4 is installed by pretensioning. After the concrete 3 is placed in a state where a tensile force is applied in advance, the hardening is waited for and the tensile force is removed to compress the concrete 3 as a prestressing force. It gives power.

As shown in FIG. 2 (B), the shaped steel material 1 has a full H-shaped cross-section at both ends which are not buried in the concrete 3, and the upper and lower flanges and the web are used. Further, a high-tensile bolt hole 1a used for joining the pillar to the bracket is formed. In addition, as shown in FIG. 2 (A), the middle portion of the shaped steel material 1 embedded in the concrete 3 has a T-shaped cross section with the portion corresponding to the lower flange removed, and is reinforced with the reinforcing bar cage 5. I am doing it.
That is, the lower flange equivalent portion is against the tension due to bending in the finished beam, but in the precast concrete beam according to the present invention, since the tensile steel material 4 is exclusively against the tension, there is no lower flange equivalent portion. However, if the concrete rather dries and shrinks, the prestressing force of the tensile steel material 4 may be weakened by its restraining force. Therefore, a T-shaped cross section with this portion removed is used to reduce the beam weight and ensure the reduction. It is intended to exert a great amount of prestress.

[Other Embodiments] Next, other embodiments of the present invention will be listed.

<1> In the above embodiment, the shaped steel material 1 has the H-shaped cross-section at both ends and the T-shaped cross-section at the middle portion, but various shaped steel materials 1 may be used instead. For example, a pair of C-shaped steels may be combined in a back-to-back manner at both ends, and a middle flange may be formed by removing a portion corresponding to the lower flange of the C-shaped steels. Further, the shaped steel material 1 is not limited to a single material, but may be a combined material or further a lattice-shaped material. Further, in the above embodiment, the shaped steel material 1 having the T-shaped cross section in the middle portion
Although both ends of the above have an H-shaped cross section in consideration of the convenience of joining with an adjacent material, the both ends may have another cross section or the T-shaped cross section may be left as it is. Absent.

<2> In the previous embodiment, the method of pretensioning was used as an example when introducing prestress to the beam. However, the introduction of prestress is instead performed in the concrete 3 that has been placed in advance. Alternatively, post-tensioning may be performed in which the sheath is buried and the tensile steel material 4 is inserted into the sheath after the concrete 3 is hardened to apply a tensile force. That is, the prestressing tension steel material 4 according to the present invention may be arranged before or after the concrete 3 is poured.

<3> In addition, in carrying out the precast concrete beam of the present invention, it is possible to change the concrete constitution without departing from the gist of the invention. For example, the ribs 2b of the rebar cage 2 are made spiral. Maybe,
The upper end position of the concrete 3 to be placed beforehand is also the rib 2
Any position can be set as long as it is below the upper end of b.

It should be noted that reference numerals are given in the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

1] Side view

2 is a cross-sectional view ((A) is an AA cross section of FIG. 1, (B) is a BB cross section of FIG. 1)

[Explanation of symbols]

 1 shaped steel 2 rebar cage 2b rib 3 concrete 4 prestressed tension steel

Claims (1)

Claims: 1. A steel bar (1) for a beam and a rebar cage (2) for reinforcing a beam which surrounds the steel bar (1), and the ribs of the rebar cage (2). (2b) A portion below the upper end except for both ends of the shaped steel material (1) is embedded in the concrete (3) in advance, and the prestressing tension steel material (4) is introduced into the concrete (3). A precast concrete beam which is provided, wherein a portion of the shaped steel material (1) corresponding to the lower flange in the concrete (3) is removed.