JPH07116790B2 - Precast concrete beams - Google Patents

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 for surrounding the shaped steel material for reinforcing the beam, and at both ends of the shaped steel material 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 buried in concrete and a tension steel material for introducing prestress is arranged in the concrete.

[0002]

2. Description of the Related Art Conventionally, as the above-mentioned precast concrete beam, [1] H-shaped steel is used as a shaped steel material with the same cross section over its entire length, and the H-shaped steel embedded in concrete in the precast concrete beam portion is used. A structure in which the lower flange of the shaped steel and the upper flange exposed from the concrete are both surrounded and provided with ribs constituting a rebar cage (see, for example, JP-A-59-59).
-165752). [2] Shaped steel material is exposed at both ends of the precast concrete, and in the precast concrete, a concrete beam is embedded in a state in which the upper ends of the ribs constituting the rebar cage are exposed. A stress-introducing tension steel material is embedded, and as the shape steel material, a shape steel material without a middle portion in the longitudinal direction is used so that the shape steel material is located only at both ends of the concrete ( (See Japanese Utility Model Laid-Open No. 2-5520). the above
The ones described in [1] and [2] are known.

[0003]

However, the above-mentioned conventional precast concrete beams have the following problems. In other words, the precast concrete beams described in [1] above are used, for example, as a formwork, and the upper part of the ribs protruding from the precast concrete beam part is placed in the concrete that is cast on site with the slab. By embedding it, an integral rigid frame structure is constructed.For example, by pulling a tension steel material inserted into a sheath material in concrete in that state and applying a compressive force to the concrete, a larger tensile strength can be obtained. However, in that state, the tension steel mainly opposes the tensile force.Therefore, there is a conventional structure in which the beam section that was concrete-cast in advance and the other sections used the section steel material of the same cross section. As a result, the lower flange portion of the shaped steel material exerts almost no tensile strength and merely increases the beam weight. Moreover, since a large restraint force is generated between the lower flange and the concrete, when the concrete dries and shrinks, the direction in which the restraint force acts is opposite to the direction in which the force for introducing the prestress is applied. Therefore, the prestressing force is weakened, and there is a possibility that the prestressed structure at the corner cannot be fully utilized. Also,
In the precast concrete beam described in the above [2], since the intermediate portion of the shaped steel material does not exist, it is advantageous in that the shaped steel material can avoid the tensile force against the introduction of the prestress. On the other hand, on the other hand, because it is necessary to withstand various loads acting on this precast concrete beam at the erection stage, the necessary cross-sectional area of the concrete part increases, and the weight of the whole precast concrete beam tends to increase. There was a problem.
In view of the above situation, it is an object of the present invention to construct a precast concrete beam that can utilize the introduced prestress without waste and that has a sufficient resistance to the load at the erection stage and is lightweight.

[0004]

Means for Solving the Problems The technical means of the present invention taken to solve the above-mentioned problems include a shaped steel material for a beam and a reinforcing bar cage for beam reinforcement surrounding the shaped steel material. Of the rebar cage, excluding both ends of the shaped steel, the rib upper end of the rebar cage and the portion below the upper flange portion of the shaped steel are embedded in concrete, and the In a precast concrete beam in which a tension steel material for stress introduction is arranged, the shaped steel material is composed of a long steel material having a length across both ends of the beam, and the shaped steel material is located above the concrete. In the exposed part, leave the upper flange part,
In addition, the lower flange portion is removed while leaving the shaped steel material web portion in the portion inside the concrete.

[0005]

The operation of adopting the above technical means is as follows. In other words, when bending is applied in the state where this type of precast concrete beam is installed in the rigid frame, the tensile force that the shaped steel material for the beam will bear if there is no prestressing tension steel material, Since the introduced prestress force resists, it is not necessary for the shaped steel material for beams to have a large tensile strength. Therefore,
This shaped steel material can be arranged mainly in the state of being positioned on the compression side, with the strength required to resist the compression force due to bending load. Then, the shaped steel material is a portion located in the concrete, by removing the lower flange equivalent portion leaving the web portion, while securing the compressive strength as the shaped steel material, restraint between the shaped steel material and concrete. The force is kept as low as possible to avoid the generation of forces that would significantly weaken the prestressing force when the concrete dries and shrinks. Further, in this concrete beam, since the shaped steel material is present on the compression side against bending load as a beam member continuous in the longitudinal direction, the bending strength of the entire concrete beam can be increased before the cast-in-place concrete is placed. It is improving from the stage. Therefore, the load of the concrete beam at the erection stage can be significantly reduced as compared with the case where the precast concrete alone is used to withstand the bending load during the erection without using the shaped steel material continuous in the longitudinal direction.

[0006]

As a result, the precast beam introduced with prestress has a large tensile strength and is excellent in workability, but the weight of the beam is reduced, and the handleability from the stage of transportation and erection work is improved. As a result of being able to reduce the restraining force between the shaped steel and concrete, which causes the attenuation of prestressing force, 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 part of a shaped steel material 1 for a beam and a rebar cage 2 provided so as to surround the shaped steel material 1 is placed in concrete 3. It is buried. This 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 the portion excluding both ends of the shaped steel material 1 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 completed beam is arranged. The tension steel material 4 is installed by pretensioning. After the concrete 3 is placed in a state in which 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.

The shaped steel material 1 uses a full H-shaped cross section at both ends thereof which are not embedded in the concrete 3, as shown in FIG. 2B, and the vertical position of the web portion 1A. Each is provided with upper and lower flange portions 1B and 1C, and is formed with a high-tensile bolt hole 1a used for joining the pillar bracket. 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 portion 1C removed, and Have been reinforced. In other words, the lower flange portion 1C is to resist 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 tension, there is no lower flange portion 1C. However, if the concrete is rather dried and contracted, the prestressing force of the tensile steel material 4 may be weakened by its restraining force. Therefore, a T-shaped cross section with this part removed is used to ensure reduction of the beam weight. It is intended to exert a great amount of prestress.

Another Embodiment Next, another embodiment 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. However, various shaped steel materials 1 may be used instead. For example, a pair of C-shaped steels may be combined back to back at both ends, and the lower flange portion 1C may be removed from the combination of the C-shaped steels at the intermediate portion. Further, the shaped steel material 1 is not limited to a single material, but may be a combined material or a lattice-shaped material. Further, in the above embodiment, the shaped steel material 1 having the T-shaped cross section in the middle portion 1
In the above description, the both ends are made to have an H-shaped cross section in consideration of the convenience of joining with an adjacent material. However, instead, the both ends may be made to have another cross section or may be left as a T-shaped cross section. Absent.

<2> In the previous embodiment, the method of pretensioning was used as an example to introduce prestress to the beam. However, the prestress is introduced into the concrete 3 pre-placed instead. Alternatively, post-tensioning may be performed in which the sheath is buried and the tension 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 in advance 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 although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the structures 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 1A Web Part 1B Upper Flange Part 1C Lower Flange Part 2 Reinforcing Bar Basket 2b Rib 3 Concrete 4 Prestressed Tension Steel

Claims (1)

[Claims] 1. A beam shaped steel material (1) and a beam reinforcing steel cage (2) surrounding the shaped steel material (1) , comprising:
The shaped steel material among the shaped steel material (1) and the reinforcing bar cage (2)
The ribs of the rebar cage (2) within the range excluding both ends of (1)
(2b) Upper flank and upper flan of the shaped steel (1)
The part below the jib part (1b) is concrete (3)
A precast concrete beam which is embedded inside and in which a prestressing tension steel material (4) is disposed in the concrete (3), wherein the shaped steel material (1) has a length extending over both ends of the beam. Shaku steel
And the shaped steel material (1) is above the concrete (3).
In the part exposed to the side, the upper flange part (1b)
Shaped steel in the remaining part and in the concrete (3)
Lower flange part, leaving the web part (1a) of material (1)
Precast concrete beam with the portion (1c) removed .