JPH0312185B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a method of constructing a beam for supporting a slab of a building.

(Problem to be solved by the invention and its characteristics) Conventionally, PC materials with prestress introduced by the pretension method have been used for small beams that support the slabs of buildings.
Total load ultimately borne by the beam (load + live load)
Since a large prestress corresponding to the beam size is applied from the beginning, the cross section of the beam inevitably becomes larger when the allowable stress level of the beam is taken into consideration.

In the present invention, the prestress introduced into the PC beam by the pretension method corresponds to the dead load (self-weight of the beam + slab own weight), and the prestress corresponding to the live load (live load) is applied to the post after the slab concrete has hardened. By applying the tension method, the cross section of the PC beam can be made smaller than in the case of the conventional method, and its structural features are described in claim 1. That's right,
Further, a preferred embodiment thereof is described in the second claim.
As described in Section 4.

(Specific explanation of the invention with drawings) First, the basic idea of the present invention will be explained with reference to Fig. 1. The left side of Fig. 1 is a stage diagram of the force applied to the PC beam 1, and the right side is a diagram of the bending moment at each stage. When manufacturing, transporting and erecting PC beam 1,
shows the time when concrete slab 2 is placed, shows the time when prestress is introduced by the post-tension method, and shows the time when live load q is applied.

In the present invention, when manufacturing the PC beam 1 in
The pre-tension steel 3 introduces a pre-stress P ₁ which counteracts the sum of bending moments M ₁ and M ₂ due to their own weight of the PC beam 1 and the concrete slab 2, and the post-tension steel 4 Introduce a prestress P ₂ corresponding to the bending moment M ₃ due to the load q.

Of course, the cross-sectional design of the PC beam 1 is rationally designed under the condition that the stress level of each part of the member at each stage is below the predetermined allowable stress level, but P ₁
It is clear from the bending moment diagram that the cross section can also be selected to be smaller since it is smaller than in the case of the conventional method.

Next, embodiments of the present invention will be described with reference to FIGS. 2 to 4.

In Fig. 2, reference numeral 5 is a steel girder, and after the PC girder 1 to which prestress P ₁ has been introduced as described above is erected between the adjacent girders 5 and 5, Concrete slab 2 was placed on
After hardening, prestress P ₂ is introduced using the post-tension steel 4 described above.

The post tension steel material 4 is made of PC as shown in the diagram.
Preferably, they are arranged in a suspended manner within the beam 1.

It is preferable to use unbonded steel material as the post tension steel material 4, but in this case, as shown in FIG. 3A, unbonded steel material 6 may be buried in the PC beam 1 in advance, In addition, as shown in B of the same figure, the sheath 7 buried in the PC beam 1
Alternatively, the unbonded steel material 6 may be inserted at the site.

When a normal PC steel material is used as the post tension steel material 4, as shown in Fig. 3C, after tensioning the PC steel material 8 inserted into the sheath 7, as usual,
Glue is injected into the sheath 7.

Tensioning of the post-tensioning steel 4 may be done for each PC beam 1 of each span as shown in Figure 4 A, but it can be applied to PC beams of multiple spans as shown in Figure 4 B and C. It is convenient to provide continuous post-tensioning steel material 4 across the small beams 1, 1, ... to perform continuous tensioning because the joint between the PC small beams 1 and the large beams 5 can be made rigid. .

In addition, B in Fig. 4 is the post tension steel material 4.
Figure 3C shows the case where the pipe passes through the concrete slab 2 on the top of the girder 5, and Fig. 2C shows the case where the pipe passes through the girder 5, and the state shown in B is also shown in Fig. 2.

The tensioned end of the post tension steel material 4 is fixed and embedded in the part 9 in the figure, but in the case of A and B in FIG. 3 where the unbonded steel material 6 is used as the post tension steel material 4, By re-tensioning the unbonded steel material 6, the deflection of the PC beam 1 can be controlled.

(Effect of the invention) The present invention is as described above, and the prestress by the pretension method that affects the cross-sectional determination of the PC beam is the dead load that the PC beam ultimately bears. , is smaller than the conventional method, so the cross section of the PC beam can be designed smaller,
In turn, it is possible to reduce the weight of the entire building.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the basic concept of the present invention, Figure 2-
FIG. 4 is an explanatory diagram of an embodiment of the present invention. 1...PC beam, 2...concrete slab, 3...
Steel material for pre-tension, 4... Steel material for post-tension,...

Claims (1)

[Claims] 1. After erecting PC beams between the large beams using the pretension method to introduce prestress corresponding to the dead load that will ultimately be borne by the small beams, concrete slabs are poured, and A method for constructing a small beam characterized by applying a prestress corresponding to the live load that the small beam will ultimately bear after hardening to the PC small beam using a post-tensioning method. 2. The method for constructing a small beam according to claim 1, wherein the prestress is applied by the post-tension method by tensioning prestressed steel members suspended in the small PC beam. 3. The method of constructing a small beam according to claim 1 or 2, in which unbonded steel is used as the post-tensioned prestressing steel. 4. Claims 1 to 3 in which prestress is applied to a plurality of spans of PC beams by a post-tensioning method by continuous tensioning of PC steel materials that are continuously arranged over a plurality of spans of PC beams. A method of constructing a small beam as described in any one of the paragraphs.