JPH04111809A - Post-tension concrete-based bottom slab - Google Patents

Abstract

PURPOSE:To greatly suppress the escape of prestress introduced to the ground by a method in which a lubricant material is provided between the ground and the base bottom slab. CONSTITUTION:In the portion beneath the column and walls of a building in the base bottom slab 5, a projected base 14 of an inverted trapezoidal box or beam form is formed integrally with the slab 5. A sand layer 11 as a lubricant material, asphalt or glass wool as an elastic filler not reducing frictional forces on the sloped face of the base 14, and a polyethylene sheet 13 having a friction-reducing effect and waterproofing effect are provided between the base 10 and the ground 6.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention provides a post-tension system that reduces the frictional force generated between the foundation and the ground of a structure in which a press I/less is introduced using a post-tension method. Regarding concrete foundation bottom plates.

[Conventional technology]

Among the direct foundations of structures conventionally used, the third
As shown in the figure, when a member has a large cross section, it is necessary to make the so-called root cut depth, which is the excavation of the soil below the ground surface, deep according to the size Hl of the cross section. In addition, in the figure, a solid foundation is constructed of an upper floor plate 1, a bottom plate 2, and a beam 4 that supports a column 3, and formwork is also required to construct the beam 4 and upper floor plate 1. In order to eliminate these drawbacks, a mat foundation (foundation bottom plate) 5 as shown in FIG. 4 has been devised and actually constructed. This mat foundation is the bottom plate 5
The foundation height H2 is significantly smaller than the foundation height Hl of the conventional example shown in FIG. Due to the shallower depth, the amount of root cutting is reduced and the amount of formwork work is significantly reduced, resulting in significant effects in terms of construction costs and construction time. In the figure, 6 indicates the supporting ground, and 7 indicates reinforcing steel bars.

However, on the other hand, compared to the conventional solid foundation (Fig. 3), there is no beam 4 or upper floor plate 1, and the foundation height H2 is small, so it is very disadvantageous in terms of stress as a foundation that supports the weight of the building. In particular, in the part directly under the pillar 3 where the load is concentrated, the design is unreasonable, and the overall thickness H2 has to be increased, which often ends up diminishing the above effect.

Therefore, in order to alleviate the above drawbacks, the
As proposed in No. 9, in the bottom plate 5, the PC steel material 8 (Fig. 4) is placed on the underside of the pine slab (bottom plate 5) at the position where the concentrated load of the columns and walls is applied, and the PC steel material 8 (Fig. In this case, the PC steel material 8 is arranged in a parabolic shape so that the PCi material 8 is located above the pine slab 5, and the base bottom plate is prestressed by a post-tension method.

[Problem to be solved by the invention]

However, generally when prestress is introduced into a reinforced concrete structure, the structure will shrink along the direction of introduction of the prestress. In above-ground structures, there are few things that prevent the structure from shrinking, but when prestress is introduced into the foundation, the introduced prestress is reduced by the action of the frictional force generated between the foundation bottom plate and the ground. escapes toward the ground, significantly reducing the effect of introducing prestress, such as dispersing the load concentrated on the bottom plate and making the ground pressure even. That is, in addition to the weight of the original building, extra force (frictional lateral force) is applied to the ground supporting the foundation, which can damage the ground.

This invention was made in view of these conventional problems, and it reduces the frictional force between the ground and the foundation by changing the point that the conventional foundation was in direct contact with the ground. The purpose is to solve the above problems by interposing materials or the like.

[Means to solve the problem]

In order to achieve the above-mentioned object, this invention applies PC to the concrete foundation bottom plate of a structure using a post-tension method.
In a structure in which steel is buried and tensioned to introduce prestress, the post-tensioned concrete foundation bottom plate has an anti-friction material interposed between the concrete foundation bottom plate and the ground to reduce the frictional force between the two. Similarly, in a structure that introduces prestress, a box-shaped or beam-shaped protruding foundation with a cross section that has an inverse diameter is formed integrally with the concrete foundation bottom plate directly below the column or wall of the structure. At the same time, the PC steel material is stretched in a catenary shape within the above-mentioned protruding foundation, and an anti-friction material is interposed between the concrete foundation bottom plate having the protruding foundation and the ground to reduce the frictional force between the two, and post-tensioning is performed. It has a concrete foundation bottom plate.

[Effect]

This invention has the above-mentioned structure, and excavates only the area directly under the column or wall, which is the weak point of the conventional post-tensioned concrete foundation base plate, into a box-like or beam-like shape with an inverted trapezoidal cross section in the area necessary for stress. , concrete is poured without using normal formwork and integrated with the foundation bottom plate, and the prestressed steel material is stretched in a catenary shape at the box-shaped or beam-shaped protrusion. Concentrated loads on the foundation bottom plate directly under columns and walls are dispersed, which makes it possible to equalize the ground pressure. Furthermore, since an anti-friction material is interposed between the ground and the foundation bottom plate, it is possible to significantly reduce the escape of the introduced prestress towards the ground, thereby dispersing the concentrated load and other effects mentioned above. It is fully demonstrated.

In addition, the box-shaped and beam-shaped protrusions have an inverted trapezoidal cross section and form a slope through anti-friction material in the direction of prestressing, so the above effect is guaranteed and the ground No damage will occur.

〔Example〕

The present invention will be explained below with reference to the drawings. FIG. 1 is an explanatory diagram of an embodiment according to the present invention. Note that the same members as in the conventional example are given the same reference numerals, and redundant explanation will be omitted.

In the figure, a box-shaped or beam-shaped protruding foundation 14 with an inverted trapezoid cross section is located directly below the foundation bottom plate 5, which has the same thickness (H2) as the conventional one, and which receives the pillars 3 and walls of the building. It is integrally formed.

This protruding foundation 14 is usually formed in a box shape at a place where it receives the pillar 3, and when it receives a wall portion or depending on the size of the pillar span, it is formed into a beam shape that is an extension of the box-shaped foundation in one direction. Further, as shown in FIG. 2, a plurality of pillars 3 are normally erected at certain intervals in the lateral direction and in the direction orthogonal to this.

18a and 18b are prestressing steel materials, both of which are stretched in a catenary shape within the protruding foundation 14. (Sometimes it's just the direction.) In addition, when placing the concrete, a sheath (not shown) is placed in the concrete to create a hole for placing the prestressing steel material, and the placed concrete reaches the required strength. Afterwards, the prestressed steel material passed through the sheath is tensed using jacks, and the ends of the prestressed steel material are fixed to the concrete to introduce prestress into the concrete foundation. Next, grout is injected into the gap within the sheath to complete the installation.

In this way, the present invention makes use of the advantages of the conventional foundation bottom plate, and excavates only the necessary area in the box shape to avoid the stress, and eliminates the disadvantage of the conventional foundation bottom plate, without using ordinary formwork. This method compensates for the drawbacks of the conventional method by constructing a foundation bottom plate with a protruding foundation. However, as shown in Figure 2, the basic 1
When 0 and the ground 6 are in direct contact, tension force (prestress) is applied to the tension material 18 (PC steel material) as described above.
When P is introduced, the tension force that is originally desired to be applied only to the foundation 10 is consumed as a frictional force generated between the foundation 10 and the ground 6, and the tension force escapes toward the ground 6.

Therefore, in the embodiment, 20 to 50 mm of anti-friction material is added between the foundation 10 and the ground 6 in order to reduce the frictional force.
sand layer 11 (or something with a similar effect) with a thickness of A polyethylene sheet 13 having a waterproof effect is interposed therebetween. Note 16
is a thin concrete layer to smooth the surface of the ground 6 (
waste concrete).

〔Effect of the invention〕

As explained above, according to the present invention, material costs can be reduced because concrete is poured without using ordinary formwork, and because the prestressing steel is stretched in a catenary shape within the protruding foundation, the foundation bottom plate The concentrated load directly under such columns and walls is dispersed, so that the ground pressure can be equalized, and the prestress introduced by the anti-friction material between the ground and the foundation bottom plate is prevented from escaping towards the ground. The dispersion and other effects are fully demonstrated, so no damage to the ground occurs, and the foundation bottom can be made shallower, so the amount of root cutting can be reduced, etc., resulting in a significant reduction in formwork work and a reduction in construction costs. Many benefits can be obtained, such as shortening the construction period.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a main part of an embodiment according to the present invention, Fig. 2 is an auxiliary explanatory diagram of the embodiment, Fig. 3 is a sectional view of a conventional method that does not rely on the post-tension method, and Fig. 4 is a post-tension method. FIG. 2 is a cross-sectional view of a conventional example.

Claims (2)

[Claims] (1) In a structure in which prestress is introduced by embedding prestressing steel materials in the concrete foundation bottom plate of a structure using a post-tension method, the friction force between the concrete foundation bottom plate and the ground is reduced. A post-tensioned concrete foundation base plate characterized by intervening abrasive material. (2) In a structure in which prestress is introduced by embedding prestressing steel materials in the concrete foundation bottom plate of a structure using a post-tension method, the cross section is inverted trapezoidal under the concrete foundation bottom plate directly below the column or wall of the structure. A box-shaped or beam-shaped protruding foundation is formed integrally with the concrete foundation bottom plate, and a PC steel material is stretched in a catenary shape within the protruding foundation, and further between the concrete foundation bottom plate having the protruding foundation and the ground. A post-tensioned concrete foundation base plate characterized by interposing an anti-friction material to reduce the frictional force between the two.