JPS5921875A - Construction of prestressed concrete tank - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] This invention relates to a method for constructing a circular prestressed concrete tank, and particularly a method for constructing a prestressed concrete tank constructed above ground or semi-underground with foundation piles, bottom slabs, side walls, etc. It is related to.

Conventionally, this type of prestressed concrete tank constructed above ground or semi-underground employs rigid connections at the joints between the foundation pile 1 and the bottom slab 2, and between the bottom slab 2 and the side walls 3, as shown in Figure 1. Met.

Therefore, it included the following problems.

That is, the first problem is that during the concrete construction of the side wall 3, volume changes due to temperature changes due to the generation of heat of hydration of the concrete and drying shrinkage of the concrete have already been formed by pouring the concrete. Bottom plate 2
In addition, by being rigidly connected to the bottom slab 2 and being restrained by the one-piece foundation pile 1, cracks 4 occur in the vertical direction of the side wall 3, as shown in FIG.

These cracks 4 occur on both the inner and outer surfaces of the side wall 3, often penetrating the inner and outer surfaces, and cause a decrease in the durability of the concrete.
This caused corrosion of concrete steel and shortened the life of the tank itself.

In order to prevent this crack 4, many reinforcing bars must be placed near the lower end of the side wall 3, and it is extremely difficult to completely repair the crack 4 that has occurred. The amount of money spent on this type of tank is enormous, and if cracks are left untreated, they will gradually expand due to vibrations such as earthquakes.
Eliminating or making it less likely to occur was an extremely important technical challenge.

The second problem is that in this type of press 1 to rest concrete tank, a sheath such as a steel pipe is buried in the side wall 3 in advance in the circumferential direction when forming the side wall 3, and the concrete of the side wall 3-3 hardens to some extent. A steel material or the like is inserted into this sheath at an appropriate time, and this steel material is tensed to introduce prestress force in the circumferential direction to the side wall 3. In this case, in the conventional construction method, the above-mentioned As shown in FIG. 2(a), the bottom plate 2 and the side wall 3 and the bottom plate 2 and the foundation pile 1 are rigidly connected, and the bottom plate 2 cannot be displaced or rotated. An extremely large vertical bending moment is generated near the joint between the side wall 3 and the bottom plate 2.

Therefore, in order to resist this huge bending moment, the side wall 3 requires a large thickness of concrete members, steel materials for prestressed concrete, etc., which also poses an economical problem.

This invention was made in view of the problems of conventional construction methods as described above, and its purpose is to economically construct prestressed concrete tanks that are less likely to cause cracks on the side walls of the constructed tank. It is a place that provides a method of construction.

4 - In order to achieve the above object, the present invention provides a construction method for a prestressed concrete tank, in which a bottom plate divided into an outer peripheral edge and an inner peripheral part is separately formed on a foundation table, and then this outer peripheral edge is After forming a side wall and introducing a prestress force to the side wall, the outer circumferential edge and the inner circumferential portion of the bottom plate are integrated by concrete pouring or the like.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

In the figure, the same or corresponding parts will be described using the same reference numerals as in the conventional construction method.

FIG. 3 shows an embodiment of a circular tank constructed by the prestressed concrete tank construction method according to the present invention.

In the prestressed comfort tank shown in the figure, a bottom plate 2 divided into an outer peripheral edge 2a and an inner peripheral part 2b is separately formed on a foundation pile 1, and then a sheath is buried in advance on the outer peripheral edge 2a. After forming the side wall 3 and introducing a prestress force to the side wall 3, concrete or the like is poured into the gap 2C between the outer circumferential edge 2a and the inner circumferential edge 2b.

The foundation piles 1 are cast-in-place concrete piles such as reinforced concrete 1, and are buried in the ground at appropriate locations, taking into consideration the surrounding soil environment, the size of the tank to be constructed, etc. be.

Moreover, the bottom plate 2 consisting of the outer peripheral edge part 2a and the inner peripheral part 2b is
It is made of concrete, etc. with reinforcing bars placed in appropriate places,
It is desirable that the width of the outer peripheral edge portion 2a be as narrow as possible.

In order to introduce a prestress force into the side wall 3, a steel sheath is buried in the circumferential direction within the side wall 3 in advance, and after the side wall 3 is formed by pouring concrete, etc., at an appropriate time. This is done by inserting a tension material such as a steel rod into the sheath and tensioning this tension material.

It is desirable that the gap 2C between the outer circumferential edge 28 and the inner circumferential portion 2b has the minimum necessary width to allow reinforcing bar joint construction for post-cast concrete.

Next, to explain the construction order, first, as shown in Fig. 4(a), the foundation pile 1 as described above is driven into the ground to a predetermined depth, and then the bottom slab 2 is placed on the foundation pile 1 at the outer peripheral edge. 2a and an inner peripheral portion 2b, and formed as shown in FIG. 4(1)).

After that, a side wall 3 in which a sheath is embedded in advance is formed on the outer peripheral edge 2a, as shown in FIG. 4(C).

Next, after introducing a prestress force to the side wall 3 at an appropriate time, as shown in FIG. 4(d), the gap 2C between the outer circumferential edge 2a and the inner circumferential edge 2b is integrated by pouring concrete. This completes the construction. - Do not place concrete in the gap 2C until at least the tensioning of the prestress in the circumferential direction of the side wall 3 is completed, and delay it as much as possible without affecting other construction work. It is desirable to perform the construction at the time when the deformation of the side wall 3 due to the introduction of the prestress force has been completely completed.

By dividing the bottom plate 2 into the outer circumferential edge part 2a and the inner circumferential edge part 2b in this way, the formation of the side wall 3]
The only members that restrain deformation due to volume changes such as drying shrinkage and bending moments due to the introduction of Presto 1 Noska are the outer peripheral edge 2a of the bottom slab 2 and the foundation pile 1 directly below it, and the foundation pile 1 is the same as in the past.

Compared to the case where both the bottom plate 2 and the side walls 3 are rigidly connected, the degree of restraint is significantly reduced, and the occurrence of cracks and vertical bending moments are significantly reduced.

This also significantly reduces the thickness of the concrete members of the side walls 3 required to resist the circumferential reinforcing bars of the side walls 3 necessary to prevent cracks and the vertical bending moment, and the steel materials for prestressed concrete in the vertical direction. It is also economically advantageous.

FIG. 5 compares the horizontal construction method according to the present invention with the conventional construction method, and the displacement of the side wall 3 when the same prestress force is introduced into the side wall 3 is shown by a broken line. As shown on the left side of the figure, this is extremely effective.

7- Fig. 6 shows another invention of the present invention, which is an IC, and to explain only its features, a sliding member such as Teflon is attached to the upper end of the foundation pile 1 that supports only the outer peripheral edge 2a of the bottom plate 2 mentioned above. 5 is attached and used as the above-mentioned foundation pile 1, and it is adopted when the soil environment is good, the seismic force is small, and there is no need to burden the horizontal force on the pile directly under the side wall 3. The outer peripheral edge 2a of the bottom slab 2 and the foundation pile 1 become movable, and the degree of restraint can be further reduced.

In this case, the bending moment 1 does not occur at all in the side wall 3, as shown in FIG. 2(b).

In other words, it is the outer peripheral edge 2 of the bottom plate 2 that restrains the deformation of the side wall 3.
This is because the gap portion 2C is formed in the bottom plate 2.

As described above, the method for constructing a prestressed concrete tank according to the present invention is to separately form a bottom plate divided into an outer circumferential edge and an inner circumferential edge on a foundation table, and then bury a sheath in advance on the outer circumferential edge. Side 8 - After forming a wall and introducing a prestressing force to the side wall by inserting and tensioning a tendon into the sheath, concrete is poured between the inner periphery and the outer periphery of the bottom slab. In contrast to conventional tanks of this type, where the joints of the M foundation pile, bottom slab, and side walls were all rigidly connected, the binding force was extremely large. By adopting this configuration, it is possible to significantly reduce the restraining force, effectively preventing cracks that occur on the side wall of the tank, and also alleviate the bending moment when prestress force is introduced to the side wall. This is an extremely useful construction method that enables economical design of steel materials for wall thickness prestressed concrete.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional perspective view showing a prestressed concrete tank constructed using the conventional construction method, and Figure 2 shows the moment of inertia when prestress force is introduced to the side wall. ) is the conventional construction method, the same figure (i
1) shows each case of the construction method of the present invention. Figure 3 is a cross-sectional view of the P1 Nostressed Concrete tank constructed using the construction method of the present invention;
The figure is a sectional view showing the construction order, and the construction is (a) to (d).
) and are done sequentially. Figure 5 is a cross-sectional view showing the displacement of the side wall when a press force is introduced to the side wall. Figure (a) shows the displacement of the construction method of the present invention, and Figure (b) shows the displacement of the conventional construction method. ing. 6th
The figure is a sectional view showing another embodiment of the present invention. 1...Foundation pile 2...Bottom plate 2a...Outer peripheral edge 2b... ...Inner peripheral part 2C...Gap part 3...Side wall 4...Crack 5... ...... Sliding member 11 - Fig. 1 Fig. 2 (CI) (b) Fig. 4 a Fig. 5 1146 Fig.

Claims (2)

[Claims] (1) In a construction method for a circular tank built above ground or semi-underground, in which a bottom slab is formed on a foundation pile buried underground, and side walls are formed on the bottom slab, the outer peripheral edge and After separately forming a bottom plate divided into an inner circumferential portion, a side wall with a sheath embedded in advance is formed on the outer circumferential edge, and a tension material is inserted into the sheath and tensioned to prestress the side wall. A construction method for a prestressed concrete tank, characterized in that after applying force, the outer peripheral edge and the inner peripheral part of the bottom slab are integrated by concrete pouring or the like. (2) A patent claim characterized in that a sliding member is attached to the upper end surface of the foundation pile to make the outer peripheral edge of the bottom plate formed on the foundation table movable, and then the side wall is formed. A construction method for a prestressed concrete tank as described in item 1.