JPH0784810B2 - How to build a prestressed structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for constructing a prestressed structure.

<< Prior Art >> As a type of tank structure, a prestress structure has been known in which a tension member is embedded in the bottom slab and side walls in advance and a tension is introduced into the tension member.

In order to construct a tank having such a structure, generally, a sheath tube is buried when constructing a bottom slab and a side wall, and after the bottom slab and the side wall are constructed, a tension material is inserted into the sheath tube to obtain a tension material. Was applied to pull the end portion of the plate, thereby applying a compressive force to the bottom plate and the side wall.

However, in such a construction method, even if tension is introduced into the tendons after the bottom slab and the side wall are constructed, the side wall is integrated on the bottom slab and is constrained, so that the action of the internal pressure is large and the most. There has been a problem that a sufficient compression force cannot be introduced in the vicinity of the joint between the bottom plate and the side wall where a large compression force is required.

Therefore, the present applicants have proposed the construction method disclosed in Japanese Patent Laid-Open No. 59-21875 in order to solve such a problem.

In the construction method disclosed in the publication, the bottom slab is divided into an outer peripheral portion and an inner peripheral portion, an annular opening is formed between them, and a side wall is constructed on the outer peripheral portion, and then tension is applied. This is a method of introducing tension into the timber and then constructing the annular opening. According to this construction method, when the tension is introduced into the tension material, the inner peripheral portion and the outer peripheral edge portion of the bottom slab are separated. Since the opening portion that forms the opening is formed, the restraining force of the side wall is reduced, and thus a large compressive force can be introduced in the vicinity of the joint between the bottom plate and the side wall. This construction method will be described below. There were technical challenges.

<< Problems to be Solved by the Invention >> That is, in the construction method of the above publication, since the bottom plate is provided with an opening, the connecting surface of the bottom plate is at a plurality of locations, and a formworker in a state where the reinforcing bar penetrates The construction will be complicated by the need for waterproofing work such as the installation of waterproofing boards.

Further, since the joint portion of the rebar of the bottom slab is provided in the annular opening, the joint portion is located on the same circumference, which is a weak point of the structure.

Further, in the case where the entire construction period is long, as in a double shell tank for low temperature liquefied gas, the opening is formed after the side wall is completely formed and the tension is introduced into the tendon. Therefore, there is also a problem that the exposure period of the reinforcing bar becomes long and rust prevention measures are required during that period.

The present invention has been made in view of such conventional problems, and an object of the present invention is to intensively and in the vicinity of a joint between a bottom plate and a side wall, which is the most severe condition in terms of stress. An object of the present invention is to provide a method for constructing a prestressed structure that can economically introduce only the compressive force.

<Means for Solving the Problems> In order to achieve the above object, the present invention includes a bottom slab and a side wall integrally formed on the bottom slab, and the tension embedded in the circumferential direction of the bottom slab and the side wall. In the method of constructing a prestressed structure in which a compressive force is introduced to the bottom slab and side walls by introducing tension to the material, only the outer peripheral portion of the bottom slab and a step of constructing a part of the side wall on the outer peripheral portion Then, a part of the tension is introduced into the tension member, then the inner periphery of the bottom plate and the remaining portion of the side wall are constructed, and then the remaining tension is introduced into the tension member.

<< Advantageous Effects of the Invention >> According to the method for constructing the prestressed structure having the above-described configuration, since the joint surface of the bottom slab is only one place where the outer peripheral portion and the inner peripheral portion are in contact with each other, the construction is more effective than the conventional constructing method. Will be easier.

Further, since the joint portion of the rebar of the bottom slab can be set at any position, the joint portion can be eliminated as a weak point of the structure.

Further, since the inner peripheral portion of the bottom slab forms a part of the side wall and can be constructed in parallel with the remaining part of the side wall after introducing a part of the tension to the tension material, no rust preventive measure for the reinforcing bar is required.

<Example> Hereinafter, a preferred example of the present invention will be described in detail with reference to the accompanying drawings.

1 to 4 show an embodiment of a method for constructing a prestressed structure according to the present invention.

The method for constructing a prestressed structure shown in the figure illustrates the case where the present invention is applied to a cylindrical tank, and the tank is formed integrally with the disc-shaped bottom plate 10 and the outer peripheral edge of the bottom plate 10. It is composed of a cylindrical side wall 12.

In the construction of the tank, as shown in Fig. 1 (A), the bottom plate 10
First, only the ring-shaped outer peripheral portion 10a is constructed, and the lower portion 12a of the side wall 12 is integrally formed on the upper surface thereof.

In this state, on the inner surface of the outer peripheral portion 10a, a reinforcing bar 13 for connection with the inner peripheral portion formed thereafter is provided in a protruding manner.

FIG. 2 shows the outer peripheral portion 10a and the lower portion 12a in this state.
The cross section of FIG. 2 is shown enlarged, and a plurality of sheath tubes 16 into which the tensioning material 14 is inserted are embedded along the outer peripheral edge of the outer peripheral portion 10a in a two-row multistage manner in the circumferential direction.

Further, in the lower portion 12a of the side wall 12, a plurality of circumferential sheath tubes 18 are arranged in a step-like manner at intervals in the height direction, and axial sheath tubes 20 are provided at intervals in the circumferential direction. Multiple lines are arranged.

Further, the outer peripheral portion 10a of the bottom slab 10 and the lower portion 12a of the side wall 12 are provided with fixing portions 10b and 12b of the tension members 14 which project outward at positions divided into four parts on the circumference.

The arrangement of the sheath tube 16 and the circumferential sheath tube 18 is the third
As shown by the phantom lines in the figure, the ends are arranged between the fixing portions 10b and 12b facing each other so as to rotate 180 degrees around the circumference, and the position of the fixing portion in the vertical direction is the circumferential direction. It is arranged so that it may shift in sequence.

When the outer peripheral portion 10a of the bottom plate 10 and the lower portion 12a of the side wall 12 are formed, the tension members 14 are inserted into the sheath tube 16 and the circumferential sheath tube 18, respectively, and both ends of the tension member 14 are pulled to fix the fixing portion. Tension is introduced by fixing to 10b and 12b.

At this time, the tension introduced into the tension member 14 is smaller than the finally introduced tension.

The more specific magnitude of this tension is that the tension applied to the tension member 14 causes the compression force introduced to the side wall 10 to be a circle applied to the side wall 10 when the contents are stored in the tank. It is of a magnitude that a compressive force corresponding to a margin b obtained by subtracting the tensile force a in the circumferential direction is introduced.

As a method of introducing such tension, for example, the second
This can be achieved by applying tension to only the black tendons 14 as shown, or by applying a small tension to all the tendons 14.

Further, as a more specific size of the height h of the lower portion 12a of the side wall 12 at this stage, for example, is a position where the bending moment in the vertical direction applied to the side wall 10 is maximized. Since the shearing force becomes zero, the side wall 12 is in an ideal condition as a joint surface.

The position at which the bending moment of the side wall 10 is maximized is about 3 to 5 m, although it varies depending on the shape of the structure.

As described above, when part of the tension is introduced into the tension members 14 embedded in the outer peripheral portion 10a and the lower portion 12a, the bottom plate 10
The inner peripheral portion 10c and the upper portion 12c of the side wall 10 are constructed in parallel by joining the outer peripheral portion 10a and the lower portion 12a, respectively.

Then, when the inner peripheral portion 10c and the upper portion 12c are formed, the remaining tension is introduced into the tension member 14, and the tension member 14 is also inserted into the axial sheath tube 20 so that the tension is similarly introduced. It

Although not shown in detail, the upper portion 12c of the side wall 12
A sheath tube is also embedded in the inside in the circumferential direction, and a tension material is inserted into each sheath tube.

FIG. 4 shows the stress state of the side wall 12 in the state where the contents are accommodated in the tank thus constructed, and the stress state of the tank formed by the conventional construction method.

In the figure, the solid line is the stress state in the present embodiment, the dotted line is the construction method shown in the above-mentioned publication,
The two-dot chain line shows the stress state when tension is introduced after the bottom plate 10 and the side wall 12 are completely formed.

As is clear from the state shown in the figure, in the case indicated by the chain double-dashed line, almost no compressive force is introduced in the vicinity of the joint between the bottom plate 10 and the side wall 12.

On the other hand, in the case shown by the dotted line, a fairly effective compressive force is introduced in the vicinity of the joint portion, but there is a problem in construction as described above.

On the other hand, in the method of the present embodiment shown by the solid line, the bottom plate
After building only the outer periphery 10a of 10 the lower part 12a of the sidewall 12
With the compressive force corresponding to the tension introduced at the stage of building on the outer peripheral portion 10a remained, the stress state of the two-dot chain line becomes almost the same as the superposed state, and the bottom plate
Since a large compressive force is introduced in the vicinity of the joint between the side wall 12 and the side wall 12, it is possible to effectively reinforce the portion of the tank where the internal pressure is most applied, and prevent the occurrence of cracks.

Moreover, since the bottom plate 10 has only one joint surface where the outer peripheral portion 10a and the inner peripheral portion 10c are in contact with each other, the construction is easier than the conventional construction method.

Furthermore, since the tension of the tension member 14 introduced at the stage where a part of the side wall 12 is formed on the outer peripheral portion 10a of the bottom plate 10 is smaller than the tension at the final stage, the outer peripheral portion 10a and the inner peripheral portion 1 of the bottom plate 10 are
No special consideration is required for the rebar 13 connecting with 0c.

Furthermore, the inner peripheral portion 10c of the bottom slab 10 forms a part of the side wall 12, and after introducing a part of the tension to the tensioning member 14, it can be constructed in parallel with the remaining part of the side wall 12, so that the reinforcement 13 is prevented. No need for rust measures.

In the stress state shown in FIG. 4, the line indicated by the alternate long and short dash line represents the axial tension force due to the internal pressure.
The difference from the two-dot chain line is the compression force margin b.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an embodiment of a method for constructing a prestressed structure according to the present invention in the order of steps, FIG. 2 is an enlarged view of a main part of FIG. 1 (A), and FIG. 3 is FIG. A plan view of (A),
FIG. 4 is an explanatory view of a stress state on the side wall of the tank constructed by the same method. 10 …… Bottom plate 10a …… Outer peripheral part 10c …… Inner peripheral part 12 …… Side wall 12a …… Lower part 12c …… Upper part 14 …… Tension material

Claims (1)

[Claims] 1. A bottom slab and a side wall integrally formed on the bottom slab, and by applying a tension to a tension member embedded in the circumferential direction of the bottom slab and the side wall, a compressive force is applied to the bottom slab and the side wall. In the method of constructing a prestressed structure for introducing, only the outer peripheral portion of the bottom slab, and a step of constructing a part of the side wall on the outer peripheral portion, introducing a part of the tension into the tension member, and then A method for constructing a prestressed structure, comprising constructing an inner peripheral portion of the bottom slab and a remaining portion of the side wall, and thereafter introducing the remaining tension to the tension member.