JPS62311B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a construction method for a prestressed concrete tank.

A prestressed concrete tank is constructed so that compression in the circumferential direction is introduced into the side wall in advance as prestress to cancel out the tensile force in the circumferential direction that acts on the side wall at high tide.

However, this prestress in the circumferential direction of the horizontal plane causes secondary stress at the corner of the tank where the tank side wall and the bottom plate intersect, due to the difference in the structural state of the corner.

This is because prestress introduced in the circumferential direction causes prestress to be uniformly introduced only in the circumferential direction in the general part of the tank side wall located above the corner. Due to the influence of the rigidity of the bottom plate, a portion of the total prestress load is transmitted to the bottom plate, and only a portion of the prestress load is effectively applied to the side wall. As a result, the general There is a difference in horizontal prestress between the tank corner and the tank corner. This difference generates an internal force, resulting in a secondary bending moment in the vertical direction.

In other words, if we focus on the corner of the tank, in the circumferential direction of the tank side wall, a part of the horizontal prestress is lost as mentioned above, and the effective prestress is less than in the general area, which is disadvantageous, and the internal force in the vertical direction A secondary bending moment occurs, and reinforcement is required to counter this.

For this reason, various improvements have been made to the connection portion between the lower end of the tank side wall and the bottom plate, as described below, but each has its own drawbacks.

As shown in FIG. 10, a sliding type structure in which the tank side wall a and the bottom plate b are completely separated has been proposed.

This is a structure in which a ring-shaped side wall is loaded on the top surface of a flat bottom plate in a structurally insulated state, and an intermediate slip material is interposed at the contact surface between the two.

In this case, when prestress is introduced to the tank side wall a, the tank corner can be freely deformed because it is insulated from the bottom plate b, reducing the prestress at the tank side wall corner and vertical direction. Phenomena such as generation of bending moment no longer occur.

However, this structure is not suitable for practical use because it has problems with horizontal stability against earthquakes, etc., and with watertightness as a container structure.

Furthermore, a structure in which the tank side wall and the bottom plate are connected by a hinge has been proposed.

This structure is characterized by the fact that the tank corner is a hinge, so there is no restriction on the bottom plate against rotation.

However, with this structure, in the circumferential direction of the tank corner, the effective amount of prestress is reduced due to the rigidity of the bottom plate, as in the case described above, and as a result, a secondary bending moment is generated in the vertical direction. Since the corner of the tank has a hinge structure, the bending moment only becomes zero at the hinge position, but the bending moment transfers from the corner of the tank to the side wall of the general section above.
The maximum bending moment will occur at the mid-height of the side wall.

As a reinforcement measure, we have introduced vertical prestress to match this.

The deficiencies of this construction type include the uncertainty of the functional reliability of the hinge structure in terms of watertightness, durability, and seismic resistance.

In addition, the tank side wall is usually cylindrical, and the hinge structure is a closed continuous circular structure that supports the side wall, so such a closed structure can reliably exhibit rotational function with zero bending moment. is extremely difficult.

Further, in order to ensure the watertightness of the hinge portion, special considerations are required, which also poses a problem in terms of economic efficiency.

Furthermore, as shown in FIG. 11, a fixing method has been proposed in which the tank side wall a and the bottom plate b are rigidly connected together.

In this method, the tank corners are rigidly connected, and because of the two phenomena described at the beginning, the horizontal prestress in the circumferential direction at the corner of the side wall is less than that in the general area, so additional prestress is added. In addition, since vertical bending moments occur at the corners, the vertical direction must be reinforced with prestress.

The present invention was proposed in view of the above circumstances, and involves constructing a tank side wall on the upper part of the horizontal sliding member 4 disposed on the foundation, and introducing prestress in the circumferential direction to the side wall. A method for constructing a prestressed concrete tank, characterized in that a bottom slab on the inside of the side wall and on the outside of the side wall is constructed on the foundation, and then prestress is introduced in the circumferential direction to the bottom slab on the outside of the side wall. The purpose is to provide an improved construction method for a prestressed concrete tank that can introduce prestress into the lower part of the tank side wall to the same level as the upper part and has good watertightness.

In the present invention, as described above, by constructing a cylindrical tank side wall on a sliding member disposed on a foundation, the tank side wall is slidably disposed on the foundation, and the tank side wall Since the prestress is introduced while the lower end portion is slidable, the required prestress in the circumferential direction can be economically introduced to the upper and lower portions of the side wall. Therefore, the prestress in the circumferential direction is uniform over the entire cylindrical portion of the tank, and since it is not affected by constraints such as the corners of the tank, no vertical bending moment occurs.

Furthermore, in the present invention, after constructing the tank side wall, the inner and outer bottom slabs of the tank side wall are constructed on the foundation, and prestress is introduced in the circumferential direction to the post-cast outer bottom slab. Thus, the side wall and the bottom plate are integrally connected.

According to the present invention, as described above, prestress in the circumferential direction is uniformly introduced into the general portion of the tank side wall and the corner portions, and the prestress does not generate a bending moment in the vertical direction.
Vertical reinforcement is no longer required, and the side walls and bottom plate are rigidly connected, improving the earthquake resistance of tank corners.
Durability and water resistance are significantly improved.

The present invention will be described below with reference to the illustrated embodiments.

A tank side wall 2 is constructed on the tank foundation 1. In this case, an insulating layer 3 filled with foamed polystyrene or the like is interposed between the two, and a sliding member 4 with low friction, for example, made of fluororesin (trade name: Teflon) is interposed between the two, and the side wall 2 is placed on the foundation 1. Constructed to allow sliding. (See Figure 1) When constructing the side wall 2 on the foundation pile 5,
The sliding member 4 is arranged on the foundation pile 5. (6th
(See figure) When the poured concrete for the side wall 2 reaches the specified concrete strength, the concrete placed inside the side wall 2
By tensioning the PC steel material 6, prestress is introduced into the same side wall 2 in the circumferential direction.

As a result, by the sliding movement of the sliding member 4 at the bottom of the lower end of the side wall 2, the side wall 2 is not subjected to horizontal restraint, and prestress is effectively introduced to the lower end of the side wall 2 as well. (See Figure 2) If there is no sliding member 4 and the side wall 2 is integrated with the foundation 1 at its lower end, the side wall 2 will be restrained by the foundation 1 when prestressing is introduced, and a part of the required prestress will be applied. As a result, the effective portion of the prestress is reduced, and additional prestress must be introduced to compensate for this.

After introducing prestress into the side wall 2 as described above, the bottom plate 7 inside the tank is constructed. (See Figure 3) At this time, after introducing prestress to the side wall 2, concrete may be poured into the inner circular open part to construct the bottom slab 7, as shown in Figure 9. As shown in , at the same time as the construction of the side wall 2, a bottom plate 7 having a diameter smaller than the radius of the circular open part inside the tank is constructed in advance, and after introducing prestress to the side wall 2, the gap between the bottom plate 7 and the side wall 2 is increased. Concrete may be poured at 8.

Next, at the same time as constructing the inner bottom plate 7, the outer bottom plate 9 is constructed, and the PC steel material 10 disposed inside the bottom plate 9 is tensed, and the bottom plate 9 is also pre-plated in its circumferential direction. By introducing stress, the inner bottom plate 7, the side wall 2,
and the outer bottom plate 9 are integrated to complete the entire tank. (See Figure 4) The bottom plate 7, side wall 2 and bottom plate 9 are connected to the side wall 2.
It is connected with reinforcing bars 11 that were previously placed inside,
(See Figures 5 and 6) When the bottom plate 7 is constructed at the same time as the side wall 2, a joint 12 is provided between the side wall 2 and the bottom plate 7, or a sheath material 13 is provided within the side wall 2. A reinforcing bar 11 is loosely passed through the inside. (7th
(See figure) After introducing prestress to side wall 2, joint 1
Concrete is cast or grouted on 2, and grout is injected into the gap between the sheathing material 13 and the reinforcing bars 11 to integrally connect the side wall 2 with the bottom plates 7 and 9.

Although the present invention has been described above with reference to embodiments, the present invention is, of course, not limited to such embodiments, and can be modified in various ways without departing from the spirit of the present invention. .

[Brief explanation of the drawing]

FIGS. 1 to 4 are longitudinal cross-sectional views showing the steps of an embodiment of the prestressed concrete tank construction method according to the present invention, and FIGS. 5 and 6 are longitudinal cross-sectional views showing the joint reinforcing bars between the side walls and the bottom slab. 7 is a longitudinal sectional view showing the implementation status of another embodiment of the method of the present invention, FIGS. 8 and 9 are longitudinal sectional views showing the construction status of the inner bottom plate, and FIGS. FIG. 11 is a partial vertical sectional view of a conventional tank. 1...Foundation, 2...Side wall, 4...Sliding member, 6...PC
Steel material, 7...Inner bottom plate, 9...Outer bottom plate, 10...
PC steel material.

Claims (1)

[Claims] 1 After constructing a tank side wall on the upper part of the horizontal sliding member 4 arranged on the foundation and introducing prestress in the circumferential direction to the same side wall, the bottom plate on the inside of the side wall and the outside of the side wall is placed on the foundation. 1. A method for constructing a prestressed concrete tank, the method comprising: constructing a prestressed concrete tank, and then introducing prestress in the circumferential direction to the bottom slab on the outside of the side wall.