JP4541573B2 - Prestressed concrete storage tank and prestressed concrete storage tank construction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention which concerns on this application is related with the construction direction of the storage tank provided with the wall body of the shell structure which consists of prestressed concrete, and a storage tank.
[0002]
[Prior art]
As a large-scale storage tank that accommodates a liquid or granular material of about 1000 m ³ to several tens of thousands m ³ , one having a shell structure made of prestressed concrete is widely used. For example, many prestressed concrete tanks having a cylindrical shell wall that is symmetrical with respect to a vertical axis have been constructed as water and sewage water storage tanks. In addition, an egg-shaped storage tank whose diameter is reduced vertically is known as a digestion tank in a sewage treatment plant. In addition, a cylindrical storage tank made of prestressed concrete may be used as a silo for storing grains, coal, or the like or a storage tank for low-temperature and normal-pressure liquefied gas.
[0003]
In such a storage tank, an internal pressure is applied by the stored material, and a tensile force is generated in the circumferential direction (horizontal direction) of the axisymmetric shell structure. On the other hand, pre-stress is introduced as if the “tangle” of the barrel is tightened by arranging the tension material in the circumferential direction and introducing the tension. In addition, a bending moment is generated in the longitudinal direction (vertical direction) of the axisymmetric shell due to the upper and lower end constraint conditions, and prestress is also introduced in the vertical direction to resist this.
[0004]
It is desirable that the circumferential prestress is introduced almost uniformly over the entire circumferential direction, and a plurality of tension materials wrapped around the end portions are arranged in a shape closed in the circumferential direction, and tension force is applied to these. Is introduced.
[0005]
In general, the tension force is introduced by pulling out the tension material to the outside of the wall body and performing the tensioning work and fixing. For this purpose, a columnar protrusion 101 called a “pilaster” as shown in FIG. It is provided outside the wall body 102.
This pilaster is continuous in the vertical direction, and is provided at several locations in the circumferential direction. The end of the circumferential tension material 103 is bent to the outside of the wall body 102, and a jack is attached to the side end surface 101a of the pilaster. Tension is introduced. Then, the tension member 103 is fixed to the wall body 102 by the fixing tool 104 in a state where the tension force is introduced into the tension member 103, and the end portion of the tension member is embedded by the post-cast concrete 105.
Reference numeral 106 denotes a PC steel material in the vertical direction, and reference numeral 107 denotes a reinforcing bar.
[0006]
[Problems to be solved by the invention]
However, the prestressed concrete storage tank having the above structure has the following problems.
When a pilaster is provided on the wall body of the shell structure, the wall thickness changes suddenly at that portion, and the stress distribution may be disturbed to generate a large stress locally. Also, prestress is not evenly introduced due to sudden changes in wall thickness.
[0007]
Furthermore, the tension material for introducing the pre-stress is disposed by being wrapped at the pilaster portion, and each is independently fixed to the side surface of the pilaster. Therefore, the tension of the tendon is transmitted from the fixing tool to the concrete, and a large stress tends to be locally generated in the concrete near the fixing tool. For this reason, reinforcement around the fixing tool or the like is necessary, the structure of this portion becomes complicated, and the number of work steps increases, which increases the work cost.
[0008]
Further, in the structure as described above, the tension material can be fixed only at the position where the pilaster is provided, and a plurality of pilasters are provided at equal intervals in the circumferential direction and fixed at this position.
The tension introduced into the tendon is uneven due to the loss of tension when it is fixed by friction and wedges on the peripheral surface. The prestress introduced is likely to be uneven.
[0009]
The present invention has been made in view of the circumstances as described above, and its purpose is to introduce prestress that is nearly equal to the circumferential direction of the concrete wall body that is an axisymmetric shell structure, and to disrupt the stress distribution. An object of the present invention is to provide a prestressed concrete storage tank capable of solving the problem and constructing a wall body and introducing a prestress by a simple operation, and to provide a method for constructing such a prestressed concrete storage tank.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention according to claim 1 is a storage tank comprising a concrete wall body having a shell structure symmetrical with respect to a vertical axis and prestressed in the circumferential direction and the vertical direction of the concrete wall body. The tension material for introducing prestress in the circumferential direction of the concrete wall is covered with a sheath made of synthetic resin on a steel wire or a steel strand, and at least until the tension force is introduced in the sheath are those materials having fluidity is filled, the large number are arranged vertically, the ends of the two tendons extending to either side are joined to form a closed circular by a fixing tool for fixing together, the The fixing tool has a shape in which two cylindrical bodies into which each of the two tendons are inserted are tensioned in the opposite directions, and both tendons are wedged. By Is intended to fix the fixing member, the constant Chakugu is embedded in the concrete wall body of uniform thickness in the circumferential direction, of the fixing member in the notch portion provided on the outer surface side of the concrete wall The tension side end face is fixed so as to be exposed, and the notch portion is provided so as to introduce a tension force by attaching a center hole jack to the tension material, and is backfilled with concrete after the tension force is introduced. Provide a prestressed concrete storage tank.
[0011]
The concrete wall body may be a cylindrical wall body raised up vertically, or may have an inner diameter that changes in the height direction. For example, an oval shape whose diameter is reduced vertically. Or a structure with an enlarged diameter at the top.
[0012]
The tendon is made of a so-called unbonded steel material, which is filled with fluid synthetic resin, oils and fats in the sheath in advance, or a so-called afterbond steel material in which the resin filled in the sheath is gradually cured over a long period of time. Can be used.
[0013]
In the prestressed concrete storage tank as described above, a fluid material is filled in the sheath covering the tension material, so that the peripheral friction when introducing the tension is small, and the tension is effectively applied over the entire length of the tension material. be introduced. In addition, the tendon is fixed so that the ends of the two tendons extending to both sides are connected by a fixing tool that integrally fixes the ends of the two tendons. Therefore, a single tension member can be arranged along the circumferential direction of the wall, and both ends can be connected by the fixing tool to form a closed shape. Also, a plurality of tendons may be connected in an annular shape using the same number of fixing tools. Then, when tension is introduced from both ends or one end of each tension material and locked to the fixing tool, the tension is transmitted between the ends of the tension material, and to the concrete around the fixing tool, the axial direction of the tension material The reaction force of is hardly transmitted. For this reason, it can be avoided that a large stress is locally generated in the concrete.
[0014]
In addition, since the fixing tool is embedded in the concrete wall having a uniform thickness in the circumferential direction, the stress and prestress due to the internal pressure are approximately equal in the circumferential direction, and the reliability of the structure is improved.
[0015]
The invention according to claim 2 is the prestressed concrete storage tank according to claim 1, wherein the tension material is fixed to the fixing tool by a wedge, and the fixing material fixes each of the tension materials adjacent vertically. The tool is buried at positions that are alternately displaced in the circumferential direction. The amount of deviation of the position at which the fixing tool is buried introduces a tension to the tendon and lowers the tension when fixing to the fixing tool by the wedge. It is assumed that it is set to be the same as the range.
[0016]
In the case where the tension material is fixed by the wedge, it is known that the tension is lost near the fixing end due to the wedge being drawn between the fixing tool and the tension material. If the fixing position is limited to the position of the pilaster as in the prior art, the circumferential prestress becomes uneven due to the loss.
However, by embedding a fixing tool in a concrete wall with an equal thickness and appropriately shifting the fixing position of the adjacent tension members in the upper and lower directions in the circumferential direction, the average value of the tension of both tendons is even even near the fixing position. It will be close.
Accordingly, it is possible to introduce prestress that is substantially uniform in the circumferential direction, and it is possible to effectively introduce prestress with a small amount of tension material.
[0017]
More specifically, it is as follows.
When the tension material introduces tension within the sheath embedded in the concrete member, the tension force gradually decreases from the tension end due to friction acting on the peripheral surface as shown in FIG. 9A. FIG. 9A shows a case where tension is introduced from both ends. The tension decreases most in the central portion, and a distribution indicated by symbols P → C → P in the figure is obtained.
On the other hand, after the tension is introduced into the tension member, when the end of the tension member is fixed to the fixing member fixed to the concrete member by the wedge, the wedge is caused by the tension of the tension member that has elastically stretched. It is drawn between the tendon and the fixing tool, and the tendon is firmly fixed on the fixing tool.
[0018]
At this time, in the vicinity of the tension end, the end of the tension material is drawn into the sheath together with the wedge, thereby causing a loss of tension. This loss of tension does not reach the entire length of the tendon because there is friction on the peripheral surface of the tendon, but as indicated by the broken line P ′ → S → C → S → P ′ in FIG. Losses occur only near the tension end.
For this reason, the prestress distribution to be introduced tends to be uneven in the vicinity of the end of the tendon.
[0019]
However, as shown in FIG. 9 (b), the tension positions of the two tension members adjacent to each other in the vertical direction are shifted by a range length L that is affected by the loss of the tension force. The average value of is equalized, and prestresses that are nearly equal to the circumferential direction of the concrete wall are introduced.
[0020]
According to a third aspect of the present invention, an outer mold is formed so that the inner surface is a curved surface symmetrical about a vertical axis, and a tension member and a reinforcing bar for introducing prestress at a predetermined position inside the outer mold A prestressed concrete storage tank including a step of forming an inner mold so as to face the outer mold at a predetermined interval, and placing concrete between the inner mold and the outer mold A fixing tool that integrally fixes the ends of two tension members extending on both sides, and a box-shaped formwork is connected to both end surfaces of the fixing jack that are in contact with the tensioning jack; The box-shaped formwork connected via the two is fixed to the inner surface of the outer formwork to support the fixing tool at a predetermined position, and then the concrete is placed, and after the concrete is hardened , Removing the outer formwork, and further, the box-shaped mold The construction method of the prestressed concrete storage tank which removes from the outer side of the hardened concrete wall body, mounts | wears with the center hole jack in the recessed part formed of this box-shaped formwork, and introduce | transduces tension | tensile_strength in the said tension material Is to provide.
[0021]
The fixing tool that integrally fixes the ends of two tension members that introduce tension force in opposite directions is provided with an end face for jacking on both sides thereof, so that the fixing tool is supported so as to be embedded in concrete. Becomes difficult. In other words, it is necessary to firmly support the fixing tool in the mold before placing concrete, and to provide notches so that both end faces are exposed and a jack for introducing tension can be installed. However, in the above method, a box-shaped form for providing a notch is connected to a fixing tool in advance, and the box-shaped form is fixed to an outer form assembled at a predetermined position on the site. The operation is remarkably simplified and it becomes easy to support the fixing device at an accurate position. Moreover, after the cast concrete is hardened, the box-shaped formwork is exposed when the outer formwork is removed, and this can be removed from the outside of the wall body. And a tension | tensile_strength can be introduce | transduced by attaching a jack to the formed recessed part.
[0022]
The invention according to claim 4 is the construction method of the prestressed concrete storage tank according to claim 3, wherein the fixing tool has a convex portion where a bolt is locked in the vicinity of an end surface joined to the box-shaped formwork. The box-shaped formwork is connected to the bolt that is locked to the convex portion through the box-shaped formwork and screwed into the bolt from the inside of the box-shaped formwork. This is done by tightening the nut.
[0023]
In such a method, the box-shaped formwork and the fixing tool can be connected easily and reliably, and after the fixing tool is embedded in the concrete, from the inside of the box-shaped formwork. Tightening with bolts and nuts can be released, and the box-shaped form can be easily detached.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a prestressed concrete (hereinafter referred to as PC) water tank that is an embodiment of the present invention.
The PC water tank includes a plurality of foundation piles 1 formed in the ground 6, a circular bottom plate 2 formed thereon, a cylindrical wall body 3 vertically raised thereon, The main part is composed of the dome roof 4 supported on the wall 3.
[0025]
The foundation pile 1 is formed by excavating a hole in the field, placing a reinforcing bar and then placing concrete, and the lower end is pushed into a strong support layer.
[0026]
The bottom slab 2 is made of reinforced concrete, and supports the weight of the wall body 3 and the stored water 7 on the foundation pile 1.
[0027]
The dome roof 4 is made of reinforced concrete and is formed so as to be continuous with the upper portion of the wall body 3. A ventilation hole 5 is provided at the top.
[0028]
The wall body 3 is made of prestressed concrete and has substantially the same thickness in the circumferential direction and the height direction. FIG. 2 is a plan sectional view (part) of the wall body 3, and the prestress of the wall body 3 places PC steel materials 12 and 11 (tension materials) in the vertical direction and the circumferential direction, and tensions them. Has been introduced. A steel bar is used as the PC steel material 12 in the vertical direction, and the lower end is embedded in the concrete of the floor slab 2, and tension is introduced from the upper part of the wall 3. On the other hand, the PC steel material 11 in the circumferential direction uses a strand of steel and is covered with a sheath made of a synthetic resin, and the sheath is filled with a resin having a long curing time. This resin has fluidity when a steel strand is placed in a predetermined position and tension is introduced after hardening of the concrete. It is adjusted so that concrete is firmly integrated.
[0029]
The steel strands 11 arranged in the circumferential direction have a length that goes around the wall as shown in FIG. 3, and both ends are fixed to one fixing tool 15 by a wedge as shown in FIG. The Therefore, the steel strand 11 in the circumferential direction is closed in an annular shape, and the cylindrical wall body 3 is tightened in the circumferential direction by installing a jack on both sides of the fixing tool 15 and introducing tension from both ends. It resists internal pressure.
[0030]
Reference numeral 16 in FIG. 2 indicates notches (recesses) provided on both sides of the fixing tool in order to mount the jack. After introducing tension to the steel strand 11, the concrete is A surface that is embedded and continuous with the outer surface of the wall body is formed. Reference numerals 13 and 14 are reinforcing bars arranged in the circumferential direction and the vertical direction, respectively.
[0031]
The fixing device 15 is a cast product, and as shown in FIG. 4, the two cylindrical bodies 15 a and 15 b through which the steel wire 11 is inserted are integrated by intersecting in an X shape. The steel wire 11 inserted through the cylindrical body can be tensioned and fixed on the opposite side.
In addition, the code | symbol 21 shown in FIG. 4 is a wedge which hold | suppresses a strand from steel, and the code | symbol 22 is a female cone to which the wedge 21 is latched. Reference numeral 23 denotes a synthetic resin sheath covering the steel strand.
[0032]
The arrangement of the fixing tool 15 is such that the fixing tools of the steel wires 11a and 11b are vertically displaced by a length L in the circumferential direction as shown in FIG. Are alternately arranged. The length L is set in a range (see FIG. 9) in which a loss of tension occurs when the steel strand 11 is fixed with a wedge. By arranging in this way, the tension is averaged as shown in FIG. 9 (b), and prestress is introduced in a state that is evenly close to the circumferential direction.
[0033]
Next, the construction method of the prestressed concrete storage tank will be described. This method is an embodiment of the invention according to claim 4 or claim 5.
First, a foundation pile 1 is formed, and a reinforced concrete bottom slab 2 is formed so as to be continuous with the head. Then, the outer mold 31 of the wall 3 is assembled on the bottom plate 2. As the outer mold 31, a metal foam, a wooden mold, or the like can be appropriately selected and used.
[0034]
On the other hand, a box-shaped frame 32 for forming a notch is connected to a fixing tool 15 for fixing a steel strand 11 (PC steel material) arranged in the circumferential direction. As shown in FIG. 5, the box-shaped mold 32 has a substantially triangular cross-sectional shape, and forms notches for mounting jacks for PC steel material tension on both sides of the fixing tool 15. is there. Therefore, the box-shaped mold 32 is brought into contact with and joined to the tension end sides of the two cylindrical portions of the fixing tool 15. As shown in FIG. 6, the box-shaped mold 32 has a bolt 34 engaged with a convex portion 15 c provided near the end face, and the bolt 34 is penetrated into the box-shaped mold 32 with a nut 35. By tightening, the fixing tool 15 is firmly connected.
[0035]
As shown in FIG. 5B, the box-shaped mold 32 connected to the fixing tool 15 is fixed at a predetermined position on the inner surface of the outer mold. Then, arrangement | positioning of a reinforcing bar, arrangement | positioning of PC steel material of the circumferential direction, arrangement | positioning of PC steel material of a perpendicular direction are performed by an appropriate procedure. The steel strand 11 in the circumferential direction is inserted from the rear into the cylindrical portion of the fixing device 15 and penetrates into the box-shaped mold 32. Then, if necessary, through holes are also provided in the outer mold 31 so as to protrude outward. The extra length protruding from the end face of the fixing tool 15 is necessary for locking with the jack when the tension is introduced.
[0036]
When the arrangement of the reinforcing bars and the PC steel materials is completed, the inner mold 33 is assembled, and concrete is placed between the inner mold 33 and the outer mold 31. And after concrete hardens | cures, the inner and outer formwork 31,33 is removed.
Generally, the wall 3 is divided into a plurality of times, and concrete is placed. The wall 3 is raised to a predetermined height by repeating the above steps. When the wall body 3 is started up, the PC steel material in the vertical direction and the circumferential direction is strained and prestress is introduced. The tension of the PC steel material may be performed for all the PC steel materials after the wall body is raised to a predetermined height, or is sequentially performed every time the wall body 3 is raised to a certain height. Also good. Further, when the wall body 3 is raised to a predetermined height, the dome roof 4 is constructed. However, the PC steel material may be tensioned after the dome roof 4 is formed.
[0037]
The dome roof 4 may be formed by assembling a supporting work, placing a concrete frame on this support, and placing concrete, or by joining precast members.
[0038]
In the construction method of the prestressed concrete storage tank as described above, the fixing tool 15 capable of integrally fixing two tendon ends from both sides can be easily supported at a predetermined position and embedded in the concrete. Therefore, the outer surface of the wall body 3 becomes a smooth curved surface, the flow of stress becomes smooth, and the wall body can be constructed at a low cost.
[0039]
FIG. 7: is a schematic sectional drawing which shows the prestressed concrete storage tank which is other embodiment of the invention which concerns on this application.
This storage tank is used as a digestion tank for a sewage treatment plant, and the wall body 43 has a symmetric shell structure with respect to a vertical axis, but has a shape close to an egg with a reduced diameter at the top and bottom. . Although the bottom plate 42 is supported by the foundation pile 41, the central portion 42 a has a concave shape downward, and the inner surface is continuous with the inner surface of the wall body 43 and has a smooth curved surface.
Moreover, the thickness of the wall gradually decreases as it goes upward, but it has a uniform thickness in the circumferential direction, and no pilaster or the like for fixing the PC steel material is provided. .
[0040]
In such a prestressed concrete storage tank, the same fixing tool as the storage tank shown in FIG. 1 can be used to fix the PC steel material in the circumferential direction in the wall of the uniform thickness in the circumferential direction, and the stress distribution is smooth. Can be.
[0041]
【The invention's effect】
As described above, in the prestressed concrete storage tank according to the present invention, the wall body is made to have a uniform thickness in the circumferential direction, and the prestress is introduced into a nearly equal state, and a large stress is prevented from being generated locally. can do.
Moreover, in the construction method of the prestressed concrete storage tank which concerns on this invention, while making a wall body uniform thickness in the circumferential direction, the fixing | fixed part of PC steel material of the circumferential direction can be formed easily with few man-hours.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a prestressed concrete storage tank according to an embodiment of the present invention.
2 is a plan sectional view of a wall of the prestressed concrete storage tank shown in FIG.
FIG. 3 is a schematic view showing the shape of a tension member (steel strand) arranged in the circumferential direction of the wall of the prestressed concrete storage tank shown in FIG. 1 and the position of the fixing tool.
FIGS. 4A and 4B are a cross-sectional view and a front view showing a tension member fixing device arranged in a circumferential direction. FIGS.
FIG. 5 is a schematic view showing a method for supporting the fixing device shown in FIG. 4 at a predetermined position.
FIG. 6 is a cross-sectional view showing a connection state between the fixing tool and the box-shaped formwork.
FIG. 7 is a schematic cross-sectional view showing a prestressed concrete storage tank according to another embodiment of the present invention.
FIG. 8 is a plan sectional view showing a fixing portion of a tension material in a circumferential direction in a conventional prestressed concrete storage tank.
FIG. 9 is a schematic view showing a tension distribution of a tendon arranged in the circumferential direction.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Foundation pile 2 Bottom plate 3 Wall body 4 Dome roof 5 Ventilation hole 6 Ground 7 Storage water 11 Circumferential PC steel (steel strand)
12 Vertical PC steel (steel bar)
13 Reinforcing bar 14 Vertical reinforcing bar 15 Fixing tool 16 Notch portion 21 Wedge 22 Female cone 23 Sheath 31 Outer frame 32 Box-shaped frame 33 Inner frame 41 Foundation pile 42 Bottom plate 43 Wall body

Claims (4)

A storage tank having a concrete wall with a shell structure symmetrical about a vertical axis, and introducing prestress in the circumferential direction and the vertical direction of the concrete wall,
Tensile material for introducing prestress in the circumferential direction of the concrete wall body,
A steel wire or a steel strand is covered with a sheath made of a synthetic resin, and the sheath is filled with a material having fluidity at least until the introduction of a tension force.
Many books are arranged on the top and bottom,
Joined in a circular closed shape by a fixing tool that fixes the ends of two tendons that extend to both sides together,
The fixing device has a shape in which two cylindrical bodies into which each of the two tendons are inserted are integrated, and the two tendons are tensioned in opposite directions to wedge both tendons. By which the fixing device is fixed.
The fixing tool is embedded in a concrete wall having a uniform thickness in the circumferential direction, and is fixed so that a tension-side end surface of the fixing tool is exposed in a notch provided on the outer surface side of the concrete wall. ,
The prestressed concrete storage tank , wherein the notch is provided so as to introduce a tension force by attaching a center hole jack to the tension material, and is backfilled with concrete after the tension force is introduced . The tendon is fixed to the fixing tool by a wedge,
Fixing tools that fix each of the above-mentioned tendons adjacent to each other vertically are buried in positions that are alternately displaced in the circumferential direction,
The displacement amount of the position where the fixing tool is embedded is set to be the same as a range in which a tension is reduced when the tension is introduced into the tension member and fixed to the fixing tool by the wedge. Item 2. A prestressed concrete storage tank according to item 1. Form the outer mold so that the inner surface is a curved surface symmetrical about the vertical axis,
Place a tension member and a reinforcing bar for introducing prestress at a predetermined position inside the outer mold,
Forming an inner mold so as to face the outer mold at a predetermined interval;
A method for constructing a prestressed concrete storage tank including a step of placing concrete between the inner mold and the outer mold,
A box-shaped formwork is connected to the end faces on both sides of the fixing tool, which are fixed to the ends of the two tension members extending on both sides, with which the tensioning jack is in contact,
Supporting the fixing tool at a predetermined position by fixing the two box-shaped molds connected via the fixing tool to the inner surface of the outer mold;
After that, placing the concrete,
After the concrete is hardened, the outer formwork is removed, and further, the box-like formwork is removed from the outside of the hardened concrete wall,
A method for constructing a prestressed concrete storage tank, wherein a center hole jack is attached to a recess formed by the box-shaped formwork to introduce a tension into the tendon. The fixing tool has a convex portion where a bolt is locked in the vicinity of an end surface joined to the box-shaped formwork,
The box-shaped formwork is connected by passing a bolt locked to the convex portion into the box-shaped formwork, and a nut screwed into the bolt from the inside of the box-shaped formwork. The method for constructing a prestressed concrete storage tank according to claim 3, wherein the method is performed by tightening.

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