JP2016023518A - Prestressed concrete structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a prestressed concrete structure capable of reducing steps involved in a sheath pipe so as to shorten the construction period and reduce costs.SOLUTION: In a low-temperature tank 1 which is a prestressed concrete structure formed by introducing prestress into a side wall 6 as the concrete structure by a tendon 8, prestress is introduced into an outer tank 2 by winding a belt-like tendon 8 with anticorrosion performance on the outer periphery of the side wall 6 in a state of obliquely intersecting with each other. The tendon 8 has anticorrosion performance and is belt-like, and is wound for a plurality of times according to the external force occurring in the concrete structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a prestressed concrete structure that is used, for example, in an outer tank of a double-shell cryogenic tank that stores liquefied natural gas.

  A large-sized low temperature tank for storing liquefied natural gas (hereinafter referred to as LNG) is composed of a double shell tank in which a heat insulating material is disposed between an outer tank made of concrete and an inner tank made of steel. The concrete outer tub is generally made of prestressed concrete (hereinafter referred to as PC).

  The outer tank of the LNG low temperature tank serves as a liquid barrier to prevent diffusion when LNG leaks from the inner tank. As this outer tub, a prestressed concrete structure having at least a disk-shaped bottom plate and a cylindrical side wall is known, and is manufactured by the following steps.

  First, a plurality of foundation piles are constructed on the ground, and a disk-shaped bottom plate is rigidly connected to the foundation piles. Next, a mold for forming the inner peripheral surface and the outer peripheral surface of the cylindrical side wall is installed over the circumferential direction of the disk-shaped bottom plate. Then, reinforcing bars are assembled in the mold and the sheath tube is arranged in the horizontal direction and the vertical direction, and concrete is placed in the mold by in-situ casting and solidified. Thereby, the annular concrete unit which comprises a part in the height direction of a side wall is shape | molded. Then, the mold is moved upward to form an annular concrete unit in the same manner, and a cylindrical side wall is manufactured by repeating this process.

  Then, a PC steel material is inserted into the sheath tube embedded in the side wall and a tension (hereinafter referred to as prestress) is applied, and in this state, the ground material is filled between the inner wall of the sheath tube and the PC steel material. As a result, the PC steel is integrated with the cylindrical side wall made of concrete and is prevented from being corroded and damaged by the influence of rainwater.

  As prior art document information related to the prestressed concrete structure described above, for example, there is Patent Document 1 below.

Japanese Patent Laid-Open No. 10-238697

  However, the above-mentioned prestressed concrete structure has to be troublesome because it is necessary to install a sheath tube in the process of manufacturing a cylindrical side wall. Further, in the subsequent steps, there were many steps related to insertion of the PC steel material into the sheath tube, a step of introducing pre-stress, a step of filling the sheath material with the groud material, and a step related to the sheath tube, and time and cost were increased. .

  Then, an object of this invention is to provide the prestressed concrete structure which reduced the process regarding a sheath pipe | tube, shortened the construction period, and reduced the cost.

  The present invention relates to a prestressed concrete structure in which prestress is introduced into a concrete structure with a tendon, and the concrete structure is pre-wound by being wound so that one tendon crosses obliquely with respect to the outer periphery. It is characterized by the introduction of stress.

  The tendon preferably has anticorrosive properties.

  The tendon is strip-shaped and is preferably wound a plurality of times according to an external force generated in the concrete structure.

  The concrete structure is preferably an outer tank of a low-temperature tank that stores a low-temperature liquid.

  According to the present invention, it is possible to reduce the cost by reducing the steps related to the sheath tube, shortening the construction period.

It is the perspective view which looked at the low temperature tank which stores LNG from diagonally upward. It is sectional drawing which shows a mode that the low-temperature tank was cut along the perpendicular direction. (A)-(f) is the schematic diagram which showed a mode that a tension material was wound around the outer tank of a low-temperature tank. It is sectional drawing of the side wall which showed the prestress introduced by the leak pressure produced in a side wall when LNG leaks from an inner tank, and a tendon. It is a schematic diagram which shows a mode that after winding from the 1st to the 4th step, it wound by shifting by a quarter in the circumferential direction.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as the present embodiment) will be described with reference to FIGS. FIG. 1 is a perspective view of a low temperature tank 1 for storing LNG as viewed obliquely from above. FIG. 2 is a cross-sectional view showing a state in which the low-temperature tank is cross-sectioned along the vertical direction. In FIG. 2, the cross section of the tendon material 8 is omitted.

  In this embodiment, a prestressed concrete structure will be described with an outer tub 2 of a low-temperature tank 1 for storing LNG. As shown in FIG. 1 and FIG. 2, the low temperature tank 1 includes an inner tank 3 for storing LNG, an outer tank 2 serving as a liquid barrier to prevent diffusion when LNG leaks from the inner tank 3, and an inner tank 3 and a heat insulating material 12 disposed between the outer tub 2.

  The outer tub 2 of the low-temperature tank 1 is a concrete structure including a bottom slab 5, a side wall 6 (outer periphery), and a roof 7, and is a prestressed concrete structure into which prestress is introduced by a tension material 8.

  The bottom plate 5 is a disk-shaped member made of concrete. The bottom plate 5 is supported at a predetermined height position from the ground by a plurality of foundation piles 10 embedded in the ground.

  The side wall 6 is made of concrete on the bottom plate 5 and constitutes a side wall in the outer tub 2 of the low-temperature tank 1. The side wall 6 has a cylindrical shape having an outer peripheral surface and an inner peripheral surface. The side wall 6 serves as a liquid barrier that prevents LNG from diffusing when LNG leaks from the inner tank 3. The side wall 6 is formed by stacking three short cylindrical concrete units 11 in the height direction.

  The concrete unit 11 is manufactured by the following process. First, a step of assembling a reinforcing bar that is a framework over the circumferential direction of the bottom plate 5 is performed. Next, a process of assembling a mold for forming the outer peripheral surface and the inner peripheral surface of the concrete unit 11 over the circumferential direction of the bottom plate 5 is performed. Subsequently, a molding process is performed in which concrete is cast into the mold to form a shape. And the reinforced concrete shape | molded by the short cylindrical shape is solidified through a curing process. Finally, the mold is removed in the demolding process. By this series of steps, the first-stage concrete unit 11a is manufactured.

  The side wall 6 has three-stage concrete units 11a, 11b, and 11c manufactured by repeating this series of processes three times. The side wall 6 is characterized in that a sheath tube for inserting the tendon material 8 is not embedded as compared with the conventional side wall. The roof 7 has a concrete dome shape, and is manufactured on the side wall 6 after the side wall 6 is manufactured.

  The side wall 6, which is a concrete structure described above, is pre-stressed by winding the tension material 8 so as to obliquely intersect the outer peripheral surface of the side wall 6, so that the low-temperature tank 1 is used as a prestressed concrete structure. The outer tank 2 is configured.

  The tension material 8 is, for example, a PC steel material, a PC steel material coated with rust prevention, a band-like carbon fiber, or the like. In this embodiment, the tension material 8 will be described by exemplifying a case where a strip-like carbon fiber having anticorrosion properties is used. The belt-like tension material 8 can have a larger contact area with respect to the outer peripheral surface of the side wall 6 than the PC steel material which is a strip material. Further, when the belt-like tension material 8 is wound around the outer peripheral surface of the side wall 6, the start end portion and the end portion are fixed with an epoxy-based adhesive.

  When the tension material 8 is wound around the outer peripheral surface of the side wall 6, the tension material 8 is wound so as to have a portion that is inclined with respect to the horizontal direction. The tension material 8 is wound in this manner, thereby introducing prestress in the circumferential direction and the vertical direction with respect to the side wall 6.

  Hereinafter, a state in which prestress is introduced by winding the tension material 8 around the outer tub 2 of the low-temperature tank 1 will be described with reference to FIG. 3. FIG. 3 is a schematic view showing a state in which the tendon material 8 is wound around the outer tub 2 of the low-temperature tank 1.

  As shown in FIG. 3 (a), the tension material 8 is wound around the side wall 6 of the outer tub 2 as a first step in the circumferential direction from the front side to the back side of the figure on the upper end portion of the outer peripheral surface of the side wall 6. Wrap around once.

  Next, as a second step, as shown in FIG. 3 (b), the tension material 8 is inclined obliquely downward from the front side of the side wall 6 from the place where the tension material 8 makes a round and returns. Wrap around. The tendon 8 is wound around the upper end of the outer peripheral surface of the side wall 6 in the first step. As a result, the upper end side of the tension material 8 wound obliquely is firmly held, and the portion of the tension material 8 wound obliquely is less likely to be displaced from the outer peripheral surface of the side wall 6.

  Next, as a third step, as shown in FIG. 3C, the tension member 8 is wound around the lower end portion of the outer peripheral surface of the side wall 6 along the circumferential direction from the back side to the near side in the drawing. As a result, the upper and lower ends of the portion of the tension member 8 that is wound obliquely downward are firmly held together with the first step.

  Next, as a fourth step, the tension member 8 is wound obliquely upward and obliquely with respect to the back side of the side wall 6 from the place where the tension member 8 has returned around the lower end of the side wall 6. The tendon 8 is wound around the lower end portion of the outer peripheral surface of the side wall 6 in the previous third step. As a result, the lower end side of the tension material 8 that is wound obliquely upward in the tension material 8 is firmly held and is less likely to be displaced. The fourth step is not illustrated because it is a step of winding the tendon material 8 from the near side to the back side of the side wall 6 (not shown) in an obliquely upward direction.

  The winding of the tension material 8 from the first to the fourth step is set as one unit, and thereafter, the winding from the winding start position to the circumferential direction is shifted in the circumferential direction and the winding from the first to the fourth step is repeated. For example, after winding from the first step to the fourth step, as shown in FIG. 3 (d), the upper end portion of the outer peripheral surface of the side wall 6 is wound half a turn, the winding start position is shifted in the circumferential direction, and again, Wrap from the first to the fourth step.

  When wound in such a manner, the tendon 8 is wound around the outer peripheral surface of the side wall 6 so as to obliquely intersect the front side and the back side of the drawing as shown in FIG. When the tension material 8 is wound so as to cross diagonally in this manner, the side wall 6 is compared with the side wall 6 that is a concrete structure as compared with the case where the tension material 8 is wound up to FIG. Prestress is evenly introduced.

  Finally, as a final step, the tendon 8 is wound around the side wall 6 a plurality of times according to the stress generated in the outer tub 2. This will be described with reference to FIG. 4 and FIG. FIG. 4 is a cross-sectional view of the side wall 6 showing the leakage pressure S1 generated in the side wall 6 when LNG leaks from the inner tank 3 and the prestress S2 introduced by the tendon 8. FIG. 1 is a perspective view of the low temperature tank 1 for storing LNG as viewed obliquely from above, and is also a perspective view showing a state in which the tension material 8 is wound around the outer peripheral surface of the side wall 6 after the final step.

  As shown in FIG. 4, when the LNG leaks from the inner tank 3, the outer tank 2 generates a higher leak pressure S1 as stress on the side wall 6 as it is closer to the bottom, and the leak pressure S1 as it goes upward. The stress due to becomes smaller. Therefore, after winding the tension material 8 to the state shown in FIG. 3 (e), as shown in FIG. 1, as it goes from the upper end to the lower end, the winding interval of the tension material 8 is spirally reduced. Wrap around. In the present embodiment, the third-stage concrete unit 11c is spirally rotated, the second-stage concrete unit 11b is spirally rotated, and the first-stage concrete unit 11a is rotated three times.

  When wound as described above, as shown in FIG. 4, a stronger prestress S <b> 2 is introduced toward the bottom from the top of the side wall 6 so as to oppose the leakage pressure S <b> 1 generated on the side wall 6. Here, after winding as shown in FIG. 1, the winding interval of the tendon material 8 becomes narrower as it goes from the lower end to the upper end as shown in FIG. You may make it wind so that it may cross | intersect the part wound spirally. As a result, the prestress S2 is uniformly introduced into the side wall 6.

  According to the prestressed concrete structure of the present invention, the side wall 6 which is a concrete structure introduces prestress by winding a single tension member 8 so as to cross obliquely with respect to the outer peripheral surface. That is, since the present invention has a configuration in which the tension member 8 is wound around the outer peripheral surface, the step of embedding the sheath tube at the time of manufacturing the side wall 6, and after the completion of the side wall 6, the tension member 8 is turned into the sheath tube. The construction period can be shortened by omitting the step of inserting and the step of filling the sheath tube with the graud material. In addition, since the sheath tube and the glove material filling the sheath tube are not necessary, the cost can be reduced. In the present invention, one tension member 8 is wound so as to cross obliquely with respect to the outer peripheral surface. The tension material 8 can be pre-stressed in both the horizontal direction and the vertical direction by wrapping diagonally, and can be pre-stressed evenly with respect to the side wall 6 by wrapping so as to intersect. Can be introduced.

  Moreover, according to the prestressed concrete structure of this invention, the tension material 8 has corrosion resistance. Thereby, even if the tendon 8 is exposed to rainwater, it is not corroded and cut. Moreover, the present invention does not require a step of spraying ganite from the tension material 8 in order to prevent rust. Therefore, the construction period can be shortened. Moreover, since ganite is not required, the cost can be reduced.

  Further, according to the prestressed concrete structure of the present invention, the tendon 8 is strip-shaped and is wound a plurality of times according to the external force generated on the side wall 6. For example, the belt-like tension material 8 can be easily wound on the same portion as the strip, and can easily be wound on a portion of the side wall 6 where the external force acts greatly to introduce prestress against the external force. . Further, the belt-like tension material 8 can apply prestress in a wider range in the width direction than the strip material such as PC steel material.

  Moreover, according to the prestressed concrete structure of this invention, a concrete structure is the outer tank 2 of the low temperature tank 1 which stores a low temperature liquid. The outer tub 2 which is a prestressed concrete structure can counteract the fluid pressure generated in the side wall 6 even if the low temperature liquid leaks from the inner tub 3, and can prevent the low temperature liquid from diffusing.

  In addition, the prestressed concrete structure of this invention is not limited to the above-mentioned Example. For example, when the tension material 8 is wound around the outer peripheral surface of the side wall 6, the series of winding from the first step to the fourth step may be repeated a plurality of times and then shifted in the circumferential direction. In this case, it is preferable that the tendon 8 is wound around the width every time it goes around.

  Moreover, although the tension | tensile_strength material 8 was wound from the 1st to the 4th step, it demonstrated by the structure wound around the circumference direction by a half turn, but it is not limited to this. For example, the winding of the tension material 8 from the first to the fourth step may be repeated by shifting by a quarter of a circle in the circumferential direction. In this case, after FIG. 3 (d), the tendon 8 is wound around the outer peripheral surface of the side wall 6 as shown in FIG. 5.

  In addition to the heat insulating material on the bottom side between the outer tub 2 and the inner tub 3, a TCP plate (thermal corner protection) is arranged to reduce the thermal stress when low temperature liquid leaks from the inner tub 3. If so, the number of windings may be reduced accordingly. Further, on the upper side of the side wall 6, a stress greater than that of other portions is generated for the purpose of supporting the roof 7. Therefore, in order to cope with this stress, it is preferable to increase the number of turns at the upper position on the outer peripheral surface of the side wall 6.

  The prestressed concrete structure of the present invention can be changed without departing from the gist of the present invention.

1 Low temperature tank 2 Outer tank (Prestressed concrete structure)
6 Side wall (concrete structure)
8 Tension material

Claims (4)

In a prestressed concrete structure in which prestress is introduced into the concrete structure by tendons,
The prestressed concrete structure is characterized in that the concrete structure introduces prestress by winding a single tension material so as to cross obliquely with respect to the outer periphery.   The prestressed concrete structure according to claim 1, wherein the tendon has anticorrosion properties.   The prestressed concrete structure according to claim 1 or 2, wherein the tendon has a belt shape and is wound a plurality of times according to an external force generated in the concrete structure.   The prestressed concrete structure according to any one of claims 1 to 3, wherein the concrete structure is an outer tank of a low-temperature tank that stores a low-temperature liquid.

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