JP4253685B2 - Prestressed concrete structure - Google Patents

Description

  The present invention relates to a prestressed concrete structure, and more particularly, to a prestressed concrete structure that has good side wall workability and can reduce the amount of tension material disposed in the side wall in the vertical direction.

  Conventional container structures such as LNG and LPG storage ground tanks and underground tanks are composed of a bottom plate, a side wall standing on the bottom plate, and a flat or dome-shaped ceiling connected to the upper end of the side wall. Yes. The bottom plate has a larger cross-sectional force (bending moment, shearing force, etc.) compared to other parts at the part where it is joined to the side wall and the lower part of the side wall. Measures such as over-barreling have been taken. Although the container structure described above has various constituent materials and structural forms depending on its use and scale, reinforced concrete structures such as above-ground tanks and underground tanks that require relatively large-scale durability are required. It is common to be constructed on site.

  By the way, when constructing the bottom plate, side walls, ceiling, etc. constituting the container structure with reinforced concrete, a tension material such as PC steel is used inside or outside the reinforced concrete for the purpose of reducing the amount of reinforcing bars or preventing cracks, The mainstream is to use prestressed concrete structures. That is, a sheath tube is embedded in the bottom plate and the side wall in advance, and after constructing the bottom plate and the side wall, the tension material is inserted into the sheath tube and the end of the tension material is pulled (hereinafter referred to as prestressing force). By introducing it into the sheath tube, a compressive force is applied to the bottom plate and the side wall (post-tension method). In addition, pre-tension that pre-stressed pre-stress force is embedded in the bottom plate and side walls, and the pre-stress force is applied to the side walls by releasing the pre-stress force from the tension material after construction of the bottom plate and side walls. There are also methods.

  Even in the case of a prestressed concrete structure, as described above, there is no change in that a relatively large cross-sectional force is generated in the lower portion of the side wall, etc. The amount of tension material and the amount of reinforcing bars increase. In the side wall of a conventional prestressed concrete structure, a plurality of vertical tension members extending from the lower part of the side wall to the vicinity of the upper part are arranged at predetermined intervals in the circumferential direction of the side wall, As described above, construction has been performed in which a plurality of circumferential tension members are arranged. One end of the tension material in the vertical direction is fixed in the bottom plate, and the other end is fixed near the upper end of the side wall via a fixing tool or the like. Although the tension material in the vertical direction extends from the lower part of the side wall to the vicinity of the upper part, the amount of the tension material is determined by the cross-sectional force of the lower part of the side wall, so that the amount of tension material at the upper part of the side wall is actually excessive. It was.

  To solve the above problem, Patent Document 1 discloses a double-shell type cryogenic tank (vertical tension material (PC steel rod) on the side wall of the outer tank of the tank that is not affected by the temperature of the cryogenic storage liquid ( An invention relating to a prestressed concrete structure) is disclosed. In such an invention, by adopting a construction method in which intermediate tension is applied to the outer tank side wall and the vertical tension material in the lower part of the side wall is closely arranged, the bending moment generated in the vertical direction due to the hydraulic pressure is large, and the pole The strength of the lower part of the side wall of the outer tub, which is greatly affected by the temperature of the low-temperature liquid, is increased. That is, as shown in FIGS. 7a and 7b, a sheath tube having a heat insulating structure is provided up to a predetermined height position in the vertical direction of the outer tank side wall 2, and an intermediate tension member 51 made of a PC steel rod is disposed therein, and its upper end After the concrete is applied to the position, intermediate tension is applied to the intermediate tension member 51 and fixed. Further, the concrete is applied to the upper part, and tension is applied to the vertical tension member 53 passing to the upper part of the side wall 2 to It is to be fixed. Here, the intermediate tension member 51 and the vertical tension member 53 extending from the lower part of the side wall 2 to the upper end are arranged on the same circumference of the side wall 2 in a state where each end is fixed in the bottom plate 3 as shown in FIG. Are alternately arranged in the circumferential direction. Further, a tension member 52 in the circumferential direction is disposed so as to surround the tension members 51 and 53, and prestressed concrete in a state where a prestressing force is introduced in the vertical direction and the circumferential direction and a compressive force acts on the side wall. A structure 1 is formed.

Japanese Patent Laid-Open No. 10-238697

  According to the construction method of the prestressed concrete structure disclosed in Patent Document 1, an excessive amount of tension material is not disposed on the upper portion of the side wall by changing the amount of tension material between the lower portion and the upper portion of the side wall. Can be effectively reduced. However, until the intermediate tension is completed, that is, until the prestressing force introduction work to the tension material, the grout filling work in the sheath tube, and the necessary strength expression confirmation work are completed, Sidewall construction work cannot be performed, and therefore a problem such as prolonging the construction period may occur. In addition, in the state where the intermediate tension material and the tension material extending to the upper end of the side wall within a certain thickness are alternately arranged in the circumferential direction, the construction for applying intermediate tension only to the intermediate tension material is arranged on the side. There is a possibility that the tension material extending to the vicinity of the upper end of the side wall becomes an obstacle to the tension device. In particular, since the vertical tension members disposed at the lower end of the side wall are disposed at a dense pitch in the circumferential direction, the separation between the intermediate tension member and the tension members extending to the vicinity of the upper end of the side wall on both sides is relatively narrow. Is common. Even if it is going to give intermediate tension to the intermediate tension material under such circumstances, the tension material extending to the vicinity of the upper end of the side wall described above becomes an obstacle to the tension device, and sufficient tension force (hereinafter referred to as pre-stress force) is applied to the intermediate tension material. It becomes difficult to introduce, and a problem that the tendon material (covering sheath tube) extending to the vicinity of the upper end of the side wall may be damaged by the tension device.

  The prestressed concrete structure of the present invention has been made in view of the above-described problems, and the prestressed concrete structure can reduce the amount of tension material by effectively changing the amount of tension material at the lower and upper side walls. The purpose is to provide. It is another object of the present invention to provide a prestressed concrete structure in which the intermediate tension work does not affect the start of the upper side wall construction work and therefore does not cause the construction period to be prolonged. It is another object of the present invention to provide a prestressed concrete structure in which a tension material extending to the vicinity of the upper end of the side wall does not become an obstacle when introducing the intermediate prestress force when an intermediate prestressing force is applied to a vertical tension material.

  In order to achieve the above object, a prestressed concrete structure according to the present invention is a prestressed concrete structure including at least a bottom plate and a side wall standing on the bottom plate, and the side wall is directed downward from the middle thereof. It has a portion where the member thickness is increased, and at least a portion where the member thickness is increased is provided with a tension material in a vertical direction or a vertical oblique direction.

  A prestressed concrete structure is a container structure composed of a bottom plate, a side wall standing on the bottom plate, a ceiling connected to the upper end of the side wall, and the bottom plate is a direct foundation supported directly on the ground. Even if it is a form, the pile foundation form supported by a pile etc. may be sufficient. Furthermore, as the shape of the ceiling, an appropriate shape such as a flat plate shape or a dome shape can be selected.

  Here, the side wall has a portion in which the member thickness increases downward from the middle of the side wall, so that the member thickness of the side wall increases from the middle of the side wall to the lower side of the side wall. It means that As a form in which the member thickness increases, a constant member thickness (hereinafter referred to as a side wall general part) is formed from the upper end of the side wall to the middle of the side wall, and is formed in a tapered shape from the middle of the side wall to the lower side of the side wall (the side wall). Side wall cross section of the general side wall (direction perpendicular to the circumferential direction of the side wall), and a cross section approximate to a 1/4 elliptical cross section cut with a major axis and a minor axis. Form added to the outside of the side wall cross section when vertically divided by, and a form formed in a multi-stage from the middle of the side wall to the lower side of the side wall as will be described later (a multi-stage part is added outside the general side wall part) (Appropriate form). The intermediate level of the side wall where the member thickness increases is a design matter, and an appropriate level is selected according to the design bending moment generated in the vertical plane of the side wall, the concrete specification, and the like.

  Further, the fact that the tension material in the vertical direction or the diagonally oblique direction is disposed at least in the portion where the member thickness is increased is that the tension material is disposed only in the portion where the member thickness is increased, This means that the tension material is disposed from the portion where the member thickness is increased to the general portion of the side wall.

  At the time of construction, at the stage where the side wall is constructed to an arbitrary level of the portion where the member thickness increases, the prestressing force is applied to the vertical or diagonally slanting material disposed in the portion where the member thickness increases. Introduce middle tension. At this time, the above-described tendon can be disposed in the vertical oblique direction in addition to the case of being disposed in the vertical direction. By arranging the tension material in the diagonally vertical direction, when the pre-stress force is introduced to the tension material and intermediate tension is applied, the compressive force on the side wall is increased to the general side wall part in addition to the part where the member thickness increases. It can work effectively. In addition, since the intermediate tension work is performed at a portion projecting outward from the side wall general portion (a portion where the member thickness is increased), the construction work of the side wall general portion above the intermediate tension level waits for the completion of the intermediate tension operation. You can start shortly. Therefore, it is possible to eliminate the use of a tension material that is essentially unnecessary on the upper portion of the side wall, and to secure the workability of the side wall.

  As another embodiment of the prestressed concrete structure according to the present invention, the portion of the side wall where the member thickness is increased is formed in a multi-stage shape toward the lower side of the side wall.

  Multi-stage means that the member thickness of the side wall gradually increases toward the lower side of the side wall, and an appropriate step shape from one stage to a plurality of stages can be selected. As described above, there are various forms of the portion where the member thickness is increased. However, in consideration of the workability during intermediate tension, the embodiment in which the side wall member thickness is increased to a multistage shape of about one or two stages. Is considered particularly preferred.

  As another embodiment of the prestressed concrete structure according to the present invention, a tension material extending from the lower end of the side wall to the vicinity of the upper end is further arranged on the side wall.

  This is a prestressed concrete structure in which a vertical tension member is also disposed in the side wall general part. One end of the tension material is fixed in the bottom plate, and the other end is a side wall (a side wall general part). ) In the vicinity of the upper end of (), for example, via a fixing tool. The portion where the compressive force needs to be applied by the tension material is the lower portion of the side wall where the cross-sectional force is particularly large, and the upper portion of the side wall may not necessarily require the tension material. The present invention relates to a case in which a tension member is disposed on a side wall general portion. For example, a circumferential pitch interval of a tension material disposed on a side wall general portion is arranged in a vertical direction or on a portion where a member thickness is increased. It is preferable to employ an arrangement method such as making the length of the tension material in the vertical oblique direction longer than the pitch interval in the circumferential direction.

  As a more preferred embodiment of the prestressed concrete structure according to the present invention, the side wall is formed in a substantially cylindrical shape, and the side wall is arranged in the vertical direction or at least disposed in a portion where the member thickness is increased. The present invention is characterized by comprising a circumferential tension member disposed so as to surround a vertical oblique tension material.

  Here, the term “substantially cylindrical” means not only a cylindrical shape but also an elliptical cross section and a hollow shape. In order to effectively introduce a prestressing force inside the side wall and to exert a compressive force, the side wall shape is preferably a cylindrical shape or an elliptical cylindrical body close to a cylindrical shape, and particularly a cylindrical shape. preferable. This is because if a prestressing force in the circumferential direction is introduced into the cylindrical side wall, only a compressive force acts in the circumferential direction and no bending moment is generated. On the other hand, in the case of an elliptical cylindrical body, a compressive force acts in the elliptical cross-section direction (corresponding to the circumferential direction in the case of a cylindrical shape), and a bending moment is also generated in the cross-section, and the arrangement of the bars Will be forced. However, the prestressing force introduced in the circumferential direction and the elliptical cross-section direction is effective in the circumferential direction by using the above-described cylindrical or elliptical cylindrical side wall as compared with the hollow rectangular cross-section side wall. Will act as a compressive force.

  In the case of a cylindrical side wall, the vertical tension members are arranged at predetermined intervals in the circumferential direction, and on the outside of the vertical tension members so as to surround the vertical tension members. Circumferential tension material is disposed. This circumferential tension member is disposed at a portion where the thickness of the member increases, and when a vertical tension member is disposed on the general side wall portion, the circumferential tension member is also disposed outside the tension member. It is preferable. However, the necessity of disposing a circumferential tension member on the side wall general part is necessary for the side wall general part due to the upper end level of the part where the member thickness increases or the liquid level stored in the structure. It is determined by the circumferential compression force. As a construction method, a circumferential tension member is disposed so as to surround a vertical or oblique slant member disposed in a portion where the member thickness is increased, and the vertical direction (or vertical oblique direction) and After pre-stressing force is introduced in the circumferential direction and intermediate tension is applied, the method of moving to the construction of the upper side wall or intermediate tension only for the vertical (or vertical diagonal) tension material, the upper side wall After completion of the construction, there is a method of introducing a prestressing force to the tension material extending to the vicinity of the upper end portion of the side wall and the tension material arranged in the circumferential direction. PC steel wire or PC steel wire is used as the tension material in the circumferential direction, and PC steel wire, PC steel wire, PC steel rod, or the like is used as the tension material in the vertical direction.

  As another embodiment of the prestressed concrete structure according to the present invention, the prestressed concrete structure is an above-ground tank or underground tank for storing LNG or LPG.

  Prestressed concrete structures (container structures) that are relatively large and have substantially cylindrical side walls that require durability are often applied to ground and underground tanks for LNG or LPG storage. The prestressed concrete structure having the bottom plate-side wall joint structure of the present invention is also preferably applied to the tank described above. Needless to say, this does not exclude container structures that are applied to small-scale tanks and other uses, such as water tanks and farm ponds.

  As can be understood from the above description, according to the prestressed concrete structure of the present invention, the amount of tension material at the lower and upper side walls can be effectively changed, and therefore the amount of tension material can be significantly reduced. . In addition, according to the prestressed concrete structure of the present invention, since the intermediate tension work does not affect the start of the upper side wall construction work, the possibility of incurring a prolonged construction period can be extremely reduced. Furthermore, according to the prestressed concrete structure of the present invention, a portion where the member thickness is increased is provided outside the general portion of the side wall, and a vertical or vertical oblique tension material for intermediate tension is provided on the portion where the member thickness increases. Due to the arrangement, the vertical tension material arranged on the side wall general part does not become an obstacle when the intermediate prestressing force is introduced. Therefore, the introduction of the intermediate prestressing force and the improvement of workability are ensured. Can be planned.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of the prestressed concrete structure of the present invention, and FIG. 2 is a side view of the prestressed concrete structure of FIG. FIG. 3 is a longitudinal sectional view showing another embodiment of the prestressed concrete structure of the present invention, and FIG. 4 is a side view of the prestressed concrete structure of FIG. . 5 and 6 are longitudinal sectional views showing other embodiments of the prestressed concrete structure of the present invention. In the following description, a side wall is cylindrical as a prestressed concrete structure, and a ceiling is described by taking up a dome-shaped ground tank. However, the prestressed concrete structure of the present invention (the shape of the prestressed concrete structure) Of course, it is not restrained by (). Furthermore, the pre-stress force introduction method may be a pre-tension method or a post-tension method. The same parts as those in FIG. 7 showing the conventional example will be described with the same reference numerals. The illustration of the sheath tube is omitted. Moreover, although the tension material arrange | positioned in the part 22 where member thickness becomes large is demonstrated as a tension material of a perpendicular diagonal direction, it cannot be overemphasized that a tension material of a perpendicular direction may be sufficient.

  FIG. 1 shows a container structure 1 which is a prestressed concrete structure. The container structure 1 includes a bottom slab 3 constructed on the ground, a cylindrical side wall 2 standing on the bottom slab 3, and a dome-shaped ceiling 4 connected to the upper end of the side wall 2. The A ground tank or the like is assumed as the container structure 1 constructed on the ground.

  The side wall 2 is composed of a side wall general portion 21 that extends in a vertical direction from the bottom plate 3 and has a cylindrical shape, and a portion 22 that is integrated with the side wall general portion 21 on the outer periphery of the side wall general portion 21 to increase the member thickness. The The portion 22 in which the member thickness shown in FIG. 1 is increased is formed in a tapered shape that spreads downward in the longitudinal section. Inside the portion 22 where the thickness of the member is increased, a plurality of tension members 51 in a vertically oblique direction are fixed to the bottom plate 3 at one end, and a plurality of tension members 51 are arranged at predetermined intervals in the circumferential direction of the side wall 2. In the illustrated embodiment, the case where the tension material 51 in the vertically oblique direction is disposed from the portion 22 where the member thickness increases to the side wall general portion 21 is shown, but the portion 22 where the member thickness increases. The embodiment in which the tendon material 51 is disposed only inside may be used. Further, circumferential tension members 52, 52,... Are disposed outside the plurality of vertically oblique tension members 51, 51,. In the construction, when the side wall 2 is constructed to an arbitrary level of the portion 22 where the member thickness is increased, a prestress force is introduced into the vertically oblique tension material 51 disposed in the portion 22 where the member thickness is increased. Then I get nervous in the middle. The construction of the side wall 2 above the portion 22 where the member thickness is increased can be performed after the intermediate tension work is completed, and can be performed simultaneously with the intermediate tension work. The prestressing force can be introduced into the circumferential tension members 52, 52,... Before and after the prestressing force is introduced into the vertically oblique tension members 51, 51,. It is possible to wait until construction until later. In addition, although illustration is abbreviate | omitted, the reinforcing material and the tension material are arrange | positioned by the bottom plate 3 and the ceiling 4, and the vertical direction and the circumferential direction reinforcement are made | formed also inside the side wall 2, of course. is there.

  FIG. 2 shows an arrangement form of the tension members 51, 51,... In the vertically oblique direction in FIG. FIG. 2a shows that a PC steel wire or a PC steel wire is used as the tension member 51 in the diagonally diagonal direction, and the PC steel wire or the like bent into a U shape is sequentially arranged in the circumferential direction. An embodiment is shown. FIG. 2b shows an embodiment in which a PC steel rod is used as the tension material 51 in the vertically oblique direction, one end of which is fixed in the bottom plate via a fixing tool, and the other end is a member thickness. Fixing is carried out via a fixing tool at the upper part of the portion 22 where becomes larger. Such tendon may be selected as appropriate in consideration of workability, economy, and the like.

  FIG. 3 shows an embodiment in which a vertical tension member 53 extending from the lower end of the side wall 2 to the vicinity of the upper end of the side wall 2 is also provided in the side wall general portion 21. As shown in FIG. 4, it is preferable that the pitching material 53 in the circumferential direction of the vertical direction is arranged to have a pitch that is appropriately longer than that of the tensioning material 51 in the diagonal direction. In addition, circumferential tension members 52, 52,... Are disposed outside the vertical tension members 53, 53,. 3 and 4 show the case where a PC steel rod is used as the vertical tension member 53 and the vertical diagonal tension member 51, the PC steel wire (or PC steel) is used as the vertical diagonal tension member 51. It is also possible to use a stranded wire) and a combination using a PC steel bar as the tension member 53 in the vertical direction.

  FIG. 5 shows another embodiment of the container structure 1 and is an embodiment in which the longitudinal section of the portion 22 where the member thickness is increased is a smooth curved shape. For example, as shown in FIG. 5, it can be formed to have a longitudinal section that is approximate to a quarter elliptical section cut with a major axis and a minor axis. In addition, although illustration is abbreviate | omitted, in this embodiment, it is also possible to arrange | position the tension | tensile_strength material of the perpendicular direction extended to side wall upper end vicinity in the side wall general part 21. FIG.

  FIG. 6 shows an embodiment in which the portion 22 where the member thickness is increased is formed so as to increase in a multi-stage shape downward, FIG. 6a shows a case of one stage, and FIG. 6b shows a case of two stages. Each case is shown. As shown in FIG. 6b, in the case of constructing a container structure 1 having a multi-stage member portion 22 having two or more stages, the container size is extremely large and the container height is very high. This is particularly effective when the external pressure such as the liquid pressure, the horizontal force during an earthquake, or the wind load becomes extremely large. In addition, the construction of the container structure 1 can be realized more economically by forming the portion 22 where the member thickness is increased into a multi-stage shape of three or more stages according to the further increase in the height of the container structure 1 or the aspect ratio. You can also

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention. For example, in the case where the container structure is a double-shell type cryogenic tank for storing LNG or LPG, the illustrated side wall may be an outer tank, and an inner tank made of a cold insulating material or the like may be provided on the inner side. Furthermore, although not shown in the drawing, a configuration in which a protruding portion that protrudes to the outside is provided in the middle of the side wall as a portion where the member thickness increases can be employed. That is, it is a structure where the protrusion part which the member thickness of the side wall swelled in the middle of the side wall continues in a strip shape in the circumferential direction. In this case, the tension material in the vertically oblique direction can be fixed in the bottom plate at one end and in the protruding portion at the other end. By making the vertical cross-sectional shape below the protrusions into a shape that is in line with the arrangement gradient of the tension material in the vertical oblique direction, the compressive force from the tension material in the vertical oblique direction can be effectively applied to the side wall. it can.

The longitudinal cross-sectional view which showed one Embodiment of the prestressed concrete structure of this invention. FIG. 2 is a side view of the prestressed concrete structure of FIG. 1, and shows a vertical diagonal tension material as a solid line, and (a) is an implementation using a PC steel wire or a PC steel wire as an intermediate tension material. The figure which showed the form. (B) is the figure which showed embodiment using PC steel rod as a tension material which carries out intermediate tension. The longitudinal cross-sectional view which showed other embodiment of the prestressed concrete structure of this invention. It is the side view of the prestressed concrete structure of FIG. 3, Comprising: The figure which showed the tension material of the perpendicular diagonal direction with the continuous line. The longitudinal cross-sectional view which showed other embodiment of the prestressed concrete structure of this invention. It is the longitudinal cross-sectional view which showed other embodiment of the prestressed concrete structure of this invention, (a) is the figure which showed embodiment provided with the part where a material thickness becomes large 1 step | paragraph. (B) is the figure which showed embodiment provided with two steps | paragraphs in which a material thickness becomes large. It is the figure which showed embodiment of the conventional prestressed concrete structure, (a) is a longitudinal section. (B) is the side view of (a), and is the figure which saw through the tendon.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Prestressed concrete structure (container structure), 2 ... Side wall, 3 ... Bottom plate, 4 ... Ceiling, 21 ... General part of side wall, 22 ... Part where member thickness becomes large, 51 ... Intermediate tension material (Tension in the vertical diagonal direction) Material), 52 ... tension material in the circumferential direction, 53 ... tension material in the vertical direction

Claims (1)

In a prestressed concrete structure composed of at least a bottom plate and a side wall standing on the bottom plate,
The side wall has a portion where the member thickness increases from the middle toward the lower outside,
Said member thickness has only been provided in the vertical direction of the intermediate tendons the portion is increased, the intermediate tendons intermediate tension in the portion where the member thickness is large, the construction work of the upper side wall than the intermediate strain levels A prestressed concrete structure which is not affected by the intermediate tension .

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