CONSTRUCTION METHOD FOR DOUBLE-SHELL TANK

Abstract

The construction method for a double-shell tank that includes a support metallic member embedded in an outer tank side wall and a metal roof supported by the support metallic member, comprising: the outer tank side wall formation step for forming the outer tank side wall by installing concrete so that an upper surface of the outer tank side wall is a water guide surface that descends toward an outside of an outer tank; and a metal roof formation step for forming the metal roof connected to the support metallic member.

Description

TECHNICAL FIELD

The present disclosure relates to a construction method for a double-shell tank.

BACKGROUND

For example, as shown in Patent Document 1, in order to store liquefied natural gas (LNG), a double-shell tank including an outer tank mainly made of concrete and a metallic inner tank disposed inside the outer tank is mainly used. Such a technique is disclosed in Patent Documents 2 to 4 as well.

DOCUMENTS OF THE RELATED ART

Patent Document

[Patent Document 1]

Japanese Unexamined Patent Application, First Publication No. 2005-247324

[Patent Document 2]

Japanese Unexamined Patent Application, First Publication No. 2003-292091

[Patent Document 3]

Japanese Unexamined Utility Model Application, First Publication No. S55-041653

[Patent Document 4]

Japanese Unexamined Utility Model Application, First Publication No. H03-084557

SUMMARY

In the case of constructing the above-described double-shell tank, a bottom cold insulating layer or the like which supports the inner tank is formed inside the outer tank. In order to maintain a cold insulation function, the bottom cold insulating layer needs to be prevented from becoming wet due to rainwater. For this reason, when the double-shell tank is constructed, a part of an outer tank ceiling is formed in advance to prevent entering of rainwater into the outer tank and then the bottom cold insulating layer is formed. More specifically, an outer tank side wall having a support metallic member embedded in its top is formed and then a part of the outer tank ceiling is formed in advance by lifting up a metal roof serving as a skeleton portion of the outer tank ceiling by air raising or the like and fixing the metal roof to the support metallic member.

However, the top of the outer tank side wall is exposed for several months until concrete is installed above the metal roof serving as the skeleton portion of the outer tank ceiling. For this reason, rainwater enters at a boundary between a concrete portion of the outer tank side wall and the embedded support metallic member and intrudes to an inner surface of the outer tank side wall in some cases. In this case, it is necessary to separately perform countermeasures or the like to prevent the bottom cold insulating layer or the like from getting wet, which causes prolonging or the like of construction or the like.

The present disclosure was made in view of the above-described problems, and an object thereof is to provide a construction method for a double-shell tank that includes an outer tank made of concrete for the purpose of preventing rainwater from intruding to an inner surface of an outer tank side wall before concrete is installed above a metal roof serving as a skeleton portion of an outer tank.

The present disclosure employs the following constitution as a means for solving the above-described problems.

The present disclosure is a construction method for a double-shell tank that includes a support metallic member embedded in an inner surface of an outer tank side wall made of concrete in a state where a part of the support metallic member is exposed and a metal roof supported by the support metallic member and forming a lower layer of an outer tank ceiling, the construction method for a double-shell tank including: an outer tank side wall formation step for forming the outer tank side wall by installing concrete so that an upper surface of the outer tank side wall is a water guide surface that descends toward an outside of an outer tank in a state where the outer tank side wall takes the support metallic member therein; and a metal roof formation step for forming the metal roof connected to the support metallic member.

According to the present disclosure, an upper surface of an outer tank side wall is a water guide surface which descends toward an outside of an outer tank. For this reason, rainwater pouring down on an upper surface of the outer tank side wall is drained from the outer tank side wall toward the outside of the outer tank side wall along a water guide surface. For this reason, a large amount of rainwater does not accumulate on the upper surface of the outer tank side wall and rainwater can be prevented from entering at a boundary between a support metallic member embedded in the outer tank side wall and a concrete portion near the support metallic member. Therefore, according to the present disclosure, rainwater can be prevented from intruding to an inner surface of an outer tank side wall before concrete is installed above a metal roof serving as a skeleton portion of an outer tank through a construction method for a double-shell tank including an outer tank made of concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing a schematic constitution of a double-shell tank constructed by a construction method for the double-shell tank according to an embodiment of the present disclosure.

FIG. 2 is an enlarged view of a region A in FIG. 1.

FIG. 3 is a schematic diagram for explaining steps of a construction method for the double-shell tank according to the embodiment of the present disclosure, showing a state where reinforcing bars are assembled therein.

FIG. 4 is a schematic diagram for explaining steps of the construction method for the double-shell tank according to the embodiment of the present disclosure, showing a state where an inner frame and an outer frame are installed.

FIG. 5 is a schematic diagram for explaining steps of the construction method for the double-shell tank according to the embodiment of the present disclosure, showing a state where concrete is installed between an inner frame and an outer frame.

FIG. 6 is a schematic diagram for explaining steps of the construction method for the double-shell tank according to the embodiment of the present disclosure, showing a state where a metal roof is installed.

DETAILED DESCRIPTION

An embodiment of a construction method for a double-shell tank according to the present disclosure will be described below with reference to the drawings. It should be noted that the scale of members may have been appropriately changed to make the members have recognizable sizes in the following drawings.

FIG. 1 is a longitudinal cross-sectional view showing a schematic constitution of a double-shell tank 1 constructed by the construction method for a double-shell tank in this embodiment. As shown in the drawing, the double-shell tank 1 in the embodiment is a pre-stressed concrete (PC) type tank including a basement floor slab 2, an outer tank 3, a bottom cold insulating layer 4, an inner tank 5, a side cold insulating layer 6, a suspended deck 7, hangers 8, retaining walls 9, and an upper cold insulating layer 10.

The basement floor slab 2 is a member serving as a foundation which supports the outer tank 3, the inner tank 5, or the like from below and is formed in a substantially disk shape with a larger diameter than the outer tank 3 when viewed from above. The basement floor slab 2 has a heater (not shown) installed therein and prevents cold heat of stored liquefied natural gas (LNG) from being transferred to the ground. The outer tank 3 is a container made of pre-stressed concrete and is erected on the basement floor slab 2 to cover the inner tank 5. The outer tank 3 is mainly made of concrete and includes a cylindrical outer tank side wall 3a and an outer tank ceiling 3b connected to an upper edge of the outer tank side wall 3a.

FIG. 2 is a schematic enlarged cross-sectional view of a connection portion (region A in FIG. 1) between the outer tank side wall 3a and the outer tank ceiling 3b. As shown in the drawing, the outer tank side wall 3a includes reinforcing bars 3a2 embedded in a concrete layer 3a1, a support metallic member 3a3 embedded in an inner surface of the outer tank side wall 3a such that a part of the support metallic member is exposed, and a water cut-off member 3a4 disposed in a boundary between the support metallic member 3a3 and the concrete layer 3a1. It should be noted that, although not shown in FIGS. 1 and 2, a sheath pipe for applying pre-stress is also installed on the outer tank side wall 3a.

A plurality of reinforcing bars 3a2 are erected from the basement floor slab 2 and are disposed over the entire region in a height direction of the outer tank side wall 3a. The plurality of reinforcing bars 3a2 are strength members which support the concrete layer 3a1 and are skeleton portions of the outer tank side wall 3a. The support metallic member 3a3 is a substantially annular member which is embedded in a top of the outer tank side wall 3a so that an inner surface thereof is flush with an inner surface of the concrete layer 3a1 (that is, an inner surface of the outer tank side wall 3a). The support metallic member 3a3 is partially connected to the reinforcing bars 3a2. The support metallic member 3a3 is a portion to which a metal roof 3b1 (which will be described later) of the outer tank ceiling 3b is connected. The water cut-off member 3a4 is a member which prevents rainwater from entering at the boundary between the concrete layer 3a1 and the support metallic member 3a3 during construction of the double-shell tank 1. Examples of the water cut-off member 3a4 can include a water-swelling water cut-off member which swells when it absorbs water.

The outer tank ceiling 3b includes the metal roof 3b1 and a concrete layer 3b2. The metal roof 3b1 is a steel framework member which forms a lower layer of the outer tank ceiling 3b, and includes a shoulder 3b3 and a central portion 3b4 as shown in FIG. 2. The shoulder 3b3 is an outer circumferential edge of the metal roof 3b1, and is welded to the support metallic member 3a3. The shoulder 3b3 includes a lower portion 3b5 and an upper portion 3b6. The lower portion 3b5 is concentric with the support metallic member 3a3a, has the same diameter as the support metallic member 3a3, and is directly joined to the support metallic member 3a3. The upper portion 3b6 is supported by the lower portion 3b5 from below, and protrudes further outside in a radial direction of the outer tank 3 than the lower portion 3b5. The central portion 3b4 is welded to the upper portion 3b6 of the shoulder 3b3. The concrete layer 3b2 is supported by the metal roof 3b1 from below, is connected to the concrete layer 3a1 of the outer tank side wall 3a, and forms an upper layer of the outer tank ceiling 3b.

Referring to FIG. 1 again, the bottom cold insulating layer 4 is placed on an upper surface of the basement floor slab 2 and supports the inner tank 5 from below. The bottom cold insulating layer 4 is formed in a substantially disk shape with a smaller diameter than the basement floor slab 2 and is disposed coaxially with the basement floor slab 2 when viewed from above. The bottom cold insulating layer 4 is made of, for example, perlite concrete, sand, and the like. The inner tank 5 is a metallic container placed on the bottom cold insulating layer 4 and has a bottomed cylindrical shape with its upper end being an opening end. LNG is stored inside the inner tank 5. The inner tank 5 includes an inner tank bottom 5a and an inner tank side wall 5b erected on an edge of the inner tank bottom 5a.

The side cold insulating layer 6 is disposed between the outer tank side wall 3a and the inner tank side wall 5b and is formed from granular perlite filled therebetween. Furthermore, as shown in FIG. 1, the side cold insulating layer 6 is formed up to an upper portion of the inner tank 5 and is disposed such that a portion up to an upper portion of an outer circumferential portion of the suspended deck 7 is filled with granular perlite through the retaining wall 9 formed on an upper portion of the suspended deck 7 and supporting the side cold insulating layer 6 from a side thereof.

The suspended deck 7 is a disk-shaped metallic member which is suspended and supported by the hangers 8 to block an upper end of the inner tank 5 which is an opening end from above. Each of the hangers 8 has an upper end fixed to the outer tank ceiling 3b and a lower end fixed to the suspended deck 7. As shown in FIG. 1, the hangers 8 are disposed between the outer tank ceilings 3b and the suspended deck 7 and suspend and support the suspended deck 7.

The retaining wall 9 is disposed in a substantially cylindrical shape along an outer edge of the suspended deck 7 and is formed from the outer tank ceiling 3b to the suspended deck 7. The retaining wall 9 prevents the side cold insulating layer 6 made of granular perlite from entering above the suspended deck 7 (inside the tank). The upper cold insulating layer 10 is placed on an upper surface of the suspended deck 7 and is disposed inside the retaining wall 9. The upper cold insulating layer 10 is formed of a polyurethane foam or the like.

Subsequently, the construction method for the double-shell tank 1 according to the embodiment will be described with reference to FIGS. 3 to 6. It should be noted that, in the following description, it is assumed that the basement floor slab 2 has already been formed.

First, as shown in FIG. 3, the reinforcing bars 3a2 are assembled and the support metallic member 3a3 to which the water cut-off member 3a4 is adhered is attached to one of the assembled reinforcing bars 3a2. Subsequently, as shown in FIG. 4, an outer frame K1 and an inner frame K2 are installed to sandwich the assembled reinforcing bars 3a2. In other words, the outer frame K1 is disposed on an outer side of a formation region of the outer tank side wall 3a and the inner frame K2 is disposed on an inner side of the formation region of the outer tank side wall 3a. Here, the inner frame K2 is disposed to be in contact with the support metallic member 3a3 from an inner side of an outer tank formation side region, and a height of the inner frame K2 is set such that an upper end of the inner frame K2 and a top of the support metallic member 3a3 are at the same position. Furthermore, a height of the outer frame K1 is set such that an upper end of the outer frame K1 is lower than an upper end of the inner frame K2.

Subsequently, as shown in FIG. 5, concrete is installed between the outer frame K1 and the inner frame K2. At this time, a water guide surface 3a5 formed as an inclined surface is formed on an upper surface of a portion made of concrete installed such that the concrete connects an upper end of the inner frame K2 (that is, a top of the support metallic member 3a3) and an upper end of the outer frame K1. The water guide surface 3a5 is the inclined surface which descends toward an outside in a radial direction of the outer tank side wall 3a.

Through the steps shown in FIGS. 3 to 5, the outer tank side wall 3a having an upper surface which is the inclined surface formed as the water guide surface 3a5 is formed in a state where the outer tank side wall 3a takes the support metallic member 3a3 therein. In other words, the steps shown in FIGS. 3 to 5 correspond to an outer tank side wall formation step in the present disclosure.

Subsequently, as shown in FIG. 6, the outer frame K1 and the inner frame K2 are removed and the metal roof 3b1 is connected to the support metallic member 3a3. Here, first, the shoulder 3b3 of the metal roof 3b1 is welded to the support metallic member 3a3. In addition, the central portion 3b4 of the metal roof 3b1 is formed on an inside of the outer tank side wall 3a and the formed central portion 3b4 is lifted up and welded to the shoulder 3b3. Through the step shown in FIG. 6, the metal roof 3b1 is connected to the support metallic member 3a3. In other words, the step shown in FIG. 6 corresponds to a metal roof formation step in the present disclosure.

As shown in FIG. 6, when the metal roof 3b1 is connected to the support metallic member 3a3, a space surrounded by the outer tank side wall 3a is covered with the metal roof 3b1. In this way, the bottom cold insulating layer 4, the inner tank 5, the side cold insulating layer 6, the suspended deck 7, the hangers 8, the retaining wall 9, and the upper cold insulating layer 10 are formed in the space covered with the metal roof 3b1. Concrete is installed on an upper portion of the metal roof 3b1 after or in parallel with the work in the space covered with the metal roof 3b1 and thus the concrete layer 3b2 of the outer tank ceiling 3b is formed. The double-shell tank 1 is completed by performing pipe installation work or the like in addition to the above steps.

Here, according to the construction method for the double-shell tank 1 in the embodiment, an upper surface of the outer tank side wall 3a is the water guide surface 3a5 which descends toward the outside in the radial direction of the outer tank 3 until the concrete layer 3b2 is formed above the metal roof 3b1. Rainwater pouring down on the upper surface of the outer tank side wall 3a drains from the outer tank side wall 3a toward the outside of the outer tank side wall 3a along the water guide surface 3a5. For this reason, a large amount of rainwater does not accumulate on the upper surface of the outer tank side wall 3a and rainwater can be prevented from entering at a boundary between the support metallic member 3a3 embedded in the outer tank side wall 3a and the concrete layer 3a1 near the support metallic member 3a3. Therefore, according to the double-shell tank 1 in the embodiment, rainwater can be prevented from intruding to an inner surface of the outer tank side wall 3a before concrete is installed above the metal roof 3b1 serving as a skeleton portion of the outer tank 3.

Also, in the construction method for the double-shell tank 1 according to the embodiment, the water guide surface 3a5 is formed as an inclined surface which descends toward the outside of the outer tank 3. For this reason, rainwater can be reliably guided toward the outside of the outer tank side wall 3a in the entire region of the upper surface of the outer tank side wall 3a. Therefore, according to the construction method for the double-shell tank 1 in the embodiment, rainwater can be more reliably prevented from entering at the boundary between the support metallic member 3a3 and the concrete layer 3a1 near the support metallic member 3a3.

In the construction method for the double-shell tank 1 according to the embodiment, in the outer tank side wall formation step, the inner frame K2 which is brought into contact with the support metallic member 3a3 from an inside of an outer tank side wall formation region and the outer frame K1 which is disposed on an outside of the outer tank side wall formation region and has an upper end lower than an upper end of the support metallic member 3a3 are positioned and concrete is installed between the outer frame K1 and the inner frame K2. For this reason, since the upper end of the support metallic member 3a3 and the upper end of the outer frame K1 are used as references and an inclined surface connecting these upper ends is formed, the water guide surface 3a5 can be easily formed. Therefore, the water guide surface 3a5 with a uniform inclination can be formed over the entire circumference of the outer tank side wall 3a.

In the construction method for the double-shell tank 1 according to the embodiment, in the outer tank side wall formation step, concrete is installed after the water cut-off member 3a4 is adhered to the support metallic member 3a3. For this reason, the water cut-off member 3a4 can be easily disposed in the boundary between the support metallic member 3a3 and the concrete layer 3a1. Since the water cut-off member 3a4 is provided, rainwater can be prevented from intruding to the inner surface of the outer tank side wall 3a even when rainwater enters at the boundary between the support metallic member 3a3 and the concrete layer 3a1 near the support metallic member 3a3.

Also, in the construction method for the double-shell tank 1 according to the embodiment, the upper portion 3b6 of the shoulder 3b3 in the metal roof 3b1 protrudes outward from the lower portion 3b5. For this reason, rainwater falling on the metal roof 3b1 can be prevented from falling to the vicinity of the support metallic member 3a3 along the lower portion 3b5. Therefore, rainwater can be more reliably prevented from entering at the boundary between the support metallic member 3a3 and the concrete layer 3a1 near the support metallic member 3a3.

While the preferred embodiments of the present disclosure have been described above with reference to the drawings, the present disclosure is not limited to the above-described embodiments. The shapes, combinations, or the like of the constituent elements shown in the above-described embodiments are merely examples and various modifications are possible on the basis of design requirements or the like without departing from the gist of the present disclosure.

For example, a constitution in which the water guide surface 3a5 is an inclined surface has been described in the above-described embodiments. However, the present disclosure is not limited thereto and a constitution in which the water guide surface 3a5 is a stepped surface which gradually descends toward the outside of the outer tank side wall 3a can also be adopted. It is possible to prevent rainwater falling on a region of the upper surface in the outer tank side wall 3a close to the outer side from flowing in a direction toward the support metallic member 3a3 disposed close to the inner side, and It is possible to prevent rainwater from entering at the boundary between the support metallic member 3a3 and the concrete layer 3a1 near the support metallic member 3a3 even when such a constitution is adopted. Furthermore, a constitution in which the water guide surface 3a5 is configured to have a shape obtained by combining an inclined surface, a stepped surface, and the like can also be adopted.

A constitution in which a guide groove is formed in the water guide surface 3a5 can also be adopted in the above-described embodiment. When this constitution is adopted, a flow of rainwater can be more reliably guided due to the guide groove, and for example, rainwater can be intensively drained from a desired portion.

A constitution in which the water guide surface 3a5 is formed by disposing the outer frame K1 having the upper end lower than the upper end of the support metallic member 3a3 and using the upper end of the support metallic member 3a3 and the upper end of the outer frame K1 so as to form the inclined surface connecting these upper ends has been described in the embodiment. However, the present disclosure is not limited thereto and a constitution in which heights of the outer frame K1 and the inner frame K2 are the same and the inclined surface is formed by another method may be adopted.

Also, a constitution in which the water cut-off member 3a4 is adhered to the support metallic member 3a3 in advance before concrete is installed has been described in the embodiment. However, the present disclosure is not limited thereto and a constitution in which the water cut-off member 3a4 is not provided, a constitution in which the water cut-off member 3a4 is provided at another location after concrete is installed, and the like can also be adopted.

INDUSTRIAL APPLICABILITY

According to the present disclosure, rainwater can be prevented from intruding to an inner surface of an outer tank side wall before concrete is installed above a metal roof serving as a skeleton portion of an outer tank.

Claims

1. A construction method for a double-shell tank that includes a support metallic member embedded in an inner surface of an outer tank side wall made of concrete in a state where a part of the support metallic member is exposed and a metal roof supported by the support metallic member and forming a lower layer of an outer tank ceiling, the construction method for a double-shell tank comprising: an outer tank side wall formation step for forming the outer tank side wall by installing concrete so that an upper surface of the outer tank side wall is a water guide surface that descends toward an outside of an outer tank in a state where the outer tank side wall takes the support metallic member therein; anda metal roof formation step for forming the metal roof connected to the support metallic member.

2. The construction method for a double-shell tank according to claim 1, wherein the water guide surface is an inclined surface that descends toward the outside of the outer tank.

3. The construction method for a double-shell tank according to claim 1, wherein, in the outer tank side wall formation step, an inner frame which is brought into contact with the support metallic member from an inside of an outer tank side wall formation region and an outer frame which is disposed on an outside of the outer tank side wall formation region and has an upper end lower than an upper end of the support metallic member are positioned and concrete is installed between the inner frame and the outer frame.

4. The construction method for a double-shell tank according to claim 2, wherein, in the outer tank side wall formation step, an inner frame which is brought into contact with the support metallic member from an inside of an outer tank side wall formation region and an outer frame which is disposed on an outside of an outer tank side wall formation region and has an upper end lower than an upper end of the support metallic member are positioned and concrete is installed between the inner frame and the outer frame.

5. The construction method for a double-shell tank according to claim 1, wherein, in the outer tank side wall formation step, concrete is installed after a water cut-off member is adhered to the support metallic member.

6. The construction method for a double-shell tank according to claim 2, wherein, in the outer tank side wall formation step, concrete is installed after a water cut-off member is adhered to the support metallic member.

7. The construction method for a double-shell tank according to claim 3, wherein, in the outer tank side wall formation step, concrete is installed after a water cut-off member is adhered to the support metallic member.

8. The construction method for a double-shell tank according to claim 4, wherein, in the outer tank side wall formation step, concrete is installed after a water cut-off member is adhered to the support metallic member.