Ground-type rectangular steel water tank and reinforcing method therefor

Abstract

To provide a ground-type rectangular steel water tank that can suppress buckling of internal reinforcement materials and deformation of partition plates in the event of a major earthquake.SOLUTION: In a ground-type rectangular steel water tank 1 having a partition plate 7 that divides the water tank, a cable 11a is installed to support the partition plate 7 and to resist tension but not compression.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an above-ground rectangular steel water tank used as a water distribution reservoir, a water storage tank, etc., and a method for reinforcing the same. [Background technology]

[0002] A distribution reservoir is a purified water storage tank that receives water from a water purification plant and distributes it according to the demand in the distribution area, and has the function of adjusting the time fluctuation of the water distribution amount as well as storing water in emergencies such as earthquakes. Although not as large as a distribution reservoir, water tanks with the same function as a distribution reservoir are also installed in large buildings such as hospitals, schools and apartment buildings.

[0003] From the viewpoint of efficient use of land and ease of maintenance, above-ground rectangular steel tanks (mainly made of stainless steel) are widely used as distribution reservoirs and storage tanks. Above-ground rectangular steel tanks are equipped with a bottom plate, side plates, and a roof plate, and are formed in a rectangular shape when viewed from above. In consideration of maintenance, the tanks are often made into a two-tank structure, and a partition plate is installed to separate the tanks.

[0004] Aboveground rectangular steel tanks can be broadly classified into (1) panel tanks and (2) integral steel tanks. The former (1) panel tanks are constructed by bonding together multiple press-formed thin plate panels. Due to their thin side panels and low rigidity, numerous earthquake damages have been reported in recent years due to the action of additional hydrodynamic pressure caused by the bulging phenomenon (coupled vibration of the side panels, partition panels, and the water inside), prompting a review of design guidelines. Rectangular tanks differ from cylindrical tanks in that not only do seismic loads vary depending on the direction of the seismic wave, but also in that one side or partition panel bears the hydrodynamic pressure acting in one direction. Therefore, they typically use internal reinforcement (also known as braces, which comprise horizontal and diagonal members) to transfer stress to the opposite side or partition panel (see Patent Document 1). Internal reinforcement materials include stainless steel flat plates and L-shaped steel beams.

[0005] The latter (2) one-piece steel tank uses reinforcing steel plates (thick plates) shaped like steel sheet piles for the side plates, and has the characteristic of having higher side plate rigidity than the above-mentioned (1) panel tank and being less susceptible to the effects of bulging. In (2) one-piece steel tanks, it is standard practice to connect the opposing side plates and partition plate with internal reinforcement (see Non-Patent Document 1). The internal reinforcement is made of stainless steel flat plates, shaped steel, or other steel materials, and is welded to a flange material called an intermediate reinforcement band. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-362682 [Non-patent literature]

[0007] [Non-Patent Document 1] Design Guidelines for Stainless Steel Rectangular Water Reservoirs WSP 073-2010 Established March 25, 2010 Published by the Japan Water Pipe Association Summary of the Invention [Problem to be solved by the invention]

[0008] Above-ground rectangular steel water tanks are required to be able to store water even during a major earthquake. However, in conventional (1) panel tanks, water leakage damage often occurs during a major earthquake due to deformation of the side plates and partition plates and fracture of welds. Because dynamic water pressure during an earthquake is alternately loaded on the side plates and partition plates, the internal reinforcement is also subjected to alternating tension and compression loads. Water leakage damage is thought to be caused by deformation of the side plates and partition plates and buckling of the internal reinforcement. Recent research has also pointed out that the impact of bulging is greater on partition plates than on side plates.

[0009] (2) Although there have been far fewer earthquake damage cases for steel monolithic tanks compared to panel tanks (1), buckling of the internal reinforcement has also occurred. It is believed that the internal reinforcement was subjected to alternating tension and compression due to the dynamic water pressure during an earthquake that acted alternately on the side plates and partition plates, and that the members with lower load-bearing capacity buckled due to the forced displacement in the compressive direction.

[0010] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an above-ground rectangular steel water tank that can suppress buckling of internal reinforcement materials and deformation of partition plates in the event of a major earthquake. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, one aspect of the present invention is an above-ground rectangular steel tank having a partition plate that separates the tank, characterized in that a cable is installed to support the partition plate and provide resistance to tension but not resistance to compression.

[0012] Another aspect of the present invention is a method for reinforcing an above-ground rectangular steel tank equipped with partition plates that separate the tank, characterized by installing cables that support the partition plates and provide resistance to tension but not compression. [Effects of the Invention]

[0013] According to the present invention, the cable that supports the partition plate and resists tension but not compression can be installed, preventing the internal reinforcement from buckling in the event of a major earthquake. Furthermore, the partition plate can be restrained by the tension force of the cable, suppressing deformation of the partition plate. Furthermore, since buckling of the internal reinforcement can be avoided, there is no need to replace the internal reinforcement after an earthquake, making maintenance easier. [Brief explanation of the drawings]

[0014] [Figure 1] This is a photograph of the exterior of a conventional above-ground rectangular steel tank (integrated steel tank). [Figure 2] FIG. 1 is a plan view of a conventional above-ground rectangular steel water tank. [Figure 3] FIG. 1 is a side view of a conventional above-ground rectangular steel water tank. [Figure 4] This is a horizontal cross-sectional view of a conventional above-ground rectangular steel water tank (showing the internal reinforcement material in the lower section). [Figure 5] This is a horizontal cross-sectional view of a conventional above-ground rectangular steel water tank (showing the internal reinforcement material in the upper section). [Figure 6] FIG. 1 is a perspective view of a side panel of a conventional above-ground rectangular steel water tank. [Figure 7] This is a schematic diagram of a conventional two-tank above-ground rectangular steel tank with a partition plate installed in the center. [Figure 8] FIG. 10 is a diagram showing the results of a time history response analysis of the lower internal reinforcement in a conventional above-ground rectangular steel water tank. [Figure 9] FIG. 10 is a diagram showing the results of a time history response analysis of the upper internal reinforcement of a conventional above-ground rectangular steel water tank. [Figure 10] 1 is a horizontal cross-sectional view (showing the diagonal members of the lower internal reinforcing members) of an above-ground rectangular steel water tank (integrated steel tank) according to a first embodiment of the present invention. FIG. [Figure 11] This is a photograph of the appearance of a flexible cable. [Figure 12] FIG. 10 is a vertical cross-sectional view of an above-ground rectangular steel water tank (panel tank) according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an above-ground rectangular steel water tank according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the above-ground rectangular steel water tank according to the present invention can be embodied in various forms and is not limited to the embodiments described in the specification. The present embodiment is provided with the intention that those skilled in the art will be able to fully understand the invention by fully disclosing the specification. (Basic structure of a conventional above-ground rectangular steel tank (integrated steel tank))

[0016] Fig. 1 shows a photograph of the exterior of a conventional above-ground rectangular steel water tank 1. Fig. 2 is a plan view of the above-ground rectangular steel water tank, Fig. 3 is a side view, Fig. 4 is a horizontal cross-sectional view (showing the lower internal reinforcement), and Fig. 5 is a horizontal cross-sectional view (showing the upper internal reinforcement). As will be described later, the basic structure of the above-ground rectangular steel water tank (integrated steel tank) of the first embodiment of the present invention is substantially the same as the conventional above-ground rectangular steel water tank 1 (integrated steel tank) shown in Figs. 1 to 5.

[0017] As shown in Figure 1, the above-ground rectangular steel tank 1 is an integral steel tank with a rectangular shape, and its main structural members are a bottom plate 2, annular plate 3, side plates 4, intermediate reinforcing strips 5a and 5b, roof plate 6, partition plate 7 (see Figure 2), and internal reinforcing members (horizontal members 8 and diagonal members 9 (see Figures 4 and 5)). These main structural members are standardized in the Design Guidelines for Stainless Steel Rectangular Water Reservoirs (WSP 073-2010, established March 25, 2010, Japan Water Steel Pipe Association).

[0018] The bottom plate 2 is installed on the foundation to stop water leakage. The annular plate 3 resists the load generated at the lowest part of the side plate 4 under normal conditions and during earthquakes.

[0019] The side plates 4 are erected on the periphery of the bottom plate 2. As shown in Figure 6, the side plates 4b(4) are made of reinforcing steel plates (thick plates) shaped like steel sheet piles. The side plates 4 may also be made flat and reinforced with side plate reinforcing materials (not shown). As shown in Figure 1, the side plates 4 are made up of multiple tiers of side plates 4a, 4b, and 4c stacked one on top of the other.

[0020] The intermediate reinforcing strips 5a and 5b are flange-shaped members. Internal reinforcing members (horizontal members 8 and diagonal members 9 (see Figures 4 and 5)) for reinforcing the side panels 4 are attached to the intermediate reinforcing strips 5a and 5b. The intermediate reinforcing strip 5a is arranged between the upper side panel 4a and the middle side panel 4b. The intermediate reinforcing strip 5b is arranged between the middle side panel 4b and the lower side panel 4c.

[0021] The roof plate 6 is placed over the side plate 4. The roof plate 6 is installed for the purpose of maintaining the quality of the stored water.

[0022] Partition plate 7 is provided to separate above-ground rectangular steel tank 1. In many cases, above-ground rectangular steel tank 1 has a two-tank structure for ease of maintenance.

[0023] Figure 4 shows the internal reinforcement members (horizontal members 8, diagonal members 9) attached to the lower intermediate reinforcement band 5b. The internal reinforcement members are made of steel materials such as shaped steel, and are members that reinforce the side plates 4-1, 4-2 and the partition plate 7 against the water pressure acting on them, and are placed on the horizontal plane where the intermediate reinforcement band 5b is placed.

[0024] The internal reinforcement members can be broadly divided into two types: horizontal members 8 and diagonal members 9. In the left-hand water tank, which is separated by partition plate 7, horizontal member 8a connects the opposing side panel 4-1 (intermediate reinforcement band 5b) to the partition plate 7, and horizontal member 8b connects the opposing side panel 4-2 (intermediate reinforcement band 5b) to the opposing side panel 4-2 (intermediate reinforcement band 5b). The horizontal members 8a and 8b are placed in a grid pattern across the side panels 4-1 and 4-2 and the partition plate 7, mainly for the purpose of resisting static water pressure at all times. Support columns 10 that support the load from the roof panel 6 are placed at the intersections of the vertical and horizontal horizontal members 8a and 8b. The same is true for the right-hand water tank, which is separated by partition plate 7.

[0025] Diagonal member 9 is attached diagonally to the lattice of horizontal members 8a and 8b to resist horizontal loads during earthquakes. In the left-hand tank, diagonal member 9a connects adjacent side panels 4-1 and 4-2 at a 90-degree angle. Diagonal member 9b connects adjacent side panel 4-2 and partition panel 7 at a 90-degree angle. In the right-hand tank, diagonal member 9c connects adjacent partition panel 7 and side panel 4-2 at a 90-degree angle. Diagonal member 9d connects adjacent side panels 4-1 and 4-2 at a 90-degree angle.

[0026] Figure 5 shows the internal reinforcement members (mainly horizontal members 8) attached to the upper intermediate reinforcement band 5a. The horizontal members 8 are placed on the horizontal plane where the intermediate reinforcement band 5a is placed. In the left-hand tank, which is separated by the partition plate 7, the horizontal member 8a connects the opposing side panel 4-1 to the partition plate 7. The horizontal member 8b connects the opposing side panel 4-2 to the opposing side panel 4-2. The horizontal members 8a and 8b are placed in a grid pattern across the side panels 4-1 and 4-2 and the partition plate 7, mainly for the purpose of resisting static water pressure at all times. Support columns 10 that support the load from the roof panel 6 are placed at the intersections of the vertical and horizontal horizontal members 8a and 8b. The same applies to the right-hand tank, which is separated by the partition plate 7.

[0027] Figure 7 shows a schematic diagram of a two-tank aboveground steel rectangular water tank 1 with a partition plate 7 installed in the center. At a certain moment during an earthquake, each side plate 4-1 and the partition plate 7 are subjected to a static water pressure P0 and a dynamic water pressure P k As a result, the left side panel 4-1 is subjected to a reduced dynamic water pressure P0-P k However, on the right side panel 4-1, the total of the hydrostatic pressure and the hydrodynamic pressure, P0+P k In addition, the static water pressure from both sides is offset on the central partition plate 7, and the dynamic water pressure during an earthquake is amplified to 2P k These loads act in opposite directions in the next cycle, so the internal reinforcement (horizontal member 8, diagonal member 9) is subjected to alternating compressive and tensile loads. (Analysis of a conventional above-ground rectangular steel tank (integrated steel tank))

[0028] Regarding the seismic design method for above-ground steel rectangular water tanks1, there is a need to move from the conventional seismic intensity method (or horizontal earthquake resistance method) to a limit state design method that includes dynamic analysis (Guidelines for Earthquake-Resistant Construction Methods for Water Supply Facilities, Commentary 2022 Edition, Japan Water Works Association).

[0029] According to the results of the FEM analysis of the conventional above-ground rectangular steel tank 1, the mechanism of earthquake damage in the above-ground rectangular steel tank 1 is as follows: (1) Dynamic water pressure during an earthquake acts on the side plates 4-1 and 4-2 and the partition plate 7 (alternate loading) ⇒ (2) deformation of the side plates 4-1 and 4-2 and the partition plate 7 (if this is large, the dynamic water pressure is amplified by the bulging phenomenon) ⇒ (3) the side plates 4-1 and 4-2 and the partition plate 7 are restrained. It can be inferred that the following occurs: alternating compression / tension deformation of the internal reinforcement members (horizontal members 8, diagonal members 9) ⇒ (4) compressive buckling of the internal reinforcement members (horizontal members 8, diagonal members 9) ⇒ (5) relaxation of constraints on intermediate reinforcement bands 5a, 5b, side plates 4-1, 4-2, and partition plate 7 ⇒ (6) increased displacement of side plates 4-1, 4-2, and partition plate 7 ⇒ (7) buckling of side plates 4-1, 4-2, and partition plate 7 ⇒ (8) cracks occur ⇒ (9) water leakage occurs. Therefore, of the main structural members used in above-ground rectangular steel water tank 1, the internal reinforcement members (horizontal members 8, diagonal members 9) will be damaged at the earliest stage.

[0030] Figure 8 shows the results of a time history response analysis of the lower internal reinforcement (horizontal member 8, diagonal member 9). Figure 8 shows a contour diagram of the minimum principal stress (maximum compressive stress) of the internal reinforcement (horizontal member 8, diagonal member 9) at a time of 5.5 seconds. In Figure 8, the deformation magnification has been set to 3 times to make the deformation of the internal reinforcement (horizontal member 8, diagonal member 9) easier to understand. The internal reinforcement (horizontal member 8, diagonal member 9) used in the analysis is steel material such as stainless steel flat plate and shaped steel.

[0031] According to the results of the time-history response analysis shown in Figure 8, the left-side side panel 4-1 deforms outward (leftward), the right-side side panel 4-1 deforms inward (leftward), and the partition panel 7 deforms leftward. This causes tension on diagonal member 9a, compression on diagonal member 9b, tension on diagonal member 9c, and compression on diagonal member 9d. Because diagonal members 9a-9d transmit the dynamic water pressure received by the pressure-receiving surface to the perpendicular surface, they are effective against dynamic water pressure. However, diagonal members 9b and 9d on the compression side buckle. In reality, seismic loads are applied in both directions, so almost all diagonal members 9a-9d buckle. When diagonal members 9a-9d buckle, the compressive support capacity of the compression side, which was anticipated at the time of design, is reduced by buckling. On the other hand, horizontal member 8 is not subject to compressive forces strong enough to buckle during an earthquake, so it is less likely to buckle.

[0032] Figure 9 shows the results of a time history response analysis of the upper internal reinforcement (mainly horizontal member 8). As shown in Figure 9, horizontal member 8 deforms in the same way as the opposite side panel 4-1, and does not resist dynamic water pressure. Horizontal member 8 does not receive a compressive force strong enough to buckle during an earthquake. (First embodiment of the above-ground rectangular steel water tank (integrated steel tank) of the present invention)

[0033] The basic structure of the above-ground rectangular steel tank (integrated steel tank) according to the first embodiment of the present invention is substantially the same as that of the conventional above-ground rectangular steel tank 1 (integrated steel tank) shown in Figures 1 to 5, and includes as its main structural members a bottom plate 2, annular plates 3, side plates 4, intermediate reinforcement bands 5a, 5b, roof plate 6, partition plate 7, and internal reinforcement members (horizontal members 8, diagonal members 9). The above-ground rectangular steel tank according to the first embodiment of the present invention differs from the conventional above-ground rectangular steel tank 1 in that it uses cables 11a, 11b as at least part of the internal reinforcement members. However, the other components are the same as those of the conventional above-ground rectangular steel tank 1, and therefore the same reference numerals will be used hereinafter and detailed description thereof will be omitted.

[0034] In the above-ground rectangular steel water tank 1 of this embodiment, as shown in FIG. 10, cable 11a is installed as at least part of the internal reinforcement, supporting the partition plate 7 and providing resistance to tension but not compression. Cable 11b is also installed as at least part of the internal reinforcement, supporting the side plate 4 and providing resistance to tension but not compression. Cable 11a connects the adjacent partition plate 7 and side plate 4-2 at a 90-degree angle. Cable 11b connects the adjacent side plate 4-1 and side plate 4-2 at a 90-degree angle. Cables 11a and 11b may be installed as at least part of the internal reinforcement, or may be installed in addition to the internal reinforcement.

[0035] By installing the cables 11a and 11b, it is possible to prevent the cables 11a and 11b from buckling in the event of a major earthquake. The tensile force of the cables 11a and 11b can restrain the partition plate 7 and the side plates 4-1 and 4-2, thereby suppressing deformation of the partition plate 7 and the side plates 4-1 and 4-2.

[0036] It is desirable to install the cables 11a on both sides of the partition plate 7. In this way, when the partition plate 7 is deformed to the left, the partition plate 7 can be restrained by the tensile force of the cable 11a on the right side, and when the partition plate 7 is deformed to the right, the partition plate 7 can be restrained by the tensile force of the cable 11a on the left side.

[0037] As mentioned above, the diagonal members 9b and 9c that support the partition plate 7 are prone to buckling, so it is desirable that at least some of the diagonal members 9b and 9c are cables 11a. If all of the diagonal members 9b and 9c are cables 11a, it is possible to reduce on-site welding during construction and significantly reduce the cost of replacing internal reinforcement members in the event of an earthquake.

[0038] On the other hand, the horizontal members 8 of the internal reinforcement are resistant to buckling, and since the horizontal members 8 are provided to withstand constant hydrostatic pressure, it is desirable that at least a portion of the horizontal members 8 be steel such as structural steel or flat plate.

[0039] As shown in Figure 11, the flexible cable 11 is, for example, a wire rope made of twisted wires. Because the interior of the above-ground rectangular steel water tank 1 is a severely corrosive environment where chlorine gas in tap water is concentrated, it is desirable to make the cable 11 out of highly corrosion-resistant stainless steel or a material such as carbon fiber that is resistant to corrosion and has the required tensile strength. The cable 11 may be provided with a device such as a turnbuckle that can adjust the tension, so that the appropriate tension can be applied during construction. (Above-ground rectangular steel water tank (panel tank) according to a second embodiment of the present invention)

[0040] FIG. 12 shows a longitudinal cross-sectional view of an above-ground rectangular steel water tank 21 (panel tank) according to a second embodiment of the present invention. The above-ground rectangular steel water tank 21 of the second embodiment is a panel tank made of multiple panels 24 welded together. The above-ground rectangular steel water tank 21 comprises, as its main structural members, a bottom plate 25, side plates 22-1 and 22-2, a roof plate 28, a partition plate 27, and internal reinforcements 23 (horizontal members, diagonal members). The partition plate 27 is provided to separate the tank. Opposing side plate 22-1 and partition plate 27 are connected by the internal reinforcement 23. Opposing side plate 22-2 and side plate 22-2 are also connected by the internal reinforcement 23. Each internal reinforcement 23 is arranged in a horizontal plane and comprises a horizontal member and a diagonal member.

[0041] In above-ground rectangular steel water tanks 21 (panel tanks), water leakage damage often occurs during major earthquakes due to deformation of the side plates 22 and partition plates 27 and fracture of welds. The water leakage damage is thought to be caused by deformation of the side plates 22 and partition plates 27 and buckling of the internal reinforcement.

[0042] For this reason, in the above-ground rectangular steel water tank 21 of the second embodiment, as in the above-ground rectangular steel water tank 1 of the first embodiment, a cable (similar to cable 11a shown in FIG. 10) is installed to support the partition plate 27 and provide resistance to tension but not compression. The cable connects adjacent partition plates 27 and side plates 22-2 at a 90-degree angle. The cable may be installed as at least a part of the internal reinforcement 23, or may be installed in addition to the internal reinforcement 23.

[0043] By installing the cables, it is possible to prevent the cables from buckling in the event of a major earthquake. The tensile force of the cables can restrain the partition plate 27, thereby suppressing deformation of the partition plate 27. It is desirable that the cables be installed on both sides of the partition plate 27, and that at least a portion of the diagonal members of the internal reinforcement member 23 be cables.

[0044] The present invention is not limited to the above-described embodiment, and may be embodied in other embodiments without departing from the spirit of the present invention. In the above-described embodiment, an example in which cables are installed as at least a part of the internal reinforcement of a newly constructed above-ground rectangular steel tank or in addition to the internal reinforcement has been described. However, in order to reinforce an existing above-ground rectangular steel tank, at least a part of the internal reinforcement of the existing above-ground rectangular steel tank may be replaced with cables, or cables may be installed in addition to the internal reinforcement.

[0045] In the above embodiment, an example has been described in which the cable is installed as at least a part of the diagonal member of the internal reinforcement member, but the cable may also be installed as at least a part of the horizontal member of the internal reinforcement member. [Explanation of symbols]

[0046] 1,21…Above-ground steel rectangular water tank 7,27...Divider 8,23...Horizontal members (internal reinforcement) 9,23...Diagonal members (internal reinforcement) 11a, 11b...cable

Claims

1. In an above-ground rectangular steel tank equipped with partition plates that separate the tank, An above-ground rectangular steel water tank characterized in that a cable is installed to support the partition plate and to resist tension but not compression.

2. 2. The above-ground rectangular steel water tank according to claim 1, wherein the cables are installed on both sides of the partition plate.

3. 3. The above-ground rectangular steel water tank according to claim 1, wherein at least a portion of the internal reinforcement comprises the cable.

4. 4. The above-ground rectangular steel water tank according to claim 3, wherein at least a portion of the diagonal members of the internal reinforcement members comprises the cables.

5. 5. The above-ground rectangular steel water tank according to claim 4, wherein at least a portion of the horizontal members of the internal reinforcement members comprises steel.

6. 3. The above-ground rectangular steel water tank according to claim 1, wherein the cables are installed in addition to the internal reinforcement members.

7. A method for reinforcing an above-ground rectangular steel tank equipped with partition plates that separate the tank, comprising: A method for reinforcing an above-ground rectangular steel water tank, characterized by installing a cable that supports the partition plate and resists tension but not compression.

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