A method for designing a tower structure, a method for manufacturing a tower structure, and a tower structure

Abstract

This invention provides a design method and manufacturing method for a tower structure that allows for the longest possible length of steel pipes constituting the tower structure, while also providing a rational structure that responds to design external forces that change in the height direction, thereby reducing the amount of steel used. [Solution] The design includes a first design step of calculating the thickness of each steel pipe by designing the tower structure using the allowable stress design method under design conditions where the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value; a second design step of calculating the thickness of each of the plurality of steel pipes under design conditions where the difference in plate thickness is not limited; and a third design step in which, if the difference in plate thickness between two vertically adjacent steel pipes among the thicknesses of the plurality of steel pipes calculated in the second design step exceeds the limit value, a second steel type having a larger yield strength is used, and the thickness of each of the plurality of steel pipes is calculated under design conditions where the difference in plate thickness between the two steel pipes is less than or equal to the limit value.

Description

[Technical Field]

[0001] The present invention relates to a method for designing tower structures such as monopiles installed on the seabed to support offshore wind power generation facilities, a method for manufacturing tower structures, and tower structures themselves. [Background technology]

[0002] In recent years, the use of renewable energy has been promoted as a solution to the challenge of reducing greenhouse gas emissions such as carbon dioxide caused by the use of fossil fuels. Wind power generation facilities, which use wind energy, a type of renewable energy, to rotate wind turbines and generate electricity from the resulting kinetic energy, are being used worldwide.

[0003] Wind power generation facilities can be installed on land or offshore. In the latter case, there are no obstructions, the site area is vast, and large wind turbines can be installed, so offshore wind power generation has been promoted in particular in recent years.

[0004] One type of foundation used to support offshore wind power generation facilities is the monopile foundation. Figure 1 schematically shows the overall configuration of an offshore wind power generation facility using a monopile foundation. Figure 2 shows an enlarged cross-sectional view of the monopile that makes up the monopile foundation. Furthermore, Figure 3 shows an enlarged cross-sectional view of the joint between the steel pipes that make up the monopile.

[0005] As shown in Figures 1 to 3, the monopile 1 installed on the seabed to support offshore wind power generation equipment is constructed by stacking and integrating multiple steel pipes (in Figure 2, some of the multiple steel pipes 11 to 14 are shown) in the height direction. As described in Patent Document 1, the monopile 1 supporting the wind turbine 2 of the offshore wind power generation equipment is formed with an outer diameter and wall thickness that can withstand loads such as earthquakes, wind, waves, and its own weight. When the wind turbine 2 becomes large, steel pipes with an outer diameter of 10 m and a plate thickness of 100 mm or more may be used as the monopile 1.

[0006] As shown in Figure 1, the tower 20, which is the support structure for the wind turbine 2, is connected to the upper end of the monopile 1 via a steel pipe called a transition piece 3. The transition piece 3 and the tower 20 of the wind turbine 2, and the transition piece 3 and the monopile 1 are typically joined by bolts or by bearing connections through grout injection.

[0007] In monopile design, it is common practice to design the monopile under allowable stress conditions against loads such as earthquakes, wind, waves, and self-weight. Here, the magnitude of the design external force acting on the monopile changes in the height direction of the monopile. That is, the required cross-sectional performance of the multiple steel pipes constituting the monopile differs depending on the height at which these pipes are installed within the monopile. For this reason, as described in Non-Patent Literature 1, for example, it is common practice to set the plate thickness of the multiple steel pipes to differ according to the change in the design external force in the height direction of the monopile. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 4606086 [Non-patent literature]

[0009] [Non-Patent Document 1] Anastasia Ioannou et al, "Design implications towards inspection reduction of large scale structures", Procedia CIRP 60 (2017), P.434-439 [Non-Patent Document 2] Coastal Engineering Research Center (ed.), "Jacket Construction Method Technical Manual (Revised Edition)," Coastal Engineering Research Center, October 2021. [Overview of the project] [Problems that the invention aims to solve]

[0010] While the length of the steel pipes that make up a monopile is usually around 2 to 4 meters, if the length of the steel pipes constituting the monopile is shortened and stacked, the plate thickness of the monopile can be continuously changed in accordance with the design external force that changes in the height direction of the monopile, thereby reducing the amount of steel material used in the monopile. However, this increases the number of welding joints, which greatly increases the construction load of the monopile and lengthens the manufacturing time. Therefore, it is now common practice to manufacture steel pipes with the longest possible length and then weld these steel pipes together to produce the monopile. Since the position where the plate thickness of the steel pipes can be changed is limited to the connection points between the steel pipes, making the length of the steel pipes as long as possible results in a problem where there is a large margin of plate thickness in each steel pipe relative to the design external force, thus increasing the amount of steel material used.

[0011] In view of the above-mentioned problems, the present invention aims to provide a method for designing a tower structure, a method for manufacturing a tower structure, and a tower structure that allows for the longest possible length of steel pipes constituting a tower structure such as a monopile, while providing a rational structure that responds to design external forces that change in the height direction of the tower structure, thereby reducing the amount of steel material used in the tower structure. [Means for solving the problem]

[0012] To solve the above problems, the present invention has the following features.

[0013] [1] A design method for a tower structure in which multiple steel pipes stacked in the height direction are welded together, wherein the first yield strength σ y1 By using a first type of steel having the above characteristics for all of the plurality of steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value, the plate thickness t of each of the plurality of steel pipes c1A first design step of calculating, using the first steel type for all of the plurality of steel pipes, and designing the tower structure by an allowable stress design method under a design condition where the difference in plate thickness between two vertically adjacent steel pipes is not restricted, thereby obtaining the plate thickness t of each of the plurality of steel pipes c2 A second design step of calculating, and when there is a height where the difference in plate thickness between two vertically adjacent steel pipes among the plate thicknesses of each of the plurality of steel pipes calculated in the second design step exceeds the limit value, further searching for the exceeding height upward from the lower end of the tower structure, and setting the first searched exceeding height as a first height h1. A first height setting step, and for the steel pipes having a height h equal to or higher than the first height h1 among the plurality of steel pipes L from, at a height h equal to or higher than a second height h2 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure H to, using a second steel type having a second yield strength σ y1 greater than the first yield strength σ, using the first steel type for the other steel pipes, and designing the tower structure by an allowable stress design method under a design condition where the difference in plate thickness between two vertically adjacent steel pipes is not more than the limit value, thereby obtaining the plate thickness t of each of the plurality of steel pipes c3 A third design step of calculating, and in all of the plurality of steel pipes, the plate thickness t calculated in the third design step c3 is, a determination step of determining whether or not the determination condition that it is not more than the plate thickness t c1 calculated in the first design step is satisfied. When it is determined in the determination step that the determination condition is not satisfied, at least one of the height h L and the height h H is changed and the processes after the third design step are performed again. When it is determined in the determination step that the determination condition is satisfied, the plate thickness and steel type of each of the plurality of steel pipes are set as designed in the third design step. A method for designing a tower structure

[0014] ​​[2] The design method for a tower structure according to [1], wherein the limit value is set to 7 mm or less.

[0015] [3] The second yield strength σ y2 The first yield strength σ y1 40 N / mm 2 The design method for tower structures described in [1] or [2] above, with the above-mentioned large settings.

[0016] [4] A method for manufacturing a tower structure in which a plurality of steel pipes stacked in the height direction are integrated by welding, wherein the first yield strength σ y1 By using a first type of steel having the above characteristics for all of the plurality of steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value, the plate thickness t of each of the plurality of steel pipes c1 A first design step involves calculating the first steel type, and designing the tower structure using the allowable stress design method under design conditions where the first steel type is used for all of the multiple steel pipes and the difference in plate thickness between two vertically adjacent steel pipes is not restricted, thereby determining the plate thickness t of each of the multiple steel pipes. c2 A second design step to calculate the limit value, and if the difference in plate thickness between two vertically adjacent steel pipes among the plate thicknesses of the plurality of steel pipes calculated in the second design step exceeds the limit value, a first height setting step to search for the height exceeding the limit value upward from the lower end of the tower structure and set the first searched height exceeding the limit value as the first height h1, and among the plurality of steel pipes, the height h L Therefore, in the bending moment distribution in the height direction of the tower structure, the height h2 or higher is the height at which the bending moment is maximum. H For steel pipes up to the range of the first yield strength σ y1 The second yield strength σ is greater than y2By using a second type of steel having the above-mentioned first type of steel for the other steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to the above limit value, the plate thickness t of each of the multiple steel pipes c3 A third design step to calculate the plate thickness t calculated in the third design step for all of the plurality of steel pipes. c3 However, the plate thickness t calculated in the first design step c1 The system includes a determination step to determine whether the following determination condition is met, and if the determination step determines that the determination condition is not met, the height h L and the aforementioned height h H A method for manufacturing a tower structure, comprising: changing at least one of the above and repeating the processing from the third design step onward; if it is determined in the determination step that the determination conditions are met, setting the plate thickness and steel type of each of the plurality of steel pipes as designed in the third design step, and manufacturing the tower structure.

[0017] [5] A tower structure constructed by stacking multiple steel pipes in the height direction and integrating them by welding, Of the plurality of steel pipes, the steel pipes in the range that include a second height h2, which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure, have a second yield strength σ y2 It is composed of a second type of steel having the first yield strength σ, and other steel pipes have the first yield strength σ y1 It is composed of a first type of steel having, The second yield strength σ y2 This is the first yield strength σ y1 40 N / mm 2 In summary, A tower structure in which the difference in plate thickness between two adjacent steel pipes, one above the other, is 7 mm or less. [Effects of the Invention]

[0018] According to the present invention's method for designing a tower structure, a method for manufacturing a tower structure, and a tower structure, by combining steel grades with different yield strengths, the plate thickness of the steel pipes constituting the tower structure can be reduced compared to the case where the tower structure is constructed using steel pipes made of a single grade of steel with a single yield strength. In this case, the first yield strength σ y1 The second yield strength σ is greater than y2 The steel grade having this property can be used in which of the multiple steel pipes constituting the tower structure, and the plate thickness of each of the multiple steel pipes can be determined in a simple manner.

[0019] This allows for a reduction in the amount of steel used in the tower structure compared to constructing the tower structure with a single steel grade having a single yield strength, resulting in cost reduction and a lighter construction load. Furthermore, it enables the tower structure to be rationally designed according to the bending moment distribution in the height direction of the tower structure, while maximizing the length of the steel pipes that make up the tower structure. [Brief explanation of the drawing]

[0020] [Figure 1] Figure 1 is a schematic side view showing the overall configuration of an offshore wind power generation facility using a monopile foundation. [Figure 2] Figure 2 shows an enlarged cross-sectional view of a monopile that makes up a monopile foundation. [Figure 3] Figure 3 is an enlarged cross-sectional view of the joint between segments that make up a monopile in a monopile foundation. [Figure 4] Figure 4 shows a flowchart of the design method for a tower structure according to the present invention. [Figure 5] Figure 5 shows an example of the distribution of plate thickness tc1 in the height direction of a tower structure, calculated by the first design step of the tower structure design method according to the present invention. [Figure 6] Figure 6 shows an example of the distribution of plate thickness tc1 in the height direction of a tower structure, calculated by the second design step of the tower structure design method according to the present invention. [Figure 7]Figure 7 shows an example of the distribution of plate thickness tc1 in the height direction of a tower structure, calculated by the third design step of the tower structure design method according to the present invention. [Modes for carrying out the invention]

[0021] The design method for a tower structure, the manufacturing method for a tower structure, and one embodiment of the tower structure of the present invention will be described in detail below with reference to the drawings.

[0022] Figure 1 schematically shows the tower structure 1 of the first embodiment installed on the seabed, and the offshore wind power generation facility supported by the tower structure 1. As shown in Figure 1, the tower structure 1 of the first embodiment is a monopile installed on the seabed to support the wind turbine 2 of the offshore wind power generation facility. The tower 20, which is the support part of the wind turbine 2, is connected to the upper end of the tower structure 1 via a transition piece 3. The transition piece 3 and the tower 20 of the wind turbine 2, and the transition piece 3 and the tower structure 1 are joined by bolt connections or bearing connections by grout injection.

[0023] Figure 2 shows an enlarged cross-sectional view of a monopile that makes up a monopile foundation. Figure 3 shows an enlarged cross-sectional view of the joint between segments that make up the monopile of the monopile foundation.

[0024] As shown in Figures 2 and 3, the tower structure 1 is constructed by stacking multiple steel pipes in the height direction, and these multiple steel pipes are integrated by welding. Specifically, the tower structure 1 is constructed by stacking approximately three layers of steel pipe segments from the bottom upwards. Each of these steel pipe segments is constructed by arranging multiple single steel pipes (in Figure 2, some of the multiple steel pipes 11-14 are shown) that are approximately 3-4m in length, and integrating them by welding. The tower structure 1 is then constructed by arranging and welding these steel pipe segments together.

[0025] Figure 4 shows the flow of the design method for the tower structure according to this embodiment.

[0026] As shown in Figure 4, the tower structure design method of this embodiment includes a first design step S1, a second design step S2, a first height setting step S3, a second design step S4, a determination step S5, and a plate thickness setting step S6. Each of these steps will be described below. (First design step) In the design method for the tower structure according to this embodiment, first, in the first design step S1 shown in Figure 4, the first yield strength σ y1 The tower structure 1 is designed using the allowable stress design method, with the design condition that a first type of steel having the following properties is used for all of the multiple steel pipes constituting the tower structure 1. Here, if the difference in plate thickness between two vertically adjacent steel pipes is large, there is a risk that plastic deformation or fracture of the steel pipes may occur prematurely due to stress concentration. Therefore, in the first design step S1, the design condition is set so that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value Δt0. In the first design step S1, the design condition is set so that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value Δt0. As a result, the plate thickness t of each of the multiple steel pipes c1 Calculate.

[0027] In this case, it is preferable to set the above limit value Δt0 to 7 mm or less. As described in Non-Patent Literature 2, in order to join steel pipes of different thicknesses by welding, in order to avoid stress concentration at the joint, it is necessary to provide a thickness change section where, for example, the ratio (gradient) of the change in the wall thickness of the steel pipe to the axial length of the steel pipe is 1 / 4, thereby eliminating the difference in wall thickness between the steel pipes to be welded together. Therefore, by setting the above limit value Δt0 to 7 mm or less, the amount of cutting required to provide the taper of the thickness change section can be kept below a certain amount, and stress concentration caused by shape discontinuity due to the difference in plate thickness can be mitigated. (Second design step) Next, in the second design step S2 shown in Figure 4, the tower structure 1 is redesigned using the allowable stress design method, with the first steel type used for all of the multiple steel pipes constituting the tower structure 1. In the second design step S2, the design conditions do not restrict the difference in plate thickness between two vertically adjacent steel pipes. This allows the plate thickness t of each of the multiple steel pipes to be... c2 Calculate.

[0028] In the second design step S2, the difference in plate thickness between two vertically adjacent steel pipes is not restricted, therefore, the plate thickness t of each of the multiple steel pipes calculated in the second design step S2 is not limited. c2 In most cases, there exists a height where the difference in plate thickness between two adjacent steel pipes, one above the other, exceeds the above-mentioned limit value Δt0. Thus, the plate thickness t of each of the multiple steel pipes calculated in the second design step S2 c2 If the difference in plate thickness between two adjacent steel pipes, one above the other, exceeds the above limit value Δt0, then the first height setting step S3, the second design step S4, the determination step S5, and the plate thickness setting step S6, which will be described later, are performed. (First height setting step) In the first height setting step S3 shown in Figure 4, the plate thickness t of the multiple steel pipes calculated in the second design step S2 c2 Of these, the plate thickness t of two steel pipes adjacent to each other vertically c2 The difference Δt c2 If the height exceeds the above limit value Δt0, i.e., Δt c2 We search for a height that satisfies the relationship >Δt0. Specifically, Δt c2 By searching for a height that satisfies the relationship >Δt0 from the lower end of the tower structure 1 upwards, the first height found is set as the first height h1. (The third design step) Next, in the third design step S4 shown in Figure 4, the tower structure 1 is designed using the allowable stress design method under different design conditions than those in the first design step S1 and the second design step S2, thereby determining the plate thickness t of each of the multiple steel pipes. c3 The first yield strength σ is calculated. In the third design step S4, the first yield strength σ is calculated for some of the steel pipes among the multiple steel pipes that make up the tower structure 1. y1The second yield strength σ is greater than y2 A second steel grade having the following characteristics will be used. Specifically, a height h greater than or equal to the first height h1 set in the first height setting step S3. L Therefore, in the bending moment distribution in the height direction of the tower structure 1, the height h2 is the height at which the bending moment is maximum. H For steel pipes up to the range of the second yield strength σ y2 A second type of steel having the above characteristics is used. In the third design step S4, the design condition is set such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to the above limit value Δt0.

[0029] At this time, the second yield strength σ y2 This is the first yield strength σ y1 40 N / mm 2 It is preferable to set the yield strength to a larger value than the above. By doing so, by combining two types of steel with different yield strengths, the plate thickness of the steel pipes constituting the tower structure can be reduced by about 5 to 10 mm compared to when the tower structure is constructed using steel pipes made of a single type of steel with a single yield strength, thereby greatly reducing the plate thickness. (Judgment step) Next, in the determination step S5 shown in Figure 4, the plate thickness t calculated in the third design step S4 is determined for all of the multiple steel pipes constituting the tower structure 1. c3 However, the plate thickness t calculated in the first design step S1 c1 Determine whether the following conditions are met.

[0030] If, in the determination step S5, it is determined that the above determination condition is not met in any of the multiple steel pipes constituting the tower structure 1, then, as shown in Figure 4, the above height h L Increase the height h mentioned above, or H Lower the height h and repeat the process of the third design step S4. L The change to the height h is made within a range that satisfies the condition that the height is greater than or equal to the first height h1 set in the first height setting step S3. HThe changes are made within a range that satisfies the condition that the height is greater than or equal to the second height h2, which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure 1. In this way, the processing of the third design step S4 is performed again, and then the processing of the judgment step S5 is performed again. This iterative processing is carried out until it is confirmed in the judgment step S5 that the above judgment conditions are met. (Plate thickness setting step) If, in the determination step S5, it is determined that all of the multiple steel pipes constituting the tower structure 1 satisfy the above determination conditions, then in the plate thickness setting step S6 shown in Figure 4, the plate thickness and steel type of each of the multiple steel pipes are set as designed in the third design step S4.

[0031] This concludes the design method for the tower structure according to this embodiment.

[0032] Furthermore, the manufacturing method of the tower structure in this embodiment is achieved by setting the plate thickness and steel type of each of the multiple steel pipes constituting the tower structure 1 as designed by the tower structure design method described above, and then manufacturing the tower structure 1.

[0033] Furthermore, the tower structure 1 of this embodiment can be manufactured by the method for manufacturing a tower structure described above. That is, the tower structure 1 is constructed by stacking a plurality of steel pipes in the height direction and integrating them by welding. Of these plurality of steel pipes, the steel pipes in the range that includes a second height h2, which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure 1, have a second yield strength σ y2 It is composed of a second type of steel having the first yield strength σ. y1 It is composed of a first type of steel having the following characteristics: Second yield strength σ y2 This is the first yield strength σ y1 40 N / mm 2 The above is too large. Also, the difference in plate thickness between two adjacent steel pipes, one above the other, is 7 mm or less. [Examples]

[0034] The following describes an example of designing a tower structure using the tower structure design method of the present invention.

[0035] This embodiment describes an example of designing a tower structure 1 with a length of 90m and a maximum diameter of 10m to support a 15MW wind turbine, using the tower structure design method of the present invention. In this embodiment, of the 90m length of the tower structure 1 to be designed, the lower 50m portion is inserted into the ground, and the upper 40m portion is located in the sea. Furthermore, the outer diameter of the tower structure 1 is continuously reduced from 10m to 8m in the upper 35m portion of the tower structure 1 so that it can be joined to a transition piece 3.

[0036] In this embodiment, the length of each steel pipe constituting the tower structure 1 was set to 4m, which is the maximum length permitted by manufacturing. Furthermore, the plate thickness of each steel pipe constituting the tower structure 1 was set so that the ratio of outer diameter to plate thickness was 120 or less, in order to prevent local buckling. The limit value Δt0 for the difference in plate thickness between two vertically adjacent steel pipes was set to 5mm. (First design step) First, in the first design step S1 shown in Figure 4, the first yield strength σ y1 The tower structure 1 was designed using the allowable stress design method, with design conditions that used a first type of steel having the specified properties for all of the multiple steel pipes constituting the tower structure 1.

[0037] In this example, the tower structure 1 was designed using steel grade A, which is equivalent to steel grade SM520B as specified in Japanese Industrial Standard JIS G3106, as the first steel grade. The design standard strength of SM520B is 325 N / mm² for plate thicknesses exceeding 70 mm and not exceeding 100 mm. 2 , 315 N / mm² in the range of plate thickness exceeding 100 mm 2 And this value is the first yield strength σ y1 It was used as such.

[0038] In the first design step S1, the design condition was set such that the difference in plate thickness between two adjacent steel pipes, one above the other, would be less than or equal to the above limit value Δt0 (=5mm).

[0039] Figure 5 shows the plate thickness t in the height direction of the tower structure 1, calculated by designing the tower structure 1 using the allowable stress design method under the design conditions described above. c1 The distribution of, that is, the plate thickness t of each of the multiple steel pipes that make up the tower structure 1 c1 This is shown. The values ​​on the vertical axis in Figure 5 are displayed with sea level height set to 0m. (Second design step) Next, in the second design step S2 shown in Figure 4, the tower structure 1 was redesigned using the allowable stress design method under the design condition that all of the multiple steel pipes constituting the tower structure 1 use steel type A. In the second design step S2, the design condition was set so that there was no restriction on the difference in plate thickness between two vertically adjacent steel pipes. As a result, the plate thickness t of each of the multiple steel pipes c2 The result was calculated.

[0040] Figure 6 shows the plate thickness t in the height direction of the tower structure 1, calculated by designing the tower structure 1 using the allowable stress design method under the design conditions described above. c2 The distribution of, that is, the plate thickness t of each of the multiple steel pipes that make up the tower structure 1 c2 This indicates. (First height setting step) Next, in the first height setting step S3 shown in Figure 4, the plate thickness t of the multiple steel pipes calculated in the second design step S2 is c2 Of these, the plate thickness t of two steel pipes adjacent to each other vertically c2 The difference Δt c1 However, the height exceeding the above limit value Δt0 (=5mm), i.e., Δt c1 We searched for heights that satisfy the relationship >Δt0. Specifically, Δt c1 The height that satisfies the relationship >Δt0 was searched upward from the lower end of the tower structure 1. The first height found was set as the first height h1. In this embodiment, the first height h1 was sea level - 6m. (The third design step) Next, in the third design step S4 shown in FIG. 4, the tower structure 1 is designed by the allowable stress design method under design conditions different from those in the first design step S1 and the second design step S2, and the plate thickness t of each of the plurality of steel pipes is c3 calculated. In the third design step S4, for some of the plurality of steel pipes constituting the tower structure 1, a steel grade B having a yield strength (second yield strength σ y1 ) greater than the yield strength of steel grade A (first yield strength σ y2 ) is used.

[0041] In this embodiment, assuming that grade 550 N / mm 2 steel is used as steel grade B, the tower structure 1 is designed. The design reference strength of grade 550 N / mm 2 steel is 385 N / mm 2 , and this value is used as the second yield strength σ y2 . The second yield strength σ y2 is set to be 40 N / mm y1 or more greater than the first yield strength σ 2 .

[0042] Then, from a height h L equal to or higher than the first height h1 set in the first height setting step S3 to a height h H equal to or higher than the second height h2, which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure 1, steel grade B is used for the steel pipes in the range.

[0043] In this embodiment, the second height h2 at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure 1 is at the position of sea level - 44 m. Therefore, from a height h L (sea level - 32 m) equal to or higher than the first height h1 (sea level - 6 m) to a height h H (sea level + 5 m) equal to or higher than the second height h2 (sea level - 44 m), the tower structure 1 is designed using steel grade B.

[0044] In FIG. 7, the plate thickness t in the height direction of the tower structure 1 calculated by designing the tower structure 1 by the allowable stress design method under the above-described design conditions c3 , that is, the plate thickness t of each of the plurality of steel pipes constituting the tower structure 1 c2 is shown. (Judgment step) Next, in the judgment step S5 shown in FIG. 4, for all of the plurality of steel pipes constituting the tower structure 1, it is judged whether or not the judgment condition that the plate thickness t calculated in the third design step S4 c3 is less than or equal to the plate thickness t calculated in the first design step S1 c1 is satisfied.

[0045] As shown in FIGS. 5 and 7, in this embodiment, it was confirmed that the above judgment condition was satisfied. That is, for all of the plurality of steel pipes constituting the tower structure 1, the plate thickness t calculated in the third design step S4 c3 was less than or equal to the plate thickness t calculated in the first design step S1 c1 . Specifically, among the plurality of steel pipes constituting the tower structure 1, in the portion using steel type A, in the ranges of height -44 m to -32 m and +5 m to +40 m, the plate thickness t calculated in the third design step S4 c3 was less than or equal to the plate thickness t calculated in the first design step S1 c1 . Also, among the plurality of steel pipes constituting the tower structure 1, in the portion using steel type B, in the range of height -32 m to +5 m, the plate thickness t calculated in the third design step S4 c3 was less than or equal to the plate thickness t calculated in the first design step S1 c1 . (Plate thickness setting step) Thus, since it was judged in the judgment step S5 that the above judgment condition was satisfied for all of the plurality of steel pipes constituting the tower structure 1, in the plate thickness setting step S6 shown in FIG. 4, the plate thickness and steel type of each of the plurality of steel pipes were set as designed in the third design step S4. Thus, the design method of the tower structure of this embodiment was completed.

Explanation of symbols

[0046] 1. Tower structure (monopile) 11~14 Steel pipe 2. Offshore wind power generation facilities 20 Towers 3 Transition Pieces h1 First height h2 Second height

Claims

1. A design method for a tower structure in which multiple steel pipes stacked in the height direction are integrated by welding, First yield strength σ y1 By using a first type of steel having the above characteristics for all of the plurality of steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value, the plate thickness t of each of the plurality of steel pipes c1 The first design step is to calculate, By using the first type of steel mentioned above for all of the multiple steel pipes, and designing the tower structure using the allowable stress design method under design conditions that do not restrict the difference in plate thickness between two vertically adjacent steel pipes, the plate thickness t of each of the multiple steel pipes is determined. c2 The second design step involves calculation, If, as calculated in the second design step, the difference in plate thickness between two vertically adjacent steel pipes exceeds the limit value, the height exceeding the limit is further searched upward from the lower end of the tower structure, and the initially searched height exceeding the limit is set to the first height h 1 The first height setting step is to set it as follows: Among the plurality of steel pipes, at a height h of the first height h 1 or more heights h L to a second height h, which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure 2 or more heights h H For the steel pipes in the range up to, use a second steel type having a second yield strength σ greater than the first yield strength σ y1 While using the first steel type for the other steel pipes, and with the design condition that the difference in the plate thickness of two vertically adjacent steel pipes is below the limit value, design the tower structure by the allowable stress design method, and calculate the plate thickness t of each of the plurality of steel pipes y2 A third design step, and c3 In all of the aforementioned steel pipes, the plate thickness t calculated in the third design step c3 However, the plate thickness t calculated in the first design step c1 A determination step to determine whether or not the following determination conditions are met: It has, If it is determined in the determination step that the determination condition is not met, the height h L and the aforementioned height h H By changing at least one of the above, the process from the third design step onward is repeated. A method for designing a tower structure, wherein, if it is determined in the determination step that the determination conditions are met, the plate thickness and steel type of each of the plurality of steel pipes are set as designed in the third design step.

2. The design method for a tower structure according to claim 1, wherein the aforementioned limit value is set to 7 mm or less.

3. The second yield strength σ y2 The first yield strength σ y1 40 N / mm 2 The design method for a tower structure according to claim 1 or 2, wherein the above-mentioned large setting is applied.

4. A method for manufacturing a tower structure in which multiple steel pipes stacked in the height direction are integrated by welding, First yield strength σ y1 By using a first type of steel having the above characteristics for all of the plurality of steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to a predetermined limit value, the plate thickness t of each of the plurality of steel pipes c1 The first design step is to calculate, By using the first type of steel mentioned above for all of the multiple steel pipes, and designing the tower structure using the allowable stress design method under design conditions that do not restrict the difference in plate thickness between two vertically adjacent steel pipes, the plate thickness t of each of the multiple steel pipes is determined. c2 The second design step involves calculation, If, as calculated in the second design step, the difference in plate thickness between two vertically adjacent steel pipes exceeds the limit value, the height exceeding the limit is further searched upward from the lower end of the tower structure, and the initially searched height exceeding the limit is set to the first height h 1 The first height setting step is to set it as follows: Among the plurality of steel pipes, the first height h 1 Height h L Therefore, the second height h is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure. 2 Height h H For steel pipes up to the range of the first yield strength σ y1 The second yield strength σ is greater than y2 By using a second type of steel having the above-mentioned first type of steel for the other steel pipes, and designing the tower structure using the allowable stress design method under design conditions such that the difference in plate thickness between two vertically adjacent steel pipes is less than or equal to the above limit value, the plate thickness t of each of the multiple steel pipes c3 The third design step is to calculate, In all of the aforementioned steel pipes, the plate thickness t calculated in the third design step c3 However, the plate thickness t calculated in the first design step c1 A determination step to determine whether or not the following determination conditions are met: It has, If it is determined in the determination step that the determination condition is not met, the height h L and the aforementioned height h H By changing at least one of the above, the process from the third design step onward is repeated. A method for manufacturing a tower structure, wherein if it is determined in the determination step that the determination conditions are met, the plate thickness and steel type of each of the plurality of steel pipes are set as designed in the third design step, and the tower structure is manufactured.

5. A tower structure constructed by stacking multiple steel pipes in the height direction and integrating them by welding, Among the plurality of steel pipes, the second height h is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure. 2 Steel pipes in the range including the second yield strength σ y2 It is composed of a second type of steel having the first yield strength σ, and other steel pipes have the first yield strength σ y1 It is composed of a first type of steel having, The second yield strength σ y2 This is the first yield strength σ y1 40 N / mm 2 In summary, A tower structure in which the difference in plate thickness between two adjacent steel pipes, one above the other, is 7 mm or less.

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