Design method for tower structure, manufacturing method for tower structure, and tower structure

Abstract

Provided are a design method for a tower structure and a manufacturing method for a tower structure which make it possible to reduce the steel material quantity of a tower structure and to provide the tower strucure with a logical configuration according to design external force that changes in the height direction of the tower structure, while also increasing the lengths of steel pipes constituting the tower structure as much as possible. Provided is a design method for a tower structure which is configured by a plurality of steel pipes stacked in a height direction being integrated via welding. The design method for a tower structure has a first design step, a second design step, a first height setting step, a third design step, and a determination step, and if it is determined in the determination step that a determination condition is not satisfied, the processing from the third design step on is repeated changing at least one among a height hL and a height hH, whereas if it is determined in the determination step that the determination condition is satisfied, the sheet thicknesses and steel types for each of the plurality of steel pipes are set as designed in the third design step.

Description

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

[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.

[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 joints created by 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 Document 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.

[0008] Patent No. 4606086

[0009] Anastasia Ioannouet al, "Design implications towards inspection reduction of large scale structures", Procedia CIRP 60 (2017), pp. 434-439. Coastal Engineering Research Center (ed.), "Jacket Construction Method Technical Manual (Revised Edition)", Coastal Engineering Research Center, October 2021.

[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 that make up 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.

[0012] To solve the above problems, the present invention has the following features: [1] A method for designing 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. c2A second design step of calculating, and when there is a height where the difference in the plate thicknesses of 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, by searching upward from the lower end of the tower structure for the exceeding height, setting the first searched exceeding height as a first height h1, a first height setting step, and among the plurality of steel pipes, a height h L from, up to a height h that is equal to or greater 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 for the steel pipes in the range, use a second steel type having a second yield strength σ y1 greater than the first yield strength σ y2 and use the first steel type for the other steel pipes, and design the tower structure by the allowable stress design method under the design condition that the difference in the plate thicknesses of two vertically adjacent steel pipes is not more than the limit value, thereby calculating the plate thickness t c3 of each of the plurality of steel pipes, a third design step of calculating, and in all of the plurality of steel pipes, determining whether the plate thickness t c3 calculated in the third design step satisfies the determination condition of being not more than the plate thickness t c1 calculated in the first design step, and if it is determined in the determination step that the determination condition is not satisfied, changing at least one of the height h L and the height h H and performing the processing after the third design step again, and if it is determined in the determination step that the determination condition is satisfied, setting the plate thickness and steel type of each of the plurality of steel pipes as designed in the third design step. A method for designing a tower structure. [2] The method for designing a tower structure according to [1], wherein the limit value is set to 7 mm or less. [3] The second yield strength σ y2 is set to be 40 N / mm y1 greater than the first yield strength σ 2The design method for a tower structure as described in [1] or [2], wherein the above is set to a large value. [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 height exceeding the limit value that is searched for 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 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 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 c1The system includes a determination step to determine whether or not the following determination condition is met, and 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 A method for manufacturing a tower structure, comprising: changing at least one of the above and repeating the process from the third design step onward; if it is determined in the determination step that the determination condition is 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. [5] A tower structure in which a plurality of steel pipes are stacked in the height direction and integrated by welding, wherein among the plurality of steel pipes, the steel pipes in the range including 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 A tower structure in which the difference in plate thickness between two adjacent steel pipes, one above the other, is 7 mm or less.

[0013] 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.

[0014] 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.

[0015] Figure 1 is a schematic side view showing the overall configuration of an offshore wind power generation facility using a monopile foundation. Figure 2 is an enlarged cross-sectional view of a monopile constituting the monopile foundation. Figure 3 is an enlarged cross-sectional view of the joint between segments constituting the monopile of the monopile foundation. Figure 4 is a flowchart showing the flow of the design method for a tower structure according to the present invention. Figure 5 shows the plate thickness t in the height direction of the tower structure calculated by the first design step of the design method for a tower structure according to the present invention. c1 This figure shows an example of the distribution. Figure 6 shows the plate thickness t in the height direction of the tower structure, calculated by the second design step of the tower structure design method according to the present invention. c1 This figure shows an example of the distribution. Figure 7 shows the plate thickness t in the height direction of the tower structure, calculated by the third design step of the tower structure design method according to the present invention. c1 This figure shows an example of the distribution.

[0016] 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.

[0017] 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 for 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.

[0018] 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.

[0019] 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 to 14 are shown) that are approximately 3 to 4 m in length, and integrating them by welding. The tower structure 1 is then constructed by arranging and welding these steel pipe segments together.

[0020] Figure 4 shows the flow of the design method for the tower structure according to this embodiment.

[0021] 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 tower structure design method of 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.

[0022] 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, when joining steel pipes with different plate thicknesses by welding, it is necessary to avoid stress concentration at the joint. For this reason, for example, a thickness change section is provided in which 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 create 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 design conditions that use the first type of steel for all of the multiple steel pipes constituting the tower structure 1. In the second design step S2, the design conditions are set so that the difference in plate thickness between two vertically adjacent steel pipes is not restricted. As a result, the plate thickness t of each of the multiple steel pipes c2 Calculate.

[0023] 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 vertically adjacent steel pipes exceeds the above limit value Δt0, then the following steps are performed. Specifically, the first height setting step S3, the second design step S4, the determination step S5, and the plate thickness setting step S6 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 is 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> The height that satisfies the relationship Δt0 is searched upward from the bottom of the tower structure 1, and the first height searched is set as the first height h1. (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 the first design step S1 and the second design step S2, and 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. y1 The second yield strength σ is greater than y2 A second type of steel having the following characteristics shall be used. Specifically, height h L From height h H For steel pipes up to the range of the second yield strength σ y2 A second type of steel having the height h shall be used. L This is a height that is greater than or equal to the first height h1 set in the first height setting step S3. Also, height h H This is a height equal to or greater 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. 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.

[0024] 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 it to be larger than the above. In this way, 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 made of steel pipes made of a single type of steel with a single yield strength. In other words, the effect of reducing plate thickness can be greatly increased. (Decision 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.

[0025] 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 Either increase the height h mentioned above. H Lower the height h and repeat the process of the third design step S4. L The change 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. H The 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 determination step S5 is performed again. This repeated processing is carried out until it is confirmed in the determination step S5 that the above determination conditions are met. (Plate thickness setting step) If it is determined in the determination step S5 that the above determination conditions are met for all of the multiple steel pipes constituting the tower structure 1, 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.

[0026] This concludes the design method for the tower structure according to this embodiment.

[0027] 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.

[0028] 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. Among 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 y2It 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 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.

[0029] The following describes an example of designing a tower structure using the tower structure design method of the present invention.

[0030] This embodiment describes an example of designing a tower structure 1 with a length of 90 m and a maximum diameter of 10 m to support a wind turbine with an output of 15 MW, using the tower structure design method of the present invention. In this embodiment, of the 90 m length of the tower structure 1 to be designed, the lower 50 m portion is inserted into the ground, and the upper 40 m portion is located in the sea. Furthermore, the outer diameter of the tower structure 1 is continuously reduced from 10 m to 8 m in the upper 35 m portion of the tower structure 1 so that it can be joined to a transition piece 3.

[0031] Furthermore, in this embodiment, the length of each steel pipe constituting the tower structure 1 was set to 4 m, which is the maximum value for manufacturing. Also, the plate thickness of each steel pipe constituting the tower structure 1 was set to a condition in which the ratio of outer diameter to plate thickness was 120 or less in order to prevent local buckling. The limit value Δt0 of the difference in plate thickness between two vertically adjacent steel pipes was set to 5 mm. (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.

[0032] 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 ２And this value is the first yield strength σ y1 It was used as such.

[0033] 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-mentioned limit value Δt0 (= 5 mm).

[0034] 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 above-mentioned design conditions. 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 not to restrict 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.

[0035] 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 above-mentioned design conditions. 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 is shown. (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 c2 Of these, the plate thickness t of two steel pipes adjacent to each other vertically c2 The difference Δt c1 However, it searched for a height exceeding the above limit value Δt0 (= 5 mm). That is, Δt c1 >We searched for a height that satisfies the relationship Δt0. Specifically, Δt c1The height that satisfies the relationship of > Δt0 was searched upward from the lower end of the tower structure 1. Then, the first searched height was set as the first height h1. In this embodiment, the first height h1 was -6 m above sea level. (Third design step) Next, in the third design step S4 shown in FIG. 4, the tower structure 1 was 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 was 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 (first yield strength σ y1 ) greater than that of steel grade A was used. y2 In this embodiment, assuming that grade 550 N / mm

[0036] steel was used as steel grade B, the tower structure 1 was designed. The design reference strength of grade 550 N / mm 2 steel is 385 N / mm 2 , and this value was used as the second yield strength σ 2 . The second yield strength σ y2 was set to be 40 N / mm y2 or more greater than the first yield strength σ y1 . 2 And, from a height h

[0037] equal to or higher than the first height h1 set in the first height setting step S3, up to a height h L 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 was used for the steel pipes in the range. H 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 was at the position of -44 m above sea level. Therefore, from a height h

[0038] equal to or higher than the first height h1 (-6 m above sea level) ( -32 m above sea level), up to a height h L equal to or higher than the second height h2 (-44 m above sea level) ( +5 m above sea level), the tower structure 1 was designed using steel grade B. H 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 was at the position of -44 m above sea level. Therefore, from a height h

[0039] Figure 7 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 above-mentioned design conditions. c3 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 is shown. (Decision step) Next, in the decision 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 that make up the tower structure 1. c3 However, the plate thickness t calculated in the first design step S1 c1 We determined whether the following conditions were met.

[0040] As shown in Figures 5 and 7, it was confirmed that the above determination conditions were met in this embodiment. That is, in all of the multiple steel pipes constituting the tower structure 1, the plate thickness t calculated in the third design step S4 was met. c3 This is the plate thickness t calculated in the first design step S1. c1 The following was observed. Specifically, in the portion of the multiple steel pipes constituting the tower structure 1 that uses steel type A, the plate thickness t calculated in the third design step S4 was used in the range of heights from -44m to -32m and from +5m to +40m. c3 However, the plate thickness t calculated in the first design step S1 c1 The following results were obtained. In addition, in the portion of the multiple steel pipes constituting the tower structure 1 that uses steel type B, the plate thickness t calculated in the third design step S4 was determined in the range of height -32m to +5m. c3 However, the plate thickness t calculated in the first design step S1 c1 The following was determined. (Plate thickness setting step) In this way, in the determination step S5, it was determined that all of the multiple steel pipes constituting the tower structure 1 satisfy the above determination conditions. For this reason, in the plate thickness setting step S6 shown in Figure 4, the plate thickness and steel type of each of the multiple steel pipes were set as designed in the third design step S4. This completes the design method of the tower structure in this embodiment.

[0041] 1. Tower structure (monopile) 11-14 Steel pipes 2. Offshore wind power generation equipment 20 Tower 3. Transition piece h1 First height h2 Second height

Claims

1. A design method for a tower structure formed by integrating a plurality of steel pipes laminated in the height direction by welding, wherein a first steel grade having a first yield strength σ y1 is used for all of the plurality of steel pipes, and the tower structure is designed by the allowable stress design method under a design condition that the difference in plate thickness between two vertically adjacent steel pipes is equal to or less than a preset limit value, thereby calculating the plate thickness t c1 of each of the plurality of steel pipes in a first design step; the tower structure is designed by the allowable stress design method under a design condition that the first steel grade is used for all of the plurality of steel pipes and the difference in plate thickness between two vertically adjacent steel pipes is not restricted, thereby calculating the plate thickness t c2 of each of the plurality of steel pipes in a second design step; when there is a height at which 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 upward from the lower end of the tower structure for the exceeding height, and setting the first searched exceeding height as a first height h1 in a first height setting step; from a height h L of the plurality of steel pipes that is equal to or higher than the first height h1 to a height h H that is 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, using a second steel grade having a second yield strength σ y1 greater than the first yield strength σ y2 for the steel pipes in the range, using the first steel grade for the other steel pipes, and designing the tower structure by the allowable stress design method under a design condition that the difference in plate thickness between two vertically adjacent steel pipes is equal to or less than the limit value, thereby calculating the plate thickness t c3 of each of the plurality of steel pipes in a third design step; and a determination step of determining whether or not all of the plurality of steel pipes satisfy a determination condition that the plate thickness t c3 calculated in the third design step is equal to or less than the plate thickness t c1 calculated in the first design step. When it is determined in the determination step that the determination condition is not satisfied, the height h L and the aforementioned height h H A method for designing a tower structure, comprising: changing at least one of the above and repeating the processing from the third design step onward; and 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.

2. The design method for a tower structure according to claim 1, wherein the 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, 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 to calculate the first steel type, and designing the tower structure using the allowable stress design method with design conditions that use the first steel type for all of the multiple steel pipes and do not restrict the difference in plate thickness between two vertically adjacent steel pipes, thereby calculating the plate thickness t of each of the multiple steel pipes. c2 A second design step to calculate the following: If the difference in plate thickness between two vertically adjacent steel pipes among the multiple steel pipes calculated in the second design step exceeds the limit value, a first height setting step further searches for the height exceeding the limit from the lower end of the tower structure upwards, and sets the first height exceeding the limit found as the first height h1; and Among the multiple steel pipes, the height h that is greater than or equal to the first 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 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 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 or not the following determination condition is met, and 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 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.

5. A tower structure constructed by stacking multiple steel pipes in the height direction and integrating them by welding, wherein, among the multiple steel pipes, the steel pipes in the range including 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 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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