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

Abstract

Provided are a design method for a tower structure, a manufacturing method for a tower structure, and a tower structure that make it possible to reduce the steel material quantity of the tower structure and to provide the tower structure with a logical structure according to design external force that changes in the height direction of the tower structure, while increasing the lengths of steel pipes constituting the tower structure as much as possible.　Provided is a design method for a tower structure constituted by integrating a plurality of steel pipes laminated in the height direction by welding, the design method including: a temporary design step for calculating the plate thickness tc1 of each of the plurality of steel pipes by designing the tower structure by an allowable stress degree design method under design conditions that a first steel type having a first yield strength σy1 is used for all of the plurality of steel pipes, and the difference in plate thickness between two steel pipes vertically adjacent to each other is equal to or less than a preset limit value; a region setting step for setting a region that includes a reference height h0 at which a bending moment becomes maximum in a bending moment distribution in the height direction of the tower structure designed in the temporary design step, and that falls within a range of 0.8-2.4 times the maximum outer diameter of the tower structure in the height direction of the tower structure; and a main design step for calculating the plate thickness tc3 of each of the plurality of steel pipes by designing the tower structure by the allowable stress degree design method under design conditions that a second steel type having a second yield strength σy2 greater than the first yield strength σy1 is used for the steel pipes in the region among the plurality of steel pipes, the first steel type is used for the steel pipes other than those in the region, and the difference in plate thickness between two steel pipes vertically adjacent to each other is equal to or less than the limit value.

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 using 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 multiple steel pipes are installed within the monopile. Since it is common to use only one type of steel for the steel pipes constituting the monopile, 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, as described in Non-Patent Literature 1, for example.

[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 Technology Research Center (ed.), "Jacket Construction Method Technical Manual (Revised Edition)", Coastal Technology Research Center, October 2021, p. 50.

[0010] Here, the length of the steel pipes that make up a monopile is usually about 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, and the amount of steel material used in the monopile can be reduced. 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. In this case, the location where the plate thickness of the steel pipes can be changed is limited to the connection points between the steel pipes. Furthermore, in order to suppress stress concentration caused by the difference in plate thickness of the steel pipes at the connection points between the steel pipes, there is a limit to the difference in plate thickness, and for example, Non-Patent Literature 2 recommends that this difference in plate thickness be 7 mm or less. For this reason, if the length of the steel pipes that make up the monopile is made as long as possible, there will be a large portion of each steel pipe where there is a margin of error in plate thickness relative to the design external force, which leads to the problem of a large amount of steel material being used.

[0011] Furthermore, since monopiles are large components and their manufacturing plants are limited, the transportation distance to the offshore wind power generation facility installation site tends to be long. The CO2 emissions from logistics when transporting monopiles from the manufacturing plant to the offshore wind power generation facility installation site can be calculated, for example, using the following formula: CO2 emissions (g - CO2) = transport weight (t) × transport distance (km) × CO2 emission intensity (g - CO2 / t・km). Here, the CO2 emission intensity is a value set according to the means of transport, and is set to about 20 when the means of transport is by ship. Since the CO2 emissions when transporting one monopile from the manufacturing plant to the installation site often exceed 2000 tons, even a 1% reduction in the weight of the monopile has a significant effect on reducing CO2 emissions.

[0012] 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 can reduce the amount of steel material used in a tower structure, such as a monopile, by making the length of the steel pipes constituting the tower structure as long as possible while providing a rational structure that responds to the design external forces that change in the height direction of the tower structure.

[0013] 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 preliminary design step to calculate the first yield strength σ; a region setting step to set a region in the height direction of the tower structure that includes a reference height h0 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure designed by the preliminary design step, and which is in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure; and a region setting step in which, among the plurality of steel pipes, the steel pipe in the region is determined to have 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 characteristics, and using the first type of steel for steel pipes outside the above region, 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 plurality of steel pipes c2A design method for a tower structure, including the present design step of calculating, and. In the present invention, the "tower structure" is not limited to the whole of the structure, but includes a part of the structure that is installed on the ground, for example, a monopile used as a foundation for supporting an offshore wind power facility. [2] The region set in the region setting step is symmetrically set up and down from the reference height h0, the design method for a tower structure according to [1]. [3] The design method for a tower structure according to [1] or [2], wherein the limit value is set to 7 mm or less. [4] The second yield strength σ y2 is set to be 40 N / mm y1 or more greater than the first yield strength σ 2 , the design method for a tower structure according to [1] or [2]. [5] A manufacturing method for a tower structure in which a plurality of steel pipes laminated in the height direction are integrated by welding, using a first steel type having a first yield strength σ y1 for all of the plurality of steel pipes, and designing the tower structure by the allowable stress design method under the design condition that the difference in the plate thickness between two adjacent steel pipes in the vertical direction is not more than a preset limit value, thereby calculating the plate thickness t c1 of each of the plurality of steel pipes, including a preliminary design step of calculating, and a reference height h0 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure designed by the preliminary design step, and setting a region in the height direction of the tower structure within a range of 0.8 to 2.4 times the maximum outer diameter of the tower structure, and for the steel pipes in the region among the plurality of steel pipes, using a second steel type having a second yield strength σ y1 greater than the first yield strength σ y2 , using the first steel type for the steel pipes outside the region, and designing the tower structure by the allowable stress design method under the design condition that the difference in the plate thickness between two adjacent steel pipes in the vertical direction is not more than the limit value, thereby the plate thickness t c2A method for manufacturing a tower structure, comprising: a main design step for calculating the second yield strength σ, and manufacturing the tower structure by setting the plate thickness and steel type of each of the plurality of steel pipes as designed in the main design step. [6] 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, a reference height h1 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure, and a steel pipe in the height direction of the tower structure in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure, has a second yield strength σ y2 It is composed of a second type of steel having the first yield strength σ, and the steel pipe outside the aforementioned region has 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, both above and below, is 7 mm or less.

[0014] 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 is used, and the plate thickness of each of the multiple steel pipes can be determined in a simple manner.

[0015] This allows for a reduction in the amount of steel used in a tower structure compared to constructing it with a single grade of steel having a single yield strength, resulting in cost reduction, easier transportation by crane or ship, reduced required bearing capacity, and reduced construction load.

[0016] In the design method of the tower structure of the present invention, the manufacturing method of the tower structure, and when the tower structure is applied to a monopile that constitutes a monopile foundation for supporting an offshore wind power generation facility, by reducing the amount of steel used in the tower structure, it is possible to reduce the logistics CO2 emissions when transporting the monopile from the monopile manufacturing factory to the installation location of the offshore wind power generation facility.

[0017] Furthermore, while making the length of the steel pipe constituting the tower structure as long as possible, the tower structure can be made into a reasonable structure according to the bending moment distribution in the height direction of the tower structure.

[0018] FIG. 1 is a side view schematically showing the overall configuration of an offshore wind power generation facility using a monopile foundation. FIG. 2 is an enlarged cross-sectional view of the monopile constituting the monopile foundation. FIG. 3 is an enlarged cross-sectional view of the joint portion between segments constituting the monopile of the monopile foundation. FIG. 4 is a diagram showing an example of the distribution of the plate thickness t1 in the height direction of the tower structure calculated by the preliminary design step of the design method of the tower structure according to the present invention. FIG. 5 is a graph showing the reduction rate of the total weight of the tower structure designed by the design method of the tower structure according to the present invention in comparison with the size of the region set in the region setting step.

[0019] Hereinafter, referring to the drawings, the design method of the tower structure of the present invention, the manufacturing method of the tower structure, and an embodiment of the tower structure will be described in detail.

[0020] In the present embodiment, as an aspect of the tower structure, a monopile used as a foundation for supporting an offshore wind power generation facility will be described as an example.

[0021] 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.

[0022] 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.

[0023] 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 multiple 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 about 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.

[0024] The tower structure design method of this embodiment comprises a preliminary design step, a region setting step, and a final design step. Each of these steps is described below. (Preliminary Design Step) In the tower structure design method of this embodiment, first, in the preliminary design step, the first yield strength σ y1The 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 preliminary design step, 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. This ensures that the plate thickness t of each of the multiple steel pipes c1 Calculate.

[0025] At this time, the first yield strength σ y1 For example, 235-325 N / mm 2 It is preferable to set it within the range.

[0026] Furthermore, 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 of different thicknesses by welding, it is necessary to avoid stress concentration at the joint. For example, it is necessary to provide a thickness change section where 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. (Region setting step) Next, in the region setting step, a reference height h0 is identified, 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 designed by the above-described preliminary design step. Specifically, external forces such as seismic force and wind force are applied to the tower structure 1 by frame analysis, FEM analysis, etc., and the reference height h0, which is the height at which the bending moment is maximum, is obtained from the bending moment distribution obtained from the analysis results. Then, as shown in Figure 4, a region is set that includes the reference height h0 and is in the height direction of the tower structure 1, ranging from 0.8 to 2.4 times the maximum outer diameter of the tower structure 1.

[0027] At this time, it is preferable that the area set in the area setting step be set symmetrically above and below the reference height h0. In this way, the area can be appropriately set in the range of the tower structure 1 where the bending moment is large. (Main design step) Next, in the main design step, the tower structure 1 is designed using the allowable stress design method under different design conditions than those in the preliminary design step, thereby determining the plate thickness t of each of the multiple steel pipes c2 The first yield strength σ is calculated. In this design step, some of the steel pipes among the multiple steel pipes that make up the tower structure 1 are given a first yield strength σ y1 The second yield strength σ is greater than y2 A second steel grade having the following characteristics is used. Specifically, the steel pipes in the region set in the region setting step, which includes the reference height h0 and is in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure 1 in the height direction of the tower structure 1, are given a second yield strength σ y2 A second steel grade having the above characteristics will be used. In this design step, 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.

[0028] At this time, the second yield strength σ y2 For example, 385-485 N / mm 2 It is preferable to set it within the range.

[0029] Also, 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. This significantly reduces the plate thickness.

[0030] This concludes the design method for the tower structure according to this embodiment.

[0031] 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.

[0032] 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 that include a reference height h1, 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, and that are in a region in the height direction of the tower structure that is in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure, have a second yield strength σ y2 It is composed of a second type of steel having the above-mentioned 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 significant. Also, the difference in plate thickness between two adjacent steel pipes, one above the other, is 7 mm or less. Note that the reference height h1, which is the height at which the bending moment is actually maximum in the height-direction bending moment distribution of the tower structure 1, does not perfectly coincide with the reference height h0 specified in the domain setting step of the tower structure design method, but it is close to the reference height h0.

[0033] The following describes an example of designing a tower structure using the tower structure design method of the present invention.

[0034] 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.

[0035] 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. (Preliminary design step) First, in the preliminary design step, 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.

[0036] In this example, the tower structure 1 was designed using steel grade A, which is equivalent to steel grade SM520 as specified in Japanese Industrial Standard JIS G3106, as the first steel grade. The design standard strength of SM520 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.

[0037] In the preliminary design step, 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).

[0038] Figure 4 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 c1This is shown. The values ​​on the vertical axis in Figure 4 are displayed with sea level height set to 0m. (Region setting step) Next, in the region setting step, a reference height h0 was identified, 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 designed by the preliminary design step described above. Then, as shown in Figure 4, regions were set that include the reference height h0 and are in the range of 8m (Inventive Example 1), 16m (Inventive Example 2), 24m (Inventive Example 3), and 30m (Comparative Example 2) in the height direction of the tower structure 1. These correspond to the range of 0.8 times (Inventive Example 1), 1.6 times (Inventive Example 2), and 2.4 times (Inventive Example 3) the maximum outer diameter of the tower structure 1, respectively, and are within the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure 1, which is a requirement of the present invention described above.

[0039] For comparison, a range was set that includes the reference height h0 and extends to 0m (Comparative Example 1) and 30m (Comparative Example 2) in the height direction of the tower structure 1. These ranges correspond to 0 times (Comparative Example 1) and 3.0 times (Comparative Example 2) the maximum outer diameter of the tower structure 1, respectively, and are outside the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure 1, which is a requirement of the present invention as described above.

[0040] The lower end of the region set in the region setting step was set to the height at which there is a difference in plate thickness t1 between two adjacent steel pipes, among the plate thickness t1 of the multiple steel pipes calculated in the design step, that is lower than the above reference height h0 and closest to the above reference height h0. In this embodiment, the height of the lower end of the region was sea level - 11 m. The upper end of the region set in the region setting step was set to a height of 0 m (Comparative Example 1), 8 m (Inventive Example 1), 16 m (Inventive Example 2), 24 m (Inventive Example 3), and 30 m (Comparative Example 2) in the height direction upward from the lower end of the tower structure 1. (Main Design Step) Next, in the main design step, the tower structure 1 was designed using the allowable stress design method under different design conditions than those in the preliminary design step, so that the plate thickness t of each of the multiple steel pipes c2 The yield strength of steel type A (first yield strength σ) was calculated for some of the steel pipes among the multiple steel pipes that make up the tower structure 1. y1 ) Second yield strength σ is greater than y2 Steel type B, which has the following properties, was used.

[0041] In this example, steel grade B is 550 N / mm 2 Tower structure 1 was designed assuming the use of graded steel. 550 N / mm 2 The design strength of grade steel is 385 N / mm². 2 And this value is the second yield strength σ y2 It was used as the second yield strength σ. y2 This is the first yield strength σ y1 40 N / mm 2 The above is set to a large value.

[0042] Then, in the region set in the region setting step, that is, the region including the reference height h0 and in the height direction of the tower structure 1, the steel pipes in the range of 0 times (Comparative Example 1), 0.8 times (Inventive Example 1), 1.6 times (Inventive Example 2), 2.4 times (Inventive Example 3), and 3.0 times (Comparative Example 2) of the maximum outer diameter of the tower structure 1 were to be made of steel type B.

[0043] Specifically, in Invention Example 1, the starting point is sea level -11m, which is the lower end of the area set in the area setting step, and steel type B is used for the steel pipes in the area within a range of 4m above and below that point, i.e., the range from sea level -7m to -15m.

[0044] In the second example of the invention, the starting point is sea level -11m, which is the lower end of the area set in the area setting step, and steel type B is used for the steel pipes in the area within a range of 8m above and below that point, i.e., the range from sea level -3m to -19m.

[0045] In Invention Example 3, the starting point is sea level -11m, which is the lower end of the region set in the region setting step, and steel type B is used for the steel pipes in the region within a range of 12m above and below this point, i.e., the range from sea level +1m to -23m.

[0046] In Comparative Example 2, the starting point was sea level -11m, which is the lower end of the region set in the region setting step, and steel type B was used for the steel pipes in the region ranging from sea level +4m to -26m, with a range of 15m above and below this point.

[0047] In Comparative Example 1, the area set in the area setting step is within the range of 0m in the height direction of the tower structure 1. Therefore, in the main design step, among the multiple steel pipes constituting the tower structure 1, there are no steel pipes using steel type B, and all steel pipes use steel type A. In other words, in Comparative Example 1, the design conditions in the main design step are the same as the design conditions in the preliminary design step, and this corresponds to the case where the tower structure 1 is designed using only the preliminary design step without performing the area setting step and the main design step.

[0048] Figure 5 shows the reduction rate of the total weight of tower structure 1 designed using the tower structure design method described above, in comparison to the size of the area set in the area setting step. In Figure 5, the reduction rate of the total weight of the monopile is shown as a relative value based on the total weight of tower structure 1 (Comparative Example 1) designed only in the preliminary design step without performing the area setting step and the main design step.

[0049] As shown in Figure 5, when the size of the region set in the region setting step was in the range of 0 times (Comparative Example 1) to less than 0.8 times (Inventive Example 1) the maximum outer diameter of the tower structure 1, the overall weight of the designed tower structure 1 was hardly reduced.

[0050] When the size of the area set in the area setting step was in the range of 0.8 times (Example 1) to 2.4 times (Example 3) the maximum outer diameter of the tower structure 1, the greater the size of the area, the greater the effect of reducing the overall weight of the designed tower structure 1. The reduction rate of the overall weight of the designed tower structure 1 was approximately 0.99 to 0.92, and the overall weight of the designed tower structure 1 could be reduced by approximately 1 to 8%.

[0051] When the size of the area set in the area setting step exceeds 2.4 times the maximum outer diameter of the tower structure 1 (Example 3 of Invention), the reduction rate of the overall weight of the designed tower structure 1 plateaus at around 0.9, and the effect of reducing the overall weight of the designed tower structure 1 does not increase any further.

[0052] Thus, the size of the region set in the region setting step is such that the steel pipes have a yield strength of steel type A (first yield strength σ) in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure 1. y1) Second yield strength σ is greater than y2 It was confirmed that by using steel grade B, which has the properties of steel grade A, the overall weight of the tower structure 1 can be effectively reduced compared to using only steel grade A.

[0053] 1. Tower structure (monopile) 11-14 Steel pipe 2. Offshore wind power generation equipment 20 Tower 3. Transition piece h0, h1 Reference height

Claims

1. A design method for 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 preliminary design step to calculate the first yield strength σ; a region setting step to set a region in the height direction of the tower structure that includes a reference height h0 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure designed by the preliminary design step, and which is in the range of 0.8 to 2.4 times the maximum outer diameter of the tower structure; and a region in the height direction of the tower structure that includes 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 characteristics, and using the first type of steel for steel pipes outside the above region, 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 plurality of steel pipes c2 A design method for a tower structure, including the main design step of calculating [a certain value].

2. The method for designing a tower structure according to claim 1, wherein the region set in the region setting step is set symmetrically above and below the reference height h0.

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

4. 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 claim 2, wherein the above-mentioned large setting is applied.

5. A method for manufacturing a tower structure configured by integrating a plurality of steel pipes laminated in the height direction by welding, wherein a first steel type having a first yield strength σ y1 is used for all of the plurality of steel pipes, and the tower structure is designed by an 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, whereby the plate thickness t c1 of each of the plurality of steel pipes is calculated in a preliminary design step; a region setting step of setting a region including a reference height h0 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure designed in the preliminary design step, and in the height direction of the tower structure, in a range of 0.8 to 2.4 times the maximum outer diameter of the tower structure; among the plurality of steel pipes, for the steel pipes in the region, a second steel type having a second yield strength σ y1 greater than the first yield strength σ y2 is used, the first steel type is used for the steel pipes outside the region, and the tower structure is designed by an 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, whereby the plate thickness t c2 of each of the plurality of steel pipes is calculated in a final design step; and a method for manufacturing a tower structure, in which the plate thickness and steel type of each of the plurality of steel pipes are set as designed in the final design step, and the tower structure is manufactured.

6. 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 that include a reference height h1 which is the height at which the bending moment is maximum in the bending moment distribution in the height direction of the tower structure, and which are in a region in the height direction of the tower structure that is in the range of 0.8 to 2.4 times the maximum outer diameter 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 the steel pipe outside the aforementioned region has 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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