Monopile

Abstract

To provide a monopile constructed by stacking a plurality of steel pipes and integrating them by welding, which can suppress labor required for processing welded joints of the steel pipes and the reduction in fatigue life due to stress concentration at the welded joints of the steel pipes while changing cross-sectional strength of the plurality of steel pipes in accordance with changes in design external force acting on the monopile in the height direction of the monopile.SOLUTION: A monopile is installed on the seabed to support an offshore wind power generation facility. The monopile is constructed by stacking a plurality of steel pipes in the height direction of the monopile and integrating them by welding, at least one of the plurality of steel pipes has a different design standard strength, and the steel pipes located above the seabed when the monopile is installed on the seabed have the same wall thickness.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a monopile installed on the seabed to support an offshore wind power generation facility. [Background technology]

[0002] Monopiles, which are installed on the seabed to support offshore wind power generation facilities, are constructed by stacking and integrating multiple steel pipe segments in the vertical direction. As described in Patent Document 1, monopiles for offshore wind power generation facilities are formed with an outer diameter and thickness that can withstand their own weight and loads such as wind and waves.

[0003] Here, the design external force acting on the monopile changes in the height direction of the monopile. In other words, the cross-sectional strength required of the multiple steel pipes that make up the monopile differs depending on the height at which these steel pipes are installed in the monopile. For this reason, as described in Non-Patent Document 1, for example, it has been common to make the wall thicknesses of the multiple steel pipes different depending on the change in the design external force in the height direction of the monopile.

[0004] FIG. 6 shows a schematic diagram of such a conventional monopile 9. The monopile 9 is constructed by stacking a plurality of steel pipes in its height direction and integrating these steel pipes by welding. Specifically, in the example shown in FIG. 6, the monopile 9 is constructed by stacking three tiers of steel pipe segments 91-93 from bottom to top of the monopile 9. Each of these steel pipe segments 91-93 is constructed by arranging a plurality of steel pipes 91a-91g, 92a-92h, 93a-93i, each consisting of a single pipe with a length of approximately 3-4 m, and integrating these steel pipes by welding. The monopile 9 is constructed by arranging these steel pipe segments 91-93 and integrating them by welding.

[0005] In the example shown in FIG. 6, all of the steel pipes 91a to 91g, 92a to 92h, and 93a to 93i that constitute the steel pipe segments 91 to 93 of the monopile 9 are made of the steel type SM520B defined in Japanese Industrial Standard JIS G3106:2024, and their design allowable strength is 325 N / mm 2 in the range where the wall thickness t satisfies 75 mm < t ≤ 100 mm, and they are the same.

[0006] Also, as the design external force acting on the monopile 9 changes in the height direction of the monopile 9, the wall thicknesses t of the plurality of steel pipes provided at each height of the monopile 9 are different. Specifically, the wall thicknesses t of the steel pipes 91a to 91g that constitute the lower steel pipe segment 91 are 85 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm, and 110 mm from the bottom to the top of the monopile 9. Also, the wall thicknesses t of all the steel pipes 92a to 92h that constitute the middle steel pipe segment 92 are all 115 mm, and the wall thicknesses t of all the steel pipes 93a to 93i that constitute the upper steel pipe segment 93 are all 110 mm.

[0007] Since the outer diameter of the monopile 9 is large, for example, several meters to more than ten meters (7545 to 10000 mm in the example shown in FIG. 6), the integration of joining three sets of steel pipes 91a to 91g, 92a to 92h, and 93a to 93i into the steel pipe segments 91 to 93 respectively, and further integrating these steel pipe segments 91 to 93 into the monopile 9 is performed by welding. Here, as described above, in order to avoid stress concentration in the joint when joining steel pipes with different wall thicknesses t by welding, for example, a wall thickness change portion is provided such that the ratio (gradient) of the change amount of the wall thickness of the steel pipe to the axial length of the steel pipe is 1 / 4, and it is necessary to eliminate the difference in the wall thicknesses of the steel pipes to be welded by welding, and machining is required. Also, the welded joint for joining steel pipes with different wall thicknesses has a problem that stress concentration is more likely to occur and the fatigue life is reduced compared to the welded joint of steel pipe segments with the same wall thickness t.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

[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 Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above-mentioned problems, the present invention aims to provide a monopile constructed by stacking multiple steel pipes and integrating them by welding, which can change the cross-sectional strength of the multiple steel pipes in accordance with changes in the design external force acting on the monopile in the height direction of the monopile, while suppressing the effort required to process the welded joints of the steel pipes and the reduction in fatigue life due to stress concentration at the welded joints of the steel pipes. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention has the following features.

[0012] [1] A monopile installed on the seabed to support offshore wind power generation facilities, the monopile being constructed by stacking a plurality of steel pipe segments in the height direction of the monopile and integrating them by welding, at least one of the plurality of steel pipe segments having a different design standard strength, and the steel pipe segments located above the seabed surface when the monopile is installed on the seabed having the same wall thickness.

[0013] [2] A monopile as described in [1], wherein two of the plurality of steel pipes that are adjacent in the vertical direction and have different design standard strengths have the same wall thickness and outer diameter.

[0014] [3] A monopile as described in [1] or [2], wherein the wall thickness of all of the plurality of steel pipe segments is set to the same. [Effects of the Invention]

[0015] According to the monopile of the present invention, when the monopile is installed on the seabed, the wall thickness of the steel pipes located above the seabed surface is uniform, thereby suppressing stress concentration at the welded joints of the steel pipes located above the seabed surface and avoiding a decrease in fatigue life. Furthermore, unlike welded joints of steel pipes with different wall thicknesses, there is no need to provide a thickness change section to suppress stress concentration, and cutting is not required, reducing the amount of work required to process the welded joints. Furthermore, because the design standard strength of at least one of the multiple steel pipes is different, the cross-sectional strength of the monopile at each height can be changed in response to changes in the design external force acting on the monopile along its height, resulting in a rational structure. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a side view that schematically shows an offshore wind power generation facility supported by monopiles. [Figure 2] 2(a) and 2(b) are side views each schematically showing a monopile according to a first embodiment of the present invention and a transition piece connected thereto. [Figure 3] 3(a) and 3(b) are side views each schematically showing a monopile according to a second embodiment of the present invention and a transition piece connected thereto. [Figure 4] 4(a) and 4(b) are side views each showing a schematic diagram of a monopile according to a third embodiment of the present invention and a transition piece connected thereto. [Figure 5] 5(a) and 5(b) are side views each schematically showing a monopile according to a fourth embodiment of the present invention and a transition piece connected thereto. [Figure 6]FIG. 6 is a side view schematically showing an example of a conventional monopile. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the monopile of the present invention will be described in detail with reference to the drawings. (First embodiment) Figure 1 shows a schematic diagram of a monopile 1 of the first embodiment installed on the seabed, and an offshore wind power generation facility 6 supported by the monopile 1. As shown in Figure 1, the monopile 1 of the first embodiment is installed on the seabed to support the offshore wind power generation facility. A tower 60, which is a support for the offshore wind power generation facility 6, is connected to the upper end of the monopile 1 via a transition piece 5.

[0018] FIG. 2(a) shows the details of the monopile 1 according to the first embodiment, and FIG. 2(b) shows a schematic diagram of the transition piece 5 that is connected to cover the upper end of the monopile 1.

[0019] As shown in Figure 2(a), the monopile 1 is constructed by stacking a plurality of steel pipes in its height direction and integrating these steel pipes by welding. Specifically, the monopile 1 is constructed by stacking three tiers of steel pipe segments 11-13 from the bottom to the top of the monopile 1. Each of these steel pipe segments 11-13 is constructed by arranging a plurality of steel pipes 11a-11g, 12a-12h, 13a-13i, each consisting of a single pipe with a length of approximately 3-4 m, and integrating these steel pipes by welding. The monopile 1 is constructed by arranging these steel pipe segments 11-13 and integrating them by welding.

[0020] As shown in Figure 2(a), the monopile 1 is installed on the seabed so that the middle of the part formed by the steel pipe segment 12 is at the seabed surface, and the middle of the part formed by the steel pipe segment 13 is at the seawater surface.

[0021] The outer diameter D of the portion of the monopile 1 composed of the steel pipe segments 11 and 12 is 10000 mm. Also, the outer diameter D of the portion of the monopile 1 composed of the steel pipe segment 13 is reduced from bottom to top, with the outer diameter D at the lower end being 10000 mm and the outer diameter D at the upper end being 7545 mm. Further, the wall thickness t of the steel pipes 11a to 11g constituting the lower steel pipe segment 11 is 85 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm from the bottom to the top of the monopile 9. Also, the wall thickness t of all the steel pipes 12a to 12h constituting the middle steel pipe segment 12 is 110 mm, and the wall thickness t of all the steel pipes 13a to 13i constituting the upper steel pipe segment 13 is also 110 mm. That is, among these steel pipe segments 11 to 13, as shown in Fig. 2(a), the wall thickness of the steel pipes constituting the steel pipe segments 12 and 13 located above the seabed surface in the state where the monopile 1 is installed on the seabed is 110 mm and is the same.

[0022] Also, in response to the design external force acting on the monopile 1 changing in the height direction of the monopile 1, the design reference strengths of the plurality of steel pipe segments 11 to 13 provided at each height of the monopile 1 are different. In the first embodiment, the portion of the monopile 1 composed of the middle steel pipe segment 12 will be described by taking the case where the design external force acting on the monopile 1 is larger than other portions as an example. In contrast, the steel pipes 11a to 11g and 13a to 13i constituting the steel pipe segments 11 and 13 are made of the steel grade SM520B specified in Japanese Industrial Standard JIS G3106:2024, and their design reference strength is 325 N / mm in the range where the wall thickness t is 75 mm < t ≦ 100 mm. 2 Also, the steel pipes 12a to 12h constituting the steel pipe segment 12 are made of a steel grade with a design reference strength of 355 N / mm 2 equivalent to the TMCP steel material HBL355 for building structures. 2

[0023] Furthermore, in the monopile 1 of the first embodiment, among the steel pipes 11a to 11g, 12a to 12h, and 13a to 13i that constitute the monopile 1, the wall thickness t and the outer diameter D of two steel pipes that are adjacent in the height direction and have different design standard strengths are set to be the same. 2 Steel pipe 11g made of steel grades and a design standard strength of 355N / mm 2 The steel pipes 12a made of the same steel type have the same wall thickness t (110 mm) and outer diameter D (10,000 mm). Similarly, the design standard strength is 355 N / mm 2 Steel pipe 12h made of steel type and design standard strength 325N / mm 2 The steel pipes 13a made of the above steel types have the same wall thickness t (110 mm) and outer diameter D (10,000 mm).

[0024] In this way, the wall thickness t of the steel pipes is set so that the wall thickness t (110 mm) of the steel pipes 12a to 12h constituting the steel pipe segment 12 in the portion of the monopile 1 where the design external force is large, that is, the wall thickness t (110 mm) of the steel pipes 12a to 12h constituting the steel pipe segment 12 is equal to or larger than the wall thickness t (85 mm to 110 mm) of the other portions of the monopile 1, that is, the steel pipes 11a to 11g and 13a to 13i constituting the steel pipe segments 11 and 13. In addition, the design standard strength (355 N / mm) of the steel pipes 12a to 12h constituting the steel pipe segment 12 in the portion of the monopile 1 where the design external force is large, that is, the wall thickness t (110 mm) of the steel pipes 12a to 12h constituting the steel pipe segment 12 in the other portions of the monopile 1, that is, the wall thickness t (85 mm to 110 mm) of the steel pipes 11a to 11g and 13a to 13i 2 ) is the design standard strength (325 N / mm 2 ) is larger than the welding strength of the steel grade. When welding different steel grades, a welding material that corresponds to the steel grade with lower strength can be selected.

[0025] Further, as shown in Fig. 2(b), the transition piece 5 connected so as to cover the upper end of the monopile 1 is composed of a steel pipe (not shown) made of a single pipe with a length of about 3 to 4 m in the height direction, and a plurality of these steel pipes are laminated and integrated by welding to form a steel pipe segment. The outer diameter of the transition piece 5 is reduced from bottom to top, with the outer diameter of the lower end being 9416 mm and the outer diameter of the upper end being 8020 mm. Also, the wall thickness t of the steel pipe constituting the transition piece 5 is 85 mm, and it is made of the steel grade SM520B specified in Japanese Industrial Standard JIS G3106:2024, and its design reference strength is 325 N / mm 2 when the wall thickness t is in the range of 75 mm < t ≤ 100 mm. At the upper end of the transition piece 5, a tower 60, which is a support part of the offshore wind power generation facility 6, is connected. The tower 60 is also composed of a steel pipe (not shown) made of a single pipe with a length of about 3 to 4 m in the height direction, and a plurality of these steel pipes are laminated and integrated by welding to form a steel pipe segment.

[0026] The transition piece 5 serves to adjust the inclination between the verticality of the monopile 1 and the verticality of the offshore wind power generation facility 6. The transition piece 5 is installed so as to cover the upper end of the monopile 1, and then grout material (not shown) or the like is injected into the gap between the transition piece 5 and the monopile 1 to fix it to the upper end of the monopile 1.

[0027] In the monopile 1 of the first embodiment, the wall thickness t (110 mm) of the steel pipes 12a to 12h constituting the steel pipe segment 12, which is the part of the monopile 1 where the design external force is large, is set to be greater than or equal to the wall thickness t (85 mm to 110 mm) of the steel pipes 11a to 11g, 13a to 13i constituting the other parts of the monopile 1, namely the steel pipe segments 11 and 13. This enables the monopile 1 to have a reasonable structure.

[0028] Furthermore, among the steel pipe segments 11-13 of the monopile 1, the steel pipes 12a-12h and 12a-12i that make up the steel pipe segments 12, 13 located above the seabed when the monopile 1 is installed on the seabed have the same wall thickness of 110 mm. This suppresses stress concentration at the welded joints of the steel pipes 12a-12h and 12a-12i that make up the steel pipe segments 12, 13 located above the seabed, which are prone to becoming weak points due to repeated external forces, and prevents a decrease in fatigue life. Furthermore, unlike welded joints between steel pipes with different wall thicknesses, there is no need to provide a thickness change section to suppress stress concentration, and cutting is not required, reducing the amount of work required to process the welded joints.

[0029] Furthermore, among the steel pipes 11a to 11g, 12a to 12h, and 13a to 13i that make up the monopile 1, the wall thickness t and outer diameter D of any two steel pipes that are adjacent in the height direction and have different design standard strengths are set to be identical. This makes it possible to suppress stress concentration at the welded joints of the two steel pipes that have different design standard strengths, which are likely to become weak points when subjected to repeated external forces. (Second embodiment) FIG. 3(a) shows the details of the monopile 2 according to the second embodiment, and FIG. 3(b) shows a schematic diagram of the transition piece 5 that is connected to cover the upper end of the monopile 2.

[0030] As shown in Fig. 3(a), the monopile 2 is constructed by stacking a plurality of steel pipes in its height direction and integrating these steel pipes by welding, similar to the monopile 1 of the first embodiment. Specifically, the monopile 2 is constructed by stacking three tiers of steel pipe segments 21-23 from the bottom to the top of the monopile 2. Each of these steel pipe segments 21-23 is constructed by arranging a plurality of steel pipes 21a-21g, 22a-22h, 23a-23i, each consisting of a single pipe with a length of approximately 3-4 m, and integrating these steel pipes by welding. The monopile 2 is constructed by arranging these steel pipe segments 21-23 and integrating them by welding.

[0031] The monopile 2 is installed on the seabed so that the middle of the part formed by the steel pipe segments 22 is at the seabed surface, and the middle of the part formed by the steel pipe segments 23 is at seawater level.

[0032] In the monopile 2 of the second embodiment, unlike the monopile 1 of the first embodiment, the wall thickness t of the steel pipes 21a to 21g, 22a to 22h, and 23a to 23i that make up all of the steel pipe segments 21 to 23 of the monopile 2 is 85 mm and is the same.

[0033] Furthermore, the design standard strength of the multiple steel pipe segments 21-23 provided at each height of the monopile 2 varies in accordance with the change in the design external force acting on the monopile 2 in the height direction of the monopile 2. In the second embodiment, as in the first embodiment, an example will be described in which the portion of the monopile 2 formed by the steel pipe segment 22 at the middle stage is subjected to a larger design external force acting on the monopile 2 than the other portions. In contrast, the steel pipes 21a-21f of the steel pipe segment 21, excluding the steel pipe 21g at the upper end, are each subjected to a design standard strength of 550 N / mm for building structures. 2 It is made of TMCP steel HBL385, and its design strength is 385N / mm 2 The steel pipe 21g at the upper end of the steel pipe segment 21 and the steel pipes 22a to 22h and 23a to 23i constituting the steel pipe segments 22 and 23 are rated at 590 N / mm for building construction. 2 It is made of TMCP steel HBL440, and its design strength is 440N / mm 2 is.

[0034] Furthermore, in the monopile 2 of the second embodiment, among the steel pipes 21a to 21g, 22a to 22h, and 23a to 23i that constitute the monopile 2, the wall thickness t and the outer diameter D of two steel pipes that are adjacent in the height direction and have different design standard strengths are set to be the same. 2 Steel pipe 21b is made of steel with a design strength of 385N / mm 2The wall thickness t (85 mm) and outer diameter D (10,000 mm) of the steel pipe 21c made of the same steel type are set to be the same. Similarly, the design standard strength is 385 N / mm 2 Steel pipe 21f consisting of steel type and design standard strength 440N / mm 2 The wall thickness t (85 mm) and outer diameter D (10,000 mm) of steel pipe 21g, which is made of the above steel type, are each assumed to be the same.

[0035] In this way, the design standard strength (440 N / mm) of the portion of the monopile 2 where the design external force is large, that is, the steel pipes 22a to 22h constituting the steel pipe segment 22, is 2 ) of the other parts of the monopile 2, i.e., the steel pipes 21a to 21g and 23a to 23i constituting the steel pipe segments 21 and 23 (385 N / mm 2 ) or more. When welding different steel types together, welding materials that correspond to the steel type with lower strength can be selected.

[0036] According to the monopile 2 of the second embodiment, the same effects as those of the monopile 1 of the first embodiment can be obtained.

[0037] Furthermore, in the monopile 2 of the second embodiment, the steel pipes 21a-21g, 22a-22h, and 23a-23i that make up all of the steel pipe segments 21-23 of the monopile 2 have the same wall thickness of 85 mm. This makes it possible to suppress stress concentration at the welded joints of the steel pipes 21a-21g, 22a-22h, and 23a-23i that make up the steel pipe segments 21-23, thereby avoiding a decrease in fatigue life. Furthermore, unlike welded joints between steel pipes with different wall thicknesses, there is no need to provide a wall thickness change portion to suppress stress concentration, and cutting is not required, so the labor required to process the welded joints is reduced. (Third embodiment) FIG. 4(a) shows the details of the monopile 3 according to the third embodiment, and FIG. 4(b) shows the transition piece 5 connected to cover the upper end of the monopile 3.

[0038] As shown in Fig. 4(a), the monopile 3 is constructed by stacking a plurality of steel pipes in its height direction and integrating these steel pipes by welding, similar to the monopile 1 of the first embodiment and the monopile 2 of the second embodiment. Specifically, the monopile 3 is constructed by stacking three tiers of steel pipe segments 31-33 from the bottom to the top of the monopile 3. Each of these steel pipe segments 31-33 is constructed by arranging a plurality of steel pipes 31a-31g, 32a-32h, 33a-33i, each consisting of a single pipe with a length of approximately 3-4 m, and integrating these steel pipes by welding. The monopile 3 is constructed by arranging these steel pipe segments 31-33 and integrating them by welding.

[0039] The monopile 3 is installed on the seabed so that the middle of the part formed by the steel pipe segments 32 is at the seabed surface, and the middle of the part formed by the steel pipe segments 33 is at seawater level.

[0040] In the monopile 3 of the third embodiment, the wall thickness t of all of the steel pipes 31a-31f of the lower steel pipe segment 31, excluding the uppermost steel pipe 31g, is 85 mm, and the wall thickness t of the uppermost steel pipe 31g is 90 mm. Furthermore, the wall thickness t of all of the steel pipes 32a-32h constituting the middle steel pipe segment 32 is 95 mm, and the wall thickness t of all of the steel pipes 33a-33i constituting the upper steel pipe segment 33 is 95 mm. In other words, of these steel pipe segments 31-33, the steel pipes constituting the steel pipe segments 32, 33 located above the seabed when the monopile 3 is installed on the seabed as shown in Figure 4(a) have the same wall thickness of 95 mm.

[0041] In addition, as the design external force acting on the monopile 3 changes in the height direction of the monopile 3, the design reference strengths of the plurality of steel pipe segments 31 to 33 provided at each height of the monopile 3 are different. In the third embodiment, similar to the first and second embodiments, the part composed of the middle and upper steel pipe segments 32 and 33 of the monopile 3 will be described by taking the case where the design external force acting on the monopile 2 is large as an example. In contrast, the steel pipes 31c to 31g excluding the steel pipes 31a and 31b at the lower end of the lower steel pipe segment 31 of the monopile 3, and the steel pipes 32a to 32h and 33a to 33i constituting the middle and upper steel pipe segments 32 and 33 are made of TMCP steel HBL385 for building structures, and their design reference strength is 385 N / mm 2 . Also, the lowermost steel pipe 31a of the steel pipe segment 31 is made of the steel grade SM520B specified in Japanese Industrial Standard JIS G3106:2024, and its design reference strength is 325 N / mm 2 in the range where the wall thickness t is 75 mm < t ≤ 100 mm. And the second steel pipe 31b from the bottom of the steel pipe segment 31 is made of TMCP steel HBL355 for building structures, and its design reference strength is 355 N / mm 2 2 . 2

[0042] Furthermore, in the monopile 3 of the third embodiment, among the steel pipes 31a to 31g, 32a to 32h, and 33a to 33i constituting the monopile 3, the wall thickness t and the outer diameter D of two adjacent steel pipes in the height direction and having different design reference strengths are the same. That is, the wall thickness t (85 mm) and the outer diameter D (10000 mm) of the steel pipe 31a made of the steel grade with a design reference strength of 325 N / mm 2 and the steel pipe 31b made of the steel grade with a design reference strength of 355 N / mm 2 are the same. Similarly, the wall thickness t and the outer diameter D of the steel pipe 31b made of the steel grade with a design reference strength of 355 N / mm 2 and the steel pipe made of the steel grade with a design reference strength of 385 N / mm 2 ​​The steel pipes 31c made of the above steel types have the same wall thickness t (85 mm) and outer diameter D (10,000 mm).

[0043] In this way, the wall thickness t of the steel pipes is set so that the wall thickness t (95 mm) of the steel pipes 32a to 32h and 33a to 33i constituting the steel pipe segments 32 and 33 in the portion of the monopile 3 where the design external force is large, that is, the wall thickness t (95 mm) of the steel pipes 32a to 32h and 33a to 33i constituting the steel pipe segments 32 and 33, is equal to or larger than the wall thickness t (85 mm or 90 mm) of the other portion of the monopile 3, that is, the steel pipes 31a to 31g constituting the steel pipe segment 31. In addition, the design standard strength (385 N / mm 2 ) is the design standard strength (325 N / mm 2 , 355N / mm 2 , or 385N / mm 2 ) The steel grades are selected so that the above-mentioned condition is satisfied. When welding different steel grades together, welding materials that correspond to the steel grade with low strength can be selected.

[0044] According to the monopile 3 of the third embodiment, the same effects as those of the monopile 1 of the first embodiment can be obtained.

[0045] In the monopile 3 of the third embodiment, the diameter-thickness ratios (ratios of outer diameter D to wall thickness t) D / t of all the steel pipes 31a to 31g, 32a to 32h, and 33a to 33i constituting the steel pipe segments 31 to 33 of the monopile 3 are limited to 120 or less, and the design standard strength (325 N / mm 2 , 355N / mm 2 ) to the design standard strength (385N / mm 2 ) This makes it possible to prevent the monopile 3 from buckling and to give the monopile 3 a more rational structure. (Fourth embodiment) FIG. 5(a) shows the details of the monopile 4 according to the fourth embodiment, and FIG. 5(b) shows the transition piece 5 connected to cover the upper end of the monopile 4.

[0046] As shown in Fig. 5(a), the monopile 4, like the monopile 1 of the first embodiment, the monopile 2 of the second embodiment, and the monopile 3 of the third embodiment, is constructed by stacking a plurality of steel pipes in its height direction and integrating these steel pipes by welding. Specifically, the monopile 4 is constructed by stacking three tiers of steel pipe segments 41-43 from the bottom to the top of the monopile 4. Each of these steel pipe segments 41-43 is constructed by arranging a plurality of steel pipes 41a-41g, 42a-42h, and 43a-43i, each consisting of a single pipe approximately 3-4 m in length, and integrating these steel pipes by welding. The monopile 4 is constructed by arranging these steel pipe segments 41-43 and integrating them by welding.

[0047] The monopile 4 is installed on the seabed so that the middle of the part formed by the steel pipe segment 42 is at the seabed surface, and the middle of the part formed by the steel pipe segment 43 is at seawater level.

[0048] In the monopile 4 of the fourth embodiment, unlike the monopile 1 of the first embodiment and the monopile 3 of the third embodiment, the wall thickness t of the steel pipes 41a to 41g, 42a to 42h, 43a to 43i that make up all of the steel pipe segments 41 to 43 of the monopile 4 is 85 mm and is the same.

[0049] Further, as the design external force acting on the monopile 4 varies in the height direction of the monopile 4, the design reference strengths of the plurality of steel pipe segments 41 to 43 provided at each height of the monopile 4 are different. In the fourth embodiment, similar to the first embodiment, the second embodiment, and the third embodiment, the portion constituted by the middle steel pipe segment 42 of the monopile 4 will be described by taking the case where the design external force acting on the monopile 4 is larger than other portions as an example. In contrast, the steel pipes 41a to 41f excluding the upper steel pipe 41g of the steel pipe segment 41, and the sixth steel pipe 43f from the bottom of the steel pipe segment 43 are made of TMCP steel HBL385 for building structures, and its design reference strength is 385 N / mm 2 In addition, the upper steel pipe 41g of the steel pipe segment 41, the steel pipes 42a to 42h constituting the steel pipe segment 42, and the steel pipes 43a to 43e from the first to the fifth from the bottom of the steel pipe segment 43 are made of TMCP steel HBL440 for building structures, and its design reference strength is 440 N / mm 2 In addition, the seventh steel pipe 43g from the bottom of the steel pipe segment 43 is made of TMCP steel HBL355 for building structures, and its design reference strength is 355 N / mm 2 In addition, the eighth steel pipe 43h from the bottom of the steel pipe segment 43 is made of the steel grade SM520 defined in Japanese Industrial Standard JIS G3106:2024, and its design reference strength is 325 N / mm when the wall thickness t is in the range of 75 mm < t ≤ 100 mm 2 In addition, the ninth steel pipe 43i from the bottom of the steel pipe segment 43 is made of the steel grade SM490 defined in Japanese Industrial Standard JIS G3106:2024, and its design reference strength is 295 N / mm when the wall thickness t is in the range of 40 mm < t ≤ 100 mm 2 In the steel pipes 43f to 43i from the sixth to the ninth from the bottom of the steel pipe segment 43, considering that the stress transmitted from the transition piece 5 gradually changes and the acting stress decreases toward the upper side, the strength of the steel grade applied is changed. 2 In addition, the upper steel pipe 41g of the steel pipe segment 41, the steel pipes 42a to 42h constituting the steel pipe segment 42, and the steel pipes 43a to 43e from the first to the fifth from the bottom of the steel pipe segment 43 are made of TMCP steel HBL440 for building structures, and its design reference strength is 440 N / mm 2 In addition, the seventh steel pipe 43g from the bottom of the steel pipe segment 43 is made of TMCP steel HBL355 for building structures, and its design reference strength is 355 N / mm 2 In addition, the eighth steel pipe 43h from the bottom of the steel pipe segment 43 is made of the steel grade SM520 defined in Japanese Industrial Standard JIS G3106:2024, and its design reference strength is 32\

[0050] Furthermore, in the monopile 4 of the fourth embodiment, among the steel pipes 41a to 41g, 42a to 42h, and 43a to 43i that constitute the monopile 4, the wall thickness t and the outer diameter D of two steel pipes that are adjacent in the height direction and have different design standard strengths are set to be the same. 2 Steel pipe 41b is made of steel with a design strength of 385N / mm 2 The wall thickness t (85 mm) and outer diameter D (10,000 mm) of the steel pipe 41c made of the same steel type are set to be the same. Similarly, the design standard strength is 385 N / mm 2 Steel pipe 41f made of steel grade and steel pipe with a design standard strength of 440N / mm 2 The wall thickness t (85 mm) and outer diameter D (10,000 mm) of the steel pipe 41g made of the above steel grades are all the same.

[0051] In this way, the part of the monopile 4 where the design external force is large, that is, the steel pipes 42a to 42h constituting the steel pipe segment 42, have a design standard strength (440 N / mm 2 ) is the design standard strength (385 N / mm 2 ) or more. When welding different steel types together, welding materials that correspond to the steel type with lower strength can be selected.

[0052] According to the monopile 4 of the fourth embodiment, in addition to obtaining the same effects as the monopile 2 of the second embodiment, by applying a more economical steel type to the upper steel pipes 43f to 43i of the steel pipe segment 43, further rationalization is achieved compared to the monopile 2 of the second embodiment.

[0053] Furthermore, in the monopile 4 of the fourth embodiment, the steel pipes 41a-41g, 42a-42h, and 43a-43i constituting all of the steel pipe segments 41-43 of the monopile 4 have the same wall thickness of 85 mm. This makes it possible to suppress stress concentration at the welded joints of the steel pipes 41a-41g, 42a-42h, and 43a-43i constituting the steel pipe segments 41-43, thereby avoiding a decrease in fatigue life. Furthermore, unlike welded joints between steel pipes of different wall thicknesses, there is no need to provide a thickness-varying portion to suppress stress concentration, and cutting is not required, reducing the amount of work required to process the welded joints. [Explanation of symbols]

[0054] 1, 2, 3, 4, 9 Monopiles 11~13, 21~23, 31~33, 41~43, 91~93 Steel pipe segments 11a~11g, 12a~12h, 13a~13i, 21a~21g, 22a~22h, 23a~23i, 31a~31g, 32a ~32h, 33a~33i, 41a~41g, 42a~42h, 43a~43i, 91a~91g, 92a~92h, 93a~93i steel pipe 5 Transition Piece 6 Offshore wind power generation facilities 60 Tower

Claims

1. A monopile installed on the seabed to support an offshore wind power generation facility, The monopile is configured by stacking a plurality of steel pipes in the height direction of the monopile and integrating them by welding, At least one of the plurality of steel pipes has a different design reference strength, A monopile, wherein, among the plurality of steel pipes, the steel pipes located above the seabed surface when the monopile is installed on the seabed have the same wall thickness.

2. 2. A monopile according to claim 1, wherein two of the plurality of steel pipes that are adjacent in the height direction and have different design standard strengths have the same wall thickness and outer diameter.

3. 3. The monopile according to claim 1, wherein the wall thicknesses of all of the plurality of steel pipes are set to be the same.

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