Semi-submersible floating foundation and method for constructing semi-submersible floating foundation

Abstract

To provide a semi-submersible floating foundation allowing its construction to be rather easily carried out and a construction method for the semi-submersible floating foundation.SOLUTION: A semi-submersible floating foundation 2 for ocean wind power generation facilities 1 is provided with: a center column 3 supporting a supporting column 12 of a wind turbine 11; four side columns 4, 4 arranged separately from each other in four radial directions of the center column 3; and four beams 5, 5 connecting the center column 3 to the side columns 4, 4. The center column 3 and the side columns 4 are formed by connecting a plurality of cylindrical precast members vertically. The beam 5 is formed through comprising a top plate 51, a bottom plate 52, and left / right side walls 53, 53 by connecting a plurality of rectangular-cylindrical precast members 54, 54 laterally.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semi-submersible floating foundation for an offshore wind power generation facility and a method for constructing a semi-submersible floating foundation. [Background technology]

[0002] Demand for renewable energy is increasing with the aim of reducing greenhouse gas emissions. Renewable energy sources include, for example, solar power generation, wind power generation, hydroelectric power generation, geothermal power generation, and biomass power generation. Wind power generation facilities are often installed in mountainous areas, far from residential areas, because the noise and vibrations produced by wind turbines can have an impact on the living environment and the impact on living spaces must be fully considered. However, it is difficult to secure land for installing large wind turbines in mountainous areas, and it is also difficult to secure transportation routes to wind power generation facilities and install transmission lines, etc. For this reason, the installation of wind power generation facilities on the sea (on water) is being considered. When constructing a structure on water, a floating structure may be used as the foundation. Floating foundation structures include semi-submersible, spar, purge, and TLP types. Of these, semi-submersible foundations (semi-submersible floating foundations) comprise a center column that supports the wind turbine's support columns, multiple side columns spaced apart around the center column, and arms that connect the center column and side columns. They have excellent stability against waves and wind, and have a relatively good track record. Semi-submersible floating foundations are often constructed primarily from steel members. However, constructing a semi-submersible floating foundation from concrete can reduce costs. For example, Patent Document 1 discloses a semi-submersible floating foundation whose main structural components are made from concrete. However, constructing a semi-submersible floating foundation using cast-in-place concrete requires a large amount of concrete, making construction time-consuming. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2015-513048 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a semi-submersible floating foundation that can be constructed relatively easily, and a method for constructing this semi-submersible floating foundation. [Means for solving the problem]

[0005] The semi-submersible floating foundation of the present invention, which solves the above-mentioned problems, comprises a center column that supports the wind turbine's support, four side columns arranged at intervals on all four sides of the center column, and four beams that connect the center column and the side columns. The center column and the side columns are formed by connecting multiple cylindrical precast members vertically. The beams are formed by connecting multiple rectangular tubular precast members horizontally, and have a top plate, a bottom plate, and left and right side walls. The pair of beams facing each other across the center column have their top and bottom plates continuous via the center column, and tension is applied to the pair of beams facing each other across the center column by beam tendons that are inserted through the top and bottom plates and penetrate the center column. The method for constructing the semi-submersible floating foundation includes the steps of: arranging a center column slab precast member that constitutes the slab of the center column; forming the beam by connecting beam precast members in all directions from the side of the center column slab precast member; and arranging side column slab precast members that constitute the slabs of the side columns at the ends of the beam. a step of applying tension to a pair of beams that face each other across the center column slab precast member by means of tendons extending from the side column slab precast member to another side column slab precast member that is disposed in an opposing position across the center column; The method includes a step of connecting a plurality of cylindrical precast members on the precast member for the center column slab, and a step of connecting a plurality of cylindrical precast members on the precast member for the side column slab.

[0006] According to this semi-submersible floating foundation and method for constructing a semi-submersible floating foundation, the foundation is formed by combining precast members, which makes it easier to construct than a semi-submersible floating foundation constructed using cast-in-place concrete. Furthermore, when constructing large-scale structures such as semi-submersible floating foundations using precast members, this method is also economically advantageous. Furthermore, by constructing the structure using precast members, the thickness of the members can be reduced, which in turn makes it possible to reduce the overall dimensions of the semi-submersible floating foundation. By reducing the size of the semi-submersible floating foundation, the construction yard can be made smaller, and the labor required to transport the semi-submersible floating foundation can also be reduced. Furthermore, by using four side columns as a floating body, it is possible to make the cross section of the side columns smaller than when using three side columns, which is expected to improve construction efficiency and lead to greater economy.

[0007] It is desirable that the cylindrical precast members constituting the center column and the side columns be connected by introducing tension along the axial direction of the center column and the side columns using column tendons arranged in the plurality of cylindrical precast members. It is also desirable that adhesive be applied to the contact surfaces of the cylindrical precast members. Furthermore, if the side column comprises a cylindrical outer tube and an inner tube formed in the internal space of the outer tube, and the space between the outer tube and the inner tube is divided into multiple sections by partition materials, buoyancy can be ensured by the inner tube even if the outer tube is damaged. In addition, the beam connects a plurality of rectangular tubular precast members by introducing tension along the axial direction of the beam using beam tendons arranged on the top plate and the bottom plate. It is desirable that adhesive be applied to the contact surfaces of the rectangular cylindrical precast members. moreover The pair of beams facing each other across the center column have the top plate and the bottom plate continuous through the center column. hand A pair of beams facing each other across the center column are tensioned by the beam tendons arranged on the top plate and the bottom plate and passing through the center column. but introduction Because This makes it possible to reduce the number of tendons and fixing devices, thereby reducing costs. [Effects of the Invention]

[0008] According to the semi-submersible floating foundation and the method for constructing this semi-submersible floating foundation of the present invention, construction can be carried out relatively easily, thereby shortening the construction period and reducing costs. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing an offshore wind power generation facility according to an embodiment of the present invention. [Figure 2] 1A and 1B are diagrams showing a semi-submersible floating foundation according to an embodiment of the present invention, in which (a) is a side view and (b) is a plan view. [Figure 3] A cross-sectional view showing a precast member for a center column slab. [Figure 4] FIG. [Figure 5] FIG. 10 is a plan view showing the arrangement of beam tendons. [Figure 6] FIG. 2 is a cross-sectional view of a side column. [Figure 7] 1 is a flowchart showing a method for constructing a semi-submersible floating foundation. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this embodiment, a foundation structure (semi-submersible floating foundation 2) of an offshore wind power generation facility (floating facility) 1 will be described. FIG. 1 is a perspective view of the offshore wind power generation facility 1. As shown in FIG. 1, the offshore wind power generation facility 1 has a wind turbine 11 and a support column 12 that supports the wind turbine 11, and is installed at a position higher than the water surface via the semi-submersible floating foundation 2. The wind turbine 11 is rotatably installed on the upper end of the support column 12. The support column 12 is installed upright on the semi-submersible floating foundation 2. The semi-submersible floating foundation 2 is a floating structure made primarily of concrete. The semi-submersible floating foundation 2 comprises a center column 3 that supports the support columns 12 of the wind turbine 11, four side columns 4, 4, ... arranged at intervals on all four sides of the center column 3, and four beams 5, 5, ... connecting the center column 3 and the side columns 4.

[0011] As shown in FIG. 1, the center column 3 has a cylindrical shape. The center column 3 is made of concrete. The center column 3 receives a load from the wind turbine 11 mounted on it, and therefore the bending moment is large. For this reason, the center column 3 of this embodiment is designed to have a design reference height of 80 N / mm 2 Concrete with a design strength of 180N / mm or more 2 The center column 3 is constructed from the above-mentioned ultra-high strength fiber reinforced concrete. The type and strength of the concrete that constitutes the center column 3 may be determined appropriately depending on the expected bending moment, the load of the wind turbine that will be placed on top, etc. Figure 2 shows a semi-submersible floating foundation 2. As shown in Figure 2(a), the center column 3 comprises a center column slab precast member 31 that forms the base of the center column 3, and a plurality of center column cylindrical precast members 32, 32, ... arranged on the center column slab precast member 31. In other words, the center column slab precast member 31 is formed by erecting an assembly of a plurality of center column cylindrical precast members 32, 32, ... connected vertically on the center column slab precast member 31.

[0012] 3 shows a cross-sectional view of the center column slab precast member 31. As shown in FIG. 3, the center column slab precast member 31 includes a top plate 33, a bottom plate 34, side walls 35, and connecting members 36. As shown in Figure 2(b), four beams 5, 5, ... are connected in a cross shape to the side surfaces (side walls 35) of the precast component for center column slab 31. That is, two pairs of beams 5, 5 are connected to the precast component for center column slab 31, facing each other with the precast component for center column slab 31 in between. An adhesive is applied to the joints (joints) between the side walls 35 and the beams 5 of the precast component for center column slab 31 to ensure waterproofing.

[0013] The beam 5 is shown in Figure 4. As shown in Figure 4, the beam 5 is in the shape of a square tube having a top plate 51, a bottom plate 52, and left and right side walls 53, 53. The beam 5 is formed by connecting multiple square tube precast members 54, 54, ... in the horizontal direction. The square tube precast members 54 are precast members made of concrete. An adhesive is applied to the end faces (joints) of the square tube precast members 54 to ensure watertightness.

[0014] As shown in FIG. 3 , a pair of beams 5, 5 facing each other across the center column 3 are continuous via the center column 3. That is, the top plate 51 and the bottom plate 52 of each of the pair of beams 5, 5 are connected to the top plate 33 or the bottom plate 34 of the precast member 31 for the center column slab, thereby arranging the pair of beams 5, 5 coaxially. As shown in FIG. 5 , beam tendons 55 are disposed in the top plate 51 and the bottom plate 52 of each of the pair of beams 5, 5 facing each other across the center column 3, penetrating the center column 3 (the top plate 33 and the bottom plate 34). The beam tendons 55 (multi-strand or single-strand) introduce tension along the axial direction of the beams 5. FIG. 5 is a plan view showing the arrangement of the beam tendons 55. In this embodiment, the beam tendons 55 are fixed to the outer wall portion of the side column 4 (the wall portion opposite the wall portion facing the center column 3), as shown in FIG. 5 .

[0015] As shown in FIG. 3 , the base slab 34 of the center column slab precast member 31 is formed at the same height as the base slabs 52 of the beams 5, and connects the base slabs 52 of the beams 5 that face each other across the center column 3. The base slab 34 has through holes formed in a lattice pattern in a plan view, through which beam tendons 55 arranged on the base slabs 52 of the beams 5 are inserted. The beam tendons 55 inserted through one pair of beams 5, 5 connected to the base slab 34 are at a different height position from the beam tendons 55 inserted through the other pair of beams 5, 5. This allows the beam tendons 55 arranged in different directions to cross each other without coming into contact with each other.

[0016] As shown in FIG. 3 , the top plate 33 of the center column slab precast member 31 is formed at the same height as the top plates 51 of the beams 5. The top plate 33 connects the top plates 51 of the beams 5 that face each other across the center column 3. The top plate 33 has through holes formed in a lattice pattern in a plan view, through which beam tendons 55 arranged on the top plates 51 of the beams 5 are inserted. The height position of the beam tendons 55 inserted through one pair of beams 5, 5 connected to the top plate 33 is different from the height position of the beam tendons 55 inserted through the other pair of beams 5, 5. This allows the beam tendons 55 arranged in different directions to cross each other without coming into contact with each other.

[0017] As shown in Figure 3, the connecting member 36 is formed on the upper surface of the top plate 51. The cylindrical precast member 32 for the center column is connected to the connecting member 36. At least the planar shape of the upper end of the connecting member 36 is the same as the cylindrical precast member 32 for the center column. As shown in Figure 2(b), the cylindrical precast member 32 for the center column is placed on the upper surface of the connecting member 36. A cylindrical pillar is formed by connecting multiple center column cylindrical precast members 32 one above the other. The topmost center column cylindrical precast member 32 is configured to be connectable to the support pillar 12 that supports the wind turbine 11. An adhesive is applied to the joints (contact surfaces) between the precast members (center column precast members 31, center column cylindrical precast members 32) that make up the center column 3 to ensure watertightness, and waterstops, gaskets, etc. are installed as needed.

[0018] Tension is introduced to the center column 3 in the axial direction of the center column 3 by center column tendons (multi-strand or single-strand) arranged in multiple center column cylindrical precast members 32, 32, ... (not shown). One end of the center column tendon is fixed to the center column cylindrical precast member 32 provided at the top, and the other end of the center column tendon is fixed to the center column slab precast member 31. The center column tendons are inserted between the beam tendons 55 arranged in a lattice pattern in the center column slab precast member 31 so as not to come into contact with the beam tendons 55.

[0019] As shown in Figure 1, four side columns 4 are arranged at intervals around the center column 3. The intervals between adjacent side columns 4 are the same. The side columns 4 are connected to the center column 3 via beams 5. The side column 4 has a cylindrical shape. Figure 6 shows the side column 4. As shown in Figure 6, the side column 4 is a double-layered structure comprising an outer cylinder 41 and an inner cylinder 42. The upper end of the side column 4 is shielded by a roof 4a. The side column 4 is formed from a side column slab precast member 43, a plurality of outer cylinder cylindrical precast members 44, 44, ... placed on the side column slab precast member 43, and a plurality of inner cylinder cylindrical precast members 45, 45, ... disposed within the side column slab precast member 43 and the outer cylinder 41.

[0020] The precast member 43 for the side column slab is a concrete member and includes a top plate 47, a bottom plate 48, and side walls 49. The side walls 49 form the outer walls of the base ends of the side columns 4. The lower ends of the side walls 49 are shielded by the bottom slab 48. In addition, adhesive is applied to the outer surfaces of the side walls 49 on the center column 3 side at the contact points (joints) with the beams 5 (top slab 51, bottom slab 52, side walls 53, 53) to ensure waterproofing.

[0021] The bottom slab 48 of the precast member 43 for the side column slab is formed at the same height as the bottom slab 52 of the beam 5. The bottom slab 52 of the beam 5 is connected to the bottom slab 48. A through hole is formed in the bottom slab 48 along the axial extension line of the beam 5. A beam tendon 55 (see Figure 3) arranged on the bottom slab 52 of the beam 5 is inserted through this through hole. The top plate 47 of the precast member 43 for side column slabs is formed at the same height as the top plate 51 of the beam 5. The top plate 47 covers the gap between the side wall 49 and the inner cylinder 42 at the upper end of the precast member 43 for side column slabs. The top plate 51 of the beam 5 is connected to the top plate 47. A through hole is formed in the top plate 47 along the axial extension line of the beam 5. A beam tendon 55 arranged on the top plate 51 of the beam 5 is inserted through this through hole.

[0022] As shown in FIG. 6 , the outer cylinder 41 is formed into a cylindrical shape by stacking multiple concrete cylindrical outer cylinder precast members 44, 44, ... one above the other on a top plate 47. Adhesive is applied to the joints (contact surfaces) between the precast members (side column slab precast members 43 and outer cylinder cylindrical precast members 44) that make up the outer cylinder 41, and water stops, gaskets, etc. are installed as needed. Tension is applied to the outer cylinder 41 along the axial direction of the side column 4 by external cylinder tendons (not shown) that are arranged in the multiple external cylinder cylindrical precast members 44, 44, ... One end of the external cylinder tendon is fixed to the uppermost external cylinder cylindrical precast member 44, and the other end of the external cylinder tendon is fixed to the side column slab precast member 43. The outer tube tendons (for example, PC steel bars) intersect with the beam tendons 55 between the beam tendons 55 so as not to come into contact with the beam tendons 55 .

[0023] As shown in FIG. 6 , the inner tube 42 is formed into a cylindrical shape by vertically connecting multiple cylindrical inner tube precast members 45, 45, .... The inner tube 42 is formed in the internal space of the outer tube 41 and the side column slab precast members 43. Tension along the axial direction of the side column 4 is introduced into the inner tube 42 by inner tube tendons (not shown) arranged in the multiple inner tube cylindrical precast members 45, 45, .... One end of the inner tube tendon is fixed to the uppermost inner tube cylindrical precast member 45, and the other end of the inner tube tendon is fixed to the bottom slab 48 of the side column slab precast member 43. The inner tube tendons cross the beam tendons 55 between the beam tendons 55 so as not to come into contact with them.

[0024] The cylindrical precast member 45 for the inner tube is made of concrete (e.g., ultra-high-strength fiber-reinforced concrete) or steel. A plurality of (four in this embodiment) steel partition members 46 are disposed at equal intervals around the circumference between the outer surface of the cylindrical precast member 45 for the inner tube and the inner surface of the cylindrical precast member 44 for the outer tube. In other words, the space between the outer tube 41 and the inner tube 42 is divided into multiple sections by the partition members 46. The partition members 46 are disposed at least within the flooded range (e.g., from 5 m above the draft to 3 m below the draft). An intermediate slab 4b is formed in the side column 4 at a height corresponding to the lower end of the flooded range to shield the gap between the outer tube 41 and the inner tube 42 and divide the space between the outer tube 41 and the inner tube 42 into upper and lower sections. Furthermore, within the precast member 43 for the side column slab, a plurality of (four in this embodiment) partition members 46, 46, ... made of steel are also arranged at equal intervals in the circumferential direction between the outer surface of the cylindrical precast member 45 for the inner cylinder and the inner surface of the side wall 49 of the precast member 43 for the side column slab. In other words, the space surrounded by the top plate 47, bottom plate 48, side wall 49 and inner cylinder 42 of the precast member 43 for the side column slab is divided into a plurality of sections by the partition members 46, 46, ...

[0025] Next, we will explain the method for constructing the semi-submersible floating foundation 2 of this embodiment. Figure 7 shows the steps of the method for constructing the semi-submersible floating foundation 2. The method for constructing the semi-submersible floating foundation 2 includes a center slab forming process S1, a beam forming process S2, a side slab forming process S3, a slab tensioning process S4, a center column forming process S5, a center column tensioning process S6, a side column forming process S7, and a side column tensioning process S8. The center slab forming step S1 is a step of disposing a precast member 31 for a center column slab. The beam forming process S2 is a process of forming the beam 5 by connecting square tubular precast members 54, 54, ... in all directions from the side of the center column slab precast member 31. Water-stopping material is placed between the square tubular precast members 54. At this time, the square tubular precast members 54, 54, ... are temporarily joined by applying compressive force using PC steel bars.

[0026] The side slab forming step S3 is a step of disposing a precast member 43 for a side column slab at the end of the beam 5 opposite the center column 3. The slab tensioning process S4 is a process of introducing tension into the beams 5 using the post-tensioning method. First, beam tension members 55 (multi-strand or single strand) are installed from the side column slab precast member 43 to another side column slab precast member 43 arranged in an opposing position across the center column 3. Next, the beam tension members 55 are used to introduce tension into a pair of beams 5, 5 that face each other across the center column slab precast member 31.

[0027] The center column formation process S5 is a process of stacking a plurality of center column cylindrical precast members 32, 32, ... on the center column slab precast member 31. At this time, the plurality of center column cylindrical precast members 32, 32, ... are temporarily joined by applying compressive force using PC steel rods. The center column tensioning process S6 is a process of introducing tension into the center column 3 by the post-tensioning method. First, the center column tension members (multi-strand or single strand) are arranged from the center column cylindrical precast member 32 arranged at the top to the center column slab precast member 31. Next, tension is introduced into the center column tension members.

[0028] The side column forming process S7 is a process of forming an outer cylinder 41 on the side column slab precast member 43 and forming an inner cylinder 42 inside the side column slab precast member 43 and the outer cylinder 41. The outer cylinder 41 is formed by stacking a plurality of outer cylinder cylindrical precast members 44 on the side column slab precast member 43. At this time, the plurality of outer cylinder cylindrical precast members 44, 44, ... are temporarily joined by applying compressive force using PC steel rods. The inner cylinder 42 is formed by stacking a plurality of inner cylinder cylindrical precast members 45 inside the side column slab precast member 43 and the outer cylinder 41. At this time, the plurality of inner cylinder cylindrical precast members 45, 45, ... are temporarily joined by applying compressive force using PC steel rods.

[0029] The side column tensioning step S8 is a step of introducing tension to the outer tube 41 and inner tube 42 by the post-tensioning method. First, outer tube tension members are arranged from the outer tube cylindrical precast member 44 arranged in the uppermost row to the side column slab precast member 43, and inner tube tension members are arranged from the inner tube cylindrical precast member 45 arranged in the uppermost row to the side column slab precast member 43. Next, tension is introduced to the outer tube tension members and inner tube tension members.

[0030] According to the semi-submersible floating foundation 2 and the method for constructing the semi-submersible floating foundation 2 of this embodiment, the foundation is formed by combining precast members, which makes it easier to construct than constructing the semi-submersible floating foundation 2 using cast-in-place concrete. Furthermore, when a large-scale structure such as the semi-submersible floating foundation 2 is constructed using precast members, this is also economically advantageous. Furthermore, by constructing the structure using precast members, the thickness of the members can be reduced, which in turn makes it possible to reduce the overall dimensions of the semi-submersible floating foundation 2. By reducing the size of the semi-submersible floating foundation 2, the construction yard can be made smaller, and the effort required to transport the semi-submersible floating foundation 2 can be reduced. Furthermore, it also makes it possible to reduce the dimensions of the barge used to transport the semi-submersible floating foundation 2. In addition, by reducing the cross-section of the precast members, it is possible to reduce the cost of transporting the precast members, thereby reducing the overall cost of the construction work.

[0031] Furthermore, by using four side columns 4 as a floating body, it is possible to make the cross section of each side column 4 smaller than when using three side columns 4, which is more economical. Furthermore, by providing four side columns 4 and arranging the beams 5 in a cross shape, it becomes possible to arrange the beam tendons 55 in a grid pattern, facilitating installation work. Furthermore, by arranging the beam tendons 55 so that they pass through the center column 3, the number of anchoring points for the beam tendons 55 can be reduced, simplifying the structure and ultimately improving workability.

[0032] Because the side column 4 has a double structure comprising an outer cylinder 41 and an inner cylinder 42, even if a ship, floating object, or the like comes into contact with the side column 4 and the outer cylinder 41 is damaged, buoyancy can be ensured by the inner cylinder 42. Furthermore, because the inside of the side column 4 is divided into multiple sections by partitions 46, even if damage occurs, the entire side column 4 will not be flooded, and the amount of water entering the interior can be limited. In addition, since a partition material 46 is arranged inside the side column 4, it is possible to reduce bending due to water pressure, which in turn allows the thickness of the precast members (precast member 43 for side column slab, cylindrical precast member 44 for outer tube, cylindrical precast member 45 for inner tube) to be reduced.

[0033] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and each of the above-described components can be appropriately modified within the scope of the present invention. For example, in the above embodiment, the side column 4 has a double structure including an outer cylinder 41 and an inner cylinder 42, but the center column 3 may have a double structure. Also, the side column 4 does not necessarily have to have a double structure. In the above embodiment, the pair of beams 5, 5 facing each other across the center column 3 are formed as a continuous structure, but the corresponding pair of beams 5, 5 do not necessarily have to be continuous.

[0034] In addition, we have explained the case where beam tendons 55 that pass through the center column 3 are placed on a pair of beams 5, 5 facing each other across the center column 3, but the beam tendons 55 placed on the beam 5 do not necessarily have to pass through the center column 3 and may be fixed to the center column 3. In the side column 4, a slab may be formed corresponding to the height position of the top plate 51 of the beam 5, and the beam tendons 55 may be fixed to the slab. The strength of the concrete that constitutes the side columns 4 and the beams 5 may be determined appropriately. The side column tensioning step S8 may be performed as needed, and may be omitted if the axial bending moment is not large.

[0035] In the above embodiment, the center column 3, side columns 4, and beams 5 are formed from precast members, but the center column 3, side columns 4, and beams 5 do not necessarily all need to be formed from precast members. For example, the beams 5 may be formed from precast members, while the center column 3 and side columns 4 are formed by conventional construction methods. Alternatively, the center column 3 and side columns 4 may be formed from precast members, while the beams 5 are formed by conventional construction methods.

[0036] In the above embodiment, the joints between the center column 3 and the beams 5, the joints between the side columns 4 and the beams 5, and the joints between the rectangular tubular precast members 54 are bonded with an adhesive. However, the waterproof structures of the joints between the center column 3 and the beams 5, the joints between the side columns 4 and the beams 5, and the joints between the rectangular tubular precast members 54 are not limited to this and may be determined as appropriate. For example, seal grooves may be formed as needed in the joints (abutment surfaces) between the center column 3 and the beams 5, the joints (abutment surfaces) between the side columns 4 and the beams 5, and the joints (abutment surfaces) between the rectangular tubular precast members 54, and waterproof materials such as sealants and gaskets may be disposed in these seal grooves. In other words, the precast members constituting the center column 3, the side columns 4, and the beams 5 may be joined together while ensuring watertightness using waterproof materials such as sealants and gaskets interposed as needed. This reduces the rigidity at the joints (seams), which in turn makes it possible to realize a flexible structure that follows wave motion and rationalize the structure by reducing cross-sectional forces. Similarly, the waterproof structure between the precast members that make up the center column 3 and the side column 4 is not limited to the content shown in the above embodiment (bonding with adhesive), but may be determined appropriately depending on the required watertightness and location (height position relative to the water level, etc.). [Explanation of symbols]

[0037] 1. Offshore wind power generation facilities 11 Windmill 12 pillars 2. Semi-submersible floating foundation 3 Center Column 31 Precast member for center column slab 32 Cylindrical precast member for center column 33 Top version 34 bottom plate 35 side wall 4 Side Columns 41 Outer cylinder 42 Inner cylinder 43 Precast members for side column slabs 44 Cylindrical precast member for outer cylinder 45 Cylindrical precast member for inner tube 46 Partition material 47 Top version 48 Bottom plate 49 Side wall 5 Beam 51 Top version 52 bottom plate 53 Side wall 54 Square cylindrical precast member 55 Beam tendons

Claims

1. a center column supporting the wind turbine support; four side columns arranged at intervals on all four sides of the center column; a semi-submersible floating foundation for a wind power generation facility, the semi-submersible floating foundation comprising four beams connecting the center column and the side columns, The center column and the side columns are formed by vertically connecting a plurality of cylindrical precast members, The beam is formed in a rectangular cylindrical shape having a top plate, a bottom plate, and left and right side walls, The pair of beams facing each other across the center column have the top plate and the bottom plate continuous with each other via the center column, A semi-submersible floating foundation, characterized in that tension is introduced into a pair of beams facing each other across the center column by beam tendons inserted through the top plate and the bottom plate and penetrating the center column.

2. a center column supporting the wind turbine support; four side columns arranged at intervals on all four sides of the center column; a semi-submersible floating foundation for a wind power generation facility, the semi-submersible floating foundation comprising four beams connecting the center column and the side columns, The beam is formed by connecting a plurality of rectangular cylindrical precast members in the horizontal direction, and has a top plate, a bottom plate, and left and right side walls, The pair of beams facing each other across the center column have the top plate and the bottom plate continuous with each other via the center column, A semi-submersible floating foundation, characterized in that tension is introduced into a pair of beams facing each other across the center column by beam tendons inserted through the top plate and the bottom plate and penetrating the center column.

3. 2. The semi-submersible floating foundation according to claim 1, wherein tension is applied to the center column and the side columns along their axial directions by column tendons arranged in the plurality of cylindrical precast members.

4. The side column comprises a cylindrical outer cylinder and an inner cylinder formed in the internal space of the outer cylinder, 4. A semi-submersible floating foundation according to claim 1, wherein the space between the outer cylinder and the inner cylinder is divided into a plurality of sections by partitions.

5. A semi-submersible floating foundation as described in claim 3, characterized in that adhesive is applied to the contact surfaces between the cylindrical precast members.

6. A semi-submersible floating foundation as described in claim 2, characterized in that adhesive is applied to the contact surfaces between the square cylindrical precast members.

7. A method for constructing a semi-submersible floating foundation comprising a center column, four side columns arranged at intervals on all four sides of the center column, and four beams connecting the center column and the side columns, comprising: a step of disposing a precast member for a center column slab that constitutes the slab of the center column; a step of forming the beam by continuously arranging beam precast members in four directions from the side surfaces of the center column slab precast member; a step of disposing a precast member for a side column slab that constitutes a slab of the side column on the end of the beam; a step of applying tension to a pair of beams that face each other across the center column slab precast member by means of tendons extending from the side column slab precast member to another side column slab precast member that is disposed in an opposing position across the center column; a step of consecutively installing a plurality of cylindrical precast members on the precast member for the center column slab; and a step of connecting a plurality of cylindrical precast members on the precast members for the side column slabs.

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