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

Abstract

To propose a semisubmersible floating type foundation which enables reduction of the weight and relatively easy construction, and to propose a construction method of the semisubmersible floating type foundation.SOLUTION: A semisubmersible floating type foundation 2 of a wind generating facility includes: a center column 3 supporting a column 12 of a wind mill 11; three side columns 4, 4, 4 arranged at intervals, centered on the center column 3; and beams 5 each connecting the center column 3 with the side column 4. The center column 3 includes: a steel slab 31; and a cylindrical body 32 erected from the slab 31. The beam 5 is made of pre-stress concrete in which beam tension materials 55 are arranged. A composite precast segment 6 formed by combining concrete with a steel material is disposed between each beam 5 and the slab 31. The composite precast segment 6 is formed with a fixation part 62 of the beam tension material 55.SELECTED DRAWING: Figure 2

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) are comprised of a center column, multiple side columns spaced around the center column, and beams connecting 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 elements are made from concrete. To reduce the construction costs of floating wind power generation facilities, semi-submersible floating foundations are sometimes moored to a quay and the wind turbines are installed using a crane on the quay. In this case, the draft must be smaller than the water depth at the quay. In addition, the draft of the semi-submersible floating foundation is adjusted by placing ballast so that it can effectively limit rocking caused by waves and wind. Concrete has a greater weight than steel, so if the main structural elements of a semi-submersible floating foundation are made of concrete, the areas that provide buoyancy must be larger, which results in an increase in the amount of concrete used. In addition, at the joint between the center column and the beam, large cross-sectional forces are generated due to wind loads and inertial forces caused by shaking, so it is necessary to place steel bars and prestressing steel members closely together, which makes construction time-consuming. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2015-513046 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 made lighter and constructed relatively easily, and a method for constructing this semi-submersible floating foundation. [Means for solving the problem]

[0005] To solve the above problems, the present invention provides a semi-submersible floating foundation for a wind power generation facility, comprising a center column supporting a support for a wind turbine, a plurality of side columns arranged at intervals around the center column, and a beam connecting the center column and the side columns. The center column comprises a steel slab and a cylindrical main body erected on the slab. The beam is made of prestressed concrete with prestressing steel bars. Furthermore, a composite precast segment made of a combination of concrete and steel is interposed between the beam and the slab, and an anchoring portion for the prestressing steel bars is formed in the composite precast segment. With this semi-submersible floating foundation, by making at least a portion of the center column out of steel, it is possible to reduce the weight and the amount of concrete compared to when it is made entirely out of concrete. In addition, because the prestressing steel members of the beams are fixed to the composite precast segments, it is possible to prevent the rebars and prestressing steel members from becoming entangled in the center column. This reduces the amount of work required during construction.

[0006] In addition, if the slab has a bottom steel plate for the slab attached to its bottom surface and an upper steel plate for the slab attached to its top surface, and the main body is made of prestressed concrete and penetrates the upper steel plate for the slab, with the lower end of the main body abutting the bottom steel plate, it is desirable to erect steel frame members at the corners between the main body and the bottom steel plate and the corners between the main body and the upper steel plate, and to arrange steel ties on the peripheral wall of the main body to connect the frame members facing each other across the peripheral wall. In this way, even if the main body of the center column is made of concrete, the main body is continuous (integrated) with the bottom steel plate and the upper steel plate, thereby obtaining the required strength at the ultimate limit state and the fatigue limit state. Furthermore, it is desirable that the composite precast segment has a steel section having a bottom segment steel plate and a top segment steel plate arranged above the bottom segment steel plate at a distance, and the anchoring sections made of concrete are formed at the beam-side end of the bottom segment steel plate and at the beam-side end of the top segment steel plate in correspondence with the positions of the PC tendons. This ensures stress transmission performance between the steel slab and the concrete beam.

[0007] The method for constructing a semi-submersible floating foundation of the present invention includes a segment fabrication process for fabricating the composite precast segments and beam segments that constitute the beams; a beam formation process for arranging the beam segments in predetermined positions to form the beams; a composite PC segment installation process for installing the composite precast segments at the base ends of the beams; a center column connection process for connecting the composite precast segments to the center columns; and a side column connection process for connecting the side columns to the ends of the beams. The segment fabrication process includes fabricating the steel sections by combining steel plates, fabricating the anchoring sections using the steel sections as gable formwork, and fabricating the beam segments using the composite precast segments as gable formwork. According to this method for constructing a semi-submersible floating foundation, the composite precast segments and the beam segments can be formed using the so-called match-cast method. In the composite PC segment installation process, any installation errors are measured and adjustment steel members are fixed to the composite precast segments, and in the center column connection process, the center column is fixed to the steel members. This makes it possible to easily integrate the beam and center column even if installation errors occur. [Effects of the Invention]

[0008] The semi-submersible floating foundation and the method for constructing this semi-submersible floating foundation of the present invention can be constructed relatively easily, thereby shortening the construction period and reducing costs. In addition, the lightweight structure ensures the desired buoyancy with the minimum necessary size. [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 plan view and (b) is a cross-sectional view taken along line IIB of (a). [Figure 3]These are diagrams showing a part of the center column, where (a) is a cross-sectional view showing the joint structure between the main body and the bottom steel plate for the slab, (b) is a longitudinal section showing the joint structure between the main body and the bottom steel plate for the slab, and (c) is a longitudinal section showing the joint structure between the main body and the top steel plate for the slab. [Figure 4] 4A and 4B are diagrams showing a composite precast segment, where (a) is a longitudinal section and (b) is a cross-sectional view taken along line IVB of (a). [Figure 5] 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 comprises a center column 3 that supports the support columns 12 of the wind turbine 11, three side columns 4, 4, 4 arranged at intervals around the center column 3, and beams 5, 5, 5 that connect the center column 3 and the side columns 4.

[0011] Figure 2 shows the semi-submersible floating foundation 2. The center column 3 includes a slab 31 and a cylindrical main body 32 erected on the slab 31, as shown in Figures 2(a) and (b). The slab 31 is formed by combining steel plates, and includes a slab bottom steel plate 33 provided on the bottom surface and a slab top steel plate 34 provided on the top surface. The slab 31 has an outer shape that is significantly larger than the outer shape of the main body 32. The slab 31 also has beam joints 35 that protrude toward the beams 5. The beam joints 35 are made of steel material with an outer shape similar to that of the beams 5 (square cylindrical in this embodiment). As shown in FIG. 2(b), the main body 32 penetrates the center of the upper slab steel plate 34, and the lower end of the main body 32 abuts against the bottom slab steel plate 33. FIG. 3 shows a part of the main body 32. The main body 32 is made of prestressed concrete, and as shown in FIG. 3(a), PC steel members (column tendons 321) are provided in the center in the thickness direction. The column tendons 321 are arranged in the vertical direction of the main body 32. As shown in FIG. 3(b), a frame member 36 made of steel plate is erected at the corner between the main body 32 and the bottom steel plate 33 for the slab. Furthermore, as shown in FIG. 3(c), a frame member 36 made of steel plate is erected at the corner between the main body 32 and the top steel plate 34 for the slab. As shown in FIG. 3(a), a plurality of frame members 36 are provided at intervals in the circumferential direction of the main body 32. Steel cylindrical bodies 37 are provided on the outer and inner surfaces of the main body 32 in correspondence with the positions of the frame members 36. The frame members 36 are fixed (welded) to the cylindrical bodies 37. As shown in Figures 3(b) and (c), vertical steel ties 38 are arranged on the peripheral wall of the main body 32. As shown in Figure 3(b), the vertical ties 38 arranged on the upper side of the slab bottom steel plate 33 are arranged at the corners between the main body 32 and the slab bottom steel plate 33, and connect the frame members 36 that face each other across the peripheral wall. As shown in Figure 3(c), the vertical ties 38 arranged on the lower side of the slab top steel plate 34 are arranged at the corners between the main body 32 and the slab top steel plate 34, and connect the frame members 36 that face each other across the peripheral wall. Both ends of the vertical ties 38 are fixed (welded) to the cylindrical body 37 corresponding to the positions of the frame members 36. As shown in FIG. 3(b), horizontal ties 39 are fixed to the lower ends of the vertical ties 38 that connect the frame members 36 provided on the slab bottom steel plate 33 together.

[0012] As shown in Figure 2(a), three side columns 4 are arranged 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. 2(a) and 2(b), the side column 4 has a cylindrical shape. The side column 4 is made of concrete, and the upper end of the side column 4 is shielded by a top plate 41.

[0013] The beam 5 is made of prestressed concrete with prestressing steel (beam tendons 55). As shown in Figures 2(a) and (b), one end of the beam 5 is connected to the slab 31 of the center column 3, and the other end of the beam 5 is connected to the side column 4. The beam 5 has a rectangular cylindrical shape with a top plate 51, a bottom plate 52, and left and right side walls 53, 53. The beam 5 is formed by connecting multiple beam segments 54, 54, ... in the horizontal direction. The beam segments 54 are precast concrete members. As shown in Figure 4(a), beam tendons 55 are arranged in the top plate 51 and the bottom plate 52. Figure 4 shows the joint between the center column 3 and the beam 5. The beam tendons 55 are arranged along the longitudinal direction of the beam 5 and penetrate the multiple beam segments 54. One end of the beam tendon 55 is fixed to the side column 4, and the other end of the beam tendon 55 is fixed to a composite precast segment 6 interposed between the beam 5 and the slab 31.

[0014] As shown in FIG. 4( a ), the composite precast segment 6 is made by combining concrete and steel, and includes a steel portion 61 , an anchoring portion 62 , and a beam connecting portion 63 . The steel portion 61 has a segment bottom steel plate 64 and a segment upper steel plate 65 arranged above the segment bottom steel plate 64 at a distance. The steel portion 61 is welded to the slab 31 of the center column 3. The anchoring portions 62 are arranged corresponding to the beam tendons 55. In this embodiment, the anchoring portions 62 are formed at the beam 5 side end of the segment bottom steel plate 64 and the beam 5 side end of the segment upper steel plate 65, respectively. The anchoring portions 62 are made of concrete, and a pressure plate 67 is fixed to the end face of the anchoring portions 62. A segment vertical steel plate 66 is fixed to the beam 5 side end of the segment bottom steel plate 64. The segment vertical steel plate 66 is formed so as to be perpendicular to the segment bottom steel plate 64. Similarly, a segment vertical steel plate 66 is also fixed to the segment upper steel plate 65.

[0015] 4(a) and 4(b), in the anchoring portion 62, perforated steel dowels 621 are fixed at predetermined intervals to the segment bottom steel plate 64. In this embodiment, a pair of perforated steel dowels 621 are provided so as to sandwich the beam tendon 55 in a plan view. Reinforcing bars 622 arranged in a direction perpendicular to the beam tendon 55 pass through the perforated steel dowels 621. One end of the perforated steel dowels 621 is fixed to the pressure plate 67, and the other end is fixed to an end of the vertical segment steel plate 66. Similarly, perforated steel dowels 621 are fixed to the segment top steel plate 65, and reinforcing bars 622 are arranged to pass through the perforated steel dowels 621. In addition, dowels 623 are fixed to the vertical segment steel plate 66 in a position corresponding to the anchoring portion 62. The fixing portion 62 is formed in a state where the perforated steel plate dowels 621 and 623 are wrapped around it, thereby ensuring the unity with the steel portion 61 .

[0016] The beam connection portion 63 is a concrete portion formed on the end face of the steel portion 61 on the beam 5 side. The beam connection portion 63 in this embodiment includes a lower joint portion 631 and an upper joint portion 632 formed in a position facing the anchorage portion 62 with the vertical segment steel plate 66 in between, and a partition wall portion 633 interposed between the lower joint portion 631 and the upper joint portion 632. The lower joint portion 631 and the upper joint portion 632 have through holes formed therein through which the beam tendons 55 are inserted. A dowel 634 is fixed to the vertical segment steel plate 66 in a position corresponding to the position of the beam connection portion 63. The beam connection portion 63 is formed with the dowel 634 wrapped around it, thereby ensuring its unity with the steel portion 61.

[0017] The construction method for a semi-submersible floating foundation of this embodiment will now be described. As shown in Figure 5, the construction method for a semi-submersible floating foundation includes a segment manufacturing process S1, a beam forming process S2, a composite PC segment installation process S3, a center column connection process S4, and a side column connection process S5. The segment manufacturing process S1 is a process for manufacturing the composite precast segments 6 and the beam segments 54 that make up the beam 5. The segment manufacturing process S1 includes work S11 for manufacturing the steel section 61 by combining steel plates, work S12 for manufacturing the anchoring section 62 and the beam connection section 63 using the steel section 61 as the end formwork, and work S13 for manufacturing the beam segments 54 using the composite precast segments 6 as the end formwork. The beam forming process S2 is a process of arranging a plurality of beam segments 54, 54, ... in predetermined positions to form the beam 5. Water-stopping materials (not shown) are interposed between the beam segments 54. At this time, the beam segments 54 are temporarily joined by applying compressive force using PC steel rods.

[0018] The composite PC segment installation process S3 is a process of installing a composite precast segment 6 at the base end of the beam 5. In the composite PC segment installation process S3, the installation error is measured, and an adjustment steel member 68 is fixed (welded) to the steel part 61 of the composite precast segment 6. The center column connecting process S4 is a process of connecting the composite precast segment 6 to the center column 3. In the center column connecting process S4, the composite precast segment 6 (adjustment steel member 68) is welded to the slab 31 of the center column 3 to integrate the center column 3 and the beam 5. The side column connecting process S5 is a process of connecting the side column 4 to the tip of the beam 5. At this time, tension is introduced into the beam 5 using the post-tensioning method. That is, one end of the beam tendon 55 (multi-strand or single strand) through which the beam 5 is inserted is fixed (anchored) to the composite precast segment 6, and the other end is fixed (anchored) to the side column 4.

[0019] According to the semi-submersible floating foundation 2 and the method for constructing the semi-submersible floating foundation 2 of this embodiment, by making the slab 31 of the center column 3 out of steel, it is possible to reduce the weight and the amount of concrete used compared to when the entire center column is made out of concrete. In addition, because the beam tendons 55 of the beams 5 are fixed to the composite precast segments 6, it is possible to prevent the reinforcing bars and beam tendons 55 from becoming tangled in the center column 3. This reduces the amount of work required during construction.

[0020] Furthermore, frame members 36 made of steel plate are erected at the corners between the main body 32 and the bottom steel plate 33 for the slab and at the corners between the main body 32 and the top steel plate 34 for the slab, and steel ties 38 are arranged on the peripheral walls of the main body 32 to connect the frame members 36 facing each other across the peripheral wall. This ensures that the main body 32 of the center column 3 is continuous (integrated) with the bottom steel plate and the top steel plate, even if the main body 32 is made of concrete. As a result, the required strength is obtained at the ultimate limit state and the fatigue limit state. In addition, the composite precast segment 6 ensures stress transmission performance between the steel slab 31 and the concrete beam 5. Because the beam tendons 55 of the beams 5 are fixed to the composite precast segments 6, workability is superior to fixing the beam tendons 55 to the center column 3. In other words, if the beam tendons 55 of the beams 5 are fixed to the center column 3 to which multiple beams 5 are connected, the beam tendons 55 would need to be crossed three times within the center column 3, which would cause the beam tendons 55 to become tangled. On the other hand, by fixing the beam tendons 55 to the composite precast segments 6, it is possible to prevent the beam tendons 55 from becoming tangled. Furthermore, the main body 32 of the center column 3 generally has a large number of vertical reinforcing bars because large cross-sectional forces are generated by wind loads and inertial forces due to the swaying of the beams 5. Therefore, when the beam tendons 55 are fixed to the main body 32, the beam tendons 55 extending from each beam 5 and the vertical reinforcing bars are arranged in the main body 32, which complicates the arrangement of the reinforcing bars and the beam tendons 55. As a result, construction efficiency is poor. On the other hand, in the semi-submersible floating foundation 2 of this embodiment, the beam tendons 55 are fixed to the composite precast segments 6, so there is no interference between the reinforcing bars of the main body 32 and the beam tendons 55.

[0021] 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 case where the main body 32 of the center column 3 is made of concrete has been described, but the main body 32 of the center column 3 may also be made of steel. Furthermore, in the above embodiment, the beam 5 is formed by combining a plurality of beam segments 54, 54, . . . , but the beam 5 may also be formed by cast-in-place concrete. In the above embodiment, the segment vertical steel plates 66 are fixed to the ends of the segment bottom steel plates 64 and the segment upper steel plates 65, but the segment vertical steel plates 66 may be formed by bending the ends of the segment bottom steel plates 64 or the segment upper steel plates 65. In addition, the segment vertical steel plates may be steel plates fixed across the segment bottom steel plates 64 and the segment upper steel plates 65. In the above embodiment, the case where there are three side columns 4 has been described, but the number of side columns 4 is not limited, and may be, for example, four or more. In the above embodiment, the perforated steel plate dowels 621 are provided in the anchoring portions 62 of the composite precast segments 6, but the perforated steel plate dowels 621 may be provided as needed. The dowel structure used to join the steel portions 61 (steel) and the anchoring portions 62 (concrete) is not limited to the use of the perforated steel plate dowels 621. [Explanation of symbols]

[0022] 1. Offshore wind power generation facilities 11 Windmill 12 pillars 2. Semi-submersible floating foundation 3 Center Column 31 Slab 32 Main body 33 Bottom steel plate for slab 34 Upper steel plate for slabs 35 Beam joint 36 Bone members 37 Steel pipe 38 Tie material 4 Side Columns 5 Beam 51 Top version 52 bottom plate 53 Side wall 54 Beam Segments 55 Beam tendons (PC steel) 6 Composite Precast Segments 61 Steel Department 62 Fixing section

Claims

1. a center column supporting the wind turbine support; a plurality of side columns arranged at intervals around the center column; A semi-submersible floating foundation for a wind power generation facility comprising: a beam connecting the center column and the side columns, The center column includes a steel slab and a cylindrical main body portion erected on the slab, The beam is made of prestressed concrete with PC steel members arranged therein, A composite precast segment made of a combination of concrete and steel is interposed between the beam and the slab, A semi-submersible floating foundation, characterized in that the composite precast segments have anchorage portions for the PC steel members.

2. The slab comprises a bottom steel plate for a slab provided on a bottom surface thereof and a top steel plate for a slab provided on a top surface thereof, The main body is made of prestressed concrete and penetrates the top steel plate for the slab, and the lower end of the main body abuts against the bottom steel plate for the slab. a frame member made of a steel plate is erected at each of the corners between the main body and the bottom steel plate for the slab and the corners between the main body and the top steel plate for the slab, 2. A semi-submersible floating foundation as described in claim 1, characterized in that steel connecting members are arranged on the peripheral wall of the main body portion to connect the frame members that face each other across the peripheral wall.

3. The composite precast segment comprises: a steel section including a bottom steel plate for a segment and an upper steel plate for a segment disposed above the bottom steel plate for a segment at an interval; 3. A semi-submersible floating foundation as described in claim 1 or claim 2, characterized in that it comprises the anchoring portions made of concrete formed at the beam side end of the bottom steel plate for the segment and at the beam side end of the upper steel plate for the segment, corresponding to the positions of the PC steel members.

4. 4. A method for constructing a semi-submersible floating foundation according to claim 3, comprising: a segment manufacturing process for manufacturing the composite precast segment and a beam segment for constituting the beam; a beam forming step of arranging the beam segments at predetermined positions to form the beam; a composite PC segment installation process in which the composite precast segment is installed at the base end of the beam; a center column connecting step of connecting the composite precast segment to the center column; a side column connecting step of connecting the side column to the tip of the beam, A method for constructing a semi-submersible floating foundation, characterized in that the segment manufacturing process involves the following operations: manufacturing the steel section by combining steel plates; manufacturing the anchoring section using the steel section as a gable formwork; and manufacturing the beam segment using the composite precast segment as a gable formwork.

5. In the composite PC segment installation process, an installation error is measured and an adjustment steel member is fixed to the composite precast segment; 5. The method for constructing a semi-submersible floating foundation according to claim 4, wherein the center column connecting step includes fixing the center column to the steel member.

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