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EP-4225635-B1 - CONCRETE SUCTION ANCHOR

EP4225635B1EP 4225635 B1EP4225635 B1EP 4225635B1EP-4225635-B1

Inventors

  • Damiani, Rick
  • FRANCHI, Massimo

Dates

Publication Date
20260513
Application Date
20211005

Claims (15)

  1. Concrete suction anchor including a cylindrical structure (100) that has a lateral cylindrical wall and a longitudinal axis, wherein the cylindrical structure (100) is open at a bottom end and closed at a top end, wherein the cylindrical structure (100) defines a main cavity (115; 175; 730) open at the bottom end, wherein said lateral cylindrical wall of the cylindrical structure (100) includes a plurality of internal channels housing at least one pair of sets of post-tensioning tendons (125, 130), characterised in that a first set of post-tensioning tendons (125) is inclined with respect to said longitudinal axis by a first angle opposite to a second angle according to which a second set of post-tensioning tendons (130) is inclined with respect to said longitudinal axis, wherein each of said first and second angles has an absolute value larger than 0° and lower than 90°, wherein the concrete suction anchor is formed by two or more cylindrical modules, so that after post-tensioning, the post-tensioning tendons firmly maintain said two or more cylindrical modules together to form the cylindrical structure of the concrete suction anchor.
  2. Concrete suction anchor according to claim 1, wherein each of said first and second angles has an absolute value larger than 15° and lower than 75°, optionally larger than 30° and lower than 60°, more optionally equal to 45°.
  3. Concrete suction anchor according to claim 1 or 2, wherein said plurality of internal channels houses two or more pairs of sets of post-tensioning tendons (125, 130).
  4. Concrete suction anchor according to any one of claims 1 to 3, wherein the post-tensioning tendons (125) of the first set, the post-tensioning tendons (130) of the second set, and said plurality of internal channels are arranged according to three-dimensional (3D) helicoidal arrangements.
  5. Concrete suction anchor according to any one of claims 1 to 4, wherein post-tensioning is applied to said at least one pair of sets of post-tensioning tendons (125, 130) by anchorage wedges placed at the ends of each one of said plurality of internal channels, wherein said anchorage wedges are optionally placed at ring plates fixed at the ends of the cylindrical structure (100).
  6. Concrete suction anchor according to any one of claims 1 to 5, wherein said two or more cylindrical modules are two or more pre-cast cylindrical modules the lateral cylindrical wall of each one of which includes a plurality of internal passages, wherein each of said plurality of internal passages of said lateral cylindrical wall of each one of said two or more cylindrical modules forms a section of an internal channel of said plurality of internal channels.
  7. Concrete suction anchor according to any one of claims 1 to 6, wherein said top end of the cylindrical structure (100) is closed by a top lid (150; 950), optionally provided with top stiffeners (155), wherein top lid (150; 950) is optionally made of steel.
  8. Concrete suction anchor according to any one of claims 1 to 6, wherein said top end of the cylindrical structure (100) is closed by a top dome (105) defining a top internal buoyancy chamber (110; 160; 700) separated from the main cavity (115; 730), wherein an internal vent (740) puts the main cavity (115; 730) in fluid communication with the top internal buoyancy chamber (110; 160; 700), wherein a first top valve (710) is configured to put the top internal buoyancy chamber (110; 160; 700) in fluid communication with an external environment and a second top valve (720) is configured to put the main cavity (115; 730) in fluid communication with the external environment by means of a duct (725).
  9. Concrete suction anchor according to any one of claims 1 to 6, wherein said top end of the cylindrical structure (100) is closed by a top dome (105) defining a top internal buoyancy chamber (170; 180), wherein the cylindrical structure (100) has an intermediate internal buoyancy chamber (174; 184) that is interposed between the top internal buoyancy chamber (170; 180) and the main cavity (175; 185), wherein a top internal vent (770) puts the top internal buoyancy chamber (170; 180) in fluid communication with the intermediate internal buoyancy chamber (174; 184) and a bottom internal vent (780) puts the main cavity (175; 185) in fluid communication with the intermediate internal buoyancy chamber (174; 184).
  10. Concrete suction anchor according to any one of claims 1 to 9, further comprising a padeye (1000) protruding from a supporting plate (1100) that is incorporated into said lateral cylindrical wall, wherein the supporting plate (1100) is received in a corresponding aperture of said lateral cylindrical wall, wherein the supporting plate (1100) includes a plurality of internal plate channels housing sections of at least part of said post-tensioning tendons (125, 130) of said at least one pair of sets of post-tensioning tendons (125, 130).
  11. Concrete suction anchor according to claim 10, wherein the supporting plate (1100) is provided with: - longitudinal stiffeners (1150), which are substantially orthogonal to the supporting plate (1100) and parallel to said longitudinal axis, and/or - transversal stiffeners (1170), which are substantially orthogonal to the supporting plate (1100) and to said longitudinal axis.
  12. Concrete suction anchor according to any one of claims 1 to 9, further comprising a padeye (2000) protruding from a supporting plate (2100) that is attached to said lateral cylindrical wall by means of attachment tendons (2200) passing through respective anchorage passages inside said lateral cylindrical wall, wherein the ends of each attachment tendon (2200) are fixed to the supporting plate (2100) by anchorage devices (2300) placed at the supporting plate (2100).
  13. Concrete suction anchor according to claim 12, wherein each of said anchorage passages is arranged along a respective circumference orthogonal to said longitudinal axis.
  14. Concrete suction anchor according to claim 12 or 13, wherein at least one of said anchorage devices (2300) is an anchorage wedge (2300), wherein said anchorage wedge (2300) optionally applies a post-tensioning to a respective attachment tendon (2200).
  15. Concrete suction anchor according to any one of claims 1 to 9, further comprising a padeye (3000) integrally coupled to two side half collars (3100), optionally having a band cylindrical shape, wherein the two side half collars (3100) are each provided, at their distal ends with respect to the padeye (3000), with a respective flange (3200), wherein the flanges (3200) are attached to each other, thereby the two side half collars (3100) are attached, optionally in a removable manner, to said lateral cylindrical wall, wherein the two side half collars (3100) are optionally attached, more optionally in a removable manner, to said lateral cylindrical wall by means of a plurality of fasteners (3300).

Description

Technical Field The present invention concerns a concrete suction anchor, provided with post-tensioning tendons, that is reliably and effectively applicable to many different environmental settings, easy to manufacture, inexpensive to manufacture, transport and install. Background Oil and gas and renewable energy floating systems benefit from anchoring for station keeping during operation, power production, and parked/idling conditions. Fundamentally, anchors can be subdivided into two major classes: horizontal and vertical load anchors. The horizontal-load anchors are normally used in combination with catenary mooring, where the mooring line is tangent to the seabed before connecting to the anchor. Gravity anchors (vertical load) can include large concrete blocks with optional skirts to increase the sliding resistance. However, they suffer from the drawback of having poor efficiency, namely lower than 1 because they can only withstand loads less than their weight. They also require vessels with heavy lift capabilities for transportation and installation. Drag embedment anchors (horizontal load) offer extremely large lateral resistance and therefore are considered of efficiencies higher than 1, i.e., they can withstand loads higher than their weight. However, they suffer from the drawback of having an extremely poor vertical load resistance. Therefore, they are generally not used with semi-taut or taut mooring. Plate anchors for vertical and horizontal loads, which are a variation of drag embedment anchors, are installed edgewise and then rotated by pulling the chain until they face broadsided to the uplift, maximizing the uplift resistance. Suction embedded plated anchors are another variation of the drag embedment anchors and they use a suction pile to get driven to the correct depth, and then they open up to offer maximum resistance to uplift (e.g., as disclosed at www.sptoffshore.com). Similarly, to drag-anchors, they must be shape-optimized with relatively complex kinematics to induce the proper embedment and thus installation is expensive. Furthermore, it does not seem possible to replace the steel with other materials for this type of anchor. Another variant involves lateral-load anchors. These plates can be driven edgewise with suction piles that are then removed (e.g., as disclosed at www.intermoor.com). Again, installation is a critical and expensive phase of this system. Prior art pile anchors for horizontal and vertical load are made of rolled and welded steel plates, and with typical aspect ratio of length-to-diameter higher than 10 and diameters of up to 2 meters. Underwater hammers are normally needed, or pile followers must be used to drive piles from the surface. If the solid stratigraphy reveals presence of rock, pre-drilled sockets and post installation grouting becomes necessary. Again, the installation of these piles is expensive, requiring specialized offshore equipment and lengthy operations. In soft soils, an alternative is offered by suction piles, with lower length-to-diameter ratios than driven piles, and diameters that can reach 10 m. They use hydrostatic pressure to embed and are expensive to manufacture. They can be removed by reversing the suction process. Piles can withstand both vertical, mainly through friction, and lateral loading, namely through soil pressure along the outer surface of the embedment pile. Therefore, semi-taut and taut mooring is possible with piles. Suction piles or suction anchors could be made of reinforced concrete. A prior art concrete suction anchor is disclosed in document WO 2020/176262 A2. However, in the prior art, the applicability of concrete or geopolymer concrete is limited to suction piles and gravity anchors, alternatively or a combination of the two. Very low costs associated with deadweight anchors are offset by more expensive lift-capacity equipment. Although existing anchoring can be effective in certain situations, still further improvements are desired. Embodiments of the present invention provide solutions for these outstanding needs. Summary of the invention It is specific subject-matter of the present invention a concrete suction anchor according to the independent claim. Further embodiments of the concrete suction anchor according to the invention are defined in the dependent claims. Embodiments of the concrete suction anchor according to the present invention generally relate to the field of anchoring for offshore installation, such as offshore energy installation, including floating offshore energy installation, having post-tensioning tendons oriented so as not only to be parallel or orthogonal to the longitudinal axis of the concrete suction anchor. Some embodiments of the concrete suction anchor according to the invention are provided with one or more buoyancy chambers, optionally domed buoyancy chambers, for increasing the ease of wet towing of the anchor itself to the installation site by means of a flotation cap. The concre