GB2508870A

GB2508870A - Circular tapered levelling shims for structures

Info

Publication number: GB2508870A
Application number: GB1222507.4A
Authority: GB
Inventors: Alan Dennis; Ian Wise
Original assignee: GRAVITAS OFFSHORE Ltd
Current assignee: GRAVITAS OFFSHORE Ltd
Priority date: 2012-12-13
Filing date: 2012-12-13
Publication date: 2014-06-18
Also published as: EP2749697A3; GB201222507D0; EP2749697A2; EP2749697B1

Abstract

The invention relates to an apparatus for adjusting the level of an interface between a foundation 6 and a structure 7 mounted to the foundation. The apparatus comprises two circular shims 1,1', each rotatable about a rotational axis with respect to the other and to the foundation 6. The shims 1,1' are used one on top of the other between the foundation 6 and the structure 7. To provide a level base for the structure, the shims are rotated relative to each other. The shims are preferably used for the assembly of offshore wind turbine towers.

Description

LEVELLING FOR STRUCTURES

The present invention relates to a method of and apparatus for adjustment of the level of an interface between a foundation and a structure to be supported thereby. In preferred embodiments the structure is a tower type structure, for example a tower for a wind turbine.

It is generally desirable that a tower, platform or other structure is precisely veitically aligned, especially for tall structuies, and for this reason it is important that the interface at which the towel, platform ci othei structure connects to its foundation is substantially horizontal, within a required tolerance. However, the foundation may not provide such an interface since in many cases it is not possible to guarantee a level foundation due to the method of construction ci installation of the foundation.

Exemplary level-critical applications include ground-based structural assemblies or offshore assemblies such as wind turbines, weather stations, lighthouses, platforms for the oil and gas industry and so on.

Typically, offshore assemblies compnse a foundation and a structure (for example, a tower or platform) mounted thereto. The height of the foundation will be such that the tower, platform or other structure remains above sea level after installation of the lower parts of the foundation. The most common installation techniques first install the foundation on the sea-bed without the upper pads. The tower, platform or other structure is then mounted on top of the foundation. It is desirable that the tower, platform or other structure is precisely vertically aligned, and for this reason it is important that the interface at which the towei, platform oi other structure connects to the foundation is horizontal.

Known foundations for offshore structures are predominantly monopiles, gravity foundations and piled jackets The basic structure of a monopile is a tube, usually made of steel. The monopile is hammeied or dulled into the sea-bed, and extends upwardly to puoject above sea level.

Connection between the monopile and the structure above (e.g. the tower of a wind turbine) is provided by a transition piece.

The nionopile transition piece is a tube that typically has a slightly larger diameter than the monopile so that it can be mounted over the monopile. The transition piece comprises a flange to connect the monopile to the toweu with nuts and bolts.

It is desirable that the foundation is level (i.e. horizontal), typically to within a normal margin of 0.5° tilt, but this is difficult to achieve whilst drilling or hammering the monopile into the soil. Therefoie an additional function of the transition piece is to level the interface to the tower.

Gravity foundations are used for many types of offshore assembly when the location and the type of the structure make it feasible or advantageous to support the structure on the sea-bed. A gravity foundation holds the structure in place using the weight of the foundation, and so drilling or hammering into the sea-bed is not necessary.

However, prior to installation of the gravity foundation, the sea-bed beneath has often been prepared by diedging, to piovide a flat and level surface by infilling the diedged area with giavel and concrete. However, wtieie the gravity foundation is placed directly on the seabed, some correction for verticality may need to be included at the foundation to structure interface to satisfy the functional requirements of the structure.

Connection of the stiucture to the gravity foundation is typically by way of a flange which is embedded in the foundation, or by an anchor bolt cage, where several long bolts are embedded in the foundation.

Where an anchor bolt cage is provided, it is common to use shims placed at each bolt to provide a horizontal surface. Howevei, fuither problems can arise trom this approach. The bolt ends are required to project a certain distance through the interface in order to fasten the bolts. In some situations, the top surface of the foundation can be so uneven that the bolts on the lower parts are too short and do not project sufficiently far above the interface. In order to overcome this problem, the concrete surrounding the affected pads can be removed. However, such a procedure is labour-and time-intensive.

There is a need for an alternative and improved means of adjusting the level of an interface between a structure and its foundation.

Viewed from a first aspect the present invention provides an apparatus for adjusting the level of an interface between a foundation and a structure to be mounted theieto, wheiein the appalatus comprises: two shims, each rotatable about a rotational axis with respect to the other and to the foundation, wherein the shims are for positioning one on top of the other between the foundation and the structure, and wherein each shim has a width generally transverse to the rotational axis and a depth generally in the direction of the iotational axis, and the depth of the shim varies generally linearly across the width of the shim.

As a result of the features of the present invention, precise fine adjustment of the level of the foundation is facilitated by rotational adjustment of one or both of the two shims. Furthermore, it is easy and quick to install the shims.

The structule may be a tower type structure, such as a tower for a wind turbine.

In some preferred embodiments, the foundation may be an offshore foundation and the structural assembly may hence be an offshore assembly.

In general, the rotational axis of the shims, in use, should be such that it allows for correction of the foundation surface to horizontal. The rotational axis may for example be generally coaxial with a central axis of the foundation or the structure, which would be the vertical axis of the foundation for a perfect installation.

Prefeiably, the shims are circular, and more pieferably have an annular, or ring-like, configuration such that each shim has an innel and an outel diametei. In a typical preferred embodiment the shims would be circular rings in order that they can rotate relatively to one another and remain aligned, although it is not essential that the shims are circles. Foi example they may be slightly oval in plan view. Design and installation considerations place limitations on the preferred inner and outer diameter (though these are not related to the levelling functionality of the shims). For ease of installation, it is preferred that the outer diameters of the shims do not project outwardly of the outer periphery of the poition of the foundation to which they are attached. It is also advantageous to maintain communication between the interiors of the foundation and structure mounted thereto, which may be hollow. In one exemplary embodiment, the structure may be a wind turbine, which may be mounted atop a ground-based or offshore foundation. Utilities such as power cables iun from the turbine at the top of the wind turbine tower, through the tower interior, through the foundation and along the sea-bed (for an offshore turbine) or along an underground trench (for a ground-based turbine).

Therefoie, the inner diameter is such to maintain the communication between the interior of the foundation and tower, to facilitate the provision of utilities between the interiors.

Typically the shim may be sized so that it fits between the foundation and the structure without protruding to any great extent.

As a result of the fact that the depth of the shim valies geneially linearly across the width of the shim, the shims each have a maximum depth and a minimum depth located at opposing ends of the width of the shim, i.e. diametrically opposite. The difference between the maximum and minimum depths is denoted A. The width (or diameter) D and quantity define a shim angle 0, such that: 0 = tan4(AID). The shim angle B is the angle of intersection of planes aligned with upper and lower surfaces of the shim. It will be understood that the upper and lower surfaces do not need to be perfectly flat, but preferably they are generally flat and sufficiently planar to allow the two shims to intelact with each other and with othei structural elements of the foundation and the structure in order to perform their levelling function. In a preferred embodiment, the shim angles B of each shim are identical. This allows for the correction to the level to be varied from no correction at all, when the maximum depth of one shim is aligned with the minimum depth of the other shim, to a maximum correction of 20 when the maximum depths of both shims are aligned.

The shim angle 0 of each shim is not particularly limited. In some embodiments, the shim angle of each shim may be less than 200, preferably less than 100 and more preferably less that 5°. Where structural tolerances are more stringent, the shim angle 0 of each shim may be less than 1°, for example between 0.25° and 0.75°, and most advantageously is 0.5°. When the shim angle B is 0.5°, the angle of tilt that can be corrected for with two shims is between 0 and 10. Any greater angle of deviation from the horizontal may not be acceptable in the installation of an offshore structure foundation, so larger shim angles may not be necessary in this particular application.

Each shim may comprise holes spaced evenly around a circumference of the shim for receiving connectors (for example, bolts) to connect the structure to the foundation.

As mentioned above, the shim preferably has a circular or annular configuration.

A circular/annular configuration is most practical for ease of rotation of each shim with respect to the other and/or the foundation. However, other configurations are possible, provided that they provide the same levelling functionality. Another example of a possible shape is a multi-sided shape, preferably with one side per hole, such that the shim is rotationally symmetric (from a plan view), with a number of lines of rotational symmetry corresponding to the number of holes.

In preferred embodiments, the apparatus comprises a fixing ring for connection to the foundation, for example a steel channel ring. The preferred fixing ring comprises a lower flange and upper flange. The lower flange is for connection to the foundation, whereas the upper flange is for mounting the shims thereto. The lower flange may have a number of holes therein suitable for mounting the flange to the foundation, for example via a bolt cage cast into a concrete gravity foundation or by connection to the transition piece of a monopile. The upper flange of this preferred embodiment has a number of holes equal to the number of holes in the shims, circumferentially spaced apart identically to the spacing between the holes in the shims. In use, the fixing ring is mounted to the foundation, a lower shim is mounted to the fixing ring and an upper shim is placed atop the lower shim. The structure is then mounted atop the upper shim, the upper surface of which is horizontal. Optionally, a circular groove is cut in both sides of the lower shim, the lower side of the upper shim and the upper side of the fixing ring. The groove is preferably positioned away from the bolt holes so that the structural integrity of the shims and fixing ring is maintained. When the fixing rin9 and shims are placed atop the foundation, the groove in the lower side of the lower shim is aligned with the groove in the upper side of the fixing ring, and the groove in the upper side of the lower shim is aligned with the groove in the lower side of the upper shim. Thus, a pair of annular cavities is formed. Each of the annular cavities may be provided with a friction reducing system, foi example, ball beatings. Provision of a friction reducing system in each annular cavity allows the lower shim to be freely iotated relative to the fixing ling, and the upper shim to be freely rotated with respect to the lower shim.

In some embodiments, each of the annular cavities also receives a sealing barrier, for example an o-iing, to prevent the ingress of water into the intelior of the assembly through the interfaces between the foundation, the shims, and the structure.

In other embodiments, a second groove is cut, concentric with, and preferably radially outward of, the first groove, in both sides of the lower shim, the lower side of the uppei shim and the upper side of the fixing ling. Thus, the annular cavities defined above may form a first pair of annular cavities and an additional second pair of annular cavities can be formed concentric with the first pair of annular cavities. In such embodiments, the second pair of annular cavities is provided with the sealing barrier, and the first pair of annular cavities does not require a sealing barrier.

The shims may be used with an offshore foundation, such as gravity foundation, a monopile, or any other suitable foundation. The shims may also be used with a ground-based foundation.

The invention also extends to a structural assembly, foundation, offshore foundation and/or offshore assembly comprising the apparatus according to the first aspect of the present invention, and optionally any of the preferable features of the first aspect.

According to a second aspect of the present invention, there is provided a method of levelling a structural assembly comprising using the apparatus according to the first aspect of the present invention, and any of the preferable features of the first aspect. The stiuctural assembly may be an offshoie assembly comprising an offshore foundation and a stiucture mounted thereto.

According to a third aspect of the present invention, there is provided a method of adjusting the level of an interface between a foundation and a structure to be mounted theieto, the method comprising: mounting two circular shims one on top ot the other atop the foundation; and rotating at least one shim to correct an angle of tilt of the foundation and to hence provide a generally horizontal plane for mounting the structure on the foundation; wherein each shim has a width generally transverse to the rotational axis and a depth generally in the direction parallel to the rotational axis, and the depth of the shim varies generally linearly across the width of the shim.

The structure may be a tower type structure, such as a tower for a wind turbine. In some preferred embodiments, the foundation is an offshore foundation.

In preferred embodiments, the method comprises attaching a fixing ring, such as a steel channel ring, to the foundation, said fixing ring preferably comprising an upper and lower flange, with the shims then being placed on top of the fixing ring. Preferably, the method further comprises: placing a lower shim atop the upper flange of the fixing ring; rotating the lower shim; placing an upper shim atop the lower shim; rotating the upper shim; placing a tower atop the shims, said tower comprising a lower flange; placing bolts through holes provided in the lower flange of the tower, the shims and the upper flange of the fixing ring.

A preferred embodiment will now be described by way of example only and with reference to the following drawings in which: Figure 1 shows a perspective view of two shims rotatable with respect to one another; Figure 2 shows two shims atop a steel channel ring; and Figure 3 shows two shims in an installed position on a foundation.

An exemplary pair of shims 1, 1' is shown in Figure 1. Each has an annular shape with an outer diameter (D) of 5500 mm and an inner diameter (d) of 4920 mm. The maximum depth is 68 mm, and the minimum depth is 20 mm. Of course, these dimensions will depend upon the particular application of use, and may vary considerably.

The shims 1, 1' are made of an appropriate steel, for example grade NV DW36 355. Each face is machined to high-precision. The assumed machine tolerances are 1.5 mm maximum level difference between any two points on the machined annular surface.

The shim angle e of each shim is 0.5°. Thus by using two shims 1, 1', the range of angles that can be corrected for is between 0 and 10. The maximum correction is achieved when the maximum depths of the two shims are circumferentially aligned (from which it of course follows that the minimum depth are also aligned). The minimum correction (i.e. no correction) is obtained by aligning the maximum depth of one shim with the minimum depth of the other shim.

For some applications, greater deviations from horizontal of greater than 10 are not to be expected, since this would mean tolerances had been exceeded in the installation of the foundation.

In the particular embodiment shown in the Figures, holes 2 with a diameter of 54 mm are evenly spaced around the shim. Each shim comprises 128 holes. Of course, these details will depend on the particular application (for example, the type of wind turbine or other structure to be mounted to the foundation).

Figure 2 shows the two shims 1, 1' resting on top of a steel channel ring 3 (fixing ring). The steel channel ring comprises an upper flange 4 and a lower flange 5. The lower flange comprises holes appropriately sized and spaced to receive bolts from a bolt cage provided in the foundation 6. The steel channel ring 3 is thereby secured to the foundation 6 (as shown in Figure 3).

A groove 10 mm wide by 5 mm deep is cut in both sides of the lower shim 1', the lower side of the upper shim 1 and the upper side of the upper flange 4 of steel channel ring 3. This groove is positioned away from the bolt holes, i.e. radially outward or radially inward of the location of the holes.

When the fixing ring 3 and shims 1, 1' are placed atop the foundation 6, the groove in the lower side of the lower shim 1' is aligned with the groove in the upper side of the upper flange 4 of the steel channel ring 3, and the groove in the upper side of the lower shim 1' is aligned with the groove in the lower side of the upper shim 1. Thus a first pair of annular cavities is formed. This first pair of annular cavities acts as a bearing race, and receives ball bearings. This reduces friction and allows the lower shim ito be freely rotated relative to the steel channel ring 3, and the upper shim 1 to be freely rotated with respect to the lower shim 1'.

In some embodiments, the first pair of annular cavities also each receive a sealing barrier, for example an 0-ring, to prevent the ingress of water into the interior of the assembly through the interfaces between the foundation, the shims, and the structure.

In other embodiments, a second groove is cut, concentric with, and preferably radially outward of, the first groove, in both sides of the lower shim 1', the lower side of the upper shim 1' and the upper side of upper flange 4 of the steel channel ring 3. A second pair of annular cavities is hence formed by the second grooves, in addition to and concentric with the first pair of annular cavities. In this case the second pair of annular cavities is provided with the sealing barrier, and the first annular cavities do not include a sealing barrier.

To correct the angle of tilt of the foundation, the lower shim 1' is placed atop the steel channel ring 3 and is rotated appropriately. In the installed position, the holes 2 in the lower shim 1' should be aligned with the holes in the upper flange 4 of the steel channel ring 3. The upper shim 1 is then placed on top of the lower shim landis also rotated. The holes 2 in the upper shim 1 should align with the holes 2 in the lower shim 1' in an installed position. The upper surface of the upper shim 1 should be horizontal in the installed position. The final tolerance on horizontal will be the finest adjustment that can be made by rotation of the shims or a single shim. This is hence the total angle that can be corrected by one shim divided by half the number of holes in the shim, since the number of holes defines the minimum rotational adjustment that can be made. In the example described herein the tolerance would be +I-0.5°164 = +1-0.008°.

Once the shims have provided a horizontal surface, within the tolerance set out above, the tower 7 can be mounted on top. This is shown in Figure 3. The lower flange 8 of the tower has holes corresponding to the aligned holes in the shims and steel channel ring 3. Bolts 9 are passed through each of the holes to secure the tower to the horizontal surface.

The preferred embodiment above has been described with reference to an offshore structure in the form of a wind turbine. It will however be appreciated that the levelling system described herein could equally well be applied to other structures where it is desired to provide levelling between a foundation and a structure to be mounted thereon. The invention thus extends to any type of structure where levelling is required.

Claims

CLAIMS: 1. An apparatus for adjusting the level of an interface between a foundation and a structure to be mounted thereto, wherein the apparatus comprises: two shims, each rotatable about a rotational axis with respect to the other and to the foundation, wherein the shims are for positioning one on top of the other between the foundation and the structure, and wherein each shim has a width generally transverse to the rotational axis and a depth generally in the direction of the rotational axis, and the depth of the shim varies generally linearly across the width of the shim.
2. An apparatus as claimed in claim 1, wherein a shim angle B of each shim, which is the angle U of intersection of planes aligned with upper and lower surfaces of the shim, is less than 10, preferably wherein the shim angle is about 0.5°.
3. An apparatus as claimed in claim 1 or 2, wherein a shim angle B of each of the shims, which is the angle B of intersection of planes aligned with upper and lower surfaces of the shim, is identical.
4. An apparatus as claimed in any preceding claim, wherein the shims are circular, and preferably are annular.
5. An apparatus as claimed in any preceding claim, wherein each shim comprises holes spaced evenly around a circumference of the shim for receiving connectors for retaining the shims in an installed position.
6. An apparatus as claimed in any preceding claim, further comprising a fixing ring for mounting the shims to the foundation.
7. An apparatus as claimed in claim 6, wherein the fixing ring comprises a flange for mounting to the foundation and a flange for supporting the shims.
8. An apparatus as claimed in claim 6 or 7, wherein a first shim for mounting to the fixing ring comprises a first circular groove provided in each of opposing first and second faces of the first shim, said first surface for contacting the fixing ring and said second surface for contacting a second shim, and wherein the second shim is provided with a corresponding first groove in a first face for contacting the first shim.
9. An apparatus as claimed in claim 8, wherein the fixing ring comprises a circular groove in the flange surface for contact with the first shim.
10. An apparatus as claimed in claim 9, wherein the groove in the first surface of the first shim is aligned with the groove in the flange surface of the fixing ring, and wherein the groove in the first face of the second shim is aligned with the groove in the second face of the first shim, a pair annular cavities being formed thereby in an installed position.
11. An apparatus as claimed in claim 10, wherein a friction reducing system is provided in each annular cavity.
12. An apparatus as claimed in claim 11, wherein the annular cavity is provided with a sealing barrier.
13. An apparatus as claimed in claim 11, wherein a further pair of annular cavities are provided by providing second grooves in each of the first and second faces of the first shim, the first surface of the second shim and the flange surface of the fixing ring; preferably wherein the further pair of annular cavities are each provided with a sealing barrier.
14. An apparatus as claimed in any preceding claim, wherein the foundation is an offshore foundation.
15. An apparatus as claimed in claim 14, wherein the foundation is a gravity foundation.
16. An apparatus as claimed in claim 14, wherein the offshore foundation is a monopile.
17. A structural assembly, foundation, offshore assembly or offshore structure comprising the apparatus of any preceding claim.
18. A method of adjusting the level of an interface between a foundation and a structure to be mounted thereto, the method comprising: mounting two shims one on top of the other atop the foundation; and rotating at least one shim to correct an angle of tilt of the foundation and to hence provide a generally horizontal plane for mounting the structure on the foundation; wherein each shim has a width generally transverse to the rotational axis and a depth generally in the direction of the rotational axis, and the depth of the shim varies generally linearly across the width of the shim.
19. A method as claimed in claim 18, comprising attaching a fixing ring atop the foundation, said fixing ring comprising an upper and lower flange.
20. A method as claimed in claim 19, comprising: placing a lower shim atop the upper flange of the fixing ring; rotating the lower shim; placing an upper shim atop the lower shim; rotating the upper shim; placing a tower atop the shims, said tower comprising a lower flange; and placing bolts through holes provided in the lower flange of the tower, the shims and the upper flange of the fixing ring.
21. An apparatus for adjusting the level of an interface between a foundation and a structure to be mounted thereto, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings.