Monopole tower foundation

Abstract

The invention relates to an onshore foundation for a monopole tower comprising a centrally located vertically upstanding pedestal for supporting a monopole tower, a peripheral ring annularly disposed about the lower end of the pedestal, a plurality of bracing members connecting between the peripheral ring and the pedestal, and a plurality of micropiles extending down from the peripheral ring for engaging ground beneath the foundation.

Description

[0001] MONOPOLE TOWER FOUNDATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a foundation for onshore wind turbines or other monopole tower structures, including those for telecommunications equipment.

[0004] BACKGROUND OF THE INVENTION

[0005] The prevalence of wind power is becoming greater as demand for renewable energy increases, but constructing a new wind tower is an expensive and time-consuming undertaking. Nevertheless, the frequency at which new towers are erected has been increasing, and the first step in the process is necessarily the construction of the foundation. Modern wind towers can now be over 100 metres tall with a weight approaching 200 tons, requiring enormous volumes of concrete and steel reinforcing to support the weight and provide the necessary moment resistance. A plethora of design factors all affect the size of the foundation required to support the tower. A minor optimisation in the design of the foundation, even one that reduces the necessary diameter a small amount, could save many tons of concrete (and / or other materials) and reduce costs significantly. One development in the field was to support the foundation with micropiles, small diameter piles that can be installed in almost any type of ground while retaining good load-bearing performance. Despite their effectiveness in constructing foundations the micropiles may be expensive and slow to install, making it important to find ways to minimise the amount used and carefully select their placement. New foundation designs that offer improvements to the established techniques may be difficult to construct in practice, increasing labour costs to the point where other savings may be offset. Thus it is desirable to develop wind tower foundation designs that are practical to construct with mostly conventional tools and equipment, while still optimising strength, load paths and moment resistance to reduce foundation size and minimise the construction materials necessary.

[0006] Other monopole tower structures, including those for communication equipment or the like, have similar foundation design considerations to those for wind towers - and thus will also benefit from improved foundation designs. However, it is desirable to adapt foundation design techniques to suit different use cases.

[0007] It is an object of the present invention to provide a wind tower foundation which overcomes or at least partially ameliorates some of the abovementioned disadvantages or which at least provides the public with a useful choice.

[0008] BRIEF DESCRIPTION OF THE INVENTION

[0009] In a first aspect, the invention provides an onshore foundation for a monopole tower, the foundation comprising: a centrally located vertically upstanding pedestal having a lower end region and an upper end region onto which, from above, a monopole tower can bear to be supported by the foundation; a peripheral ring annularly disposed about the lower end of the pedestal; a plurality of micropiles extending down from the peripheral ring for engaging ground beneath the foundation; and a plurality of bracing members connecting between the peripheral ring and the pedestal. The plurality of bracing members comprise : a plurality of struts connecting between the upper end region of the pedestal and the peripheral ring, wherein the struts are arranged in bifurcated groups, each group converging from spaced apart positions on the pedestal. The bracing members further comprise a plurality of radial beams connecting between a hub and the perhiperal ring, the hub being centrally located within the pedestal at the lower end region.

[0010] With this arrangement, the foundation of the present invention can provide improved stiffness and resistance to compression forces, moment forces and / or torsional forces subjected to the foundation from the wind tower. This may be particularly advantageous for large wind turbines for which the loads experienced by the foundation may be significant.

[0011] Preferably, each group of struts is a pair of struts. Preferably, the radial beams connect to the perhiperal ring at the convergences of bifurcated pairs of struts. This arrangement can increase the rotational stiffness of the foundation.

[0012] Preferably, each strut converges at the pedestal with a strut of an adjacent pair, such that the plurality of struts together form a star shape. This arrangement can further increase the stiffness of the foundation.

[0013] Preferably, the peripheral ring is a substantially regular polygon shape and wherein the struts and / or radial beams are connected at vertices of the polygonal peripheral ring. Alternatively, the peripheral ring could be an irregular polygon shape.

[0014] Preferably, the hub is substantially the same shape as the peripheral ring.

[0015] Preferably, the hub is sized such that the radial beams are substantially coextensive a footprint of the foundation. With this arrangement, the rotational stiffness of the foundation can be further increased. For example, the hub may have a diameter of 0.25x the diameter of the pedestal or less.

[0016] Preferably, the radial beams penetrate the lower end region of the pedestal to connect to the hub.

[0017] Preferably, the foundation further comprises a base plate on which at least the pedestal, peripheral ring and radial beams are supported. The base plate may be 20mm thick.

[0018] Preferably, the base plate comprises a plurality of holes. The holes may be cut-out annular sectors. With this arrangement, the material consumption may be reduced. Additionally, the load path may be preferentially focussed at the extremities of the foundation.

[0019] Preferably, the plurality of holes is radially symmetric.

[0020] Preferably, the holes are located within annular sectors defined between the peripheral ring, pedestal and radial beams. Preferably, the surface area of the base-plate relative the number and depth of the micropiles is sufficient to optimally distribute loading between the micropiles and the base plate such that moment resistance is maximised, preventing the micropiles from mobilising substantially all loading of the foundation.

[0021] Preferably, the onshore foundation further comprises a concrete blinding on top of which the base plate is supported.

[0022] Preferably, the pedestal is an annular cylinder. For example, the pedestal may be a metal tube. The pedestal may have an outside diameter of 4-5 metres (preferably 4.5 metres, corresponding to a common base section diameter for wind towers) and a wall thickness of 60-70mm (preferable 65mm). The pedestal may have a height of 5-6 metres (preferably about 6 metres).

[0023] Preferably, the pedestal comprises an annular plate atop the upper region for supporting a monopole tower. The monopole tower may be secured (e.g., bolted) to the annular plate.

[0024] Preferably, the pedestal is adapted to support a wind tower.

[0025] Preferably, the pedestal is adapted to support a telecommunications tower.

[0026] Preferably, the pedestal and / or peripheral ring and / or struts and / or radial beams are made of metal, preferably steel.

[0027] Preferably, the foundation is fabricated and compoments are welded or mechanically fastened together.

[0028] The footprint of the foundation may be 12-13 metres across (preferably 12.5 metres). The micropiles may be 8 metres in length. Each side of the polygonal ring may have three piles extending therefrom.

[0029] Preferably, the hub is a unitary cast body. Preferably, a moment-resisting connection between the hub and the radial beams is sufficiently rigid to substantially eliminate flexing at the connection when the foundation is loaded.

[0030] Preferably, the moment-resisting connection is made by bolting each radial beam to a corresponding face of the hub.

[0031] In a further aspect the present invention provides a method of configuring the onshore foundation, the method comprising: performing load analysis of bearing pressure beneath the base plate compared to loading of the micropiles at depth for candidate foundation configurations; selecting a foundation configuration which, according to the load analysis, improves or optimises load distribution between the micropiles and the base plate such that moment resistance is improved or maximised, and the micropiles are prevented from mobilising substantially all loading of the foundation; and fabricating the onshore foundation according to the selected foundation configuration.

[0032] Preferably, the load analysis is a 3D finite element modelling analysis.

[0033] In a further aspect the present invention provides an onshore concrete foundation for a monopole tower, the foundation comprising: a centrally located vertically upstanding pedestal having lower end region and an upper end region onto which, from above, a monopole tower can bear to be supported by the foundation vertically and in moment and torsionally; a peripheral ring annularly disposed about lower end of the pedestal; and a plurality of bracing members each extending radially outward from the pedestal to the ring and connected to the pedestal at least at the upper end region and to the ring at discrete peripheral locations wherein for use the ring is adapted to micropiles extending down from the peripheral ring.

[0034] Preferably, the peripheral ring is polygonal shaped. Preferably, each bracing member extends from the pedestal to a respective vertex of the polygonal shaped ring.

[0035] Preferably, at each vertex of the ring at least two bracing members extend from the ring to the pedestal.

[0036] Preferably, at each vertex of the ring at least three bracing members extend from the ring to the pedestal.

[0037] Preferably, at each vertex of the ring at least two bracing members extend from the ring to the upper region of the pedestal.

[0038] Preferably, at each vertex of the ring at least two bracing members extend from the ring to two spaced apart locations at the upper region of the pedestal.

[0039] Preferably, at each spaced apart locatation a bracing member extends to a one vertex of the ring and another bracing member extends to an adjacent vertex.

[0040] Preferably, the bracing members are end to end connected to define a continuity of bracing members extending in a tortured path between the pedestal and the ring.

[0041] Preferably, at each vertex of the ring at least one bracing member extend from the ring to the lower region of the pedestal.

[0042] Preferably, at each vertex of the ring at least one bracing member extend purely radially from the ring to the lower region of the pedestal.

[0043] Preferably, each bracing member is a beam.

[0044] Preferably, each bracing member is a linear beam.

[0045] Preferably, the beam is of circular cross section.

[0046] Preferably, the beam is RHS in shape.

[0047] Preferably, the beam is of steel. Preferably, the pedestal is a tube.

[0048] Preferably, the tube is of steel.

[0049] Preferably, a metal flange is secured to the tube at its upper end.

[0050] Preferably, the ring comprises of beam sections extending between each vertex.

[0051] Preferably, the foundation is fabricated and compoments are welded or mechanically fastened together.

[0052] Preferably, the centrally located upstanding annular pedestal is configured to receive and connect with a wind tower.

[0053] Preferably, the bracing members are ribs radially extending outward from the pedestal.

[0054] Preferably, the ribs tapered down, from the pedestal to the ring.

[0055] Preferably, the ribs having distal ends distal the pedestal that are connected to the ring.

[0056] Preferably, the ring is a upstanding peripheral ring.

[0057] Preferably, the ring is integrally formed with ribs at the distal ends. Preferably, micropiles extend down from the peripheral ring and are located both radially out from the distal ends and intermediate adjacent distal ends.

[0058] Preferably, the pedestal, ribs, and ring are composed of steel reinforced concrete poured on-site, the lowermost surfaces of the foundation being substantially horizontal and planar with each other and supported by the ground in operation.

[0059] Preferably, the pedestal, ribs, and ring are poured integrally with each other.

[0060] Preferably, the peripheral ring is continuous around the distal ends. Preferably, the peripheral ring comprises linear segments extending between adjacent distal ends of the ribs, such that at each point at which one of the ribs meets the peripheral ring is a corner of the peripheral ring.

[0061] Preferably, the peripheral ring is circular.

[0062] Preferably, the foundation comprises eight ribs.

[0063] Preferably, the pedestal is hollow.

[0064] Preferably, the foundation further comprises a base slab formed in gaps between the pedestal, ribs and ring.

[0065] Preferably, the steel reinforcing is at full depth in the ribs.

[0066] In another aspect the present invention provides an onshore concrete foundation for a monopole tower comprising: a centrally located upstanding pedestal configured to receive and connect with a monopole tower; cantilevered ribs extending radially outward from the pedestal, each rib comprising a distal end distal the pedestal; an upstanding peripheral ring, integrally formed with and continuous around the distal ends; a base slab adjoining the pedestal, ribs, and ring; micropiles extending down from the ring and located both radially out from the distal ends and intermediate the adjacent distal ends; wherein the pedestal, ribs, base slab, and ring are composed of steel reinforced concrete poured on-site as an integral unit, the lowermost surfaces of the unit being substantially horizontal and planar with each other and supported by the ground.

[0067] Preferably, the ribs further comprise a top surface that tapers vertically downwards from the pedestal to the peripheral ring.

[0068] Preferably, the pedestal is annular.

[0069] Preferably, the peripheral ring is polygonal shaped. Preferably, the peripheral ring comprises linear segments extending between adjacent distal ends of the ribs, such that each point at which one of the ribs meets the peripheral ring is a corner of the peripheral ring.

[0070] Preferably, the number of ribs is eight.

[0071] Preferably, the foundation comprises between three and twenty ribs, preferably the foundation comprises eight ribs.

[0072] Preferably, the base slab is formed only in gaps between the pedestal, ribs, and ring.

[0073] Preferably, the steel reinforcing is at full depth in the ribs.

[0074] In another aspect the present invention provides a method of constructing an onshore concrete foundation for a monopole tower, the method comprising the steps of: a. assembling a cage of steel reinforcing to form an internal structure of the foundation, the cage comprising: the internal structure of a centrally located pedestal configured to receive and connect with a monopole tower; the internal structure of cantilevered ribs radially extending outward from the pedestal; the internal structure of an upstanding peripheral ring adjoining the distal ends of the ribs; the internal structure of a base intermediate the ribs, pedestal and peripheral ring; b. pouring concrete over sections of the cage to form the pedestal, peripheral ring, and ribs to the full depth of the foundation; and c. pouring concrete over the remaining sections of the cage to form the base slab as an infill between the ribs, wherein the base's lowermost surfaces are substantially horizontal and planar with each other and supported by the ground. Preferably, the cage is constructed in stages, and concrete is poured over some sections of the cage before the cage is completely assembled.

[0075] Preferably, the method further comprises a step of digging a passage underneath the foundation through which electrical cables can be run.

[0076] Preferably, the method further comprises boring micropile holes underneath the foundation and subsequently inserting micropiles into the holes.

[0077] Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

[0078] As used herein the term "and / or" means "and" or "or", or both.

[0079] As used herein "(s)" following a noun means the plural and / or singular forms of the noun.

[0080] The term "comprising" as used in this specification "consisting at least in part of". When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0081] The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference.

[0082] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. For the purpose of this specification, where method steps are described in sequence, the sequence does not necessarily mean that the steps are to be chronologically ordered in that sequence, unless there is no other logical manner of interpreting the sequence.

[0083] BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The invention will now be described by way of example only and with reference to the drawings in which:

[0085] Figure 1: shows a perspective view of one example of a monopole tower foundation;

[0086] Figure 2: shows a perspective view of the monopole tower foundation of figure 1 with the micropiles visible;

[0087] Figure 3: shows a top view of the monopole tower foundation of figure 1;

[0088] Figure 4: shows a bottom view of the monopole tower foundation of figure 1;

[0089] Figure 5: shows a side view of the monopole tower foundation of figure 1;

[0090] Figure 6: shows a cross-sectional side view of the the monopole tower foundation of figure 1 with the monopole tower on top;

[0091] Figure 7: shows a perspective view of the internal steel reinforcing of the monopole tower foundation of figure 1;

[0092] Figure 8: is a perspective view of an alternative monopole tower foundation;

[0093] Figure 9: shows an alternative view of the monopole tower foundation of figure 8 in which obscured elements are illustrated;

[0094] Figure 10: shows a side view of the monopole tower foundation of figure 8 with micropiles shown in part projecting downwardly;

[0095] Figure 11: is a cross-sectional view through the monopole tower foundation of figure 8;

[0096] Figure 12: is a plan view of the monopole tower foundation of figure 8; and

[0097] Figure 13: is a flow chart of a method for configuring a foundation using load analysis.

[0098] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to the above drawings, in which similar features are generally indicated by similar numerals, a monopole tower foundation according to a first aspect of the invention is generally indicated by the numeral 1.

[0099] In one embodiment now described, there is provided a monopole tower foundation 1 comprising a central pedestal 10. A plurality of bracing members such as the ribs 20 may extend radially from the pedestal 10 to a peripheral ring 30. The ring 30 preferably extends around the pedestal at the outer edge of the foundation 1. A base slab 40 may be provided which fills gaps between the ribs to form a planar base for the foundation 1. Micropiles 50 can extend downwards into the ground from the peripheral ring 30 when the foundation 1 is installed. An internal steel reinforcing cage 60 may be provided where the foundation is made from a poured concrete.

[0100] In one embodiment, the pedestal 10 is an upstanding annular structure with a an outside surface 12. It may have an upper region 400 and a lower region 500. Bracing members such as the ribs 20 extend from the pedestal to to the ring. A plurality of radially spaced inner bolts 34 may be configured to connect to the inside of a monopole tower 2, and a plurality of radially spaced outer bolts 35 may be configured to connect with the outside of the monopole tower 2.

[0101] The base of monopole tower 2, when installed (as shown in figure 6), sits atop the pedestal 10, connected with inner bolts 34 and outer bolts 35. Most preferably the monopole tower 2 is a wind tower presenting a wind turbine, however the pedestal 10 could also be adapted to receive another type of monopole tower such as one for telecommunications equipment.

[0102] The pedestal 10 has dimensions specific to the type and model of monopole tower 2 to be received, and sufficient to transfer loads and moment and torsional forces to other structural elements of the foundation 1 without failure.

[0103] Prefereably, the pedestal 10 is hollow and has a vertical and inwardly facing inside surface 11. Cables 4 may run out of the monopole tower 2, through the interior of the pedestal 10, through the ground 3 and to a site external to the foundation 1. In a preferred embodiment, the shape of the pedestal outside surface 12 is that of a circular cylinder with vertical walls. In alternative embodiments the shape may be a polygonal cylinder, the walls may be sloped, or the pedestal 10 may be split into tiers such that different sections of the outside surface 12 have different diameters.

[0104] In embodiments where the shape of the pedestal outside surface 12 is that of a circular cylinder, the radially extending ribs 20 are preferably evenly spaced around the circumference. In embodiments where the shape of the pedestal outside surface 12 is that of a polygonal cylinder, ribs 20 may extend from corners of the outside surface 12 or alternatively they may extend from sections of the outside surface 12 intermediate the corners. In either case the number of ribs 20 is between three and twenty, and preferably it is eight.

[0105] In one embodiment, the radially extending ribs 20 have a proximal end 23 integral with the pedestal outside surface 12, a distal end 22 which is integral with peripheral ring 30, and a top surface 21 facing generally upwards.

[0106] In a preferred embodiment the proximal end 23 is the same height as the pedestal 10 and the distal end is the same height as the peripheral ring 30, the pedestal 10 is of a greater height than the peripheral ring 30, and the top surface 21 of the radially extending ribs 20 tapers linearly downwards from the proximal end 23 to the distal end 22.

[0107] In an alternative embodiment, the pedestal 10, the ribs 20 and the peripheral ring 30 are all the same height, such that the top surface 21 of the ribs 20 is flat and does not taper.

[0108] In other alternative embodiments, the proximal ends 23 or the distal ends 22 of the ribs 20 may be a lower height than the pedestal 10 or the peripheral ring 30 respectively.

[0109] In a preferred embodiment, the peripheral ring 30 is comprised of a plurality of linear wall segments 31 which form a polygonal perimeter around the rib distal ends 22. Each segment 31 extends between two adjacent rib distal ends 22, such that each distal end 22 is located at a corner 32 of the peripheral ring 30 and is integral with it. In alternative embodiments, the peripheral ring 30 may be a circular shape, or the rib distal ends 22 may be integral with the centres of wall segments 31 rather than the corners 32.

[0110] In a preferred embodiment, micropiles 50 extend downwards into the ground from peripheral ring 30. Placing the micropiles 50 at the peripheral ring 30 rather than in alternative locations such as along the ribs 20 provides an advantage of higher moment resistance, which is increased the further away from the monopole tower the micropiles 50 are. To fit a greater number of micropiles 50 along the peripheral ring 30, preferably distal end micropiles 51 are placed at peripheral ring corners 32, and intermediate micropiles 52 are placed in the middle of each wall segment 31.

[0111] In alternative embodiments, there may be two or more intermediate micropiles 51 placed in the wall segments 31 to maximise the moment resistance of foundation 1, or there may be additional micropiles 50 placed along the ribs 20, or there may only be micropiles at the corners 32. In embodiments where the shape of peripheral ring 30 is circular, micropiles 50 may be evenly spaced around the circumference.

[0112] In a preferred embodiment, the peripheral ring 30 is continuous around the outside of the rib distal ends 22 while also being integral with them. Compared to alternative embodiments in which the wall segments 31 are placed in between the ribs 20, an improved load path is provided between the micropiles 50 and the ribs 20.

[0113] In a preferred embodiment, the internal steel reinforcing cage 60 is assembled in the foundation site before any of the other components are formed. Reinforcing cage 60 forms the internal structure of the foundation 1 and reinforces the concrete cast around it. Concrete is cast over the reinforcing cage 60 to form the pedestal 10, ribs 20 and peripheral ring 30 to the full depth of the foundation 1. After this has set, the concrete of base slab 40 is poured as an infill between gaps of the pedestal 10, ribs 20 and peripheral ring 30. Compared to alternative embodiments where the base slab is poured first and the other components are formed on top of it, having the primary structural elements of the foundation cast at full depth maximises the strengthening provided by the reinforcing cage 60. Reinforcing cage 60 has steel beams at the bottom of ribs 20 which are put into tension when the foundation 1 is loaded, and it is structurally beneficial for those beams to be at full depth rather than above the base slab 40.

[0114] In alternative embodiments, the entire foundation 1 may be cast in one concrete pour, or the construction process may involve alternating the laying of reinforcing and the pouring of concrete.

[0115] An alternative form of a monopole tower foundation 1A is shown in figures 8-12. In this variation, the monopole tower foundation 1A is preferably a fabricated metal (e.g., steel) assembly in which the bracing members take the form of struts and beams.

[0116] Like the previous embodiments, the foundation comprises a pedestal 10A, preferably an upstanding annular cylinder having an upper region 400A for supporting a monopole tower and a lower region 500A supported on a base plate 600A. The pedestal 10A may in this case be a metal tube or the like (preferably having a constant diameter along its length).

[0117] The foundation 1A is preferabily designed for supporting a monopole tower that may for example be bolted or otherwise secured to a flange (e.g., annular plate) 610A atop the upper end of the upper region 400A of the pedestal 10A. The pedestal 10A is preferably adapted to receive a wind tower, but fabricated metal construction as preferred for this embodiment may be more suitable than concrete construction for scaling the foundation to smaller monopole towers (e.g. for telecommunications).

[0118] Also like the previous embodiments, the foundation 1A comprises a peripheral ring 30A that extends around the pedestal 10A at the outer edge of the foundation 1A, preferably horizontally aligned with the lower region 500A of the pedestal 10A. The ring 30A may in this case comprise of a plurality of (preferably steel) perimeter beams.

[0119] As shown in figure 10, micropiles 50A may project downwards from the peripheral ring 30A of the foundation 1A and, when the foundation is in position, into the ground on which the foundation is installed. The bracing members are provided by a plurality of (preferably steel) struts 20A that extend between the upper region 400A of the pedestal 10A and the peripheral ring 30A. The struts 20A may be secured, such as by welding, to the outer (external) surface

[0120] 12A of the pedestal 10A.

[0121] In a preferred form, such as that illustrated, the ring 30A is a substantially regular polygon shape and may for example be eight-sided (i.e. octagonal) as seen in figure 12. A pair of struts 20A may be secured, such as by welding, at each vertex of the polygonal shape and from that vertex extend upwardly and (approximately) radially inwards in a splayed or bifurcated manner towards the pedestal 10A such that the struts 20A in each pair meet the outer surface 12A at spaced apart positions from one another (preferably such that each strut also converges with a strut of an adjacent pair to form a star shape, as shown). Thus, a triangulation of the struts with the pedestal may be established.

[0122] In this configuration the struts 20A can transmit forces from the pedestal 10A to the peripheral ring 30A, to accommodate loads from the monopole tower 2. Such forces may for example be forces that are in compression acting substantially vertically downwards on the pedestal as well as a moment force that may be experienced by the foundation from the tower when it is for example under wind loading. Additionally, the triangular arrangement of struts 20A can also resist torsional forces acting on the pedestal 10A about a substantially vertical axis. As such, the foundation 1A can provide improvements for larger wind turbines, where the torsional loads acting on the tower can be significant due to the large swept area of the blades. In general, the arrangement of struts 20A extending between the ring and the pedstal in a bifurcated manner can help resolve forces to the ring and hence the supporting ground and micropiles.

[0123] Radial beams 620A may also be provided as bracing members of the foundation for structural rigidity and stiffness, wherein the radial beams 620A are arranged to extend substantially horizontally from the ring 30A through the lower region 500A of the pedestal to a central hub 640A. The radial beams 620A effectively penetrate the lower region 500A of the pedestal. The central hub 640A is smaller in diameter than the pedestal 10A and is located centrally within the lower region 500A thereof. The central hub 640A may be small in diameter such that the radial beams 620A are effectively continuous across the base of the foundation 1A, which can increase the rotational stiffness of the foundation and thereby reduce rotation of the foundation 1A under moment loading of the pedestal 10A. The radial beams 620A can also help to resolve forces that are experienced by the pedestal from the monopole tower that it supports to help ensure that the foundation and - by means of the micropiles 50A - the surrounding ground work to keep the tower upright and resolve the forces to the surrounding ground.

[0124] The central hub 640A may be a polygonal ring having the same number of sides and vertices as the peripheral ring (e.g., 8 as shown) and the radial beams 620A may extend from a respective vertex of the peripheral ring 20A to a respective side of the central hub 620A.

[0125] Preferably the central hub 640A is a unitary cast body, manufactured using an appropriate metal casting process. This facilitates highly rigid connection to the radial beams 620A, which is beneficial in that it can substantially prevent flexing at the connection when the foundation is under load. Such flexing is undesirable because it can reduce the overall foundation stiffness and may impede load transfer via the radial beams 620A. Various connection means to the central hub 640A may provide suitable rigidity, including welding or bolting, however a moment-resisting bolted connection may be preferable in order to avoid a need for onsite welding of the connections during installation.

[0126] In a preferred form the struts 20A are substantially round, such as tubular, in cross-section while the beams (radial beams 620A and / or perimeter beams of the ring 30A) are preferably rectangular, or l- / H-shaped, in cross-section. A different cross- sectional shape, such as a rectangular hollow section (RHS), may also be used for the struts and / or beams.

[0127] Fabrication of the struts and the pedestal and the ring may involve welding and or mechanical fastening to connect the assembly of the foundation for use in providing support to a monopole tower. The pedestal 10A, peripheral ring 30A and radial beams 620A may be supported (e.g., mounted or secured) on a base plate 600A, which is preferably provided at the lower end of the foundation and may be extensive across the entire footprint of the foundation. Preferably, the base plate 600A comprises a plurality of gaps or holes 602A that can reduce the amount of material and also provide a preferential load path. In particular, the gaps 602A may be arranged to generate bearing pressure at the extremities of the foundation (i.e., at or proximate the peripheral ring 30A) where the bearing pressures are more effective at mobilising rotational resistance. The gaps 602A may be located within annular sectors defined between the radial beams and between the pedestal 10A and the peripheral ring 30A. The gaps 602A may thus each have the shape of an annular sector, or a substantially trapezoidal shape, the gaps 602A being aligned with their respective annular sectors. With this arrangement, the foundation 1A can focus bearing pressure at the radial extremities, where it may be more effective.

[0128] A concrete blinding 630A may be provided to locate intermediate of the ground and the foundation and ontop of which the base plate 600A is able to be supported.

[0129] Performance of the foundation 1A may be improved by optimally distributing loading between the base plate 600A and the micropiles 50A, as opposed to substantially mobilising load in only the micropiles 50A. To this end the surface area of the base plate 600A, relative the number and depth of the micropiles 50A, may be configured during the foundation design process to optimise this load distribution.

[0130] For example, as shown in figure 13 a method of configuring the foundation (beginning in the design phase) may involve a first step 130 of performing load analysis of candidate foundation configurations (for a given use case) to compare the bearing pressure beneath the base plate 600A to the loading of the micropiles 50A at depth. This allows the contribution of each to the overall moment resistance of the foundation to be determined, such that the overall moment resistance can be optimised by modifying relevant variables.

[0131] The candidate configurations may vary in terms of relevant dimensions of the various components, for example the overall diameter of the foundation 1A (and in turn the length of the radial beams 620A, the circumference of the peripheral ring 30A, and the surface area of base plate 600A), the diameter of the pedestal 10A, and the depth / size of the micropiles 50A. Other variables may include the materials used, the number of bracing members, the number of micropiles or the like.

[0132] Candidate foundation configurations may include some number which are independently derived and then each subjected to load analysis individually, however some may be transient artifacts of an optimisation process performed in the course of the load analysis. Adjustument of candidate configurations may be performed in between multiple rounds of load analysis, until an optimised (or at least improved) foundation configuration is identified. Preferably, the load analysis is a 3D finite element modelling analysis, which may include the use of an optimiser program.

[0133] In any case, a second step 131 of selecting a suitable foundation configuration is preferably based at least in part on optimising load distribution between the base plate 600A and the micropiles 50A, as described above, according to the results of the load analysis. This is equivalent to an optimisation of contributions to the overall moment resistance, such that the overall moment resistance of the foundation is maximised (under appropriate constraints, and with respect to the relevant variables). The second step 131 may be a direct output of an optimisation process associated with the first step 130, however final selection may also involve other factors.

[0134] A third step 132 is fabricating the foundation 1A for installation to meet its intended use case, thus realising the benefits of the optimisation.

[0135] The foundation 1A as described above has a number of key advantages over existing foundation designs:

[0136] Firstly, the bifurcated arrangement of the struts 20A provides improved torsional resistance. This is especially useful for 3-bladed turbines with long blades, as such blades create significant cyclic torsional loads. The struts 20A still also serve to complement the moment resistance provided by the radial beams 620A and the peripheral ring 30A. Where bracing struts are utilised between base and pedestal in other foundation designs, they generally are only angled in a radial-vertical plane, and are not angled at all in a tangential direction - so they provide some degree of improvement to moment resistance, but a far lesser degree of improvement to torsional resistance.

[0137] Secondly, having the radial beams 620A penetrate the pedestal 500A and connect at a central hub 640A, and making this connection highly rigid (e.g. via manufacturing the hub as a unitary cast body), provides a significant improvement in the moment resistance added by the radial beams 620A. For other foundation designs utilising radial beams, the beams typically terminate where they meet the pedestal, resulting in inferior moment resistance.

[0138] Thirdly, the combination of micropiles 50A with a base plate 600A allows for optimal distribution of load between the two (for example by way of the load analysis described above), which has been found to result in generally more economical foundations. For existing foundation designs, it is typical to adopt either a 'gravity pad' style of foundation where loading is mobilised in a large diameter base, or a micropile design where all loading is substantially mobilised in micropiles, but not to combine the two via analysis of the load distribution therebetween.

[0139] Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth.

[0140] Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and / or improvements may be made without departing from the scope or spirit of the invention.

Claims

CLAIMS1. An onshore foundation for a monopole tower, the foundation comprising: a centrally located vertically upstanding pedestal having a lower end region and an upper end region onto which, from above, a monopole tower can bear to be supported by the foundation; a peripheral ring annularly disposed about the lower end region of the pedestal; a plurality of micropiles extending down from the peripheral ring for engaging ground beneath the foundation; and a plurality of bracing members connecting between the peripheral ring and the pedestal, the plurality of bracing members comprising: a plurality of struts connecting between the upper end region of the pedestal and the peripheral ring, wherein the struts are arranged in bifurcated groups, each group converging from spaced apart positions on the pedestal; and a plurality of radial beams connecting between a hub and the perhiperal ring, the hub being centrally located within the pedestal at the lower end region such that the radial beams penetrate the lower end region of the pedestal to reach the hub.

2. The onshore foundation of claim 1, wherein each group of struts is a pair of struts.

3. The onshore foundation of claim 1 or claim 2, wherein the radial beams connect to the perhiperal ring at the convergences of bifurcated pairs of struts.

4. The onshore foundation of any preceding claim, wherein each strut converges at the pedestal with a strut of an adjacent pair, such that the plurality of struts together form a star shape.

5. The onshore foundation of any preceding claim, wherein the peripheral ring is a substantially regular polygon shape and wherein the struts and / or radial beams are connected at vertices of the polygonal peripheral ring.

6. The onshore foundation of any preceding claim, wherein the hub is substantially the same shape as the peripheral ring.

7. The onshore foundation of any preceding claim, wherein the hub is sized such that the radial beams are substantially co-extensive a footprint of the foundation.

8. The onshore foundation of any preceding claim, further comprising a base plate on which at least the pedestal, peripheral ring and radial beams are supported.

9. The onshore foundation of claim 8, wherein the base plate comprises a plurality of holes.

10. The onshore foundation of claim 9, wherein the plurality of holes is radially symmetric.

11. The onshore foundation of claim 9 or claim 10, wherein holes are located within annular sectors defined between the peripheral ring, pedestal and radial beams.

12. The onshore foundation of any one of claims 8 to 11, wherein the surface area of the base-plate relative the number and depth of the micropiles is sufficient to optimally distribute loading between the micropiles and the base plate such that moment resistance is maximised, preventing the micropiles from mobilising substantially all loading of the foundation.

13. The onshore foundation of any one of claims 8 to 12, further comprising a concrete blinding on top of which the base plate is supported.

14. The onshore foundation of any preceding claim, wherein the pedestal is an annular cylinder.

15. The onshore foundation of claim 14, wherein the pedestal comprises an annular plate atop the upper region for supporting a monpole tower.

16. The onshore foundation of any preceding claim, wherein the pedestal is adapted to support a wind tower.

17. The onshore foundation of any preceding claim, wherein the pedestal is adapted to support a telecommunications tower.

18. The onshore foundation of any preceding claim, wherein the pedestal and / or peripheral ring and / or struts and / or radial beams are made of metal, preferably steel.

19. The onshore foundation of any preceding claim, wherein the foundation is fabricated and components are welded or mechanically fastened together.

20. The onshore foundation of any preceding claim, wherein the hub is a unitary cast body.

21. The onshore foundation of claim 20, wherein a moment-resisting connection between the hub and the radial beams is sufficiently rigid to substantially eliminate flexing at the connection when the foundation is loaded.

22. The onshore foundation of claim 21, wherein the moment-resisting connection is made by bolting each radial beam to a corresponding face of the hub.

23. A method of configuring the onshore foundation of any one of claims 8 to 13, the method comprising: performing load analysis of bearing pressure beneath the base plate compared to loading of the micropiles at depth for candidate foundation configurations; selecting a foundation configuration which, according to the load analysis, improves or optimises load distribution between the micropiles and the base plate such that moment resistance is improved or maximised, and the micropiles are prevented from mobilising substantially all loading of the foundation; and fabricating the onshore foundation according to the selected foundation configuration.

24. The method of claim 23, wherein the load analysis is a 3D finite element modelling analysis.

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