MODULAR SURFACE FOUNDATION FOR WIND TURBINE SPACE FRAME TOWERS
A modular surface foundation for wind turbine space frame towers, an apparatus to form panels of housing members of modular surface foundation, and method of forming the modular surface foundation for wind turbine space frame towers is provided. The modular surface foundation comprises a plurality of footing members, and a housing member disposed on each of the footing members, the housing members extending from the footing members and attaching to one or more structural members forming a portion of a wind turbine tower, wherein the housing member provides support and increased height for the space frame tower and includes an interior space.
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The present disclosure is directed to a modular surface foundation for wind turbine space frame towers, an apparatus to form a plurality of panels of the housing member of the modular surface foundation, and a method of forming the modular surface foundation for wind turbine space frame towers.
BACKGROUNDRecently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable, efficient, and cost effective to install.
Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted via a hub, main shaft and bearing to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., blade lengths of 30 meters or more). In addition, the wind turbines are typically mounted on towers that are at least 60 meters in height. Typically, a wind turbine tower is constructed from a single steel tube configuration or a space frame configuration. Both types of towers require a proper foundation to support the tower and turbine. In general, the foundation design is based on the weight and configuration of the proposed turbine, the expected maximum wind speeds as well as turbine load, and the soil characteristics of the site. Typical foundation approaches for space frame or lattice towers include a thick reinforced concrete mat foundation, a reinforced concrete monoplie, a single drilled shaft foundation, or micropile-supported footings at each foot of the space frame tower.
As power requirements increase, the size of wind turbine rotor blades increase which causes an increase in the overall size of the wind turbine, resulting in further increases in tower bottom load which also increases the foundation requirements. As a result of the power increases, foundations must be made larger, heavier, and buried deeper in the ground to support the massive wind turbine structures and loads. The current foundation approaches for space frame towers suffer from various obvious draw-backs. Typically, special crews are needed to excavate and pour the massive foundations, and soil characteristics must be taken into consideration, which includes adequate subsurface investigation such as cone penetration tests. Although material requirements for the foundations for wind turbine space frame towers are substantially less than that of traditional single steel tube towers, the amount of concrete, rebar and other reinforcements is still costly. Furthermore, because of the design of traditional wind turbine space frame towers, additional structures must be built on-site to house any necessary down tower equipment or components, because inadequate storage exists in traditional wind turbine space frame towers.
What is needed is a wind turbine space frame tower foundation that does not require major excavation or special crews to install. What is also needed is a foundation for wind turbine space frame towers that does not require a large amount of material. What is also needed is a wind turbine space frame tower foundation that also contributes to tower height to reduce the cost of materials used in building a wind turbine tower. An additional need includes a wind turbine space frame tower foundation that allows for storage of down tower equipment, maintenance supplies, or components within the foundation.
SUMMARY OF THE DISCLOSUREOne aspect of the present disclosure includes a modular surface foundation for wind turbine space frame towers comprising a plurality of footing members, and a housing member disposed on the footing members. The housing member extends from the footing member and attaches to one or more structural members forming a portion of a wind turbine tower. The housing member also provides support and increased height for the space frame tower and includes an interior space.
Another aspect of the present disclosure includes a method of forming a modular surface foundation for wind turbine space frame towers comprising fabricating a plurality of housing members having a series of post-tensioning cables, forming a plurality of shallow trenches to hold footing members, fabricating a plurality of footing members and placing the footing members in the shallow trenches, applying the plurality of housing members to the plurality of footing members and securing the housing members to the footing members, applying tension to housing members using the post-tensioning cables wherein the housing member provides support and increased height for the space frame tower and includes an interior space, and attaching structural members of wind turbine space frame tower to housing members.
Another aspect of the present disclosure provides an apparatus having a body closable to form a plurality of panels of a housing member of a modular surface foundation, wherein the formed panels are joined together to form the housing member, wherein the housing member is disposed on a footing member and attached to one or more structural members forming a portion of a wind turbine tower, and wherein the housing member provides support and increased space for a space frame tower and includes an interior space.
One advantage of the present disclosure is that the modular surface foundation provides reduced excavation costs and requires less material to install compared to current space frame tower foundations.
Another advantage of the present disclosure is that the modular surface foundation provides storage for down tower equipment.
Yet another advantage of the present disclosure is that the modular surface foundation provides additional height to the space frame tower.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
DETAILED DESCRIPTIONAs shown in
Modular surface foundation 100 comprises a plurality of modular surface foundation elements 10. Each modular surface foundation element 10 further comprises a footing member 46 and a housing member 44, wherein housing member 44 is disposed on each footing member 46, and wherein housing member 44 extends from footing member 46 and attaches to one or more structural members 40 forming a portion of wind turbine tower 30. As shown in
As shown in
As shown in
As shown in
Table I provides an exemplary embodiment of the ratio of the center-to-center dimension (B) relative to the diameter of modular surface foundation element MSFE) 10, having three, four, five, or six modular surface foundation elements 10.
Although Table I provides an exemplary embodiment of the ratios of the center-to-center dimension (B), it is not limiting. The range of ratios can be different for different tower design parameters such as hub height, rotor thrust, overall turbine and foundation weight and allowable soil bearing pressure. The ratio values of center-to-center dimension (lctc) relative to the diameter of the modular surface foundation element can be as high as 2.0 for three modular surface elements 10 and as high as 1.18 for six modular surface foundation elements 10.
In the present embodiment, equilateral triangular spacing exists between each modular surface foundation element 10. The equilateral triangular spacing varies depending on the size of wind turbine 16 and required space frame tower 30 height. The equilateral triangular spacing is calculated from the center of each modular surface foundation element 10, such that, if a line were drawn between each center of each modular surface foundation element 10 to an adjacent modular surface foundation element 10, an equilateral triangle would be formed (see
The diameter of each modular surface foundation element 10 includes the outer diameter of each concrete footing 58 of each corresponding footing member 46. A suitable diameter of modular surface foundation element 10 may be approximately 4 meters to approximately 20 meters. Diameter of modular surface foundation element 10 allows for tower heights of approximately 60 meters to approximately 150 meters and will easily support an 800 kW to 10 MW wind turbine. Larger or smaller diameters of modular surface foundation 10 are possible and depend on the size of the wind turbine, the required tower height, and the allowable soil bearing pressure.
In the present embodiment, each housing member 44 has a height of approximately 6 meters to approximately 30 meters. The following formula is used to calculate the height of modular surface foundation element 10, hmsfe=1.5×dmsfe, wherein hmsfe is the height of modular surface foundation element 10 and dmsfe is the diameter of modular surface foundation element 10. In an alternative embodiment, the factor of 1.5 in the above formula can be modified in the range of approximately 1.25 to approximately 1.75 to calculate the height of modular surface foundation element 10. The height of modular surface foundation element 10 is independent from the number of modular surface foundation elements 10. The dimensions of footing member 46 and housing member 44 allow for an interior volume 140 of at least approximately 15 cubic meters per modular surface foundation element 10 for an 800 kW rated wind turbine through over 2,000 cubic meters per modular surface foundation element 10 for a 10 MW wind turbine. Interior volumes 140 are approximately 45 cubic meters to approximately 6,000 cubic meters total for the overall modular surface foundation 100 (i.e., per wind turbine) and provide space otherwise not provided by conventional foundations for storage within housing member 44 or to house down tower equipment 56.
In the present embodiment, housing member 44 is substantially centered relative to the width of concrete footing 58. Typically, the width of concrete footing 58 is a function of the thickness of housing member 44. In the present embodiment, the width of the concrete footing 58 is greater than or equal to 2.5 times the thickness of housing member 44. In an alternative embodiment, width of concrete footing 58 can be considerably wider to provide suitable bearing capacity, which is dependent on local soil bearing pressure capability. The depth of concrete footing 58 is a function of the thickness of the housing member 44 or a function of the width of the concrete footing 58, which ever is greater. Generally, the depth of concrete footing 58 is greater than or equal to 1.25 times the thickness of housing member 44 or greater than or equal to 0.5 times the width of concrete footing 58, whichever is greater. A suitable diameter of concrete footing 58 is approximately 4 meters to approximately 30 meters, and more specifically approximately 4.3 meters to approximately 20.7 meters. Top surface 66 of concrete footing 58 of footing member 46 receives housing member 44. Footing member 46 further includes a fastener 146 to connect and secure housing member 44 to footing member 46.
Modular surface foundation element 10 can be made from any material and combination of materials that provides the desired structural, weight, and space requirements to support a space frame tower. Modular surface foundation element 10 can be made from materials such as, but not limited to, carbon fiber composites, reinforced carbon fiber composites, glass fiber composites, reinforced glass fiber composites, concrete, reinforced concrete, steel, and combinations thereof. Housing member 44 of modular surface foundation element 10 can be made from materials, such as, but not limited to, carbon fiber composites, reinforced carbon fiber composite, glass fiber composites, reinforced glass fiber composites, concrete, reinforced concrete, metals, such as steel, and combinations thereof. In the present embodiment, modular surface foundation element 10 is made from a combination of concrete, reinforced concrete, and metals, and housing member 44 is made from a combination of concrete, reinforced concrete, and metals.
Housing member 44 is made at an off-site location and transported to the part fabrication site of modular surface foundation element 10. Alternatively, housing member 44 can be made at the tower erection site. In one embodiment, housing member 44 can be a single monolithic concrete structure. In another embodiment, housing member 44 can be fabricated by joining a two monolithic concrete pieces, a top piece and a bottom piece (not shown) together. Alternatively, housing member 44 can be fabricated using a plurality of panels 105 joined together to form housing member 44 (See
Tensioning cables 111, 112 are made from steel or any other suitable reinforcing material, such as, but not limited to, glass fiber, carbon fiber and other cable materials. Tensioning cables 111, 112 are single strand, a bar of reinforcing material, or a plurality of strands of reinforcing material woven, wound, or braided together. Tensioning cables 111, 112 are approximately 3 millimeters (approximately ⅛ inch) to approximately 50 millimeters (approximately 2 inches), more specifically, approximately 3 millimeters (approximately ⅛ inch) to approximately 30 millimeters (approximately 1 inch), or, even more specifically, 3 millimeters (approximately ⅛ inch) to approximately 10 millimeters (approximately ⅜ inch) in thickness, and all subranges therebetween, but may be thinner or thicker depending on the tension required for modular surface foundation element 10 to form modular surface foundation 100. Tensioning cables 111, 112 are part of an unbonded or bonded post-tensioning system. In an unbonded post-tensioning system, tensioning cables 111, 112 are coated with a specially formulated grease and an outer layer of seamless plastic to provide protection against corrosion. In a bonded post-tensioning system, tensioning cables 111, 112 are encased in a corrugated metal or plastic duct, and after the tensioning cables 111, 112 are stressed, a cementitious type grout or epoxy is injected into the duct to bond the tensioning cables 111, 112 to the surrounding concrete.
The number of post tensioning cables used, both vertical tensioning cables 111 and horizontal tension cables 112, depends on the turbine size and load. The number of post-tensioning cables used for either of the above described embodiments can also vary depending on the thickness of the post-tensioning cables. In the present invention, at least two horizontal tensioning cables 112 are used to provide the desired tension but up to one hundred horizontal tension cables 112 can be used, and more specifically approximately ten to thirty horizontal tensioning cables 112 can be used, depending on housing member 44 height and desired tension. At least three vertical tensioning cables 111 are used in the present invention but up to three hundred vertical tensioning cables 111 can be used, and more specifically, approximately twenty to fifty vertical tensioning cables 111 can be used, depending on housing member 44 height and desired tension. Rebar 122 is also used to provide further reinforcement to housing member 44.
Vertical tensioning cables 111 are strung through one stub anchor 128 and then run height-wise or vertically through vertical through-tubes 110, to the next stub anchor 128 above or below (not shown). The process of stringing vertical tensioning cables 111 is repeated until all of the stub anchors 128 in a vertical line are connected through the vertical through-tubes 110 by vertical tensioning cables 111 (not shown).
The present disclosure also provides a method of forming a modular surface foundation 10 for wind turbine space frame towers 30 comprising: fabricating a plurality of housing members 44 having a series of post-tensioning cables 111, 112, forming, by digging or other means, a plurality of shallow trenches 62 to hold footing members 46, placing the footing members 46 in shallow trenches 62, applying the plurality of housing members 44 to the plurality of footing members 46 and securing housing members 44 to footing members 46, applying tension to housing members 44 using the post-tensioning cables 111, 112 wherein the housing member provides support and increased height for the space frame tower and includes an interior space, and attaching structural members 40 of wind turbine space frame tower 30 to housing members 44. Footing member 46 may be pre-fabricated off-site and assembled on site or may be poured into a concrete mold formed within shallow trench 62.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims
1. A modular surface foundation for wind turbine space frame towers comprising,
- a plurality of footing members; and
- a housing member disposed on each of the footing members, the housing member extending from the footing member and attaching to one or more structural members forming a portion of a wind turbine tower, wherein the housing member provides support and increased height for the space frame tower and includes an interior space.
2. The modular surface foundation of claim 1, wherein each footing member further comprises a concrete footing disposed in a shallow trench, wherein the trench is substantially shaped like the concrete footing.
3. The modular surface foundation of claim 1, wherein the housing member comprises a carbon fiber composite, a reinforced carbon fiber composite, a glass fiber composite, a reinforced glass fiber composite, concrete, reinforced concrete, a metal, or combinations thereof.
4. The modular surface foundation of claim 1, wherein the housing member comprises a concrete structure wherein the concrete structure is further supported by rebar and compressed by post-tensioning members.
5. The modular surface foundation of claim 4, wherein the concrete structure further comprises a plurality of panels joined together to form the housing member.
6. The modular surface foundation of claim 4, wherein the plurality of panels further includes a series of vertical chambers for receiving vertical post-tensioning members.
7. The modular surface foundation of claim 4, wherein the plurality of panels further includes a series of horizontal chambers for receiving horizontal post-tensioning members.
8. The modular surface foundation of claim 5, wherein each of the plurality of panels further includes a top portion disposed on and mechanically connected to a bottom portion, and wherein the bottom portion is disposed on and mechanically connected to the footing.
9. The modular surface foundation of claim 8, wherein both the top portion and the bottom portion further include a series of vertical chambers for receiving vertical post-tensioning members, and a series of horizontal chambers for receiving horizontal post-tensioning members.
10. The modular surface foundation of claim 1, wherein a center-to-center dimension of the modular surface foundation is approximately 1.0 to approximately 1.5 times the diameter of the modular surface foundation element.
11. The modular surface foundation of claim 1, wherein height of the modular surface element is approximately 1.25 to approximately 1.75 times the diameter of the modular surface element.
12. The modular surface foundation of claim 1, wherein the housing member is conical shaped, frusto-conical shaped, triangular pyramid shaped, square pyramid shaped, cylindrical shaped, cube shaped, pentagonal prism shaped, hexagonal prism shaped, heptagonal prism shaped, octagonal prism shaped, nonagonal prism shaped, or decagonal prism shaped.
13. The modular surface foundation of claim 1 wherein the interior space holds down tower equipment for the wind turbine.
14. A method of forming a modular surface foundation for wind turbine space frame towers comprising,
- (a) fabricating a plurality of housing members having a series of post-tensioning cables;
- (b) forming a plurality of shallow trenches to hold footing members;
- (c) placing the footing members in the shallow trenches;
- (d) applying the plurality of housing members to the plurality of footing members and securing the housing members to the footing members;
- (e) applying tension to housing members using the post-tensioning cables, wherein the housing member provides support and increased height for the space frame tower and includes an interior space; and
- (f) attaching structural members of wind turbine space frame tower to housing members.
15. The method of claim 14, wherein the housing member further comprises one or more selected from the group consisting of a door, a thermal exchange duct, a vent, steps, and combinations thereof.
16. The method of claim 14, wherein footing member is pre-fabricated off-site.
17. The method of claim 14, wherein the housing member holds down tower equipment.
18. An apparatus having a body closable to form a plurality of panels of a housing member of a modular surface foundation, wherein the body further comprises a top portion containing an aperture for receiving concrete and a bottom portion containing tubes running horizontally and vertically throughout, wherein the formed panels are joined together to form the housing member, wherein the housing member is disposed on a footing member and attached to one or more structural members forming a portion of a wind turbine tower, and wherein the housing member provides support and increased height for a space frame tower and includes an interior space.
19. The apparatus of claim 18, wherein the tubes of the bottom portion are removable from the formed panels of the housing member after the concrete has cured.
20. The apparatus of claim 18, wherein the bottom portion of the body further includes rebar.
Type: Application
Filed: Jul 8, 2009
Publication Date: Jun 3, 2010
Applicant: General Electric Wind Energy & Energy Services (Schenectady, NY)
Inventors: Lawrence WILLEY (Simpsonville, SC), Danian Zheng (Simpsonville, SC)
Application Number: 12/499,406
International Classification: E04H 5/04 (20060101); E02D 27/32 (20060101); E04B 1/19 (20060101);