U.S. patent application number 12/499406 was filed with the patent office on 2010-06-03 for modular surface foundation for wind turbine space frame towers.
This patent application is currently assigned to General Electric Wind Energy & Energy Services. Invention is credited to Lawrence WILLEY, Danian Zheng.
Application Number | 20100132270 12/499406 |
Document ID | / |
Family ID | 42221527 |
Filed Date | 2010-06-03 |
United States Patent
Application |
20100132270 |
Kind Code |
A1 |
WILLEY; Lawrence ; et
al. |
June 3, 2010 |
MODULAR SURFACE FOUNDATION FOR WIND TURBINE SPACE FRAME TOWERS
Abstract
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.
Inventors: |
WILLEY; Lawrence;
(Simpsonville, SC) ; Zheng; Danian; (Simpsonville,
SC) |
Correspondence
Address: |
McNees Wallace & Nurick, LLC
100 Pine Street, P.O. Box 1166
Harrisburg
PA
17108-1166
US
|
Assignee: |
General Electric Wind Energy &
Energy Services
Schenectady
NY
|
Family ID: |
42221527 |
Appl. No.: |
12/499406 |
Filed: |
July 8, 2009 |
Current U.S.
Class: |
52/79.5 ; 52/299;
52/745.17 |
Current CPC
Class: |
F03D 13/10 20160501;
E02D 27/42 20130101; Y02E 10/728 20130101; F03D 13/22 20160501;
F03D 13/20 20160501; E02D 27/38 20130101; E02B 2017/0091 20130101;
E02D 27/425 20130101; E02B 17/0004 20130101; F03D 80/00 20160501;
F05B 2240/9121 20130101 |
Class at
Publication: |
52/79.5 ; 52/299;
52/745.17 |
International
Class: |
E04H 5/04 20060101
E04H005/04; E02D 27/32 20060101 E02D027/32; E04B 1/19 20060101
E04B001/19 |
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.
Description
FIELD
[0001] 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.
BACKGROUND
[0002] Recently, 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.
[0003] 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.
[0004] 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.
[0005] 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 DISCLOSURE
[0006] One 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] Another advantage of the present disclosure is that the
modular surface foundation provides storage for down tower
equipment.
[0011] Yet another advantage of the present disclosure is that the
modular surface foundation provides additional height to the space
frame tower.
[0012] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side view of a wind turbine according to an
embodiment of the present disclosure.
[0014] FIG. 2 is a perspective view of a portion of the modular
surface foundation element according to an embodiment of the
present disclosure.
[0015] FIG. 3 is a partial perspective view of the modular surface
foundation element showing staggered joints of the housing member
according to an embodiment of the present disclosure.
[0016] FIG. 4 is a front sectional view of the footing member
according to an embodiment of the present disclosure.
[0017] FIG. 5 is a sectional view of the modular surface foundation
element of FIG. 2 taken in direction 5-5 showing the interior
surface according to an embodiment of the present disclosure.
[0018] FIG. 6 is a perspective view of the mold used to make a
portion of the housing member of the modular surface foundation
element according to an embodiment of the present disclosure.
[0019] FIG. 7 is a perspective transparent view of a portion of the
housing member of the modular surface foundation element according
to an embodiment of the present disclosure.
[0020] FIG. 8 is a perspective view of the internal surface of a
portion of the housing member of the modular surface foundation
element according to an embodiment of the present disclosure.
[0021] FIG. 9 is a sectional view of the internal surface of a
portion of FIG. 8 taken in direction 9-9 showing the interior
surface of the modular surface foundation element according to an
embodiment of the present disclosure.
[0022] FIG. 10 is a sectional view of the modular surface
foundation of FIG. 1 taken in the 10-10 direction showing the
dimensions of the modular surface foundation and modular surface
foundation elements.
[0023] Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.
DETAILED DESCRIPTION
[0024] As shown in FIG. 1, a wind turbine 16 generally includes a
nacelle 20 housing a generator (not shown). Nacelle 20 is mounted
atop a tower transition piece 32 with a flange (not shown) on top
of a space frame tower 30. The height of tower 30 is selected based
upon factors and conditions known in the art, and may extend to
heights of 60 meters or more. The wind turbine 16 may be installed
on any terrain providing access to areas having desirable wind
conditions. The terrain may vary greatly and may include, but is
not limited to, mountainous terrain or off-shore locations. Wind
turbine 16 also comprises a rotor 22 that includes one or more
rotor blades 24 attached to a rotating hub. Although wind turbine
16 shown in FIG. 1 includes three rotor blades 24, there are no
specific limits on the number of rotor blades 24 required by the
present invention. Space frame tower 30 includes a plurality of
vertical tower support members 34, a plurality of horizontal tower
support members 36, and a plurality of bracing tower support
members 38 integrally connected. Space frame tower 30 further
includes a plurality of structural members 40 that support and
connect space frame tower 30 to housing members 44. As shown in
FIG. 1, space frame tower 30 has a tripole construction, having
three structural members 40. In alternative embodiments, space
frame tower 30 may be constructed using more than three structural
members 40 to form tower 30.
[0025] 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 FIG. 1,
modular surface foundation 100 comprises three modular surface
foundation elements 10, each modular surface foundation element 10
further comprises housing member 44 extending from footing member
46 that attaches to each structural member 40 of space frame tower
30. In alternative embodiments, modular surface foundation 100 may
have more than three modular surface foundation elements 10, and
each modular surface foundation element 10 further comprises
housing member 44 and footing member 46. In another alternative
embodiment, modular surface foundation 100 has a smaller or greater
number of modular surface foundation elements 10 than the number of
structural members 40 that form space frame tower 30.
[0026] As shown in FIG. 1, housing member 44 of each modular
surface foundation element 10 includes a plurality of panels 105
joined together to form housing member 44. In another embodiment,
not shown in the figures, housing member 44 can be a single
monolithic integrally formed concrete structure further supported
by rebar and compressed by post-tensioning members.
[0027] FIG. 2 shows a single modular surface foundation element 10
of the modular surface foundation 100 of the present embodiment.
Housing member 44 of modular surface foundation element 10 is
comprised of a plurality of panels 105 joined together to form
housing member 44. Panels 105 can further include a plurality of
top panel sections 102 and a plurality of bottom panel sections
104. Top panel sections 102 are formed to rest on and attach to
each respective bottom panel section 104 by vertical
post-tensioning members 111 (see FIG. 7) and other fastening
mechanisms (not shown). As shown in FIG. 2, top panel section 102
and bottom panel section 104 are connected and have aligned joints
142. In an alternative embodiment, as shown in FIG. 3, top panel
section 102 and bottom panel section 104 are connected by unaligned
or staggered joints 144. Staggered joints 144 are offset
circumferentially, such that staggered joints 144 are situated in
the middle of top panel section 102 and middle of bottom panel
section 104, to provide adequate support to form housing member 44.
As shown in FIG. 2, top panel section 102 of housing member 44 is
further attached to a connecting member 42, wherein connecting
member 42 is connected to the structural member 40 of tower 30.
Connecting member 42 contains fasteners (not shown) to secure and
attach the housing member 44 of modular surface foundation element
10 to structural member 40 of tower 30 (see FIG. 1). Bottom panel
section 104 of housing member 44 is further connected to footing
member 46 by a fastening mechanism 146 (see FIG. 4). Suitable
fastening mechanisms include, but are not limited to, bolts, nuts,
screws, pins, gussets, grouting, and other fastening mechanisms
well known in the art. Fastening mechanism 146 can also be
integrally formed within bottom panel section 104 of housing member
44 or integrally formed within the footing member 46. In the
present embodiment, housing member 44 further comprises a vent 48
for airflow, a door 50 to access area inside housing member 44,
stairs 52 to reach door 50, and a thermal exchange duct 54. In
another embodiment, door 50 may include a vent for airflow to
supplement or replace vent 48. As shown in FIG. 2, down tower
equipment 56 is located inside the housing member 44. Examples of
typical down tower equipment 56, are, but not limited to, turbine
control panels, wires, cables, control structures, spare parts, and
transformers.
[0028] As shown in FIG. 2, housing member 44 is frusto-conical
shaped. However, any conical shaped, triangular pyramid shaped,
square pyramid shaped, cylindrical shaped, cube shaped, or may
sided prism, such as pentagonal prism shaped, hexagonal prism
shaped, heptagonal prism shaped, octagonal prism shaped, nonagonal
prism shaped, or decagonal prism shaped may be possible as long as
the desired structural and support properties of modular surface
foundation element 10 of modular surface foundation 100 are
obtained. In the present embodiment, footing member 46 is annularly
shaped. In an alternative embodiment, footing member 46 can be
substantially shaped like bottom of housing member 44.
[0029] As shown in FIG. 10, modular surface foundation 100 includes
three modular surface foundation elements 10. The overall diameter
of modular surface foundation 100 is approximately 9.8 meters to
approximately 48.8 meters, which allows for space frame towers 30
supporting wind turbines 16 rated from 800 kilowatt (kW) to 10
megawatt (MW) respectively. The outermost extent prescribed by the
overall diameter of modular surface foundation 100 includes the
outermost edge of concrete footing 58 of footing member 46, which
is also the outer edge of modular surface foundation element 10
bearing on undisturbed earth. The diameter range for modular
surface foundation 100 is approximately 9.8 meters to approximately
48.8 meters and is specific for modular surface foundation element
10 having center-to-center dimensions (B) equal to 1.25 times the
diameter of modular surface foundation element 10. The
center-to-center dimension (l.sub.ctc) is measured from the center
of one modular surface foundation element 10 to the center of
another adjacent modular surface foundation element 10, shown in
FIG. 10 as dimension (B). In another embodiment, the
center-to-center dimension (B) may range from approximately 1.0 to
approximately 1.5 times or more of the diameter of the modular
surface foundation element 10, resulting in a potential for
additional overall diameter values for modular surface foundation
100.
[0030] 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.
TABLE-US-00001 TABLE I Ratio of center-to-center dimension (B)
Number of l.sub.ctc = number (provided below) * diameter.sub.MSFE
MSFEs Average Min Max 3 1.25 1 1.5 4 1.12 1 1.25 5 1.07 1 1.15 6
1.04 1 1.1
[0031] 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 (l.sub.ctc) 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.
[0032] 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 FIG. 10). In the present
embodiment, dead load center 200 of modular surface foundation 100
has no side loads applied and is directly in the center of the
equilateral triangle formed by modular surface foundation elements
10. Longest moment arm (l.sub.max), dimension (A), of the present
embodiment which is resistant to overturning is measured from dead
load center 200 of modular surface foundation 100 to the outermost
edge of concrete footing 58 of modular surface foundation element
10. The shortest moment arm (l.sub.min), dimension (C), of the
present invention which is resistant to overturning is equal to the
diameter of the concrete footing 58 of modular surface foundation
element 10. In the present embodiment, modular surface foundation
100 has an average effective diameter approximately 8.3 meters to
approximately 41.6 meters. The average effective diameter of
modular surface foundation 100 is equal to the average of the
diameters for the minimum (l.sub.min) (dimension (C)) and maximum
(l.sub.max) (dimension (A)) moment arms defined from dead center
200 of the modular surface foundation 10 to the extreme edge of the
foundation (i.e. outermost edge of the concrete footing 58) for
space frame tower 30 and modular surface foundation 100 system to
resist overturning with respect to opposing the direction of the
oncoming wind (as viewed from the side). The average effective
diameter of modular surface foundation 100 decreases as the number
of modular surface foundation elements increases. As the physical
limit to the number of modular surface foundation elements 10 is
approached shortest moment arm (l.sub.min) and longest moment arm
(max) will theoretically approach the same value.
[0033] 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.
[0034] 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, h.sub.msfe=1.5.times.d.sub.msfe,
wherein h.sub.msfe is the height of modular surface foundation
element 10 and d.sub.msfe 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.
[0035] FIG. 4 shows a front sectional view of footing member 46.
Footing member 46 further comprises a concrete footing 58 disposed
in a shallow trench 62. Trench 62 is substantially shaped like
concrete footing 58. A suitable depth of trench 62 is approximately
less than 1 meter in depth and approximately less than 1 meter in
width, but greater depths and widths of trench 62 are possible.
Footing member 46 further includes a floating slab of concrete 65
or gravel 64, both or one of which is disposed on the ground 68
inside and/or outside of footing member 46. Floating slab of
concrete 65 and/or gravel 64 found inside modular surface
foundation element 10 provides a surface for receiving down tower
equipment 56. Floating slab of concrete 65 or gravel 64 found
outside modular surface foundation element 10 provides a surface
for parking vehicles and other equipment near wind turbine space
frame tower 30. Floating slab of concrete 65 is understood in the
art to mean that the wearing surface of the floating concrete slab
65 is not relied on for structural strength in the structure, and
that floating slab of concrete 65 is free from restraint by other
concrete features that can be load-bearing. In the present
embodiment, floating slab of concrete 65 is located on gravel 64,
which permits water movement and drainage under floating concrete
slab 65. Floating slab of concrete 65 "floats" laterally within the
housing member 44 but is supported vertically at top surface 66 of
concrete footing 58 which is the interface of footing member 46
with the housing member 44. Concrete footing 58 of footing member
46 is further reinforced by rebar 60. Concrete footing 58 is poured
on site or pre-fabricated in a facility and assembled on-site.
[0036] 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.
[0037] FIG. 5 is a sectional view of the modular surface foundation
10 of FIG. 2 taken in direction 5-5 showing the interior space or
volume 140 of housing member 44. Interior space 140 may have a
floating slab of concrete 65 or gravel 64 (not shown) to provide a
place for down tower equipment (not shown) storage. As shown in
FIG. 5, interior space 140 is located inside of housing member 44
proximate to interior wall 106 of housing member 44.
[0038] 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.
[0039] 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 FIG. 1). In yet another embodiment, housing member
44 can be fabricated from a plurality of panels 105 having a top
panel section 102 and a bottom panel section 104 that are joined
together to form housing member 44 (See FIGS. 2, 3 and 6).
[0040] FIG. 6 shows a perspective view of an apparatus or mold 130
having a body closable to form a plurality of panels 105 of housing
member 44 of modular surface foundation 10. Housing member 44 can
be fabricated using any number of pieces and mold combinations to
achieve the desired structure. Mold 130 for fabricating panels 105
and/or top panel sections 102 and bottom panel sections 104, of
housing member 44 comprises two pieces, a top mold 136 and a bottom
mold 132. Top mold 136 further comprises an opening 138 to pour
concrete into mold 130. Opening 138 can also be used to vibrate the
concrete to provide adequate dispersion of concrete in mold 130.
Alternatively, a shaking table can be used to vibrate the concrete
to provide adequate dispersion of concrete in mold 130. In one
embodiment, bottom portion 132 comprises a plurality of vertical
inserts 148 and a plurality of horizontal inserts 150. Vertical
inserts 148 are used to form pre-fabricated vertical recesses 152
used to adjust vertical tensioning cables 111, as shown in FIG. 7.
Horizontal inserts 150 are used to form pre-fabricated horizontal
recesses 154 used to adjust horizontal tensioning cables 112, as
shown in FIG. 7. Inserts 148, 150 can be made from any plastic,
steel, or other suitable material that will withstand concrete
setting. Inserts 148 can be partially or fully removed from the
concrete after it has been cured to provide pre-fabricated recesses
152, 154. Bottom portion 132 of mold 130 further comprises a
plurality of tubes 134 placed vertically and horizontally along the
length of bottom portion 132. Tubes 134 can run through inserts
148, 150 (as shown) or tubes 134 can attach to inserts 148, 150. In
an alternative embodiment, anchor stubs 128 are integrally formed
in panels 105 using mold 130. Suitable material for tubes 134
includes, but is not limited to, plastic, steel, or other materials
that can withstand concrete setting. Tubes 134 stay in formed panel
105 after the concrete has cured. In an alternative embodiment,
tubes 134 can be removed from panel 105 after concrete has cured.
The hollow portions in panel 105 of housing member 44 from tubes
134 provide horizontal through-tubes 114 and vertical through-tubes
110 for the horizontal and vertical tensioning cables or tendons
(post-tensioning members) 111, 112. Mold 130 typically also
contains rebar (not shown) running vertically and/or horizontally
inside bottom portion 132. The thickness of the cured concrete of
housing member 44 is approximately 100 millimeters (approximately 4
inches) to about approximately 500 millimeters (approximately 20
inches), more specifically, approximately 150 millimeters
(approximately 6 inches) to approximately 300 millimeters
(approximately 12 inches), or, even more specifically, 200
millimeters (approximately 8 inches) to approximately 250
millimeters (approximately 10 inches), and all subranges
therebetween. The thickness of cured concrete of housing member 44
is a function of structural loading requirements and varies
according to the size of wind turbine.
[0041] FIG. 7 shows a portion of the interior 106 of housing member
44. Horizontal through-tubes 114 run hoop-wise through housing
member 44. Vertical through-tubes 110 run vertically through
housing member 44. FIG. 7 depicts a single horizontal tensioning
cable 112 shown running through horizontal through-tube 114 and a
single vertical tensioning cable 111 shown running through vertical
through-tube 110; however, a plurality of horizontal tensioning
cables 112 and a plurality of vertical tensioning cables 111 are
used to provide adequate tension to the assembled housing member
44. Housing member 44 further includes a fastener 146 (See FIG. 4)
to secure housing member 44 to top surface 66 of concrete footing
member 46. In the present embodiment, tensioning cables 111, 112
are threaded through vertical through-tubes 110, and horizontal
through-tubes 114, to join the panels 105 of housing member 44.
Vertical tensioning cables 111 provide tension height-wise or
vertically to panels 105. Vertical tensioning cables 111 are
tightened at the top edge of panel 105 in a series of vertical
pre-fabricated recesses 152. Alternatively, when panels 105 contain
a top section 102 and a bottom section 104, vertical tensioning
cables 111 join and provide tension height-wise or vertically to
top section 102 and bottom section 104 of panels 105. As shown in
FIG. 7, a series of pre-fabricated vertical recesses 152 are
provided at the top and bottom of top section 102 and bottom
section 104 of panel 105 to allow vertical tensioning cables 111 to
be adequately adjusted to provide the required tension. Horizontal
tensioning cables 112 join and provide tension to plurality of
panels 105 of housing member 44, in a hoop-wise direction. As shown
in FIG. 7, a series of pre-fabricated horizontal recesses 154 are
provided at the sides of panels 105 to allow horizontal tensioning
cables 112 to be adequately adjusted to provide the required
tension. Alternatively, when housing member 44 contains plurality
of top sections 102 and plurality of bottom sections 104,
horizontal tensioning cables 112 join and provide tension hoop-wise
to adjacent top sections 102 and adjacent bottom sections 104 of
housing member 44. Once housing member 44 is formed, tensioning
cables 111, 112 are tightened at a series of pre-fabricated
recesses 152, 154 at the vertical edges and horizontal edges of
panels 105 from inside housing member 44 to provide adequate
post-tensioning stress on the formed concrete structure of housing
member 44.
[0042] 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 1/8 inch) to approximately 50
millimeters (approximately 2 inches), more specifically,
approximately 3 millimeters (approximately 1/8 inch) to
approximately 30 millimeters (approximately 1 inch), or, even more
specifically, 3 millimeters (approximately 1/8 inch) to
approximately 10 millimeters (approximately 3/8 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.
[0043] FIG. 8 shows the interior 106 of housing member 44 as an
alternative embodiment of the present disclosure. In this
embodiment, horizontal tensioning cables 112 are strung through one
stub anchor 128 and then run hoop-wise through horizontal
through-tubes 114, to an adjacent stub anchor 128 (See FIG. 9) of
housing member 44. The process of stringing horizontal tensioning
cables 112 is repeated until all of stub anchors 128 in a circular
plane are connected hoop-wise, through horizontal through-tubes
114, by horizontal tensioning cables 112. 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. 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. Stub anchors
128 are concrete structures integrally formed on the interior
surface 106 of housing member 44 using a mold having depressions
and tubes. Horizontal tensioning cables 112 and vertical tensioning
cables 111 are tightened to provide the desired post-tensioning
stress to housing member 44. Alternatively, this post-tensioning
technique using stubs 128 can be used on external surface 108 of
housing member 44 to provide desired post-tensioning stress to
housing member 44.
[0044] 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.
[0045] FIG. 9 shows a sectional view of the internal space 140 of a
portion of FIG. 8 taken in direction 9-9. FIG. 9 shows the whole
interior space 140 according to an embodiment of the present
disclosure. In the present embodiment, there are four panels 105
each having two (shown) stub anchors 128. In an alternative
embodiment, the number of panel members 105 can be larger or
smaller than four, and each panel member 105 contains at least one
stub anchor 128. Stub anchors 128 are integrally formed on the
inside wall 106 of panels 105 of housing member 44. In one
embodiment, horizontal tensioning cables 112 are strung through a
channel 158 in stub anchors 128 and threaded through horizontal
through-tube 114 to the adjacent stub 128 to join panels 105 and to
provide desired post-tensioning once horizontal tensioning cables
112 are tightened. In another alternative embodiment (not shown),
the horizontal tensioning cables are strung through a channel in
the stub anchor of one panel and strung through horizontal
through-tube skipping the adjacent stub anchor and strung through
the channel of the next stub anchor located in an adjacent panel.
In yet another alternative embodiment (not shown), the horizontal
tensioning cables are strung through the channel in the stub anchor
of one panel and strung through the horizontal through-tube
skipping the stub anchors in the adjacent panel and strung through
the channel in the stub anchor of the next adjacent panel. The
anchoring at stub 128 utilizes an anchoring end device which
typically consists of split tapered clap inserts and anchoring
metal blocks with matching tapered holes, which is well known in
the art of post-tensioning for concrete structures. The process of
stringing horizontal tensioning cables 112 through channels 158 of
stub anchor 128 and threading through horizontal through-tube 114
to adjacent stub anchor 128 is repeated until all stub anchors 128
are connected hoop-wise by horizontal tensioning cables 112. Any
combination of stringing horizontal tensioning cables 112 through
channels 158 of stub anchors 128 and threading through horizontal
through-tube 114 to various adjacent and semi-adjacent stub anchors
128 is possible and one or more of the above described methods can
be used to provide the desired post-tensioning stress to housing
member 44.
[0046] 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).
[0047] 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.
[0048] 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.
* * * * *