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`US 20020124502Al
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0124502 Al
`Sep. 12, 2002
`Henderson
`( 43) Pub. Date:
`
`(54) PERIMETER WEIGHTED FOUNDATION
`FOR WIND TURBINES AND THE LIKE
`
`(76)
`
`Inventor: Allan P. Henderson, Bakersfield, CA
`(US)
`
`Correspondence Address:
`JACOBSON HOLMAN PLLC
`400 SEVENTH STREET N.W.
`SUITE 600
`WASHINGTON, DC 20004 (US)
`
`(21) Appl. No.:
`
`10/067,999
`
`(22) Filed:
`
`Feb. 8, 2002
`
`Related U.S. Application Data
`
`(63) Continuation of application No. 09/671,282, filed on
`Sep. 27, 2000, now abandoned.
`
`Publication Classification
`
`Int. Cl.7 ........................... E02D 27/00; E02D 27/32
`(51)
`(52) U.S. Cl.
`...................... 52/296; 52/741.14; 52/741.15
`
`(57)
`
`ABSTRACT
`
`A perimeter weighted foundation has a central pier pedestal
`and an enlarged base spaced outwardly and extending below
`the pedestal. The enlarged base includes an outer concentric
`perimeter wall section with a radially extending, disk(cid:173)
`shaped spread section interconnecting the bottom of the
`pedestal section and the top of the perimeter wall section.
`The pedestal section includes vertically extending post(cid:173)
`tensioning anchor bolts sleeved through substantially the
`entire height of the cylindrical pedestal in accordance with
`earlier U.S. Pat. Nos. 5,586,417 and 5,826,387 and the
`spread section includes two layers of similarly sleeved
`post-tensioning bolts which extend through the bottom of
`the pedestal section and into or through the top of the
`perimeter wall section, thus tying together the enlarged base
`to the pier pedestal. After the concrete is poured, hardened
`and cured, the vertical bolts of the pedestal section and the
`radially extending horizontal bolts in the spread section are
`post-tensioned to impart a heavy unit compressive loading
`on the concrete in the pier pedestal and enlarged base. After
`back filling soil onto the spread section and to the interior of
`the pedestal section, the foundation is able to withstand high
`upset forces imparted to the foundation by any large struc(cid:173)
`ture supported thereon.
`
`________ ___, __ - - i ' - - - - - -~ - - - - - - - - - - - - - - - - . -1
`
`/7'(
`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 1
`
`

`

`Patent Application Publication Sep. 12, 2002 Sheet 1 of 9
`
`US 2002/0124502 Al
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`
`FIG.1
`(PRIOR ART)
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`(PRJORART)
`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 2
`
`

`

`Patent Application Publication Sep. 12, 2002 Sheet 2 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 3
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`

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`Patent Application Publication Sep. 12, 2002 Sheet 3 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 4
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`Patent Application Publication Sep. 12, 2002 Sheet 4 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 5
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`Patent Application Publication Sep. 12, 2002 Sheet 5 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 6
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`Patent Application Publication Sep. 12, 2002 Sheet 6 of 9
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`US 2002/0124502 Al
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 7
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`patent J\.p\l\\cation Publication Se\l· 12, 2002 S1teet 7 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 8
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`Patent Application Publication Sep. 12, 2002 Sheet 8 of 9
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`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 9
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`

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`Patent Application Publication Sep. 12, 2002 Sheet 9 of 9
`
`US 2002/0124502 Al
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`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 10
`
`

`

`US 2002/0124502 Al
`
`Sep. 12,2002
`
`1
`
`PERIMETER WEIGHTED FOUNDATION FOR
`WIND TURBINES AND THE LIKE
`
`BACKGROUND OF THE INVENTION
`
`[0001] 1. Field of the Invention
`
`[0002] This invention relates to concrete foundations, and
`more particularly, to reinforced concrete pier foundations
`useful for the support of tall, heavy and/or large towers
`which may be used to support power lines, communication
`systems, street lighting and signals, bridge supports, com(cid:173)
`mercial signs, freeway signs, ski lifts and the like, and
`especially wind turbines which are subject to very high upset
`forces.
`
`[0003] 2. Background of the Invention
`
`[0004] Various different forms of foundations utilizing
`some of the general structural and operational features of the
`instant invention have been known. However, these previ(cid:173)
`ously known foundations do not include some of the basic
`features of the instant invention. The combination of fea(cid:173)
`tures incorporated in the disclosed embodiments of the
`instant invention enable a heavy duty foundation to be
`formed in situ or be precast and transported to the construc(cid:173)
`tion site, and be placed in position in a manner not requiring
`the use of large drilling rigs or pile drivers. The present
`invention is particularly useful in locations where the ground
`water is high and/or the depth clearance for placement of the
`foundation is low. The foundation of the present invention is
`capable of resisting very high upset loads and in a manner
`independent of the concrete of the foundation experiencing
`alternating localized compression and tension loading.
`
`[0005]
`In a conventional concrete pier foundation the
`concrete bears the compressive loads and the contained
`reinforcing bars (rebar) are sized to bear the tensile loads.
`Anchor bolts are typically utilized solely for the purpose of
`attaching the supported structure to the foundation. The
`anchor bolts are typically placed within a reinforcing steel
`(rebar) matrix or cage using a removable template at the top
`and a separate anchor plate at the bottom of each bolt to
`prevent anchor bolt pullout. The entire module is poured in
`concrete. Conventional foundations typically resist over(cid:173)
`turning movement by their weight.
`
`[0006] Further, when the foundation is loaded by the
`structure supported thereon, the foundation is subjected to
`varying tensile and compressive loads with there being a
`boundary at the bolt anchor plates where the loading on the
`concrete alternates from a compressive load to a tensile load
`depending upon the various forces on the supported struc(cid:173)
`ture. The tensile load from the overturning moment of the
`supported structure is applied near the top of the foundation
`by the anchor bolts and subjects the large portion of the
`foundation below the point of application to tension. The
`large foundation typically requires a great amount of rein(cid:173)
`forcing steel and a large amount of concrete to encase the
`reinforcing steel. Extensive labor is also necessary to
`assemble the reinforcing steel matrix and fill the volume of
`the foundation with concrete and fix the anchor bolts. A
`typical cylindrical foundation also requires the use of a large
`drill to excavate the hole.
`
`[0007] My two prior U.S. patents, U.S. Pat. Nos. 5,586,
`417 and 5,826,387, hereby incorporated by reference in their
`entirety as if fully set forth, are hereinafter sometimes
`
`referred to as "my prior patents". My prior patents disclose
`concrete pier foundations under high unit compression
`which eliminate the necessity for large quantities of rein(cid:173)
`forcing steel bars (rebar or tension bars) and substantially
`reduce the amount of concrete necessary. Therefore, the cost
`of these foundations is substantially less when compared to
`conventional designs. Furthermore, the foundations of my
`prior patents simplify the placement of the supported struc(cid:173)
`ture on the foundation and eliminate alternating cyclical
`compression and tension loading on the foundation, thereby
`substantially reducing fatigue. Also, these patented founda(cid:173)
`tions allow for the replacement of the tower anchor bolts in
`the unlikely event of bolt failure and allow for removal of
`the upper four to five feet of the foundation in the event such
`action is desired for decommissioning purposes.
`
`[0008] The foundations of my prior patents are preferably
`in the shape of a concrete cylinder. The outer boundary shell
`of the concrete may be formed by corrugated metal pipe
`(CMP). The inner boundary, preferably in large hollow
`cylinder foundations, also may be formed by CMP of a
`lesser diameter. Elongated high strength steel bolts are
`positioned around the periphery of the concrete cylinder and
`extend from a peripheral anchor plate or ring near the bottom
`of the cylinder vertically up through the concrete portion of
`the foundation to a peripheral connecting plate or flange
`adjacent the upper end of the structure. The bolts are
`received in "hollow tubes" to isolate the bolts from the
`concrete. The steel bolts preferably serve as anchor bolts for
`attachment of the base flange of the supported tower struc(cid:173)
`ture, and the anchor bolt pattern may thus be determined by
`the bolt hole pattern on the lower base plate or flange of the
`supported tower. The steel bolt pattern may also be engi(cid:173)
`neered into the construction of the foundation by a remov(cid:173)
`able template.
`
`[0009] The "hollow tubes" are preferably elongated plas(cid:173)
`tic tubes or sleeves which encase the bolts substantially
`through the entire vertical extent of the concrete and prevent
`the bolts from adhering to the concrete. Then, the bolts can
`be tensioned after the concrete has hardened and cured in
`order to post-tension the entire concrete foundation. Alter(cid:173)
`natively, the elongated bolts can be wrapped in plastic tape,
`or otherwise sheathed to prevent the bolts from adhering to
`the concrete during curing and allow the bolts to stretch
`under tension over the entire operating length of the bolt
`through substantially the full vertical extent of the concrete.
`There is typically no conventional rebar reinforcing steel in
`the foundation, except perhaps in large foundations where a
`small amount of incidental re bar may be used to stabilize the
`bolts during construction of the foundation.
`
`[0010] The center of a large hollow cylindrical foundation
`according to my prior patents is filled with excavated soil
`and then capped. Excavation for the foundation may be done
`using widely available, fast, low cost excavating machines
`instead of relatively rare, slow, costly drills necessary for
`conventional cylindrical foundations.
`
`[0011] The foundations of my prior patents use the
`mechanical interaction with the earth to prevent overturning
`instead of the mass of the foundation typically used by other
`foundations for turbine towers and other large structures
`subject to high upset forces. The high strength anchor bolts
`are tightened to provide heavy tension on the foundation
`from a heavy top flange through which the bolts pass to the
`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 11
`
`

`

`US 2002/0124502 Al
`
`Sep. 12,2002
`
`2
`
`anchor flange or plate adjacent the bottom of the foundation,
`thereby post-stressing the concrete in great compression and
`placing the entire foundation, between the heavy top plate or
`flange and lower anchor plate or flange, under high unit
`compression loading. The bolts are tightened so as to exceed
`the maximum internal tension expected from overturning
`forces of the tower structure on the foundation. Therefore,
`the entire foundation withstands the various loads with the
`concrete thereof always remaining in compression and the
`bolts always in static tension. The concrete pier foundations
`of my prior patents may be formed in situ in a remote
`location or be formed in a precast concrete section placed
`under heavy compression.
`
`[0012] To describe a portion of the foundation structure
`incorporated in the foundation of the present invention,
`reference is now made to FIGS. 1, 2 and 3 which are taken
`from my prior patents. In these Figures, the numeral 10
`generally designates the pier foundation. The foundation 10
`includes inner and outer upstanding corrugated metal pipe
`(CMP) sections 12 and 14. The outer section 14 is initially
`placed within a hole or excavation 16 formed in the ground
`18 and rests upon the bottom of the excavation 16. The inner
`section 12 is then placed and positioned within the excava(cid:173)
`tion 16. The interior of the inner CMP 12 is partially back
`filled and the excavation 16 outwardly of the outer CMP 14
`is partially back filled to stabilize the CMP sections gener(cid:173)
`ally in position within the excavation and relative to each
`other.
`
`[0013] The foundation 10 additionally includes a series of
`tensioning bolts 20 and 21 spaced circumferentially about
`the annulus defined between sections 12 and 14. The ten(cid:173)
`sioning bolts are preferably in side-by-side pairs which are
`spaced radially from the center of the foundation. In a
`typical embodiment, the inner ring of bolts 20 has a slightly
`shorter diameter than the outer ring of bolts 21. Forty-eight
`tensioning bolts 20 and forty-eight tensioning bolts 21, or a
`total of ninety-six, are provided. The rings of bolts have
`diameters which are several inches apart and which gener(cid:173)
`ally equal about 12 feet.
`
`[0014] The lower ends of the bolts 20 and 21 are anchored
`to a lower annular plate or anchor ring 22, sometimes also
`called an embedment ring, which preferably may be con(cid:173)
`structed of several circumferentially butted and joined sec(cid:173)
`tions. The anchor or embedment ring 22 is radially spaced
`relative to the inner CMP section 12 preferably by utilizing
`circumferentially spaced horizontal and radially extending
`positioning bolts 24 threaded through nuts 26 secured to the
`under side of the anchor ring 22 at points spaced circum(cid:173)
`ferentially thereabout. Further, the bolts 20 and 21 have all
`but their opposite ends slidingly received through hollow
`tubes, such as PVC pipes 30, which are sized to receive and
`loosely grip bolts 20 and 21 but still permit free movement
`therethrough. The hollow tubes or PVC tubing 30 need not
`extend through the entire vertical height of concrete 68, but
`only through as much of the central portions and extending
`as close to the top and bottom as to allow the tensioning bolts
`to extend evenly through the concrete during post-tension(cid:173)
`ing.
`
`[0015] The PVC pipes 30 and other suitable tubing or
`isolating mechanism serve to allow bolts 20 and 21 to move
`relatively freely through the concrete after curing so as to
`allow post-tensioning of the elongate rods. In addition, rebar
`
`wraps 28 are used and secured to the tubes 30 associated
`with outer bolts 21 at approximately five foot intervals along
`the vertical extent of the bolts 21 in order to maintain the
`bolts longitudinally straight during the pour of concrete.
`
`[0016] The upper ends of the bolts 20 are supported from
`a template 32 which consists of upper and lower rings 34 and
`36 or ring sections secured together. Upwardly opening
`radial channel members 38 and mounting blocks 40 received
`in the channel members 38 are clamped between the upper
`and lower rings 34 and 36 through the utilization of upper
`and lower nuts 42 and 44 threaded on the bolts 20 and 21.
`The inner ends of the radial channel members 38 are joined
`by a center circular plate 46. The inner portions of the radial
`channel members 38 include lateral stabilizers 45 in the
`form of inverted channel members downwardly embrac(cid:173)
`ingly engaged thereover and equipped with opposite side set
`screws 47 clamp engaged with the corresponding channel
`members 38. The depending flanges of the channel members
`45 are slotted for stabilizing engagement with adjacent
`upper edge portions of the inner pipe 12 while the outer ends
`of the channel members 38 include threadingly adjustable
`channel member feet 50 abutingly engageable with the
`ground 18. A cylindrical form plate 52 is clamped about the
`upper end of the outer pipe 14 and has its opposite ends
`secured together in overlapped relation.
`
`[0017] Thereafter, concrete 68 may be poured to the
`bottom of each of the radial channel members 38 and to the
`top of each of the blackout bodies 64. After the concrete 68
`has hardened, the upper nuts 42 are removed and the entire
`template 32 including the upper and lower rings 34 and 36,
`the channel members 38 and attached feet 50 are lifted up
`from the bolts 20 and 21 and the form plate 52, the blackout
`bodies 64 being exposed from above by removal of the
`template 32 to thus allow removal of the blackout bodies 64.
`
`[0018] When the concrete 68 has sufficiently hardened, it
`must be determined that the groove 70 is level. If groove 70
`is not level, a coating of high compression hardenable grout
`82 should be placed within the groove 70 to achieve a
`levelness for the tower base. Further, even if groove 70 is
`level, it may be desirable to place grout 82 in the groove 70.
`The nuts 44 are removed or threaded downwardly on the
`bolts 20 and 21 at least % inch. A tower (not shown) to be
`supported from the foundation 10 is thereafter lowered into
`position with the upper exposed ends of the bolts 20 and 21
`upwardly received through suitable bores formed in the
`inner and outer peripheries of the heavy annular plate or base
`flange of the tower and the lower lug defining portion of the
`base flange seated in the groove or grout trough 70. Initially
`the upper nuts 42 are again threaded down onto the upper
`ends of the bolts 20 and 21 and preferably torqued to about
`50 foot pounds. The nuts 42 are thereafter sequentially
`torqued (in a predetermined pattern of tightening) preferably
`to about 600 foot pounds which places each of the bolts 20
`and 21 under approximately 40,000 pounds tension at
`approximately 1/3 the stretch limit of the bolts 20 and 21.
`
`[0019] By placing the bolts 20 and 21 under high tension,
`the cylindrical structure comprising the concrete 68 is placed
`under heavy unit compressive loading from the upper end
`thereof downwardly to a level adjacent the lower end of the
`cylindrical structure, and the unit compressive loading is
`considerably greater than any upset tensional forces which
`must be overcome to prevent upset of the tower and faun-
`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 12
`
`

`

`US 2002/0124502 Al
`
`Sep. 12,2002
`
`3
`
`dation 10. As a result, the concrete foundation 68 is always
`under compression and never subject to alternating com(cid:173)
`pression and tension forces.
`
`SUMMARY OF THE INVENTION
`
`[0020] The perimeter weighted foundation of the present
`invention incorporates the above described post-stressed
`annular foundation of my prior patents as a pier pedestal or
`pedestal section of the foundation of the present invention.
`The present invention differs from the structures disclosed in
`my prior patents in that the foundation of the present
`invention includes an expanded base positioned adjacent the
`bottom of the pedestal section which has a cylindrical
`perimeter wall that is substantially larger in diameter than
`the cylindrical wall of the pedestal section and that extends
`to a depth substantially below the bottom of the pedestal
`section. The expanded base also includes a generally hori(cid:173)
`zontal disk-like spread section which interconnects the bot(cid:173)
`tom of the pedestal section and the top of the perimeter wall
`or perimeter wall section. This combination greatly
`increases the foundation's resistance to an overturning
`moment by use of skin friction along the exterior sides of the
`perimeter wall and pedestal section and by the additional
`weight and size concentration at the perimeter of the foun(cid:173)
`dation, including the back fill on top of the horizontal spread
`section.
`
`[0021] The foundation of the present invention also elimi(cid:173)
`nates alternating cyclical compression and tension loading
`stresses, thereby substantially increasing internal stiffness
`and reducing fatigue. Vertically extending anchor bolts in
`the pedestal section are sleeved in PVC or equivalent
`shielding to prevent bolt bonding with concrete for com(cid:173)
`pression of the concrete as disclosed in my prior patents.
`Radially extending bolts are embedded horizontally in the
`disk-like spread section for reinforcement. The radially
`extending horizontal bolts are also sleeved in PVC or
`equivalent sheathing for high compression loading of the
`annular spread section. It has not been found necessary to
`post-tension the cylindrical perimeter wall and post-tension
`bolts are preferably omitted from this section. However,
`such bolts may be included as part of the present invention
`if high unit compression of the exterior perimeter wall
`section is desired.
`
`[0022] The foundation of the present invention reduces
`time, and reduces cost by allowing excavation by conven(cid:173)
`tional backhoes and/or truck excavators. Further, the ten(cid:173)
`sionless pedestal section can be assembled and poured at a
`fabrication yard and shipped as a precast component to the
`foundation site. The corrugated metal pipe (CMP) forms
`provide reinforcing steel and establish a boundary for the
`concrete pour. The bolt holes in the CMP provide support
`and positioning for the horizontal radial arrangement of the
`laterally extending bolts in the spread section, along with
`eliminating the need for temporary perimeter forms and
`reinforcing steel supporting chairs and blocks. The founda(cid:173)
`tion may be poured continuously (monolithically) or sequen(cid:173)
`tially, first the perimeter wall, then the spread section and
`finally the pedestal section. Alternatively, the pedestal sec(cid:173)
`tion can be poured first, then the perimeter wall and finally
`the spread section in two separate pours.
`
`[0023] The exterior cylindrical or perimeter wall section is
`made of concrete preferably formed between two corrugated
`
`metal pipes (CMPs). In one embodiment, the outer CMP of
`the perimeter wall is a few feet taller than the inner CMP of
`the perimeter wall in order to define the outer circumference
`of the horizontal spread section. Initially, a circular excava(cid:173)
`tion having a diameter slightly greater than the diameter of
`the perimeter wall is dug to the depth of the pedestal section.
`An annular shaped trench for forming the perimeter wall is
`excavated to a depth of the desired bottom of the perimeter
`wall. In this embodiment, the initial circular excavation to
`the depth of the pedestal section leaves a raised perimeter
`section whose inner diameter is greater than the outer
`diameter of the pedestal section and whose outer diameter
`extends to the outer wall of the circular excavation. Then
`when the annular shaped trench for forming the perimeter
`wall is dug, a slightly raised annular berm-like earth ring is
`left inside the perimeter wall trench and above the bottom of
`the excavation for supporting the pedestal section.
`
`[0024] The two CMPs forming the exterior and interior of
`the perimeter wall are placed into the perimeter wall exca(cid:173)
`vation. Sand cement slurry is placed between the exterior of
`the CMPs and the sides of the perimeter wall excavation.
`The CMPs to form the pedestal section are then placed on
`the bottom of the interior circular shaped excavation and
`plumbed and properly centered within the interior of the
`CMPs for the perimeter wall section.
`
`[0025] A first or lower set of radially extending bolts
`extend through the interior and exterior CMPs of the ped(cid:173)
`estal section and pass preferably to a mid-point between the
`interior and exterior CMPs of the perimeter wall section, at
`which point, the lower bolts are bent 90 degrees to extend
`downwardly between the two CMPs forming the perimeter
`wall. The horizontally extending portion of the radially
`extending lower bolts is jacketed to prevent engagement
`with
`the subsequently poured concrete. Threading is
`included on the terminal end of the lower bolts passing
`through the interior CMP of the pedestal section to receive
`suitable posttensioning fasteners such as a large washer and
`nut. The opposite ends of the lower bolts which project
`downwardly between the CMPs of the perimeter wall do not
`include a protective sleeve so as to be able to form a strong
`bond with the subsequently poured concrete to strengthen
`the perimeter wall.
`
`[0026] Progressively
`larger diameter circles of high
`strength cable are placed on top of the lower layer of radially
`extending bolts and secured at the cross-over intersections.
`These cables referred to as "tendons", are used instead of
`rebar to strengthen the horizontal spread section. The ten(cid:173)
`dons are placed such that each successive tendon diameter
`preferably is approximately two feet greater than the pre(cid:173)
`ceding tendon diameter. The opposed ends of each tendon
`are preferably overlapped by approximately 60° or about
`eight feet.
`
`[0027] Located above the first or lower layer of radially
`extending bolts is a second or upper layer of radially
`extending PVC sleeved bolts passing through the inner CMP
`of the pedestal section and out to the outer CMP of the
`perimeter wall section. The opposed ends of the upper
`radially extending bolts are secured interiorly of the pedestal
`section and exteriorly of the perimeter wall by suitable
`fastening, such as a large washer and nut, for post-tensioning
`of these bolts. These bolts also have a series of increasing
`
`Exhibit - 1011
`NV5, Inc. v. Terracon Consultants, Inc.
`Page 13
`
`

`

`US 2002/0124502 Al
`
`Sep. 12,2002
`
`4
`
`diameter circles of tendons on their upper surface which are
`preferably aligned with the tendons on the lower layer of
`radially extending bolts.
`
`[0028] Once the upper layer of radially extending bolts are
`secured to the circularly extending tendons, concrete is
`poured for the perimeter wall section and the steel reinforced
`slab forming the spread section. The annular earth berm
`below the underside of the spread section forms a depending
`annular shoulder on the bottom surface of the spread section
`adjacent the base of the pedestal section. Electrical and
`communication conduits are installed. The surrounding soil
`is backfilled to a finish grade from the edge of the excavation
`to the exterior CMP of the pedestal section. Concrete is then
`poured between the CMPs for the pedestal section to within
`about two feet of the finish grade. The radially extending
`bolts passing through sleeves in the spread section are
`post-tensioned preferably to about fifty percent of their yield
`strength. This places the concrete in the spread section under
`high unit compression load. The interior of the pedestal is
`backfilled. No compaction of the soil is required.
`
`[0029] As in my prior patents, the center drain pipe, form
`rings, styrofoam block outs and leveling nuts are installed.
`The remaining pedestal portion is poured along with the
`concrete tower floor. The form rings and templates are
`removed for subsequent securing of the supported tower into
`place, and the vertical anchor bolts are post-tensioned to
`place the pedestal section in high unit load as described in
`my prior patents.
`
`[0030]
`In an alternate embodiment of the present inven(cid:173)
`tion, the perimeter wall section and spread section can be
`formed as separate components. In addition, the annular
`shoulder on the bottom of the spread section can be omitted
`if desired. Instead of the interior and exterior CMPs for
`forming the perimeter wall having different heights, the
`interior and exterior CMPs of the perimeter wall section are
`about the same height. The two layers of posttensioning
`bolts extend horizontally through the interior and exterior
`CMPs of the perimeter wall section as well as the interior
`and exterior CMPs of the pedestal section. The concrete for
`the perimeter wall section and spread section can then be
`poured separately and the generally horizontal bolts embed(cid:173)
`ded in the spread section can be post-tensioned as described
`in the previous embodiment.
`
`[0031] The concrete foundation of the present invention
`can be utilized on all sizes of wind turbines currently being
`commercially marketed and constructed, which range in size
`from 500 KW to 2500 KW. These towers range in height
`from the ground to the hub from 40 to 100 meters, and the
`weight of the towers, including the tower, blades, and
`nacelle ( containing gear boxes, generators, etc.) connected
`atop the tower, range from 150,000 pounds to 700,000
`pounds. The overturning moments for the larger units are
`from 6,000,000 to 50,000,000 ft-lbs. Further, by expanding
`the outer diameter of the perimeter wall in the present
`invention to 50 feet and increasing the thickness of the
`spread section to 6 feet, it is believed that the concrete
`foundation of the present invention could be designed to
`handle overturning moments up to as much as 100,000,000
`ft-lbs, which would be encountered with tower heights in the
`neighborhood of 400 feet.
`
`[0032]
`It is believed that the concrete foundation of the
`present invention is adaptable to very large overturning
`
`moments and is capable of supporting larger turbines than
`the tensionless foundations of my prior patents, which
`currently have depth limitations imposed by economic fac(cid:173)
`tors of around 35 feet. While the pedestal portion of the
`present invention can always be the same size as the
`tensionless hollow cylinder of my prior patents, the perim(cid:173)
`eter foundation of the present invention has the ability to
`extend the diameter of the perimeter wall to even greater
`diameters. The depth of the perimeter wall could approach
`30 feet and the moment resistance of such a wall depth
`coupled with the increased diameters could support any
`foreseeable size tubular wind turbine tower.
`
`[0033] Accordingly, it is a first object of the present
`invention to provide a post-tensioned concrete foundation
`which has increased resistance to overturning moments,
`especially for larger wind turbines and other large tower
`structures.
`
`[0034] A further object of the present invention is to
`provide a post-tensioned concrete foundation which maxi(cid:173)
`mizes resistance to overturning by situating weight concen(cid:173)
`tration and skin friction resistance at the perimeter of the
`foundation.
`[0035] A still further object of the present invention is to
`provide a post-tensioned concrete foundation which has high
`upset resistance by including an expanded base to a pedestal
`section of the foundation.
`[0036] Another object of the present invention is to pro(cid:173)
`vide a foundation in accordance with the preceding objects
`and in which the expanded base includes a cylindrical
`perimeter wall section spaced a substantial distance outward
`from the wall of the pedestal section and a horizontal spread
`section which interconnects the bottom of the pedestal
`section and the top of the perimeter wall section.
`[0037] Still another object of the present invention is to
`utilize excavated soil as backfill to add weight to the pedestal
`section, the top of the spread section and the top of the
`perimeter wall section to resist overturning forces while
`using inexpensive on-site materials.
`[0038] Yet another object of the present invention is to
`provide a post-tensioned concrete tower foundation having
`an expanded base which can be constructed without tempo(cid:173)
`rary independent forms and shoring.
`[0039] Still a further object of the present invention is to
`provide a post-tensioned concrete foundation for weak soils
`such as with shallow ground water in which the top of the
`expanded base of the foundation can be positioned at, above,
`or below the ground water surface.
`[0040] Yet a further object of the present invention is to
`provide a post-tensioned concrete foundation adaptable for
`areas with deep frost depths in which the top of the expanded
`base of the foundation is set below the frost line.
`[0041] Stil