Tower segment and method utilizing segmented bearing plate

A concrete wind turbine tower segment is provided with a bearing plate formed by a plurality of individual smaller plates secured within the concrete body of the tower segment. The tower segment may include an anchor bar cage assembly made of an embedded plate with a plurality of anchor bars extending there through and through the plates. A protective sleeve may be positioned over the anchor bars. A method of forming the tower segment includes attaching the plate segments to a precision formed template ring as part of the cage assembly, pouring concrete/grout around the cage assembly against the plates, and removing the template ring to reveal a precision mate face of the bearing plate. The single large, expensive ring may be reused to form multiple tower segments.

FIELD OF THE INVENTION

This invention relates generally to the field of equipment towers, and more particularly, to a concrete wind turbine tower with at least one tower segment having a segmented bearing plate surface, and a method of forming a tower segment incorporating a segmented bearing plate.

BACKGROUND OF THE INVENTION

Existing methods of constructing towers used to support different types of equipment, such as lighting, antennae, cellular telephone equipment or wind turbine equipment, vary depending on whether the tower materials are steel or concrete. The decision process used to select whether the tower is to be built out of steel or concrete may depend upon the geographic location, regional resources, height and weight bearing requirements for the tower, and access to the site for constructing the tower. Steel towers are commonly built by bolting steel tubular sections together at intermediate flanges. Generally, as the height of a tower increases, the diameter of the tower's base increases to accommodate higher loads generated by the taller tower. The heights of steel towers are often limited by the diameter of the steel tubular sections that can be physically transported to the construction site without significant modifications to existing roads, bridges, or other right of way constraints. Transporting large diameter steel tubular sections and associated components also increases the cost of tower construction.

Concrete towers have advantages over steel towers because they can be fabricated at or near the tower location when the materials of construction are locally available. Cast-in-place construction methods allow for pouring concrete into forms erected at the tower location. Drawbacks to cast-in-place methods include reduced construction speed and sensitivity to inclement weather. Also, the shape of a typical concrete wind tower is tapered, which creates complexity in the concrete pouring process. Alternatively, concrete tower sections can be fabricated or precast and then stacked at the job site to form the tower. Joints between tower segments may require grout to ensure sufficiently strong connections, and it may be necessary to pump grout to tower heights of up to 300 feet or more, which is time consuming, requires specialized equipment and is weather dependent, thereby adding cost to the tower construction.

U.S. Pat. No. 8,720,139 B2 issued on May 13, 2014, to Henderson describes a post-tensioned concrete foundation for supporting a tower whereby a base flange of the tower is set in grout inside a grout trough molded by a template ring extending around the top surface of the foundation cap. The tower may be plumbed vertically by shim packs positioned in the grout trough below the base flange while grout is poured or pumped into the grout trough under the flange and cured. The template ring may be positioned with respect to a tower anchor bolt cage to form a grout trough during the concrete pour. The template ring may then be removed and reused for the formation of grout troughs of other concrete foundations. A tower or other structure may then be secured in place within the grout trough with an appropriate amount of grout placed therein. This creates a connection where the tower base flange is secured with post-tensioning anchor bars directly within the grout trough of the concrete foundation.

DETAILED DESCRIPTION OF THE INVENTION

Certain precast concrete tower designs may require the grinding and/or grouting of mating annular concrete surfaces to achieve a quality load bearing connection. Alternatively, a load bearing structure having a flat bearing surface may be fabricated of steel or other appropriate load bearing material, and that structure then attached to the concrete either during the concrete casting process or thereafter. Some towers are hybrid towers using both concrete and steel segments. Such hybrid towers may require a concrete segment to be joined with a steel segment. In such instances, it may be advantageous to incorporate a steel load bearing surface into the concrete section to establish a steel to steel connection to assure a tighter tolerance between segments and a strong and stable connection. For instance, if a steel to steel connection is desired between the uppermost concrete segment of a wind turbine tower and a steel top or tip section to which a nacelle may be attached, a steel ring having a sufficiently large diameter could be cast into the top of the concrete tower segment, in a manner somewhat similar to the process described in the Henderson patent mentioned above. However, such a large diameter steel ring would need to be transported to the casting yard or the tower construction site to be positioned and secured within the uppermost tower segment. If this method were used for a cast-in-place tower, the ring would need to be lifted to height and grout would need to be pumped to height in order to secure the ring within the tower segment. The ring would also need to be machined to a relatively tight tolerance to assure a proper interface for connection with a steel flange of the top or tip section. Machining such a large diameter ring, which could be up to or exceeding 17 feet in diameter, and then transporting the ring to the construction site would add cost to the tower construction.

It has been determined by the present inventor that utilizing a plurality of smaller individual plates to form a larger segmented bearing plate is advantageous over using a single one piece bearing plate for a concrete tower segment. This approach may seem counterintuitive since it is important that the mateface surface of the bearing plate is held to a tight tolerance, and the use of multiple pieces to form this surface would complicate the task of making the surface perfectly flat. The present inventor solves that problem by mounting the individual segmented plates to a flat template during the concrete casting process to establish the required tight tolerance surface, then removing the template from the individual plates once they are attached to the concrete tower segment. In this manner, a single template may be reused multiple times to establish a tight tolerance mating surface on multiple tower segments, and the cost of machining and transporting a single large diameter tight tolerance ring can be amortized over multiple towers, lowering the cost of each individual tower.

FIG. 1illustrates an exemplary equipment tower100in accordance with an embodiment of the present invention. The tower100is a wind turbine tower, which supports various types of equipment. Such equipment may be affixed at or proximate the top of the equipment tower100or other desired locations along the length of the tower100depending on a particular application. Tower100may include a foundation102, a bottom tower portion104, a middle tower portion106, a top tower portion108and a steel tip adapter110. Each tower portion104,106,108may be formed with a plurality of tower segments105,107,109, respectively, that may be formed of precast concrete. In an exemplary embodiment of the invention, each tower segment105may have a first constant diameter and a first height, each tower segment107may have a second constant diameter and a second height and each tower segment109may have a third constant diameter and a third height. As illustrated inFIG. 1, the first constant diameter of tower segments105may be greater than the second constant diameter of tower segments107, which in turn may be greater than the third constant diameter of tower segments109thereby forming an equipment tower100that decreases in diameter from the bottom tower portion104to the top tower portion108. Transition segments114and116may be positioned between appropriate tower portions104,106,108to accommodate the progressive step down in the diameter of tower segments105,107,109from bottom to top of tower100.

Steel tip adapter110may connect to the topmost concrete annular tower segment of the tower100using flange111. Flange111may have a plurality of apertures113(FIG. 7) used to connect steel tip adapter110to the topmost tower segment132. A nacelle of the wind turbine (not shown) is connected to the top of the steel tip adapter110to house the equipment used in the wind turbine, such as the rotor blades, rotor, drivetrain, gearbox, generator, electrical controls, etc. as needed to convert the wind's kinetic energy into electrical energy.

Tower segments105,107,109may be precast concrete with each having a constant diameter and a constant height. Tower segments105,107,109may also be match cast together to achieve a precision fit between adjacent sections. Such match cast joints may incorporate a shear key configuration used to transfer shear across the segment joints under transverse loads to the equipment tower100and to assist with aligning segments with each other during construction. An exemplary match cast configuration is disclosed in U.S. Pat. No. 9,175,670 issued to Lockwood et al., which is incorporated herein by reference in its entirety. In some instances, epoxy may be applied onto a segment joint prior to closing the gap between two segments. The epoxy may lubricate the annular face of the segments when placing sections on top of one another then seal the joint after the epoxy cures. Further, grout may be used to secure tower segments105,107,109together depending on site specific parameters.

FIG. 1further illustrates foundation102that may include a platform118and a tapered subsection126. A pedestal or plinth120may extend out of platform118and have an inside surface that defines an internal chamber124. The tapered subsection126may extend from platform118so it is located below ground level128. In the construction of tower100, a base of the tapered subsection126may be round, square, polygonal or other appropriate shapes depending on site specific parameters. The top portion of subsection126may be rounded or formed with a plurality of contiguous flat surfaces as the site specific parameters require. Foundation102may be cast-in-place then, after the concrete is cured, subsection118may be back filled with dirt to cover its top surface.

FIG. 2illustrates a perspective, cross sectional view of topmost tower segment132having exemplary post-tensioning tendons130connected thereto and configured prior to steel tip adapter110being attached thereto. An upper end138of each tendon130is connected by conventional techniques with topmost tower segment132by attachment with a respective pair of upper anchor rods140that may be embedded within a diaphragm portion142of topmost tower segment132.FIG. 2further illustrates plate segments150affixed within topmost tower segment132with a plurality of anchor rods152extending through respective plate150for receipt of flange111of steel tip adapter110. Anchor rods152may extend from an embedded plate153with a lower end of anchor rods having a nut155threaded thereon. Embedded plate153may be made in one piece or it may be formed as a plurality of segment plates. Segmented plate150may be affixed within a layer of grout151injected within grout trough157of the tower segment concrete body132.

FIG. 3illustrates a plan view of a plurality of segmented plates150forming an annular segmented bearing plate154in accordance with aspects of the invention. In an exemplary embodiment, segmented bearing plate154may be formed from six (6) equally sized plates150each having the same constant radius of curvature. InFIG. 3, bearing plate154is formed as an annulus, but it will be appreciated that segmented bearing plates in other embodiments may have other geometric shapes. Each segmented plate150may have one or more apertures156formed therein to receive a corresponding anchor rod152. In an exemplary embodiment, each plate150may have twelve equally spaced apertures156for alignment with and receipt of respective anchor rods152extending from topmost tower segment132.

Further apertures158may be formed within each plate150to be used for removably or releasably attaching the plates150to a mock-up flange or template ring170, as shown inFIG. 4, to form the segmented bearing plate154. Template ring170is intended to be a mock-up of the lower surface of flange111of steel tip adapter110that will be used to connect steel tip adapter110to topmost tower segment132. In one embodiment, template ring170was, in fact, the lower flange111cut away from a spare tip adapter110. Template ring170may be formed as a one piece ring having a pattern of apertures that match the pattern of apertures formed within the segmented plates150when the segmented plates150are attached to template ring170. For example, template ring170may include a plurality of apertures156′ that align with the plurality of apertures156of the segmented bearing plate154, and a plurality of aperture pairs158′ that align with the plurality of aperture pairs158of the segmented bearing plate154. Because the plurality of apertures156′ will align with the plurality of apertures156when the segmented plates150are releasably attached to template ring170. The plurality of apertures156′ will also align with and receive corresponding anchor rods152when placed there over.

FIG. 4further shows that the plurality of aperture pairs158of a respective segmented plate150will align with respective ones of the plurality of aperture pairs158′ of template ring170. This allows for conventional threaded bolts, for example, to be inserted through the holes and nuts threaded over the bolts to releasably secure the plurality of segmented plates150to the underside of template ring170. In an exemplary embodiment, each plate segment150may have three (3) sets of aperture pairs158evenly spaced along the radius of the plate150. Alternate means may be used to releasably secure segmented plates150and template ring170together, such as magnets, clamps, etc., provided that the plates150are tightly secured against template ring170during formation of the tower segment132in order to transfer the precision surface of the template ring170to the mate face of the segmented bearing plate154after the template ring170is removed once the tower segment132has been formed. Template ring170may be formed from flat stock steel or other structurally stable material (aluminum, plastic, fiberglass, etc) and has a mate face147(underside surface as illustrated inFIG. 4) formed to a desired flatness tolerance, such as plus or minus about 25 mils. The back side surface of ring170(top surface as illustrated inFIG. 4) may be formed to less of a flatness tolerance than the mate face surface147and may be left in its as-rolled condition without additional machining. Once removed from segmented plates150, template ring170may be reused to form other segmented bearing plates154for other tower segments.

Alternate embodiments of the invention allow for segmented bearing plate154to be formed with varying numbers of segmented plates150of like or different shapes, each having the same or different quantities of apertures156and aperture pairs158formed therein depending on the diameter of topmost tower segment132or other tower specific parameters. The template170may be formed from more than one piece of material joined together, provided that the desired degree of flatness can be maintained in the mate face147. Topographies other than a flat plane may be desired for the mate faces147,149in other embodiments, such as a flat surface with a notch useful for carrying shear loads in the assembled tower100.

FIG. 5illustrates an anchor bar cage assembly180that may be used as part of a method for securing segmented bearing plate154within the topmost tower segment132. Once embedded within topmost tower segment132, segmented bearing plate154will be connected with flange111of steel tip adapter110to secure the steel tip adapter110in place on the top of the topmost tower segment132. Anchor bar cage assembly180may be formed with an embedded plate153and a plurality of anchor bars152inserted through and extending from a corresponding plurality of apertures within embedded plate153. Each anchor bar152may have a protective sleeve182inserted there over, as shown inFIG. 6. Plate segments150may be bolted or otherwise releasably connected with template ring170prior to placement over respective anchor bars152. Alternatively, segmented plates150may be placed over anchor bars152first, then template ring170placed over anchor bars152. This sequencing may depend on the size of segmented plates150and template ring170and/or the technique used to releasably secure segmented plates150and template ring170together.

FIG. 6illustrates a cross section of an exemplary portion of anchor bar cage assembly180. Anchor bar152is illustrated passing through embedded plate153and having nut155threaded on its lower end. A protective sleeve182, such as a PVC sleeve, may be positioned over each anchor bar152to prevent them from becoming encased in concrete and so they may be tensioned when securing steel tip adapter110to topmost tower segment132. For ease of illustration, protective sleeves182and nuts155are not shown for each anchor bar152inFIG. 5. With segmented plates150connected tightly to template ring170, the combination may be placed over anchor bars152to rest on the upper ends of protective sleeves182. The anchor bar cage assembly180may be placed or assembled within an appropriate form sized and shaped to receive concrete poured around the assembly180to form topmost tower segment132.

In an exemplary embodiment of the invention, the plurality of segmented plates150may be cut from flat stock steel and machined flat on a mate face to any desired tolerance. Forming a segmented bearing plate154from a plurality of smaller plates150allows for cost effective cutting, machining and transporting of the segments versus a one piece bearing plate having a mate face of the same tolerance. Further, since the mate face (upper) surfaces149of segmented plates150will be pulled tight to the mate face (lower) surface147of template ring170, any thickness differences among segmented plates150are accounted for in the subsequently poured concrete and grout layer151formed beneath the segmented plates150during forming of the segment132. In other words, with segmented plates150pulled tight to template ring170, the lower surface of segmented plates150does not need to be machined to a tight tolerance. This is because after concrete is poured to form grout trough157, grout layer151can be injected within the trough until it sufficiently contacts the lower surface of each segmented plate150, regardless of each segment's thickness or whether the lower surface has undulations, voids or other abnormalities. The flatness (or other desired topography) of template mate face147is imposed against the bearing plate mate face149; i.e. the smaller plates150are all held with their mate faces149flat and parallel against the template mate face147. The upper surfaces of plates150collectively form the mate face surface149of bearing plate154for abutment against flange111when the segment132is installed in the tower100. This reduces the necessity of machining each plate150to a tight thickness tolerance, and only one side149of a plate150need be flat to a tolerance, thereby reducing cutting and machining costs.

It has further been determined by the present inventor that pouring certain concrete compositions until they contact the bottom surface of plates150may cause air bubbles to collect against the bottom surface of the plates150, thereby potentially weakening the strength of the bond between the concrete and plates150. To avoid this situation, with plates150and template170releasably connected together and placed over anchor bars152, concrete may be poured within the form used to form topmost tower segment132to a height that is below segmented plates150, thereby defining grout trough157(FIG. 2). In an exemplary embodiment of the invention, concrete may be poured to a height that is about 2 inches below plates150. Once the concrete has sufficiently set, grout may be injected into the trough157to form grout layer151that sufficiently contacts the lower surface of segmented plates150to secure the segmented plates150within the trough. The depth of grout trough157may vary as a function of specific tower and material design parameters. Once grout layer151has set, template ring170may be removed to expose the mate face or upper surface of segmented bearing plate154. In alternate embodiments, concrete may be poured until it contacts segmented plates150provided that an appropriate concrete composition is used to ensure a sufficiently strong bond between segmented plates150and the concrete.

FIG. 7is a bottom view of flange111of steel tip adapter110illustrating the plurality of apertures113that will align with the plurality of apertures156formed within segmented bearing plate154when steel tip adapter110is connected with topmost tower segment132. Steel tip adapter110may be connected with topmost tower segment132by inserting the upper end of respective anchor bars152through the plurality of apertures113in flange110so that the lower surface of flange110rests upon the mateface or upper surface formed by segmented bearing plate154. The upper ends of anchor bars152may be threaded so that conventional nuts may be threaded thereon and tightened to a specified load or torque to secure steel tip cap110with topmost tower segment132. It will be appreciated that the thickness and width of flange111may be sized as a function of specific tower design parameters. Because segmented bearing plate154is formed from a plurality of individual smaller plates150, the individual plates150serve as load distributors from the steel tip adapter110into the concrete body portion of topmost tower segment132.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. For example, exemplary embodiments of the present invention are described with respect to the connection of topmost tower segment132with steel tip adapter110; however, alternate embodiments of the invention may be adapted to connect any two or more tower segments together. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.