US 20090044482 A1
An apparatus for use in providing a level grout surface for placement of a wind turbine tower flange, the apparatus comprising a template member levelly suspended on the anchor bolts above the grout trough, wherein the template member comprises a surface to which grout will not adhere. The template member can comprise an upper layer and a lower grout engagement layer, wherein the grout engagement layer comprises a surface to which grout will not adhere. The upper layer can comprise a metallic layer, and the lower layer can comprise a plastic layer, wherein the upper layer and the lower layer are bonded together. The lower layer can comprise polypropylene. The means of bonding are selected from the group consisting of mechanical bonding, thermal bonding and chemical bonding. The grout can comprise an epoxy grout. The template member can be suspended through the use of magnetic nuts or the use of a rotating sleeve. The template member can comprise a plurality of sections, and can comprise a circular form.
1. An apparatus for use in providing a level grout surface for placement of a wind turbine tower flange wherein the wind tower flange supports and stabilizes a wind turbine tower, the wind turbine tower flange installed on a foundation comprising a concrete base, a grout trough formed in the cement base for the placement of a grout used to support the wind turbine flange, and a plurality of upwardly disposed anchor bolts extending through the grout, wherein the anchor bolts retain and support the wind turbine flange, the apparatus comprising:
a template member levelly suspended on the anchor bolts above the grout trough, wherein said template member comprises a surface to which grout will not adhere.
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11. An apparatus for use in leveling a wind turbine tower flange installed on a foundation comprising a plurality of upwardly disposed anchor bolts, the apparatus comprising:
a template member and a plurality of anchor bolt engagement means, the anchor bolt engagement means comprising a means for leveling said template member relative to the anchor bolts.
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15. A method for levelly installing a wind turbine tower onto a wind turbine foundation, the method comprising the steps of:
installing an anchor bolt assembly using a circular template to lift said anchor bolt assembly and place said anchor bolt assembly into an excavation and pouring concrete to form a foundation;
removing said circular template from the foundation thereby creating a grout trough;
suspending a template member above said grout trough using suspension means attached to said anchor bolts;
leveling said template member;
introducing a grout into the space defined by said template member and said grout trough and allowing said grout to cure;
removing said template member; and installing the wind turbine flange.
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This is a continuation-in-part of U.S. application Ser. No. 12/012,137 filed on Jan. 30, 2008, which application claimed priority to U.S. Provision Application 60/898,452 filed on Jan. 30, 2007 and U.S. Provisional Application No. 60/905,399 filed on Mar. 5, 2007, for which applications this inventor claims domestic priority.
This invention generally relates to wind turbines, and anchoring devices, such as bolts, which are used in the foundations of wind turbines because of the high overturning moments to which wind turbines are subjected. The invention more specifically relates to a plastic bolt sleeve used in combination with a threaded anchor, where the plastic sleeve is plastically deformed or “crimped” onto a portion of the threads of the bolt. The invention further discloses methods and devices for crimping the sleeve onto a portion of the bolt threads. Among other benefits, the crimped bolt sleeve protects the anchor bolts from moisture and resulting corrosive attack and, when utilized with the disclosed template member, allows for the use of high compressive strength, low viscosity grouts, such as epoxy grout, to be used in the construction of the wind turbine foundation. The use of the template member obviates the need for a crane to place and level the foundation flange prior to the grout setting and before the grout has cured and reached its full strength. This results in less time spent rigging the crane as the foundation flange may be set and the turbine tower placed in a single crane deployment.
The bolts used for anchoring wind turbines may either be set in concrete or drilled into the rock. The integrity of the foundation of a wind turbine is subject to failure if the anchor bolts are not adequately protected. In particular, anchors are subject to corrosive attack caused by the accumulation of water or other electrolytes in the anchoring hole which results in the creation of a corrosion cell. As described below, the practices employed in preparing the foundation for a wind turbine often create an environment in which the anchor bolt is exposed to water or other liquid.
By way of background for wind turbine foundations, U.S. Pat. Nos. 5,586,417 and 5,826,387, both by Henderson, disclose a pier foundation “which can be poured-on-site monolithically and is of cylindrical construction with many post-tensioned anchor bolts which maintain the poured portion of the foundation under heavy compression, even during periods when the foundation may be subject to high overturning moment.” Henderson's foundation is preferably in the shape of a cylinder, having an outer boundary shell and an inner boundary shell each formed of corrugated metal pipe which are set within an excavation.
In the fabrication of foundations for wind turbines, elongated high strength steel bolts, generally fashioned from 1¼″ (#10) rebar material or 1⅜″ (#11) rebar material are set within the foundation excavation and concrete is poured into the excavation such that the bolts extend vertically up through the concrete from a peripheral anchor plate or ring near the bottom of the cylinder to a peripheral connecting plate or flange at the base of the wind turbine tower. The bolts are typically threaded at the top and bottom ends for a length of approximately 24 inches. The bolts are largely contained within hollow sleeves made of PVC which prevent adhesion of the concrete to the bolts. The sleeves are typically installed prior to delivery of the bolts to the job site, and nuts must be placed on each end of the anchor bolt to retain the PVC sleeve on the anchor bolt material.
Henderson further discloses the post-stressing of the concrete in great compression by tightening the high strength bolts to provide heavy tension from the heavy top flange (i.e, the flange at the base of the wind turbine) through which the bolts pass to the anchor plate or ring at the bottom of the foundation, thereby placing the entire foundation from the heavy top plate or flange to the lower anchor plate or ring under high unit compression loading. The nuts on the bolts are tightened so as to apply tension to the bolts exceeding the maximum expected overturning force of the wind turbine tower structure on the foundation. Therefore, the entire foundation withstands various loads with the concrete always in compression and the bolts always in static tension. Because the bolts are each largely contained within a PVC sleeve, each bolt is free to move within its sleeve as the bolts are tensioned by tightening the nuts abutting the top flange. Steps are typically taken before the concrete is poured to seal the tops of the PVC sleeves to prevent the flow of concrete into the sleeves, such as wrapping duct tape around the tops of the sleeves. This can be a time-consuming process.
Based upon the discussion above, it is clear that the integrity of this type of foundation is dependent upon the integrity of the anchor bolts—the failure of a bolt creates a stress riser on the remaining bolts, leading to the potential failure of the entire foundation. The integrity of the steel anchor bolts can be compromised by corrosive attack. As described above, according to the current practice each anchor bolt is enclosed for most of its length within a PVC sleeve. However, because the outside diameter of the PVC sleeve is too large for the sleeve to enter the bolt hole of the flange of the tower structure, the sleeve typically terminates at approximately the top of the concrete foundation, with the bare metal of the anchor bolt extending above the sleeve, where the bolts extend through the flange and have a nut and bolt cap installed on the top side of the flange.
The tower flange is usually set on a grout base which overlies the concrete foundation. The grout base is placed within a circular “grout trough” which is formed by the pouring of the concrete foundation around a circular template. This circular template is utilized to collectively lift and place the anchor bolt assembly within the excavation prepared for the foundation. As with the holes of the flange of the tower base, the bolt holes in the circular template are sized to accommodate the bolt diameter, but not the diameter of the PVC sleeve, so the tops of the bolt sleeves will generally be flush with the bottom of the grout trough formed by the circular template.
In order to prevent dehydration of the grout—thus adversely impacting the grout strength—it is a common practice to place water within the grout trough prior to the pouring of the grout to keep the grout properly hydrated during the curing process. However, water placed in the trough will gravitate into the ends of the PVC sleeves which are flush with the bottom of the grout trough. In the current installation practice, a foam sleeve is typically placed around a portion of each bare bolt extending above the bottom of the grout trough, with each foam sleeve held in place with duct tape. The length (or height) of the foam sleeve is sized to extend above the anticipated thickness of the grout layer within the grout trough. In the known practice, the tower flange is set on the grout before the grout sets so that the tower base may be leveled. It is hoped that the foam sleeve will prevent grout from adhering to the body of the bolt, such that when the grout fully cures the bolt may be tensioned and slide through the foam sleeve without damage to the grout. However, in reality the foam sleeve is likely so deformed by the flange of the tower base that the bolts will not slide freely through the sleeves once the grout cures.
In particular, the use of the template member would eliminate the need for leveling shims and allow the grout to be poured and adequately cure before setting the flange onto the grout, as opposed to the current practice of setting and leveling the tower flange before the grout cures. The current practice requires the service of a high capacity crane for the initial setting of the tower flange and subsequently for the assembly of the complete turbine. However, if the tower flange can be placed at the same time as the other turbine tower components, only a single use of the crane is required, resulting in less rigging up and rigging down time at each turbine tower installation.
Once the tower has been installed and a nut and bolt cap installed on the bolt ends extending above the tower flange, the annulus between the bolt and PVC is sealed. However, during the known installation method, the annulus between the bolt and the PVC sleeve is open thereby providing a pathway for water and other fluids to enter the annulus and be trapped between the PVC sleeve and the metallic bolt, forming a corrosion cell. Because of this opening, steps are usually taken to protect the bolt from corrosive attack and/or to seal the sleeve-bolt annulus during installation. Unfortunately, the currently practiced installation procedure aggravates the situation, because, as described above, the procedure typically includes pouring water in the grout trough to allow the grout to cure. This practice allows water to accumulate at the top of the PVC sleeve, and potentially migrate into the sleeve-bolt annulus.
The initial attempt at solving the anchor bolt corrosion problem was to paint the anchor bolts along the entire length. However, this solution is labor intensive and does not prevent liquid accumulation around the anchors. In addition, this protection method requires that the anchors be repainted periodically, as well as after re-tensioning the anchor if required in the particular application. The currently practiced method of protecting the anchor bolts is to seal the annulus between the top of the PVC sleeve and the bolt with a sealant, such as a silicon gel.
As discussed above, the current practice also includes placing foam or other material around the portion of the bolt extending above the PVC sleeve, so as to prevent adhesion of the grout to the bolt and to block the migration of water into the sleeve-bolt annulus. Typically, foam cylinders with longitudinal slits are placed around the bolts, with duct tape wrapped around each cylinder, and the cylinder pushed downwardly into contact with the top of the PVC sleeve. However, with the large number of bolts utilized in these types of foundations, it is time consuming and difficult to seal the top of each PVC sleeve with sealant and to install the foam cylinders or similar devices. If hurried, the annulus may not be adequately sealed to prevent the intrusion of water into the PVC-bolt annulus. Moreover, once the tower base flange is set upon the foam cylinders, the cylinders are greatly deformed. It is not unlikely that when the anchor bolts are tensioned, the bolt does not slide through the foam cylinder, but that the deformed foam cylinder moves within the grout, potentially damaging the integrity of the grout. The PVC sleeves, because of the outside diameter, displace, in totality, a significant volume of concrete in the foundation, thereby reducing the overall compressive strength of the foundation. Likewise, the use of the foam cylinders around the anchor bolts in the grout trough displaces a significant volume of grout, and thereby reduces the compressive strength of the flange foundation.
The present application is directed toward a method and apparatus which addresses the problems identified above. In embodiments of the disclosed invention, rather than utilizing PVC sleeves which terminate at the bottom of the grout trough, the present invention comprises anchor bolts comprising a sheath or sleeve which extends above the grout trough and, if desired, may partially extend inside the base flange of the wind turbine base. The sleeve may be manufactured from polypropylene, polyethylene or other materials having satisfactory mechanical properties, primarily that the material be capable of withstanding sufficient plastic deformation to cause the material to conform to the shape of the threads of the anchor bolts without failing. The term “polypropylene” when used below, not only includes polypropylene materials, but other plastic materials having mechanical properties which allow those materials to be substituted for polypropylene. In the present application, each anchor bolt comprises a polypropylene sleeve in which a portion of the sleeve is “swaged” onto a portion of the threads of the bolt thereby creating a mechanical seal between the interior of the sleeve and the threads of the bolt. For purposes of distinguishing the presently disclosed sleeve from the prior art sleeves, the presently disclosed sleeve is hereinafter referred to as the “crimped sleeve”, although it is to be appreciated that only a portion of the sleeve actually comprises crimping or swaging.
The use of the polypropylene sleeve and the swaging of the sleeve onto a portion of the bolt threads accomplishes several improvements over the known apparatus and methods. The bolt package (i.e. a bolt/sleeve combination) has an overall diameter less than the overall diameter of the currently utilized bolt-PVC sleeve combination. This reduced diameter allows the bolt and crimped sleeve to extend through the bolt holes of the circular template, and into the bolt holes of the tower flange, which under the known apparatus and method, only a sleeveless bolt would extend. Because the crimped sleeve extends above the top of the grout trough, the encased bolts will not be exposed to water placed within the grout trough. Moreover, because a seal is formed between the top of the crimped sleeve and a portion of the threads of the bolt, access to the annulus between the bolt and the crimped sleeve is either eliminated or substantially reduced, thereby preventing or greatly limiting the axial migration of water or other electrolytes along the length of the bolt. In addition, because the top of the crimped sleeve extends above the level of the grout, the crimped sleeve prevents adhesion of the grout to the bolt, thereby allowing the bolt to move relative to the grout.
The disclosed apparatus provides a template member that comprises a surface to which grout will not adhere. The template member is suspended by the anchor bolts, and is leveled across the grout trough. Once the template member is leveled, either by the use of a laser level or a conventionally leveling means, grout is added to the space defined by the template member and the grout trough. The grout may be introducing into the trough through fill holes that extend through the template member. The grout is placed into the grout trough until the grout reaches the surface of the lower layer of the template member across the entirety of the grout trough. The template may then be removed and the grout allowed to cure, or the template may be left in place atop the grout until the grout has cured, depending upon the environmental conditions present at the time.
The template member may comprise an upper layer and a lower layer, and the lower layer comprises a surface to which grout will not adhere. The layers can be bonded together, and the bonding means can be thermal, chemical or mechanical bonding. The upper layer may comprise a metallic layer. The lower layer may comprise a plastic layer, and the plastic layer may comprise polyethylene.
The template member utilized in one embodiment of the disclosed device may be sectional, and can be placed sequentially around the grout trough and leveled. By placing the template member over the anchor bolts and then leveling the template member, the top surface of the grout placed into the area defined by the grout trough and the template member is thereby leveled. When the grout cures, the tower flange is installed on a level surface. No shims or blocks are required using this method to obtain a level foundation for the tower flange, as required in the known method.
A large number of anchor bolts 16 is typically used for this type of foundation. For example, Henderson discloses an embodiment having forty-eight tensioning bolts in the inner ring and forty-eight tensioning bolts in the outer ring for a total of ninety-six. In Henderson's foundation, the lower ends of the bolts are anchored at the bottom of the foundation to a lower anchor ring which may be constructed of several circumferentially butted and joined sections. Although it is to be appreciated that other means may be employed for anchoring the bolts, including drilling a portion of the anchor bolt into the ground.
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The critical distinction between the presently disclosed crimped sleeves from the prior art sleeves 22 is that the wall thickness of the crimped sleeve 38 is substantially reduced, and the tolerance between the internal diameter of the crimped sleeve 38 and the outer diameter of the bolt threads is substantially reduced, resulting in an external diameter of the crimped sleeve which is smaller than possible with the thicker-walled PVC sleeves, allowing the crimped sleeves to extend into the bolt holes 13 of the base flange 14. For example, a crimped sleeve 38 comprising polypropylene sleeves has a closer tolerance than the available PVC, such that the crimped sleeves 38 may have a clearance of 20 thousands of an inch between the internal diameter of the crimped sleeve 38 and the outer diameter of the anchor bolt threads. As shown in
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The swaging further inhibits the flow of liquids into the annulus between the crimped sleeve 38 and the anchor bolt 16′, although it is to be appreciated that the exposure of the sleeve end to liquid is reduced or eliminated, because of the capability of placing the top of the crimped sleeve 38 within the base flange 14 rather than disposed at the bottom 34 of the grout trough 28. It has been found that swaging approximately two inches of the top of the crimped sleeve 38 forms a sufficient length of “crimps” 17 (i.e., portions of the crimped sleeve 38 which conform to the shape of individual threads 21) to form an interference fit which adequately inhibits liquid penetration into the sleeve-bolt annulus. It has been found that crimped sleeves 38 comprising polypropylene, or similar materials, have the desired mechanical properties for swaging the sleeve material such that it conforms to the shape of the threads. The mechanical properties of the polypropylene are such that the material has a “memory” and retains the crimps 17 once the swaging operation has been completed. It is also to be appreciated that when the anchor bolts 16′ are tensioned by the tightening of the nuts 18, the mechanical properties of the sleeve material are such that upon tensioning of the anchor bolt 16′, the material will plastically deform and the crimps 17 will relax and allow relative movement of the anchor bolt with little resistance.
Also disclosed are swaging devices utilized in forming the crimped sleeves 38.
The rollers 58 a through 58 f are disposed within the tool 50 to follow the threads 21 of an anchor bolt 16′, compressing the sleeve into the threads to create the crimps 17. The rollers are disposed such that the center of each roller is a different radial distance from the longitudinal axis L. It is to be appreciated that a different swaging tool 50 may be fashioned for each bolt diameter and thread type, including right-handed and left-handed threads.
By way of example only, for a tool having an overall radius of 2.0 inches, an inside diameter of 0.680 inches, and individual roller diameters of 1.250 inches, the centers of the rollers may have the following radial distances from the longitudinal axis L:
roller 58 a: 1.391 inches
roller 58 b: 1.415 inches
roller 58 c: 1.295 inches
roller 58 d: 1.319 inches
roller 58 e: 1.343 inches
roller 58 f: 1.367 inches
Swaging tool 50, which may comprise suitable material such as 1080 steel, is made up on at the end of a sleeve-encased anchor bolt, with the swaging end 56 made up first. As swaging tool 50 is screwed onto the threads, the bolt will ultimately engage internal threads 52, which assist in guiding the tool. Once the swaging tool reaches the polypropylene sleeve, roller 58 f will be the first roller to engage the sleeve, followed by 58 e, etc., the rollers compressing the sleeve into the threads 21. The swaging tool 50 may be attached to both power tools and hand tools.
While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, the size, shape, and/or material of the various components may be changed as desired. Thus the scope of the invention should not be limited by the specific structures disclosed.