Abstract:
In a foundation for a wind turbine, the foundation has a large number of anchor bolts which are axially placed within the bore hole for mounting a tower flange of the wind turbine. In contrast to the practiced method, the present invention utilizes the fabrication of separate bolt packages, in which the bolts of each bolt package are configured to have an inner arc of bolts and outer arc of bolts, where each bolt in the bolt package is retained, by position retention means, in a fixed position with respect to the position of the other anchor bolts in the pre-assembled package. The present invention describes the position retention means for forming each pre-assembled package and a method of using the position retentions for constructing a foundation for a wind turbine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     U.S. Provisional Application No. 61/333,231 for this invention was filed on May 10, 2010, for which application this inventor claims domestic priority. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to concrete foundations set within excavations or bore holes which are installed to support wind turbines. More particularly, this invention comprises an apparatus and method for configuring, installing, and setting the anchor bolts for a cylindrical foundation for a wind turbine prior to pouring the concrete. 
     U.S. Pat. Nos. 5,586,417 and 5,826,387, both by Henderson, disclose a 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&#39;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. Between the outer boundary shell and the inner boundary shell elongated high strength steel bolts extend vertically up through concrete from a peripheral anchor plate, called an inbed plate, located near the bottom of the cylinder. The bolts extend upwardly from the inbed plate to a connecting plate or flange above the ground surface. The bolts extend through hollow tubes to prevent adhesion of the concrete to the bolts. The foundation typically uses no rebar reinforcing steel. This design uses the mechanical interaction with the earth to prevent over turning instead of the mass of the foundation typically used by other foundations for tower structures.  FIG. 1  schematically shows an embodiment of the Henderson foundation. 
     The “hollow tubes” of this foundation are typically elongated plastic tubes which encase the bolts substantially through the entire vertical extent of the concrete and allow the bolts to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. Alternatively, the elongated bolts can be wrapped in plastic tape, or coated with a suitable lubrication, which will allow the bolts to stretch under tension over the entire operating length of the bolt through the vertical extent of the concrete. 
     Henderson further discloses the post-stressing of the concrete in great compression by tightening the high strength bolts to provide heavy tension between a heavy top flange and the inbed plate at the bottom of the foundation, thereby placing the entire foundation under high unit compression loading. The bolts are tightened so as to exceed the maximum expected overturning force of the turbine tower on the foundation. Therefore, the entire foundation withstands various loads with the concrete always in compression and the bolts always in static tension. 
     The tensioning bolts in the cylindrical foundation are preferably in side-by-side pairs, the pairs extending radially from the center of the foundation, forming an inner ring of bolts and an outer ring of bolts as shown in  FIG. 2 . As shown in  FIG. 2 , the inner ring of bolts has a slightly shorter diameter than the outer ring of bolts. The bolt pattern is, of course, determined by the bolt pattern on the mounting flange of the turbine tower to be installed on the foundation. A large number of bolts in typically used for this type of foundation. Typically seventy tensioning bolts are used in the inner ring and seventy tensioning bolts in the outer ring for a total of one hundred forty. In Henderson&#39;s foundation, the lower ends of the bolts are anchored to the inbed plate at the bottom of the foundation which may be constructed of several circumferentially butted and joined sections. 
     The following known procedure is typically followed in constructing the cylindrical foundation. A bore hole is drilled or excavated and an outer boundary shell of corrugated metal pipe (“CMP”) is set within the hole. Bolt bundles are lowered into the borehole. The bolt bundles typically comprise about thirty bolts, with each bolt weighing up to two hundred pounds per bolt. Workers are lowered into the CMP lined bore hole. Working from the bottom of the bore hole, the workers lift and/or position each individual bolt so it can be inserted into a template at the surface, which is suspended above the bore hole by a crane having a capacity of approximately 100 tons. Once each bolt is inserted into the template, a nut made up onto the threads extending above the template, such that the weight of each bolt is suspended by the template. 
     Once all of the bolts have been suspended from the template, the entire assembly is lifted out of the bore hole so the inbed plates may be placed at the bottom end of the bolts. As the assembly is lowered back into the bore hole, bands or rebar wraps are placed around the collective bolts to hold the bolts in position during the pouring of the concrete.  FIG. 3  shows such an assembly suspended by a lifting frame which is connected to the template. The entire assembly is then lowered back into the bore hole and an inner boundary shell of CMP is lowered into the bore hole such that the bolts are extending upwardly through the annulus formed by the outer boundary shell and the inner boundary shell. Concrete is poured into this annulus around the upwardly extending bolts, with the template at the top of the bolts used to form a “grout trough” in the upper surface of the concrete. The upwardly facing ends of the bolts extend into the grout trough and, following the hardening of the concrete, the grout trough is filled with a high strength grout upon which the tower flange is placed when the grout has adequately cured. 
     It is to be appreciated that the above-described procedure anticipates that a number of workers will be working below a very heavy assembly (i.e., the template with all of the suspended bolts) as shown in  FIG. 3 . After all of the bolts are hung from the template, the entire assembly, including the lifting frame, is very heavy, requiring the use of a crane having a lifting capacity of approximately 100 tons. This procedure has a number of disadvantages. For example, it requires a large number of workers working below a very heavy assembly, creating a potential safety hazard. It also requires a large number of personnel in the borehole to expeditiously hang the bolts from the template. A comparable number of personnel are required at the surface to install and tighten the nuts on the upwardly facing ends of the bolts. A large crane is required for lifting and suspending the bolt-template assembly. 
     SUMMARY OF THE INVENTION 
     Embodiments of the method and apparatus disclosed herein provide a solution to the disadvantages described above. For purposes of this disclosure, the phrase “downwardly facing end” when referencing a bolt refers to the end of a bolt facing downward within a bore hole and the phrase “upwardly facing end” refers to the end of a bolt facing upward within the bore hole. 
     An embodiment of the method first involves preparing a foundation bore hole according to Henderson or other method. The total number of tower flange bolts to be utilized for the foundation is divided into a plurality of groups. Each of the bolts is encased within a hollow tube or other encasement (“sleeve”) which allows movement of the bolt relative to the sleeve once the bolt and sleeve are set within a concrete foundation. Each group of bolts is assembled into a bolt package where each bolt package comprises a plurality of bolts, where each bolt is either encased within a sleeve or wrapping to allow motion of the bolt with respect to the sleeve or wrapping. Within each bolt package, each bolt, is retained, by position retention means, in a position, with respect to the position of adjacent bolts, which is substantially the same position as when the bolt package is later placed within the foundation bore hole. The downwardly facing ends of the bolts of each bolt package are attached to an arc-shaped in-bed plate having holes for an inner arc of bolts and an outer arc of bolts. Each assembled bolt package may thereafter be individually placed within the bore hole. The bolt packages are arranged such that the inner arc of bolts of each anchor bolt package form an inner circle of upwardly facing anchor bolts and the outer arc of each bolt package form an outer circle of upwardly facing anchor bolts. 
     The number of bolts in each bolt package will generally be about ten to twelve bolts. Of course this number may vary according to various design and installation factors, without changing the basic concept of the embodiments of the method and apparatus disclosed herein. The installation of the above-described bolt packages eliminates the need for a large number of personnel inside the bore hole lifting each individual bolt so that the upwardly facing end of each bolt may be attached to a template. It further eliminates the need to lift the entirety of the bolts with the template as depicted in  FIG. 3  so that the downwardly facing ends may be set within the anchor plates, because the anchor plates have already been installed in sections to each bolt package. The utilization of the position retention means for each bolt package eliminates the need for the placement of bands or rebar around the collective bolts to hold the bolts in position during the pouring of the concrete, because the position retention means accomplishes this purpose. As yet another benefit, the known method requires that each bolt be attached to the template with a nut in order for the bolt to be suspended by the template. Because the present method does not require the template to support the collective weight of all of the anchor bolts, a much lighter template may be utilized for the formation of the grout trough and not every bolt needs to have a nut attached to the template at the upwardly facing end of the bolt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the foundation of Henderson following installation of the anchor bolts. 
         FIG. 2  shows a completed foundation, showing an inner ring of anchor bolts and an outer ring of anchor bolts with a tower flange attached. 
         FIG. 3  shows the prior art method of placing the anchor bolts, where all of the anchor bolts are suspended from the template above the borehole. 
         FIG. 4  shows a plurality of assembled bolt packages awaiting installation into the bore hole of a foundation. 
         FIG. 5  depicts an embodiment of a bolt package in a vertical position as it would be when lowered into position. 
         FIG. 6  depicts an embodiment of a bolt package being lowered into position within a bore hole. 
         FIG. 7  shows the top of a borehole with several bolt packages installed. 
         FIG. 8  schematically shows the configuration of one embodiment of a position retention means, referred to hereinafter as a “lattice assembly,” utilized to maintain the bolts within a bolt package in position with respect to one another. 
         FIG. 8A  shows a detailed view of how the lattice assembly in  FIG. 8  may be attached to the bolt sleeves. 
         FIG. 9  shows a perspective view of an embodiment of a lattice assembly in accord with  FIG. 8 . 
         FIG. 10  shows the lattice assembly of  FIG. 9  with bolts disposed within the bolt sleeves. 
         FIG. 11A  shows a portable assembly jig which may be utilized for assembly and/or transport of bolt packages. 
         FIG. 11B  shows the portable assembly jig of  FIG. 11A  with a bolt package disposed on the assembly jig. 
         FIG. 12  shows a detailed view of a retention plate at one end of the assembly jig of  FIG. 11 . 
         FIG. 13  shows how an inbed plate of a bolt package may be supported and retained within the assembly jig. 
         FIG. 14  shows an alternative embodiment of an alternative embodiment of a lattice assembly. 
         FIG. 15  shows a detailed view of how the embodiment of  FIG. 14  may be attached to a bolt sleeve. 
         FIG. 16  shows the embodiment of lattice assembly shown in  FIG. 14  may be attached to the bolt sleeves of a bolt package. 
         FIG. 17  shows an alternative embodiment of an assembly jig which may be utilized in assembling a bolt package with the embodiment of lattice assembly shown in  FIGS. 14-16 . 
         FIG. 18  shows how the assembly jig of  FIG. 17  supports the bolts and bolt sleeves. 
         FIG. 19  shows the assembly jig of  FIG. 17  in an exploded condition. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring specifically to the figures,  FIG. 1  depicts an embodiment of a known foundation  10  utilized for installation of a relatively tall vertical structure, such as a wind turbine. It is to be appreciated that while the disclosed method and apparatus may be utilized to obtain a foundation  10  such as that depicted in  FIG. 1 , the procedure for obtaining the foundation is entirely different from the known methods. Foundation  10  comprises a bore hole  12 , an outer boundary shell  14  and an inner boundary shell  16 , each typically fashioned of corrugated metal pipe (“CMP”), set within the bore hole hole. An inner ring  18  of bolts  40  and an outer ring  20  of bolts  40  are disposed within the annulus formed between the outer boundary shell  14  and the inner boundary shell  16 , with the bolts  40  anchored at the lower end of the bore hole  12  to an inbed plate  22 . The annulus between the outer boundary shell  14  and the inner boundary shell  16  is filled with concrete  24  and the portion of the bore hole  12  inside the inner boundary shell  16  typically filled with loosely compacted soil  26 . 
       FIG. 2  depicts a typical surface view of a wind turbine base, showing the inner ring  18  of bolts  40  and the outer ring  20  of bolts  40  extending through a base flange  28  of a wind turbine tower  30  set upon a base  32  formed by concrete  24 . 
       FIG. 3  depicts the currently practiced method for obtaining the configurations depicted in  FIGS. 1 and 2 . As described above, a bolt assembly is formed by first lowering individual bolts  40  into bore hole  12 , and then manually raising each bolt until it is attached to template  34 . Once all of the bolts have been attached to template  34 , the bolt assembly is lifted by a lifting assembly  36  connected to a high capacity crane  38 . 
     The present invention is utilized to obtain the configurations depicted in  FIGS. 1 and 2  but largely avoiding the method depicted in  FIG. 3 . The described method, and the apparatus utilized in the method, are substantially more efficient and safer than the currently practiced method. As with the known method, a bore hole  12  is drilled and lined with outer boundary shell  14 . However, rather than transferring bolt bundles into the bore hole and lifting each individual bolt  40  and inserting the bolt into template  34  according to the known method, in the disclosed method prefabricated bolt packages  50  are assembled outside of the bore hole  12  as depicted in  FIG. 4 . 
     The bolt packages  50  are formed by dividing the total number of anchor bolts  40  to be installed in the foundation bore hole into a plurality of groups. Each bolt package  50  is made up of a number of individual bolts  40 . Typically, each bolt package  50  will have ten to twelve (and typically no more than twenty) individual bolts  40  which are placed in axial alignment with one another and are configured into an inner arc  52  and an outer arc  54  of bolts. Each bolt  40  in the bolt package  50  is retained into a fixed position with respect to the position of the adjacent bolts by fixing the position of each bolt by position retention means. A first embodiment of position retention means is depicted in  FIGS. 8-10  and a second embodiment is depicted in  FIGS. 14-16 . The position of each bolt  40  within the bolt package  50  with respect to the adjacent bolts in the package will be, with respect to the position of adjacent bolts, will be substantially the same position as when the bolt package is placed within the foundation bore hole  12  and when the bolt package  50  is placed in its final disposition within the foundation. As depicted in  FIG. 6 , each bolt package  50  is thereafter lowered into the bore hole  12  and arranged such that the inner arc  52  of bolts  40  of each anchor bolt package form an inner circle  18  of upwardly facing anchor bolts and the outer arc  54  of each bolt package form an outer circle  20  of upwardly facing anchor bolts as indicated by  FIG. 7 . As indicated by  FIG. 6 , a lifting plate  56  may be utilized for lifting and lowering the bolt package  50 , but other means may also be utilized for lifting and lowering the bolt package as well, such that lifting plate  56  is optional. 
     Each bolt  40  contained within the bolt package  50  must be configured in such a manner as to allow tensioning of the bolt after it has been set in concrete  24 . Usually this means each bolt  40  of the bolt package  50  will be contained within a bolt sleeve  58 , where the bolt sleeves are typically elongated plastic tubes which encase the bolts substantially through the entire vertical extent of the concrete  24  and allow the bolts to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. Alternatively, the bolts  40  can be wrapped in plastic tape, or coated with a suitable lubrication, which will allow the bolts to stretch under tension over the entire operating length of the bolt through the vertical extent of the concrete. 
     Each bolt package  50  further comprises an arc-shaped inbed plate  60  which is attached to what will be the downwardly facing ends of each bolt  40  when the bolt package is placed within the bore hole  12 . A nut  70  is made up on each downward facing end of bolts  40  to attach the inbed plate  60  to the bolts. As discussed above, a lifting plate  56  may be likewise attached to the upwardly facing ends of each bolt  40 , with sufficient nuts made up on the upwardly facing ends of the bolts to adequately secure the lifting plate to the bolt package  50 . The lifting plate  56  may be installed temporarily to facilitate the lifting of the bolt package  50  from an assembly jig, such as assembly jig  100  described below, and for lowering the bolt package into the bore hole  12 . 
     The bolt package  50  further comprises means for retaining the positions of each bolt  40  in the bolt package with respect to the other bolts in the bolt package as the bolt package is assembled and later lifted from the assembly jig  100  and lowered into the bore hole  12 . One such means for setting the relative positions of the bolts  40  in a bolt package comprises a plurality of lattice assemblies  62 , each lattice assembly fabricated as generally depicted in  FIGS. 8-10 . This embodiment of lattice assembly  62  may be fabricated utilizing robotic welding for rapid and precise fabrication. Three or more lattice assemblies  62  will typically be used in the assembly and installation of a single bolt package  50 , where a lattice assembly is placed at various intervals along the lengths of the bolts  40 . The utilization of the lattice assemblies  62  replaces the bands or rebar wraps of the known method, which are placed around the collective bolts to hold the bolts in position during the pouring of the concrete. 
       FIG. 8  depicts how an embodiment of the lattice assembly  62  may be utilized for fabricating a bolt package  50 . A lower group  35  of bolts  40 , typically the bolts forming the inner arc  52 , are placed in a horizontal position, with the bolts set within the desired arc configuration. It is to be appreciated that while arc configurations are not depicted in  FIGS. 8-10 , the bolts are arranged and retained together to form the required inner arc  52  and outer arc  54  as generally depicted in  FIG. 5 . 
     Setting the bolts  40  in the desired arc configuration is most conveniently obtained by utilizing a jig assembly  100  such as one similar to that shown in  FIGS. 11-13  or to the jig assembly  200  shown in  FIGS. 17-19 . As shown in  FIGS. 8-10 , an embodiment of lattice assembly  62  may comprise a plurality of X-shaped members  72 , each member having a pair of bolt engagement members  64  for engaging the bolts which, during assembly, are beneath the lattice assembly. For example, as indicated in  FIG. 8 , the bolts  40  forming the inner arc  52  may be placed in position first. Thereafter, a plurality of lattice assemblies are placed on top of the bolts  40  forming the inner arc  52 , with the bolt engagement members  64  engaging the bolts. Each lattice assembly  62  further comprises a plurality of bolt support members  66  which support bolts  40  which may be placed on the support members  66  during assembly. If bolt sleeves  58  are utilized, the bolt engagement members  64  and the bolt support members  66  are each configured to engage the bolt sleeves which encases the body of each bolt  40 . Means for attaching the bolt engagement members  64  and the bolt support members  66  to the bolts  40  are utilized to retain the bolts  40  to the lattice assemblies  62 , such as wire, clips, or other suitable attachment means such as attachment wires  67  shown in  FIG. 8A . The lattice assembly  62  may further comprise supplemental support members  68  which provide additional rigidity to the lattice assembly. 
       FIGS. 11 through 13  depict an assembly jig  100  which may be utilized when fabricating bolt packages  50  utilizing lattice assembly  62 , or similar embodiments. It is to be appreciated that because of the configuration of lattice assembly  62 , once the position of the bolts  40  forming the inner arc  52  (or, conversely the outer arc  54 ) are placed within the jig, the rigid construction of the lattice assemblies fixes the position of the bolts  40  forming the outer arc  54  (or conversely the inner arc  52 ). 
     Assembly jig  100  comprises a frame work of sufficient structural capacity to support the weight of an assembled bolt package  50 . Each bolt package  50  is assembled on the assembly jig  100  with the bolts  40 , typically within a bolt sleeve  58 , consecutively laid horizontally across the frame work. The inner arc  52  of bolts is usually placed in the assembly jig  100  first, however it is to be appreciated that the assembly jig may be configured such that the outer arc  54  of bolts is laid in first. The assembly jig  100  comprises at least two parallel rails  102 , and a plurality of arc-shaped cross-supports  104  disposed between the parallel rails. The cross-supports  104  are configured to have the same arc configuration (i.e., having the same degree) as the desired arc of the inner arc  52 . Each cross-support  104  comprises a support seat  106  which is adapted to engage and support the underside of each bolt  40  (which may be enclosed within a bolt sleeve  58 ) as each bolt is laid across the lower cross-support. The bolt support seats  106  are configured to set the relative positions of the bolts  40  which will comprise an inner arc  52  which will, when the foundation construction is completed, will form the inner ring  18  of bolts. The bolt support seats  106  retain the bolts  40  in the proper relative position as the bolt package  50  is assembled. As shown in  FIG. 13 , an embodiment of the assembly jig  100  may comprise supports  108  placed on posts  110 , at one end for retaining the inbed plate  60  at the proper position. The assembly jig  100  may also comprise an end plate  112  at the opposite end, which provides a positive stop for proper positioning of the bolts  40 . As bolts  40  are set within the assembly jig  100 , the inbed plate  60  is retained by the supports  108  and posts  110  while the opposite ends of the bolts are abutted against the end plate  112 , which causes all of the bolts in the bolt package  40  to be aligned at each end. The assembly jig  100  may further comprise wheels  114  and a hitch  116  to allow the assembly jig to be easily transported to the construction site and allow assembly of bolt packages  50  at the on site of the installation. 
     It is to be appreciated that other means may be utilized for retaining the positions of each bolt  40  in the bolt package  50  with respect to the other bolts in the bolt package as the bolt package is assembled and lowered into the bore hole  12 . For example, another embodiment of lattice assembly  62 ′ is configured from bar stock  74 , such as steel rebar, configured to wrap around the adjacent bolt bodies as shown in  FIGS. 14-16 . As with other embodiments of lattice assembly, the embodiments of lattice assembly  62 ′ made with bar stock  74  will be configured to engage the bolts  40 , or bolt sleeves  58 , in several locations along the length of each bolt. As with the lattice assembly  62  depicted in  FIGS. 8-10 , the embodiment of a lattice assembly  62 ′ shown in  FIGS. 14-16  may be attached to each bolt  40  or bolt sleeve  58  with wire  67 ′. As indicated in  FIG. 16 , this embodiment of lattice assembly  62 ′ may be prefabricated prior to installation upon a group of bolt sleeves  58  and/or bolts  40 . Alternatively, this embodiment of lattice assembly  62 ′ may be fabricated as bolts are positioned within a jig assembly. If the lattice assembly is not utilized to provide a support for the upper layer of bolts in the manner shown in  FIGS. 8-10 , it is necessary to utilize a jig assembly  200  such as that depicted in  FIG. 17  to assemble the bolt packages  50 . This jig assembly comprises at least two parallel rails  202 , and a plurality of arc-shaped lower cross-supports  204  disposed between the parallel rails. The lower cross-supports  204  are configured to have the same arc configuration (i.e., having the same degree) as the desired arc of the inner arc  52  of bolts  40 . Each lower cross-support  204  comprises a support seat  206  which is adapted to engage and support the underside of each bolt  40  (which may be enclosed within a bolt sleeve  58 ) as each bolt is laid across the lower cross-support. The bolt support seats  206  are configured to set the relative positions of the bolts  40  which will comprise an inner arc  52  which will, when the foundation construction is completed, will form the inner ring  18  of bolts. The bolt support seats  206  retain the bolts  40  in the proper relative position as the bolt package  50  is assembled. 
     The jig assembly  200  shown in  FIGS. 17-19  further comprises a plurality of upper cross-supports  208  disposed between posts  210  which extend upwardly from parallel rails  202 . Each upper cross-support  208  comprises a plurality of hangers  215  which support the bolts  40  which will form the outer arc  54 . Jig assembly  200  further comprises an end plate  212  at one end which provides a positive stop for proper positioning of the bolts  40 . Jig assembly  200  further comprises posts  214  and supports  216  which support inbed plate  60 . 
     As best shown in the exploded view in  FIG. 19 , jig assembly  200  may further comprise a lifting assembly  220  which allows either the transport of the jig assembly  200  or the lifting of the bolt package  50  from the lower portion of the jig assembly  200 . Lifting assembly may either be lifted by crane or fork lift. 
     Once all of the bolt packages  50  are installed within the bore hole  12 , unless designed otherwise, the arcs of the adjacently positioned inbed plates  60  will form a complete circle forming the lower anchor ring, with each inbed plate of a bolt package attached to the inbed plates of the two adjacent bolt packages. In a similar manner, as best shown in  FIG. 7 , arc-shaped sections are connected to form template member  34 ′. 
     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. Instead the true scope of the invention should be determined by the following appended claims.