Abstract:
A foundation for a tall vertical structure, such as a wind turbine installation, features anchor bolts having a grout cap slid over the anchor bolt, where the grout cap has a flared skirt which seals against the open annulus formed by the anchor bolt and its accompanying PVC sleeve, where the top of the PVC sleeve is generally flush with the bottom of the grout trough. The grout cap extends from its bottom which abuts the bottom of the grout trough, up and extending at least partially into a bolt hole in the tower flange. A method of protecting anchor bolts utilizing the grout cap is also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    U.S. Provisional Application No. 61/209,135 for this invention was filed on Mar. 3, 2009, for which application these inventors claim domestic priority. 
     
    
     BACKGROUND 
       [0002]    This device and method of protection relates to anchoring devices, such as bolts, which are used to install tall, heavy and/or large structures which are subject to high overturning moments. The disclosed device more specifically relates to a grout sleeve for an anchor bolt used in combination with a threaded anchor, and a method for installing the same. 
         [0003]    The anchor bolts may either be set in concrete or drilled into the rock. Among other applications, the anchor bolts are used for supporting wind turbines, power line towers, structures used for street lighting and traffic signals, bridge supports, gondola and ski lift support structures, and large signage supports. More particularly, this invention comprises an apparatus, and a method for installing the apparatus, where the apparatus protects the anchor bolts from moisture and corrosive attack caused by water or other liquid entering the annulus formed between the anchor bolt and the anchor bolt sleeve. 
         [0004]    The integrity of the foundation of a tall structure 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 and retained by the anchor bolt sleeve, which can cause 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. 
         [0005]    The initial attempt at solving the anchor bolt corrosion problem was to paint the anchor bolts. However, this solution is labor intensive and does not prevent liquid accumulation around the anchors. In addition, this protection method requires that the anchor bolts be repainted periodically, as well as after re-tensioning the anchor bolts if required in the particular application. 
         [0006]    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&#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. 
         [0007]    In the fabrication of one type of foundation for wind turbines, elongated high strength steel bolts, generally fashioned from 1¼″ (#10) rebar material or 1⅜″ (#11) rebar material, 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 or other structure. The bolts extend through hollow tubes or sleeves to prevent adhesion of the concrete to the bolts. The sleeves are installed prior to delivery of the bolts to the job site, and nuts are generally be placed on each end of the anchor bolt to retain the sleeve on the anchor bolt material. 
         [0008]    Henderson further discloses the post-stressing of the concrete in great compression by tightening the nuts on 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 flange or plate at the bottom of the foundation, thereby placing the entire foundation, between the heavy top plate or flange and lower anchor plate or flange, under high unit compression loading. The nuts on the bolts are tightened so as to preload the bolts to exceed the maximum expected overturning force of the 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. 
         [0009]    The concrete foundation for a turbine tower typically comprises a grout trough which is formed by the placing of a circular template that holds the anchor bolts when pouring the uppermost part of the concrete foundation. Thus, the bottom surface of the grout trough is formed by the top surface of the concrete foundation. The grout trough forms a ring into which high compressive strength grout is poured, where the ends of the anchor bolts extend above the concrete and through the grout poured into the grout trough. Because the tower flange must be set nearly perfectly level, the current practice is to place shims in the grout trough and level the tower flange with laser leveling techniques. Once the shims are leveled, high strength grout is poured into the grout trough and the flange set down on the anchor bolts and the grout allowed to set up. 
         [0010]    Proper alignment of the anchor bolts is important as the anchor bolts must fit within the bolt holes provided in the flange. While there is a slight tolerance for misalignment, in the range of ⅛ to ¼ inches for an individual anchor bolt, the anchor bolts as an anchor bolt package must be nearly perpendicular to the flange and closely matched to ensure a correct and safe tower installation. The ability to align the bolts within the poured and set foundation is helpful to ensure matching the anchor bolts to the bolt holes in the flange. 
         [0011]    The anchor bolts may be placed 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. The bolt pattern is, of course, determined by the bolt pattern on the mounting flange of the structure to be installed on the foundation. A large number of bolts are 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. Alternative foundations can utilize more bolts, compounding the problem of anchor bolt alignment with the flange. 
         [0012]    In Henderson&#39;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. 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. 
         [0013]    The bolts usually used for the anchors for wind turbines are approximately thirty feet in length, and usually have outside diameters of 1¼ inch or 1⅜ inch. The hollow tubes or sleeves are typically elongated plastic tubes fabricated from polyvinyl chloride (“PVC”) which encase the bolts substantially through the entire vertical extent of the concrete. The room provided by the PVC sleeves allows the bolts to move under the tension generated by applied pressure, and to be tensioned after the concrete has hardened and cured, thereby post-tensioning the entire concrete foundation. The open ends of the PVC sleeves are generally flush with the top surface of the concrete foundation within the grout trough, thus presenting an opening into the annulus between the anchor bolt and the PVC sleeve. 
         [0014]    However, the PVC sleeves do not extend along the entire length of the anchor bolts. Specifically, the PVC sleeves do not extend through the peripheral connecting plate or through the bolt holes in the flange at the base of the wind turbine. The hole diameters of flanges used at the base of wind turbines are approximately 1½ inch, and the external diameters of the commonly available PVC sleeves which may be utilized for 1¼ inch to 1⅜ inch diameter bolts are too large to be inserted within the holes in the peripheral connecting plate or flange. 
         [0015]    The inability to insert the PVC sleeves into the flange at the base of the wind turbine creates a problem with respect to preventing the flow of water or other liquids down the annulus formed between the anchor bolt and the PVC sleeve. In the known installations, water may flow into and accumulate in the annulus created by the PVC sleeve and the anchor bolt. The accumulation of water or other liquids can result in the formation of a corrosion cell and cause corrosion in the anchor bolts thus affected. Compounding the problem is that it is a common practice to place water within the grout trough prior to pouring the grout to prevent uneven drying of the grout. However, placing the water in the trough causes it to gravitate into the open PVC sleeve ends which are flush with the top surface of the concrete foundation forming the bottom of the grout trough. Prior art methods of sealing the annulus included wrapping a piece of foam material around the bolt and wrapping the foam sleeve with duct tape to retain the sleeve around the anchor bolt, or running a bead of sealant such as caulking compound around the anchor bolt and grout trough juncture. These are labor intensive processes which are not always successful in preventing the flow of water or other fluids into the anchor bolt/PVC sleeve annulus. Additionally, the foam sleeves are extremely compressed and deformed when the heavy tower flange is set down atop the sleeves. The compressed and deformed foam sleeves displace grout, thus diminishing the overall compressive strength of the grout. 
       SUMMARY OF THE INVENTION 
       [0016]    The present application is directed toward a method and apparatus which addresses the problem identified above. The present apparatus comprises a grout sleeve which extends from the base of the grout trough, through the grout layer, and penetrating into the bolt opening on the bottom side the tower flange. The apparatus comprises a sleeve member having a top and a bottom, the sleeve member defining a longitudinal axis, where the internal diameter of the sleeve member may gradually increase from the top to the bottom. The apparatus further comprises a flared skirt which extends outwardly from the exterior of the bottom of the sleeve. An embodiment of the apparatus is configured such that prior to completion of the installation, only the peripheral edge of the bottom of the flared skirt is in facing contact with the bottom of the grout trough. However, once installation has been completed, substantially all of the bottom of the flared skirt is in facing contact with the bottom of the grout trough, thereby forming a seal around the open upwardly facing annulus between the bolt and the bolt sleeve located at the bottom of the grout trough. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an embodiment of the grout sleeve. 
           [0018]      FIG. 2  is a cross sectional view of an embodiment of the apparatus of the disclosed device prior to installation. 
           [0019]      FIG. 3  is a cross sectional view of the embodiment of  FIG. 2  following installation. 
           [0020]      FIG. 4  is a partial perspective view of the base of a tower, such as a wind turbine, showing the bolt configuration. 
           [0021]      FIG. 5  is a side view of a bolt package being installed into an excavated foundation hole. 
           [0022]      FIG. 6  is a partial view of a grout trough prior to the pouring of the grout, and showing a prior art method for protecting the bolt-sleeve annulus. 
           [0023]      FIG. 7  is a partial perspective view of a tower flange installation prior to the lowering of the tower flange onto the top of the grout trough. 
           [0024]      FIG. 8  is a cross sectional view of a prior art method of sealing the annulus following pouring of the grout and placement of the flange. 
           [0025]      FIG. 9  is a cross sectional view of an embodiment of the disclosed grout sleeve placed between the bottom of the grout trough and extending up into the tower flange. 
           [0026]      FIG. 10  is a partial perspective view of the cement foundation, anchor bolts, grout trough, grout and flange. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0027]    Referring now to the drawings,  FIG. 1  shows an embodiment of the disclosed grout sleeve  110 . The device  110  has a sleeve  112  having an top end  114  and a bottom end  116 , wherein the bottom end  116  is connected to a “flared skirt” or skirt  118 . Embodiments of the disclosed grout sleeve may be manufactured from polypropylene, polyethylene, rubber or other materials having satisfactory mechanical properties. The term “polypropylene” as used below not only includes polypropylene materials, but other plastic materials having mechanical properties which allow those materials to be substituted for polypropylene. 
         [0028]    Shown in  FIGS. 2 and 3  are cross sectional views of an embodiment of a grout sleeve  110  as disposed around an anchor bolt  16 . The grout sleeve  110  comprises an top end  114  having a diameter D 1  and a bottom end  116  having a diameter D 2 . An embodiment of the device may be configured such that D 1  is less than D 2 , such that the diameter tapers from the top end to the bottom end, with the diameter increasing along the axis of the grout sleeve. D 1  is sized to cause a tight interference fit with the thread of the anchor bolt  16  such that the grout sleeve  110  is installed by pressing the device firmly down the top of anchor bolt  16 , causing the top end to stretch to encompass the anchor bolt  16 . As shown in  FIG. 2 , the grout sleeve  110  is fabricated such that skirt or skirt  118  is angled relative to sleeve  112 . However upon installation, skirt  118 ′ is compressed such that it is parallel to and in substantial facing contact with the top surface of the foundation  12 , which forms the bottom of the grout trough  28 . As shown in  FIG. 3 , skirt  118 ′ provides a beveled surface at the juncture of the skirt  118 ′ and the foundation  12  to assist in providing a liquid tight seal over the annulus  36  formed by the anchor bolt  16  and the PVC sleeve  22 . The grout sleeve might include an O-ring or similar gasket underneath the skirt  118  or the installer might place a bead of caulk, silicone gel, or similar sealant either underneath the skirt  118 ′ or encircling the skirt  118 ′. 
         [0029]      FIG. 4  shows a partial perspective view of the base of a tower  10 , such as a wind turbine. The tower flange  14  is placed atop a foundation  12 , and is held in place by nuts  18  threadedly tightened to the anchor bolts  16 . The nuts  18  are tightened to provide sufficient prestress to anchor bolts  16  to exceed the maximum expected overturning force of the tower  10  on the foundation  12 . 
         [0030]    Shown in  FIG. 5  is an anchor bolt package  20  being installed into an excavated foundation hole. The crane  26  lifts the anchor bolt package  20  by the cradle  24 , and lowers the anchor bolt package  20  into the excavation, thereby controlling the placement of the anchor bolt package  20 . The grout trough  28  is formed by the circular form  23  holding the anchor bolt package  20  when concrete is poured into the excavation around the anchor bolt package  20 , forming foundation  12 , comprising a structure of cementitious material. Once the cement has adequately hardened, the bolts may be preloaded, thus placing the structure into compression. 
         [0031]      FIGS. 6 and 7  depict a prior art method of attempting to prevent water from accessing the annulus  36  (not shown) between the PVC sleeve  22  and the anchor bolt  16 . As shown in  FIG. 6 , foam sleeves  32 , typically having a slit to allow the foam sleeve to form around the anchor bolt  16 , are placed around the anchor bolt  16  in an effort to inhibit the flow of liquid down the annulus  36 , which is otherwise opened at the bottom of trough  28 . Often, duct tape will be wrapped around the foam sleeves  32  in an effort to create a tighter seal. However, preparing and placing the foam sleeves  32  around the anchor bolts  16  is time consuming, resulting in additional expense for labor and equipment. More importantly, it is ineffective in preventing the flow of water into the annulus  36 . 
         [0032]      FIG. 7  shows a partial perspective view of a tower flange  14  being lowered onto a foundation  12  in the prior art method. As shown, the anchor bolts  16  are wrapped in the foam sleeves  32  prior to and during the pouring or placement of grout into the grout trough  28 . It is of great importance that tower flange  14  is installed in a completely level position. Thus, in the known installation method, the tower flange must be leveled before the grout is completely poured and hardens. Following the leveling process, the flange  14  is lowered onto anchor bolts  16 , and nuts  18  made up to the required torque to provide the necessary pre-load on the foundation. The foam sleeves  32  will be within the grout in the trough  28  and will be deformed as the flange is lowered into the trough, thus displacing a certain volume of the grout. The risk of cracking or otherwise weakening the grout through compression and the resultant expansion of the foam sleeve  32  is a problem common with the use of the foam sleeves  32  because the expansion of the foam sleeves  32  can be significant. Additionally, the foam sleeve  32  can allow grout to adhere to the anchor bolt  16  and thereby restrict proper setting movement of the anchor bolt  16  during flange  14  placement and preloading of the anchor bolts  16 . 
         [0033]    Shown in  FIG. 8  is a cross sectional view of the prior art method of sealing the annulus  36 . The foam sleeve  32  is shown in an ideal deformation and it is to be appreciated that the foam sleeve  32  will not always compress evenly or prevent the flow of grout  30  into the annulus  36  formed between the anchor bolt  16  and the PVC sleeve  22 . The annulus  36  is not completely sealed by the foam sleeve  32 , therefore any water or other liquid placed into the grout trough  28  may enter annulus  36 . 
         [0034]      FIG. 9  shows an embodiment of the presently disclosed grout sleeve  110  as installed. It is to be noted that the top end  114  of the grout sleeve  110  penetrates into the bolt hole  13  in flange  14  with the bottom of skirt  118  disposed against the base of the grout trough formed by top surface  34  of the concrete foundation  12 . Thus, skirt  118  thereby forms a seal against annulus  36 , thereby inhibiting liquid flow into the annulus. The seal of the skirt  118  against top surface  34  may be enhanced by the utilization of an optional sealant placed underneath or encircling the skirt  118 , or an O-ring placed within the bottom surface of the skirt. 
         [0035]      FIG. 10  is a partial perspective view of the cement foundation  12 , anchor bolts  16 , grout trough  28 , grout  30  and flange  14 , as installed. The grout  30  (and shims if utilized) provides a level surface for flange  14  on the foundation  12 . A low viscosity high strength grout may be utilized, which facilitates the leveling of flange  14  as the grout  30  is essentially self-leveling because of its low viscosity. That is, the grout may be sufficiently self-leveling because of its low viscosity that leveling shims are not are required, and the grout may actually be allowed to reach full compressive strength before setting the tower flange upon the top surface of the grout. However, it is to be appreciated that the use of low viscosity grout requires that access into the bolt-sleeve annulus  36  be minimized to prevent corrosion of the anchor bolts  16 . The grout sleeve  110  disclosed herein is one means of inhibiting the flow of liquids into the annulus  36 . 
         [0036]    The method of installing a grout sleeve  110  on an anchor bolt  16  for a vertical structure, including wind turbines, comprises the steps of sliding the grout sleeve with the flared skirt or skirt  118  downwards over a portion of the threaded length of an anchor bolt protruding above the base the grout trough, and until the bottom of skirt of the grout sleeve is in facing contact with the surface  34  forming the bottom of the grout trough  28 , which typically will be the top surface of the concrete forming the foundation  12 . The tower flange  14  is lowered over the anchor bolts  16  such that the top end  114  of the grout sleeve  110  penetrates a portion of the bolt hole  13  in flange  14 . Tower flange  14  is leveled, and grout  28  placed into the grout trough and allowed to cure. 
         [0037]    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. Thus the scope of the invention should not be limited according to these factors, but according to the following appended claims.