A modular guy anchor includes an anchor head and an anchor shaft. The anchor head includes a tubular region for receiving the anchor shaft. The anchor shaft has one end that extends into or through the tubular region and is retained therein. The anchor shaft is preferably galvanized steel coated over at least a portion of its length with a corrosion-resistant material. The corrosion-resistant material is preferably applied over any portion of the anchor shaft that is exposed to soil during normal use. The modularity of the guy anchor facilitates stocking, shipping, and installation, while the corrosion resistance of the anchor shaft promotes longevity.

CROSS-REFERENCES TO RELATED APPLICATIONS 
     This is a continuation application of U.S. application Ser. No. 12/899,878, filed on Oct. 7, 20120, which claims the benefit of U.S. Provisional Application No. 61/363,646, filed Jul. 13, 2010, which are incorporated herein by reference in their entireties. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable 
     REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to guyed construction techniques, and, more particularly, to techniques for anchoring guyed and additionally guyed towers. 
     2. Description of Related Art 
     Towers are widely used in many industries, including television transmission, radio communication, cell phone communication, wind turbines, and power transmission, to name a few. 
     Some towers, known as “guyed towers” or “additionally guyed towers,” rely on guy wires to maintain or assist in maintaining the towers in a vertical orientation. Generally speaking, these towers include a vertical main body, or “mast,” that stands on one end atop a base, which is generally concrete. Guy wires attach to the mast along its length, extend down and away from the mast, and attach securely to the ground using anchors. Most guyed towers are triangular in cross-section, and a minimum of three guy anchors are typically provided and are spaced apart by approximately 120-degrees to provide a stable base for holding the mast vertically. Often, guyed towers require three, six, or more guy anchors with multiple guy wires originating from different vertical levels of the tower attached to each guy anchor. 
     The term “guyed towers” describes towers whose masts have no independent means of support. They rely entirely upon guy wires to hold them upright. By contrast, the term “additionally guyed towers” describes towers that are essentially free standing, although they require guy wires to provide reinforcement and stability. 
       FIG. 1  shows a conventional guy anchor  100  for an erected tower. As shown in this example, four guy wires  110  originating from the tower's mast attach to an anchor head  114 . The guy wires  110  are generally composed of steel or some other high tensile strength metal. A shaft  116  extends from the anchor head  114  and into the ground  124 . Typically, the anchor head  114  and shaft  116 , which are also generally made of steel, are provided as a single unit, with the shaft  116  permanently welded to the head  114 . The distal end of the shaft  116  is typically buried in a steel-reinforced mass of concrete  118 , also known as a “dead-man.” The weight of the dead-man  118  and the earth above it holds the shaft  116  securely in place, even in the presence of large forces on the tower due to wind and precipitation. 
     The typical guy anchor assembly  100  may also include turnbuckles  112 . One turnbuckle  112  is generally provided for each guy wire  110 . The role of the turnbuckles  112  is to fine-tune the tightness of each guy wire  110 . 
     To prevent damage due to lightning strikes, the guy wires  110  are each electrically connected via a conductive cable  120  to a ground spike  122 . The ground spike  122  is typically made of copper. The cable  120  and ground spike  122  form a low impedance path to ground. This arrangement is designed to conduct high current surges away from the shaft  116 , thereby preventing damage to the shaft which could otherwise compromise the mechanical stability of the tower. 
     One drawback of the conventional guy anchor assembly  100  is that the anchor shaft  116  often corrodes over time. Over several years of use (and sometimes less time), corrosion may lead to a complete failure of the anchor shaft  116 , which can result in a collapse of the tower it supports. 
     Guy anchor shaft corrosion typically affects the area of the shaft exposed to soil, i.e., underground but excluding the region encased within the dead-man  118 . Corrosion may be galvanic or electrolytic in nature, or may be caused by other factors. In an effort to prevent corrosion, guy anchor shafts are typically galvanized. 
     BRIEF SUMMARY OF THE INVENTION 
     We have recognized that galvanizing the shaft is often insufficient. The galvanized coatings can become cracked or suffer abrasions during handling, thereby exposing the underlying, ungalvanized metal. The exposed metal is especially prone to concentrated corrosion, which may lead to premature failure of the anchor shafts. 
     We have also recognized that the conventional guy anchor assemblies  100  are sometimes difficult to stock, ship, and install. As indicated, the guy anchor head  114  and shaft  116  are provided as a single unit. Manufacturers make them with varying lengths (generally 4.9-6.1 m, or 16-20 ft.) to accommodate a variety of conditions, and with a variety of different size anchor heads (e.g., for accommodating different numbers of guy wires and/or different amounts of tension). Consequently, a large number of different units are generally stocked. Often, a unit will be selected when a tower project is commenced, but the length of that unit may be deemed inappropriate once all the details are known about the foundation, soil conditions, and other factors. Installers are warned not to cut anchor shafts, at the risk of impairing their function or longevity, so an anchor whose shaft is the wrong size must often be replaced before installation can resume. Such replacement entails delays and additional cost. 
     What is needed, therefore, is a guy anchor assembly that is resistant to corrosion and is relatively inexpensive and convenient to stock, ship, and install. 
     According to one embodiment hereof, a modular guy anchor includes an anchor head and an anchor shaft. The anchor head has a tubular region. The anchor shaft has one end extending into or through the tubular region of the anchor head, and the anchor shaft is retained within the tubular region. 
     According to another embodiment, a modular guy anchor includes an anchor head having an internally threaded, tubular region and an anchor shaft having an end that is externally threaded. The end of the anchor shaft and the tubular region are threaded together. 
     According to yet another embodiment, a guy anchor includes an anchor shaft, wherein the anchor shaft is galvanized and coated over at least a portion of its length with a material including a combination of Kevlar and at least one of urethane, epoxy, and latex. 
     According to still another embodiment, an anchor head for a modular guy anchor includes a head plate having a plurality of holes arranged substantially along a line for attaching to guy wires. The anchor head further includes a tube for receiving an anchor shaft. The tube is permanently affixed to or integral with the head plate and oriented perpendicularly to the line formed by the plurality of holes. 
     According to yet another embodiment, a method of installing a guy anchor for a tower includes assembling the guy anchor on-site, including fastening together an anchor head and an anchor shaft. The method further includes placing the assembled guy anchor into a hole and pouring concrete into the hole to secure the guy anchor. 
     According to a still further embodiment, a tower includes a tower mast, a plurality of guy anchors spaced around the tower mast, and a plurality of guy wires connecting the tower mast to the plurality of guy anchors. Each of the plurality of guy anchors includes an anchor head connected to at least one of the plurality of guy wires. Each guy anchor further includes a tubular region and an anchor shaft having an end. The end of the anchor shaft extends into or through the tubular region, and the anchor shaft is retained within the tubular region. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an elevation view of a conventional guy anchor for supporting a tower according to the prior art; 
         FIG. 2  is a front view of a modular guy anchor according to an illustrative embodiment of the invention; 
         FIG. 3  is a top view of the modular guy anchor of  FIG. 2 ; 
         FIG. 4  is a perspective view of the modular guy anchor of  FIGS. 2-3 ; 
         FIGS. 5-8  are different views of an anchor head used in the modular guy anchor of  FIGS. 2-4 ; 
         FIGS. 9-11  are different views of some of the component parts of the anchor head of  FIGS. 5-8  prior to welding; 
         FIG. 12  is a view of a threaded bar that may be used in the modular guy anchor of  FIGS. 2-4 , showing locations where a corrosion-resistant coating is applied; 
         FIG. 13  is a perspective view of a nut used in the modular guy anchor of  FIGS. 2-4 ; and 
         FIGS. 14-15  are front and side views of an anchor bearing plate used in the modular guy anchor of  FIGS. 2-4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The modular guy anchor as presented herein resists corrosion from contact with soil. It is generally more convenient and less expensive than conventional guy anchors from the standpoints of stocking, shipping, and installation. 
     As used throughout this document, the words “comprising,” “including,” and “having” are intended to set forth certain items, steps, elements, or aspects of something in an open-ended fashion. In addition, the terms “thread” and “threaded” describe any object with a helical pattern of ridges that may be screwed to another object with a complementary pattern. They include both machined threads and thread-like deformations formed using other processes. Although certain embodiments are disclosed herein, it is understood that these are provided by way of example only and that the invention is not limited to these particular embodiments. 
       FIGS. 2-4  show a modular guy anchor  200  according to an illustrative embodiment of the invention. The guy anchor  200  includes an anchor head  210 , an anchor shaft  212 , and a retaining structure, such as a bearing plate  214 . The anchor shaft  212  attaches to the anchor head  210  at a proximal end of the anchor shaft  212 , and attaches to the bearing plate  214  at a distal end. 
     The anchor shaft  212  is preferably a threaded bar. At the proximal end, the anchor shaft  212  is screwed into a threaded, tubular region of the anchor head  210 . Jamb nut  216  is preferably provided to secure the attachment between the shaft  212  and the anchor head  210  and to prevent rotation of the head with respect to the shaft. At the distal end, the threaded bar  212  is preferably affixed to the bearing plate  214  using nuts  220  and  222 . 
       FIGS. 5-8  show different views of the anchor head  210 . The anchor head  210  includes a head plate  510 , a tubular region, or coupler,  512 , and a pair of rigging plates  610 . Holes  516  are provided in the head plate  510  to facilitate attachment of the guy anchor to guy wires, in a manner similar to that shown in  FIG. 1 . The coupler  512  is preferably internally threaded, with a thread pattern that complementarily matches that of the guy shaft  212 . The coupler  512  is preferably a separate component that is positioned along a central axis  518  of the of the head plate  510  and welded to the head plate. The rigging plates  610  are preferably welded to the coupler  512 . They have holes  710 , which may be used to facilitate the attachment of guy wires during guy tower installation or upgrade. 
       FIGS. 9-11  show some of the component parts of the guy anchor head  510 . It can be seen in  FIG. 9  that the head plate  510  includes a channel  910 , and that the channel has an end  912 . During construction, the top and bottom of the channel are preferably welded to the coupler  512  to hold the coupler securely in place. 
       FIG. 12  shows a preferred embodiment of the anchor shaft  212 . Here, the anchor shaft is a threaded bar. The bar is preferably galvanized over its entire length. After the bar is galvanized, it is coated with a corrosion-resistant material. Region  1212  is where the anchor head is attached, and region  1214  is where the bearing plate is attached. Region  1216  is between regions  1212  and  1214 . After installation, region  1212  is above ground and region  1214  is encased in concrete (within the dead-man). Therefore, only region  1216  is exposed to soil. To reduce cost and to prevent the corrosion-resistant coating from interfering with the threaded attachments, only the region  1216  is preferably coated with the corrosion-resistant material. The coating is preferably not applied to regions  1212  and  1214 . 
     Various corrosion-resistant materials and techniques were tried. One included greasing the portions of the anchor shaft exposed to soil and wrapping the greased anchor shaft with rubber. The method proved partially successful but inconsistent. Another included a powder coating called Plascoat PPA 571, available from Plascoat Systems, Ltd. of Surrey, UK. 
     The best performing material for this purpose discovered as of the time of this writing is Line-X Xtra®. Line-X Xtra is a composite coating that includes urethane and DuPont™ Kevlar® micro pulp. This material provides numerous advantages. It resists corrosion by sealing out water, salts, acids, and other materials in soil. It electrically insulates the anchor shaft from the soil, thereby inhibiting galvanic and electrolytic corrosion. It also resists abrasion and scratches, helping to preserve the integrity of the galvanized surface of the anchor shaft. The Line-X Xtra coating is preferably sprayed on. Optimal coating thickness has yet to be determined, although we have found that a coating of 0.36 mm (14 mils) provides excellent corrosion resistance. Line-X Xtra is available through dealers, which may be contacted through Advanced Protective Coatings, dba LINE-X, of Huntsville, Ala. 
       FIG. 13  shows a jamb nut, which may be used for the nuts  216 ,  220 , and  222  of the modular guy anchor  200 . The jamb nuts  216 ,  220 , and  222  have internal threads, which complementarily match the threads of the anchor shaft  212 . 
       FIGS. 14 and 15  show the bearing plate  214 . The bearing plate  214  is designed to be embedded within to the concrete dead-man  118  so that the load from the anchor shaft  212  can be transferred to the dead-man. Preferably, the bearing plate  214  is a square metal plate having a central clearance hole  1410  through which the anchor shaft  212  is passed during assembly. The bearing plate  214  is preferably attached to the anchor shaft  212  as shown in  FIGS. 2-4  using nuts  220  and  222 . 
     As is known, guy anchors must withstand high tensile forces from guy wires, which can reach tens of kilo-Newtons. Most arrangements of screws, nuts, and couplers cannot withstand those forces. The process of machining threads into materials generally weakens the materials. There are other methods of forming threads, however. In particular, threads may be formed in a material by rolling in a continuous pattern of threads or thread-like deformations. These may be applied during the forging process of the material. The resulting threaded material is much stronger than the same material in which threads are machined. 
     Bars, couplers, and nuts having threads formed in this manner are commercially available from DYWIDAG-Systems International (DSI). The DYWIDAG THREADBAR® series includes threaded rods, couplers, and nuts, which may be used advantageously in the modular guy anchor  200 . 
     In the preferred embodiment, the anchor shaft  212  is a DYWIDAG THREADBAR rod, and the coupler  512  is a DYWIDAG THREADBAR coupler. The jamb nuts  216 ,  220 , and  222  are preferably DYWIDAG THREADBAR lock nuts. 
     DYWIDAG THREADBAR components are available in different sizes. We have found that #14 components (i.e., rods, nuts, and couplers) are suitable for most tower applications; however the size of the components may be varied as the target site requires. DYWIDAG THREADBAR rods are preferably cut to 4.57 m (15 ft.) lengths. They are preferably 75 KSI steel, or higher. The #14 rods typically have a cross-sectional area of 1452 mm 2  (2.25 in 2 ) and a yield strength of 751 kN (168.8 Kips). The rods are galvanized and then coated with a layer of Line-X Xtra. The coating preferably covers region  1216  but does not extend to regions  1212  and  1214  (see  FIG. 12 ). Typically, region  1212  is 0.36 M (1 ft, 2 in.) long and region  1214  is 0.61 M (2 ft.) long. 
     The size of the anchor head  210  varies with the number of guy wires to which it must attach and the resultant tensile force to be borne. However, a typical anchor head is about 48 cm (1 ft., 7 in.) long and wide, and is about 1.9 cm (0.75 in.) thick. 
     The optimal size of the bearing plate  214  will also vary based on load. A typical size is approximately 20 cm (8 in.) square and about 1.3 cm (0.5 in.) thick. 
     The DYWIDAG THREADBAR #14 couplers are typically 198.6 mm long (7.82 in.) long, and the #14 lock nuts are typically 36.8 mm (1.45 in) long. Sizes may be varied based on site requirements. For example, #18 rods, couplers, and nuts may be used for heavier duty applications. The DWYIDAG lock nuts are preferably galvanized per ASTM A123. 
     The anchor plate  510 , rigging plates  610 , and bearing plate  214  are preferably grade A572, 50 KSI steel. The completed anchor head weldment, including the anchor plate  510 , coupler  512  and rigging plates  610 , are preferably hot-dipped galvanized per ASTM A123 after fabrication. 
     Preferably, the anchor head  210  is available in a series of discrete sizes, such as small, medium, and large, to accommodate a wide range of site requirements. Similarly, the anchor shaft is preferably available in different stock lengths. 
     The guy anchor  200  can be used in a similar manner to the conventional guy anchor of  FIG. 1 . Guy anchors  200  may be installed around a tower mast, preferably at 120-degree spacing, and attached to the tower mast using guy wires. Each guy anchor may be installed in the conventional manner. A hole is excavated for each guy anchor, the guy anchor is placed in the hole oriented toward the tower, at an angle that substantially aligns with the expected resultant force from the guy wires. The hole is generally rectangular, with one side facing the tower mast. The anchors are each set in a concrete dead-man, and the holes are filled with earth. Once the concrete sets, the anchors may be rigged to the tower mast and the tower can be erected. 
     The installation process for the guy anchor  200  differs from the conventional process, however, because the guy anchor  200  may be assembled on-site. To assemble the guy anchor  200 , an installer typically first checks the length of the anchor shaft  212 . Many times, planned length and ultimate installed length of an anchor shaft may differ once details of soil composition, rockiness, and other factors are more fully known. If the anchor shaft  212  is too long, it may be cut on site by the installer to the preferred length. The cut is preferably made at the distal end of the shaft  212 . Any field-cut edges are preferably galvanized with two coats of zinc rich galvanizing compound. 
     Once the shaft is the correct length, the installer attaches the anchor head  210  and bearing plate  214  to the shaft  212 . The order of attachment is not important, although it is generally easier to install the bearing plate first. 
     The bearing plate is attached by spinning the jamb nut  220  onto the distal end of the shaft and advancing it approximately 15 cm (6 in.). The plate  214  is then applied, with the shaft  212  passed through the hole  1410 , and the jamb nut  222  is applied over the end of the shaft  212 . The nuts  220  and  222  are tightened together with the bearing plate  214  held fast between them. 
     Next, the installer attaches the anchor head  210  to the proximal end of the shaft  212 . The installer inserts the jamb nut  216  over the end of the shaft, spins it down approximately 30 cm, and then threads the coupler  512  of the anchor head onto the shaft  212 . The installer generally spins the anchor head down until the shaft  212  butts against the end  912  of the channel  910 . The installer typically adjusts the location of the nut  216  and may unscrew the anchor head  210  to achieve the desired height and orientation of the anchor head. The nut  216  is then tightened to the coupler  512  to firmly fasten the anchor head  210  to the anchor shaft  212 . 
     The modular guy anchor  200  is typically easier to install than the conventional, integral unit. As indicated, installations do not always go as planned. The ability to cut the anchor shaft  212  on-site thus provides the installer with an option not generally available with conventional designs. It may not even be necessary to cut the anchor shaft. Since the guy anchor  210  is modular, little extra cost is involved in transporting extra anchor shafts  212  to the installation site. A shaft that is too long can simply be swapped out for a smaller one, without costly delays. The modular components are generally easy to carry in the installer's truck. The anchor heads  210  can be stacked and the shafts  212  can be laid flat on the truck bed. In contrast, conventional integral guy anchors, which include both the head and the shaft, are bulky and typically longer than their modular counterparts. 
     For the same reasons, the modular guy anchor  200  can reduce shipping costs. Longer, bulkier items are more costly to ship than smaller, more compact ones. Also, since the modular design of the guy anchor  210  helps make it easier to have all the parts on hand that are needed to complete an installation, shipping costs are avoided that would otherwise be incurred from returning and replacing materials. 
     The modular guy anchor  200  is also simpler to stock. For example, if the anchor head  210  and anchor shaft  212  are each offered in three different sizes, then a warehouse need only stock three types of anchor heads and three types of shafts—a total of six parts. To get the same range of sizes with the conventional design, a warehouse would have to stock nine different types of parts. The more standard sizes there are, the greater the advantage of modularity. Also, with the conventional, integral design, each guy anchor is used relatively seldomly. Therefore, warehouses need to stock a lot of infrequently used parts if they are to be available quickly. This increases inventory and costs. The alternative would be to stock few parts and have guy anchors made to order. However, this option introduces long delays. These delays can be especially troublesome if an installation has already started, the guy anchor the installers initially planned to use does not fit, and the installers have to wait for a new one to be manufactured. 
     The use of corrosion-resistant materials, such as Line-X Xtra, provides a promising option for extending the useful life of guy anchor shafts. By preventing corrosion, costly repairs can be avoided. Tower safety is expected to improve, with reduced risk to human life and property. 
     Having described one embodiment, numerous alternative embodiments or variations can be made. For example, in the preferred embodiment, DWYIDAG THREADBAR components are used for the shaft  212 , coupler  512 , and jamb nuts  216 ,  220 , and  222 . However, this is not required. Other components may be used, such as those of Williams Form Engineering Corp. of Belmont, Mich. Although parts with threads formed with a rolled in pattern during forging are preferred because they tend to be stronger, they are not strictly required. In fact, any threaded rods, couplers, and nuts may be used, provided they meet the strength requirements. 
     As shown and described, a jamb nut  216  is used to attach the anchor head  210  to the anchor shaft  212 . Alternatively, this nut may be eliminated as long as other provisions are made to prevent the anchor head  210  from rotating on the anchor shaft. 
     It is not strictly necessary that the tubular region  512  of the anchor head  210  have internal threads. The anchor shaft  212  may alternatively be held in place with pins or other modes of attachment. 
     According to one variant, the head plate  510  includes a central open region continuous with the channel  910 . This open region is large enough so that the anchor shaft  212  may be inserted completely through the tubular region  512  and made to extend into the open region. A nut can be applied to the end of the anchor shaft within the open region. This nut may be used in place of or in addition to the nut  216 . The tubular region  512  may be threaded or unthreaded in this scenario. 
     As shown and described, the anchor shaft  212  is threaded over its entire length. However, this is merely an example. Alternatively, the anchor shaft  212  may be threaded only at its proximal end and its distal end, for attaching the anchor head  210  and bearing plate  214 , respectively. Indeed, the anchor shaft need not be threaded at all, provided other modes of attachment are provided to the anchor head and bearing plate. 
     As shown and described, a coating of Line-X Xtra is used as the corrosion-resistant material over the anchor shaft  212 . However, other materials may be used, including other coatings incorporating a combination of urethane and DuPont Kevlar. In addition, other materials besides urethane can be combined with Kevlar to provide acceptable results. These include epoxy and latex, for example. 
     As shown and described, the coupler  512  is welded to the head plate  510 / 1612  and the rigging plates  610  are welded to the coupler  512 . Alternatively, all three components, or any two of the three, may be formed integrally. 
     Those skilled in the art will therefore understand that various changes in form and detail may be made to the embodiments disclosed herein without departing from the scope of the invention. 
     REFERENCES USED IN THE FIGURES 
     
       
         
               
               
             
               
               
             
           
               
                   
               
               
                 Reference Numeral 
                 Description 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 100 
                 Guy Anchor 
               
               
                 110 
                 Guy Wire(s) 
               
               
                 112 
                 Turnbuckle(s) 
               
               
                 114 
                 Guy Anchor Head 
               
               
                 116 
                 Guy Anchor Shaft 
               
               
                 118 
                 Dead-Man 
               
               
                 120 
                 Electrically Conductive Cable 
               
               
                 122 
                 Ground Spike (Copper) 
               
               
                 124 
                 Ground or Grade Level 
               
               
                 200 
                 Modular Guy Anchor 
               
               
                 210 
                 Anchor Head 
               
               
                 212 
                 Threaded Bar 
               
               
                 214 
                 Anchor Bearing Plate 
               
               
                 216, 220, 222 
                 Nuts 
               
               
                 510 
                 Anchor Head Plate 
               
               
                 512 
                 Coupler 
               
               
                 516 
                 Holes for Guy Wires 
               
               
                 518 
                 Center Axis of Anchor Head Plate 
               
               
                 610 
                 Rigging Plate 
               
               
                 710 
                 Hole in Rigging Plates 
               
               
                 910 
                 Channel in Anchor Head Plate 
               
               
                 912 
                 End of channel 910 
               
               
                 1210 
                 Threads of Threaded Bar 
               
               
                 1212 
                 Proximal Region without Corrosion-Resistant 
               
               
                   
                 Material 
               
               
                 1214 
                 Distal Region without Corrosion-Resistant Material 
               
               
                 1216 
                 Region with Corrosion-Resistant Material 
               
               
                 1310 
                 Internal Threads of Nut 
               
               
                 1410 
                 Hole in Bearing Plate