Abstract:
A concrete pole includes an attachment mechanism which provides a structurally sound means of attaching to the pole and permits the use of short, inexpensive bolts. The attachment mechanism includes reinforcing bars, a base plate, an internally threaded fastener insert fixed to the base plate, which provides a path from the base plate, which is embedded in the concrete pole, to the finished outside surface of the pole. One embodiment includes a pipe connecting opposing fastener inserts for added strength.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to concrete poles, and, in particular, to an attachment mechanism for a concrete pole which permits items to be bolted to the pole. 
   In the prior art, the most common way to attach structural appurtenances to a centrifugally cast concrete pole is to pass bolts completely through the pole and connect nuts to the bolts on the opposite side of the pole. This requires casting or drilling holes through the pole, which is labor intensive. Even more importantly, this means that, in order to attach anything near the base of the pole, which can have a very large diameter, very long bolts are required. These long bolts are very expensive, and, in order to be able to attach to the pole at a variety of different heights on a tapered pole, a variety of different length bolts must be stocked, which is also very expensive. 
   Also, since the centrifugally cast concrete poles are hollow and relatively thin-walled, the bolts are not very well supported by the pole and therefore cannot support much attachment load. 
   U.S. Pat. No. 5,761,875, Reinforced Concrete Pole with Attachment Mechanism, issued Jun. 9, 1998, which hereby incorporated by reference, discloses an improved attachment mechanism which introduces the use of shorter, standard size bolts, as well as material and labor cost savings, and improves the versatility of the concrete poles. However, as is discussed in more detail in the specification, this improvement has weaknesses, including a cantilevered load on the nuts and bolts securing the attachment to the pole. 
   SUMMARY OF THE INVENTION 
   The present invention provides an attachment mechanism which does not require drilling through the concrete pole in order to attach items to the pole, thereby saving labor. Also, the present invention provides an attachment mechanism which permits a single length bolt to be used to attach items to the pole at any elevation on the pole, even though the thickness of the concrete may vary and the diameter of the pole may vary with elevation, thereby permitting the use of less expensive bolts and permitting the stocking of only a single length bolt, which saves considerable cost. 
   The present invention also provides an attachment mechanism which provides excellent support to anything that is bolted onto the attachment mechanism, allowing heavier loads to be attached to the pole or providing better support for the same load than prior designs. Furthermore, the bolts are not supporting a cantilevered load, but are instead supported the length of the bolt by the concrete pole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an example of a centrifugally cast concrete pole made in accordance with the present invention, with arms attached to the pole; 
       FIG. 2  is a broken away, perspective view, partially in section, of a centrifugally cast concrete pole of the prior art, with vertical reinforcing rods or prestressing strands, a spiral reinforcement, and bolts extending to a plate embedded in the pole in order to attach an arm to the pole; 
       FIG. 3  is an exploded perspective view of a portion of the attachment mechanism used in the pole of  FIG. 1 ; 
       FIG. 4  is a schematic top view of the assembled attachment mechanism used in the pole of  FIG. 1 , with the concrete shown in phantom; 
       FIG. 5  is a broken-away perspective view, partially in section, of the concrete pole of  FIG. 1 ; 
       FIG. 6  is a perspective view of one of the insert fasteners of  FIG. 3 ; 
       FIG. 7  is a perspective view of the opposite end of the insert fastener of  FIG. 6 ; 
       FIG. 8  is an exploded perspective view of the insert fastener of  FIG. 6  combined with a pipe, which, when assembled, become part of a second embodiment of the pole attachment mechanism of the present invention, shown in  FIG. 10 ; 
       FIG. 9  is a broken away perspective view of the fastener and pipe of  FIG. 8 , as prepared for being joined with a full perimeter fillet weld; 
       FIG. 10  is a perspective view of a second embodiment of a pole attachment mechanism made in accordance with the present invention, with the upper connecting pipe removed for illustration clarity; and 
       FIG. 11  is a broken-away portion, partially in section, of a pole made in accordance with the present invention, showing two different connecting mechanisms at different elevations on the pole. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows an example of a plurality of concrete poles  10 , used for carrying electric power. Of course, it is known that similar poles could be used for other purposes, such as to support lighting fixtures, communications antennas, signs, and other structures. In this view, each pole  10  has three arms  12  attached to the pole  10 , and the arms  12  carry the power lines  14 . 
     FIG. 2  shows our previous invention for connecting the arms to the pole. The pole defines a central vertical axis  11 . A vertical base plate  18  has annular members or rings  16  welded to it. Between the top two rings  16 , a hole is drilled through the base plate  18 , and a threaded nut (not shown) is welded to the inner surface of the base plate  18  at the hole. Also, a piece of pipe or tube  24  is fixed to the outer surface of the base plate  18  and projects outwardly from the base plate  18  through the top two rings  16 , at the hole. The tube  24  is long enough that, as the concrete is poured, the unattached end of the tube  24  projects just beyond the outer surface of the concrete pole, leaving a path from the outside of the pole  10  to the nut. The pipe  24  surrounds the hole, so that a bolt  22  can extend through the pipe  24  and be threaded into the nut. One drawback of this prior art design is that the arm  12 , secured to the concrete pole  10  via the bolts  22 , creates a cantilevered load on the bolts  22 . The arm  12  imposes a vertical load on the bolts  22  at the face or outer surface of the pole  10 , while the bolts  22  are secured to the nut and thus to the base plate  18  inside the pole  10 , some radial distance away from the surface of the pole  10 . Thus, the load imposed by the arm  12  is a cantilevered load with a moment arm equal to the distance from the outer surface of the pole  10  to the nut welded to the inner surface of the base plate  18 . 
     FIGS. 3–7  show a first embodiment of an attachment assembly for the concrete pole  10 .  FIG. 3  is an exploded view of an attachment mechanism  30 , including a substantially vertical base plate  32 , having an inner surface  32 A, facing toward the central vertical axis  11  of the pole  10 , and an outer surface  32 B, facing away from the central vertical axis  11 . Two substantially vertical reinforcing bars  34  are secured, as by welding, to the inner surface  32 A and define a space between the reinforcing bars  34 . The base plate  32  defines upper and lower, vertically-aligned holes  36 , aligned with the space between the reinforcing bars  34 . Insert fasteners  38  are secured, also as by welding, to the base plate  32  at the holes  36  as explained below. 
   As seen in  FIGS. 6 and 7 , each of the insert fasteners  38  has first and second ends  40 ,  42 , respectively, and defines internal threads  38 A throughout a substantial portion of its length. Each insert fastener  38  has an enlarged annular portion  43  between its first and second ends  40 ,  42 . The enlarged annular portion  43  defines an outer shoulder  44  and an inner shoulder  46 . The inner shoulder  46  defines a beveled edge  48 . 
   As shown in  FIG. 4 , the outer shoulder  44  abuts the inner surface  32 A of the base plate  32 . The insert fastener  38  is secured, as by welding, to the base plate  32 . In this particular prototype, the fastener insert  38  is made of ASTM A 36 steel, is machined and threaded, and has a two inch outside diameter at the enlarged annular portion  43 . 
   The attachment mechanism  30  of  FIG. 3  is inserted into the existing reinforcing members that are normally used in making a concrete pole  10  before the concrete is cast. Looking at  FIGS. 4 and 5 , it can be seen that the assembly includes the vertical reinforcing rods  50 , which are spaced apart from each other, with all the reinforcing rods  50  being the same distance from the central axis  11  of the pole  10 . The rods  50  extend the full length of the pole  10 . While the rods  50  are referred to as vertical, they are actually at a slight angle to the vertical, to account for the taper of the pole  10 . The spiral reinforcing wire  54  surrounds the vertical rods  50  and is tied to the rods  50 . (The spiral wire  54  may be referred to as including a plurality of annular members, even though they do not exactly close to form a complete ring.) The rods  50  and spiral or annular members  54  form a cage. 
   The base plate  32  and the reinforcing bars  34  of the attachment mechanism  30  preferably are placed inside the spiral reinforcing wire  54 , as shown here. The reinforcing bars  34  of the attachment mechanism may be tied to the spiral reinforcing wire  54 . The base plate  32  preferably is welded to the reinforcing bars  34 , as well as to the insert fasteners  38 , before the attachment mechanism  30  is inserted inside the cage, and the base plate  32  is located so that the fastener inserts  38  project beyond the cage in order for their first ends  40  to be flush with the finished outer surface of the pole  10 . Then the concrete is cast around the rods  50 , the spiral wire  54 , the reinforcing rods  34 , the base plate  32 , and the fastener inserts  38 , preferably by spin casting. Several of the attachment mechanisms  30  of  FIG. 3  may be installed at various elevations of the pole  10 . In any case, the base plates  32  are installed so that the first ends  40  of the fasteners inserts  38  are substantially flush with the finished outer surface of the pole  10 , so that their internal threaded surface  38 A is accessible from outside the pole  10 . 
   In order to attach an arm  12  or any other attachment  12  to the pole  10 , bolts  56  are inserted through upper and lower holes  56 A in the attachment  12  and are threaded into the internal threads  38 A of the respective fastener inserts  38 . The holes  56 A in the attachment  12  have the same spacing as the holes  36  in the base plate  32 , so they align directly with each other for bolting the attachment  12  to the pole  10 . 
   The bolts  56  are very well supported by the structure of the pole  10  for several reasons. First, the base plate  32 , on which the fastener insert  38  is fixed, is very well supported. The base plate  32  is prevented from moving in any direction by the concrete  58  that surrounds it and by the reinforcing rods  34 , the vertical rods  50 , the spiral wire cage  54 , and the concrete  58  surrounding them. Furthermore, not only is the fastener insert  38  fully welded to the base plate  32 , but the outer shoulder  44  on the fastener insert  38  abuts the inside surface  32 A of the base plate  32 , providing an even stronger joint which is unlikely to pull out of the pole  10 . Since the bolts  56  are threaded into the fastener inserts  38  substantially over the entire length of the bolts  56 , and preferably up to the finished outer surface of the pole  10 , the bolts  56  are supported along their length, experiencing no cantilevered load, and making the attachment  12  stronger and less likely to fail. 
     FIGS. 8–11  show a second embodiment of an attachment mechanism  30 A for a concrete pole made in accordance with the present invention. Referring briefly to  FIG. 10 , this second embodiment  30 A comprises two of the attachment mechanisms  30  described above, which are diametrically opposed to each other and are joined by separators  60 , which interconnect the respective second ends  42  of the opposing fastener inserts  38 . In this preferred embodiment, the separators  60  are hollow pipes, although other rigid separator members could also be used. (The upper pipe  60  has been removed in  FIG. 10  for clarity of illustration.) 
   The ends of the pipe  60  fit axially over the second ends  42  of the opposed fastener inserts  38 . The pipe  60  slides over the second ends  42  of the fastener inserts  38  until the ends of the pipe  60  abut the inner shoulders  46  of the fastener inserts  38 . The pipe  60  is then fixed, as by welding, to the respective fastener inserts  38 . As shown in  FIG. 9 , the bevel edge  48  of the inner shoulder  46  allows for a full penetration fillet weld between the ends of the pipe  60  and the respective fastener inserts  38 . Of course, the length of the pipe  60  is carefully selected based on the pole diameter at that elevation, so that the first ends  40  of the respective fastener inserts  38  are substantially flush with the finished outer surface of the concrete pole  10  when the pipe  60  is abutting the shoulders  46  of the corresponding fastener inserts  38 . 
   Not only does this second embodiment provide a second attachment site for an arm  12 , but the pipe  60  also provides additional strength to the attachment mechanism  30 A. In a typical installation involving two bolts  56  affixing an arm  12 , the upper bolt  56  is in tension as the weight of the arm  12  tries to pull it away from the pole  10 , while the lower bolt  56  is under compression as the arm pushes in against the side of the pole  10 . The pipe  60  helps transfer some of the tensile and compressive forces across from one side of the pole  10  to other side. Furthermore, if another arm  12  is mounted to the other side of the pole  10  (as shown in the bottom embodiment of  FIG. 11 ), and if the loadings on both arms  12  are approximately equal, the pipe  60  itself bears much of the tensile or compressive force and tends to neutralize the loadings on the concrete portion of the pole. 
   Thus, the present invention provides a concrete pole with an attachment mechanism that is functionally far superior to the prior art. It will be obvious to those skilled in the art that modifications may be made to the embodiments described above without departing from the scope of the present invention.