Abstract:
A new reinforced monopole cellular telephone tower comprises a plurality of flanged pipes strapped to the exterior of the monopole tower. The straps retain the pipes to the monopole tower in a spaced relationship, and the flanges permit the pipes to be bolted together. The flanged pipes form columns about the monopole tower. Elastomeric pads are placed between the flanges at some or all of the bolted flanged connections to reduce the bending moment at the connections. The thickness of the pads may vary depending on vertical location, and some connections at lower levels may not require the pads. The elastomeric pads allow the upper portion of the monopole tower to retain most of its flexibility without unduly overstressing the pipe reinforcing that is undergoing high compression during high wind conditions.

Description:
This application claims the benefit of provisional patent application No. 60/475,672 filed Jun. 4, 2003. 

   BACKGROUND OF THE INVENTION 
   The field of the invention pertains to antenna towers and, in particular, to towers for cellular phone antennas, sometimes popularly known as cell towers. Cell towers commonly are constructed in one of two forms. Either the towers are constructed of open steel truss work or a single hollow tube of welded steel typically referred to as a monopole. In both varieties, the towers are fastened to a concrete base and gracefully taper upwardly more than 100 feet to sometimes 220 feet. Cellular telephone antennas are quite massive in appearance in comparison with radio and other common antennas; therefore, considerable windloading is applied to a cell tower by the one or two antennas normally installed. 
   The popularity of cellular telephones has resulted in a demand for additional capacity and, therefore, a demand for additional cellular telephone antennas and cell towers; however, cell towers are expensive to install and considered very unaesthetic by the general public. As a result, there is a demand for devices to reinforce existing cell towers to thereby permit installation of additional cellular telephone antennas. Examples of monopole cell towers and cellular telephone antennas are disclosed in U.S. Pat. No. 5,333,436 and U.S. Pat. No. 6,028,566. The former reveals a modular bolt-together form of cell tower with a massive antenna. The latter reveals the size and complexity of a cellular telephone antenna thereby emphasizing the bending moment that may be applied to the cell tower by the windage of the antenna. U.S. Pat. No. 6,173,537 illustrates a monopole with paraboloidal antennas commonly in use and likewise capable of producing considerable windage. 
   Numerous attempts have been made to reinforce monopole cell towers and previous antenna and utility towers prior to the development of cellular telephones. U.S. Pat. No. 6,453,636 discloses a plurality of half cylinders bolted about a monopole tower. Likewise, U.S. Pat. Appln. Pub. No. US2002/0056250 discloses a plurality of half cylinders bolted about a monopole tower. In contrast, U.S. Pat. Appln. Pub. No. US2002/0140621 discloses a concrete fill placed inside the monopole to provide more stiffening in compression to the monopole and the addition of external steel plates to the monopole. 
   U.S. Pat. Appln. Pub. No. US2002/0170261 discloses a plurality of square tubes attached by straps to the exterior of the monopole tower. The straps include square tubing collars through which the square tubing passes. U.S. Pat. Appln. Pub. No. US2002/0176951 discloses a load redistribution mechanism generally about the base of the monopole tower. U.S. Pat. Appln. Pub. No. US2003/0000165 discloses a precast post-tensioned segmental pole system wherein the post tensioning cables are located within the hollow interior of the tower. Fiber reinforced polymer composite panels bonded to the exterior surfaces of a steel monopole tower to strengthen the tower are disclosed in U.S. Pat. Appln. Pub. No. US2003/0010426. Various ways of covering the tower are shown. 
   U.S. Pat. Appln. Pub. No. US2003/0026923 discloses semi-circular sleeves to enclose and reinforce a monopole tower. In one embodiment, a compressible material is snugly fitted between the sleeve and the tower to transmit shear forces between the tower and the sleeve. 
   Historically, earlier utility towers of reinforced design are shown in U.S. Pat. No. 811,435 and U.S. Pat. No. 4,216,636 wherein a plurality of rods and connectors are used in open lattice patterns to construct the towers. An open lattice tower construction is shown in U.S. Pat. No. 854,366 wherein the open lattice surrounds and supports an insulated conduit therein. U.S. Pat. No. 1,786,631 discloses an early monopole utility tower with features to insulate the electric cables within the tower. 
   SUMMARY OF THE INVENTION 
   The new reinforced monopole construction comprises a plurality of flanged pipes strapped to the exterior of the monopole tower. The straps retain the pipes to the monopole tower in a spaced relationship, and the flanges permit the pipes to be bolted together. The flanged pipes form columns about the monopole tower. 
   Elastomeric pads are placed between the flanges at some or all of the bolted flanged connections to reduce the bending moment at the connections. The thickness of the pads may vary depending on vertical location, and some connections at lower levels may not require the pads. The elastomeric pads allow the upper portion of the monopole tower to retain most of its flexibility without unduly overstressing the pipe reinforcing that is undergoing high compression during high wind conditions. 
   As an option, the pipe reinforcing may be extended above the monopole tower to form a structure for attaching the additional antennas, or the monopole tower itself may be extended above its previous height. 
   Although directed to reinforcing cellular telephone towers, the new reinforced monopole construction is equally applicable to monopole electric utility towers and lighting towers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a reinforced monopole tower in elevation view from base to antennas; 
       FIG. 2  is a first typical cross-section of the reinforced monopole construction; 
       FIG. 3  is a second alternative typical cross-section of the reinforced monopole construction; 
       FIG. 4  is an elevational section showing a typical attachment between the reinforcement pipes and the monopole and a typical attachment between the pipes; 
       FIG. 5  is a plan view of the foundation attachment; 
       FIG. 6  illustrates a first alternative top extension of a reinforced monopole tower; 
       FIG. 7  illustrates a second alternative top extension of a reinforced monopole tower; 
       FIG. 8  is a plan view of an alternative construction that avoids field welding; 
       FIG. 9  is an elevational view of a pipe column reinforcement connection that avoids field welding; 
       FIG. 10  is an elevational view of a pipe column reinforcement foundation connection that avoids field welding; 
       FIG. 11  is a plan view of a typical pipe column bracket that avoids field welding; 
       FIG. 12  is an elevational view of the bracket of  FIG. 11 ; 
       FIG. 13  is a plan view of a typical pipe column stabilizer that avoids field welding; 
       FIG. 14  is an elevational view of the stabilizer of  FIG. 13 ; 
       FIG. 15  is a plan view of an alternative construction that uses field welding to advantage; 
       FIG. 16  is an elevational view of a pipe column connection that uses field welding to advantage; 
       FIG. 17  is an elevational view of a pipe column foundation connection that uses field welding to advantage; 
       FIG. 18  is a plan view of a typical pipe column bracket that uses field welding to advantage; and 
       FIG. 19  is a plan view of a typical pipe column stabilizer that uses field welding to advantage. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Illustrated in  FIG. 1  is a monopole tower  10  typically having a polygonal shape in cross-section and tapering gracefully from the base  12  to the top at  14 . Such towers are usually 100 feet to 220 feet in height and constructed of steel plates welded together. The towers are hollow, thereby allowing electric cables and microwave guides to be contained and protected inside. Above the tower top  14  is an antenna mast  16  and a pair of previously existing antenna arrays  18  and  20 . Outside the tower  10  are pipe columns  22  extending from the tower base  12  to the tower top  14 . As explained below, the pipe columns  22  are strapped  28  to the tower  10  and constructed of pipe lengths bolted together. The reinforcing pipe columns  22  permit the addition of antenna arrays  24  and  26  to the tower  10  and mast  16 . 
     FIG. 2  and  FIG. 3  illustrate a four-pipe column and three-pipe column reinforcement of the tower  10 , respectively. The pipe columns  22  are strapped to the tower  10  by curved clamp segments  30  which bolt  32  together and to plates  34 . The plates  34  are welded  36  to the pipe columns  22 . This basic configuration can be adapted to permit additional pipe columns, if required. The bolted configuration spaces the pipe columns  22  from the tower  10 , in effect creating a much larger diameter tower with increased resistance to bending.  FIG. 4  illustrates in elevation the curved clamp segment  30  and attachment to the tower  10  and pipe columns  22 . 
   The pipe columns  22  are formed from pipe lengths typically 20 feet long with flanges or splice plates  38  welded to the pipe ends. Bolts  40  fasten the splice plates  38  together to form the pipe columns  22 . At lower elevations, the splice plates  38  are directly bolted together; however, at upper elevations, elastomeric pads  42  are bolted between the splice plates to provide compressible cushions in the pipe columns  22 . The elastomeric pads  42  reduce the bending moment on the pipe columns  22  at higher elevations thereby allowing the lower cross-section higher portions of the monopole tower to continue to flex without undue compressive stress on the pipe columns. Thus, under high wind loading, the tower neutral axis shifts toward the pipes on the tension side of the tower. The thickness or compressibility of the elastomeric pads  42  may vary with the vertical elevation on the monopole tower  10 . Each tower design and the proposed new antennas thereon will determine the need for elastomeric pads  42 , their compressibility and thickness. 
   At the tower base  14 , as shown in  FIG. 5 , the monopole tower  10  is bolted  44  to the concrete base  46  by a base flange  48 . Outside of the base flange  48  are separate base plates  50  for each pipe column  22 . The base plates  50  are directly welded to the lower most pipes of the pipe columns  22  and also bolted  52  to the concrete base  46 . 
     FIG. 6  illustrates a monopole tower  10  that is reinforced with pipe columns  22 , as explained above. The monopole tower  10  is equipped with an existing antenna array  54 ; however, the pipe columns  22  add sufficient strength to the monopole tower  10  that an additional vertical extension  56  of the monopole tower can be added to support another antenna array  58 . Ten to twenty feet may be added merely by welding the extension  56  to the existing tower at  60 . 
   As an alternative, in  FIG. 7  the pipe columns  22  are extended above the monopole tower  10 . The extended pipe columns  62  support an additional antenna array  64  above the existing antenna array  54 . At the very top, straps or plates  66  join the pipe columns  62  together by welding or bolting as desired. 
     FIGS. 8 through 19  illustrate alternative constructions where certain of the polygonal panels of the monopole tower  10  must not be encumbered by straps about the tower.  FIG. 8  illustrates in plan view the monopole tower  10  and a plurality of pipe columns  22  and flanges  68  at elevations above the concrete base  46 . 
   In  FIG. 9 , an elevational view of a typical flanged pipe connection is shown. The upper flange comprises a collar plate  70  welded to the bottom of a pipe column  22  and a base plate  72  bolted  74  thereto. Similarly, a collar  76  is welded to the top of a pipe column  22  therebelow and bolted  78  to a cap plate  80 . A single central threaded rod  82  passes through the base plate  72 , an optional shim plate  84 , a top neoprene pad  86 , the cap plate  80 , a bottom neoprene pad  88  and a distribution plate  90 . The connection provides a flexible joint in both compression and tension, and, with pre-loading of the rod  82 , no separation of the pads from the cap and base plates will occur, regardless of tension or compression forces caused by wind loading of the monopole towers. Moreover, no field welding of the connection is required. 
   In a similar manner, in  FIG. 10  a lowermost pipe column  22  has a collar  92  welded thereto. The collar  92  is bolted  94  to a base plate  96 . A central threaded rod  98  passes through a top distribution plate  100 , top neoprene pad  102 , the base plate  96 , a bottom neoprene pad  104  and a bottom distribution pad  106 . The bottom distribution pad  106  is, in turn, supported above the concrete base  46  by a steel pipe  108  and plate  110  resting on the concrete base. 
   In  FIGS. 11 through 14 , attachments of the pipe columns  22  to the monopole tower that avoid field welding are shown. In  FIGS. 11 and 12 , vertical plates  112  are welded to each side of the pipe column  22  and bolted  114  through vertical slots to angles  116 . The angles  116 , in turn, are welded to a back plate  118  which is blind bolted  120  to the tower  10 . 
   In a similar manner, stabilizer attachments shown in  FIGS. 13 and 14  are blind bolted  122  to the tower  10  and comprise a back plate  124  and a pair of side plates  126  welded thereto. The side plates  126 , located to each side of a pipe column  22 , are bolted thereto by a threaded rod  128  passing through the column and slotted holes in the side plates. 
     FIG. 15  illustrates that, in some instances, climbing pegs  130  attached to the monopole tower  10  can interfere with the flanges, brackets, stabilizers and straps disclosed above. In such situations, the connections disclosed below are advantageous. 
     FIG. 16  illustrates a connection wherein a pipe column  22  is welded to a top pipe sleeve  132 , in turn welded to a base plate  134 . In like manner, a pipe column  22  therebelow is welded to a bottom pipe sleeve  136 , in turn welded to a cap plate  138 . The assembly is connected together by a center threaded rod  140  passing through a distribution plate  142 , a neoprene pad  144 , the base plate  134 , a second neoprene pad  146  and the cap plate  138 . The connection provides a flexible joint in both compression and tension, and, with pre-loading of the rod  140 , no separation of the pads from the cap and base plates will occur. 
   In a similar manner, in  FIG. 17 , a lowermost pipe column  22  is welded to a top pipe sleeve  148 , in turn welded to a base plate  150 . A center threaded rod  152  passes through a distribution plate  154 , a neoprene pad  156 , the base plate  150 , a second neoprene pad  158  and a bottom distribution pad  160 . The bottom distribution pad  160  is, in turn, supported above the concrete base  46  by a steel pipe  108  and plate  110  resting on the base as above. 
     FIG. 18  illustrates a bracket assembly comprising a back plate  162  bolted by blind bolts  164  to the tower  10 . Welded to the back plate  162  are a pair of side plates  166 , in turn field welded to the pipe column  22 . The stabilizer assembly shown in  FIG. 19  is constructed in a manner similar to the bracket of  FIG. 18  comprising a back plate  168  bolted with blind bolts  170  to the tower  10 . Welded to the back plate  168  are a pair of side plates  172  having vertical slotted holes through which passes a threaded rod  174  that also passes through the pipe column  22 . Thus, the stabilizer differs from the bracket in providing limited vertical freedom between the tower  10  and the pipe column  22 .