Reinforced monopole construction

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.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Illustrated inFIG. 1is a monopole tower10typically having a polygonal shape in cross-section and tapering gracefully from the base12to the top at14. 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 top14is an antenna mast16and a pair of previously existing antenna arrays18and20. Outside the tower10are pipe columns22extending from the tower base12to the tower top14. As explained below, the pipe columns22are strapped28to the tower10and constructed of pipe lengths bolted together. The reinforcing pipe columns22permit the addition of antenna arrays24and26to the tower10and mast16.

FIG. 2andFIG. 3illustrate a four-pipe column and three-pipe column reinforcement of the tower10, respectively. The pipe columns22are strapped to the tower10by curved clamp segments30which bolt32together and to plates34. The plates34are welded36to the pipe columns22. This basic configuration can be adapted to permit additional pipe columns, if required. The bolted configuration spaces the pipe columns22from the tower10, in effect creating a much larger diameter tower with increased resistance to bending.FIG. 4illustrates in elevation the curved clamp segment30and attachment to the tower10and pipe columns22.

The pipe columns22are formed from pipe lengths typically 20 feet long with flanges or splice plates38welded to the pipe ends. Bolts40fasten the splice plates38together to form the pipe columns22. At lower elevations, the splice plates38are directly bolted together; however, at upper elevations, elastomeric pads42are bolted between the splice plates to provide compressible cushions in the pipe columns22. The elastomeric pads42reduce the bending moment on the pipe columns22at 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 pads42may vary with the vertical elevation on the monopole tower10. Each tower design and the proposed new antennas thereon will determine the need for elastomeric pads42, their compressibility and thickness.

At the tower base14, as shown inFIG. 5, the monopole tower10is bolted44to the concrete base46by a base flange48. Outside of the base flange48are separate base plates50for each pipe column22. The base plates50are directly welded to the lower most pipes of the pipe columns22and also bolted52to the concrete base46.

FIG. 6illustrates a monopole tower10that is reinforced with pipe columns22, as explained above. The monopole tower10is equipped with an existing antenna array54; however, the pipe columns22add sufficient strength to the monopole tower10that an additional vertical extension56of the monopole tower can be added to support another antenna array58. Ten to twenty feet may be added merely by welding the extension56to the existing tower at60.

As an alternative, inFIG. 7the pipe columns22are extended above the monopole tower10. The extended pipe columns62support an additional antenna array64above the existing antenna array54. At the very top, straps or plates66join the pipe columns62together by welding or bolting as desired.

FIGS. 8 through 19illustrate alternative constructions where certain of the polygonal panels of the monopole tower10must not be encumbered by straps about the tower.FIG. 8illustrates in plan view the monopole tower10and a plurality of pipe columns22and flanges68at elevations above the concrete base46.

InFIG. 9, an elevational view of a typical flanged pipe connection is shown. The upper flange comprises a collar plate70welded to the bottom of a pipe column22and a base plate72bolted74thereto. Similarly, a collar76is welded to the top of a pipe column22therebelow and bolted78to a cap plate80. A single central threaded rod82passes through the base plate72, an optional shim plate84, a top neoprene pad86, the cap plate80, a bottom neoprene pad88and a distribution plate90. The connection provides a flexible joint in both compression and tension, and, with pre-loading of the rod82, 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, inFIG. 10a lowermost pipe column22has a collar92welded thereto. The collar92is bolted94to a base plate96. A central threaded rod98passes through a top distribution plate100, top neoprene pad102, the base plate96, a bottom neoprene pad104and a bottom distribution pad106. The bottom distribution pad106is, in turn, supported above the concrete base46by a steel pipe108and plate110resting on the concrete base.

InFIGS. 11 through 14, attachments of the pipe columns22to the monopole tower that avoid field welding are shown. InFIGS. 11 and 12, vertical plates112are welded to each side of the pipe column22and bolted114through vertical slots to angles116. The angles116, in turn, are welded to a back plate118which is blind bolted120to the tower10.

In a similar manner, stabilizer attachments shown inFIGS. 13 and 14are blind bolted122to the tower10and comprise a back plate124and a pair of side plates126welded thereto. The side plates126, located to each side of a pipe column22, are bolted thereto by a threaded rod128passing through the column and slotted holes in the side plates.

FIG. 15illustrates that, in some instances, climbing pegs130attached to the monopole tower10can interfere with the flanges, brackets, stabilizers and straps disclosed above. In such situations, the connections disclosed below are advantageous.

FIG. 16illustrates a connection wherein a pipe column22is welded to a top pipe sleeve132, in turn welded to a base plate134. In like manner, a pipe column22therebelow is welded to a bottom pipe sleeve136, in turn welded to a cap plate138. The assembly is connected together by a center threaded rod140passing through a distribution plate142, a neoprene pad144, the base plate134, a second neoprene pad146and the cap plate138. The connection provides a flexible joint in both compression and tension, and, with pre-loading of the rod140, no separation of the pads from the cap and base plates will occur.

In a similar manner, inFIG. 17, a lowermost pipe column22is welded to a top pipe sleeve148, in turn welded to a base plate150. A center threaded rod152passes through a distribution plate154, a neoprene pad156, the base plate150, a second neoprene pad158and a bottom distribution pad160. The bottom distribution pad160is, in turn, supported above the concrete base46by a steel pipe108and plate110resting on the base as above.

FIG. 18illustrates a bracket assembly comprising a back plate162bolted by blind bolts164to the tower10. Welded to the back plate162are a pair of side plates166, in turn field welded to the pipe column22. The stabilizer assembly shown inFIG. 19is constructed in a manner similar to the bracket ofFIG. 18comprising a back plate168bolted with blind bolts170to the tower10. Welded to the back plate168are a pair of side plates172having vertical slotted holes through which passes a threaded rod174that also passes through the pipe column22. Thus, the stabilizer differs from the bracket in providing limited vertical freedom between the tower10and the pipe column22.