Patent Publication Number: US-2011067322-A1

Title: Porthole Retrofit Apparatus for a Monopole Tower

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     None. 
     FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention generally relates to the field of monopole towers. In particular, the invention is an apparatus which is mechanically fastened about a rough opening cut into a wall of a monopole tower so as to provide a porthole facilitating the passage of cables into and out of the tower. The apparatus and mechanical fastening means ensure the structural integrity of the tower and completely avoid the use of welding methods which are a primary cause of fires within monopole towers. 
     2. Background 
     A monopole tower is a cylindrically-shaped, hollow structure, typically composed of steel, fixed at its lower end to a foundation and having a support structure at its upper end. Monopole towers are used by the telecommunications industry within cell sites to form a cellular telephone network. 
     A cell site usually includes at least one monopole tower, two or more antennas, and other electronic equipment. Antennas are placed onto the support structure at the top of the monopole tower. Transmitters, receivers, transceivers, digital signal processors, control electronics, GPS receivers, and power sources are provided within a shelter immediate adjacent to the base of the tower. Cables are provided within the interior of the monopole between the antennas at the top of the tower and equipment within the shelter at the base of the tower. 
     The expansion of antenna capacity at the top of a monopole could require the addition of new openings at one or both ends of a tower. The addition of a new opening along a monopole tower requires a skilled welder to cut a crude opening into the wall structure of a tower. A typical crude opening includes irregular edges which cut or otherwise damage cables entering and exiting the tower. A porthole apparatus is secured about the hole and then welded onto the monopole structure to as to provide a smooth and uniform opening through which cables pass without damage. The welding process produces molten metal which invariably falls into the hollow center of the monopole often initiating a fire. Such fires are particularly difficult to extinguish due to the stack effect. 
     The stack effect is the movement of air caused by buoyancy into and out of a vertically-disposed, hollow structure, such as a monopole tower. A positive or upward buoyancy results when hot, less-dense air is produced within a monopole surrounded by cooler, more-dense air. The greater the thermal difference between internal and external conditions and the taller the structure, the greater the buoyancy force and stack effect. The stack effect enables a fire at the base of a monopole tower to quickly progress up along the length of the tower, thus consuming cables within the tower and damaging antennas at the top of the tower. Furthermore, heat generated within the tower is often sufficient to melt or weaken the structure causing it to bend and/or collapse. 
     Coberly, U.S. Pat. No. 7,234,276, describes a porthole apparatus having a rectangular frame with a planar-shaped bar disposed about the periphery of the frame. The rectangular frame traverses a crude opening within the monopole so that the bar contacts the interior surface of the monopole. The rectangular frame and bar are then welded onto the tower. The weld specifications for monopole towers require welds to traverse the wall thickness of the pole so as to avoid a mechanical weakening of the tower. Accordingly, the design and method described by Coberly are unable to prevent molten metal from falling into the center cavity of a tower so as to avoid the possibility of a fire therein. 
     As is readily apparent from the discussions above, the related arts do not provide an apparatus for use about a crude opening along a monopole tower which avoids the fire hazards associated with welding while maintaining the structural integrity of the tower. 
     Therefore, what is required is a frame apparatus which is mechanically attachable to a monopole structure about a crude opening so as to avoid the fire hazard associated with welding, to minimize the structural impact of the crude opening along the tower, and to provide a port through which cables enter and exit the tower without damage. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a frame apparatus which is mechanically attachable to a monopole structure about a crude opening so as to avoid the fire hazard associated with welding, to minimize the structural impact of the crude opening along the tower, and to provide a port through which cables enter and exit the tower without damage. 
     Various embodiments of the apparatus include a frame, a front plate, a back plate, and a plurality of fasteners. The center open portion of the frame forms the porthole. The front plate has an opening which fits about the frame and is contoured to match the exterior surface of the tower. The back plate has an opening shaped so as to also fit about the frame. The back plate is fixed to the frame so that the frame extends from both sides of the back plate and through the crude opening cut into a side of a monopole tower. The back plate is contoured to match the interior surface along the tower. The front and back plates are disposed about the crude opening and attached to the wall via the fasteners. Each fastener passes through holes mutually aligned along each of the front plate, back plate, and tower. 
     Several advantages are offered by the invention. The invention avoids onsite welding, thus avoiding a primary cause of fires within monopole towers. The invention is customizable for a variety of monopole designs. The invention eliminates pre-heating of a monopole during cold weather installations. The invention maximizes antenna capacity of a monopole tower while minimizing attachment of cables along the exterior of the tower. 
     
       
         
           
               
             
               
                   
               
               
                 REFERENCE NUMERALS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1 
                 Apparatus 
               
               
                   
                 2 
                 Frame 
               
               
                   
                 3 
                 Front plate 
               
               
                   
                 4 
                 Back plate 
               
               
                   
                 5 
                 Fastener 
               
               
                   
                 6 
                 Porthole 
               
               
                   
                 7 
                 Weld seam 
               
               
                   
                 8 
                 Width 
               
               
                   
                 9 
                 Length 
               
               
                   
                 10 
                 Height 
               
               
                   
                 11 
                 Opening 
               
               
                   
                 12 
                 Monopole 
               
               
                   
                 13 
                 Wall 
               
               
                   
                 14 
                 Interior surface 
               
               
                   
                 15 
                 Exterior surface 
               
               
                   
                 16 
                 Bend 
               
               
                   
                 17 
                 Bolt 
               
               
                   
                 18 
                 Washer 
               
               
                   
                 19 
                 Lock washer 
               
               
                   
                 20 
                 Nut 
               
               
                   
                 21 
                 Interlayer 
               
               
                   
                 22 
                 Interlayer 
               
               
                   
                 23 
                 Opening 
               
               
                   
                 24 
                 Opening 
               
               
                   
                 25 
                 Opening 
               
               
                   
                 26 
                 Opening 
               
               
                   
                 27 
                 Opening 
               
               
                   
                 28 
                 Interior 
               
               
                   
                 29 
                 Exterior 
               
               
                   
                 30 
                 Opening 
               
               
                   
                 31 
                 Front surface 
               
               
                   
                 32 
                 Back surface 
               
               
                   
                 33 
                 Thickness 
               
               
                   
                 34 
                 Crude opening 
               
               
                   
                 35 
                 Thickness 
               
               
                   
                   
               
            
           
         
       
     
    
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
       Additional aspects, features, and advantages of the invention will be understood and will become more readily apparent when the invention is considered in the light of the following description made in conjunction with the accompanying drawings. 
         FIG. 1  is a perspective view illustrating the apparatus including a frame with porthole, front plate, back plate, and a plurality of fasteners in accordance with an embodiment of the invention. 
         FIG. 2  is a front view illustrating attachment of a front plate about a central frame with porthole via a plurality of fasteners in accordance with an embodiment of the invention. 
         FIG. 3  is a back view illustrating attachment of a back plate about a central frame with porthole in accordance with an embodiment of the invention. 
         FIG. 4  is an exploded section view illustrating attachment of a back plate about a central frame with porthole via a weld seam and placement of a front plate about the frame in accordance with an embodiment of the invention. 
         FIG. 5  is a partial section view illustrating attachment of an apparatus along three side walls of a twelve-sided monopole in accordance with an embodiment of the invention. 
         FIG. 6  is an enlarged partial section view illustrating arrangement of a fastener through a front plate, side wall, and back plate in accordance with an embodiment of the invention. 
         FIG. 7  is an enlarged partial section view illustrating arrangement of a fastener through a front plate, optional interlayer, side wall, optional interlayer, and back plate in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to several preferred embodiments of the invention that are illustrated in the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts. The drawings are not to precise scale. 
     Referring now to  FIGS. 1-3 , the apparatus  1  includes a frame  2  which is shaped so as to form a porthole  6  and extends in a generally horizontal arrangement. The frame  2  could be composed a several planar-shaped or arcuate-shaped plates which are welded or otherwise joined to form a single structure. For example,  FIGS. 1-3  show a four-sided frame  2  composed of four planar-shaped elements. The frame  2  could likewise include a single circular-shaped element, two or more arcuate-shaped elements, or three or more planar elements. It is also possible for the frame  2  to include both arcuate and generally linear elements providing an infinite variety of opening configurations for the porthole  6 . 
     A front plate  3  and a back plate  4  are disposed about the frame  2  in a substantially perpendicular arrangement. The front plate  3  is a shaped element having an opening  11  which closely approximates the outer perimeter of the frame  2 . For example,  FIG. 2  shows the front plate  3  disposed about the frame  2  so that the dimensions of the opening  11  are slightly larger than the width  8  and length  9  of the rectangular-shaped frame  2 . The back plate  4  is likewise a shaped element having an opening  30  which closely approximates the outer perimeter of the frame  2 . For example,  FIG. 3  shows the back plate  4  disposed about the frame  2  so that the dimensions of the opening  30  are slightly larger than the width  8  and length  9  of the rectangular-shaped frame  2 . In preferred embodiments, the front plate  3  and back plate  4  should freely slide along the frame  2  without binding. The openings  11 ,  30  are cut into the front plate  3  and back plate  4 , respectively, via methods understood in the art. The lateral dimensions and thickness of the front plate  3  and back plate  4  are design dependent, and based in part on the size the porthole  6  and load requirements imposed by the modified monopole tower. In preferred embodiments, the lateral dimensions for the front plate  3  and back plate  4  are approximately the same. 
     The front plate  3  and back plate  4  are mechanically fastened to each other via a plurality of fasteners  5 . The fasteners  5  are disposed adjacent to the outer edge of the front plate  3  and back plate  4  and the respective openings  11 ,  30 . The location and number of fasteners  5  are design dependent and determined in part by the stress field within the monopole structure adjacent to the apparatus  1 . 
     In preferred embodiments, the front plate  3 , back plate  4 , frame  2 , and fasteners  5  could be composed of a metal coated with a rust inhibitor, one example being zinc, and having at least the mechanical strength of the material comprising the monopole. In other embodiments, the front plate  3 , back plate  4 , frame  2 , and/or fasteners  5  could be composed of a non-metallic composite with or without fiber reinforcement or other high-strength, low-weight material. 
     Referring now to  FIG. 4 , the frame  2  is disposed within the opening  30  along the back plate  4  with a height  10  so that a portion of the frame  2  extends beyond the front surface  31  and the back surface  32  of the back plate  4 . In preferred embodiments, the length of extension beyond the front surface  31  should be greater than that beyond the back surface  32  so as to accommodate the thickness  33  of the wall  13  comprising the monopole  12 , as represented in  FIGS. 4 and 5 , and the thickness  35  of the front plate  3  with or without angular adjustments, and further to allow a portion of the frame  2  to extend beyond the front plate  3 . The frame  2  is fixed or otherwise attached to the edges of the opening  30  along the back plate  4  via a weld seam  7 . The back plate  4  is welded to the frame  2  prior to installation onto a monopole  12 . 
     The front plate  3  is separately movable within the exterior  29  with respect to the sub-assembly formed by the frame  2  and back plate  4 . The front plate  3  is placed over the frame  2  so that the opening  11  surrounds the frame  2 . Alignment of the openings  11 ,  30  about the frame  2  ensures an unobstructed porthole  6  enabling the passage of one or more cables between the interior  28  and exterior  29 . 
     In preferred embodiments, the frame  2  could closely approximate the general shape of the crude opening  34  cut into the monopole  12 . The frame  2  should be dimensionally smaller than the crude opening  34  so as to allow the frame  2  to be freely insertable into the crude opening  34  from the interior  28  of the monopole  12 , as represented in  FIG. 4 . 
     The crude opening  34  is cut into the monopole  12  using a flameless device and/or method in order to avoid the introduction of hot or molten metal into the center of the monopole  12 . Exemplary flameless devices include, but are not limited to, a saw with diamond tip cutting blade, a water jet, and a laser. The frame  2  covers the otherwise jagged or irregular shaped crude opening  34 . 
     Referring now to  FIG. 5 , the apparatus  1  is shown attached to a portion of a monopole  12  having a cross section comprised of twelve generally planar walls  13 . It is important to note that the apparatus  1  is applicable to a variety of monopole  12  designs, including configurations having more or less than twelve planar-shaped walls  13 , as well as circular and other shaped walls  13 . 
     The apparatus  1  is attached to the monopole  12  so that the back plate  4  contacts the interior surface  14  and the front plate  3  contacts the exterior surface  15  of two or more walls  13  comprising the monopole  12 . This arrangement places the front plate  3  along the exterior  29  and the back plate  4  within the interior  28  of the monopole  12 . The angular contour of the monopole  12  is replicated along the front plate  3  and back plate  4  by bends  16  disposed in a symmetrical arrangement about the frame  2 . In preferred embodiments, the front plate  3  and back plate  4  should contact the respective exterior and interior surfaces  15 ,  14  along the monopole  12 . In other embodiments, the front plate  3  and back plate  4  could include three or more bends  16  or a curved or arcuate profile. 
     A plurality of fasteners  5  are used to secure the front plate  3  to the back plate  4  and frame  2 . This arrangement ensures the apparatus  1  is secured to the walls  13  via compression of the walls  13  between the front plate  3  and the back plate  4 . 
     Referring now to  FIG. 6 , an exemplary fastener  5  is shown including a bolt  17 , a washer  18 , a lock washer  19 , and a nut  20 . However, other high-strength fasteners  5  are likewise applicable. The front plate  3 , wall  13 , and back plate  4  each include an opening  23 ,  24 , and  25 , respectively, which align to allow the passage of the bolt  17  without binding. Openings  23 - 25  could be mechanically drilled into the front plate  3 , wall  13 , and back plate  4  either during fabrication of the apparatus  1  or during installation of the apparatus  1  onto a monopole  12 . 
     In preferred embodiments, the bolt  17  is positioned perpendicular to the plane of the front plate  3  and back plate  4  immediately surrounding the bolt  17 . The washer  18  and lock washer  19  are separately disposed about the front plate  3 , wall  13 , and back plate  4 , as represented in  FIG. 6 , so as to be perpendicular to the centerline of the bolt  17 . The nut  20  is threaded onto the bolt  17  and tightened so as to apply a compressive force onto the front plate  3  and back plate  4 , and thereafter onto the wall  13 . 
     In some embodiments, it might be advantageous to include an interlayer  21 ,  22  between the front plate  3  and wall  13  and/or between the back plate  4  and wall  13 , as shown in  FIG. 7 . The interlayers  21 ,  22  could completely or partially surround the frame  2  or reside immediately adjacent to and surround each fastener  5 . The interlayers  21 ,  22  could be a composition that is applied in flowable form, much like a paint or a caulk, or solid form, examples including but not limited to a film, gasket, or plate-shaped element, between the respective elements. 
     The front plate  3 , interlayer  21 , wall  13 , interlayer  22 , and back plate  4  each include an opening  23 ,  26 ,  24 ,  27 , and  25 , respectively, which align to allow the passage of the bolt  17  without binding. Openings  23 - 27  could be mechanically drilled into the respective elements either during fabrication of the apparatus  1  or during installation of the apparatus  1  onto a monopole  12 . When the interlayer  21 ,  22  is applied in a flowable form, the opening  26 ,  27  through each interlayer  21 ,  22  could be formed by masking the applicable surface. In some embodiments, the interlayers  21 ,  22  could extend into the respective openings  23 ,  25  along the front plate  3  and back plate  4 . In other embodiments, the interlayers  21 ,  22  could extend into the respective openings  23 ,  25  along and cover the respective front plate  3  and back plate  4  immediately adjacent to contact surface with the lock washer  19  and washer  18 . 
     In one example, the interlayers  21 ,  22  could be an adhesive which resides along one surface of the front plate  3  and back plate  4  and immediately contacts the exterior surface  15  and interior surface  14  of the walls  13 , respectively. The adhesive could temporarily hold the front plate  3  and back plate  4  onto the monopole  12  during assembly of the apparatus  1  onto the monopole  12 . 
     In other embodiments, the interlayers  21 ,  22  could provide a thermal or electrical barrier or short circuit between the monopole  12  and the front plate  3 , back plate  4 , and/or fastener  5 . The interlayers  21 ,  22  could be composed of materials including, but not limited to, a compressible or non-compressible polymer, elastomer, or rubber composition. These embodiments might also require the fasteners  5  to be composed of or coated with a thermally or electrically non-conductive material. 
     In yet other embodiments, the interlayers  21 ,  22  could provide a fluid barrier which prevents water or air infiltration along the exterior  29  into the interior  28  of the monopole  12 . The interlayers  21 ,  22  could be composed of materials including, but not limited to, a compressible or non-compressible polymer, elastomer, or rubber composition. This arrangement would be beneficial when the interior  28  of the monopole  12  is sealed from the outside environment. 
     The description above indicates that a great degree of flexibility is offered in terms of the invention. Although various embodiments have been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.