Patent Publication Number: US-7905069-B1

Title: Reinforcing systems to strengthen monopole towers

Description:
BACKGROUND OF THE INVENTION 
     One method for reinforcing monopole tower structures, such as a tower supporting communication antennas and herein referred to as a monopole or tower, comprises attaching flat plates or tubes to the monopole by welding or structural adhesives or bolts, for example, as disclosed in U.S. Pat. No. 6,694,698. These reinforcing elements or members are placed against the flat surfaces of an 8-sided, 12-sided, 16-sided or 18-sided monopole and act integral with the modified structure once connected. The challenge facing a welded solution is that fires can ignite if sparks fall onto exposed cables or the surrounding ground surface. The challenge facing adhered reinforcing members is that the monopole surface must be carefully prepared in advance of bonding reinforcing plates with adhesive to the pole and installations become difficult to manage in rain or in very cold weather conditions. The challenge facing bolted-on members using flat plates is that the bolt spacing must be short to control localized buckling of the flat plates in compression due to the low moment of inertia of a plate section. Other methods and apparatus for reinforcing monopole towers are disclosed in U.S. Pat. No. 6,453,636, No. 6,901,717, No. 6,915,618, No. 7,116,282 and published U.S. application No. 2004/0139665. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to monopole reinforcing systems that include new reinforcing members and members which connect the reinforcing members to an existing monopole such that 1) local buckling of the reinforcing members do not occur under axial compression forces, 2) no overstress conditions occur in the reinforcing members in tension or compression, and 3) axial forces are transferred from the pole to the reinforcing members through shear resistance of the connector members. A desirable feature is that the reinforcing systems of the invention optimize the vertical distance or spacing between the connectors along the length of the reinforcing members to reduce field installation time. 
     The reinforcing members of the invention have cross-sections which provide increased moments of inertia to increase their local buckling capacity. Connectors are installed between the ends of the reinforcing members to resist tensile forces normal to the surface of the pole shaft. These connectors may also transfer shear forces or be used only for the purpose of carrying tension. The reinforcing members are placed symmetrically around the monopole structure and can use as few as three members and up to any practical limit not exceeding the total number of flats or space available around the monopole. 
     The present invention includes reinforcing members of three cross-section types and three types of connectors for attaching the reinforcing members to an existing monopole. Splice connectors allow for accommodating slip joints in the existing monopole, and the reinforcing systems allow for strengthening an 8-sided, 12-sided, 16-sided, 18-sided, and a round monopole. The selection of the connector used depends on the load transfer method preferred and the location of the connector along the length of the reinforcing member. These locations are identified as the reinforcing member&#39;s end, splice and mid-section. The types of reinforcing members are (1) a folded or angle type, (2) a channel type, and (3) a ribbed type. 
     The connector types are (1) a tensile connector, (2) a tensile shear connector, and (3) a plate with shear pins. The purpose of the connectors are to transfer excess axial loads being placed into the monopole under wind loading into the external reinforcing members, thereby maintaining allowable stress levels in the monopole. These axial loads are transferred from the monopole into the reinforcing members using tensile shear connectors and/or plates with shear pins. Another purpose of the connectors is to eliminate localized buckling in the reinforcing members when they are under compression. This is accomplished by restraining each reinforcing member from movement out of its generally vertical plane. This is accomplished by using tensile connectors or tensile shear connectors. 
     Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary section of a monopole wall with a folded or angled reinforcing member mounted on the wall in accordance with one embodiment of the invention; 
         FIG. 2  is a fragmentary section of a monopole wall with a channel-type reinforcing member mounted on the wall in accordance with a second embodiment of the invention; 
         FIG. 3  is a fragmentary section of a monopole wall with a rib-type reinforcing member mounted on the wall in accordance with a third embodiment of the invention; 
         FIG. 4  are fragmentary sections of a monopole wall and reinforcing member with a tensile-type connector for securing the reinforcing member to the wall; 
         FIG. 5  are fragmentary sections of a monopole wall and reinforcing member with a tensile shear connector connecting the reinforcing member to the wall; 
         FIG. 6  are fragmentary sections of a monopole wall and reinforcing member with a shear plate and pin connector connecting the reinforcing member to the wall; 
         FIG. 7  is an end view of the angle-type reinforcing member shown in  FIG. 1  and mounted on a monopole wall; 
         FIG. 8  is a greatly reduced horizontal section through a monopole wall and having folded or angle reinforcing members connected to the wall in accordance with the invention; 
         FIG. 9  is a greatly reduced horizontal section of a round monopole wall and having folded or angle reinforcing members connected to the wall in accordance with the invention; 
         FIG. 10  is a fragmentary elevational view of a monopole and an attached reinforcing member as shown in  FIG. 8 ; 
         FIG. 11  is a fragmentary elevational view of a round monopole and an attached reinforcing member as shown in  FIG. 9 ; 
         FIG. 12  is a fragmentary elevational view similar to  FIG. 10  and with an angle reinforcing member attached to the monopole corner with the tensile connectors and tensile shear connectors shown in  FIGS. 4 and 5 ; 
         FIG. 13  is a fragmentary elevational view similar to  FIG. 12  and showing the assembly of shear pin connectors at opposite end portions of the reinforcing member; 
         FIG. 14  is a perspective view of a shear pin connector as shown in  FIG. 13 ; 
         FIG. 15  is a horizontal section of a shear pin connector on a folded or angled reinforcing member; 
         FIG. 16  is a fragmentary elevational view of two vertically aligned angle reinforcing members joined together by splice plates and holes for receiving tensile shear connectors; 
         FIGS. 17 and 18  are fragmentary elevational views similar to  FIG. 16  and showing splice plates connecting two angle reinforcing members together with shear pin and tensile shear connectors; 
         FIG. 19  is a fragmentary elevational view of two vertically aligned reinforcing members joined together with double shear splice plates anchored to ribs welded to the reinforcing members; 
         FIGS. 20 and 21  are sections similar to  FIG. 2  and showing attachment of channel-type reinforcing members to a monopole wall; 
         FIG. 22  is a horizontal section similar to  FIG. 8  and showing the attachment of the channel-type reinforcing members of  FIG. 20  to a monopole wall; 
         FIG. 23  is a fragmentary elevational view of a monopole with attached channel-type reinforcing members as shown in  FIG. 20 ; 
         FIG. 24  is a fragmentary elevational view of a splice connection of two channel-type reinforcing members shown in  FIG. 21 ; 
         FIGS. 25 and 26  are fragmentary elevational views similar to  FIG. 24  and showing installed splice connectors for the reinforcing members shown in  FIG. 21   
         FIG. 27  is a fragmentary elevational view of a splice connector similar to  FIG. 19  for joining two vertically aligned reinforcing members with attached ribs; 
         FIG. 28  is a section through a rib-type reinforcing member having the rib interrupted for center connectors to a monopole wall; 
         FIG. 29  is a section similar to  FIG. 28  and showing a continuous rib-type reinforcing member mounted on a monopole wall; 
         FIGS. 30 and 31  are greatly reduced horizontal sections similar to  FIGS. 8 and 9  and showing the attachment of the rib-type reinforcing members of  FIGS. 28 and 29  to a monopole wall, respectively; 
         FIG. 32  is a fragmentary elevational view of the monopole and attached reinforcing members shown in  FIGS. 28 and 30 ; 
         FIG. 33  is a fragmentary elevational view of the monopole with a rib-type reinforcing member shown in  FIGS. 29 and 31 ; 
         FIGS. 34-36  are fragmentary perspective views showing splice connections of the rib-type reinforcing members shown in  FIGS. 28 and 29 ; 
         FIG. 37  is a larger fragmentary perspective view of the splice connector shown in  FIG. 27 ; 
         FIG. 38  is a fragmentary perspective view of the splice connector shown in  FIG. 37 ; and 
         FIG. 39  is a cross-section of the splice connector shown in  FIG. 38  after receiving connector bolts. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An elongated folded or bent or angled reinforcing plate or member  45  is shown in  FIG. 1  and provides optimal effectiveness of a reinforcing member to reduce forces in a vertical monopole tower  50 , herein referred to as monopole or tower, by the fact that it is located at the outermost distance from the neutral or vertical center axis of the monopole. The bend or fold of the reinforcement plate provides for a significant increase of the moment of inertia of the reinforcing member which improves its resistance to localized buckling under compression. The folded or bent member  45  can be applied to any multi-sided monopole  50  ( FIG. 8 ) and to a circular monopole  55  ( FIG. 9 ). The member  45  may also be applied to tapered or uniform diameter monopoles. 
     Local buckling of the folded or angled reinforcing member  45  is restrained by intermediate blind connector bolts or connectors  58  ( FIG. 4 ) or connectors  60  ( FIG. 5 ) extending through holes  59  within the flanges or wings  61  of the member  45  and monopole  50  and having a staggered bolt pattern along its vertical length as shown in  FIG. 10 . The spacing of these bolts varies as a function of the angle of the member, the thickness of the member, total width and strength of the reinforcing member. For example, a 12 sided monopole having the folded or angled reinforcing member  45  may have a fold or angle of 30 degrees between the wings  61 , a thickness of one inch, and be ten inches in total width (five inches each wing) and have a yield strength of 65,000. lbs per square inch. The bolt spacing may typically be twenty four inches between bolts in the cross section (staggered pattern) or forty eight inches on each wing of the angle section  45 . The width of the member  45  may typically vary from six inches to twelve inches and is placed onto two adjacent flat wall sections of the monopole  50  over a corner of the monopole. 
     The folded or angle member  45  is fabricated in three standard geometries or configurations. For a 12 sided monopole ( FIG. 8 ), the obtuse angle between the wing portions is 150 degrees, and the member extends in a generally vertical direction of the monopole. For an 18 sided monopole, the angle member  45  has an obtuse angle of 160 degrees at its centerline and between the wing portions  61 . For round monopoles  55  ( FIG. 9 ), the angle is such that the wing portions  61  are tangent to the surface of the monopole at approximately the quarter points in (using total width) from the edges of the member  45 , as shown in  FIG. 9 . 
     The folded or angle reinforcing member  45  is typically 20 feet in length ( FIGS. 10 &amp; 11 ) between splices or ends. This length is determined by weight and handling considerations. The reinforcing member  45  is connected to an existing vertical monopole  50  using tensile bolts or connectors  58  ( FIG. 4 ) and/or tensile bolt shear connectors  60  ( FIG. 5 ), and sometimes shear pin connectors  62  ( FIG. 6 ). In most circumstances, a combination of two connector types are used on a reinforcing member. One form of tensile shear connector  60  which eliminates a clearance gap  63  ( FIG. 4 ) and has provided a satisfactory connection is a blind fastener assembly produced by Huck International, Inc. and of the general type, for example, disclosed in U.S. Pat. No. 7,033,120. Each tensile connectors  58  ( FIG. 5 ) may include a pressed-on surrounding shear sleeve  64  ( FIG. 5 ) forming a tight-fit within the hole  59  and between the tensile connector  58  and the wall of the monopole. 
     When the connectors are placed at the ends of the reinforcing members  45  ( FIG. 12 ), the ends of reinforcing members must be capable of transferring excess axial loads from the existing monopole tower to the reinforcing member. This is accomplished through shear transfer between the existing monopole and the reinforcing member. Shear transfer is achieved using tensile shear connectors  60  ( FIG. 12 ) or a shear plate and pin assembly  65  ( FIGS. 6 &amp; 14 ) that includes a plurality of shear pins  62  ( FIGS. 13 &amp; 14 ). The shear plate and pin assembly  65  of  FIG. 13  includes a flat plate  66  with pressed in shear dowels or pins  62 . The shear plate and pin assembly  65  is secured to the reinforcing member and monopole  50  with tensile shear bolts  60  or tensile bolts  58 . In  FIG. 14 , the shear plate and pin assembly  65  is shown with two shear pins  62  and two outside holes  59  where the tensile shear bolts  60  or tensile bolts  58  are installed. A cross section of the shear plate and pin assembly  65  mounted on each wing portion  61  of a reinforcing member  45  is shown in  FIG. 15 . 
       FIGS. 16-18  show splice connections between the end portions of two vertically aligned reinforcing members  45 . The splices have extended plates  66  with tensile shear connectors  60  in holes  59  ( FIG. 16 ), extended shear plate and pin assemblies  65  ( FIG. 17 ) which are connected to the monopole reinforcing member  45  with tensile shear connectors  60  or in combination with only tensile connectors  58 . The total number of shear pins in the shear plate and pin assembly  65  may be reduced when tensile shear connectors  60  are used to fasten the shear plate and pin assembly. 
     Referring to  FIG. 19 , another splice method is achieved by attaching double splice plates  70  onto both sides of vertically aligned ribs  72  welded onto the angle reinforcement members  45 . Tensile shear connectors  60  are inserted within the aligned cross holes  73  formed within the splice plates  70  and ribs  72 . The ribs  72  may also be doubled by welding one rib on each wing portion  61  of the angle reinforcement member  45 . This method takes advantage of the double shear action of the bolts installed through holes within each rib and double splice plates on each wing portion  61 . 
     The location of a splice may occur at any location along the height of the monopole. At locations of monopole joints where a slip joint is used to join the monopole sections together, a slight step occurs in the monopole. This step may be accommodated by fabricating the reinforcing member steel so that the reinforcing member splice is located at this same location as the slip joint, and shims are used if required, under the reinforcing member splice. The reinforcing member may also pass over the monopole slip joint, and shims may be placed, if necessary, between the reinforcing member and monopole. 
     A reinforcing member may also be connected to the tower or monopole at mid-section locations along the length of the reinforcing members. A mid-section connector type is determined by how the shear forces are preferred to be transferred into the reinforcing member, that is, concentrated at the ends of the reinforcing member only or distributed along the length of the reinforcing member incrementally through shear flow. When the shear forces are transferred in a concentrated area at the ends of the reinforcing member  45  using tensile shear connectors  60  and/or shear pins  62 , only intermediate bolts are required to resist out of plane buckling. This is accomplished using only tensile connectors  58  which are typically spaced at 48 inches apart on center on each wing portion  61  of the member  45 . Preferably, the connectors  58  are staggered so that there is 24 inches vertical spacing between the blind bolt connectors. 
     When the shear forces are distributed along the length of a reinforcing member  45  incrementally through shear flow, each mid-section connector must be capable of carrying shear. This is accomplished using tensile shear connectors  60  or shear pins  62  located along the length of the reinforcing member. The same staggered connector pattern as used for the tensile connectors  58  is used for the tensile shear connectors  60 . 
     Referring to  FIGS. 2 &amp; 20 , channel-type reinforcing members  75  ( FIG. 2 ) or  80  ( FIG. 20 ) provide for a significant increase of the moment of inertia of the reinforcing member which improves its resistance to localized buckling under compression. The channel-type cross-section also hides the appearance of the exposed anchor heads of the connectors  58  and  60 , which has a benefit for zoning approval. The channel-type section may be used for monopoles fabricated of multiple flat sides. The channel member  75  ( FIG. 2 ) is welded to a flat base plate  82 . The channel member  80  ( FIG. 20 ) is formed as a one-piece member. When the same strength grade of steel is used to form the channel member  75  with the welded flat plate  82 , the combined two members perform as one channel member such as the channel member  80 . When the components of the channel member  75  have different strengths or when channel  75  is used for local buckling purposes only, it may not be necessary to weld the flat base plate  82  and channel  75  together. 
     The channel section or member  75  or  80  may be fabricated to widths much narrower than the angle member  45 , allowing more flexibility in the positioning of the reinforcement members when interferences (e.g., step bolts, port holes, safety cables, etc.) exist on the monopole. As an example, a channel member width may typically vary from 4 inches to 8 inches, and the member is mounted on one flat wall section of the monopole. The channel member may be fabricated using a channel and plate welded together ( FIG. 2 ) or be formed as a single section ( FIG. 20 ) or the channel  75  and plate  82  may be bolted together, as shown in  FIG. 21 , with connectors  60 . Each channel member is attached to the monopole in a manner that the flanges of the channel are facing outwardly and the web of the channel is adjacent the monopole  50 , as shown in  FIGS. 2 ,  20 ,  21  and  22 . 
     The channel section reinforcing member is typically 20 ft in length between splices or ends. This length is determined by weight and handling considerations and is installed as shown in  FIG. 21  or  22 . The channel section reinforcing member is connected to the monopole using tensile connectors ( FIG. 4 ), tensile shear connectors ( FIG. 5 ), or shear plate and pin assemblies  65  ( FIG. 6 ). The connectors are placed at the ends of the reinforcing members so that the ends of reinforcing members are capable of transferring excess axial loads from the existing monopole to each reinforcing member. This is accomplished through shear transfer between the existing monopole and the reinforcing member. 
     Shear transfer is achieved using tensile shear bolts  60  or a shear plate and pin assemblies  65  ( FIG. 14 ). The same connectors used for fastening each side or wing portion of the folded or angle section or member  45  are used for fastening a channel section or member. The connectors or shear assemblies extend through the web between the flanges of a channel member, or the channel member may be located on a plate  82  which projects at opposite ends to provide a flat section for making a splice connection. Splices between two channel reinforcing members  75  or  80  are accomplished using splice plates  66  which overlap the web portions of adjacent end portions of vertically aligned channels  80  or overlap extensions of the base plates  82  of the channels  75  ( FIGS. 24 &amp; 25 ). The splice plates are secured by tensile shear connectors  60  in the holes  59  ( FIG. 24 ), or by a combination of shear pins  62  with tensile shear connectors  60  ( FIG. 25 ) in the holes  59  or the combination of shear pins  62  with only tensile connectors  58  ( FIG. 26 ). The total number of shear pins  62  in a splice plate  65  may be reduced when tensile shear connectors  60  are used to fasten a splice plate  66 . 
     The splice methods described above in connection with  FIG. 19  may also be used with channel sections by attaching double splice plates  70  onto opposite sides of ribs  72  welded to the web portions of adjacent channel members  80  or to the channel member reinforcement base plates  82  ( FIG. 27 ). These methods take advantage of the double shear action of tensile shear bolts installed through holes in the ribs and double plates. The channel members  75  ( FIG. 26 ) are recessed back from the ends of the base plates  82  which are welded to the ribs  72 . The location of a splice may occur at any location along the height of a monopole. At locations of monopole joints where a slip joint is used to join monopole sections together, a step occurs in the monopole. This step is accommodated by using shims, if necessary, under the reinforcing member splice plate or between the reinforcing member and the monopole. 
     Connectors  58  or  60  are located along the length of the reinforcing members and are determined by how the shear forces are preferred to be transferred into the reinforcing member, that is, concentrated only at the ends of the reinforcing member or distributed along the length of the reinforcing member. When the shear forces are transferred in a concentrated area at the ends of the reinforcing member using tensile shear connectors  60  and/or shear pins  62 , only intermediate connectors  58  are used to resist out of plane buckling. The tensile connectors  58  are typically spaced at 24 inches apart on centers. When the shear forces are distributed along the length of the reinforcing member incrementally through shear flow, each mid-section connector must be capable of carrying shear. This is accomplished using tensile shear connectors  60  and/or shear plate and pin assemblies  65  located along the length of the reinforcing member. The geometry or profile of the reinforcing member is selected to provide a 24 inch spacing of the connectors. 
     A ribbed-type reinforcing member  90  (FIGS.  3  &amp;  28 - 39 ) also provides for a significant increase of the moment of inertia of the reinforcing member which improves its resistance to localized buckling under compression. This section or member is used for monopoles fabricated of multiple flat sides. Connectors  58  or  60  are placed in the center of the base plate  92  when the ribs  94  are interrupted ( FIGS. 28 ,  30  &amp;  32 ) or in the base plate  92  on opposite sides of a continuous rib ( FIGS. 29 ,  31  &amp;  33 ). 
     A ribbed-type reinforcing member or rib section  90  (FIGS.  3  and  28 - 39 ) may be fabricated in widths much narrower than the angle member or section  45 , allowing for more flexibility in positioning of the reinforcement members when interferences (e.g., step bolts, port holes, safety cables, etc.) exist on the monopole. As an example, a rib section or member width typically varies from 4 inches to 8 inches and is placed on a flat wall of the monopole  50 . Rib sections may be spliced together using double shear side plates as described above in connection with  FIG. 27 . The ribbed section reinforcing member  90  is typically 20 ft in length between splices or ends. This length is determined by weight and handling considerations. 
     The rib section reinforcing member  90  is connected to the existing monopole  50  using tensile connectors  58 , tensile shear connectors  60 , or shear pins  62  with connecter plates  66 . When the connectors are placed at the ends of the reinforcing members, the ends of reinforcing members must be capable of transferring excess axial loads from the existing monopole to the reinforcing member. This is accomplished through shear transfer between the existing monopole and the reinforcing member. Shear transfer is achieved using tensile shear connectors  60  or a shear plate and pin assembly  65  ( FIG. 14 ) having shear pins  62 . The same connector details used for fastening each wing portion  61  of the folded or angle section  45  are used for fastening a rib section  90 . The rib  94  welded to the plate  92  is recessed back from the end of the plate to provide a flat section of the plate for making a splice connection. 
     The splices may be located between two ribbed-type reinforcing members  90  and may be accomplished using all tensile shear connectors  60  in the holes  59  in the splice plate  65  ( FIG. 34 ) or shear plate and pin assemblies  65  and tensile connectors  58  in holes  59  ( FIGS. 35 &amp; 36 ). The total number of shear pins  62  in a shear plate and pin assembly  65  may be reduced when tensile shear connectors  60  are used to splice with the shear plate and pin assembly  65 . 
     Referring to  FIGS. 37 &amp; 38 , a splice method for rib-type reinforcing members  90  may be achieved by attaching double splice plates  70  on opposite sides of ribs  94  that are welded on the plates  92  of the reinforcement members  90 . This method takes advantage of the double shear action of the bolts installed through holes within the rib and double plates. The connection of the rib-type members  90  are determined by how the shear forces are preferred to be transferred into the reinforcing members, that is, concentrated at the ends of each reinforcing member only or distributed along the length of each reinforcing member  80  or  90  incrementally through shear flow. 
     When the shear forces are transferred in a concentrated area at the ends of the reinforcing member, for example, by using tensile shear connectors  60  or shear pins  62 , intermediate bolts or tensile connectors  58  are only required to resist out of plane buckling. Tensile connectors  58  are typically spaced at 48 inches apart on centers between intermittent ribs  94  ( FIG. 32 ) or can be staggered on opposite sides of a continuous rib  94  in an alternating manner and spaced 48 inches apart, as shown in  FIG. 33 . 
     When the shear forces are distributed along the length of the reinforcing member incrementally through shear flow, each mid-section connector must be capable of carrying shear. This is accomplished using tensile shear connectors  60  or shear plate and pin assemblies  65  located along the length of the reinforcing member. The plate  92  of the section or member  90  is selected to allow for a 48 inch spacing of the connectors  60 . The same linear or staggered connector pattern used for the tensile connectors  58  can also be used for the tensile shear connectors  60 . 
     Additional details associated with a splice connector of  FIGS. 27 &amp; 37  include the relation of the monopole  50  to the reinforcing member  90  so that raising up of the reinforcing member  90  does occur under axial loads in the member  90 . When the ribbed section in  FIG. 38  or member  90  is under compression or tension, the connectors  58  located in holes  59  assist in keeping the plate  92  of the ribbed member  90  against the monopole  50 . This behavior is a result of the double splice plates.  70  being eccentric to the neutral axis of the ribbed member  90 . 
     While the forms of monopole reinforcing members and their methods of attachment herein described constitutes preferred embodiments of the invention, it is to be understood that the invention is not limited to the precise methods and reinforcing members described, and that changes may be made therein without departing from the scope and spirit of the invention as defined in the appended claims.