Patent Publication Number: US-2005120644-A1

Title: Precast post-tensioned segmental pole system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. patent application Ser. No. 10/184,349, filed Jun. 27, 2002, which claims benefit of U.S. Provisional Application No. 60/301,189, filed Jun. 27, 2001. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
      Not Applicable.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to a post-tensioned pole system. In particular, the present invention relates to a post-tensioned pole system includes one or more precast segments which are coupled to one another by a connector and post-tensioned through the use of at least one strand that is external to the wall thickness of the pole segments.  
      It is well known that poles are used in a wide variety of applications including electrical transmission and distribution environments, lighting, telecommunications and as supports for wind energy turbines. When used in these environments, the poles are subjected to forces from the wind, water and structural loads such as the weight of wire transmission lines or a wind turbine. These forces create a moment or torque that the pole must resist in order to remain in an upright position. In resisting these forces, the pole has a tendency to flex thereby putting the bottom portion of the pole in compression and the top portion of the pole in tension.  
      In the past, the poles have been formed of various materials such as steel, wood, concrete, masonry materials and any combination thereof. The use of concrete to form the poles is relatively common due to its availability. However, the use of concrete to form the poles suffers from a number of drawbacks. For instance, while concrete is capable of withstanding a substantial amount of compression force, its ability to resist tension is considerably low. Therefore, different techniques have been established in an effort to enhance the concretes ability to withstand the tension forces imposed on the pole.  
      One technique used to enhance the ability of the concrete to withstand tension forces is pre-tensioning. Pre-tensioning the concrete has been accomplished by embedding strands within the concrete walls of the concrete using a spun or static cast technique. In the static cast method, the strands are arranged within the form prior to pouring the concrete. Both ends of each strand are jacked to place the strands in tension. The concrete is then placed into the form embedding the strands therein. The strands are cut after the concrete has gained adequate strength, releasing the force to the concrete. The tension in the strands places the concrete pole into compression thereby allowing it to withstand a greater amount of tension force. The spun cast technique is similar to the static method in that the strands are placed in the form prior to the addition of the concrete. However, instead of placing the concrete into a static form, the concrete is poured into a machine that spins the concrete forcing the concrete to the outer walls of the form and embedding the strands within the wall of the structure.  
      The aforementioned pre-tensioning techniques also suffer from a number of deficiencies. One problem with the spun cast method is that the concrete aggregate separates due to centrifugal force thereby making concrete weak and susceptible to cracking due to unequal distribution of aggregate. In addition, the equipment used to spin the concrete is expensive. In addition, both of the aforementioned methods of pre-tensioning concrete poles are problematic in that it takes a considerable amount of time to properly position the strands in the form prior to pouring the concrete.  
      Additionally, there other problems associated with current concrete pole structures. For example, the concrete structures that are used in these environments are typically unitary structures that extend to a height of about 80-90 feet. This is problematic because certain power transmission line applications may require the poles to extend to greater heights. Additionally, given the fact that poles are a unitary structure, it is very difficult to transport the pole structures from an off-site location to the construction site. Once the poles arrive at the site, they require large cranes and heavy machinery to lift them into position due to the weight and length of the pole.  
      Accordingly, there remains a need for a segmental post-tensioned pole system that increases maximum height of pole while reducing the difficulty in transporting the pole from off-site location to the construction site. In addition, there is also a need to simplify the installation and manufacture of the pole. The present invention fills these needs as well as various other needs.  
     BRIEF SUMMARY OF THE INVENTION  
      In order to overcome the above-stated problems and limitations, and to achieve the noted objects, there is provided a precast post-tensioned segmental pole system that is capable of supporting a load and withstanding other external forces.  
      In general, the pole system includes several pole segments with similar connectors anchoring them together. For example, the first and second pole segments each have top and bottom ends with a cavity formed therein. The connector is adapted to couple the top end of the first pole segment with the bottom end of the second pole segment. The connector includes upper and lower pieces. The upper piece includes a channel band coupled to the second pole segment and having an inner edge. The connector further includes a stiffener being disposed within the channel band. The lower piece includes a base plate coupled to the first pole segment and a cover plate coupled to the base plate and having an outer edge that is adapted to interlock with an inner edge of the upper piece. The strands are placed in tension and can either continue through or be anchored at any of the segment connectors.  
      Additionally, the pole system may also include an anchor that couples the anchored strand to the connector. The anchor may include a cylinder, a clasping mechanism slidably received within the cylinder, a pipe coupled to the cylinder and a spring mounted within the pipe. The spring retains the clasping mechanism within the cylinder when the strand is coupled when the clasping mechanism is releasably coupled to the anchored strand.  
      Further objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the drawings which follows, when considered with the attached figures. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are employed to indicate like parts in the various views:  
       FIG. 1  is an elevational view of a post-tensioned segmental pole system according to the present invention;  
       FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1  showing a connector mounted to a pole segment;  
       FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 2  showing a plurality of strands extending within the cavity of the pole segment;  
       FIG. 4  is an enlarged view of the area encompassed by “4” in  FIG. 3  showing the connector mounted between two pole segments;  
       FIG. 5  is an enlarged view of the area encompassed by “5” in  FIG. 4  showing an anchor coupled to a strand;  
       FIG. 6  is a perspective view showing an upper piece of the connector mounted to a pole segment;  
       FIG. 7  is a perspective view of an external form used to form the external shape of a pole segment;  
       FIG. 8  is an elevational view of the external mold with an internal mold positioned therein;  
       FIG. 9  is an elevational view of the external mold showing a top piece rotating about a hinge point as illustrated in dashed lines;  
       FIG. 10  is an elevational view of the internal mold having a tapered top piece; and  
       FIG. 11  is an elevational view of an internal mold similar to  FIG. 10  having a non-tapered top piece. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to the drawings in detail, and initially to  FIG. 1 , numeral  10  generally designates a post-tensioned segmental pole system constructed in accordance with a first preferred embodiment of the present invention. Pole system  10  may include one or more pole segments  12  coupled to one another by a connector  14  to form a monopole structure. As best seen in  FIG. 3 , pole system  10  also includes a plurality of strands or tendons  16  that extend through a hollow interior cavity  18 , and which are external to pole segment  12 . Strands  16  are placed under tension and coupled between pole segments  12 .  
      Pole system  10  may be used to support a load such as a structural appurtenance, insulator anchor, antenna in various types of service environments including, but not limited, to electrical transmission and distribution, lighting, communications and wind power generation. In addition, pole system  10  may also withstand external forces such as, but not limited to, wind, water and the like. It will be understood that a number of pole systems may be used in conjunction to form a multi-pole system to increase the height capability of pole system  10 . For instance, a number of pole systems may be arranged in a tripod configuration to provide support for a single pole system that would extend upwardly from the apex of the tripod. This configuration would essentially double the overall height capabilities of the present invention.  
      As best seen in  FIG. 1 , pole system  10  may include one to four pole segments  12  that may form a monopole structure of up to 120 feet (36 meters). With additional reference to  FIGS. 2 and 3 , each pole segment  12  may be approximately 30 feet (9 meters) in length having a tapered hexagonal cross-section. It is desirable to use a pole segment  12  having a cross-section that has stiffness characteristics that are independent of lateral applied loads such as, but not limited to, wind or wave forces. Therefore, it is preferable to use a pole segment  12  having a radial symmetrical cross-section with a flat outer surface  20  so that appurtenances may be fastened to pole segment  12 . Although a hexagonal cross-section is described and shown herein, it is within the scope of the present invention to use a pole segment  12  having cross-section in the shape of an octagon or any other radially symmetric cross-sectional shape.  
      As best seen in  FIG. 1 , outer surface  20  of pole segment may be tapered at the rate of 1 inch (25 mm) over a distance of 10 feet as pole segment  12  extends from a bottom portion  22  to a top portion  24 . As best seen in  FIGS. 3 and 4 , an inner surface  26  of pole segment  12  also tapers inwardly at approximately the same rate as outer surface  20  and defines hollow interior cavity  18 . Top portion  24  of inner surface  26  may include a thickened portion  28  where inner surface  26  tapers inwardly at a greater rate compared to bottom portion  22  of inner surface  26 . Thickened portion  28  may begin at an intermediate portion of inner surface  26  and extend to a rim  30  at top portion  24 . Further, a plurality of apertures  32  are formed in inner surface  26  and extend through thickened portion  28  to a top surface  34  of pole segment  12 . Apertures  32  are hexagonally disposed within hollow interior cavity  18  and adapted to allow strands  16  to pass therethrough. The number of apertures  32  formed in segment  12  preferably corresponds with the number of strands  16  extending within cavity  18 .  
      Pole segments  12  may be formed of various types of concrete including, but not limited to, high performance concrete (HPC) which is capable of higher than normal compressive strengths. High performance concrete utilizes fibers that are used to reinforce the concrete instead of using standard reinforced bars to enhance the concrete strength. The high performance concrete may have a minimum compressive strength of 8000 pounds per square inch, a RCP factor of 1000 coulombs, and a minimum freeze-thaw capacity for cold weather environments. However, pole system  10  may also utilize reinforcement bars or welded wire fabric within the walls of pole segments  12  to increase the strength of pole segment  12 .  
      As best seen in  FIG. 1 , connector  14  is used to couple two pole segments  12  to one another. As best seen in  FIG. 4 , connector  14  includes an upper piece  36  and a lower piece  38 . Upper piece  36  includes a channel band  40  and a plurality of studs  42 . Studs  42  are mounted within bottom portion  22  of pole segment  12 . With additional reference to  FIG. 6 , channel band  40  includes top and bottom plates  44 ,  46 , a cross piece  48  and a stiffener  50 . Top plate  44  is fixedly coupled to studs  42  and extends inwardly towards cavity  18 . Cross piece  48  extends downwardly from top plate  44  and is coupled to bottom plate  46 . Bottom plate  46  extends inwardly and parallel with top plate  44 . As best seen in  FIGS. 2 and 6 , bottom plate has a inner edge  52  that is adapted to interlock with lower piece  38 . Although, inner edge  52  is in the shape of a hexagon, it should be understood that it may be formed in any shape that will allow it to interlock with lower piece  38 . Stiffeners  50  extend between top and bottom plates  44 ,  46  and are used to stiffen channel band  40 .  
      As best seen in  FIGS. 2 and 4 , lower piece  38  is mounted to top portion  24  of pole segment  12  and is used to interlock with upper piece  36 . Lower piece  38  includes a cover plate  54 , a base plate  56  and studs  58 . Studs  58  are mounted within top portion  24  of pole segment and is fixedly mounted to base plate  56 . Base plate  56  is a hexagonal ring and has a support surface  60 . Cover plate  54  is also a hexagonal ring and mounted to a portion of a support surface  60  on base plate  56 . Further, cover plate  54  includes an outer edge  62  adapted to interlock with inner edge  52  of channel band  40 . Although outer edge  62  is shaped in the form of a hexagon, it should be understood and appreciated that outer edge  62  may be other shapes that will allow it to interlock with inner edge  52  of channel band  40 . Outer edge  62  is sized so that there is a gap  64  between inner edge  52  and outer edge  62 . However, gap  64  is small enough that the rotation between channel band  40  and cover plate  54  is minimized. Cover plate  54  also includes a rim  66  that may be aligned with rim  30  formed in top portion  24  of pole segment  12 . Further, as best seen in  FIG. 5 , cover plate  54  has a plurality of holes  68  formed therein that are aligned with apertures  32  formed in thickened portion  28  so that strands  16  may pass therethrough. With reference to  FIGS. 2 and 5 , cover plate  54  also has a top surface  70  where one or more strand anchors  72  may be mounted thereon which will be described more fully below.  
      The post-tensioning of pole system  10  is accomplished through the use of a plurality of strands  16  that extend within hollow interior cavity  18 , but which are external to the walls of pole segments  12 . Strands  16  are adapted to be placed in tension so that pole segments  12  in pole system  10  are capable of withstanding an increased amount of tensile force. Strands  16  may be 0.5 inches (12 mm) in diameter and arranged within cavity  18  as shown in FIGS.  2  and  3 . In particular, strands  16  may be arranged in repeats on each of the side of the hexagonal cross-section of pole segment  12  so the resulting radial symmetry provides relatively constant moments of inertia for flexural stiffness independent of lateral force direction. With specific reference to  FIG. 4 , strands  16  may extend through thickened portion  28  to ensure that strands  16  are positioned near inner surface  26  to allow them to make a maximum contribution to flexural stiffness. One strand  16  may extend from bottom portion  22  and be coupled to top end  22 ,  24  of the same pole segment  12 . In addition, strand  16  may also extend from bottom portion  22  of a base pole segment  12  to a top portion  24  of a pole segment positioned on top of the base pole segment. Further, strands  16  may continue to extend to a pole segment further up the pole system  10 .  
      As best seen in  FIGS. 2 and 5 , strands  16  are coupled to top portion  24  of pole segment  12  through the use of at least one anchor  72 . Specifically, anchor  72  rests against top surface  70  of cover plate  54  and prevents strand  16  from being pulled downwardly towards bottom portion  22  of pole segment  12 . Anchors  72  include a cylinder  74  having a clamping mechanism  76  slidably coupled within an interior portion of cylinder  74 . Clamping mechanism  76  is a two-piece jaw structure having a variable diameter hole formed therein. The hole is tapered as it extends through the jaws and has one or more teeth or protrusions extending therein to grip and hold onto strand  16 . Anchor  72  further includes a pipe  78  with a helical spring  80  fixedly mounted therein. Pipe  78  is fixedly mounted to the top ring of cylinder  74  and spring  80  is positioned to bias jaws  76  toward top surface  70  of cover plate  54 .  
      In operation, pole system  10  may be a single pole segment  12  used alone, or in combination with one or more pole segments. A single or monopole system may extend to a height of 30 feet. Therefore, a system with four pole segments may extends to a height of 120 feet. Furthermore, a tripod system may extend to a height of approximately 240 feet. If one pole segment  12  is used by itself as the supporting structure, strands  16  are fed through hollow interior cavity  18  of pole segment and threaded through apertures  32  and holes  68  in cover plate  54  as best seen in  FIGS. 3 and 4 . Referring now to  FIG. 5 , a portion of each strand  16  that extends through holes  68  is coupled to anchor  72 . In particular, strand  16  is pushed upwardly against jaws  76  to place the end portion of strand  16  within the hole formed between jaws  76 . As strand  16  is being pushed upwardly, jaws  76  slide upwardly to compress spring  80 . Spring  80  prevents the jaws  76  from being dislodged from cylinder  74 . The angled portion of the jaws slides along an inner edge of cylinder  74  and the jaws splits apart. Once jaws  76  open enough to allow strand  16  to enter the inner diameter, the upward force on strands is release and spring  80  biased jaws  76  downwardly so that the hold formed between the jaws decreases and the teeth within the hole grips onto strand  16 . The remaining strands  16  are coupled to top portion  24  of pole segment in a similar fashion. Strands  16  then proceed to extend downwardly to bottom portion  22  of pole segment  12 . Bottom portion  22  of pole segment  12  is placed in a foundation hole and backfill such as compact fill, flowable concrete mix or reinforced concrete is added to the hole to support pole segment  12 . Strands  16  are placed in tension by jacking or by other conventional methods to complete the post-tensioned pole system  10 .  
      Two or more pole segments  12  may also be used to form pole system  10 . Strands  16  are first fed through hollow interior cavity  18  of the bottom or base pole segment and external to the pole segment structure  12 . Strands  16  are threaded through apertures  32  and holes  68  in cover plate  54 . Some of strands  16  are then coupled to top surface  70  of cover plate  54  by anchors  72  as described in detail above. The remaining strands continue to extend through the hollow interior cavity  18  of the second pole segment. Bottom plate  48  is placed on support surface  60  and inner edge  52  is interlocked with outer edge  62  as best seen in  FIGS. 2 and 4 . Thus, the second pole segment is resting on top of the bottom or base pole segment. The remaining strands  16  are threaded through apertures  32  and holes  68  in cover plate  54  of the second pole segment.  
      All the remaining strands  16  may be coupled to cover plate  54  of the second pole segment by using strand anchors  72 , or in the alternative, some strands  16  may be coupled to cover plate  54  while the remaining strands  16  continue to extend to a third pole segment. This process may continue in a similar fashion as described above until the desired height is achieved. For example, in a four pole system as shown in  FIG. 1 , thirty-six strands may extend within the cavity  18  of a bottom or base pole segment. At the juncture between the base segment and second segment, twelve of those strands may be mounted to cover plate on the base segment and twenty-four would continue to extend within cavity of the second pole segment. The juncture between the second and third pole segments is best shown in  FIGS. 2 and 3 . At this juncture, twelve of those strands may be mounted to cover plate  54  of the second pole segment and twelve would continue to extend within cavity  18  of the third pole segment. At the juncture between the third and fourth pole segments, six of those strands may be mounted to cover plate of the third pole segment and six would continue to extend within cavity of the fourth pole segment. Finally, the six remaining strands would then be coupled to the cover plate of the fourth pole segment. It will be understood that the joining of pole segments  12  and strands  16  may be conducted on the ground so the pole segments extend in a horizontal direction, or may be stacked on top of each other for vertical construction. Regardless of the number of strands in pole system  10 , strands  16  in the multi-segmented construction are then placed in tension to create a post-tensioned pole system  10  and placed in the appropriate foundation as described above. In addition, concrete may then be poured through rims  30 ,  66  into hollow interior portion  18  in either the single or multi-pole segment structures to create a solid pole structure.  
      The present invention further includes a mold unit  82  that may be used to precast pole segments  12  that are used in pole system  10  as best seen in  FIG. 8 . Mold unit  82  includes an external mold  84 , internal mold  86  and a yoke  88 . Mold unit  82  shown in the accompanying drawings is an example of a typical mold structure, and it will be understood that the proportions of the molds may vary depending on where the pole segment will be located in the pole system  10 . For instance, a pole segment that will be positioned at the base or bottom of pole system will be much larger than a mold for a segment that will be positioned at the upper portions of pole system  10 .  
      As best seen in  FIG. 7 , external mold  84  includes a bottom piece  90  and a pair of top pieces  92 . In particular, top pieces  92  are coupled to bottom piece  90  by a set of hinges  94  which allow external mold  84  to be placed in closed and open positions. As best seen in  FIG. 7 , external mold  84  is in a closed position where bottom piece  90  and top pieces  92  are arranged to form a channel  96  which will define the outer surface  20  of pole segment  12 . In addition, channel  96  may also taper inwardly along the longitudinal axis of external mold  84 . As best seen in  FIG. 9 , top pieces  92  may be rotated outwardly about hinges  94  so that external mold  84  is in the open position so that pole segment  12  may be removed from external mold  84 . As best seen in  FIG. 8 , external mold  84  also has a plurality of bolts  98  adjustably mounted within bottom piece  90 . Bolts  98  are mounted within bottom piece  90  so that a portion of each bolt  98  can be independently adjusted to extend variable distances within channel  96  and contact internal mold  86 . It is also within the scope of this invention to include bolts  98  in top pieces  92 . Yoke  88  is removably coupled to a top surface  98  top pieces  92  and has a bolt  100  mounted thereto that is adapted to extend within channel  96  and contact internal mold  86 . Yoke  88  is used to prevent top pieces  92  from floating or rotating relative to bottom piece  90  when the concrete is placed within mold unit  82 .  
      As best seen in  FIG. 10 , internal mold  86  is tubular member having a top piece  102 , a bottom piece  104  and a plurality of tubes  106 . With additional reference to  FIG. 8 , bottom piece has an outer surface  108  that has a similar taper compared to channel  96 , but is sized so there is a space between channel  96  and outer surface  108 . Further, a collar  110  removably couples bottom piece  104  to top piece  102 . An outer surface  112  of top piece  102  extends upwardly from collar  110  at the same taper as bottom piece  104  and then proceeds to narrow even further as it extends toward a rim  114 . The increased taper towards the top portion of top piece  102  creates a larger space between channel  96  and outer surface  112  to allow for the formation of thickened portion  28  as seen in  FIG. 4 . Tubes  106  are used to form apertures  32  in thickened portion  28  of pole segment  12 . In particular, tubes  106  are mounted to top piece  102  and extend outwardly therefrom in a direction parallel to the longitudinal axis of top and bottom pieces  102 ,  104 . The distal ends of tubes  106  are tapered to make it easier to remove tubes with top and bottom pieces  102 ,  104  after the concrete hardens.  
      As best seen in  FIG. 11 , top piece  102  may also have a uniform taper that is similar to bottom piece  104  as it extends from collar  110  to rim  114 . To change top pieces  102 , collar  110  is loosened, and the new top piece is slid onto bottom piece  104 . Collar  110  is tightened and the change is complete. The uniform taper in top piece  102  results in a pole segment  12  with uniform wall thickness along its entire length. In this case, there would be no thickened portion  28  or apertures formed in pole segment  12  since strands  16  may pass through hollow interior cavity  18  without interfering with the walls of pole segment  12 .  
      In forming a pole segment using mold unit  82 , top pieces  92  on external mold  84  are rotated outwardly about hinges  94  to an open position. As best seen in  FIG. 8 , internal mold  86  is then placed within channel  96  and supported by bolts  100 . Bolts  100  are adjusted in such a manner so that there is an equal amount of space between channel  96  and outer surfaces  108 ,  112  of internal mold  86 . Top pieces  92  are then moved to the closed position. Yoke  88  is then placed on top surface  98  and is coupled to each top piece  92  to prevent top pieces  92  from rotating outwardly relative to bottom piece  90 . Concrete is then poured between channel  96  and outer surfaces  108 ,  112 . After the concrete cures, internal mold  86  is removed from the hardened pole segment  12  thereby forming hollow interior cavity  18  and apertures  32 . Yoke  88  is then removed from top pieces  92  and top pieces  92  are moved to the open position. Pole segment  12  may them be removed from external mold  84  and used in pole system  10 . It should be understood that pole segments may be formed either at an off-site location or a construction site.  
      It can, therefore, be seen that the invention is one that is designed to overcome the drawbacks and deficiencies existing in the prior art. The invention provides a pole system that includes one or more pole segments that are post-tensioned by strands that are positioned within a hollow interior cavity and external to the wall structure of the pole segments. The use of separate pole segments to form the pole system reduces the difficulty in transporting the components of the pole system. Each pole segment is relatively easy to maneuver and lift through the use of a crane, winch system, or helicopter to simplify installation. In addition, the fact that the strands are positioned within the hollow interior cavity of the pole segment reduces the amount of time it takes to manufacture the pole segments since each strand does not have to be positioned within the form prior to pouring the concrete in the form. Further, the connectors provided in the present invention simplify the process of coupling two pole segments to one another. Additionally, the forms of the present invention eliminates the need to purchase expensive spinning equipment for forming pole segments having a interior cavity.  
      While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Reasonable variation and modification are possible within the scope of the foregoing disclosure of the invention without departing from the spirit of the invention.