Precast post-tensioned segmental pole system
A precast post-tensioned segmental pole system capable of supporting a load is provided. The pole system includes a plurality of pole segments that use connectors and strands to anchor them together. The strands extend within a cavity formed in the pole segments and are external to the wall structure of the pole segments. The strands may be coupled between both of the pole segments, or be anchored to a connector. The connector includes an upper piece that is coupled to one pole segment, and a lower piece that is coupled to the other pole segment. Upper and lower pieces interlock with each other to join the pole segments to one another. The strands are placed in tension so that pole system is capable of withstanding forces imposed by the load.
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 DEVELOPMENTNot Applicable.
BACKGROUND OF THE INVENTIONThe 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 INVENTIONIn 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 DRAWINGSIn 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:
Referring now to the drawings in detail, and initially to
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.
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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.
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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
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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
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
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
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
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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
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.
Claims
1. A device for precasting a pole segment comprising:
- an external mold comprising a bottom piece and a plurality of top pieces, said top pieces being hingedly coupled with said bottom piece, said bottom piece and said top pieces having inner surfaces defining a channel;
- a yoke coupled to said top pieces; and
- an internal mold having an outer surface, said internal mold adapted to be placed within said channel to thereby define a cavity between said outer surface of said internal mold and said inner surfaces of said bottom piece and said top pieces, whereby said inner surfaces shape an exterior surface of a pole segment and said outer surface of said internal mold shapes an interior surface of said pole segment when a formable material is placed between said external mold and said internal mold.
2. The device of claim 1, further comprising an adjustable holding mechanism that extends through said external mold and braces said internal mold to hold said internal mold in position within said channel.
3. The device of claim 3, wherein the adjustable holding mechanism consists of at least one bolt.
4. The device of claim 1, wherein said internal mold includes top and bottom pieces.
5. The device of claim 4 wherein said bottom piece is tapered along its length.
6. The device of claim 4 wherein said top piece is tapered along its length.
7. The device of claim 6, wherein a top portion of said top piece is further tapered to form a thickened portion in the pole segment.
8. The device of claim 7, further comprising at least one tube coupled to said tapered portion of said internal mold.
9. A method for forming a pole segment used in a post-tensioned pole system, said method comprising:
- providing an external form;
- providing an internal form;
- placing said internal form within said external form;
- securing said internal form within said external form to thereby define a cavity between said internal form and said external form; and
- placing a formable material within said cavity to form the pole segment.
10. The method of claim 9 wherein the external form includes a plurality of top pieces and a bottom piece.
11. The method of claim 10, wherein the top pieces are hingedly coupled to said bottom pieces to form a channel.
12. The method of claim 11 further comprising providing at least one adjustable holding mechanism coupled to the external form.
13. The method of claim 12 further comprising adjusting said holding mechanism to secure internal form within said channel.
14. The method of claim 9, wherein said internal form is tapered to form a thickened portion of the pole segment.
15. The method of claim 9 wherein said external form is tapered along its length.
16. The method of claim 15, further including:
- providing at least one tube; and
- coupling said tube to said tapered portion of said internal mold prior to placing concrete mixture between said external and internal forms to create an aperture in the thickness portion of the pole segment.
17. A method for forming a pole segment used in a post-tensioned pole system, said method comprising:
- providing a external form having a plurality of top pieces and a bottom piece, said top pieces being hingedly coupled to said bottom piece having inner surfaces defining a channel;
- providing at least one adjustable holding mechanism coupled to said external form;
- providing an internal form with an outer surface;
- placing said internal form within said channel to thereby define a cavity between said outer surfaces of said internal form and said inner surfaces of said bottom and top pieces;
- adjusting said holding mechanism so that said internal form is secured within said channel; and
- placing a concrete mixture within the cavity to form the pole segment.
18. The method of claim 17, wherein said internal form is tapered to form a thickened portion of the pole segment.
19. The method of claim 18, further including:
- providing at least one tube; and
- coupling said tube to said tapered portion of said internal mold prior to placing concrete mixture between said external and internal forms to create an aperture in the thickness portion of the pole segment.
20. The method of claim 19 wherein said external form is tapered along its length.
Type: Application
Filed: Dec 13, 2004
Publication Date: Jun 9, 2005
Inventors: Maher Tadros (Omaha, NE), E. Foster (Omaha, NE), Sherif Yehia (Omaha, NE), Audra Hansen (Elkhorn, NE)
Application Number: 11/011,275