Abstract:
Composite utility pole core systems wherein at least one core member fits within, but is not bonded to, the composite pole. The core systems provide increased bending strength in a hollow composite pole by preventing collapse of the cross section of the pole, the normal precursor to failure in bending of a tubular structure. The core members may be separately manufactured, and used individually or in plurality, being spaced equally along the length of the pole, or spaced unevenly, using closer spacing in the lower regions of the utility pole where bending stress are likely to be the largest.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/278,221 filed on Mar. 23, 2001. 

   BACKGROUND OF THE INVENTION 
   Composite utility poles have recently been introduced to offer various advantages over other types of poles historically used or more recently introduced. Such composite utility poles are hollow structures having a polygonal-shaped outer surface and an inner channel fabricated of rovings of fibers located in a zero degree orientation and layers of fibers or mats embedded in resin. The poles are ultraviolet light resistant, corrosion resistant, resistant to bugs, birds and the like, and are not subject to rot. 
   In such composite pole structures, it is desired to minimize the amount of material required for the fabrication of the pole while still maintaining accurate strength, as weight and cost are both highly dependent on the amount of each material used. 
   In normal use, utility poles may be subject to various forces, some of which are relatively constant, some of which are dependent upon and vary with the environment and some of which will vary dependent upon the position and application of the pole in the system. By way of example, poles are normally required to carry their own weight, the weight of one or more cross-arms and the weight of the wires supported thereby. Additionally, they may encounter the weight of a transformer or other parts of the distribution system. Variable forces include, the weight of birds perched on the wires, and the unequal tension in the wires because of the birds, windage, snow and ice on the pole, cross-arms, wires and any other components supported thereby such as by way of example, transformers. Other forces that may be encountered by utility poles include side forces arising from the fact that utility poles are not always placed directly inline with each other. By way of example, utility poles positioned along a curving street will similarly be positioned in a curved arc so that the tension on the wires together with any increased tension due to birds on the wires, etc. will provide a side force adjacent the top of the pole, tending to pull the top of the pole toward the center of the curve. Since horizontal forces at the top of a pole create large bending moments along the pole and particularly at the base of the pole, it is particularly important that such composite poles have adequate resistance to such bending moments without failure of the structural integrity of the pole. As a further illustration of a situation wherein high horizontal forces, may be exerted on a pole, consider a windstorm situation wherein trees fall across power lines (or phone lines). Preferably, the wires will fail, but the poles will be left standing. Further, however, it is important that with wires on one side of the pole being severed, the tension in the wires on the other side of the pole, given windage, perhaps ice accumulation, etc. will not cause a failure in the pole, as otherwise a domino effect may be encountered where each pole in a row would fail one after another. 
   Because of the aspect ratio of a typical utility pole is high, the high bending moments encountered along the pole and particularly adjacent the bottom of the pole normally impose more severe structural requirements on the pole than are imposed by the weight of the structure, wire, birds, etc. that must be supported by the pole through the compressive loads imposed thereon. 

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   First referring to  FIG. 1 , an illustration of a composite utility pole shown standing upright and shown in phantom with the exaggerated deflection to the side as might be caused by tension in the wires extending to adjacent utility poles which are not co-linear with the pole shown, wind forces, etc. may be seen. Though the deflection is exaggerated, it does illustrate the point that the bending moments due to horizontal forces adjacent to the top of the pole cause maximum bending moments adjacent to the bottom of the pole. 
     FIG. 2  schematically illustrates a section  22  of pole  20  in a high bending moment region of the pole. Assuming that pole  20  is unstressed when standing vertically (therefore neglecting the compressive stresses on the pole), it may be seen from  FIG. 2  that part of the pole on one side of the neutral axis is in tension and the other part of the pole on the other side of the neutral axis, in compression. Further, the tensile forces at section B—B are not collinear with the tensile forces at section A—A, with the net effect of the resultant forces pushing inward on the cross-sectional of the beam. Similarly, the compressive forces on sections A—A and B—B also do not align, the same also creating resultant forces pushing inward on the opposite side of the beam. These forces are illustrated in FIG.  3 . In that regard, for the specific composite beam illustrated, the outer corner are filled with pre-stressed longitudinal rovings and accordingly, the forces shown in  FIG. 3  have been drawn through those corner regions, though in fact the forces will be more distributed around the cross-section of the pole. Also, while the pre-stressing of the rovings and/or fabrics and rovings in the rest of the cross-section complicates the analysis, a point to be made is that when one end of a pole is held and a lateral force is applied to the other end of the pole, structural failure of the pole will occur not by the failure of the rovings, etc. in tension on the outside of the curvature of the pole or failure of the structure in compression on the inside of the curvature of the pole, but rather by the cross-section of the pole collapsing due to the forces illustrated in FIG.  3 . When the cross section collapses, the pole easily bends around the collapsed cross-section, much like a soda straw will collapse and easily bend once its bending resistance is exceeded. Accordingly, the purpose of the present invention is to provide simple means for maintaining the integrity of the cross-section of the composite pole structure, either eliminating or grossly reducing one of the most prominent failure modes in such composite utility poles. This allows the fabrication of lighter poles, reducing costs and resulting in poles that may be more easily handled, erected, etc. 
   In accordance with the present invention, provisions are made to maintain the cross section of the interior of the pole at substantially its original cross section at various positions spaced along the length of the pole. The effect of this may be envisioned from FIG.  2 . Assume by way of example that the cross-section of the pole is to be maintained at sections A—A and B—B. With respect to the part of the pole which is in tension, and recognizing that a curvature between sections A—A and B—B is exaggerated, it may be seen that any distortion of the cross-section due to tension in that part of the beam will tend to somewhat straighten out the part of the beam in tension between regions where the cross-section is maintained. This limits the extent of distortion of the cross-section that is possible. With respect to the part of the beam that is in compression between sections A—A and B—B, the same may be thought of as a slightly curved column. Provided the length of the column is purposely and adequately limited, the same may be caused to fail in compression rather than buckling inward. Thus if the cross-section of the pole is maintained in spaced apart areas which are sufficiently close together, pole strength may be grossly increased (or material requirements decreased) so that the pole strength approaches or is equal to that resulting from compressive failure or tensile failure of the pole and not loss of integrity of the cross-section of the pole. In that regard, since the outermost structure of the cross section of  FIG. 3  are the corners of the cross-section having the longitudinal rovings in tension, much of the compression on the inside of the curvature of the beam is in fact a reduction in the tension in those rovings, further inhibiting a loss of cross-section integrity of the pole between spaced apart regions where that integrity is enforced. 
     FIGS. 4 ,  5 ,  6  and  7  illustrate one embodiment of the invention. In this embodiment, rigid foam members  28  just fitting within the inside of a pole  20  are provided, the foam members  28  being supported on a pedestal-like structure  24  holding the foam members  28  in spaced apart positions along the length of the polo. Alternatively, these members may be placed only in the lower sections of a pole where the bending moment is the largest. The pedestals  24  may be a foam member integrally molded with foam members  28  or of a different material. As an alternative, multiple pedestals and foam members may be molded as one piece, the pedestal members being free to break, if they will, where they arm joined to adjacent foam members  28  as illustrated in  FIG. 5 , during deflection of the pole. In that regard, preferably the foam members  28  have a sufficient thickness in the vertical direction to maintain themselves substantially coaxial with the axis of the pole to avoid cocking within the pole. If desired, a rigid plastic, plywood, or other member  26  may be inserted or molded in place to provide additional rigidity to the foam members  28 , though stress concentrations on the inner wall of the pole preferably should be avoided 
     FIGS. 8 and 10  illustrate another embodiment of the present invention. As may be seen in  FIG. 10 , a rigid plastic member  30  is molded with a spoked wheel-like structure, with the periphery of the wheel just fitting within the inner periphery of the pole  20 . These wheel-like members are molded with an adequate thickness in the vertical direction to distribute the pole cross section retaining forces along the local area of the polo so as to avoid stress concentrations of a point contact. These plastic members may be molded, by way of example, from reground plastic, commercially available at a fraction of the cost of new plastic injection molding material. The wheel-like members  30  may be supported in spaced apart positions along the pole  20  by an inner pipe  32  running along the axis of the pole, such as a steel pipe to which spacers are fastened to hold the wheel-like members  30  in spaced apart disposition. 
   The embodiment of  FIG. 9  is similar to the embodiment of  FIGS. 8 and 10 , though with a round periphery not as accurately matching the inner periphery of the pole  20  of the preferred embodiment. In that regard, the preferred embodiments of the present invention may be used, by way of example, with poles in accordance with U.S. Pat. No. 6,155,017, which may have by way of example, a generally octagonal inner periphery, though with substantially rounded corners. 
     FIGS. 11 through 13  are schematic representations illustrating the possible positioning of the pole core-like structures of the present invention, such as those illustrated in  FIGS. 4 through 10 . More specifically,  FIG. 11  illustrates the uniform positioning of the core members on some form of central pipe or support structure. Such positioning is convenient, though not necessarily the most efficient.  FIG. 12  illustrates unequal spacing of core structures of the present invention, the core structures being spaced closer together adjacent the bottom of the pole where bending stresses are the highest, with the spacing increasing going up the pole.  FIG. 13  is similar, though with the spaced apart core structures only going partway up the pole in recognition of the fact that bending moments continue to decrease further up the pole while compressive load requirements for load support do not significantly decrease. In that regard, the present invention may be used in poles having a tapered wall thickness along their length or along part of their length, so that the poles&#39; resistance to bending will decrease along their length approximately in proportion to the decrease in the bending moment. In this case, equal spacing of the core structures along the length or along a substantial portion of the length of the poles may be preferred. 
     FIGS. 14 ,  15 ,  16  and  17  illustrate additional core structures, specifically core structures which are held in spaced apart position on multiple pipes or tubes  40 , such as in the examples shown, 2, 3 or 4, such pipes or tubes preferably rigidly connecting the core members  42  on pipes  40 . Such pipes, which may be by way of example, steel pipes, will provide further resistance to bending of the pole in addition to that resulting from the spacers maintaining the integrity of the cross section of the pole in the presence of high bending stresses. 
   The core structures of the present invention may be fabricated in various configurations and from various materials, as desired, including steel, plastic, plastic foam and combinations of such materials.