Sometimes transmission poles in urban areas must fit into tight locations. Such is the case for poles located in a sidewalk when the line is built in a road right-of-way. To maintain wheelchair accessibility to the sidewalk, the Americans with Disabilities Act restricts the groundline diameter of such poles to 24 inches (61 cm). Historically, the only options to meet this restriction were to use steel poles fabricated with thick steel plate or to use short spans, which caused the transmission line to resemble a picket fence.
Florida Power & Light (FPL; Miami, Florida, U.S.) and Newmark International (Birmingham, Alabama, U.S.) worked together to develop the concrete-filled steel pole, and thus provide another more economical solution. The multisectioned pole offers functionality and ease of construction. The direct-embedded bottom section is a thin-plate steel shell filled with concrete. Shear connectors allow for composite action between the steel shell and the concrete. This composite action gives a capacity of about 2.5 times the capacity of an equivalent thin-plate steel pole.
The companies performed extensive testing, including fatigue testing, to ensure durability of the composite action under cyclic loading. This testing also included testing several shear connection systems to develop a design that is effective, economical and easily fabricated. All other sections of the pole are regular thin-plate steel. Sections are joined by slip or flange joints as necessary.
The composite pole is lightweight when compared to its concrete equivalent and costs less than an all-steel pole. Additionally, it meets small-butt-diameter restrictions that the traditional concrete or steel pole could not meet. The first composite poles are now in service: self-supported deadends designed for 125-mph wind speeds.
FPL and Newmark have applied for a joint patent for the composite pole.
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