Tapered steel poles are widely used for transmission, sub-transmission and distribution lines because they are strong, predictable and quick to install. These are the main decisions in a pole specification.
Design standards and loads
Steel transmission poles are commonly designed to ASCE/SEI 48, Design of Steel Transmission Pole Structures. Loads come from the utility's specification. In Canada, overhead line loading is governed by CSA C22.3 No. 1 and CSA C22.3 No. 60826, which define weather loads such as ice and wind for each region.
Shaft shape
Shafts are formed from plate into round or polygonal sections, typically 8, 12 or 16 sided, and seam welded. More sides give a rounder appearance and more even stress distribution, while fewer sides simplify forming.
Joints between sections
Long poles are made in sections. Slip joints, where one tapered section slides over the next with an overlap of at least about 1.5 times the diameter, need no field welding or bolting. Flange joints are bolted and are used where slip joints are not practical.
Foundations
Poles can be direct embedded in the ground, or fitted with a base plate bolted to anchor bolts cast in a concrete foundation. Anchor bolts are commonly supplied to ASTM F1554 with templates for setting.
Corrosion protection
Hot-dip galvanizing to ASTM A123 or CSA G164 is the usual choice. Weathering steel to ASTM A871 is an alternative where a brown patina is acceptable and the site conditions suit it. Galvanized poles can also be painted for appearance.
See our steel utility poles page for typical specifications.