PacTrans: Investigation of High-Mast Light Pole Anchor Bolts

AUTC project number: S16920

PI(s):
  • Scott Hamel
  • Jeffrey Hoffman
Funding:
  • PacTrans
  • AKDOT
  • Start Date: Jun 1, 2012
  • End Date: Oct 31, 2013

Project Summary

The Alaska Department of Transportation (AKDOT) owns and maintains over onehundred high-mast light poles that are up to 170 feet tall. These poles are used to illuminate intersections and freeways in the central and south-central regions of Alaska. The poles, which are also used throughout the lower 48, have experienced scrutiny in the last decade after a number of catastrophic failures across the country. Studies have been conducted to investigate the welds near the base and baseplate thickness. The results of these studies and associated recommendations have been implemented by AKDOT. As part of its review of these structures, AKDOT has found widespread and continual loosening of the anchor bolt nuts at the base of the poles. The loosening of anchor nuts presents a great danger as it greatly reduces the fatigue resistance of the anchor bolts, a condition that could cause significant overstress and failure of these elements. Given their height and proximity to major roadways, collapse of these poles would likely cause significant damage and multiple fatalities. AKDOT has combated this problem by instituting a labor-intensive inspection program in which each pole is inspected every 4 years. Loose nuts found by inspectors are re-tightened by maintenance crews. This program has served as a stop-gap measure, but the level of safety provided by the four-year interval is not known. A more permanent solution is required to ensure the safety of the structures and reduce inspection and maintenance efforts. The following proposal outlines the problem background, the efforts thus far to solve the problem, and the approach of this project to determine the cause or causes of the nut loosening and recommend procedures to eliminate the phenomenon. One of the final results of this project will be the development of specific guidelines for remediating the problem in current poles, and recommendations for alternative designs for future installations.