High-Mast Light Poles Anchor Nut Loosening in Alaska: An Investigation Using Field Monitoring and Finite-Element Analysis.

摘要

High mast lighting poles (HMLPs) are tall, roadside structures effective for lighting large areas of highways and intersections. The Alaska Department of Transportation and Public Facilities (AKDOT&PF) maintains 118 such poles in the greater Anchorage and Fairbanks areas. Some of these HMLPs have experienced anchor nut loosening at their foundation connection and an in-depth review of inspection reports suggests that the foundation type and the number of anchor rods affect loosening. In this study, two HMLPs were field instrumented and the axial force in their anchor rods was recorded during tightening. Excessively high anchor rod pre-tensions were recorded on the first pole, after which a modified tightening procedure was created and used successfully on the 2nd pole. Finite-element (FE) modeling was conducted to examine the mechanical behavior of the foundation connections and recreate the clamp-load loss. The monitoring and modeling results indicate that plastic deformation of the anchor rods is the likely cause of clamp-load loss in flange-type connections. Anchor rods in double nut moment connections, high strength rods, and increased flange plate thickness were all shown to reduce clamp-load loss. Recommendations for existing and yet to be installed HMLPs are presented based on these results.