Experimental Performance of High Mast Illumination Poles with Pre-Existing Cracks

Abstract

High Mast Illumination Poles (HMIPs) are tall structures used to provide lighting along highways. There are a large number of in-service HMIPs in Texas that have pre-existing cracks at the weld that joins the pole shaft with the baseplate. Previous research has shown these pre-existing cracks occur during the galvanizing process, before the poles are put into service. Once in service, these pre-existing cracks can grow under repeated loading generated by wind, and most notably by vortex shedding. While none of these HMIPs in Texas have failed, the presence of the pre-existing cracks and potential for wind-induced crack growth raises safety concerns. . The work reported in this thesis is part of TxDOT Research Project 0-6829: “Fatigue Resistance and Reliability of High Mast Illumination Poles (HMIPs) with Pre-Existing Cracks.” TxDOT Project 0-6829 is aimed at generating data and information to support a probabilistic based assessment of the remaining life of pre-cracked HMIPs. The scope of Project 0-6829 includes laboratory fatigue tests on galvanized HMIPs with pre-existing cracks, field studies and measurements to characterize the wind response of Texas HMIPs, the development of a reliability based framework to assess the fatigue life of in-service pre-cracked HMIPs, and recommendations for possible retrofit techniques for in-service HMIPs. The research reported in this thesis focuses on the task of conducting laboratory fatigue tests of galvanized HMIP specimens with pre-existing cracks at the shaft to baseplate weld. The objective of this work was to develop additional experimental data, to supplement experimental data collected in earlier studies, to characterize the fatigue performance of galvanized HMIPs with pre-existing cracks. A more specific objective was to collect fatigue test data on pre-cracked HMIPs at low stress ranges, representative of the stress ranges seen by in-service HMIPs subject to vortex induced vibration. This thesis reports the results of a series of fatigue tests on HMIP specimens, including a description of the test setup and test procedures, a presentation of ultrasonic test results that measured crack growth during the course of the fatigue tests, and the test results.