United States Department of Transportation
i
Fatigue Resistance and Reliability of High Mast Illumination Poles (HMIPs) with Pre-Existing Cracks: Final Report
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2018-11-01
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[PDF-62.10 MB]
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Edition:Final Report
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Abstract:High mast illumination poles (HMIPs) are used throughout Texas and the U.S. to provide lighting along highways and at interchanges. Texas currently has about 5000 HMIPs, varying in height from 100 to 175 ft. Failures of HMIPs have been reported in several states, attributed to failures at the shaft-to-base plate connection. No collapses of HMIPs have been reported in Texas. However, recent studies have shown that many galvanized HMIPs in Texas have pre-existing cracks at their shaft-to-base plate connection, most likely caused by the galvanization process before the poles were placed in service. Previous research has also shown that pre-existing cracks may significantly reduce the fatigue life of galvanized HMIPs. The Texas Department of Transportation (TxDOT) has identified three major issues/concerns with respect to HMIPs with pre-existing cracks: the lack of reliable experimental data about the fatigue life of pre-cracked HMIP base-connection details; the significant uncertainty regarding the natural wind response of HMIPs to the various major wind environments in Texas (much of this uncertainty is related to the lack of measured data from comprehensive field studies); and, due to this lack of data, the ‘safe/serviceable’ life of in-service TxDOT HMIPs with pre-existing cracks cannot be reliably predicted. The main goal of this research project was to generate data and information to support a probabilistic-based assessment of the remaining life of HMIPs with pre-existing cracks. The research included extensive laboratory fatigue testing of HMIPs with pre-existing cracks, field monitoring of in-service HMIPs at five locations across Texas, and the development of a reliability based framework to assess the safety of in-service HMIPs with pre-existing cracks. The results of this study show a wide range in the predicted lives of HMIPs with pre-existing cracks at different locations throughout the state. Based on a probability of failure of 5 percent, the predicted fatigue life at a number of locations analyzed throughout the state showed predicted lives varying from approximately 30 years to over 300 years. The variation in predicted lives is mainly affected by differing wind characteristics at each location.
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