This research investigation studied the effects of galvanization on the fatigue life of high mast illumination poles. Reports that galvanization of high masts caused initial cracks to form at the toe of the weld connecting the base plate to the shaft of the pole were first validated. The effects of these initial cracks on fatigue strength were then checked through experimental testing. A variety of variables were tested for both their effects on the occurrences of the initial cracks and effects on fatigue life. These variables included testing galvanized against ungalvanized specimens, testing of varying fabricators and galvanizers, and testing of various types of connection details. These test results were compared against inspection results provided by Texas Department of Transportation inspectors. Also, methods of mitigating the effects of toe cracks on the fatigue life of poles were investigated. A method for repairing specimens both in the fabrication shop and in the field were developed and tested. Both methods showed strong improvement in fatigue life of the specimens providing a possible repair solution. / text

Failures of high mast illumination poles (HMIP) around the US have raised the concerns of officials because of their location close to areas with important human activity. Previous research, conducted at the University of Texas proved that those failures were fatigue type failures and that cracking initiated at the shaft to baseplate connection, specifically at the bends of the shaft. However, no research has been conducted on the remaining fatigue life of poles after they have been in service. This thesis investigates the remaining fatigue life of a pole, removed from service after severe cracking has been observed on it, via laboratory testing. Moreover, nondestructive and destructive testing procedures were implemented to investigate the initiation and evolution of fatigue cracks. The results validated the procedures for the in-situ validation of the remaining fatigue life of those poles. Last, the destructive test results enhanced the arguments that initial cracking at the toe of the weld at the shaft to baseplate connection is a result of the galvanizing process. / text

High mast illumination poles (HMIPs) are tall cantilevered structures used to efficiently illuminate large portions of highways and interchanges. Great interest in the performance of HMIPS has arisen from the discovery of extensive premature cracking at the toes of base plate to pole shaft welds of poles currently in service. These cracks, in some cases, have become so severe that HMIPs have actually collapsed, and therefore present a great threat to public safety. Previous research at the University of Texas at Austin sought to solve the design problems posed by these pole failures by conducting both full-scale and analytical tests on optimized designs of HMIPs for fatigue loads. These studies indicated that using full penetration welds to connect 3" thick base plates to relatively thin shaft walls minimized warping of the base plate during fatigue loading, and maximized fatigue performance. Toward the end of these studies when researchers sought to test an uncoated optimized HMIP back-to-back against a galvanized HMIP of the same design and material, researchers discovered the galvanized specimen had cracked during the galvanizing process. This finding prompted an in-depth study to determine the cause of these cracks, and to determine if practices could be implemented to prevent crack formation. Initially, bend radius, chemistry, and shaft to base plate thickness studies were conducted to find how these parameters affect HMIPs during galvanizing. These parameters were found to play a minor role in the cracking of HMIPs relative to the thermal effects induced during the galvanizing process. Full-scale and analytical tests verified the impact of thermal straining within HMIPs during galvanizing. Instrumenting HMIPs and smaller HMIP stub sections with thermocouples and strain gages provided temperature and initial strain gradients resulting from exposure to the molten zinc bath. This data, as well as observations of cracks in the tested HMIP sections, aided the development of a finite element parametric study comparing HMIPs of the same 150' length and 80 mph design but varying shaft thicknesses. This research concludes that reducing the pole shaft diameter to thickness ratio reduces the likelihood of galvanizing crack formation. / text