Fatigue Performance of Multi-Sided High-Mast Lighting Towers

This study investigated the fatigue performance of multi-sided high-mast lighting towers. Recent failures of high-mast lighting towers have increased the awareness of the problems associated with these cantilevered structures. The failures of these steel poles primarily occur just above the weld at the base plate connection indicating a fatigue type failure. Although these structures are designed to the current 2001 AASHTO Specification, their susceptibility to fatigue failure has become a nationwide problem.

The objective of this research was to evaluate the fatigue performance of typical fatigue critical connection details used in high-mast lighting towers. Laboratory fatigue testing was performed on full-scale specimens utilizing fillet welded socket connections, full penetration weld connections, as well as a stool base connection detail. The results of the study found that that the design provisions for high-mast lighting towers do not accurately predict the fatigue life of the structures. Common details designed in accordance with the AASHTO specification did not meet the required minimum fatigue life categories as specified by the design provisions. It was also found that significant fatigue resistance can be gained with an increase in base plate thickness and an increase in number of bolts used in the base plates.