Iowa Department of Transportation
Alice Alipouralipour@iastate.edu email >
Structure and Infrastructure Engineer, BEC
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer
About the research
High-mast lighting towers have been widely used to illuminate large areas such as freeways, airports, stadiums, and sports facilities throughout the nation and across the world. A hand hole is commonly found near the base of these structures as the access to the electrical wires inside the structure. The current American Association of State Highway and Transportation Officials (AASHTO) design standard of high-mast lighting towers with a tube diameter larger than 30 in. and sign and signal support structures requires that the width of the hand hole shall not be greater than 40% of the tube diameter. It also specifies that when calculating the nominal stress at the hand hole, it should be magnified by a stress concentration of 4.0. However, this design standard is actually difficult to follow in some pole structures with a small diameter.
A limited review of the currently fabricated structures showed that high-mast lighting towers in the range of 55 to 100 ft in height are most affected, where openings as large as 87% of the pole diameter have been used. The application of the stress concentration factor of 4.0 on these poles results in either increasing the thickness of the tubes or increasing the dimeter of the tube, which leads to a much more expensive pole and overall luminaire system.
The goal of the research is to identify the fatigue resistance of high-mast pole specimens with different opening ratios of the hand hole. Particularly, this study included the following objectives:
- Conduct fatigue experiments on two types of high-mast pole specimens with opening ratios of 46% and 54% and identify their fatigue resistance
- Build finite element models for pole specimens with different opening ratios to observe the change of the stress response at the pole base
- Use the results from the fatigue experiment and finite element analysis to study the influence of the opening ratio on the fatigue resistance of a high-mast lighting tower