Fatigue life assessment and comparison of two types of bridge-mounted welded aluminum light pole support structures

Abstract

The primary objective of this work was to perform fatigue life assessment for two types of mounted bridge aluminum light poles, which can lead to a better understanding of the structural behavior of both types of details, currently used as secondary structural elements mounted on various bridges and highways. Included in this study are shoe base and through plate socket connection details. Fatigue tests showed a relatively low life for through plate details as compared with the shoe base connections at the same stress range. Fracture mechanics studies indicated that lower bound design curves could be predicted using higher stress ratio fatigue crack growth data superimposed with the effect of compressive residual stresses at the surface of the tubes. Parametric studies demonstrated the importance of base plate thickness on the through thickness bending of the tube wall, which can be extremely effective on mounted bridge poles due to open terrain wind dynamic loads. A research study revealed that shoe base socket connection fatigue life is on average seven times better than a 25.4 mm (1 inch) plate socket connection details and when 76 mm (3 inch) plate thickness is used, fatigue life for shoe base socket connections is 1.5 times the 25.4 mm through plate socket connection. It is recommended that whenever a through plate socket connection light pole is chosen for bridge luminary, 63 – 76 mm (2.5 – 3 inch) plate thickness should be used to ensure an infinite fatigue life.

Keywords:

• Fatigue life
• Stress range
• S – N curve
• Finite element
• Fracture

Acknowledgements

The authors would like to thank HAPCO – Aluminum Pole Products of Abingdon, Virginia for their support of this work. Mr Dave McVaney and Mr Steve Gerbetz at The University of Akron provided encouragement, training and assistance in making the measurements. Thanks are always due to the late Mr Mauri Sharp for teaching the authors to continually question and evaluate conventional wisdom. Thanks also to Mr Tom Brannon (Chief) and Mr Isam Tabshouri for their support and encouragement to expand research studies.