Fatigue Life Study on Welded Aluminum Shoe-Base Details with Handholes

Light poles have been used alongside streets and roadways for illuminating travel and to increase pedestrian and driver safety during the evening and early morning hours. Classified as slender structures, they are subjected to fluctuating loads due to the wind. In this study, a welded aluminum handhole detail subjected to two different heat treatments was considered. Specimens with welded handholes were either non-postweld heat treated (NPWHT) or postweld heat treated (PWHT). Ten combination samples, which included both welded shoe-base and handhole details (NPWHT), were fatigue tested in the Structures Laboratory of the University of Akron. Of the 10 tested, 9 specimens failed around the handhole and 1 failed adjacent to the cast shoe-base during testing. Fatigue data were used to develop a best-fit S-N curve, as well as a lower bound assuming a log-normal distribution. The proposed S-N curve was compared to categories D and E of the Aluminum Design Manual (ADM) to find the specific category that best represented the fatigue test results. Results of the fatigue tests of combination specimens were compared to those with only PWHT handhole details. A best-fit S-N curve developed from results of handhole failures of NPWHT combination specimens had a larger slope compared to the PWHT samples. The postweld heat treatment of the specimens may relieve some residual stress around the handholes, resulting in an improved S-N curve. Strain and thermographic measurements, in conjunction with finite-element analysis, assisted with an explanation of the observed behavior.