High-cycle fatigue performance of high-mast illumination pole bases with pre-existing cracks

This paper presents the results of high-cycle fatigue testing of high-mast illumination poles (HMIPs) with pre-existing cracks at the pole-to-base plate connection detail. Resonant bending fatigue tests were conducted on five pairs of HMIP base specimens at nominal stress ranges of 41.4 MPa (± 20.7 MPa), 27.6 MPa (± 13.8 MPa), 20.7 MPa (± 10.3 MPa) and 6.9 MPa (± 3.4 MPa). The length and depth of pre-existing cracks was measured and the propagation of the individual crack was monitored throughout the testing using an ultrasonic inspection technique. The experimental results suggested that the fatigue lives of the tested specimens can exceed the predicted life for AASHTO fatigue category E details and approach category D details even in the presence of pre-existing cracks. The results provide insight into the fatigue response of HMIP with pre-existing cracks at the base connections at very low stress ranges and high cycle counts. The findings suggest that the pre-defined constant amplitude fatigue limits for AASHTO details may not strictly apply to HMIP details with pre-existing cracks.