Service stresses and implications for fatigue strength in dragline tubular structures

Draglines are the powerhouses of open cut mining in the coal industry in Australia. They have the capability of moving more than 100 tonnes of overburden in a cycle. Following site measurements of stress in one of the clusters where cracking is prevalent under service, this paper looks at the applicability of predicting fatigue life in draglines clusters using cumulative damage analysis. The design curves used in the analysis are in the hot stress method. Variable stress as well as equivalent stress range is used in estimating the fatigue life of the cluster. In the main chord of the cluster, where the cycle is largely compressive it is found that predicting fatigue life using a compressive stress reduction based on the British Standard BS7608 results in a prediction that is relatively closer to observed fatigue lives for new clusters. Using the full stress range on the other hand predicts fatigue lives in the main chord that are comparable to the fatigue life in repaired connections.