Service loads in dragline tubular structures : a case study of cluster A5

Draglines are used extensively for removal of overburden in the coal mining industry. Draglines with tubular booms are among the structures most susceptible to fatigue cracking due to the large number of high load cycles to which they are subjected during operation. Circular hollow section tubes are used as both lacing and chord members. In this paper, a study was carried out to better understand the stresses in a 4-lacing cluster during operation. Strain gauges were installed on a typical dragline cluster A5 to measure strains generated while in operation. Static and dynamic (swing and digging) tests were carried out, and strains obtained during the different tests were used to calculate both nominal stresses and hot spot stresses. For cluster A5, the hot spot stresses at weld toes in the lacing members were found to be significantly larger than those at weld toes in the chord members. Bending stresses were found to form a relatively larger portion of the nominal stresses at the weld toes in the lacing members compared to chord members. The results of this work highlight a conclusion found in the authors' previous work that the high tensile residual stresses resulting from welding are an important issue not measured in hot spot stress testing, but these stresses are relevant to the levels and location of cracking observed in practice.