Site testing of dragline tubular structures

Draglines with tubular booms are susceptible to fatigue cracking due to the large number of cycles they are subjected to during operation. Circular hollow section (CHS) 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 onto a dragline cluster to measure strains during operation. Static tests, dynamic (swing) tests and dynamic (digging) tests were carried out and strains obtained during the different tests were analysed. Both nominal stresses as well as hot spot stresses were determined from the strain measurements. 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. Nominal bending and axial stresses were also determined and a relationship between the two shown in the form of graphs. 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.