Structural health monitoring of a dragline cluster using the hot spot stress method

Abstract

‘Hot spot stress’ is an approach often used to consider fatigue loadings in heavily welded tubular joints. This article reports the determination of hot spot stresses in mining dragline booms, which are often ≥100 m in length, using strain gage measurements and finite element analysis (FEA) modeling as part of a structural health monitoring concept. Strain gages were installed on a typical A11 cluster for estimating hot spot stresses, as recommended in the existing fatigue design guidelines by the International Institute of Welding (IIW) and the International Committee for the Development and Study of Tubular Construction (CIDECT). The results from the experimental measurements and the FEA were found to be comparable to a large measure. It was concluded that while hot spot stresses were high enough at the weld toes to cause cracking, they could not explain the cracking that occurs at the welds in the main chords on their own. Issues in comparing theoretical and experimental measurements are discussed.

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

“…A total of 50 strip gauges, each containing five strain‐sensitive gauges, were installed at weld toes around the connection to measure the hot spot stresses. Detailed measurements similar to those presented in this paper have been reported previously by Joshi et al for a different 4‐lacing cluster, designated as cluster A11 and illustrated in Figure c. There is a significant difference in the lacing arrangement between clusters A5 and A11.…”

“…Details of the location of strip strain gauges in plane AB for the cluster are shown in Figure b and d. A fifth strain gauge was installed on the footprint where lacing members A5D4, A5D5 and A5F5 overlap at the weld toe on the chord member. Details Y and Z in Figure b and d show the same distances as those reported in Joshi et al for cluster A11, viz. the distance between the toe of the weld and the center of the first strain gauge in a strip and the extrapolation distance determined using recommendations from CIDECT Design Guide No.…”

“…The ‘W’ series gauges are waterproof type strain gauges and are molded with special epoxy resins. This encapsulation means that for the ‘W’ series, there is an increased protection against moisture from the thick layer of silicon applied externally on and around the gauges as done for cluster A11 in Joshi et al . Kyowa KFG‐2‐120‐D9‐11 N10C2 strip strain gauges were used (gauge factor = 2.5) as for cluster A11.…”

“…The nature of these tests is already described in detail in Joshi et al for cluster A11 and relisted in Table . For cluster A5, one typical stress plot for each of the static, dynamic (swing) and dynamic (digging) tests is shown in Figure for the first gauge closest to the weld toe in strip strain gauge 1 designated C05O13S01G01 located in the chord member, and also for the first gauge closest to the weld toe in strip strain gauge 2 designated C05O14S02G01 located in the lacing member.…”

“…(a) Location of cluster A5 in a BE 1370 boom, (b) 4‐lacing cluster A5, (c) 4‐lacing cluster A11 studied in Joshi et al .…”