PSI - Issue 75

Jeroen Van Wittenberghe et al. / Procedia Structural Integrity 75 (2025) 111–119 Jeroen VAN WITTENBERGHE and Vitor ADRIANO / Structural Integrity Procedia (2025)

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Figure 9: Measured values of the dynamic factor for high and low speed during lifting up and down at three positions along the length of the crane.

In this set of tests, dynamic factors between 1.04 and 1.13 are found. A weld detail with a fatigue life of 1,000,000 cycles calculated with ϕ = 1.04 will only have a fatigue life of 780,000 cycles when ϕ = 1.13 is applied instead. For this reason, an accurate assessment of the dynamic effects is important for accurate remaining lifetime calculation of a crane. The frequency of the dynamic oscillations is plotted in Figure 10. Values are only plotted for the high speed, but measurements performed at low speed show no relevant differences from these. Also, no relevant differences are observed between lifting up and lowering the load. The cases where the cable stiffness and crane girder bending stiffness is the lowest, the lowest oscillation frequencies are observed (low lifting height and trolley closest to the centre of the girder). The highest oscillation frequencies are measured at high lifting height with the trolley closest to the end of the crane. This corresponds to the cases with highest stiffness. Tests performed with different payloads showed that a heavier payload will result in a lower resonance frequency. This confirms that the crane acts as a mass-spring system: for a simple mass-spring system, the natural resonance frequency of such a system is a function of the square root of the spring stiffness divided by the mass.