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)

114

4

Δσ are determined using rainflow counting. Mean-stress influence is not considered. This is in line with EN13001 because in large welded structures weld residual stresses are typically present in the as-welded conditions without stress relieving. For each stress range Δσ and corresponding number of cycles n , the fatigue damage D is calculated as D = n/N , where N is the number of cycles to failure from the S-N curve. The accumulated damage is calculated using Miner’s Rule The fatigue damage calculations are executed automatically through proprietary coding routines developed in house and operated on the SHM server. After every run of the model, the estimated damage is cumulatively added to the previously accumulated damage. The results are presented in a visualization interface, which will be discussed in detail in the next section. Based on the calculated progression of accumulated damage, the remaining lifetime of the

structure can be extrapolated. 3. Output of the SHM system 3.1. Load spectrum vs load history

The output of the SHM system is made available to the end user through an online dashboard that is updated automatically. The dashboard combines statistical and usage data with the fatigue damage data of the digital twin model. In the following paragraphs a selection of these features are discussed using output for the Crane-AM. The crane load spectrum in terms of number of lifts is being kept. A lifting event is starting from the moment a load is picked up to the moment when it is put down again. This information is particularly interesting to compare with crane design data. The load spectrum below contains two load clusters: one around 1200kN and another around 4500 kN. These loads correspond to the weights of an empty and a full ladle that are manipulated by the casting crane.

Figure 4: Load histogram of the Crane-AM during the measurement period.

However, for a detailed fatigue analysis, this load spectrum is not sufficiently accurate. This is due to the very basic definition of a lifting event. While a load is being lifted, several manipulations or movements of the trolleys can take place resulting in important differences of the local stress cycles and hence influencing fatigue damage accumulation. This is illustrated by the example which is plotted in Figure 5. This figure contains two separate lifting events which are plotted in the same graph. The graph contains the measured load lifted by the hook of the main trolley, the main trolley position and strain values measured by 3 strain gauges on one of the main crane girders. The strain gauges (labelled SG1, SG3 and SG5) are located on a line from South to North at the top plate on the main girder. In both lifts a similar mass is being lifted and put down again. Only the main trolley is used during both lifts. However, in the first lift, the trolley starts at the North position (main trolley position 26m), moves to the center of the crane and returns to the North position where the load is put down again. During the second lift, the load is picked near the South