Finite element modelling of frictional slip in heavy lift sling systems

A new finite element model and a corresponding computational procedure for analysing sling systems with frictional slip are presented in this study. In the model, the magnitudes of the slip are introduced as new unknowns in the element nodal displacement vector, and additional relations between frictional forces are imposed to make the system of equations complete. The major advantage of this model is that there is no longer any need to iterate for the magnitudes of slip. The model is used to derive formulations for the doubled sling and butterfly loop arrangements, which are used in heavy lift operations. Rigging sling systems with doubled slings, a butterfly loop and make-up doubled slings are analysed to demonstrate the effectiveness of the present model. The results indicate that, the effect of frictional slip on the sling tensions is significant for doubled and looped slings, and the present model gives more realistic solutions.