Static sling tensions in heavy lifts with doubled sling arrangement

Abstract

The force split ratio, α, for doubled sling arrangements is highlighted in this paper. Three analytical models - namely, the free-slipping model, the fixed model and the friction model - are presented to analyze the tensions of doubled slings. A corresponding computational model is developed to include the effects of structural stiffness, the slippage of doubled slings at the hook, and the sling misfits on the sling tensions. It is found, through both theoretical study and field measurement, that the force split ratio for doubled slings is significantly dependent on the equivalent coefficient of friction and lift configuration. A larger force split ratio, α, for doubled slings may therefore be appropriate for rigging selection and design of lift components to ensure consistent factors of safety during certain lifting operations.