Dynamical overloading influence on duration of life evaluation of lifting appliances

In this paper, the authors, on the basis of their last study about random fatigue design of crane mechanisms, are particularly making evident the influence of dynamical (vibratory) overloading on duration of life. An exhaustive theoretical analysis of one degree of freedom hoisting system, subjected to different vertical lifting modalities (sudden lifting of load on stationary ground, constant acceleration lifting of suspended load, etc.), is performed and relevant analytical formulations and figures are given for the time stress history, quick evaluation of the considered component, during a complete working cycle. For a dutiful completion of current crane standards declared overloading coefficients, the analysis is made taking in to exact consideration the viscous damping of the system and well founded rules for negligible cycles exclusion, based upon logarithmic decrement, are proposed. A detailed practical calculation example is submitted to reader's attention, for the purpose of a clear explanation of viscous damping influence on negligible cycles number and for comparison with current standard rules and other author's proposals.