Random fatigue of plane frames via lumped damage mechanics

Fatigue of metal structures has long been recognized as a random process, subject to significant uncertainties. To avoid excessive conservativeness, design and maintenance of such structures require explicit consideration of uncertainties in material properties and loading. This can severely impact computation times, when numerical models are employed in the analysis. In this context, this paper presents a novel application of Lumped Damage Mechanics (LDM) to the random fatigue analysis of plane frames subject to cyclic loading. The method is based on the observation that, in plane frames subject to dynamic loading, fatigue damage concentrates at the joints. Parameters of the proposed lumped damage model are obtained from parameters of linear elastic fracture mechanics. These parameters are calibrated in a cantilever beam problem, for which S-N data is given in building codes. Efficiency of the method is then demonstrated in application to 6 and 25-element plane frames. The proposed method has obvious applications to the reliability-based design and maintenance scheduling of frame structures subject to random wind and wave loadings.