Fatigue Fragility Curves for Overhead Conductors Subjected to Varying Amplitude at Suspension Clamps

Overhead conductors undergo multiple cycles of varying bending amplitude at suspension clamps due to aeolian vibration. The current approach for evaluating fretting fatigue damage relies on using constant amplitude experimental tests on conductor classes grouped according to the Poffenberger-Swart relation. This approach neglects the effect of sequence of amplitudes. A probabilistic fatigue life assessment model is developed using the Poisson binomial model and various cumulative damage theories for sets of vibrations with different amplitudes. Fragility curves are presented for the failure of the first wire to the fourth wire failure in a conductor for experimental data sets with increasing and decreasing amplitudes of vibration. A comparison of predicted fragility curves with the conductor fatigue data shows that although the contact stresses as a function of amplitude of vibration are independent of the loading sequence, the material fatigue resistance is affected by the loading sequence. Cumulative damage theories that include the order of loading on the wires predict fragilities that are closer to experimental observations.