Fatigue property assessment of parallel wire stay cable II: fatigue life model for stay cable

This paper presents the second part for the assessment on fatigue properties of parallel wire stay cable. On the basis of the fatigue life model of steel wires proposed in the first part of the research, the models of fatigue cycles for the arbitrary wire in the cable are deduced from two aspects considering the load redistribution of the unbroken wires in the cable. One aspect is the Miner linear cumulative damage law of wires and the other aspect is the equivalent damage paths of PSN curves of wires. It is proved that the results from the two aspects are equivalent. Furthermore, the boundary estimation method of cumulative distribution for fatigue life of a cable is put forward based on the order statistics of wire fatigue life in the cable under the constant stress range. The Monte Carlo method is proposed to simulate the probability distribution of cable fatigue life in terms of the probability model of fatigue life for wires. The termination conditions for evaluating fatigue life of a cable are studied in the light of the percent of broken wires in the cable. Finally, the influence factors on fatigue life of a cable are discussed and PSN curves of a cable are established. The results indicate that the fatigue life of a cable is controlled by a fraction of wires with short fatigue life. It shall be reasonable that 10% broken wires is used to define fatigue failure for a cable. The fatigue life of a cable appears to be asymptotically normally distributed and its variability decreases as the wires increase in the cable. The mean fatigue life of a cable is independent of the number of wires in the cable. However, the variability of cable fatigue life decreases as the number of wires increases, and the variability of wire fatigue life significantly affect cable fatigue life.