平行钢丝斜拉索疲劳性能评定Ⅱ:斜拉索疲劳寿命模型

摘要

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.%该文为平行钢丝斜拉索疲劳性能评定研究的第二部分:斜拉索疲劳寿命模型,在钢丝疲劳寿命模型研究的基础上,从线性累积损伤和钢丝PSN曲线等效损伤路径两个角度推导斜拉索内任意一根钢丝疲劳破坏所经历的循环次数,并证明两个角度得到结果的等价性,在此基础上基于次序统计提出斜拉索疲劳寿命界限估计方法;采用Monte Carlo方法模拟斜拉索疲劳寿命的概率分布,研究斜拉索疲劳寿命的终止条件,深入探讨斜拉索疲劳寿命的影响因素并通过数值模拟建立斜拉索PSN曲线.研究表明:斜拉索疲劳寿命由其内一小部分疲劳寿命较小的钢丝控制,以10％断丝率作为斜拉索疲劳寿命终止条件比较合理;斜拉索疲劳寿命服从正态分布,其变异性显著降低.斜拉索疲劳寿命均值与其内钢丝数无关,钢丝数增加会减小斜拉索疲劳寿命的变异性,钢丝疲劳寿命的变异性对斜拉索疲劳寿命影响较大.