基于 Kitagawa- Takahashi 图提出了一种计算起重机金属结构等效初始裂纹尺寸及其统计学分布的方法，此方法的优点在于只用到疲劳寿命极限和疲劳裂纹扩展门槛值，与随机变化的载荷应力无关．为计及载荷次序以及裂纹闭合效应对疲劳寿命的影响，基于载荷的功率谱密度，给出了一种频域分析的起重机疲劳寿命预测方法．为验证所提方法的有效性，将文中方法的预测结果与文献中的起重机箱形梁的疲劳实验结果进行对比，结果表明估算寿命与实验寿命吻合，文中方法具有实用性和可靠性．

Proposed in this paper is a method to calculate the equivalent initial flaw size (EIFS) and its statisticaldistribution for crane's metal structure.The method,which is based on the Kitagawa- Takahashi diagram,uses fatiguelimit and fatigue crack growth threshold to calculate the EIFS,without the participation of randomly applied loads.Moreover,considering the effects of load sequence and crack closure on the predicted fatigue life,a frequency- do-main analysis method for crane fatigue life prediction is proposed based on the power spectral density of the load.Thefatigue life of crane box girder predicted by the proposed method is compared with the test ones presented in litera-tures,and a good consistency is revealed,which means that the proposed prediction method is applicable and reliable.