A research on ZQ5t-40 m-A8 grab crane of Zhejiang JuHua group outdoor coal thermal power plant was made. On the one hand, the thickness of multiple cross section of the main girder was measured by using the ultrasonic thickness meter(model:CT160) to determine whether the intensity and stiffnessmeeting the requirements;on the other hand by using fracture mechanics, analyzing the expansion of the elastic-plastic crack and the regularity of instability of the welded box girders under the action of alternating load loop, and the fatigue life of cranewas accurately estimated. It is signiifcant thatthe main girder stiffness, strength and fatigue life are analyzed and calculated for reducing the crane corrosion and fatigue damage accidents, and has an important guide on the crane design, manufacturing, maintenance and special equipment inspection analysis.%以浙江巨化集团热电厂露天煤场ZQ5t-40m-A8抓斗装卸桥为研究对象，一方面采用超声波测厚仪（型号：CT160）现场测量主梁多个截面的板厚，以此数据来计算主梁的强度和刚度是否满足使用要求；另一方面运用断裂力学，分析焊接箱型主梁在循环往复的交变载荷作用下弹塑性裂纹的扩展和失稳规律，并相对准确的预估出起重机的疲劳寿命。通过主梁刚度、强度和疲劳寿命的分析计算，对于减少起重机腐蚀、疲劳破坏事故的发生，指导起重机设计、制造、维护和特种设备检验分析等方面具有极其重要的意义。
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