Fatigue Reliability Analysis For Structures Considering Load Shedding

Cracked structures are very common in the project, and the growth of fatigue cracks in them will directly impact on the life of the structures. To do fatigue reliability analysis for the cracked structures can give us some reference for the safety evaluation of such structures, so it has great practical significance.In the basic theory, this paper first introduce some kinds of structural reliability calculation method, such as Hasofer-Lind and Monte-Carlo, and also give one example of Hasofer-Lind. Then, some theory of stress intensity factor and geometric correction factor and several calculation method for stress intensity factor have also been introduced, at last the geometric correction factor for two cases have been given, the two cases are a plate containing a run through crack and a plate containing a semi-elliptical surface crack.After the introduction of the basic theory for the structural reliability and the basic theory for the linear elastic fracture mechanics, this paper describes the load shedding characteristics of the cracked structures during fatigue fracture,discusses the load shedding mechanism of marine structure details, and analyses the reason of load shedding. Load shedding is, in essence, the load redistribution in cracked components. It reduces the stress intensity factors of crack tips, inhibits the growth of fatigue cracks, and enhances the life of cracked structures. Then we also build several load shedding models in fracture mechanics analysis for cracked structures, and calibrate the load shedding with approximate equations.At last, we can get the safety margin equation of cracked structures for fatigue reliability analysis of life, and through an example, the reliability index considering load shedding and without considering load shedding can be got. By analyzing, we know that the reliability considering load shedding is bigger than that not considering load shedding. This conclusion means that the load shedding mechanism based on fracture mechanics has great application value.