同时考虑结构系统强度和疲劳的可靠性分析

Reliability analysis of structural system considering strength and fatigue

在以往的结构可靠性分析过程中,结构系统的静载和疲劳载荷失效情况大多是分别考虑的,这与许多实际工程结构(如船舶等结构)是不相符的.根据疲劳载荷造成的疲劳累积损伤对结构极限承载力的影响情况,研究了结构承载能力的可靠度计算方法.以结构累积损伤和结构初始抗力的形式给出了一个综合结构抗力变化历程的等效抗力,讨论了结构系统在静载和疲劳载荷作用下的两种失效模式,并考虑了二者之间的相关性对结构系统可靠性的影响;用改进的分枝限界法寻找主要失效模式,并用二阶矩方法计算各失效模式的可靠性指标;然后用PNET法计算结构系统可靠性.算例表明,虽然分别考虑静载或疲劳载荷作用下的结构系统可靠性较高,但综合考虑两种失效状态时,结构系统可靠性却较低.即疲劳累积损伤会降低结构的极限承载能力可靠性.因此,对结构系统同时考虑强度和疲劳的可靠性分析是必要,是符合工程实际的.

At present, structure failure subjected to dead load and fatigue load has been mostly considered separately in the process of reliability analysis. But this is not suitable for many engineering structures (for example, ship structures). Based on the understanding of passive impact of accumulated damage induced by fatigue load on ultimate bearing capacity, the ultimate bearing capacity reliability analysis method for structures subjected to fatigue load was presented. Equivalent strength was given in the form of accumulated damage and initial strength of structures and considered the process of strength deterioration. Discussed was the reliability analysis method of a structural system simultaneously considering the dead load and the fatigue load and the relativity of two failure modes influencing on the structural system reliability. The significant failure modes are identified by using the advanced branch-and-bound method, and their reliability index were calculated by using second-order moment reliability method. The reliability of structural system was evaluated by PNET method. A numerical example was analyzed and indicated that the reliability of structural system only subjected to dead load or fatigue load is higher. However, when simultaneously considering the two failure modes, the reliability is possibly lower, and the accumulated fatigue damage will lead to lower ultimate bearing capacity reliability. Thus, reliability analysis of structural system considering strength and fatigue is necessary, and is suitable for engineering case.