Research On System Reliability Of Structures At Different Estimation Levels

The research on the reliability is mostly devoted to element reliability and system reliability in practical engineering. The element reliability usually indicates the safety of a single member of the structure, but several members in failure don’t mean the failure of the system, so it is of more practical significance to research the reliability of system for the sake of the structure safety.There are three working states for the member or the whole structure, namely safety, extremity and failure, by the comparison between value of safety margin and zero. The safety margin is a random variable, of which the mean to the standard deviation is the reliability index. To calculate the reliability index of every member of the integrated structure and then choose the minimal one as the level 0 system reliability, which is used for statically determinate structures. If to choose the reliability indexes in the interval close to the minimal reliability index, then these corresponding members will be called critical elements. Finally, the structure is simplified as a series system of the critical elements, the reliability of which is the level 1 system reliability.Next, considering the failure of one single critical element in level 1 and reanalyzing the structure, which is also for the determination of new critical elements. Then the critical elements of the former one and later one compose a parallel critical element pair, by which the structure is simplified as a series system, and the corresponding reliability is the level 2 system reliability. According to the process, level n system reliability will be calculated when the structure becomes a mechanism, and also all the failure modes of the structure can be found. But it is not applicable for the enormous reanalyzing of the structure.For elastic-plastic structure a natural definition of system failure is the formation of a mechanism, while the symbol of which is the singular of the integral matrix of the structure. Combining the displacement of the nodes, the deformation of the elements and the compatible of the displacement, the fundamental mechanisms of the beam structure and link structure are formed. Then each failure mode is the linear combination of the fundamental mechanisms,which however are usually not the real failure mechanism.Considering the fully correlation of the extreme capacity of every member and ignore the sequence of the elements in the failure modes, this dissertation proposes a efficient method for the calculation of the complex structure, which change the system reliability to the element reliability. Lastly, the accuracy of the method is proved by the comparison to the Monte Carlo.This dissertation analyses and compares the system reliability of frame, truss, spatial grid structure and single-layer latticed shell at different levels.