Study On The Computation Methods Of Structural System Failure Probability

The development of structural reliability analysis can be divided into two stages, component analysis stage and system analysis stage. After years of diligent research, the component reliability analysis has achieved quite good level and has been applied to the actual projects. Although most of the scholars reached an agreement that the structural system reliability should be spreaded and applied to the engineering, yet there are still quite long way to go for this aim. There are mainly two difficulties for the structural system reliability application:â‘ how to search for the major failure modes?â‘¡how to calculate the structural system failure probability? This paper concentrates on the study of structural system failure probability calculation methods. The main research findings are as follows:(1) If the component reliability index is large and correlation of failure modes is strong, the PCM (Product of Conditional Marginal) method can usually cause quite large error for the series system failure probability calculation. So, a further improved PCM method (FIPCM) is proposed in this paper. The same problem also exists for the parallel system failure probability calculation if the EPM (Equivalent Plane Method) is used. So, an improved EPM method (IEPM) is also put forward.(2) Based on the conception of reliability index vector and the idea of equivalent failure mode, the reliability index vector formulae are deduced for the series system, parallel system and conditional equivalent failure modes. The correlation coefficient between the failure modes can be determined by the reliability index vectors, and then the structural system failure probability and reliability index vector can be obtained.(3) It has been found that the correlation coefficient between system failure modes is insensitive for the series and parallel system in a certain range of reliability indices. According to this characteristic, the maximum correlation coefficient between failure modes is taken as the approximate equivalent correlation coefficient when the equivalent plane method is used to calculate the structural system reliability.(4) Because the calculation accuracy of system reliability by the approximate method is strongly influenced by the calculation sequences, a grouping calculation method is proposed, in which the strength degree of correlations and the magnitude of reliability index are the main controlling factors. (5) The above mentioned principles and methods are applied to an actual project analysis, in which the grouping calculation method is used and the correlation of failure modes of groups are determined on the principle of reliability index vectors.