Abstract: Through analysis the effects of deviation of the component strength and the common environment load to each failure mode in redundant structural systems, the mechanism of common cause failures when all components strength variables are independent is illustrated. As a kind of dependent failures, the basic root cause of common cause failures is discussed in detail. Using the results of JC method, the multiplicity failure probability of systems can be expressed approximately by component individual failure probability and 2-class union failure probability. An approximate approach to failures probability estimation is developed. By means of the new model derived from environment load-component property analysis, common cause failures probability of r-out-of-n: g systems can be easily evaluated. An example is given to show availability and effectiveness of the method. The results of calculation and Monte Carlo simulation are in good conformity to each other.

Key words: Common cause failure, Failure-dependency, JC method, Reliability, Structural system