System Reliability Bounding by Conditioning

Series systems that may fail in one of several unimodes and which have normally distributed unimode safety margins may be analysed with respect to reliability in terms of bounds reported in literature. For the majority of the correlation coefficients between the safety margins smaller than about 0.5 these bounds are very narrow Provided the total reliability is high and even if there is not just some very few dominating unimodes. It is shown how these bounds may be applied in a method of conditional sounding to give close bounds also in a case where most or all of the correlation coefficients are high. In a specific example the method is compared to another known method based on product form correlation coefficients.