Abstract: In the light of components failure dependency in structural systems, effects of the common load and components strengths stochastic characteristics upon components failure dependency are described. And the mechanism of the common load giving rise to elements failure dependency whereas strengths of components are independent is studied. For parallel, series and r-out-of-n systems made up of identically distributed components with total load dependency, a feasible approach to system reliability estimation considering failure dependency due to the common environment load is developed. By means of orthonormalization of variables, the calculation can be simplified when the covariance matrix of safety margin variables is figured out, which can give more valuable information to reliability design and optimization.

Key words: Common cause failure, Correlative coefficient, Load dependency, Reliability, Structural system