A procedure is presented for the optimization of truss structures under system reliability constraints using an elemental reliability approach. The structure is weight-optimally designed by imposing on it a set of elemental reliability constraints. The optimum point is assumed to be on the boundary region and is reached through a recurrence relation based on an optimality criterion. The approach, different from the one widely adopted from electronic systems in which the failure inducing loads are componental and the systems are generally working under low loading roughness, is based on the fundamentally different phenomenon that failure inducing loads on structural systems are systemic. The systemic nature of the failure inducing loads on structural systems leads to the so-called common-mode failures and the system reliability is solely determined by the component with the smallest reliability; the weakest link. A less fundamental phenomenon which, nevertheless, emphasizes the approach is that the structural systems as a whole are under a frequently high loading roughness. Although the conclusion is on the optimistic side, compared to the a priori modelled series systems for just-stiff configurations, this can be further proven by estimating the structural system reliability of the resulting optimal design by a critical path incremental loading model which highlights the conditional and interdependent nature of member reliabilities after the weakest is systematically made to fail.
