Recently reliability-based limit state design has been recognized as one of useful design methods. In order to make the most of limit state design in practice, target reliability should be appropriately determined. Structural design is expected to be rational and balanced in terms of function, safety and cost. So far it is shown that the concept of minimizing total expected life-cycle cost is effective in determining the optimum reliability. The failure cost model, the cost up ratio and the probabilistic load model are examined as major factors to exemplify their effects on the optimum reliability. Through numerical examples basic considerations on the structural safety and serviceability are demonstrated.
