Bridge Lifetime System Reliability under Multiple Limit States

A system reliability approach to minimizing the life-cycle cost of a deteriorating structure offers significant advantages such as a rational assessment of the assumed risk of failure, and an understanding of the importance and contribution of individual components to the overall reliability of the structure. The reliability of a structural system as a whole is the measure of its overall performance. This measure has to include both ultimate and serviceability limit states. A system model of a structure traditionally consists of a series-parallel combination of strength-based component limit states. Serviceability limit states however, can play a tremen­ dously important role in optimizing the inspection and repair of a deteriorating structure. This paper proposes the use of serviceability flags as a means to incorporate serviceability concerns into a strength-based reliability analysis. Using highway bridges as an example, available data sources for serviceability flags are considered. The effect of including serviceability flags in an optimum life-cycle analysis is illustrated on a specific highway bridge.