Failure time prediction of deteriorating fail-safe structures

Structural evaluation and design have been dominated by component safety checks. In fact, current reliability-based codes for buildings and bridges are largely limited to individual structural component checks and do not generally include requirements for system reliability. Also, these codes-do not consider the potential damaged states of a structural system and the ability of the damaged system to continue to carry loads. Furthermore, current codes do not entail the prediction of the failure time of deteriorating structural systems under time-varying loads. In this study, the reliability of deteriorating fail-safe structures is investigated using a time-variant parallel system reliability approach in which both load and resistance are time dependent. Monte Carlo simulation is used to find the cumulative-time system failure probability. Numerical examples are presented to illustrate the effects of various parameters such as variabilities in live loads, live load occurrence rate, live to dead load ratio, strength loss rate, resistance correlation, and number of degrading members on the cumulative-time failure probability of a deteriorating fail-safe system. Postfailure behavior of components and load redistribution effects are also considered. The results can be used to better predict the failure time of deteriorating fail-safe structures, such as redundant reinforced concrete bridges under corrosion attack and to develop optimal lifetime reliability-based maintenance strategies for these structures.