Optimal inspection scheduling with alternative fatigue reliability formulations for steel bridges

ABSTRACT: A reliability-based method for inspection scheduling of steel bridges is proposed to yield the optimal (most economical) inspection strategy that meets an acceptable safety level through the planned ser-vice life. Two fatigue reliability formulations that can be applied for most details in steel bridges are pre-sented. For details classified according to AASHTO fatigue categories, a limit state function related to the number of stress cycles to failure based on Miner’s rule is used to evaluate the fatigue reliability; for details not classified according to AASHTO fatigue categories, a limit state function related to crack size and growth rate is used to evaluate the fatigue reliability. The inspection scheduling problem is modeled as an optimiza-tion problem with an objective function that includes the total expected cost of inspection, repair, and failure formulated using an event tree approach, appropriate constraints on the interval between inspections, and a specified minimally acceptable (target) structural reliability. An optimal inspection-scheduling plan can thus be developed for any specified fatigue details or fracture-critical sections in steel bridges. Examples pre-sented demonstrate the advantage of the reliability-based optimal inspection scheduling in cost saving and structural reliability control over alternative inspection plans. Two case studies related to steel bridges – one for a plate girder and the other for a box girder – are presented to demonstrate the proposed reliability-based optimal inspection scheduling procedure