Optimal Inspection of Fracture-Critical Steel Trapezoidal Girders

A reliability-based procedure 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 service life. Two fatigue reliability formulations that can be applied for most details in steel bridges are presented. 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 optimization 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 presented demonstrate the advantage of the reliability-based optimal inspection scheduling in cost saving and structural reliability control over alternative inspection plans.