Reliability-Based Condition Assessment of Welded Miter Gate Structures

The U.S. Army Corps of Engineers is working to develop rational policies for prioritizing in-service inspection, maintenance, and repair policies for aging locks and dams on the inland waterway system using structural reliability methods and principles of risk management. Comparisons of miter gate design criteria and performance observed in service reveal differences that are examined through finite-element-based reliability analysis. Finite-element analyses show that miter gates are overdesigned for ultimate strength limit states and have low-to-moderate stresses. However, premature fatigue damages have been found in a number of miter gates. Stochastic fracture mechanics identified contributing factors that significantly impact the probability of reaching the fatigue limit state: initial flaw size at weld details, inspection frequency, and inspection quality. The role of parameter uncertainty in gate fatigue performance during service life is depicted by a fragility that includes uncertainties in the strength of the gate structure, loads due to gate operations, and initial flaw size. Fragility assessment of the fatigue performance observed in two miter gates provides a means to evaluate observed performance. Fatigue performance can be enhanced by modest improvements in detailing practices and inspection methods.