Reliability and Durability of Marine Structures

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Abstract
A study of the dynamic response of offshore towers to wind‐generated random ocean waves is presented. The analysis is performed in the frequency domain and the equations of motion are solved using equivalent linearization techniques. Two methods of reliability analysis are considered in this study: a statistical fatigue damage analysis using the American Welding Society model (high‐cycle fatigue analysis) to demonstrate the influence of the design stress level for fatigue‐critical members on the fatigue reliability and a first‐passage failure probability with periodic inspections. For the latter, a crack growth analysis is performed using the fracture mechanics method to estimate propagated crack size and corresponding residual strength under random service loading conditions. The effect of periodic inspections is very important if a fatigue crack already exists. It is also shown that there is always a limit in the number of inspections beyond which no significant improvement can be achieved.