Random Sea and Reliability of Offshore Foundations

A probabilistic model is developed for the long-term representation of sea state and for the degradation of offshore foundations. Parameters of the sea state model are: (1)The mean arrival rate of storms with soil degradation potential; (2)the joint probability distribution of storm duration and average intensity; and (3)the random process that describes the time variation of significant wave height during each storm. Although the model itself is stationary, the evolution of significant wave height within each storm is represented by a nonstationary random process with parameters that depend on storm duration and average intensity. This feature allows the modeling of the initial build-up and terminal decay of storm intensity. The necessary parameters can be derived from ordinary historical records, and specific estimates are obtained using data from a North Atlantic weather ship. Offshore foundation degradation is described in terms of reduction of horizontal stiffness, with degradation dependent on the current state of damage and the current value of significant wave height.