Seasonal Effect in the Reliability Analysis of Offshore Structures

Abstract eng:
In the recent past an increasing number of failure events have been observed for offshore structures due to exceptional environmental loading conditions such as large waves. The increased frequency of occurrence of these exceptional loading conditions indicates a possible change in the environmental characteristics, which are the basis for the load models for structural analysis and design. The question arises whether the current load models reflect the recently observed exceptional events to a sufficient extent or whether an adjustment would be appropriate. Some supporting information towards an adjustment can be found in meteorological studies, which report an increasing wave height in the Northeast Atlantic Ocean. This change possesses potential severe effects on the reliability of offshore structures in the concerned region. In this paper, the seasonal effects in the modeling of the significant wave height for structural reliability analysis are studied. The peak over threshold (POT) method is selected to model the extremes in the non-stationary point process for the wave heights. The time-varying parameters are taken into account with a cyclic changing pattern to reflect the seasonal behavior. Both the extreme values and the storm occurrence rate are investigated in the different seasons. The results are utilized for the load characterization of offshore structures to investigate their sensitivity to the changing seasonal effects in reliability analyses. Examples of selected structures are discussed.

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