This paper is based on the JIP study for the oceanographic hindcast and environmental load statistics of fixed steel structures at South China Sea under tropical cyclone conditions. It focuses on the sensitivity and comparison studies by exploring the degrees and reasons of variability that may occur in determination of design environmental conditions resulting from the selection of the design standards and approaches. The bias and efficiency in extreme values prediction are examined with respect to modeling uncertainty and statistical uncertainty. The long term distributions of maximum wave height as well as the associated wave period conditional on the design wave height are derived following the storm event based method. The approaches for combing wave, current and wind to define the design conditions and the associated biases on design load are investigated. Second order random and spreading wave theory is adopted to estimate the extreme wave crest height distributions. The extreme water level issue is addressed and recommendations are given for setting the deck elevation to achieve the explicit wave-in-deck probabilities.
The studies are carried out by applying a dataset of a grid point containing 182 typhoons spanning 40 continuous years to demonstrate the analytical procedures in an understandable fashion. The results of this paper should lead to improvements in prediction of the environmental conditions for design of new-built structures to attain their target safety levels, as well as for assessment of existing structures to demonstrate their fitness-for-purpose.