Structural Reliability of Monopods Under Storm Overload

The structural reliability of a generic caisson under storm overload is investigated usingtypical Australian North West Shelf (NWS) environmental data. The bending moment dueto the hydrodynamic loading is shown to increase in proportion to the fourth power of thewave height in certain critical cases, rather than the more usual exponent of a'2.Combined with the steep wave height return period curve on the NWS, this may lead tolow structural reliability, as much as two orders of magnitude smaller than more typicalstructures in other locations. The wave height exponent a varies with water depth andenvironmental force type (e.g. shear or bending moment) and increases rapidly nearwater line. This nonproportional nature of the loading is not addressed in design codes ofpractice or in traditional pushover analysis.