Influence of Non-Proportional Environmental Loading on the Reliability of Production Jack-ups

Inherent features of jack-up units, including their mobility and their integrated and standardized form, make them well suited for certain field developments. An overview of the configurations and attributes of production jack-ups is presented, including a database of applications to date. The relationship between jack-up configuration and structural reliability under storm overload is then explored. Critical values of the wave height exponent α are presented for a wide range of water depths and jack-up geometries, along with selected pushover analysis results. There is a strong tendency for the structural reliability to decrease in shallower water depths and when the jack-up is elevated in the water column by a storage tank or braced base. The latter is due essentially to the non-proportional increase in environmental loading down the structure with increasing return period.