On the relationship between platform topology, topside weight and structural reliability under storm overload

The relationship between platform configuration and structural reliability is investigated by comparing the collapse behaviour of simple jacket, jack-up and monopod topologies under storm loading in moderately shallow North West Shelf (NWS) waters. Two different pushover analysis methods are used to find the ultimate strength, which give quite different reserve strength ratio (RSR) results for certain structures. The effect on the structural reliability of varying topside weight is also assessed. It is found that the reliability trends are strongly dependent on structural topology — an effect that is not included in current Codes of practice. It is also shown that a single set of partial load factors for dead and environmental loads cannot achieve uniform reliability across different platform configurations in the same environment. Furthermore, in some cases, a working stress design format gives more consistent reliability results than the load and resistance design factor approach.