Ship impact on concrete offshore platform legs

Abstract

The majority of offshore oil platforms are of tubular steel construction which, because of the plasticity of the steel, are tolerant of damage from ship impact. Some platforms are supported by reinforced, pre-tensioned concrete legs, in which there is little capacity for energy absorption. To resist ship impact, the local strength of the concrete leg must therefore be greater than the crushing strength of the ship. The effect of a low-speed ship impact on the integrity of a reinforced concrete platform leg has been investigated using finite-element methods. The dynamic impact analysis has been run in Abaqus/Explicit. The concrete-damaged plasticity material model implemented in Abaqus has been used to model the behaviour of the concrete, with elastic–plastic properties used for the steel reinforcement. The model has been calibrated against scale tests carried out on a cylindrical reinforced shell and simple slab test experiments, and showed good agreement. A comparison is made between the finite-element model and an accident in which a low-energy ship impact occurred on a concrete platform leg. The damage predicted by the finite-element model is found to agree well with that observed following the accident, indicating that the approach is applicable to modelling the impact.