Preloading Effects on the Behaviour of Cylindrical Members of Jacket Platforms Subjected to Ship Impact

Abstract

Steel tubes are widely encountered in industrial applications and in offshore structures. This is mostly because of their superior axial load carrying performance, low resistance against fluid loads and easy handling during construction and transportation. Cylindrical structural members, however, very often happen to become subject to accidental lateral damages which are detrimental to their load carrying performance. Collision between supply ships and legs and bracings of offshore oil platforms, impact from heavy dropped objects on these members or denting during installation of marine structures are examples of such accidents. Prior to an accident, cylindrical members are usually carrying their normal operational loads. It is very important to include the effects of this service load (pre-loading) in evaluation of the behaviour of impacted member. The pre-loading may change the dynamic characteristics of the member or degrade its load carrying capacity. While the performance of cylindrical members subjected to lateral impact has been extensively researched, few studies can be found on the impact behaviour of pre-loaded tubular members. This paper reports results from a numerical study on axial pre-loading effects on the dynamic and quasi-static behaviour of cylindrical shells subjected to transverse impact loads. Results obtained appear useful for a more realistic design of tubular members and in choosing feasible and reasonable post impact repairing and strengthening schemes.