Residual Strength of Damaged Jacket Type Offshore Platform and the Effects of Local Repair Available to Purchase

In the design of offshore platforms, the aim is to have a characteristic capacity higher than the characteristic environmental loads with a return period of typically 100 years multiplied by some partial safety factors for loads and resistance. Simplified of the assumptions is inherent in the derivation of force components. In addition, any potential of the structure for yielding and load redistribution, giving the inherent “reserve capacity” is neglected in the design stage. Reserve strength is commonly defined as the ability of a structure to sustain loads in excess of the design value. The frame action and system redundancy are implicit sources of reserve strength which are not generally controlled or quantified in design. Reserve strength should not be solely considered as overdesigning of structures. However, there are situations where such reserve strength may be demonstrated, for example in case of reassessment of existing structures, e.g. improved exploitation methods or increased petroleum service may call for service life extension, the characteristic loads may increase due to installation of new modules. It is also important that a structure can sustain damage without collapse so that it has sufficient remaining or “residual” strength. Such damage may result from extreme overloading of structures as a whole, or from localized damage such as ship impact or dropped object. This paper is concerned with the reserve strength of a jacket evaluated by pushover analysis in intact and damaged conditions. The tested structure is a PP (Production Platform) jacket, a K-braced space frame, located in the Persian Gulf. The loading on the structure contains functional and environmental loads. The test is carried out under displacement control. The influence of damages including “Local Denting” and “Out of Straightness” on the critical members is investigated, and then reassessment and Probabilistic Collapse Analysis of the platform are considered to illustrate the mechanisms of failure caused by each damage The effects of some repair scenarios is investigated too.